Power-Limit Reporting in a Communication System
using Carrier Aggregation
Field of the Invention
The invention relates to methods for informing an eNodeB on the transmit power status
of a user equipment in a mobile communication system using component carrier
aggregation. Furthermore, the invention is also related to the implementation/
performance of these methods in/by hardware, i.e. apparatuses, and their
implementation in software. The invention further relates to the definition of per-UE and
per-component carrier power headroom reports and their signaling by means of MAC
control elements.
Technical Background
Long Term Evolution (LTE)
Third-generation mobile systems (3G) based on WCDMA radio-access technology are
being deployed on a broad scale all around the world. A first step in enhancing or
evolving this technology entails introducing High-Speed Downlink Packet Access
(HSDPA) and an enhanced uplink, also referred to as High Speed Uplink Packet Access
(HSUPA), giving a radio-access technology that is highly competitive.
In order to be prepared for further increasing user demands and to be competitive
against new radio access technologies 3GPP introduced a new mobile communication
system which is called Long Term Evolution (LTE). LTE is designed to meet the carrier
needs for high speed data and media transport as well as high capacity voice support to
the next decade. The ability to provide high bit rates is a key measure for LTE.
The work item (Wl) specification on Long-Term Evolution (LTE) called Evolved UMTS
Terrestrial Radio Access (UTRA) and UMTS Terrestrial Radio Access Network (UTRAN)
is to be finalized as Release 8 (LTE Rel. 8). The LTE system represents efficient packet-
based radio access and radio access networks that provide full IP-based functionalities
with low latency and low cost. In LTE, scalable multiple transmission bandwidths are
specified such as 1.4, 3.0, 5.0, 10.0, 15.0. and 20.0 MHz, in order to achieve flexible
system deployment using a given spectrum. In the downlink, Orthogonal Frequency
Division Multiplexing (OFDM) based radio access was adopted because of its inherent
immunity to multipath interference (MPI) due to a low symbol rate, the use of a cyclic
prefix (CP), and its affinity to different transmission bandwidth arrangements. Single-
carrier frequency division multiple access (SC-FDMA) based radio access was adopted
in the uplink, since provisioning of wide area coverage was prioritized over improvement
in the peak data rate considering the restricted transmit power of the user equipment
(UE). Many key packet radio access techniques are employed including multiple-input
multiple-output (MIMO) channel transmission techniques, and a highly efficient control
signaling structure is achieved in LTE Rel. 8/9.
LTE architecture
The overall architecture is shown in Fig. 1 and a more detailed representation of the E-
UTRAN architecture is given in Fig. 2. The E-UTRAN consists of eNodeB, providing the
E-UTRA user plane (PDCP/RLC/MAC/PHY) and control plane (RRC) protocol
terminations towards the user equipment (UE). The eNodeB (eNB) hosts the Physical
(PHY), Medium Access Control (MAC), Radio Link Control (RLC), and Packet Data
Control Protocol (PDCP) layers that include the functionality of user-plane header-
compression and encryption. It also offers Radio Resource Control (RRC) functionality
corresponding to the control plane. It performs many functions including radio resource
management, admission control, scheduling, enforcement of negotiated uplink QoS, cell
information broadcast, ciphering/deciphering of user and control plane data, and
compression/decompression of downlink/uplink user plane packet headers. The
eNodeBs are interconnected with each other by means of the X2 interfaee.
The eNodeBs are also connected by means of the S1 interface to the EPC (Evolved
Packet Core), more specifically to the MME (Mobility Management Entity) by means of
the S1-MME and to the Serving Gateway (SGW) by means of the S1-U. The S1 interface
supports a many-to-many relation between MMEs/Serving Gateways and eNodeBs. The
SGW routes and forwards user data packets, while also acting as the mobility anchor for
the user plane during inter-eNodeB handovers and as the anchor for mobility between
LTE and other 3GPP technologies (terminating S4 interface and relaying the traffic
between 2G/3G systems and PDN GW). For idle state user equipments, the SGW
terminates the downlink data path and triggers paging when downlink data arrives for the
user equipment. It manages and stores user equipment contexts, e.g. parameters of the
IP bearer service, network internal routing information. It also performs replication of the
user traffic in case of lawful interception.
The MME is the key control-node for the LTE access-network. It is responsible for idle
mode user equipment tracking and paging procedure including retransmissions. It is
involved in the bearer activation/deactivation process and is also responsible, for
choosing the SGW for a user equipment at the initial attach and at time of intra-LTE
handover involving Core Network (CN) node relocation. It is responsible for
authenticating the user (by interacting with the HSS). The Non-Access Stratum (NAS)
signaling terminates at the MME and it is also responsible for generation and allocation
of temporary identities to user equipments. It checks the authorization of the user
equipment to camp on the service provider's Public Land Mobile Network (PLMN) and
enforces user equipment roaming restrictions. The MME is the termination point in the
network for ciphering/integrity protection for NAS signaling and handles the security key
management. Lawful interception of signaling is also supported by the MME. The MME
also provides the control plane function for mobility between LTE and 2G/3G access
networks with the S3 interface terminating at the MME from the SGSN. The MME also
terminates the S6a interface towards the home HSS for roaming user equipments.
QoS control
Efficient Quality of Service (QoS) support is seen as a basic requirement by operators for
LTE. In order to allow best in class user experience, while on the other hand optimizing
the network resource utilization, enhanced QoS support should be integral part of the
new system.
Aspects of QoS support is currently being under discussion within 3GPP working groups.
Essentially, the QoS design for System Architecture Evolution (SAE)/LTE is based on the
QoS design of the current UMTS system reflected in 3GPP TR 25.814, "Physical layer
aspects for evolved Universal Terrestrial Radio Access (UTRA)", v.7.1.0 (available at
http://www.3gpp.org and incorporated herein by reference). The agreed SAE Bearer
Service architecture is depicted in Fig. 5. The definition of a bearer service as given in
3GPP TR 25.814 may still be applicable:
"A bearer service includes all aspects to enable the provision of a contracted QoS. These
aspects are among others the control signaling, user plane transport and QoS
management functionality".
In the new SAE/LTE architecture the following new bearers have been defined: the SAE
Bearer service between the mobile terminal (User Equipment - UE) and the serving
gateway, the SAE Radio Bearer on the radio access network interface between mobile
terminal and eNodeB as well as the SAE Access Bearer between the eNodeB and the
serving gateway.
The SAE Bearer Service provides:
- QoS-wise aggregation of IP end-to-end-service flows;
- IP header compression (and provision of related information to UE);
- User Plane (UP) encryption (and provision of related information to UE);
- if prioritized treatment of end-to-end-service signaling packets is required an additional
SAE Bearer Service can be added to the default IP service;
- provision of mapping/multiplexing information to the UE;
- provision of accepted QoS information to the UE.
The SAE Radio Bearer Service provides:
- transport of the SAE Bearer Service data units between eNodeB and UE according to
the required QoS;
- linking of the SAE Radio Bearer Service to the respective SAE Bearer Service.
The SAE Access Bearer Service provides:
- transport of the SAE Bearer Service data units between serving gateway and eNodeB
according to the required QoS;
- provision of aggregate QoS description of the SAE Bearer Service towards the
eNodeB;
- linking of the SAE Access Bearer Service to the respective SAE Bearer Service.
In 3GPP TR 25.814 a one-to-one mapping between an SAE Bearer and an SAE Radio
Bearer. Furthermore there is a one-to-one mapping between a radio bearer (RB) and a
logical channel. From that definition it follows that a SAE Bearer, i.e. the corresponding
SAE Radio Bearer and SAE Access Bearer, is the level of granularity for QoS control in
an SAE/LTE access system. Packet flows mapped to the same SAE Bearer receive the
same treatment.
For LTE there will be two different SAE bearer types: the default SAE bearer with a
default QoS profile, which is configured during initial access and the dedicated SAE
bearer (SAE bearers may also be referred to as SAE bearer services) which is
established for services requiring a QoS profile which is different from the default one.
The default SAE bearer is an "always on" SAE bearer that can be used immediately after
LTEJDLE to LTE_ACTIVE state transition. It carries all flows which have not been
signaled a Traffic Flow Template (TFT). The Traffic Flow Template is used by serving
gateway to discriminate between different user payloads. The Traffic Flow Template
incorporates packet filters such as QoS. Using the packet filters the serving gateway
maps the incoming data into the correct PDP Context (Packet Data Protocol Context).
For the default SAE bearer, several service data flows can be multiplexed. Unlike the
default SAE Bearer, the dedicated SAE Bearers are aimed at supporting identified
services in a dedicated manner, typically to provide a guaranteed bit-rate. Dedicated
SAE bearers are established by the serving gateway based on the QoS information
received in Policy and Charging Control (PCC) rules from evolved packet core when a
new service is requested. A dedicated SAE bearer is associated with packet filters
where the filters match only certain packets. A default SAE bearer is associated with
"match all" packet filters for uplink and downlink. For uplink handling the serving gateway
builds the Traffic Flow Template filters for the dedicated SAE bearers, The UE maps
service data flows to the correct bearer based on the Traffic Flow Template, which has
been signaled during bearer establishment. As for the default SAE Bearer, also for the
dedicated SAE Bearer several service data flows can be multiplexed.
The QoS Profile of the SAE bearer is signaled from the serving gateway to the eNodeB
during the SAE bearer setup procedure. This profile is then used by the eNodeB to
derive a set of Layer 2 QoS parameters, which will determine the QoS handling on the
air interface. The Layer 2 QoS parameters are input to the scheduling functionality. The
parameters included in the QoS profile signaled on S1 interface from serving gateway to
eNodeB are currently under discussion. Most likely the following QoS profile parameters
are signaled for each SAE bearer: Traffic Handling Priority, Maximum Bit-rate,
Guaranteed Bit-rate. In addition, the serving gateway signals to the eNodeB the
Allocation and Retention Priority for each user during initial access.
Uplink Access scheme for LTE
For uplink transmission, power-efficient user-terminal transmission is necessary to
maximize coverage. Single-carrier transmission combined with FOMA (Frequency
Division Multiple Access) with dynamic bandwidth allocation has been chosen as the
evolved UTRA uplink transmission scheme. The main reason for the preference for
single-carrier transmission is the lower peak-to-average power ratio (PAPR), compared
to multi-carrier signals (OFDMA - Orthogonal Frequency Division Multiple Access), and
the corresponding improved power-amplifier efficiency and assumed improved coverage
(higher data rates for a given terminal peak power). During each time interval, eNodeB
assigns users a unique time/frequency resource for transmitting user data thereby
ensuring intra-cell orthogonality. An orthogonal access in the uplink promises increased
spectral efficiency by eliminating intra-cell interference. Interference due to multipath
propagation is handled at the base station (eNodeB), aided by insertion of a cyclic prefix
in the transmitted signal.
The basic physical resource used for data transmission consists of a frequency resource
of size BWgrant during one time interval, e.g. a sub-frame of 0.5 ms, onto which coded
information bits are mapped. It should be noted that a sub-frame, also referred to as
transmission time interval (TTI), is the smallest time interval for user data transmission. It
is however possible to assign a frequency resource BWglBnl over a longer time period
than one TTI to a user by concatenation of sub-frames.
The frequency resource can either be in a localized or distributed spectrum as illustrated
in Fig. 3 and Fig. 4. As can be seen from Fig. 3, localized single-carrier is characterized
by the transmitted signal having a continuous spectrum that occupies a part of the total
available spectrum. Different symbol rates (corresponding to different data rates) of the
transmitted signal imply different bandwidths of a localized single-carrier signal.
On the other hand, as shown in Fig. 4, distributed single-carrier is characterized by the
transmitted signal having a non-continuous ("comb-shaped") spectrum that is distributed
over system bandwidth. Note that, although the distributed single-carrier signal is
distributed over the system bandwidth, the total amount of occupied spectrum is, in
essence, the same as that of localized single-carrier. Furthermore, for higher/lower
symbol rate, the number of "comb-fingers" is increased/reduced, while the "bandwidth" of
each "comb finger" remains the same.
At first glance, the spectrum in Fig. 4 may give the impression of a multi-carrier signal
where each comb-finger corresponds to a "sub-carrier". However, from the time-domain
signal-generation of a distributed single-carrier signal, it should be clear that what is
being generated is a true single-carrier signal with a corresponding low peak-to-average
power ratio. The key difference between a distributed single-carrier signal versus a multi-
carrier signal, such as e.g. OFDM (Orthogonal Frequency Division Multiplex), is that, in
the former case, each "sub-carrier" or "comb finger" does not carry a single modulation
symbol. Instead each "comb-finger" carries information about all modulation symbols.
This creates a dependency between the different comb-fingers that leads to the low-
PAPR characteristics. It is the same dependency between the "comb fingers" that leads
to a need for equalization unless the channel is frequency-non-selective over the entire
transmission bandwidth. In contrast, for OFDM equalization is not needed as long as the
channel is frequency-non-selective over the sub-carrier bandwidth.
Distributed transmission can provide a larger frequency diversity gain than localized
transmission, while localized transmission more easily allows for channel-dependent
scheduling. Note that, in many cases the scheduling decision may decide to give the
whole bandwidth to a single user equipment to achieve high data rates.
Uplink Scheduling scheme for LTE
The uplink scheme allows for both scheduled access, i.e. controlled by eNodeB, and
contention-based access.
In case of scheduled access the user equipment is allocated a certain frequency
resource for a certain time (i.e. a time/frequency resource) for uplink data transmission.
However, some time/frequency resources can be allocated for contention-based access.
Within these time/frequency resources, user equipments can transmit without first being
scheduled. One scenario where user equipment is making a contention-based access is
for example the random access, i.e. when user equipment is performing initial access to
a cell or for requesting uplink resources.
For the scheduled access eNodeB scheduler assigns a user a unique frequency/time
resource for uplink data transmission. More specifically the scheduler determines
- which user equipment(s) that is (are) allowed to transmit,
- which physical channel resources (frequency),
- Transport format (Transport Block Size (TBS) and Modulation Coding Scheme (MCS))
to be used by the mobile terminal for transmission
The allocation information is signaled to the user equipment via a scheduling grant, sent
on the so-called L1/L2 control channel. For simplicity, this downlink channel is referred to
the "uplink grant channel" in the following.
A scheduling grant message (also referred to as an resource assignment herein)
contains at least information which part of the frequency band the user equipment is
allowed to use, the validity period of the grant, and the transport format the user
equipment has to use for the upcoming uplink transmission. The shortest validity period
is one sub-frame. Additional information may also be included in the grant message,
depending on the selected scheme. Only "per user equipment" grants are used to grant
the right to transmit on the Uplink Shared Channel UL-SCH (i.e. there are no "per user
equipment per RB" grants). Therefore the user equipment needs to distribute the
allocated resources among the radio bearers according to some rules, which will be
explained in detail in the next section.
Unlike in HSUPA there is no user equipment based transport format selection. The base
station (eNodeB) decides the transport format based on some information, e.g. reported
scheduling information and QoS information, and user equipment has to follow the
selected transport format. In HSUPA eNodeB assigns the maximum uplink resource and
user equipment selects accordingly the actual transport format for the data
transmissions.
Uplink data transmissions are only allowed to use the time-frequency resources assigned
to the user equipment through the scheduling grant. If the user equipment does not have
a valid grant, it is not allowed to transmit any uplink data. Unlike in HSUPA, where each
user equipment is always allocated a dedicated channel there is only one uplink data
channel shared by multiple users (UL-SCH) for data transmissions.
To request resources, the user equipment transmits a resource request message to the
eNodeB. This resources request message could for example contain information on the
buffer status, the power status of the user equipment and some Quality of Services
(QoS) related information. This information, which will be referred to as scheduling
information, allows eNodeB to make an appropriate resource allocation. Throughout the
document it's assumed that the buffer status is reported for a group of radio bearers. Of
course other configurations for the buffer status reporting are also possible. Since the
scheduling of radio resources is the most important function in a shared channel access
network for determining Quality of Service, there are a number of requirements that
should be fulfilled by the uplink scheduling scheme for LTE in order to allow for an
efficient QoS management (see 3GPP RAN WG#2 Tdoc. R2- R2-062606, "QoS operator
requirements/use cases for services sharing the same bearer", by T-Mobile, NTT
DoCoMo, Vodafone, Orange, KPN; available at http://www.3gpp.org/ and incorporated
herein by reference):
- Starvation of low priority services should be avoided
- Clear QoS differentiation for radio bearers/services should be supported by the
scheduling scheme
- The uplink reporting should allow fine granular buffer reports (e.g. per radio bearer or
per radio bearer group) in order to allow the eNodeB scheduler to identify for which
Radio Bearer/service data is to be sent.
- It should be possible to make clear QoS differentiation between services of different
users
- It should be possible to provide a minimum bit-rate per radio bearer
As can be seen from above list one essential aspect of the LTE scheduling scheme is to
provide mechanisms with which the operator can control the partitioning of its aggregate
cell capacity between the radio bearers of the different QoS classes. The QoS class of a
radio bearer is identified by the QoS profile of the corresponding SAE bearer signaled
from serving gateway to eNodeB as described before. An operator can then allocate a
certain amount of its aggregate cell capacity to the aggregate traffic associated with radio
bearers of a certain QoS class.
The main goal of employing this class-based approach is to be able to differentiate the
treatment of packets depending on the QoS class they belong to. For example, as the
load in a cell increases, it should be possible for an operator to handle this by throttling
traffic belonging to a low-priority QoS class. At this stage, the high-priority traffic can still
experience a low-loaded situation, since the aggregate resources allocated to this traffic
is sufficient to serve it. This should be possible in both uplink and downlink direction.
One benefit of employing this approach is to give the operator full control of the policies
that govern the partitioning of the bandwidth. For example, one operator's policy could be
to, even at extremely high loads, avoid starvation of traffic belonging to its lowest priority
QoS Class. The avoidance of starvation of low priority traffic is one of the main
requirements for the uplink scheduling scheme in LTE. In current UMTS Release 6
(HSUPA) scheduling mechanism the absolute prioritization scheme may lead to
starvation of low priority applications. E-TFC selection (Enhanced Transport Format
Combination selection) is done only in accordance to absolute logical channel priorities,
i.e. the transmission of high priority data is maximized, which means that low priority data
is possibly starved by high priority data. In order to avoid starvation the eNodeB
scheduler must have means to control from which radio bearers a user equipment
transmits data. This mainly influences the design and use of the scheduling grants
transmitted on the L1/L2 control channel in downlink. In the following the details of the
uplink rate control procedure in LTE is outlined.
Medium Access Control (MAC) and MAC Control Elements
The MAC layer is the lowest sub-layer in the Layer 2 architecture of the LTE radio
protocol stack (see 3GPP TS 36.321, "Medium Access Control (MAC) protocol
specification", version 8.7.0, in particular sections 4.2, 4.3, 5.4.3 and 6, available at
http//www.3gpp.org and incorporated in its entirety herein by reference). The connection
to the physical layer below is through transport channels, and the connection to the RLC
layer above is through logical channels. The MAC layer performs multiplexing and
demultiplexing between logical channels and transport channels. The MAC layer in the
transmitting side (in the following examples the user equipment) constructs MAC PDUs,
also referred to as transport blocks, from MAC SDUs received through logical channels,
and the MAC layer in the receiving side recovers MAC SDUs from MAC PDUs received
through transport channels.
In the multiplexing and demultiplexing entity, data from several logical channels can be
(de)multiplexed into/from one transport channel. The multiplexing entity generates MAC
PDUs from MAC SDUs when radio resources are available for a new transmission. This
process includes prioritizing the data from the logical channels to decide how much data
and from which logical channel(s) should be included in each MAC PDU. Please note
that the process of generating MAC PDUs in the user equipment is also referred to a
logical channel prioritization (LCP) in the 3GPP terminology.
The demultiplexing entity reassembles the MAC SDUs from MAC PDUs and distributes
them to the appropriate RLC entities. In addition, for peer-to-peer communication
between the MAC layers, control messages called 'MAC Control Elements' can be
included in the MAC PDU.
A MAC PDU primarily consists of the MAC header and the MAC payload (see 3GPP TS
36.321, section 6). The MAC header is further composed of MAC sub-headers, while the
MAC payload is composed of MAC Control Elements, MAC SDUs and padding. Each
MAC sub-header consists of a Logical Channel ID (LCID) and a Length (L) field. The
LCID indicates whether the corresponding part of the MAC payload is a MAC Control
Element, and if not, to which logical channel the related MAC SDU belongs. The L field
indicates the size of the related MAC SDU or MAC Control Element. As already
mentioned above, MAC Control Elements are used for MAC-level peer-to-peer signaling,
including delivery of BSR information and reports of the UE's available power in the
uplink, and in the downlink DRX commands and timing advance commands. For each
type of MAC Control Element, one special LCID is allocated. An example for a MAC PDU
is shown in Fig. 6.
Power Control
Uplink transmitter power control in a mobile communication system serves the purpose
of balancing the need for sufficient transmitter energy per bit to achieve the required QoS
against the need to minimize interference to other users of the system and to maximize
the battery life of the user equipment. In achieving this, the uplink power control has to
adapt to the characteristics of the radio propagation channel, including path loss,
shadowing and fast fading, as well as overcoming interference from other users within
the same cell and neighboring cells. The role of the Power Control (PC) becomes
decisive to provide the required SINR (Signal-to-lnterference plus Noise Ratio) while
controlling at the same time the interference caused to neighboring cells. The idea of
classic PC schemes in uplink is that all users are received with the same SINR, which is
known as full compensation. As an alternative, the 3GPP has adopted the use of
Fractional Power Control (FPC) for LTE Rel. 8/9. This new functionality makes users with
a higher path-loss operate at a lower SINR requirement so that they will more likely
generate less interference to neighboring cells.
The power control scheme provided in LTE Rel. 8/9 employs a combination of open-loop
and closed-loop control. A mode of operation involves setting a coarse operating point
for the transmission power density spectrum by open-loop means based on path-loss
estimation. Faster operation can then be applied around the open-loop operating point by
closed-loop power control. This controls interference and fine-tunes the power settings to
suit the channel conditions including fast fading.
With this combination of mechanisms, the power control scheme in LTE Rel. 8/9
provides support for more than one mode of operation. It can be seen as a toolkit for
different power control strategies depending on the deployment scenario, the system
load and operator preference.
The detailed power control formulae are specified in LTE Rel. 8/9 for the Physical Uplink
Shared Channel (PUSCH), Physical Uplink Control Channel (PUCCH) and the Sounding
Reference Signals (SRS) in section 5.1 in 3GPP TS 36.213, "Physical layer procedures",
version 8.8.0, available at http://www.3gpp.org and incorporated herein by reference.
The formula for each of these uplink signals follows the same basic principles; in all
cases they can be considered as a summation of two main terms: a basic open-loop
operating point derived from static or semi-static parameters signaled by the eNodeB.
and a dynamic offset updated from sub-frame to sub-frame.
The basic open-loop operating point for the transmit power per resource block depends
on a number of factors including the inter-cell interference and cell load. It can be further
broken down into two components, a semi-static base level/£, further comprised of a
common power level for all user equipments in the cell (measured in dBm) and 9 UE-
specific offset, and an open-loop path-loss compensation component. The dynamic
offset part of the power per resource block can also be further broken down into two
components, a component dependent on the MCS and explicit Transmitter Power
Control (TPC) commands.
The MCS-dependent component (referred to in the LTE specifications as A lf, where TF
stands for "Transport Format") allows the transmitted power per resource block to be
adapted according to the transmitted information data rate.
The other component of the dynamic offset is. the UE-specific TPC commands. These
can operate in two different modes: accumulative TPC commands (available for PUSCH,
PUCCH and SRS) and absolute TPC commands (available for PUSCH only). Tor the
PUSCH, the switch between these two modes is configured semi-statically for each UE
by RRC signaling - i.e. the mode cannot be changed dynamically. With the accumulative
TPC commands, each TPC command signals a powarstep relative to the previous level.
Uplink transmitter power control in a mobile communication system serves the purpose
of balancing the need for sufficient transmitter energy per bit to achieve the required QoS
against the need to minimize interference to other users of the system and to maximize
the battery life of the user equipment.
In achieving this, the uplink power control has to adapt to the characteristics of the radio
propagation channel, including path loss, shadowing and fasf fading, as well as
overcoming interference from other users within the same cell and neighboring cells.
The setting of the UE Transmit power^p-jsai [dBm] for the PUSCH transmission in
reference sub-frame / is defined by (see section 5.1.1.1 of 3GPP TS 36.213):
- PcMAxis the maximum UE transmit power chosen by UE in the given range (see
below); MPUSCH is the number of allocated physical resource blocks (PRBs). The
more PRBs are allocated, the more uplink transmit power is allocated.
- P0 PUSCH (j) indicates the base transmission power signaled by RRC. For semi-
persistent scheduling (SPS) and dynamic scheduling this is the sum of a'cell specific
nominal component fonominal.puschO)g[_126,'>24] and a UE specific component
•Po_uE_puscHC/)eH27.....-96] For RACH message 3: 0ffset from preamble
transmission power
- a denotes a cell-specific parameter (that is broadcast on system information). This
parameter indicates how much path-loss PL is compensated. a =! means the
received signal level at eNodeB is same regardless of the user equipment's position.
For SPS and dynamic scheduling a e {0, 0.4,0.5,0.6,0.7,0.8, 0.9, l}, and for the case
of RACH Message 3, a{f) = 1.
- PL is the UE path-loss derived at the user equipments based on Reference Signal
Received Power (RSRP) measurement and signaled Reference Signal (RS)
transmission power. PL can be defined as
PL = reference signal power - higher layer filtered RSRP.
- ATF is a modulation and coding scheme (transport format) dependent power offset.
- f{i) is a function of the closed loop power control commands signaled from the
eNodeB to the UE. -'0 represents accumulation in case of accumulative TPC
commands. Whether closed loop commands are relative accumulative or absolute is
configured by higher layers. For the accumulative TPC commands two sets of power
step values are provided: (-1,1) dB for DCI format 3A and (-1,0+1,+3)dB for DCI
format 3. The set of values which can be signaled by absolute TPC commands is (-
4,-1,1,4) dB indicated by DCI format 3.
Power Headroom Reporting
In order to assist the eNodeB to schedule the uplink transmission resources to different
user equipments in an appropriate way, it is important that the user equipment can report
its available power headroom to eNodeB.
The eNodeB can use the power headroom reports to determine how much more uplink
bandwidth per sub-frame a user equipment is capable of using. This helps to avoid
allocating uplink transmission resources to user equipments which are unable to use
them in order to avoid a waste of resources.
The range of the power headroom report is from +40 to -23 dB (see 3GPP TS 36.133,
"Requirements for support of radio resource management", version 8.7.0, section
9.1.8.4, available at http//www.3gpp.org and incorporated in its entirety herein by
reference). The negative part of the range enables the user equipment to signal to the
eNodeB the extent to which it has received an UL grant which would require more
transmission power than the UE has available. This would enable the eNodeB to reduce
the size of a subsequent grant, thus freeing up transmission resources to allocate to
other UEs.
A power headroom report can only be sent in sub-frames in which a UE has an UL grant.
The report relates to the sub-frame in which it is sent. A number of criteria are defined to
trigger a power headroom report. These include:
- A significant change in estimated path loss since the last power headroom report
- More than a configured time has elapsed since the previous power headroom report
- More than a configured number of closed-loop TPC commands have been
implemented by the UE
The eNodeB can configure parameters to control each of these triggers depending on
the system loading and the requirements of its scheduling algorithm. To be more
specific, RRC controls power headroom reporting by configuring the two timers
periodicPHR-Timer and prohibitPHR-Timer, and by signalling dl-PathlossChange which sets
the change in measured downlink pathloss to trigger a power headroom report.
The power headroom report is send as a MAC Control Element. It consists of a single
octet where the two highest bits are reserved and the six lowest bits represent the dB
values mentioned above in 1 dB steps. The structure of the MAC Control Element is
shown in Fig. 7.
The UE power headroom/1// [dB] valid for sub-frame i is defined by (see section
5.1-1.2 of 3GPPTS 36.213):

The power headroom is rounded to the closest value in the range [40; -23] dB with steps
of 1 dB. PCUAX is the total maximum UE transmit power (or total maximum transmit power
of the user equipment) and is a value chosen by user equipment in the given range of
paux_i. and ^cMAv_HDased on ,ne following constraints:

PHMAX is the value signaled by the network and LTC , MPR and AMPR (also denoted A-
MPR - Additional Maximum Power Reduction) are specified in 3GPP TS 36.101,
"Evolved Universal Terrestrial Radio Access (E-UTRA); User Equipment (UE) radio
transmission and reception", version 8.7.0, section 6.2 available at http//www.3gpp.org
and incorporated herein by reference.
MPR is a power reduction value, the so-called Maximum Power Reduction, used to
control the Adjacent Channel Leakage Power Ratio (ACLR) associated with the various
modulation schemes and the transmission bandwidth. An adjacent channel may be for
example either another Evolved Universal Terrestrial Radio Access (E-UTRA) channel or
an UTRA channel. The maximum allowed power reduction {MPR) is also defined in
3GPP TS 36.101. It is different depending on channel bandwidth and modulation
scheme. The user equipment's reduction may be less than this maximum allowed power
reduction (MPR) value. 3GPP specifies a MPR test which verifies that the maximum
transmit power of a user equipment is greater than or equal to the nominal total
maximum transmit power minus the MPR while still complying with the ACLR
requirements
As indicated above, AMPR is the Additional Maximum Power Reduction. It is band
specific and is applied when configured by the network.
As can be seen from the explanations above, PCMAX is UE-implementation specific and
hence not known by the eNodeB.
Fig. 25 shows exemplary scenarios for a UE transmission power status and
corresponding power headroom. On the left hand side of Fig. 25, the user equipment is
not power limited (positive PHR), whereas on the right hand side of Fig. 25 a negative
power headroom is implying a power limitation of the user equipment. Please note that
the Pa,M_Ls PCmm £ ™:.Pp^k:,,,,) wherein the lower boundary ?„_, is
typically mainly dependent on the maximum power reduction MPR and the additional
maximum power reduction AMPR , i.e. PCMML = Pr„Mas, - MPR - AMPR
Further Advancements for LTE (LTE-A)
The frequency spectrum for IMT-Advanced was decided at the World
Radiocommunication Conference 2007 (WRC-07). Although the overall frequency
spectrum for IMT-Advanced was decided, the actual available frequency bandwidth is
different according to each region or country. Following the decision on the available
frequency spectrum outline, however, standardization of a radio interface started in the
3rd Generation Partnership Project (3GPP). At the 3GPP TSG RAN #39 meeting, the
Study Item description on "Further Advancements for E-UTRA (LTE-Advanced)" was
approved. The study item covers technology components to be considered for the
evolution of E-UTRA, e.g. to fulfill the requirements on IMT-Advanced. Two major
technology components which are currently under consideration for LTE-A are described
in the following.
Carrier Aggregation in LTE-A for support of wider bandwidth
In carrier aggregation, two or more component carriers (component carriers) are
aggregated in order to support wider transmission bandwidths up to 100MHz. All
component carriers can be configured to be LTE Rel. 8/9 compatible, at least when the
aggregated numbers of component carriers in the uplink and the downlink are the same.
Not all component carriers aggregated by a user equipment may necessarily be Rel. 8/9
compatible.
A user equipment may simultaneously receive or transmit one or multiple component
carriers depending on its capabilities. A LTE-A Rel. 10 user equipment with reception
and/or transmission capabilities for carrier aggregation can simultaneously receive
and/or transmit on multiple component carriers whereas an LTE Rel. 8/9 user equipment
can receive and transmit on a single component carrier only, provided that the structure
of the component carrier follows the Rel. 8/9 specifications.
Carrier aggregation is supported for both contiguous and non-contiguous component
carriers with each component carrier limited to a maximum of 110 Resource Blocks in
the frequency domain using the Rel. 8/9 numerology. It is possible to configure a user
equipment to aggregate a different number of component carriers originating from the
same eNodeB and of possibly different bandwidths in the uplink and the downlink:
- The number of downlink component carriers that can be configured depends on the
downlink aggregation capability of the user equipment;
- The number of uplink component carriers that can be configured depends on the
uplink aggregation capability of the user equipment;
- It is not possible to configure a user equipment with more uplink component carriers
than downlink component carriers;
In typical TDD deployments, the number of component carriers and the bandwidth of
each component carrier in uplink and downlink is the same.
Component carriers originating from the same eNodeB need not to provide the same
coverage.
The spacing between centre frequencies of contiguously aggregated component carriers
shall be a multiple of 300 kHz. This is in order to be compatible with the 100 kHz
frequency raster of Rel. 8/9 and at the same time preserve orthogonality of the
subcarriers with 15 kHz spacing. Depending on the aggregation scenario, the n x 300
kHz spacing can be facilitated by insertion of a low number of unused subcarriers
between contiguous component carriers.
The nature of the aggregation of multiple carriers is only exposed up to the MAC layer.
For both uplink and downlink there is one HARQ entity required in MAC for each
aggregated component carrier. There is (in the absence of SU-MIMO - Single User
Multiple Input Multiple Output - for uplink) at most one transport block per component
carrier. A transport block and its potential HARQ retransmissions need to be mapped on
the same component carrier. The Layer 2 structure with activated carrier aggregation is
shown in Fig. 19 and Fig. 20 for the downlink and uplink respectively.
When carrier aggregation is configured, the user equipment only has one RRC
connection with the network. At RRC connection establishment/re-establishment, one
cell provides the security input (one ECGI, one PCI and one ARFCN) and the non-
access stratum mobility information (e.g. TAI) similarly as in LTE Rel. 8/9. After RRC
connection establishment/re-establishment, the component carrier corresponding to that
cell is referred to as the downlink Primary Cell (PCell). There is always one and only one
downlink PCell (DL PCell) and one uplink PCell (UL PCell) configured per user
equipment in connected mode. Within the configured set of component carriers, other
cells are referred to as Secondary Cells (SCells). The characteristics of the downlink and
uplink PCell are:
- The uplink PCell is used for transmission of Layer 1 uplink control information
- The downlink PCell cannot be de-activated
- Re-establishment is triggered when the downlink PCell experiences Rayleigh fading
(RLF), not when downlink SCells experience RLF
- The downlink PCell cell can change with handover
- Non-access stratum information is taken from the downlink PCelll.
The reconfiguration, addition and removal of component carriers can be performed by
RRC. At intra-LTE handover, RRC can also add, remove, or reconfigure component
carriers for usage in the target cell. When adding a new component carrier, dedicated
RRC signaling is used for sending component carriers' system information which is
necessary for component carrier transmission / reception (similarly as in LTE Rel. 8/9 for
handover).
When carrier aggregation is configured, a user equipment may be scheduled over
multiple component carriers simultaneously, but at most one random access procedure
should be ongoing at any time. Cross-carrier scheduling allows the Physical Downlink
Control Channel (PDCCH) of a component carrier to schedule resources on another
component carrier. For this purpose a component carrier identification field (CIF) is
introduced in the respective Downlink Control Information (DCI) formats. A linking
between uplink and downlink component carriers allows identifying the uplink component
carrier for which the grant applies when there is no-cross-carrier scheduling. The linkage
of downlink component carriers to uplink component carriers does not necessarily need
to be one to one. In other words, more than one downlink component carrier can link to
the same uplink component carrier. At the same time, a downlink component carrier can
only link to one uplink component carrier.
(De)Activation of a Component Carrier and DRX operation
In carrier aggregation, whenever a user equipment is configured with only one
component carrier, LTE Rel. 8/9 discontinuous reception (DRX) applies. In other cases,
the same DRX operation applies to all configured and activated cells, respectively
component carriers (i.e. identical active time for PDCCH monitoring). When in active
time, any component carrier may always schedule Physical Downlink Shared Channel
(PDSCH) on any other configured and activated component carrier (further restrictions
are free for study).
To enable reasonable user equipment battery consumption when carrier aggregation is
configured, a component carrier activation/deactivation mechanism for downlink SCells is
introduced (i.e. activation/deactivation does not apply to the PCell). When a downlink
SCell is not active, the user equipment does not need to receive the corresponding
PDCCH or PDSCH, nor is it required to perform CQI measurements (CQI is short for
Channel Quality Indicator). Conversely, when a downlink SCell is active, the user
equipment shall receive PDSCH and PDCCH (if present), and is expected to be able to
perform CQI measurements. In the uplink however, a user equipment is always required
to be able to transmit on PUSCH on any configured uplink component carrier when
scheduled on the corresponding PDCCH (i.e. there is no explicit activation of uplink
component carriers).
Other details of the activation/deactivation mechanism for SCells are:
- Explicit activation of downlink SCells is done by MAC signaling;
- Explicit deactivation of downlink SCells is done by MAC signaling;
- Implicit deactivation of downlink SCells is also possible;
- downlink SCells can be activated and deactivated individually, and a single
activation/deactivation command can activate/deactivate a subset of the configured
downlink SCells;
- SCells added to the set of configured component carriers are initially "deactivated".
Uplink Power Control for Carrier Aggregation
Even though most details of the uplink power control algorithm for the carrier aggregation
case are still open or under discussion in the 3GPP working groups, the general
agreement is that LTE-A Rel. 10 supports component carrier specific uplink power
control, i.e. there will be one independent power control loop for each uplink component
carrier configured for the user equipment. Furthermore it was decided that power
headroom should be reported per-component carrier. In case of power limitation, i.e. UE
transmission power is exceeding the total maximum UE transmit power, the following
power scaling is applied.
For power scaling, the PUCCH power should be prioritized and the remaining power may
be used by PUSCH (i.e. PUSCH power is scaled down first, maybe to zero). Further, a
PUSCH with uplink control information (UCI) is prioritized over PUSCH without UCI,
Additionally, equal power scaling for PUSCH transmissions without UCI is considered.
As each component carrier can be assumed to have its own power control loop and each
transport block on each component carrier is transmitted with a power individually set for
the component carrier, power headroom reporting should be performed per component
carrier. Since carrier aggregation can be seen as a multiplication of several LTE Rel. 8/9
(component) carriers, it can be assumed that also the power headroom reporting on the
individual component carriers will reuse the LTE Rel. 8/9 power headroom reporting
procedures.
Hence each user equipment transmits power headroom reports for each component
carrier on that component carrier. This means that each component carrier that has an
uplink transmission in a specific sub-frame could also transmit a power headroom report
given that the conditions for sending such a report are fulfilled.
Power headroom reporting as know form LTE Rel. 8/9 is controlled, respectively
triggered on a component carrier basis (by employing different timers). Applying this
concept to the individual component carriers of a system utilizing carrier aggregation, this
means that it almost never happens that within one sub-frame each of the component
carriers with an uplink transmission is transmitting a power headroom report. Hence,
even if the timers relating to power headroom reporting (the periodicPHR timer and the
prohibitPHR timer) are set to the same values for all component carriers, synchronous
power headroom reports on all component carriers within a sub-frame will only happen
by chance.
Fig. 10 shows exemplary power headroom reporting in a LTE-A system, assuming that
the power headroom reporting of LTE Rel. 8/9 is applied to each of the exemplary three
component carriers (CoCal to CoCa3). At Tt, there is an uplink assignment on all three
component carriers and an uplink transport block, respectively MAC PDU, including a
power headroom report for the respective component carrier is sent on each component
carrier. As there is a per-component carrier (per-CC) power headroom report for each
component carrier, the eNodeB is informed on the user equipment's power status.
Furthermore, the respective timers periodicPHR-Timer and prohibitPHR-Timer are
restarted for each component carrier. For component carriers CoCa2 and CoCa3, it is
assumed that after expiry of the periodicPHR-Timer there is no uplink allocation in the
next sub-frame, so that no periodic power headroom report can be sent immediately.
Hence at T2, the user equipment transmits a transport block/MAC PDU with a power
headroom report only on component carrier CoCal. As there is only a resource
assignment on component carrier CoCal, the eNodeB may again conclude on the user
equipment's power status from the per-CC power headroom report at T2.
However at T3, Tt, andTj, only some transport blocks/PDUs of the component carriers
within a sub-frame carry a power headroom report. Regarding the power headroom
report on component carrier CoCa3 at T5. A path-loss change on component carrier
CoCa3 is assumed to trigger the power headroom report, but at the time of the path-loss
change none of the component carriers with uplink transmissions (i.e. component
carriers CoCal and CoCa2) have a power headroom report included. Therefore, T2 ,Tt,
and T5, the eNodeB is not aware of the actual transmit power spend on the uplink
transmissions within the respective sub-frames.
Furthermore, in LTE Rel.10 within the scope of carrier aggregation there are two
maximum power limits, a total maximum UE transmit power PcmAX and a component
carrier-specific maximum transmit power /'cmCe. 3GPP RAN4 working group already
indicated that both (nominal) maximum transmit power per user equipment PCNUAX and
the (nominal) maximum component carrier-specific transmit power PCMACf should be the
same regardless of the number of carriers supported, in order not to affect the link
budget of a carrier aggregation capable user equipment in the single carrier operation
mode.
Different to LTE Rel. 8/9, in LTE-A Rel. 10 the user equipment has also to cope with
simultaneous PUSCH - PUCCH transmission, multi-cluster scheduling, and simultaneous
transmission on multiple component carriers, which requires larger MPR values and also
causes a larger variation of the applied MPR values compared to 3GPP Rel. 8/9.
It should be noted that the eNodeB does not have knowledge of the power reduction
applied by the user equipment on each component carrier, since the actual power
reduction depends on the type of allocation, the standardized MPR value and also on the
user equipment implementation. Therefore eNodeB doesn't know the component carrier-
specific maximum transmission power relative to which the user equipment calculates
the power headroom. In LTE Rel. 8/9 for example the user equipment maximum transmit
power PCNUAX can be within some certain range as described above (PCMAX ,,£ PCMAX s
°cmaxh)-
Due to the reduction of the component carrier-specific maximum transmission
power Pcmacc which is not known to eNodeB as explained above, the eNodeB cannot
really know how close a user equipment is operating to its total maximum transmission
power PCNMAX. Therefore there might be situations where user equipment is exceeding
the total user equipment maximum transmission power PCNMAX which would hence
require power scaling. Fig. 26 shows an exemplary scenario where user equipment is
power limited, i.e. applying power scaling on component carriers CC#1 and CC#2
configured in the uplink. Even though the user equipment is power limited, the
component carrier-specific power headroom reports according to the LTE definitions
indicate sufficiently large power headroom.
Summary of the Invention
One object of the invention is to propose procedures that allow the eNodeB to recognize
the power usage status of a user equipment in a mobile communication system using
carrier aggregation.
The object is solved by the subject matter of the independent claims. Advantageous
embodiments are subject to the dependent claims.
A first aspect of the invention is to enable to user equipment to indicate to the eNodeB
when it is potentially becoming power limited or is power limited, i.e. when being close to
using its total maximum UE transmit power (also referred to as "user equipment's total
maximum transmit power", "total maximum UE transmit power of the user equipment" or
"user equipment's total maximum UE transmit power" in the following) or the resource
allocations and power control commands of the eNodeB would require using a transmit
power exceeding the total maximum transmit power of the user equipment.
In line with this first aspect of the invention and in accordance with a first exemplary
implementation the user equipment uses an indicator in the MAC protocol data units
(MAC PDUs) of each sub-frame to signal to the eNodeB, whether the user equipment
applied power scaling to the transmission (of the MAC PDUs) within the respective sub-
frame. The indicator(s) may be for example included in one or more MAC sub-headers of
the MAC PDUs.
In an enhancement of the first exemplary implementation, an indicator is provided for
each configured (or alternatively for each active) component carrier in the uplink so as to
allow the indication of the use of power scaling for individual component carriers in the
uplink. For example, this may be realized by multiplexing respective indicators to the
MAC PDUs transmitted by the user equipment on the respective configured (or
alternatively active) component carriers in the uplink, so that the indicator can be
associated to the configured (or alternatively active) component carrier on which it is
transmitted.
If the an indication of the power status of the user equipment should be made prior to the
user equipment actually reaching its total maximum UE transmit power, a threshold value
(e.g. a certain percentage) could be defined relative to the total maximum UE transmit
power, that when exceeded, triggers the user equipment to set an indicator. In this case,
when set, the indicator would indicate to the eNodeB that the user equipment is close to
using the total maximum UE transmit power (i.e. exceeded the threshold value). Also this
indicator may be signaled for each configured uplink component carrier individually and
may be for example included in one or more MAC sub-headers of the MAC PDUs.
Still in line with the first aspect and according to another, second exemplary
implementation, if the user equipment needs to apply power scaling to a transmission of
MAC PDUs in a given sub-frame, the user equipment is transmitting in this sub-frame a
power headroom report for each configured (or alternatively for each active) uplink
component carrier (also referred to as per-component carrier power headroom report(s))
together with an indicator that the per-component carrier power headroom report(s) are
triggered by the estimated transmit power required for transmitting the MAC PDUs within
the given sub-frame exceeding the total maximum transmit power of the user equipment
(alternatively, the indicator could also be interpreted as an indication of power scaling
having been applied to the transmissions within the given sub-frame by the user
equipment due to this event).
Hence, in this second exemplary implementation, when the transmit power required for a
transmission of the MAC PDUs on uplink component carriers within the respective sub-
frame will exceed a total maximum transmit power of the user equipment, an aperiodic
per-component carrier power headroom report for all the configured (or active) uplink
component carrier(s) is triggered and sent by the user equipment. The indication of the
trigger for the per-component carrier power headroom report(s) may be for example
included in a MAC-sub header of a MAC PDU carrying a per-component carrier power
headroom report in a MAC control element.
This second exemplary implementation may also be modified so as to signal an
indication of the power status of the user equipment should prior to the user equipment
actually reaching its total maximum UE transmit power. Again, a threshold value (e.g. a
certain percentage) could be defined relative to the total maximum UE transmit power,
that when exceeded, triggers the user equipment to send a power headroom report for
each configured uplink component carrier.
Furthermore, a power headroom report for each configured (or alternatively for each
active) uplink component carrier may be optionally sent together with an indication that
the respective power headroom report was triggered by exceeding the total maximum
transmit power of the user equipment or a threshold relative thereto. For example, such
indication could be comprised in a MAC sub-header of a MAC control element conveying
a power headroom report for a configured uplink component carrier of the user
equipment.
According to a further, third exemplary implementation in line with the first aspect of the
invention, the user equipment is indicating to the eNodeB the amount of power reduction
applied to the maximum transmit power of a component carrier. Alternatively, instead of
the power reduction, the maximum transmit power of each configured uplink component
carrier (after having applied the component carrier-specific power reduction) could be
signaled to the eNodeB.
The amount of power reduction may be for example signaled per configured or per active
uplink component carrier.
In one further example, the amount of power reduction applied to the maximum transmit
power of a component carrier is signaled together with a power headroom report for each
configured uplink component carrier to the eNodeB.
The information on the user equipment's power status may be signaled in form of one or
more MAC control elements that are comprised within the MAC PDU(s) of a given sub-
frame. Furthermore, the signaled power status information enables the eNodeB to derive
the power status for each user equipment that is signaling its power status information.
The scheduler of the eNodeB may for example take into account the power status of the
respective user equipments in its dynamic and/or semi-persistent resource allocations to
the respective user equipments.
In another fourth exemplary implementation in line with the first aspect of the invention,
the user equipment is enabled to indicate to the eNodeB when it is potentially becoming
power limited or is power limited by defining a new MAC control element that is inserted
by the user equipment to one or more protocol data units transmitted on respective
(assigned) component carriers within a single sub-frame that is providing the eNodeB
with a corresponding indication.
Furthermore, in addition to the indication of the user equipment approaching its total
maximum UE transmit power, the control element inserted to the protocol data units may
further indicate a per-user equipment (per-UE) power headroom. For example, the per-
user equipment power headroom indicates the transmit power unused by the user
equipment when transmitting the protocol data units (including the MAC control element)
within the sub-frame relative to the user equipment's total maximum UE transmit power.
The MAC control element may be inserted to the protocol data units of a sub-frame. For
example, the MAC control element may be inserted into one of the protocol data units
transmitted by the user equipment within the sub-frame or all of the protocol data units
transmitted by the user equipment within the sub-frame.
In another exemplary, fifth implementation and in line with the first aspect of the
invention, the object is solved by the user equipment sending per-component carrier
power headroom reports for all assigned component carriers within a single sub-frame
when the user equipment is potentially becoming power limited or is power limited; i.e.
when being close to using its total maximum UE transmit power or the resource
allocations and power control commands of the eNodeB would require using a transmit
power exceeding the user equipment's total maximum UE transmit power.
Another second aspect of the invention is to suggest a definition for a per-component
carrier power headroom when reporting the power headroom in a mobile communication
system using carrier aggregation in the uplink. According to one exemplary definition,
per-component carrier power headroom of a configured (or alternatively active) uplink
component carrier is defined as the difference between the maximum transmit power of
the configured uplink component carrier and the used uplink transmit power.
The used uplink transmit power is the power used (or emitted) by the user equipment for
the transmission of the MAC PDUs within the given sub-frame. The used uplink transmit
power may also be referred to as the transmitted PUSCH power. The used uplink
transmit power is therefore considering power scaling (if applied to the transmission).
Therefore, the used transmit power may be different from the estimated transmit power
which is the transmit power required for a transmission of the MAC PDUs on uplink
component carriers within the respective sub-frame as a result of the power control
formula.
Alternatively, a power headroom of a configured uplink component carrier may be
defined as the difference between the maximum transmit power of the configured uplink
component carrier and an estimated PUSCH power. The PUSCH power is for example
calculated by the power control formula for the respective component carrier.
Furthermore, the maximum transmit power of the (configured) uplink component carrier
may take into according a power reduction due to simultaneous transmissions on
another or other uplink component carriers in the sub-frame. Optionally, the power
headroom reports are sent for active uplink component carriers of the user equipment
only.
The per-component carrier power headroom according to the second aspect of the
invention may be provided in form of a per-component carrier power headroom report.
The per-component carrier power headroom report is for example signaled in form of a
MAC control element within a MAC PDU. As mentioned above, the MAC control element
carrying the per-component carrier power headroom report may be associated to a MAC
sub-header in a header section of the MAC PDU that can be further employed to indicate
that the per-component carrier power headroom is triggered by a power limited situation
of the user equipment requiring power scaling.
In all aspects of the invention and also in all embodiments and exemplary
implementations described herein, the user equipment may optionally report only on
configured component carriers that are active, which may be referred to as active
component carriers (i.e. indicators, power headroom reports, etc. may only be signaled
for active component carriers only). This may be for example advantageous, if the
configuration and (de)activation of uplink component carriers of a user equipment can be
controlled separately.
One embodiment of the invention relates to a method for informing an eNodeB on the
transmit power status of a user equipment in a mobile communication system using
component carrier aggregation. This method comprises the following steps performed by
the user equipment for each sub-frame where the user equipment makes a transmission
in the uplink. The user equipment determines whether an estimated transmit power
required for a transmission of MAC protocol data units on the uplink component carriers
within the respective sub-frame will exceed a total maximum transmit power of the user
equipment. If so, the user equipment performs a power scaling of the transmit power to
reduce the transmit power required for the transmission of the MAC protocol data units
such that it is no longer exceeding the total maximum transmit power of the user
equipment, and transmits the MAC protocol data units to the eNodeB within the
respective sub-frame. The transmitted MAC protocol data units comprise an indicator
that indicates to the eNodeB whether power scaling has been performed by the user
equipment for transmitting the MAC protocol data units in the respective sub-frame.
The indicator may be for example comprised within a MAC header of at least one of the
MAC protocol data units. For example, the indicator may be a flag within one or more of
the MAC sub-headers of a respective MAC header comprised in the at least one MAC
protocol data unit.
Furthermore, in a more advanced exemplary embodiment of the invention, the power
scaling may be performed for each configured uplink component carrier individually. For
each uplink component carrier on which a MAC protocol data unit is transmitted, at least
one MAC protocol data unit transmitted on the respective uplink component carrier
comprises an indicator that indicates to the eNodeB whether power scaling has been
applied to the transmission on the respective uplink component carrier within the sub-
frame.
Another embodiment of the invention provides a further method for informing an eNodeB
on the transmit power status of a user equipment in a mobile communication system
using component carrier aggregation. According to this embodiment, a user equipment
determines whether an estimated transmit power required for a transmission of MAC
protocol data units on uplink component carriers within the respective sub-frame will
exceed a total maximum transmit power of the user equipment. If this is the case, the
user equipment performs a power scaling of the transmit power to reduce the transmit
power required for the transmission of the MAC protocol data units such that it is no
longer exceeding the total maximum transmit power of the user equipment, and further
triggers the generation of a power headroom report for each configured uplink
component carrier of the user equipment. The user equipment transmits the MAC
protocol data units to the eNodeB within the respective sub-frame together with a power
headroom report for each configured uplink component carrier of the user equipment and
an indication of the power headroom report(s) having been triggered by the transmit
power required for a transmission of MAC protocol data units on uplink component
carriers exceeding the total maximum transmit power of the user equipment.
Furthermore, the user equipment may optionally further determine, in response to the
trigger, a power headroom report for each configured uplink component carrier of the
user equipment, wherein the power headroom for a configured uplink component carrier
is defined as the difference between the maximum transmit power of the configured
uplink component carrier and the used uplink transmit power. Hence, this definition of the
power headroom considers power scaling.
Alternatively, or in addition thereto, the user equipment may determine, in response to
the trigger, a power headroom report for each configured uplink component carrier of the
user equipment, wherein the power headroom of a configured uplink component carrier
is defined as the difference between the maximum transmit power of the configured
uplink component carrier and the estimated uplink transmit power on the respective
component carrier. Therefore, this alternative definition of the power headroom is not
considering power scaling.
Optionally, the power headroom according to both definitions above may be determined
by the user equipment for each configured uplink component carrier and may be
provided to the eNodeB within a power headroom report.
In a further exemplary embodiment of the method, the power reduction applied to the
maximum transmit power of a configured uplink component carrier that is determined by
the user equipment considers transmission(s) on other configured uplink component
carrier(s) of the user equipment within the sub-frame.
Moreover, according to another exemplary embodiment, the indication of the power
headroom report(s) having been triggered by the estimated transmit power exceeding
the total maximum transmit power of the user equipment is provided by setting a flag in a
MAC sub-header for a MAC control element carrying at least one of the power headroom
reports(s). For example, a MAC sub-header could be included in a header section of the
MAC protocol data unit to which the MAC control element is multiplexed for each MAC
control element comprising a respective power headroom report. A flag in the MAC sub-
header indicates that the power headroom report within the MAC control element has
been triggered by the estimated transmit power required for a transmission of MAC
protocol data units on uplink component carriers within the respective sub-frame
exceeding the total maximum transmit power of the user equipment.
In another exemplary embodiment, a further method for informing an eNodeB on the
transmit power status of a user equipment in a mobile communication system using
component carrier aggregation. Optionally, this method may be performed for each sub-
frame where the user equipment makes a transmission in the uplink. According to the
method, the user equipment determines whether an estimated transmit power required
for a transmission of MAC protocol data units on the uplink component carriers within the
respective sub-frame will exceed a total maximum transmit power of the user equipment.
If this is the case, the user equipment performs a power scaling of the transmit power to
reduce the transmit power required for the transmission of the MAC protocol data units
such that it is no longer exceeding a total maximum transmit power of the user
equipment, and transmits the MAC protocol data units to the eNodeB within the
respective sub-frame. The transmitted MAC protocol data units comprise at least one
MAC control element indicating the amount of power reduction applied to the maximum
transmit power of the user equipment for the configured uplink component carriers.
Alternatively, the user equipment could signal the maximum transmit power of the user
equipment for the configured uplink component carriers, which may however imply more
overhead in the signaling than signaling the amount of power reduction at the same level
of granularity.
Optionally, the MAC control element(s) indicating the amount of power reduction for the
configured uplink component carriers could be included to the MAC PDUs within a sub-
frame only, if the estimated transmit power required for a transmission of MAC protocol
data units on the uplink component carriers within the respective sub-frame will exceed
the total maximum transmit power of the user equipment, i.e. if the user equipment has
to apply power scaling.
In one more detailed exemplary embodiment of this method, it may be assumed that
power scaling is performed for each configured uplink component carrier individually. For
each uplink component carrier on which a MAC protocol data unit is transmitted, at least
one MAC protocol data unit transmitted on the respective uplink component carrier
comprises a MAC control element that indicates the amount of power reduction applied
to the maximum transmit power of the respective uplink component carriers.
According to a further exemplary embodiment of the invention, in case the estimated
transmit power required for a transmission of MAC protocol data units on the uplink
component carriers within the respective sub-frame will exceed the total maximum
transmit power of the user equipment, the user equipment further generates a power
headroom report for each configured uplink component carrier and transmits the power
headroom reports together with the MAC protocol data units including the MAC control
element for reporting the power reduction to the eNodeB.
According to another exemplary embodiment of the invention, the user equipment
signals the power reduction and a power headroom report for the respective configured
uplink component carrier in response to the (de)activation of an uplink component carrier
or in response to a predefined change of the amount of power reduction applied to the
maximum transmit power for a uplink component carrier.
In another embodiment of the invention, the format of the MAC control element signaling
the amount of power reduction is identified by
- a predetermined logical channel identifier defined for MAC control elements signaling
the amount of power reduction, or
- a predetermined logical channel identifier defined for MAC control elements signaling
a power headroom report and one or more flags,
included in the MAC sub-header of the MAC control element.
The different exemplary embodiments of the method for informing an eNodeB on the
transmit power status of a user equipment may - according to another embodiment of
the invention - comprise the steps of receiving by the user equipment at least one uplink
resource assignment, wherein each uplink resource assignment is assigning resources
for the transmission of at least one of the MAC protocol data units on one of the plural
component carriers to the user equipment, and generating for each received uplink
resource assignment at least one of the MAC protocol data units for transmission on the
respective assigned component carrier. Each MAC protocol data unit is transmitted via a
corresponding one of the component carriers according to one of the received resource
assignments (Please note that in case MIMO is used, two MAC PDUs may be
transmitted via an uplink component carrier on which resources have been granted to the
user equipment). The generation of the protocol data units may be for example
performed by executing a logical channel prioritization procedure.
In line with the second aspect of the invention and according to another exemplary
embodiment of the invention, a MAC control element for transmission from a user
equipment to an eNodeB in a mobile communication system using component carrier
aggregation is provided. According to this embodiment the MAC control element
comprises a power headroom report for a configured uplink component carrier that
reports the difference between the maximum transmit power of the configured uplink
component carrier and a transmitted PUSCH power (or the used uplink transmit power).
In one example the transmitted PUSCH power PrapuscH.c(0 of the sub-frame i is defined
by

where PSFC is the power scaling factor applied for the respective configured uplink
component carrier c.
Furthermore, in another exemplary embodiment of the invention, the MAC control
element may further comprise a power headroom report of the configured uplink
component carrier that reports the difference between the maximum transmit power of
the configured uplink component carrier and an estimated PUSCH power (or estimated
uplink transmit power on the respective component carrier).
Still in line with the second aspect of the invention and according to an alternative
exemplary embodiment of the invention, another MAC control element for transmission
from a user equipment to an eNodeB in a mobile communication system using
component carrier aggregation is provided. This MAC control element comprises a
power headroom report of the configured uplink component carrier that reports the
difference between the maximum transmit power of the configured uplink component
carrier and an estimated PUSCH power.
In both embodiments of the MAC control element, the maximum transmit power of the
configured uplink component carrier considers a power reduction due to transmission(s)
on other configured uplink component carrier(s) of the user equipment.
Another exemplary embodiment of the invention is related to a MAC protocol data unit for
transmission from a user equipment to a eNodeB in a mobile communication system
using component carrier aggregation. The MAC protocol data unit comprises a MAC
control element including a power headroom report according to one of the different
embodiments described herein and a MAC sub-header. The MAC sub-header comprises
an indicator, that when set, indicates to the eNodeB that the power headroom report has
been triggered by the transmit power required for a transmission of MAC protocol data
units on uplink component carriers exceeding the total maximum transmit power of the
user equipment.
Furthermore, the invention also relates to the realization of the methods for informing an
eNodeB on the transmit power status of a user equipment in hardware and/or by means
of software modules. Accordingly, another embodiment of the invention is related to a
user equipment for informing an eNodeB on the transmit power status of a user
equipment in a mobile communication system using component carrier aggregation. The
user equipment comprises a determination section that determines whether an estimated
transmit power required for a transmission of MAC protocol data units on the uplink
component carriers within the respective sub-frame will exceed a total maximum transmit
power of the user equipment. Furthermore, the user equipment comprises a power
control section that performs a power scaling of the transmit power to reduce the transmit
power required for the transmission of the MAC protocol data units such that it is no
longer exceeding the total maximum transmit power of the user equipment, and a
transmission section for transmitting the MAC protocol data units to the eNodeB within
the respective sub-frame. The transmitted MAC protocol data units comprise an indicator
that indicates to the eNodeB whether power scaling has been performed by the user
equipment for transmitting the MAC protocol data units in the respective sub-frame.
Another exemplary embodiment provides a user equipment for informing an eNodeB on
the transmit power status of a user equipment in a mobile communication system using
component carrier aggregation. The user equipment comprises a determination section
adapted to determine whether an estimated transmit power required for a transmission of
MAC protocol data units on uplink component carriers within the respective sub-frame
will exceed a total maximum transmit power of the user equipment, and to trigger the
generation of a power headroom report for each configured uplink component carrier of
the user equipment, and further a power control section adapted to perform a power
scaling of the transmit power to reduce the transmit power required for the transmission
of the MAC protocol data units such that it is no longer exceeding the total maximum
transmit power of the user equipment. Moreover, the user equipment includes a
transmission section adapted to transmit the MAC protocol data units to the eNodeB
within the respective sub-frame together with a power headroom report for each
configured uplink component carrier of the user equipment and an indication of the
power headroom report(s) having been triggered by the transmit power required for a
transmission of MAC protocol data units on uplink component carriers exceeding the
total maximum transmit power of the user equipment.
In further embodiment of the invention, the user equipment comprises a determination
section adapted to determine whether an estimated transmit power required for a
transmission of MAC protocol data units on the uplink component carriers within the
respective sub-frame will exceed a total maximum transmit power of the user equipment,
and a power control section adapted to perform a power scaling of the transmit power to
reduce the transmit power required for the transmission of the MAC protocol data units
such that it is no longer exceeding the total maximum transmit power of the user
equipment, and further a transmission section adapted to transmit the MAC protocol data
units to the eNodeB within the respective sub-frame. The transmitted MAC protocol data
units comprise at least orie MAC control element indicating the amount of power
reduction applied to the maximum transmit power of the user equipment for the
configured uplink component carriers.
Furthermore, according to another embodiment of the invention, the user equipment is
adapted to perform the steps of the methods for informing an eNodeB on the transmit
power status of a user equipment according to one of the various embodiments
described herein.
Another embodiment of the invention provides a computer readable medium storing
instructions that, when executed by a processor of a user equipment, cause the user
equipment to inform an eNodeB on the transmit power status of a user equipment for
each sub-frame where the to be transmitted by the user equipment makes a
transmission in the in the uplink within a mobile communication system using component
carrier aggregation, by determining whether an estimated transmit power required for a
transmission of MAC protocol data units on the uplink component carriers within the
respective sub-frame will exceed a total maximum transmit power of the user equipment,
and if so, performing a power scaling of the transmit power to reduce the transmit power
required for the transmission of the MAC protocol data units such that it is no longer
exceeding the total maximum transmit power of the user equipment, and transmitting the
MAC protocol data units to the eNodeB within the respective sub-frame. The transmitted
MAC protocol data units comprise an indicator that indicates to the eNodeB whether
power scaling has been performed by the user equipment for transmitting the MAC
protocol data units in the respective sub-frame.
A computer readable medium of another embodiment of the invention is storing
instructions that, when executed by a processor of a user equipment, cause the user
equipment to inform an eNodeB on the transmit power status of a user equipment in a
mobile communication system using component carrier aggregation, by determining
whether an estimated transmit power required for a transmission of MAC protocol data
units on uplink component carriers within the respective sub-frame will exceed a total
maximum transmit power of the user equipment, and if so, performing a power scaling of
the transmit power to reduce the transmit power required for the transmission of the MAC
protocol data units such that it is no longer exceeding the total maximum transmit power
of the user equipment, and triggering the generation of a power headroom report for
each configured uplink component carrier of the user equipment, and transmitting the
MAC protocol data units to the eNodeB within the respective sub-frame together with a
power headroom report for each configured uplink component carrier of the user
equipment and an indication of the power headroom report(s) having been triggered by
the transmit power required for a transmission of MAC protocol data units on uplink
component carriers exceeding the total maximum transmit power of the user equipment.
According to a further embodiment of the invention, a computer readable medium storing
instructions is provided. The instructions, when executed by a processor of a user
equipment, cause the user equipment to inform an eNodeB on the transmit power status
of a user equipment for each sub-frame where the to be transmitted by the user
equipment makes a transmission in the in the uplink within a mobile communication
system using component carrier aggregation, by determining whether an estimated
transmit power required for a transmission of MAC protocol data units on the uplink
component carriers within the respective sub-frame will exceed a total maximum transmit
power of the user equipment, and if so, performing a power scaling of the transmit power
to reduce the transmit power required for the transmission of the MAC protocol data units
such that it is no longer exceeding the total maximum transmit power of the user
equipment, and transmitting the MAC protocol data units to the eNodeB within the
respective sub-frame, wherein the transmitted MAC protocol data units comprise at least
one MAC control element indicating the amount of power reduction applied to the
maximum transmit power of the user equipment for the configured uplink component
carriers.
Furthermore, according to another embodiment of the invention, the computer readable
medium may further store instructions that when executed cause the user equipment to
perform the steps of the methods for informing an eNodeB on the transmit power status
of a user equipment according to one of the various embodiments described herein.
Another embodiment of the invention related to the first aspect of the invention provides
a method for informing an eNodeB on the power status of a user equipment in a mobile
communication system using component carrier aggregation. The user equipment
determines whether an estimated transmit power required for transmitting protocol data
units on respective component carriers within a sub-frame will exceed a threshold value
relative to a total maximum UE transmit power of the user equipment. If the threshold
value is exceeded, the user equipment multiplexes a MAC control element to the
protocol data units and transmits the protocol data units including the MAC control
element to the eNodeB within the sub-frame. The MAC control element indicates to the
eNodeB that the transmit power spent by the user equipment for transmitting the
generated protocol data units on uplink exceeded the threshold value, i.e. is reporting the
power headroom per-user equipment. The threshold value may be for example defined
as a percentage of the maximum the user equipment is allowed to use.
According to a further embodiment of the invention, the MAC control element provides
the eNodeB with a per-user equipment power headroom relative to all uplink protocol
data units transmitted in the sub-frame. For example, in a 3GPP-based communication
system such as LTE-Advanced, the per-user equipment power headroom could account
for all transmissions on a physical uplink shared channel (PUSCH) and a physical uplink
control channel (PUCCH) within the sub-frame.
In another embodiment of the invention, at least one uplink resource assignment is
received, wherein each uplink resource assignment is assigning resources for the
transmission of one of the protocol data units on one of the plural component carriers to
the user equipment. For each received uplink resource assignment a protocol data unit is
generated for transmission on the respective assigned component carrier. Each protocol
data unit is transmitted via a corresponding one of the component carriers according to
one of the received resource assignments.
According another embodiment of the invention, generating for each received uplink
resource assignment a protocol data unit comprises said multiplexing of the MAC control
element to at least one of said protocol data units. In a further embodiment of the
invention the MAC control element is multiplexed to one of the protocol data units or to
each of the protocol data units. The protocol data units may be for example generated by
executing a joint logical channel prioritization procedure.
According to an advantageous embodiment of the invention, the component carriers
each have a priority, and the MAC control element is multiplexed to the protocol data unit
to be transmitted on the highest priority component carrier for which a resource
assignment has been received.
In an alternative embodiment of the invention, the component carriers each have a
priority, and the MAC control element is multiplexed to the protocol data unit to be
transmitted on the component carrier achieving the lowest block error rate, having the
largest power headroom or experiencing the best channel quality, and for which a
resource assignment has been received.
With regard to a further embodiment of the invention, the estimated transmit power is
estimated based on the resource assignments for the protocol data units to be
transmitted in the sub-frame and the status of a transmit power control function.
According to further embodiment of the invention radio resource control signaling is
received from the eNodeB indicating said threshold value as a percentage of the
maximum the user equipment is allowed to use. The threshold value is configured
according to the indicated percentage.
Another embodiment of the invention provides another alternative method for informing
an eNodeB on the power status of a user equipment in a mobile communication system
using component carrier aggregation. Protocol data units are transmitted in each of a
predetermined number of successive sub-frames (monitoring period) from the user
equipment to the eNodeB. At the user equipment a MAC control element is multiplexed
to the protocol data units of the last sub-frame of said predetermined number of
successive sub-frames transmitted by the user equipment, if one of the following
conditions is met:
- the transmit power required for transmitting the protocol data units in each of the
successive sub-frames exceeds a threshold value relative to the user equipment's
total maximum UE transmit power, or
- the transmit power required for transmitting protocol data units in a subset of sub-
frames of said successive sub-frames exceeds a threshold value relative to the user
equipment's total maximum UE transmit power, or
- the average transmit power required for transmitting the protocol data units in said
successive sub-frames exceeds a threshold value relative to the user equipment's
total maximum UE transmit power.
The MAC control element thus indicates to the eNodeB that the respective condition was
met.
In a further embodiment of the invention the number of sub-frames of said subset is
configured by RRC control signaling received at the user equipment from the eNodeB or
is predefined.
According to another embodiment of the invention, a MAC control element for
transmission from a user equipment to a eNodeB in a mobile communication system
using component carrier aggregation is provided. The MAC control element comprises a
power headroom field consisting of a predetermined number of bits for comprising a per-
user equipment power headroom with respect to all uplink transmissions of the user
equipment on a plurality of component carriers within a sub-frame containing the MAC
control element, relative to the total maximum UE transmit power of the user equipment.
In a further advantageous embodiment of the invention, the MAC control element
comprises a component carrier indicator field for indicating
- the number of component carrier for which the user equipment has received resource
assignments, or
- a bitmap indicating the component carriers for which the user equipment has
received resource assignments.
In another embodiment of the invention, the power headroom field comprises either said
per-user equipment power headroom or a per-component carrier power headroom. The
MAC control element comprises a component carrier indicator field that is indicating
whether the power headroom field comprises said per-user equipment power headroom
or said per-component carrier power headroom.
An additional embodiment of the invention provides a MAC protocol data unit for
transmission from a user equipment to a eNodeB in a mobile communication system
using component carrier aggregation. The MAC protocol data unit comprises a MAC sub-
header and a MAC control element according to one of the embodiments thereof
described herein. The MAC sub-header comprises a logical channel identifier (LCID) that
is indicating the content and format of said MAC control element.
According to another embodiment of the invention, a user equipment is provided for
informing a eNodeB on the power status of a user equipment in a mobile communication
system using component carrier aggregation. An determining section of the user
equipment determines whether an estimated transmit power required for transmitting
protocol data units on respective component carriers within a sub-frame will exceed a
threshold value relative to a total maximum UE transmit power of the user equipment. A
protocol data unit generation section of the user equipment multiplexes a MAC control
element to the protocol data units, if the threshold value is exceeded. A transmitting
section of the user equipment transmits the protocol data units including the MAC control
element to the eNodeB within the sub-frame. The MAC control element indicates to the
eNodeB that the transmit power spent by the user equipment for transmitting the
generated protocol data units on uplink exceeded the threshold value.
In an advantageous embodiment of the invention the MAC control element provides the
eNodeB with a per-user equipment power headroom relative to all uplink protocol data
units transmitted in the sub-frame.
For another embodiment of the invention a receiving section of the user equipment
receives at least one uplink resource assignment. Each uplink resource assignment is
assigning resources for the transmission of one of the protocol data units on one of the
plural component carriers to the user equipment. A protocol data unit generation section
of the user equipment generates for each received uplink resource assignment a
protocol data unit for transmission on the respective assigned component carrier. The
transmitting section transmits each protocol data unit via a corresponding one of the
component carriers according to one of the received resource assignments.
According to a further embodiment of the invention, the component carriers each have a
priority, and a protocol data unit generation section of the user equipment multiplexes the
MAC control element to the protocol data unit to be transmitted on the highest priority
component carrier for which a resource assignment has been received.
With regard to another embodiment of the invention, the component carriers each have a
priority, and a protocol data unit generation section of the user equipment multiplexes the
MAC control element to the protocol data unit to be transmitted on the component carrier
achieving the lowest block error rate, having the largest power headroom or experiencing
the best channel quality, and for which a resource assignment has been received.
In a further embodiment of the invention a power control section of the user equipment
performs power control, and the determining section determines the estimated transmit
power based on the resource assignment for the protocol data units to be transmitted in
the sub-frame and the status of a transmission power control section.
According to an advantageous embodiment of the invention, a receiving section of the
user equipment receives radio resource control signaling from the eNodeB indicating
said threshold value as a percentage of the maximum the user equipment is allowed to
use. A configuration section of the user equipment configures the threshold value
according to the indicated percentage.
A further embodiment of the invention provides a computer readable medium storing
instructions that, when executed by a processor of a user equipment, cause the user
equipment to inform am eNodeB on the power status of a user equipment in a mobile
communication system using component carrier aggregation. This is done as follows. It
is determined whether an estimated transmit power required for transmitting protocol
data units on respective component carriers within a sub-frame will exceed a threshold
value relative to a total maximum UE transmit power of the user equipment. If the
threshold value is exceeded, a MAC control element is multiplexed to the protocol data
units. The protocol data units including the MAC control element are transmitted to the
eNodeB within the sub-frame. The MAC control element indicates to the eNodeB that the
transmit power spent by the user equipment for transmitting the generated protocol data
units on uplink exceeded the threshold value.
Brief description of the Figures
In the following the invention is described in more detail in reference to the attached
figures and drawings. Similar or corresponding details in the figures are marked with the
same reference numerals.
Fig. 1 shows an exemplary architecture of a 3GPP LTE system,
Fig. 2 shows an exemplary overview of the overall E-UTRAN architecture of
LTE,
Fig. 3 and 4 show an exemplary localized allocation and distributed allocation of the
uplink bandwidth in a single carrier FDMA scheme,
Fig. 5 shows an exemplary SAE Bearer Architecture,
Fig. 6 shows the format of an exemplary MAC PDU,
Fig. 7 shows the format of a MAC control element for reporting a per-
component carrier power headroom (PH),
Fig. 8 shows a flow chart of an exemplary operation of a user equipment
according to one embodiment of the invention in line with the first aspect
of the invention,
Fig. 9 shows a flow chart of an exemplary operation of a user equipment
according to one embodiment of the invention in line with the first aspect
of the invention,
Fig. 10 shows power headroom reporting in a LTE-A system, where the known
power headroom reporting of LTE Rel. 8/9 is employed for each
component carrier individually,
Fig. 11 shows power headroom reporting in a LTE-A system according to an
embodiment of the invention, where the exemplary operation of a user
equipment according to Fig. 8 is employed,
Fig. 12 shows an exemplary power headroom reporting in a LTE-A system
according to an embodiment of the invention, where the exemplary
operation of a user equipment according to Fig. 9 is employed,
Fig. 13 shows another exemplary power headroom reporting in a LTE-A system
according to a further embodiment of the invention, where the exemplary
operation of a user equipment according to Fig. 9 is employed,
Fig. 14 to 16 show different formats of a power-limit MAC CE according to different
embodiments of the invention in line with the first aspect of the invention,
Fig. 17 shows an exemplary structure of a MAC PDU according to an
embodiment of the invention, wherein the MAC PDU contains three PHR
MAC CEs and corresponding sub-headers reporting on the power
headroom of three assigned component carriers within a single sub-
frame,
Fig. 18 show an exemplary MAC CE format ("multiple PHR MAC CE") according
to an embodiment of the invention in line with the first aspect of the
invention, allowing to report multiple power headroom reports in a single
MAC CE,
Figs. 19 & 20 show the Layer 2 structure with activated carrier aggregation for the
downlink and uplink respectively,
Fig. 21 shows a flow chart of an exemplary operation of a user equipment
according to one embodiment of the invention in line with the first aspect
of the invention, where a power scaling flag is used to signal indicate a
power limit situation of the user equipment to the eNodeB,
Fig. 22 shows a flow chart of an exemplary operation of a user equipment
according to one embodiment of the invention in line with the first aspect
of the invention, where a power status flag(s) and per-CC power
headroom report(s) are signaled to the eNodeB for indicating a power
limit situation of the user equipment,
Fig. 23 shows a flow chart of an exemplary operation of a user equipment
according to one embodiment of the invention in line with the first aspect
of the invention, where an per-CC amount of power reduction and per-
CC power headroom reports are signaled to the eNodeB for indicating a
power limit situation of the user equipment,
Fig. 24 shows a flow chart of an exemplary operation of a user equipment
according to one embodiment of the invention in line with the first aspect
of the invention, where an per-CC amount of power reduction and per-
CC power headroom reports are signaled to the eNodeB for indicating a
power limit situation of the user equipment.
Fig. 25 shows exemplary scenarios for a UE transmission power status and
corresponding power headroom, resulting in positive and negative power
headrooms,
Fig. 26 shows an exemplary scenario where user equipment is power limited,
i.e. applying power scaling on component carriers CC#1 and CC#2
configured in the uplink,
Figs. 27 & 28 show the definition of a per-component carrier power headroom
according to different embodiments of the invention,
Fig. 29 shows an exemplary structure of a MAC PDU according to an
embodiment of the invention, wherein Power Scaling (PS) flags are
included in the MAC sub-headers of the MAC PDU,
Fig. 30 shows an exemplary structure of a MAC sub-header for a per-CC PHR
MAC CE according to an embodiment of the invention, wherein the MAC
sub-header comprises a flag (PS flag) to indicate that the power
headroom report was triggered by a power limit situation of the user
equipment,
Fig. 31 shows an exemplary structure of a MAC PDU according to an
embodiment of the invention, wherein the MAC PDU contains three PHR
MAC CEs and corresponding sub-headers reporting on the power
headroom of three configured component carriers within a single sub-
frame, wherein the MAC sub-headers include a flag to indicate that the
power headroom report was triggered by a power limit situation of the
user equipment,
Fig. 32 shows a MAC CE according to an embodiment of the invention, wherein
the MAC CE is indicating the amount of power reduction applied to the
corresponding uplink component carrier, and
Fig. 33 shows a MAC CE according to an embodiment of the invention, wherein
the MAC CE is indicating the power scaling factor applied to the
transmission on the corresponding uplink component carrier.
Detailed Description of the Invention
The following paragraphs will describe various embodiments of the invention. For
exemplary purposes only, most of the embodiments are outlined in relation to an
orthogonal single-carrier uplink radio access scheme according to the LTE-Advanced
(LTE-A) mobile communication system discussed in the Technical Background section
above. It should be noted that the invention may be advantageously used for example in
connection with a mobile communication system such as the LTE-Advanced
communication system previously described, but the invention is not limited to its use in
this particular exemplary communication network.
The explanations given in the Technical Background section above are intended to better
understand the mostly LTE-Advanced specific exemplary embodiments described herein
and should not be understood as limiting the invention to the described specific
implementations of processes and functions in the mobile communication network.
Nevertheless, the improvements proposed herein may be readily applied in the
architectures/systems described in the Technical Background section and may in some
embodiments of the invention also make use of standard and improved procedures of
theses architectures/systems.
In the following exemplary description of the aspects and embodiments of the invention,
it is assumed that the transmit power available for uplink transmissions in a user
equipment (total maximum UE transmit power) is not set per component carrier, but per
user equipment. As a consequence the power setting in one component carrier has
influence on the power setting in another component carrier. If user equipment includes
only power headroom reports of some of the assigned component carriers, the eNodeB
cannot determine how much power was actually spent by the user equipment for
transmitting the sub-frame and if the user equipment still has power available to a
transmission with increased power (i.e. there is a power headroom) in one of the
following sub-frames or if there were already problems and the user equipment reached
it's power limit, hence already transmitting on some of the component carriers with less
power than was demanded by eNodeB. The UE reaching its power limit means that the
UE is utilizing or exceeding the total maximum UE transmit power it has available for
uplink transmission.
As mentioned earlier herein, one first aspect of the invention is to enable to UE to
indicate to the eNodeB when it is potentially becoming power limited or is power limited,
i.e. when being close to using its total maximum UE transmit power (also referred to as
"user equipment's total maximum transmit power", "total maximum UE transmit power of
the user equipment" or "user equipment's total maximum UE transmit power" in the
following) or the resource allocations and power control commands of the eNodeB would
require using a transmit power exceeding the user equipment's total maximum UE
transmit power.
Please note that in this document, the transmission of (MAC) protocol data units or
transport blocks in a sub-frame means that there has been a resource allocation for a
respective one of the protocol data units on a respective one of the component carriers
usable by the user equipment. Usable means that the user equipment can be assigned
resources on each of these component carriers - however, the component carriers on
which the user equipment is allowed to transmit data (in form of protocol data units or
transport blocks) within a given sub-frame is decided by the scheduler (e.g. implemented
in the eNodeB) and is controlled by the resource assignments to the user equipment.
The usable (uplink) component carriers of a user equipment are also referred to as
configured (uplink) component carriers herein. In most examples herein, it is assumed
that the configured component carriers are active, i.e. configured component carrier and
active component carrier are synonyms. In this case, it can be assumed that the user
equipment can be scheduled on the configured component carriers. Accordingly, the
power status of the user equipment will be reported for component carriers for which the
user equipment can receive a resource allocation from the scheduler, i.e. the configured
component carriers (or available component carriers).
Please note that besides a configured/non-configured state of a component carrier, there
may be optionally an additional active/inactive state defined for a configured component
carrier. In this case, the user equipment may receive a resource allocation for a
component carrier that is configured and active i.e. the user equipment is monitoring for
resource assignments (e.g. PDCCH) allocating uplink resources on those configured
respectively activated uplink component carriers. The invention may also be applied in
systems where these two kinds of states are distinguished, for example, where a
component carrier may have the states: non-configured, configured but inactive
("inactive"), and configured and active ("active"). In these systems, the power status
reporting for a user equipment according to one of the different aspects discussed herein
may be performed only for the active component carriers of the user equipment in the
uplink. Further, for these type of systems, the configured component carriers mentioned
in the different exemplary embodiments of the invention herein would correspond to
configured and active component carriers (or active component carriers for short).
Furthermore, in this document, a transmission on an "assigned component carrier" refers
to a transmission of a protocol data unit (MAC PDU) on a component carrier for which
the user equipment has received a resource assignment (also referred to as scheduling
grant, grant (for short) or PDCCH).
In one exemplary implementation of the first aspect of the invention, the user equipment
signals its uplink power status by means of an indicator to the eNodeB that is indicating
whether the user equipment applied power scaling to the transmission power within the
respective sub-frame. The indicator may be provided for each configured or assigned
component carrier individually, i.e. the user equipment may include multiple indicators to
the protocol data units to indicate for each assigned component carrier, whether the user
equipment has scaled down the transmission power for the transmission on the
respective component carrier. For example, the indicator(s) may be transmitted by the
user equipment in the protocol data units (MAC PDUs) of each sub-frame. The
indicator(s) may be for example included in one or more MAC sub-headers of the MAC
PDUs.
In case the power status indicator should be provided per assigned component carrier,
the respective indicators may be for example multiplexed to the protocol data units (MAC
PDUs) transmitted by the user equipment on the respective assigned component carriers
in the uplink, such that each of the indicators can be associated to a respective
configured component carrier. For example, this may be realized by ensuring that the
power status indicator for a given component carrier is multiplexed to a protocol data unit
(MAC PDU) that is transmitted on the given component carrier.
If the an indication of the power status of the user equipment should be made prior to the
user equipment actually reaching its total maximum UE transmit power (pro-active
indication of the uplink power status), one or more threshold values (e.g. certain
percentage(s)) could be defined relative to the total maximum UE transmit power, that
when exceeded, trigger(s) the user equipment to set the power status indicator. When
set, the indicator would indicate to the eNodeB that the user equipment is close to using
the total maximum UE transmit power (i.e. exceeded the threshold value).
Optionally, the power status indicator and threshold value(s) could be defined per
configured or assigned component carrier individually relative to the maximum transport
power of the respective configured component carrier. Hence, the indicator may be
signaled for each configured assigned uplink component carrier individually and may be
for example included in one or more MAC sub-headers of the MAC PDUs.
In another, second exemplary implementation of the first aspect of the invention the user
equipment is transmitting a power headroom report for each configured uplink
component carrier (also referred to as per-component carrier power headroom report(s)),
if the user equipment has to apply power scaling to a transmission of MAC PDUs in a
given sub-frame in view of the resource allocations and power control commands. The
per-component carrier (per-CC) power headroom report(s) are transmitted together with
an indicator that the per-CC power headroom report(s) has/have been triggered by the
estimated transmit power required for transmitting the protocol data units within the given
sub-frame exceeding the total maximum transmit power of the user equipment.
Alternatively, the indicator could also be interpreted as an indication of power scaling
having been applied to the transmissions within the given sub-frame by the user
equipment due to this event.
Hence, in when the transmit power required for a transmission of the protocol data units
on uplink component carriers within the respective sub-frame will exceed a total
maximum transmit power of the user equipment, an aperiodic per-CC power headroom
report for all configured uplink component carrier(s) is triggered and sent by the user
equipment. The indication of the trigger for the per-CC power headroom report(s) being
may be for example included in a MAC-sub header of a MAC PDU carrying a per-CC
power headroom report in a MAC control element.
This second exemplary implementation may also be adapted to pro-actively report the
power status of the user equipment. Similar to the example described above, one or
more threshold values may be defined relative to the total maximum UE transmit power,
that when exceeded, triggers the user equipment to send a power headroom report for
each configured uplink component carrier, if there is no grant available for a component
carrier, the user equipment may for example calculate the power headroom from this
component carrier based on some predefined uplink grant or respectively predefined
PUSCH power.
Furthermore, a power headroom report for each configured uplink component carrier
may be optionally sent together with an indication that the respective power headroom
report was triggered by exceeding the total maximum transmit power of the user
equipment or a threshold relative thereto. For example, such indication could be
comprised in a MAC sub-header of a MAC control element conveying a power headroom
report for a configured uplink component carrier of the user equipment.
According to a further, third exemplary implementation of the first aspect of the invention,
the user equipment reports to the eNodeB the amount of power reduction applied to the
maximum transmit power of a component carrier. Alternatively, instead of the power
reduction for a component carrier, the effective maximum transmit power of the
configured uplink component carrier after applying the component carrier-specific power
reduction could be signaled to the eNodeB. The amount of power reduction may be for
example signaled per configured uplink component carrier of the user equipment. If the
power reduction for a given component carrier is considering the transmissions on other
configured component carriers, the power reduction applied to the component carriers
might become equal (but not necessarily). In one further example, the amount of power
reduction may be signaled together with a power headroom report for each configured
uplink component carrier to the eNodeB.
The information on the user equipment's power status may be signaled in form of one or
more MAC control elements that are comprised within the MAC PDU(s) of a given sub-
frame.
In another fourth exemplary implementation of the invention, a new MAC control element
is defined to enable to UE to indicate to the eNodeB when it is potentially becoming
power limited or is power limited. This new MAC CE is inserted by the user equipment to
one or more protocol data units transmitted on respective (assigned) component carriers
within a single sub-frame that is providing the eNodeB with a corresponding indication.
The MAC control element may be inserted to the protocol data units of a sub-frame. For
example, the MAC control element may inserted into one of the protocol data units
transmitted by the user equipment within the sub-frame or all of the protocol data units
transmitted by the user equipment within the sub-frame.
Furthermore, in addition to the indication of the user equipment approaching its total
maximum UE transmit power, the control element inserted to the protocol data units may
further indicate a per-user equipment (per-UE) power headroom. For example, the per-
user equipment power headroom indicates the transmit power unused by the user
equipment when transmitting the protocol data units (including the MAC control element)
within the sub-frame relative to the user equipment's total maximum transmit power.
Unlike the power headroom indicated in LTE Rel. 8/9, the power headroom indicated in
the MAC control element is considering the transmissions (protocol data units) on all
assigned or configured component carriers (i.e. more than one component carrier) within
the sub-frame and is therefore not a per-component carrier power headroom, but per-
user equipment power headroom.
in one exemplary embodiment of the invention, this per-user equipment power headroom
is not only taking into account the transmit power required for the transmission of
protocol data units via physical uplink data channels, but also the transmit power
required for the transmission of control signaling via physical control channels. In one
more detailed implementation is thus accounting for the transmit power required for
transmitting user data and control data (protocol data units) on the assigned or
configured component carriers via the physical uplink shared channel (PUSCH) and the
physical uplink control channel (PUCCH).
In a fifth exemplary implementation of the first aspect of the invention, the user
equipment sends per-CC power headroom reports for all assigned component carriers
within a single sub-frame when the user equipment is potentially becoming power limited
or is power limited, i.e. when being close to using its total maximum UE transmit power
or the resource allocations and power control commands of the eNodeB would require
using a transmit power exceeding the user equipment's total maximum UE transmit
power. Hence, the estimated transmit power exceeding a given threshold value or the
total maximum UE transmit power, as applicable, triggers the generation and
transmission of per-CC power headroom reports within the sub-frame for which one of or
both events occurred.
Please note that according to an exemplary embodiment of the invention, the per-CC
power headroom reports for ail assigned or configured component carriers are
transmitted on the respective assigned or configured component carriers to which they
refer. In case of reporting on all configured component carriers, and in case resources
are not granted on all configured component carriers for the given sub-frame, the user
equipment may assume a predefined resource allocation or alternatively predefined
PUSCH power on those configured component carriers for which no uplink resource
assignment is applicable in the given sub-frame.
In the exemplary fifth implementation, a potentially employed prohibit timer controlling the
power headroom reporting on a respective one of the assigned component carrier may
be overwritten/ignored, so that the per-CC power headroom reports can be sent in the
instant sub-frame.
In an alternative exemplary embodiment of the invention, the per-CC power headroom
reports may also be transmitted within a single protocol data unit on one of the assigned
component carriers. In this example, the respective component carrier to which a
respective per-CC power headroom report refers may be for example identified by
including a component carrier identifier into the power headroom reports. Alternatively,
there may be a new MAC control element defined ("all component carrier power
headroom report") that is indicating the power headrooms of the assigned or configured
component carriers ordered according to the priority of the component carriers to which
they refer.
Furthermore, please note that in the first and the second aspect of the invention, the
decision of whether the user equipment is approaching (or is in) a power limit situation
may be determined in different fashions. In one exemplary implementation, the user
equipment determines (or more correctly estimates) the transmit power it will have to
spend for transmitting the protocol data units on the uplink component carriers within a
sub-frame and compares the determined (or estimated) transmit power to a threshold.
This threshold may be for example a certain percentage (e.g. in the range 80% to 100%)
of the total maximum UE transmit power. The transmit power required for transmitting the
protocol data units on the uplink component carriers may be for example determined
using a transmit power control formula. In other exemplary implementations, the user
equipment determines (or more correctly estimates) the transmit power it will have to
spend for transmitting the protocol data units on the assigned component carriers within
a sub-frame for a given number of successive sub-frames (i.e. a monitoring time period)
and decides based on criteria further outlined below, whether to include a MAC control
element to indicate a power limit situation to the protocol data units of the last sub-frame
of said monitoring time period.
Independent on which of the different implementations of the first aspect of the invention
is used, the signaled power status information enables the eNodeB to derive the power
status for each user equipment that is signaling its power status information. The
scheduler of the eNodeB may for example take into account the power status of the
respective user equipments in its dynamic and/or semi-persistent resource allocations to
the respective user equipments.
Another second aspect of the invention is to suggest a definition for a per-CC power
headroom when reporting the power headroom in a mobile communication system using
carrier aggregation in the uplink. According to one exemplary definition, per-CC power
headroom of a configured uplink component carrier is defined as the difference between
the maximum transmit power of the configured uplink component carrier and the used
uplink transmit power. In a 3GPP system, the used uplink transmit power may also be
referred to as the transmitted PUSCH power. Alternatively the used uplink transmit
power may additionally include the transmitted PUCCH power.
As the used uplink transmit power is considering power scaling (if applied), it may be
different from the estimated transmit power which is the transmit power required for a
transmission of the MAC PDUs on uplink component carriers within the respective sub-
frame as a result of the power control formula. The used transmit power may therefore
by considered to be equal to the product of the power scaling factor and the estimated
transmit power. In case no power scaling is applied (scaling factor = 1) the two values of
the transmit power are equal.
Alternatively, a power headroom of a configured uplink component carrier may be
defined as the difference between the maximum transmit power of the configured uplink
component carrier and an estimated transmit power. In a 3GPP system, the estimated
uplink transmit power may also be referred to as the estimated PUSCH power. The
estimated uplink transmit power respectively the estimated PUSCH power is for example
calculated by the power control formula for the respective uplink component carrier.
Furthermore, the maximum transmit power of the (configured) uplink component carrier
may take into account a power reduction due to simultaneous transmissions on another
or other uplink component carriers in the sub-frame. The maximum transmit power of a
configured uplink component carrier may thus not be the same as the total maximum UE
transmit power.
The per-CC power headroom according to the second aspect of the invention may be
provided in form of a per-CC power headroom report. The per-CC power headroom
report is for example signaled in form of a MAC control element within a MAC PDU. As
mentioned above, the MAC control element carrying the per-CC power headroom report
may be associated to a MAC sub-header in a header section of the MAC PDU that can
be further employed to indicate that the per-CC power headroom is triggered by a power
limited situation of the user equipment requiring power scaling.
In the following different embodiments of the invention will be outlined. It is assumed in
these embodiments that the user equipment is operated in a mobile communication
system that is using carrier aggregation and that the user equipment is configured with
plural component carriers, i.e. is capable of transmitting uplink data on plural component
carriers simultaneously within individual sub-frames. Uplink transmissions are assumed
to be scheduled by a scheduler by means of resource assignments. The resources may
be assigned on a semi-persistent or per-sub-frame/per-TTI basis. The scheduler is for
example implemented in the eNodeB.
Furthermore, it should be noted that the scheduler may assign one or more (up to all) of
the plurality of configured component carriers for a given sub-frame and the user
equipment is transmitting a respective transport block/protocol data unit on each
assigned component carrier, i.e. each component carrier for which a resource
assignment has been received. Please note that when using MIMO in the uplink, two or
more protocol data units may be transmitted in one sub-frame on one component carrier,
the actual number of protocol data units per component carrier depending on the MIMO
scheme. Using the 3GPP terminology, the resource assignments may also be referred to
as grants or PDCCH. In addition, the there may be a respective transmit power loop
implemented per component carrier configured for the user equipment, i.e. the transmit
power control function implemented in the user equipment and the eNodeB perform
transmit power control for each component carrier individually.
Moreover, in a further exemplary embodiment of the invention, a joint logical channel
prioritization procedure may be used for to the generation of the protocol data units for
transmission within a sub-frame. Different exemplary implementations of such joint
logical channel prioritization procedure are described in the co-pending European patent
application no. 09005727.4 (attorney's docket no. EP64934DKFH) and the co-pending
European patent application no. 09013642.5 (attorney's docket no. EP649341DKFH).
The two European patent applications will be referred to as Application 1 and
Application 2 in the following where appropriate.
Per-UE power headroom MAC CE
Fig. 8 shows a flow chart of an exemplary operation of a user equipment according to
one embodiment of the invention in line with the first aspect of the invention. The user
equipment receives 801 plural resource assignments for a given sub-frame and
estimates 802 the transmit power (ETP) required for uplink transmissions on assigned
component carriers according to received resource assignments. In one exemplary
embodiment of the invention, the transmit power is estimated by the user equipment
based on the received resource assignments for the protocol data units to be transmitted
in the sub-frame and the status of a transmit power control function of the user
equipment. For example, the user equipment may estimate the transmit power needed
for each of the transport blocks depending on which component carrier they are located
on and based on the state of the transmit power function of the component carrier. The
estimated transmit power is then the sum of the individual transmit power for all assigned
transport blocks.
Next, the user equipment determines 803, whether the estimated transmit power (ETP)
is exceeding a certain threshold value. In the example of Fig. 8, this threshold is defined
as a certain percentage P of the total maximum UE transmit power (MATP) of the user
equipment. Please note that this would be equivalent to determining whether the ratio of
the estimated transmit power (ETP) and the total maximum UE transmit power (MATP),
is exceeding a threshold value, that would be equivalent to the percentage P, i.e.
-™->P.
MATP
If the threshold value is not exceeded, the user equipment is not in a power limit
situation, so that no report thereon needs to be signaled to the eNodeB. Accordingly, the
user equipment will next generate 804 the protocol data units for transmission on the
respective assigned component carriers and transmits 805 the protocol data units (which
are referred to as transport blocks in the Physical layer) to the eNodeB via the assigned
component carriers. Please note that the generation of the protocol data units can be for
example implemented as described in Application 1 or Application 2.
If the threshold value is exceeded, the user equipment determines 806 the per-user
equipment power headroom for all transmissions according to the resource assignments.
As outlined above, this per-user power headroom is determined for all protocol data units
to be transmitted within the given sub-frame on the assigned component carriers. The
per-user equipment power headroom essentially indicates how much transmit power on
top of what is to be used for transmitting the protocol data units in the sub-frame
(estimated transmit power) is remaining relative to the total maximum UE transmit power
of the user equipment. Simplified, the power headroom (PH) indicates the difference
between total maximum UE transmit power of the user equipment and the estimated
transmit power, i.e. PH = MATP- ETP .
The user equipment further generates 807 a MAC control element that is comprising the
determined per-user equipment power headroom ("per-UE power headroom MAC CE")
and provides the per-UE power headroom MAC CE to a protocol data generation section
that generates 808 the protocol data units for transmission according to the resource
assignments, similar to step 804. However, in step 808 the per-UE power headroom
MAC CE is included in this generation process, so that depending on the implementation
per-UE power headroom MAC CE is included in one of the protocol data units or all of
the protocol data units. Subsequently the generated protocol data units including the per-
UE power headroom MAC CE are transmitted 809 to the eNodeB on the assigned
resources.
Fig. 11 shows power headroom reporting in a LTE-A system according to an
embodiment of the invention, where the exemplary operation of a user equipment
according to Fig. 8 is employed. In most situations, the operation is corresponding to the
operation of the user equipment as has been outlined with respect to Fig. 10 previously
herein. In contrast to Fig. 10, it is assumed that at Tt the user equipment has received
three resources assignments for all three component carriers for the sub-frame at Ts,
however the transmit power control function has is yielding a gain factor for the
transmission that high that given the resource allocation, the estimated transmit power
exceeds the total maximum UE transmit power (see step 803 of Fig. 8). Accordingly, in
this case the user equipment determines the per-UE power headroom and multiplexes
the per-UE power headroom MAC CE (also referred to as power-limit MAC CE in the
following) to the protocol data unit transmitted on component carrier CoCal. The
scheduler in the eNodeB receiving the uplink transmission can now detect based on the
per-UE power headroom MAC CE that the user equipment is in a power limit situation
and can adapt the further scheduling and/or power control of the user equipment
accordingly.
As apparent from the above, per-UE power headroom MAC CE may basically have two
functions. The first and most important function is that the sole reception of the per-UE
power headroom MAC CE by eNodeB already informs eNodeB that a problem with the
transmit power for the uplink transmissions existed in the sub-frame. Secondly, the per-
UE power headroom MAC CE may also be reporting the per-user equipment power
headroom of the user equipment, thus yielding more detailed information on the exact
power situation in the user equipment to the eNodeB.
In one alternative exemplary implementation according to another embodiment of the
invention, the user equipment is not immediately including a power-limit MAC CE to the
protocol data units transmitted on the uplink if the estimated transmit power exceeds the
threshold. For example when the threshold is exceeded, instead of transmitting the
power-limit MAC CE immediately, the user equipment start monitoring the estimated
transmit power for a certain number of sub-frames, i.e. for a given monitoring period of
sub-frames. Having monitored the given number of sub-frames, the user equipment
decides whether or not a power-limit MAC CE is to be included to the protocol data units
to be transmitted in the next sub-frame following certain criteria. Please note that the
power-limit MAC CE may for example be transmitted in the last sub-frame transmitted in
the monitoring period, if the user equipment decides to insert same.
These criterions may be for example:
- Estimated transmit power of the uplink transmissions in each of the sub-frames within
the monitoring period was above a threshold value.
- Estimated transmit power of the uplink transmission in some of the sub-frames within
the monitoring period was above the threshold. The number of sub-frame required for
sending the power-limit MAC CE at the end of the monitoring period is configured by
eNodeB per UE through RRC signaling or alternatively can be set to a fixed value
defined in the specifications.
- The average estimated transmit power of the uplink transmissions in the sub-frames
within the monitoring period was above the threshold.
The monitoring of the estimated transmit power for a given time period, i.e. a certain
number for sub-frames, has the advantage that the power-limit MAC CE is not reported
immediately when the threshold is crossed, which may avoid unnecessary reporting of a
power-limit situation to the eNodeB if the threshold is exceeded only sporadically.
However, since the power-limit MAC CE is indicating an emergency situation to the
eNodeB and countermeasures should be taken by eNodeB after receiving the power-
limit MAC CE, the drawback of introducing a monitoring period is the delay in the
transmission of the power-limit MAC CE, once user equipment's transmit power has
crossed the threshold.
In a further alternative embodiment of the invention, the user equipment is configured
with two thresholds. Also the second, "additional" threshold may be for example set by
the eNodeB by RRC signaling. This second threshold may for example also be a fraction
of the total maximum UE transmit power of the user equipment, but is preferably higher
than the first threshold. Similar to the exemplary embodiments discussed above, the user
equipment again determines for each sub-frame whether the estimated transmit power of
a sub-frame exceeds the first threshold. If this is the case, i.e. the first threshold is
exceeded for a sub-frame, the user equipment starts monitoring the estimated transmit
power as described in the paragraphs above, for example for a given monitoring period.
If the second threshold is exceeded by the estimated transmit power of a sub-frame
within the monitoring period, the user equipment transmits a power-limit MAC CE within
that sub-frame for which the estimated transmit power exceeded the second threshold
was crossed.
In another alternative embodiment of the invention, the user equipment is multiplexing
the power-limit MAC CE to each of the protocol data units sent in the sub-frame via the
assigned component carriers. This may be advantageous in that the reliability of the
reception of the control element by eNodeB is increased.
Reporting Format of the per-UE power headroom MAC CE
The format for the per-UE power headroom MAC CE indicating a potential power
limitation of the user equipment ("power-limit MAC CE") could be based on the LTE Rel.
8/9 MAC CE format used for power headroom reporting as exemplified in Fig. 7. The
power headroom MAC CE consists of 8 bits, i.e. one octet. The first two bits are reserved
bits, and the remaining 6 bits indicate the power headroom. In one embodiment of the
invention, the format is maintained, but the 6 bit-field PH of the MAC CE format shown in
Fig. 7 includes the a per-UE power headroom determined by the user equipment (see for
example step 806 of Fig. 8). Optionally, in one embodiment of the invention, the per-UE
power headroom does not only transmissions on the PUSCH but also transmissions on
the PUCCH is taken into account while calculating the per-UE power headroom.
In order to distinguish the power-limit MAC CE from a LTE Rel. 8/9 power headroom
MAC CE, one of the two reserved bits (R) of the octet shown in Fig. 8, e.g. the highest bit
in the octet, is used to differentiate power headroom MAC CEs and power-limit MAC CEs
(i.e. the per-UE power headroom CEs). For example, if the highest bit in the octet is set
to 0, the MAC CE represents a power headroom report for that component carrier, i.e. a
per-CC MAC CE reporting a power headroom for the given component carrier - the per-
CC MAC CE reporting on the power headroom is thus a component carrier-specific MAC
control element. If the bit is set to 1, the reported power headroom is the per-UE power
headroom of the power-limit MAC CE. Please note that the power-limit MAC CE (i.e. the
per-UE power headroom CE can be considered to be UE specific, so that the power-limit
MAC CE can be considered a UE-specific MAC control element.
Please note that the differentiation of UE-specific and component carrier-specific MAC
control elements may lead to a different treatment and multiplexing of the MAC control
element to the transport block (MAC protocol data units) as explained in Application 2.
When user equipment is sending a power-limit MAC CE, it may be of additional value to
the eNodeB to acquire knowledge for which component carriers the user equipment
actually received resource assignments (uplink grants) in order to know, if the user
equipment obeyed all uplink grants correctly, or if it missed one or more of the uplink
grants. This information allows the eNodeB to determine, if the power-limit situation
exists already for a situation where the user equipment did not even transmit on all the
granted resources due having missed one or more of the uplink grants.
Therefore, in another embodiment of the invention, the another exemplary format for the
power-limit MAC CE is proposed which is including information on the component
carriers for which uplink grants have been received, respectively on the number of
received uplink grants.
An exemplary format of the power-limit MAC CE according to another embodiment of the
invention is shown in Fig. 14. This power-limit MAC CE consists of two fields, a first field
CCI (Component Carrier Indicator field) and a second field PH (Power Headroom) for
indicating the per-UE power headroom. The power-limit MAC CE is again one octet long.
Assuming that there are five component carriers configured for the user equipment, a
total of 25 =32 combinations of resource assignments are possible. As the user
equipment already indicates by sending data (including the power-limit MAC CE) via one
of the five component carriers, it is apparent that the user equipment has received an
uplink grant for this component carrier. Hence, 24 =16 combinations of resource
assignments remain for the four other configured component carriers, i.e. the CCI field
would consist of 4 bits for signaling all combinations (for example by indicating by means
of a bitmap, for which of the four other component carriers further uplink grants have
been received). Hence, the remaining four bits of the MAC CE format are left for the PH
field, allowing differentiating 16 per-UE power headroom values. The component carriers
other than the one on which the MAC CE is signaled, for which an uplink grant has been
received may be for example indicated by means of a bitmap. The actual mapping of
which bit in the bitmap represents which component carrier could be for example
configured by eNodeB through RRC signaling or can be determined by a priority order of
the component carriers, as for example outlined in Application 1 and Application 2.
In another embodiment, another MAC CE format shown in Fig. 15 is suggested. The CCI
field is only 3 bits in size, while the PH field has 5 bits. This format may be considered a
modification of the LTE Rel. 8/9 power headroom report MAC CE format in Fig. 7 in that
the two reserved bits (R) and one additional bit from the PH field are reused as the CCI
field. This implies of course reducing the granularity of the per-UE power headroom
values that can be reported from 6 to 5 bits.
As highlighted in Fig. 16 and as will be shown in Table 1 below, the MAC CE format for
reporting a per-UE power headroom as shown in Fig. 15 allows for indicating the number
of component carriers for which the user equipment received an uplink assignment while
also indicating the whether the MAC control element is a LTE Rel. 8/9 power headroom
MAC CE or a per-UE power headroom MAC CE, without requiring the assignment of a
new logical channel identifier (LCID) to the new per-UE power headroom MAC CE but
being able to also use the same LCID for a LTE Rel. 8/9 power headroom MAC CE and
per-UE power headroom MAC CE . The eNodeB would have to evaluate the first two bits
of the control element to determine whether a LTE Rel. 8/9 power headroom MAC CE or
a per-UE power headroom MAC CE.
If the first two bits are both set to 0, i.e. the reserved bits as shown in Fig. 7 are set to
zero, the MAC control element is a LTE Rel. 8/9 power headroom report as shown in
Fig. 7.
In any other case, the MAC control element is a per-UE power headroom MAC CE. If the
first two bits are not set to 0, the eNodeB needs to also evaluate the third bit within the
octet, as the first three bits yield the number of uplink grants received by the user
equipment. The remaining five bits (see Fig. 15) - the PH field - indicate the per-UE
power headroom value.
When user equipment has a power limit situation, one way the eNodeB may react to the
reporting thereof by a power-limit MAC CE is to reduce the number of the component
carriers on which the user equipment is simultaneously scheduled. It would be
advantageous, if the user equipment assists the eNodeB in choosing on which of the
component carriers resources should be scheduled to the UE. Accordingly, in another
embodiment of the invention, the power-limit MAC CE may be used to not only signal the
per-UE power headroom in a PH field, but to also suggest to the eNodeB for which
component carriers the eNodeB should further send resource assignments. In one
example, this is implemented in a similar fashion as described previously herein with
respect to Fig. 14. Instead of indicating the component carriers for which a uplink grant
has been received, the four bits of the CCI field may be used to signal a bitmap that
indicates on which the component carriers (other than the one on which the power-limit
MAC CE is received), the eNodeB should continue to give grants on. Alternatively, the
bitmap could represent the component carriers the eNodeB should stop giving grants on.
In a further embodiment of the invention, the MAC CE as shown in Fig. 7 is used for the
per-UE power headroom reporting. One of the two reserved bits, e.g. the first reserved
bit shown in Fig. 7 is used to identify whether the MAC CE is a LTE Rel. 8/9 power
headroom MAC CE or a per-UE power headroom MAC CE. In both cases the PH field
may be 6 bits and indicates a per-CC headroom as in LTE Rel. 8/9 or the per-UE power
headroom. Furthermore, if the MAC control element is a per-UE power headroom MAC
CE, the component carrier on which the control element has been transmitted is the
component carrier the user equipment is suggesting to the eNodeB for further resource
assignments thereon.
As indicated above, the MAC control element formats discussed above with respect to
Fig. 7, and Fig. 14 to 16 have the advantage that - in comparison to LTE Rel. 8/9 - no
new logical channel identifier needs to be assigned for the per-UE power headroom
reports. As shown in Fig. 6, a MAC PDU yields the format of the MAC control elements
included in the MAC PDU payload by respective logical channel identifiers in the sub-
header of the respective MAC control elements. In another embodiment of the invention
a new logical channel identifier (LCID) is defined for indicating a per-UE power headroom
MAC CE. Hence this embodiment of the invention provides a MAC PDU comprising a
sub-header ("per-UE power headroom MAC CE sub-header") and the related MAC CE,
The per-UE power headroom MAC CE sub-header comprises a LCID that is identifying
the related MAC CE being a per-UE power headroom MAC CE.
The format of the per-UE power headroom MAC CE may be again that described in one
of the embodiments relating to Fig. 7, Fig. 14 or Fig. 15 above, however, no indicating of
a LTE Rel. 8/9 power headroom MAC CE may need to be included in the format
definition any more, as the differentiation of the LTE Rel. 8/9 power headroom MAC CE
and per-UE power headroom MAC CE is now achieved by means of the LCID in the sub-
header of the MAC PDU.
Selection of the Component Carrier for transmitting the
per-UE power headroom MAC CE
When user equipment include the power-limit MAC CE into the protocol data units
transmitted in the given sub-frame, the transmit power that is available for UL
transmissions is already critical. Therefore the transport block of the most reliable
component carrier needs to be chosen for the inclusion of the power-limit MAC control
element.
The criterion for the selection of the most reliable component carrier can be based on the
following conditions. One option would be to choose the component carrier which is the
"special cell", i.e. the component carrier where the UE camps on and reads system
information from. Another option would be to choose from the set of component carriers
with UL transmissions the one with the best physical parameters. Parameters could be
for example the target BLER or the actual power headroom of a component carrier.
Furthermore, if a priority ranking of the component carriers is already known to UE the
UE could send the power-limit MAC CE always on the component carrier with the highest
priority.
Setting of the Threshold Value
In each sub-frame where user equipment has been assigned resources for uplink
transmission in at least one of it's aggregated component carriers, the user equipment
may calculate the transmit power needed to fulfill all uplink grants (resource
assignments) in that sub-frame, i.e. determines the estimated transmit power required in
this sub-frame. As explained above, a threshold may be configured relative to the total
maximum UE transmit power which essentially indicates the maximum transmit power
the user equipment is allowed to (or able to) spend on all uplink transmissions on the
component carriers in the given sub-frame.
The threshold may be, for example, configured by the eNodeB in relation to the total
maximum UE transmit power. The threshold may be, for example, set by eNodeB for
each user equipment individually and the value of the threshold could be, for example,
conveyed to respective user equipments via RRC signaling. The threshold may be for
example a fractional value of (or percentage P) of the total maximum UE transmit power.
As outlined previously, in case the user equipment would need more power for all uplink
transmissions on the uplink component carriers than defined by the threshold value or
the total maximum UE transmit power, an indication of user equipment's power status,
e.g. a power-limit MAC CE, is included in the uplink transmissions of the sub-frame.
It should be noted that the user equipment's estimated transmit power might not only
cross the configured threshold but may be even above the total maximum available
power of the user equipment. In the latter case user equipment is already in a severe
power-limited situation and cannot fulfill all uplink resource assignments as demanded by
eNodeB.
Furthermore, it should also be noted that according in all aspects and embodiments of
the invention, the reporting of the user equipment's power status does not necessarily
need to be proactive, i.e. ETP > P ¦ MAT? , but that the threshold value may not be use
(P = l). Basically, this means that the user equipment is triggered to report the power
status when the estimated transmit power exceeds the total maximum US transmit power
(i.e. ETP > MATP). In this case, the power status information (indicator, power-limit MAC
CE, etc.) indicate whether, respectively, that the user equipment applied power scaling in
the given sub-frame, while in case of using a threshold value the power status
information may already be signaled prior to the user equipment having to use power
scaling on the uplink component carriers.
Power Scaling Flag
According to another exemplary embodiment of the invention in line with the first aspect
of the invention, the user equipment is not sending any detailed information to the
eNodeB regarding its power status, but indicates to the eNodeB in each transmission,
whether the user equipment applied power scaling to the transmissions in the uplink or
not. For this purpose, one or more indicators may be comprised in the protocol data units
transmitted by the user equipment. This indicator is also referred to as a power scaling
flag. The power scaling flag may be provided on one of the assigned component carriers
or on all assigned component carriers. For example, the power scaling flag to be
transmitted on a given component carrier may be included to a protocol data unit
transmitted on the given assigned component carrier.
According to one embodiment of the invention, the power scaling flag is defined in one of
the two reserved/unused bits of a MAC PDU sub-header known from the LTE Rel. 8/9
sub-header format. If the power-scaling (PS) flag is set (e.g. =1) the estimated transmit
power for the transmissions within a sub-frame has been scaled down, i.e. the estimated
transmit power exceeded the total maximum UE power. If the PS flag is not set (e.g. =0)
the user equipment did not apply power scaling within the sub-frame.
Alternatively, if the PS flag is provided for individual configured component carriers, the
flag indicates whether the transmit power, e.g. PUSCH power, for the respective
configured component carrier has been scaled down. For example, if uplink control
information (UCI) is multiplexed with a transport block (MAC PDU) for an assigned uplink
component carrier in the physical layer, the transmission on this assigned uplink
component carrier may not be scaled down, although other PUSCH transmission(s) on
the other uplink component carrier(s) - comprising no uplink control information - are
power scaled.
3GPP based system using carrier aggregation in the uplink, like LTE-A, the setting of the
PS flag may indicate that the PUSCH power for the corresponding transport block (MAC
PDU) was scaled down due to power limitations. Consequently the bit set to zero
indicates that no power scaling was applied.
Fig. 29 shows an exemplary MAC PDU according to an embodiment of the invention.
Since there is one MAC PDU sub-header in a MAC PDU for every MAC SDU (Service
Data Unit) which contains RLC PDUs of a logical channel (identified by the LCID) which
has data in the MAC PDU, the PS flag could be set in any one of, all of or a sub-set of
the MAC PDU sub-headers within a given MAC PDU. In principle it is sufficient, if only
one of the MAC PDU sub-header, e.g. the first MAC PDU sub-header of a MAC PDU
contains a power-scaling flag (PS flag). This may simplify the processing of the MAC
PDUs in the user equipment and eNodeB, as only one bit would need to be set in one of
the MAC PDU sub-headers, respectively analyzed by the eNodeB.
Furthermore as already mentioned before, it could be alternatively defined that instead of
setting the power scaling flag when being power limited, the flag could be set when the
required uplink transmission power exceeds a certain predefined or signaled threshold of
the maximum allowed transmission power.
According to another exemplary embodiment of the invention, per-CC power headroom
reports for the configured or assigned component carriers may be triggered, if the
estimated transmit power for a given sub-frame exceeds the total maximum UE transmit
power or a threshold relative thereto. This will be outlined in further detail below. In this
embodiment, the power status flag (or also referred to as power-scaling flag) is signaled
together with the per-CC power headroom reports. Hence, a power status flag is
provided in each MAC PDU sub-header for the MAC CE comprising the per-CC power
headroom for the respective assigned or configured component carrier. In this
embodiment, the power status flag may be thus considered as an indication that the per-
CC power headroom report signaled within the MAC CE of the MAC PDU for a given
assigned or configured component carriers has been triggered by the estimated transmit
power for the given sub-frame exceeded the total maximum UE transmit power or a
threshold relative thereto. Alternatively the power status flag could be signaled using one
of the two reserved/unused bits in the MAC control element containing the per- CC
power headroom report itself.
Fig. 30 shows an exemplary embodiment of a MAC PDU sub-header for a power
headroom report MAC CE including a power status flag. In case the MAC PDU with the
per-CC power headroom MAC CE for a configured component carrier is signaled on the
respective assigned component carrier, no extra identification of the component carrier to
which the per-CC power headroom MAC CE pertains.
In case the per-CC power headroom MAC CE is to be signaled for a configured
component carrier for which there is no resource assignment available in the given sub-
frame the user equipment may for example calculate the power headroom from this
component carrier based on some predefined uplink grant or respectively predefined
PUSCH power. The per-CC power headroom MAC CEs for the configured component
carrier may be signaled in one MAC PDU on an assigned component carrier. Fig. 31
shows an exemplary MAC PDU comprising per-CC power headroom MAC CEs for three
configured component carriers of a user equipment. IN this exemplary embodiment,
special logical channel IDs (LCIDs) are defined for the respective component carriers, so
as to be able to associate the per-CC power headroom MAC CEs with the respective
component carrier they refer to.
Fig. 21 shows a flow chart of an exemplary operation of a user equipment according to
one embodiment of the invention in line with the first aspect of the invention. The user
equipment receives 2101 (similar to step 801 of Fig. 8) plural resource assignments for a
given sub-frame and estimates 2102 (similar to step 802 of Fig. 8) the transmit power
(ETP) required for uplink transmissions on assigned component carriers according to
received resource assignments. In one exemplary embodiment of the invention, the
transmit power is estimated by the user equipment based on the received resource
assignments for the protocol data units to be transmitted in the sub-frame and the status
of a transmit power control function of the user equipment as explained with respect to
Fig. 8 above.
Next, the user equipment determines 2103, whether the estimated transmit power (ETP)
is exceeding the total maximum UE transmit power (MAT? or PCUAX). If the total
maximum UE transmit power is not exceeded, the user equipment is not in a power limit
situation, so that no power status report thereon needs to be signaled to the eNodeB.
Accordingly, the user equipment will next generate 2104 (similar to step 804 of Fig. 8)
the protocol data units for transmission on the respective assigned component carriers.
Please note that the generation of the protocol data units can be for example
implemented as described in Application 1 or Application 2. For example as part of this
generation process of step 2104, the user equipment further sets 2105 one or more
indicator(s) - i.e. power scaling flag(s) - in the MAC PDUs to indicate that no power
scaling has been applied by the user equipment to the transmission of the MAC PDUs
generated in step 2104. For example, each MAC PDU may comprise a respective power
scaling flag in one or more of the MAC PDU sub-headers for a given assigned
component carrier on which the MAC PDU's are transmitted in step 2106.
In case the estimated transmit power exceeds the total maximum UE transmit power in
step 2103, the user equipment will next generate 2107 (similar to step 2104 of Fig. 21)
the protocol data units for transmission on the respective assigned component carriers
further sets 2108 one or more indicator(s) - i.e. power scaling flag(s) - in the MAC PDUs
to indicate that power scaling has been applied by the user equipment to the
transmission power, i.e. PUSCH power, of the MAC PDUs. For example, each MAC
PDU may comprise a respective power scaling flag in one or more of the MAC PDU sub-
headers for a given assigned component carrier that indicates whether the respective
transmission power for transmission on the component carrier has been scaled.
Furthermore, the user equipment performs 2109 a power scaling to reduce the
transmission power to at least one of the assigned component carriers in order to reduce
the overall transmit power for the transmissions on the assigned component carriers
below (or equal to) the maximum UE transmit power. As explained above, no power
scaling may be applied to the transmission on a component carrier, if for example uplink
control information is transmitted on this component carrier together with the MAC PDU
in a given sub-frame, i.e. also referred to as PUSCH with UCI as explained above. The
MAC PDUs are then transmitted 2110 on the respective assigned uplink component
carriers using the reduced transmit power.
Please note that the order of the steps 2107 to 2110 in Fig. 21 may not represent the
correct chronological order of the steps in time, since some of the steps may require
interaction - as apparent from the explanations above.
Synchronous per-CC Power Headroom Reports in one Sub-frame
In line with the first aspect of the invention, another alternative implementation and
embodiment of the invention for informing the eNodeB on a power-limit situation of the
user equipment, the user equipment sends a per-CC power headroom report for each
assigned or configured component carrier of the sub-frame to inform the eNodeB on a
situation where the user equipment is close to using its total maximum UE transmit
power or the resource allocations and power control commands of the eNodeB would
require using a transmit power exceeding the user equipment's total maximum UE
transmit power. The per-CC power headroom may be for example defined according to
one of the definitions provided in the section "Definition of the Per-CC Power Headroom"
below.
The per-CC power headroom reports are sent within a single sub-frame in the uplink.
Basically, this can be considered as defining a new trigger for sending power headroom
reports.
Optionally, in order to "identify that the power headroom report for a component carrier is
non-periodic, respectively, triggered by a power limit situation, one bit in the MAC PDU
sub-header of the MAC CE for the per-CC power headroom report (per-CC PHR MAC
CE) could be used, similar to the power status flag described above. Accordingly, also in
this embodiment, one of the two reserved bits in the MAC PDU sub-header
corresponding to the per-CC PHR MAC CE is used for indication of power limitation
and/or this being the cause for the transmission of the power headroom report. The
logical channel ID (LCID) for the power limitation triggered power headroom report by
means of the per-CC PHR MAC CE may be the same as for power headroom report
triggered by periodic reporting or by path loss change, e.g. 11010 as shown in Fig. 30
(the PS flag would indicate that the corresponding MAC CE contains an power headroom
report triggered by power limitation). Alternatively the flag could be signaled using one of
the two reserved/unused bits in the MAC control element containing the per- CC power
headroom report itself.
In another implementation, instead of using a flag, a new LCID may be defined to
indicate that the power headroom report for a configured or assigned uplink component
carrier was triggered by power limitation.
In a further exemplary implementation, individual LCIDs could be defined for the
configured uplink component carriers, so that the LCID may be used to indicate to which
configured uplink component carrier the MAC CE (and the power headroom report
thereof) belongs. Fig. 31 shows an exemplary MAC PDU comprising per-CC PHR MAC
CEs for three configured component carriers (CoCal, CoCa2 and CoCa3) of a user
equipment according to an exemplary embodiment of the invention. In the MAC PDU
sub-header section three MAC sub-headers are provided that include special LCIDs
defined for the respective component carriers configured for the user equipment in the
uplink- (LCID CoCal, LCID CoCa2, and LCID CoCa3). Based on the LCIDs in the sub-
headers of the MAC PDU, the eNodeB can associate the per-CC power headroom
reports in the MAC CEs within the MAC PDU's payload section to the respective
configured component carriers of the user equipment.
Please note that in this example, the same LCID is used irrespective of the trigger.
Therefore, the sub-header for the respective per-CC PHR MAC CEs comprises a flag in
the first (or second) bit of the sub-header (similar to the power scaling flag) that, when
set, respectively not set, indicates that the power headroom report in the per-CC PHR
MAC CE is a event-triggered power headroom report triggered by a power limit situation.
If the component carrier specific LCIDs would be used only for power headroom reports
due to a power limit situation, no flag in the sub-header is required.
In this exemplary embodiment, the user equipment may optionally re-use the power
headroom reporting mechanism (including the user of the timers periodic? HR-Timer and
prohibit? HR-Timer) and their format as shown in Fig. 7 know from LTE Rel. 8/9 for each
respective report sent in the sub-frame. When the user equipment is in a situation where
it is close to using its total maximum UE transmit power or the resource allocations and
power control commands of the eNodeB would require using a transmit power exceeding
the user equipment's total maximum UE transmit power, the user equipment will send on
each assigned component carrier a per-CC power headroom report as known from LTE
Rel. 8/9 for the respective component carrier. In doing so the user equipment ignores the
timer pwhibiiPHR-Timer, if running. Subsequent to the transmission of the multiple per-
CC power headroom reports, the timers periodic?'HR-Timer and prohibitPHR-Timer may
be restarted.
Upon reception of all power headroom reports in the sub-frame, the eNodeB has the full
picture of the total power situation of the user equipment.
In a further exemplary implementation according to another embodiment of the invention,
the per-CC power headroom reports on all configured or assigned component carriers
could be send in only one MAC PDU on one of the assigned component carriers. The
selection of this component carrier on which the power headroom reports are to be sent
can be implemented as described previously herein (see inter alia section Selection of
the Component Carrier for transmitting the per-UE power headroom MAC CE).
In one exemplary implementation of this embodiment, the multiple per-CC power
headroom reports could be included into one MAC PDU. An exemplary format of a MAC
PDU containing multiple PHR MAC CEs is shown in Fig. 17, where a report of three
power headroom reports on assigned component carriers CoCal, CoCa3 and CoCa4 is
exemplified.
The MAC PDU comprises first the component carrier-specific logical channel identifiers
(LCIDs) within respective sub-headers field that allow the identification of the component
carriers reported on and indicate that the MAC PDU's payload section comprises three
PHR MAC CEs. Each sub-header (indicating the LCID) is 8 bits long (one octet), wherein
the first two bits of the octet (R) are reserved bits, and the third bit (E) indicates whether
the next octet in the MAC PDU is another sub-header of the MAC PDU header or
whether the payload section of the MAC PDU is following the octet (i.e. whether the next
octet is PHR MAC CE in this example), and the last 5 bits are the LCID.
For example, if the E bit is set (e.g. 1), another sub-header is present in the next octet of
the MAC PDU; if the E bit is not set (e.g. 0), the next octet is part of the payload section
of the MAC PDU that is assumed to start with the first PHR MAC CE.
In another alternative implementation, the power headroom reports on multiple
component carriers may also be included into a single MAC control element ("multiple
PHR MAC CE").
The multiple PHR MAC CE comprises in its first octet a bitmap of 5 bits indicating for
which component carrier a PHR field is included in the multiple PHR MAC CE. A priority
order of the component carriers, as described in Application 1 and Application 2, may
define the meaning of the individual positions of bits within the bitmap. Generally, a bit
set (e.g. 1) at a certain position of the bitmap means that there is a PHR field for the
associated component carrier including in the MAC CE. Following the octet comprising
the component carrier bitmap, the respective PHR field(s) with the power headroom
value for the component carrier is/are included. The PHR field may for example have the
same format as shown in Fig. 7 and reports the power headroom (PH) for a component
carrier. An example of a multiple PHR MAC CE, where a report of three power headroom
reports on assigned component carriers CoCal, CoCa3 and CoCa4 is exemplified in
Fig. 18.
Please note that for this alternative implementation, LTE Rel. 8/9 power headroom
reports and the multiple PHR MAC CE could use the same logical channel identifier, and
the two formats may be distinguished by setting or not setting the first or second
reserved bit in the first octet of the control element. Of course, the multiple PHR MAC CE
may also be assigned its own logical channel identifier (LCID) in the MAC PDU header.
The multiple PHR MAC CE may be further assigned its own logical channel identifier, so
that it can be identified by a corresponding sub-headers in the MAC PDU's header (see
Fig. 6).
Fig. 9 shows a flow chart of an exemplary operation of a user equipment according to
one embodiment of the invention in line with the second aspect of the invention. Similar
to Fig. 8, the user equipment receives 801 plural resource assignments for a given sub-
frame and estimates 802 the transmit power (ETP) required for uplink transmissions on
assigned component carriers according to received resource assignments. Next, the
user equipment determines 803, whether the estimated transmit power (ETP) is
exceeding a certain threshold value. If the threshold value is not exceeded, the user
equipment is not in a power limit situation, so that report thereon needs to be signaled to
the eNodeB. Accordingly, the user equipment will next generate 804 the protocol data
units for transmission on the respective assigned component carriers and transmits 805
the protocol data units (which are referred to as transport blocks in the Physical layer) to
the eNodeB via the assigned component carriers. Please note that the generation of the
protocol data units can be for example implemented as described in Application 1 or
Application 2.
If the user equipment is in a power limit situation as determined in step 803, the user
equipment determines 906 for each component carrier for which a resource assignment
has been received a per-CC power headroom.
Next, the user equipment may generate 907 for each assigned component carrier an
individual per-CC power headroom MAC CE (for example using the format shown in
Ftg. 7) and further generates 908 the MAC PDUs including each the corresponding per-
CC power headroom MAC CE according to the resource assignments. Subsequently the
user equipment transmits the PDUs including per-CC power headroom MAC CEs on the
assigned component carriers to the eNodeB.
Please note that alternatively to steps 907 and 908, there could also be a single multiple
PHR MAC CE formed and transmitted in one of the MAC PDUs, as outlined above.
Fig. 12 shows power headroom reporting in a LTE-A system according to an
embodiment of the invention, where the exemplary operation of a user equipment
according to Fig. 9 is employed. In most situations, the operation is corresponding to the
operation of the user equipment as has been outlined with respect to Fig. 10 previously
herein. In contrast to Fig. 10, it is assumed that at Tt the user equipment has received
three resources assignments for all three component carriers for the sub-frame at T6,
however the transmit power control function has is yielding a gain factor for the
transmission that high that given the resource allocation, the estimated transmit power
exceeds the total maximum UE transmit power (see step 803 of Fig. 9). Accordingly, in
this case the user equipment determines the per-CC power headroom values for all three
component carriers and sends PDUs each comprising a per-CC power headroom report
for the respective component carrier in the uplink. As can be recognized from Fig. 12, the
theprohibitPHR-Timer is running at Tt for the component carrier CoCa3, but is ignored by
the user equipment. Upon sending the per-CC power headroom reports the respective
timers are restarted for each component carrier.
Fig. 13 shows another exemplary power headroom reporting in a LTE-A system
according to an embodiment of the invention, where the exemplary operation of a user
equipment according to Fig. 9 is employed. The example shown therein is the same as in
Fig. 12, except for the user equipment having been assigned only resources on
component carriers CoCal and CoCa3 for the sub-frame at T6. Similar to Fig. 12, the
user equipment still is in a power limit situation for this sub-frame, but sends a single
multiple PHR MAC CE in the PDU transmitted on component carrier CoCal that reports
the power headrooms for component carriers CoCal and CoCa3. Thereupon the timers
periodicPHR-Timer and prohibitPHR-Timer are restarted for the component carriers for
which a per-CC power headroom report has been sent, i.e. component carriers CoCal
and CoCa3 in this example.
Fig. 22 shows a flow chart of an exemplary operation of a user equipment according to
one embodiment of the invention in line with the first aspect of the invention. The user
equipment receives 2101 (similar to step 801 of Fig. 8) plural resource assignments for a
given sub-frame and estimates 2102 (similar to step 802 of Fig. 8) the transmit power
(ETP) required for uplink transmissions on assigned component carriers according to
received resource assignments. In one exemplary embodiment of the invention, the
transmit power is estimated by the user equipment based on the received resource
assignments for the protocol data units to be transmitted in the sub-frame and the status
of a transmit power control function of the user equipment as explained with respect to
Fig. 8 above. Further, the user equipment determines 2103, whether the estimated
transmit power (ETP) is exceeding the total maximum UE transmit power (MATP or
If the total maximum UE transmit power is not exceeded, the user equipment is not in a
power limit situation, so that no power status report thereon needs to be signaled to the
eNodeB. Accordingly, the user equipment will next generate 804 the protocol data units
for transmission on the respective assigned component carriers. The generation of the
protocol data units can be for example implemented as described in Application 1 or
Application 2. Then the user equipment transmits 805 the MAC PDUs to the eNodeB.
In case the estimated transmit power exceeds the total maximum UE transmit power in
step 2103, the user equipment generates 2201 for each configured (alternatively for each
assigned) uplink component carrier a respective power headroom report (per-CC power
headroom report) and further generates 2202 for each configured component carrier an
individual per-CC power headroom MAC CE (for example using the format shown in
Fig. 7). In case no uplink grant is available for a given component carrier, the user
equipment may for example assume a predefined resource allocation or alternatively
predefined PUSCH power on those configured component carriers for which no uplink
resource assignment is applicable in the given sub-frame.
Next, the user equipment forms 2203 the MAC PDUs including the per-CC power
headroom MAC CEs. The MAC PDUs are formed according to the resource
assignments. Subsequently the user equipment transmits the PDUs including per-CC
power headroom MAC CEs on the assigned component carriers to the eNodeB,
In case the identification of the transmission of the power headroom reports in the per-
CC PHR MAC CEs have been triggered by the estimated transmit power of the sub-
frame exceeding the total maximum UE transmit power is not provided otherwise, the
user equipment may optionally set 2204 indicator(s) - i.e. flag(s) - in the MAC PDUs to
indicate the cause for sending the per-CC power headroom reports. For example, each
MAC sub-header for a PHR MAC CE or each PHR MAC CE may comprise a respective
flag that indicates whether the estimated transmit power exceeded the total maximum
UE transmit power.
Furthermore, the user equipment performs 2109 power scaling to reduce the
transmission power to at least one of the assigned component carriers in order to reduce
the overall transmit power for the transmissions on the assigned component carriers
below (or equal to) the maximum UE transmit power. As explained above, no power
scaling may be applied to the transmission on a component carrier, if for example uplink
control information is transmitted on this component carrier together with the MAC PDU
in a given sub-frame, i.e. also referred to as PUSCH with UCI. The MAC PDUs including
the per-CC PHR CEs are then transmitted 2206 on the respective assigned uplink
component carriers using the reduced transmit power.
Please note that the order of the steps in Fig. 22 may not represent the correct
chronological order of the steps in time, since some of the steps may require interaction
- as apparent from the explanations above.
Definition of the Per-CC Power Headroom
Currently there is no clear definition of the component carrier specific power headroom
report. For example it's not clear yet, whether the power reduction applied to the
(nominal) component carrier-specific maximum transmit power (PCMM,.) takes into
account only the uplink transmission (resource allocation) on the corresponding CC or
also transmissions on other assigned uplink component carriers. For example in case
there are uplink transmissions scheduled on multiple component carriers simultaneously,
the amount of power reduction, sometimes also referred to as power back-off, may be
increased in order to avoid unwanted emissions. Simultaneous transmission of PUSCH
and/or PUCCH across aggregated component or clustered PUSCH within a component
carrier may generate additional inter-modulation products in the UE transmitter chain that
may consequently necessitate a transmitter power back-off in order to meet the ACLR
requirements.
PH Definition 1
In one exemplary embodiment of the invention, as shown in Fig. 28, the per-CC power
headroom is not taking into account power scaling on a given component carrier. The
power headroom is defined as the difference between the maximum transmit power of
the component carrier Pcmax,c (sfter power reduction) minus the estimated transmit
power of the UE for the component carrier c prior to power scaling. The estimated
transmit power of the UE for the component carrier c may be given by a transmit power
control of the user equipment for the component carrier c.
In one exemplary implementation and in line with this embodiment, the per-CC power
headroom may be for example determined as described in 3GPP TS 36.213, version
8.8.0, section 5.1.1 mentioned already earlier herein. Hence, Equation 2 above is reused
and applied for the respective assigned or configured component carriers as follows.
The per-CC power headroom PHc{t) of component carrier cmay be for example
defined as

where PCMAXc is the maximum transmit power of component carrier c (after power
reduction), obeying:

The index c of the different parameters indicates that this is for component carrier c.
Furthermore, some of the parameters in the equation may be UE specific. The meaning
of the parameters in Equation 3 are otherwise defined as in the Technical Background
section (for the respective component carrier c where applicable or per-user equipment).
The estimated transmit power ^usc^O') of the UE for the component carrier c as given
by a transmit power control of the user equipment for the component carrier cmay be
defined as follows:

PH Definition 2
In one exemplary embodiment of the invention, as shown in Fig. 27, the per-CC power
headroom is taking into account power scaling on a given component carrier (if applied).
The power headroom is defined as the difference between the maximum transmit power
of the component carrier PCUAX c (after power reduction) minus the used transmit power
of the UE for the component carrier c after potential power scaling.
In one example, the used transmit power of the UE for the component carrier cafter
power scaling is the transmitted PUSCH power />/>spusch.c(0 of the sub-frame i as
defined by:

where PSFC is the power scaling factor applied for the respective configured uplink
component carrier c.

where ^usc^O') is the estimated transmit power for component carrier c according to
the applicable resource allocation within the sub-frame i:

According to Definition 2, the power headroom may be expressed as:

Optionally, the power reduction applied to the (nominal) maximum transmit power of a
component carrier may be determined taking into account simultaneous uplink
transmissions on other aggregated component carriers. For example, the nominal
maximum transmit power for a component carrier Paux H c is reduced by a power
reduction PR that takes into account uplink transmissions on other aggregated
component carriers within a given sub-frame. The result of the application of the power
reduction is defining the maximum transmit power of the component carrier PCUA!, c:

where PRC < MPRC. Hence, PCUAX c in Equation 3 and Equation 8 may optionally include
the applied power reduction PR that may optionally take into account uplink
transmissions on other aggregated component carriers within a given sub-frame.
Optional Enhancements
In Equations 3 to 9 above, the parameters comprising the index c may be component
carrier specific. However, some or all of the parameters may be still configured or set per
UE. For example, the parameters P0 rosoll(j) and ctc(j) may be defined per UE.
Furthermore, a power headroom according to Definition 2 should in principle never be
negative, since the total used transmit power, i.e. sum of all uplink transmission powers
across the assigned uplink component carriers, should never exceed (after power
scaling) the total UE maximum transmit power. On the other hand, a power headroom
according to Definition 1 could be negative. In order to have the same power headroom
value range for both power headroom definitions, a negative power headroom value for a
power headroom according to Definition 2 could therefore be defined to have a special
meaning. For example it could be defined that a negative value indicates that the used
transmit power is a result of power scaling, i.e. total maximum UE transmission power is
exceeded. Thereby, the power headroom report would already convey some information
on the power status of the user equipment
Reporting the Amount of Power Reduction
As mentioned previously, the eNodeB may be assumed unaware of the maximum power
reduction (MPR). As a consequence thereof, the power reduction applied by the user
equipment to the maximum transmit power of a given component carrier is also unknown
to the eNodeB. Thus the eNodeB essentially does not know the maximum transmit
power of the component carrier relative to which the power headroom is calculated.
Therefore according to a further embodiment of the invention, the user equipment
informs the eNodeB about the amount of power reduction (also referred to as power
back-off) applied to an uplink component carrier.
In one exemplary implementation, the user equipment signals the amount of power
reduction when reporting a power headroom. Based on the power headroom and the
applied amount of power reduction the eNodeB can calculate the actual used transmit
power on a given component carrier and hence knows the UE power status.
Unlike in the previous exemplary embodiments, the amount of power reduction for the
configured or assigned uplink component carriers may not necessarily be reported when
the user equipment is in a power-limit situation or approaching same, but the amount of
power reduction applied to a component carrier may be sent/updated by the user
equipment periodically or in response to a change beyond a given threshold value,
similar to the reporting of power headrooms. In order to reduce the signaling overhead
the user equipment may only report the amount of power reduction in case the user
equipment is in a power limit situation or is approaching same, as exemplified before.
Fig. 23 shows a flow chart of an exemplary operation of a user equipment according to
one embodiment of the invention in line with the first aspect of the invention. The user
equipment receives 2101 (similar to step 801 of Fig. 8) plural resource assignments for a
given sub-frame and estimates 2102 (similar to step 802 of Fig. 8) the transmit power
(ETP) required for uplink transmissions on assigned component carriers according to
received resource assignments. In one exemplary embodiment of the invention, the
transmit power is estimated by the user equipment based on the received resource
assignments for the protocol data units to be transmitted in the sub-frame and the status
of a transmit power control function of the user equipment as explained with respect to
Fig. 8 above. Further, the user equipment determines 2103, whether the estimated
transmit power (ETP) is exceeding the total maximum UE transmit power (MATP or
"cM AX ) •
If the total maximum UE transmit power is not exceeded, the user equipment is not in a
power limit situation, so that no power status report thereon needs to be signaled to the
eNodeB. Accordingly, the user equipment will next generate 804 the protocol data units
for transmission on the respective assigned component carriers. The generation of the
protocol data units can be for example implemented as described in Application 1 or
Application 2. Then the user equipment transmits 805 the MAC PDUs to the eNodeB.
In case the estimated transmit power exceeds the total maximum UE transmit power in
step 2103, the user equipment generates 2201 for each configured (alternatively for each
assigned) uplink component carrier a respective power headroom report (per-CC power
headroom report) and further generates 2202 for each configured component carrier an
individual per-CC power headroom MAC CE (for example using the format shown in
Fig. 7), In case no uplink grant is available for a given component carrier, the user
equipment may for example assume a predefined resource allocation or alternatively
predefined PUSCH power on those configured component carriers for which no uplink
resource assignment is applicable in the given sub-frame. The power headroom may be
calculated using for example Definition 1 or Definition 2 outlined above.
Furthermore, the user equipment generates 2301 for each assigned or configured
component carrier in the uplink a per-CC power reduction MAC CE that is indicating the
amount of power reduction (e.g. in dB) that is applied to the respective component
carrier. Next, the user equipment forms 2302 the MAC PDUs the per-CC power
headroom MAC CEs and per-CC power reduction CEs. The MAC PDUs are formed
according to the resource assignments.
The per-CC power reduction MAC CE comprises the amount of power reduction applied
to the component carrier and may be defined similar to the PHR MAC CE in LTE Rel. 8,
as shown in Fig. 32. A new logical channel ID (LCID) could be reserved for identification
of the per-CC power reduction MAC CE.
The user equipment performs 2109 power scaling to reduce the transmission power to at
least one of the assigned component carriers in order to reduce the overall transmit
power for the transmissions on the assigned component carriers below (or equal to) the
maximum UE transmit power. The MAC PDUs including the per-CC PHR CEs and per-
CC power reduction MAC CEs are then transmitted 2303 on the respective assigned
uplink component carriers using the reduced transmit power.
Please note that the order of the steps in Fig. 23 may not represent the correct
chronological order of the steps in time, since some of the steps may require interaction
- as apparent from the explanations above.
Instead of signaling individual per-CC PHR CEs and per-CC power reduction CEs, the
per-CC power headroom and the per-CC power reduction applied to the component
carrier may also be signaled in one MAC CE. In order to identify this new MAC CE
(power reduction & power headroom), a one-bit flag could be used to indicate the format
of the MAC CE. For example, the flag could be one of the two reserved bits (R) provided
in the MAC sub-header. The flag being set (e.g. 1) may for example indicate that amount
of power reduction and a power headroom report according to Definition 1 or Definition 2
is comprised in the MAC CE. The flag not being set (e.g. 0) indicates that only a power
headroom report according to Definition 1 or Definition 2 is signaled.
Alternatively instead of signaling the amount of power reduction, the user equipment may
signal a power headroom report for all configured or assigned component carriers when
the applied power reduction to the maximum transmit power of an component carrier
changes beyond some predefined threshold. Basically a new trigger for per-CC PHR
reporting would be introduced.
Signaling the Amount of Power Scaling
Another alternative implementation and embodiment of the invention for informing the
eNodeB on a power-limit situation of the user equipment, the user equipment signals the
amount of power scaling applied to the different configured or assigned uplink
component carriers. The amount of power scaling (in dB) may be for example signaled
for each uplink component carrier when the user equipment is power limited, i.e. the
estimated overall transmit power for the sub-frame exceeds the total maximum UE
transmit power.
Fig. 24 shows a flow chart of an exemplary operation of a user equipment according to
one embodiment of the invention in line with the first aspect of the invention. The user
equipment receives 2101 (similar to step 801 of Fig. 8) plural resource assignments for a
given sub-frame and estimates 2102 (similar to step 802 of Fig. 8) the transmit power
(ETP) required for uplink transmissions on assigned component carriers according to
received resource assignments. In one exemplary embodiment of the invention, the
transmit power is estimated by the user equipment based on the received resource
assignments for the protocol data units to be transmitted in the sub-frame and the status
of a transmit power control function of the user equipment as explained with respect to
Fig. 8 above. Further, the user equipment determines 2103, whether the estimated
transmit power (ETP) is exceeding the total maximum UE transmit power (MATP or
If the total maximum UE transmit power is not exceeded, the user equipment is not in a
power limit situation, so that no power status report thereon needs to be signaled to the
eNodeB. Accordingly, the user equipment will next generate 804 the protocol data units
for transmission on the respective assigned component carriers. The generation of the
protocol data units can be for example implemented as described in Application 1 or
Application 2. Then the user equipment transmits 805 the MAC PDUs to the eNodeB.
In case the estimated transmit power exceeds the total maximum UE transmit power in
step 2103, the user equipment generates 2201 for each configured (or alternatively for
each assigned) uplink component carrier a respective power headroom report (per-CC
power headroom report) and further generates 2202 for each assigned component
carrier an individual per-CC power headroom MAC CE (for example using the format
shown in Fig. 7). In case no uplink grant is available for a given component carrier, the
user equipment may for example assume a predefined resource allocation or
alternatively predefined PUSCH power on those configured component carriers for which
no uplink resource assignment is applicable in the given sub-frame. The power
headroom may be calculated using for example Definition 1 or Definition 2 outlined
above.
Furthermore, the user equipment generates 2401 for each assigned component carrier in
the uplink a per-CC power scaling MAC CE that is indicating the power scaling factor
(e.g. in dB) that of the power scaling applied to the transmission of the respective
component carrier. Next, the user equipment forms 2402 the MAC PDUs the per-CC
power headroom MAC CEs and per-CC power scaling CEs. The MAC PDUs are formed
according to the resource assignments.
For signaling, a new MAC CE may be defined that comprises the power scaling factor
(PSF). This (per-CC) power scaling MAC CE could be defined similar to the PHR MAC
CE in LTE Rel. 8, as shown in Fig. 33. A new logical channel ID (LCID) could be
reserved for identification of the per-CC power scaling MAC CE.
The user equipment performs 2109 power scaling to reduce the transmission power to at
least one of the assigned component carriers in order to reduce the overall tfansmit
power for the transmissions on the assigned component carriers below (or equal to) the
maximum UE transmit power. The MAC PDUs including the per-CC PHR CEs and per-
CC power scaling MAC CEs are then transmitted 2403 on the respective assigned uplink
component carriers using the reduced transmit power.
Please note that the order of the steps in Fig. 24 may not represent the correct
chronological order of the steps in time, since some of the steps may require interaction
- as apparent from the explanations above.
In an alternative embodiment, the amount of power scaling could be signaled by means
of the power headroom report. Instead of reporting the absolute amount of power
scaling the user equipment reports a per-CC power headroom according to Definition 1
and a per-CC power headroom according to Definition 2 simultaneously for one
component carrier. The eNodeB can then calculate the amount of power scaling by
taking the difference of the two power headrooms.
Since reports a per-CC power headroom according to Definition 1 and a per-CC power
headroom according to Def nition 2 will report the same values when no power scaling is
applied, it's only useful to report both power headrooms if the user equipment is power
limited. In order to distinguish the different reporting formats, one reserved bit (R) of the
MAC PDU sub-header corresponding to the per-CC PHR MAC CE may be used. For
example, the reserved bit being set (e.g. 1) indicates that power scaling was applied, that
a per-CC power headroom according to Definition 1 (or Definition 2) together with the
absolute amount of power scaling, or alternatively, a per-CC power headroom according
to Definition 1 and a per-CC power headroom according to Definition 2 is reported. The
reserved bit not being set (e.g. 0) may indicates that no power scaling was applied and
normal per-CC PHR is reported.
Hardware and Software Implementation of the Invention
Another embodiment of the invention relates to the implementation of the above
described various embodiments using hardware and software. In this connection the
invention provides a user equipment (mobile terminal) and a eNodeB (base station). The
user equipment is adapted to perform the methods described herein. Furthermore, the
eNodeB comprises means that enable the eNodeB to determine the power status of
respective user equipments from the power status information received from the user
equipments and to consider the power status of the different user equipments in the
scheduling of the different user equipments by its scheduler.
It is further recognized that the various embodiments of the invention may be
implemented or performed using computing devices (processors). A computing device or
processor may for example be general purpose processors, digital signal processors
(DSP), application specific integrated circuits (ASIC), field programmable gate arrays
(FPGA) or other programmable logic devices, etc. The various embodiments of the
invention may also be performed or embodied by a combination of these devices.
Further, the various embodiments of the invention may also be implemented by means of
software modules, which are executed by a processor or directly in hardware. Also a
combination of software modules and a hardware implementation may be possible. The
software modules may be stored on any kind of computer readable storage media, for
example RAM, EPROM, EEPROM, flash memory, registers, hard disks, CD-ROM, DVD,
etc.
If should be further noted thai the individual features of the different embodiments of the
invention may individually or in arbitrary combination be subject matter to another
invention.
It would be appreciated by a person skilled in the art that numerous variations and/or
modifications may be made to the present invention as shown in the specific
embodiments without departing from the spirit or scope of the invention as broadly
described. The present embodiments are, therefore, to be considered in all respects to
be illustrative and not restrictive.
Claims
1. A method for informing an eNodeB on the transmit power status of a user
equipment in a mobile communication system using component carrier
aggregation, wherein the method comprises the following steps performed by
the user equipment for each sub-frame where the user equipment makes a
transmission in the uplink:
determining whether an estimated transmit power required for a transmission
of MAC protocol data units on the uplink component carriers within the
respective sub-frame will exceed a total maximum transmit power of the user
equipment,
if so, performing a power scaling of the transmit power to reduce the transmit
power required for the transmission of the MAC protocol data units such that
it is no longer exceeding the total maximum transmit power of the user
equipment, and
transmitting the MAC protocol data units to the eNodeB within the respective
sub-frame,
wherein the transmitted MAC protocol data units comprise an indicator that
indicates to the eNodeB whether power scaling has been performed by the
user equipment for transmitting the MAC protocol data units in the respective
sub-frame.
2. The method according to claim 1, wherein the indicator is comprised within a
MAC header of at least one of the MAC protocol data units.
3. The method according to claim 2, wherein the indicator is a flag within one or
more of the MAC sub-headers of a respective MAC header comprised in the
at least one MAC protocol data unit.
4. The method according to one of claims 1 to 3, wherein power scaling is
performed for each configured uplink component carrier individually, and
wherein for each uplink component carrier on which a MAC protocol data unit
is transmitted, at least one MAC protocol data unit transmitted on the
respective uplink component carrier comprises an indicator that indicates to
the eNodeB whether power scaling has been applied to the transmission on
the respective uplink component carrier within the sub-frame.
5. A method for informing an eNodeB on the transmit power status of a user
equipment in a mobile communication system using component carrier
aggregation, wherein the method comprises the following steps performed by
the user equipment:
determining whether an estimated transmit power required for a transmission
of MAC protocol data units on uplink component carriers within the respective
sub-frame will exceed a total maximum transmit power of the user equipment,
if so, performing a power scaling of the transmit power to reduce the transmit
power required for the transmission of the MAC protocol data units such that
it is no longer exceeding the total maximum transmit power of the user
equipment, and triggering the generation of a power headroom report for
each configured uplink component carrier of the user equipment, and
transmitting the MAC protocol data units to the eNodeB within the respective
sub-frame together with a power headroom report for each configured uplink
component carrier of the user equipment and an indication of the power
headroom report(s) having been triggered by the transmit power required for
a transmission of MAC protocol data units on uplink component carriers
exceeding the total maximum transmit power of the user equipment.
6. The method according to claim 5, further comprising the step of determining,
in response to the trigger, a power headroom report for each configured
uplink component carrier of the user equipment,
wherein the power headroom for a configured uplink component carrier is
defined as the difference between the maximum transmit power of the
configured uplink component carrier and the used uplink transmit power.
7. The method according to claim 5 or 6, further comprising the step of
determining, in response to the trigger, a power headroom report for each
configured uplink component carrier of the user equipment.
wherein the power headroom of a configured uplink component carrier is
defined as the difference between the maximum transmit power of the
configured uplink component carrier and the estimated uplink transmit power
on the respective component carrier.
8. The method according to claim 5, further comprising the step of determining,
in response to the trigger, a power headroom report for each configured
uplink component carrier of the user equipment,
wherein the power headroom of a configured uplink component carrier reports
the difference between the maximum transmit power of the configured uplink
component carrier and a used uplink transmit power, and reports the
difference between the maximum transmit power of the configured uplink
component carrier and an estimated uplink transmit power on the respective
component carrier,.
9. The method according to one of claims 5 to 8, wherein the maximum transmit
power of a configured uplink component carrier is determined by the user
equipment considering a power reduction due to transmission(s) on other
configured uplink component carrier(s) of the user equipment within the sub-
frame.
10. The method according to one of claims 5 to 9, wherein the indication of the
power headroom report(s) having been triggered by the estimated transmit
power exceeding the total maximum transmit power of the user equipment is
provided by setting a flag in a MAC sub-header for a MAC control element
carrying at least one of the power headroom reports(s).
11. The method according to claim 10, wherein for each MAC control element
comprising a respective power headroom report, a MAC sub-header is
included in a header section of the MAC protocol data unit to which the MAC
control element is multiplexed,
wherein the a flag in the MAC sub-header indicates that the power headroom
report within the MAC control element has been triggered by the estimated
transmit power required for a transmission of MAC protocol data units on
uplink component carriers within the respective sub-frame exceeding the total
maximum transmit power of the user equipment.
12. The method according to one of claims 5 to 11, wherein a power headroom
reports are sent for active uplink component carriers of the user equipment
only.
13. A method for informing an eNodeB on the transmit power status of a user
equipment in a mobile communication system using component carrier
aggregation, wherein the method comprises the following steps performed by
the user equipment for each sub-frame where the user equipment makes a
transmission in the uplink:
determining whether an estimated transmit power required for a transmission
of MAC protocol data units on the uplink component carriers within the
respective sub-frame will exceed a total maximum transmit power of the user
equipment,
if so, performing a power scaling of the transmit power to reduce the transmit
power required for the transmission of the MAC protocol data units such that
it is no longer exceeding a total maximum transmit power of the user
equipment, and
transmitting the MAC protocol data units to the eNodeB within the respective
sub-frame,
wherein the transmitted MAC protocol data units comprise at least one MAC
control element indicating the amount of power reduction applied to the
maximum transmit power of the configured uplink component carriers.
14. The method according to claim 13, wherein the wherein power scaling is
performed for each configured uplink component carrier individually, and
wherein for each uplink component carrier on which a MAC protocol data unit
is transmitted, at least one MAC protocol data unit transmitted on the
respective uplink component carrier comprises a MAC control element that
indicates the amount of power reduction of the respective uplink component
carriers.
15. The method according to claim 13 or 14, wherein in case the estimated
transmit power required for a transmission of MAC protocol data units on the
uplink component carriers within the respective sub-frame will exceed the
total maximum transmit power of the user equipment, the user equipment
further generates a power headroom report for each configured uplink
component carrier and transmits the power headroom reports together with
the MAC protocol data units including the MAC control element for reporting
the power reduction to the eNodeB.
16. The method according to one of claims 13 to 15, wherein the user equipment
signals the power reduction and a power headroom report for the respective
configured uplink component carrier in response to a predefined change of
the amount of power reduction applied to the maximum transmit power of a
uplink component carrier.
17. The method according to one of claims 13 to 16, wherein the format of the
MAC control element signaling the amount of power reduction is identified by
- a predetermined logical channel identifier defined for MAC control
elements signaling the amount of power reduction, or
- a predetermined logical channel identifier defined for MAC control
elements signaling a power headroom report and one or more flags,
included In the MAC sub-header of the MAC control element.
18. The method according to one of claims 1 to 17, further comprising the steps
of:
receiving at least one uplink resource assignment, wherein each uplink
resource assignment is assigning resources for the transmission of at least
one of the MAC protocol data units on one of the plural component carriers to
the user equipment, and
generating for each received uplink resource assignment at least one of the
MAC protocol data units for transmission on the respective assigned
component carrier,
wherein each MAC protocol data unit is transmitted via a corresponding one
of the component carriers according to one of the received resource
assignments.
19. The method according to claim 18, wherein generating the protocol data units
is performed by executing a logical channel prioritization procedure.
20. A MAC control element for transmission from a user equipment to an eNodeB
in a mobile communication system using component carrier aggregation, the
MAC control element comprising:
a power headroom report for a configured uplink component carrier that
reports the difference between the maximum transmit power of the configured
uplink component carrier and a transmitted PUSCH power.
21. The MAC control element according to claims 20, wherein the transmitted
PUSCH power (i) of the sub-frame i is defined by:

where PSFC is the power scaling factor applied for the respective configured
uplink component carrier c.
22. The MAC control element according to claim 20 or 21, wherein the MAC
control element further comprises a power headroom report of the configured
uplink component carrier that reports the difference between the maximum
transmit power of the configured uplink component carrier and an estimated
PUSCH power.
23. A MAC control element for transmission from a user equipment to an eNodeB
in a mobile communication system using component carrier aggregation, the
MAC control element comprising:
a power headroom report of the configured uplink component carrier that
reports the difference between the maximum transmit power of the configured
uplink component carrier and an estimated PUSCH power.
24. The MAC control element according to one of claims 20 to 23, wherein the
maximum transmit power of the configured uplink component carrier
considers a power reduction due to transmission(s) on other configured uplink
component carrier(s) of the user equipment.
25. A MAC protocol data unit for transmission from a user equipment to a
eNodeB in a mobile communication system using component carrier
aggregation, the MAC protocol data unit comprising:
a MAC control element according to one of claims 20 to 24, including a power
headroom report and
a MAC sub-header, wherein the MAC sub-header is comprising an indicator,
that when set, indicates to the eNodeB that the power headroom report has
been triggered by the transmit power required for a transmission of MAC
protocol data units on uplink component carriers exceeding the total
maximum transmit power of the user equipment.
26. A user equipment for informing an eNodeB on the transmit power status of a
user equipment in a mobile communication system using component carrier
aggregation, the user equipment comprising:
a determination section adapted to determine whether an estimated transmit
power required for a transmission of MAC protocol data units on the uplink
component carriers within the respective sub-frame will exceed a total
maximum transmit power of the user equipment,
a power control section adapted to perform a power scaling of the transmit
power to reduce the transmit power required for the transmission of the MAC
protocol data units such that it is no longer exceeding the total maximum
transmit power of the user equipment, and
a transmission section adapted to transmit the MAC protocol data units to the
eNodeB within the respective sub-frame,
wherein the transmitted MAC protocol data units comprise an indicator that
indicates to the eNodeB whether power scaling has been performed by the
user equipment for transmitting the MAC protocol data units in the respective
sub-frame.
27. A computer readable medium storing instructions that, when executed by a
processor of a user equipment, cause the user equipment to inform an
eNodeB on the transmit power status of a user equipment for each sub-frame
where the to be transmitted by the user equipment makes a transmission in
the in the uplink within a mobile communication system using component
carrier aggregation, by:
determining whether an estimated transmit power required for a transmission
of MAC protocol data units on the uplink component carriers within the
respective sub-frame will exceed a total maximum transmit power of the user
equipment,
if so, performing a power scaling of the transmit power to reduce the transmit
power required for the transmission of the MAC protocol data units such that
it is no longer exceeding the total maximum transmit power of the user
equipment, and
transmitting the MAC protocol data units to the eNodeB within the respective
sub-frame,
wherein the transmitted MAC protocol data units comprise an indicator that
indicates to the eNodeB whether power scaling has been performed by the
user equipment for transmitting the MAC protocol data units in the respective
sub-frame.
28. The computer readable medium according to claim 27, further storing
instructions that, when executed by the processor of the user equipment
cause the user equipment to perform the steps of the method according to
one of claims 1 to 5.
29. A user equipment for informing a eNodeB on the transmit power status of a
user equipment in a mobile communication system using component carrier
aggregation, the user equipment comprising:
a determination section adapted to determine whether an estimated transmit
power required for a transmission of MAC protocol data units on uplink
component carriers within the respective sub-frame will exceed a total
maximum transmit power of the user equipment, and to trigger the generation
of a power headroom report for each configured uplink component carrier of
the user equipment,
a power control section adapted to perform a power scaling of the transmit
power to reduce the transmit power required for the transmission of the MAC
protocol data units such that it is no longer exceeding the total maximum
transmit power of the user equipment, and
a transmission section adapted to transmit the MAC protocol data units to the
eNodeB within the respective sub-frame together with a power headroom
report for each configured uplink component carrier of the user equipment
and an indication of the power headroom report(s) having been triggered by
the transmit power required for a transmission of MAC protocol data units on
uplink component carriers exceeding the total maximum transmit power of the
user equipment.
30. A computer readable medium storing instructions that, when executed by a
processor of a user equipment, cause the user equipment to inform an
eNodeB on the transmit power status of a user equipment in a mobile
communication system using component carrier aggregation, by:
determining whether an estimated transmit power required for a transmission
of MAC protocol data units on uplink component carriers within the respective
sub-frame will exceed a total maximum transmit power of the user equipment,
if so, performing a power scaling of the transmit power to reduce the transmit
power required for the transmission of the MAC protocol data units such that
it is no longer exceeding the total maximum transmit power of the user
equipment, and triggering the generation of a power headroom report for
each configured uplink component carrier of the user equipment,
transmitting the MAC protocol data units to the eNodeB within the respective
sub-frame together with a power headroom report for each configured uplink
component carrier of the user equipment and an indication of the power
headroom report(s) having been triggered by the transmit power required for
a transmission of MAC protocol data units on uplink component carriers
exceeding the total maximum transmit power of the user equipment.
31. The computer readable medium according to claim 30, further storing
instructions that, when executed by the processor of the user equipment
cause the user equipment to perform the steps of the method according to
one of claims 6 to 13.
32. A user equipment for informing an eNodeB on the transmit power status of a
user equipment in a mobile communication system using component carrier
aggregation, the user equipment comprising:
a determination section adapted to determine whether an estimated transmit
power required for a transmission of MAC protocol data units on the uplink
component carriers within the respective sub-frame will exceed a total
maximum transmit power of the user equipment,
a power control section adapted to perform a power scaling of the transmit
power to reduce the transmit power required for the transmission of the MAC
protocol data units such that it is no longer exceeding the total maximum
transmit power of the user equipment, and
a transmission section adapted to transmit the MAC protocol data units to the
eNodeB within the respective sub-frame,
wherein the transmitted MAC protocol data units comprise at least one MAC
control element indicating the amount of power reduction applied to the
maximum transmit power of the configured uplink component carriers.
33. A computer readable medium storing instructions that, when executed by a
processor of a user equipment, cause the user equipment to inform an
eNodeB on the transmit power status of a user equipment for each sub-frame
where the to be transmitted by the user equipment makes a transmission in
the in the uplink within a mobile communication system using component
carrier aggregation, by:
determining whether an estimated transmit power required for a transmission
of MAC protocol data units on the uplink component carriers within the
respective sub-frame will exceed a total maximum transmit power of the user
equipment,
if so, performing a power scaling of the transmit power to reduce the transmit
power required for the transmission of the MAC protocol data units such that
it is no longer exceeding the total maximum transmit power of the user
equipment, and
transmitting the MAC protocol data units to the eNodeB within the respective
sub-frame,
wherein the transmitted MAC protocol data units comprise at least one MAC
control element indicating the amount of power reduction applied to the
maximum transmit power of the configured uplink component carriers.
34. The computer readable medium according to claim 31, further storing
instructions that, when executed by the processor of the user equipment
cause the user equipment to perform the steps of the method according to
one of claims 14 to 17.
35. A method for informing a eNodeB on the power status of a user equipment in
a mobile communication system using component carrier aggregation,
wherein the method comprises the following steps performed by the user
equipment:
determining whether an estimated transmit power required for transmitting
protocol data units on respective component carriers within a sub-frame will
exceed a threshold value relative to a maximum available transmit power of
the user equipment,
if the threshold value is exceeded, multiplexing a MAC control element to the
protocol data units, and
transmitting the protocol data units including the MAC control element to the
eNodeB within the sub-frame,
wherein the MAC control element indicates to the eNodeB that the transmit
power spent by the user equipment for transmitting the generated protocol
data units on uplink exceeded the threshold value.
36. The method according to claim 35, wherein the MAC control element provides
the eNodeB with a per-user equipment power headroom relative to all uplink
protocol data units transmitted in the sub-frame.
37. The method according to claim 36, wherein the per-user equipment power
headroom accounts for all transmissions on a physical uplink shared channel
(PUSCH) and a physical uplink control channel (PUCCH) within the sub-
frame.
38. The method according to one of claims 35 to 37, wherein the MAC control
element is multiplexed to one of the protocol data units or to each of the
protocol data units.
39. The method according to one of claims 35 to 38, wherein the component
carriers each have a priority and the MAC control element is multiplexed to
the protocol data unit to be transmitted on the highest priority component
carrier for which a resource assignment has been received, or to the protocol
data unit to be transmitted on the component carrier achieving the lowest
block error rate, having the largest power headroom or experiencing the best
channel quality, and for which a resource assignment has been received.
40. The method according to one of claims 35 to 39, wherein the threshold is
defined as a percentage of the maximum the user equipment is allowed to
use.
41. The method according to claim 40, further comprising the steps of receiving
radio resource control signaling from the eNodeB indicating said threshold
value as a percentage of the maximum the user equipment is allowed to use,
and configuring the threshold value according to the indicated percentage.
42. A method for informing a eNodeB on the power status of a user equipment in'
a mobile communication system using component carrier aggregation, the
method comprising the steps of:
transmitting protocol data units in each of a predetermined number of
successive sub-frames from the user equipment to the eNodeB,
multiplexing at the user equipment a MAC control element to the protocol
data units of the last sub-frame of said predetermined number of successive
sub-frames transmitted by the user equipment, if one of the following
conditions is met:
- the transmit power required for transmitting the protocol data units in each
of the successive sub-frames exceeds a threshold value relative to the
user equipment's maximum available transmit power, or
- the transmit power required for transmitting protocol data units in a subset
of sub-frames of said successive sub-frames exceeds a threshold value
relative to the user equipment's maximum available transmit power, or
- the average transmit power required for transmitting the protocol data
units in said successive sub-frames exceeds a threshold value relative to
the user equipment's maximum available transmit power;
wherein the MAC control element indicates to the eNodeB that the respective
condition was met.
43. A MAC control element for transmission from a user equipment to a eNodeB
in a mobile communication system using component carrier aggregation, the
MAC control element comprising:
a power headroom field consisting of a predetermined number of bits for
comprising a per-user equipment power headroom with respect to all uplink
transmissions of the user equipment on a plurality of component carriers
within a sub-frame containing the MAC control element, relative to the
maximum available transmit power of the user equipment.
44. The MAC control element according to claim 43, wherein the MAC control
element comprises a component carrier indicator field for indicating
- the number of component carrier for which the user equipment has
received resource assignments, or
- a bitmap indicating the component carriers for which the user equipment
has received resource assignments.
45. A MAC protocol data unit for transmission from a user equipment to a
eNodeB in a mobile communication system using component carrier
aggregation, the MAC protocol data unit comprising a MAC subheader and a
MAC control element according to claim 9 or 10, wherein the MAC subheader
is comprising a logical channel identifier (LCID) that is indicating the content
and format of said MAC control element.
46. A user equipment for informing a eNodeB on the power status of a user
equipment in a mobile communication system using component carrier
aggregation, the user equipment comprising:
an determining section for determining whether an estimated transmit power
required for transmitting protocol data units on respective component carriers
within a sub-frame will exceed a threshold value relative to a maximum
available transmit power of the user equipment,
a protocol data unit generation section for multiplexing a MAC control element
to the protocol data units, if the threshold value is exceeded, and
a transmitting section for transmitting the protocol data units including the
MAC control element to the eNodeB within the sub-frame,
wherein the MAC control element indicates to the eNodeB that the transmit
power spent by the user equipment for transmitting the generated protocol
data units on uplink exceeded the threshold value.
47. The user equipment according to claim 46, further comprising a receiving
section for receiving at least one uplink resource assignment, wherein each
uplink resource assignment is assigning resources for the transmission of one
of the protocol data units on one of the plural component carriers to the user
equipment, and
wherein the a protocol data unit generation section is adapted to generate for
each received uplink resource assignment a protocol data unit for
transmission on the respective assigned component carrier,
wherein the transmitting section is adapted to transmit each protocol data unit
via a corresponding one of the component carriers according to one of the
received resource assignments.
48. The user equipment according to claim 46 or 47, further comprising a power
control section for performing power control, and wherein the determining
section is adapted to determine the estimated transmit power based on the
resource assignment for the protocol data units to be transmitted in the sub-
frame and the status of a transmission power control section.
49. The user equipment according to one of claims 46 to 48, wherein user
equipment comprises a receiving section for receiving radio resource control
signaling from the eNodeB indicating said threshold value as a percentage of
the maximum the user equipment is allowed to use, and
a configuration section for configuring the threshold value according to the
indicated percentage.

ABSTRACT

The invention relates to methods for informing an eNodeB on the transmit power status of a user equipment in a
mobile communication system using component carrier (CC) aggregation. Furthermore, the invention is also related to the imple-
mentation of these methods by hardware and their implementation in software. The invention proposes procedures that allow the
eNodeB to recognize the power usage status of a UE in a communication system using carrier aggregation. The UE indicates to
the eNodeB, when the UE is close to using its total maximum UE transmit power or when it has exceeded same. This is achieved
by the UE including indicator(s) and/or new MAC CEs to one or more protocol data units transmitted on respective component
carriers within a single sub-frame that is providing the eNodeB with power status information The MAC CEs may report a per-
UE power headroom. Alternatively, the MAC CEs may report per-CC power headrooms and/or power reductions applied to the
respective uplink CCs.