Specification
Transmit Power Control for
Physical Random Access Channels
FIELD OF THE INVENTION
The invention relates to methods for controlling the power in the uplink in scenarios where an
uplink transmission and a random access preamble, or a multiple random access preambles
are transmitted in the same transmission time interval. Furthermore, the invention is also
related to the implementation/performance of these methods in/by hardware, i.e.
apparatuses, and their implementation in software.
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. The detailed system requirements are given in. 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 transmission power of the user
equipment (UE). Many key packet radio access techniques are employed including multipleinput
multiple-output (MIMO) channel transmission techniques, and a highly efficient control
signaling structure is achieved in LTE Rel. 8.
LTE architecture
The overall architecture is shown in Fig. 1 and a more detailed representation of the EUTRAN
architecture is given in Fig. 2. The E-UTRAN consists of eNode B, providing the EUTRA
user plane (PDCP/RLC/MAC/PHY) and control plane (RRC) protocol terminations
towards the user equipment (UE). The eNode B (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 eNode Bs are interconnected with each
other by means of the X2 interface.
The eNode Bs are also connected by means of the S 1 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 S 1 interface supports a
many-to-many relation between MMEs/Serving Gateways and eNode Bs. The SGW routes
and forwards user data packets, while also acting as the mobility anchor for the user plane
during inter-eNode B 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.
Uplink Access scheme for LTE
For uplink transmission, power-efficient user-terminal transmission is necessary to maximize
coverage. Single-carrier transmission combined with FDMA (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 poweramplifier
efficiency and assumed improved coverage (higher data rates for a given terminal
peak power). During each time interval, eNode B 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
(eNode B), 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 BWgrant 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 signalgeneration
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-nonselective
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 eNode B 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 eNode B 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 eNode B 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.
Uplink Rate Control / Logical Channel Prioritization procedure
For UMTS long term evolution (LTE) uplink transmissions there is a desire that starvation be
avoided and greater flexibility in resource assignment between bearers be possible, whilst
retaining the per user equipment, rather than per user equipment bearer, resource allocation.
The user equipment has an uplink rate control function which manages the sharing of uplink
resources between radio bearers. This uplink rate control function is also referred to as
logical channel prioritization procedure in the following. The Logical Channel Prioritization
(LCP) procedure is applied when a new transmission is performed, i.e. a transport block
needs to be generated. One proposal for assigning capacity has been to assign resources to
each bearer, in priority order, until each has received an allocation equivalent to the minimum
data rate for that bearer, after which any additional capacity is assigned to bearers in, for
example, priority order.
As will become evident from the description of the LCP procedure given below, the
implementation of the LCP procedure residing in the user equipment is based on the token
bucket model, which is well known in the IP world. The basic functionality of this model is as
follows. Periodically and at a given rate, a token which represents the right to transmit a
quantity of data is added to the bucket. When the user equipment is granted resources, it is
allowed to transmit data up to the amount represented by the number of tokens in the bucket.
When transmitting data the user equipment removes the number of tokens equivalent to the
quantity of transmitted data. In case the bucket is full, any further tokens are discarded. For
the addition of tokens it could be assumed that the period of the repetition of this process
would be every TTI, but it could be easily lengthened such that a token is only added every
second. Basically instead of every 1 s a token is added to the bucket, 1000 tokens could be
added every second.
In the following the logical channel prioritization procedure used in LTE Rel. 8 is described
(see for further details: 3GPP TS 36.321 , "Evolved Universal Terrestrial Radio Access (EUTRA);
Medium Access Control (MAC) protocol specification", version 8.5, available at
http://www.3gpp.org and incorporated herein by reference).
RRC controls the scheduling of uplink data by signalling for each logical channel: priority
where an increasing priority value indicates a lower priority level, prioritisedBitRate which
sets the Prioritized Bit Rate (PBR), bucketSizeDuration which sets the Bucket Size Duration
(BSD). The idea behind prioritized bit rate is to support for each bearer, including low priority
non-GBR bearers, a minimum bit rate in order to avoid a potential starvation. Each bearer
should at least get enough resources in order to achieve the prioritized bit rate (PRB).
The UE shall maintain a variable Bj for each logical channel j . Bj shall be initialized to zero
when the related logical channel is established, and incremented by the product PBR x TTI
duration for each TTI, where PBR is Prioritized Bit Rate of logical channel j . However, the
value of Bj can never exceed the bucket size and if the value of Bj is larger than the bucket
size of logical channel j , it shall be set to the bucket size. The bucket size of a logical channel
is equal to PBR x BSD, where PBR and BSD are configured by upper layers.
The UE shall perform the following Logical Channel Prioritization procedure when a new
transmission is performed. The uplink rate control function ensures that the UE serves its
radio bearer(s) in the following sequence:
1. All the logical channel(s) in decreasing priority order up to their configured PBR
(according the number of tokens in the bucket which is denoted by Bj);
2. If any resources remain, all the logical channels are served in a strict decreasing
priority order (regardless of the value of Bj) until either the data for that logical channel or the
UL grant is exhausted, whichever comes first. Logical channels configured with equal priority
should be served equally.
In case the PBRs are all set to zero, the first step is skipped and the logical channel(s) are
served in strict priority order: the UE maximizes the transmission of higher priority data.
The UE shall also follow the rules below during the scheduling procedures above:
- the UE should not segment an RLC SDU (or partially transmitted SDU or
retransmitted RLC PDU) if the whole SDU (or partially transmitted SDU or
retransmitted RLC PDU) fits into the remaining resources;
- if the UE segments an RLC SDU from the logical channel, it shall maximize the size
of the segment to fill the grant as much as possible;
- UE should maximize the transmission of data.
Even though for LTE Rel. 8 only a Prioritized Bit Rate (PBR) is used within the LCP
procedure there could be also further enhancements in future releases. For example similar
to the PBR, also a maximum bit rate (MBR) per GBR bearer and an aggregated maximum bit
rate (AMBR) for all Non-GBR bearers could be provided to the user equipment. The MBR
denotes bit rates of traffic per bearer while AMBR denotes a bit rate of traffic per group of
bearers. AMBR applies to all Non-GBR SAE Bearers of a user equipment. GBR SAE
Bearers are outside the scope of AMBR. Multiple SAE Non-GBR bearers can share the
same AMBR. That is, each of those SAE bearers could potentially utilize the entire AMBR,
e.g. when the other SAE bearers do not carry any traffic. The AMBR limits the aggregated bit
rate that can be expected to be provided by the Non-GBR SAE bearers sharing the AMBR.
HARQ Protocol operation for unicast data transmissions
A common technique for error detection and correction in packet transmission systems over
unreliable channels is called hybrid Automatic Repeat request (HARQ). Hybrid ARQ is a
combination of Forward Error Correction (FEC) and ARQ.
If a FEC encoded packet is transmitted and the receiver fails to decode the packet correctly
(errors are usually checked by a CRC (Cyclic Redundancy Check)), the receiver requests a
retransmission of the packet
In LTE there are two levels of re-transmissions for providing reliability, namely, HARQ at the
MAC layer and outer ARQ at the RLC layer. The outer ARQ is required to handle residual
errors that are not corrected by HARQ that is kept simple by the use of a single bit errorfeedback
mechanism, i.e. ACK/NACK. An N-process stop-and-wait HARQ is employed that
has asynchronous re-transmissions in the downlink and synchronous re-transmissions in the
uplink. Synchronous HARQ means that the re-transmissions of HARQ blocks occur at pre¬
defined periodic intervals. Hence, no explicit signaling is required to indicate to the receiver
the retransmission schedule. Asynchronous HARQ offers the flexibility of scheduling re¬
transmissions based on air interface conditions. In this case some identification of the HARQ
process needs to be signaled in order to allow for a correct combing and protocol operation.
In 3GPP, HARQ operations with eight processes is used in LTE Rel. 8. The HARQ protocol
operation for Downlink data transmission will be similar or even identical to HSDPA.
In uplink HARQ protocol operation there are two different options on how to schedule a
retransmission. Retransmissions are either scheduled by a NACK, synchronous nonadaptive
retransmission, or explicitly scheduled by a PDCCH, synchronous adaptive
retransmissions. In case of a synchronous non-adaptive retransmission the retransmission
will use the same parameters as the previous uplink transmission, i.e. the retransmission will
be signaled on the same physical channel resources respectively uses the same modulation
scheme. Since synchronous adaptive retransmissions are explicitly scheduled via PDCCH,
the eNode B has the possibility to change certain parameters for the retransmission. A
retransmission could be for example scheduled on a different frequency resource in order to
avoid fragmentation in the uplink, or the eNode B could change the modulation scheme or
alternatively indicate user equipment what redundancy version to use for the retransmission.
It should be noted that the HARQ feedback (ACK/NACK) and PDCCH signaling occurs at the
same timing. Therefore user equipment only needs to check once whether a synchronous
non-adaptive retransmission is triggered, only NACK is received, or whether the eNode B
requests a synchronous adaptive retransmission, i.e. PDCCH is signaled.
L1/L2 Control Signaling
In order to inform the scheduled users about their allocation status, transport format and
other data related information (e.g. HARQ), L1/L2 control signaling needs to be transmitted
on the downlink along with the data. The control signaling needs to be multiplexed with the
downlink data in a sub-frame (assuming that the user allocation can change from sub-frame
to sub-frame). Here, it should be noted, that user allocation might also be performed on a TTI
(Transmission Time Interval) basis, where the TTI length is a multiple of the sub-frames. The
TTI length may be fixed in a service area for all users, may be different for different users, or
may even by dynamic for each user. Generally, then the L1/2 control signaling needs only be
transmitted once per TTI. The L1/L2 control signaling is transmitted on the Physical Downlink
Control Channel (PDCCH). It should be noted that assignments for uplink data
transmissions, uplink grants, are also transmitted on the PDCCH.
Generally, the PDCCH information sent on the L1/L2 control signaling may be separated into
the Shared Control Information (SCI) and Dedicated Control Information (DCI).
Shared Control Information (SCI)
Shared Control Information (SCI) carries so-called Cat 1 information. The SCI part of the
L1/L2 control signaling contains information related to the resource allocation (indication).
The SCI typically contains the following information:
- User identity, indicating the user which is allocated
- RB allocation information, indicating the resources (Resource Blocks, RBs) on which a
user is allocated. Note, that the number of RBs on which a user is allocated can be
dynamic.
- Duration of assignment (optional) if an assignment over multiple sub-frames (or TTIs) is
possible
Depending on the setup of other channels and the setup of the Dedicated Control
Information (DCI), the SCI may additionally contain information such as ACK/NACK for uplink
transmission, uplink scheduling information, information on the DCI (resource, MCS, etc.).
Dedicated Control Information (DCI)
Dedicated Control Information (DCI) carries the so-called Cat 2/3 information. The DCI part
of the L1/L2 control signaling contains information related to the transmission format (Cat 2)
of the data transmitted to a scheduled user indicated by Cat 1. Moreover, in case of
application of (hybrid) ARQ it carries HARQ (Cat 3) information. The DCI needs only to be
decoded by the user scheduled according to Cat 1. The DCI typically contains information
on:
- Cat 2: Modulation scheme, transport-block (payload) size (or coding rate), MIMO related
information, etc. Note, either the transport-block (or payload size) or the code rate can be
signaled. In any case these parameters can be calculated from each other by using the
modulation scheme information and the resource information (number of allocated RBs).
- Cat 3: HARQ related information, e.g. hybrid ARQ process number, redundancy version,
retransmission sequence number
L1/L2 control signaling information for Downlink Data Transmission
Along with the downlink packet data transmission, L1/L2 control signaling is transmitted on a
separate physical channel (PDCCH). This L1/L2 control signaling typically contains
information on:
- The physical channel resource(s) on which the data is transmitted (e.g. subcarriers or
subcarrier blocks in case of OFDM, codes in case of CDMA). This information allows the
user equipment (receiver) to identify the resources on which the data is transmitted.
- The transport Format, which is used for the transmission. This can be the transport block
size of the data (payload size, information bits size), the MCS (Modulation and Coding
Scheme) level, the Spectral Efficiency, the code rate, etc. This information (usually
together with the resource allocation) allows the user equipment (receiver) to identify the
information bit size, the modulation scheme and the code rate in order to start the
demodulation, the de-rate-matching and the decoding process. In some cases the
modulation scheme maybe signaled explicitly.
- HARQ information:
- Process number: Allows the user equipment to identify the HARQ process on which
the data is mapped.
Sequence number or new data indicator: Allows the user equipment to identify if the
transmission is a new packet or a retransmitted packet.
- Redundancy and/or constellation version: Tells the user equipment, which hybrid
ARQ redundancy version is used (required for de-rate-matching) and/or which
modulation constellation version is used (required for demodulation)
- user equipment Identity (user equipment ID): Tells for which user equipment the L1/L2
control signaling is intended for. In typical implementations this information is used to
mask the CRC of the L1/L2 control signaling in order to prevent other user equipments to
read this information.
L1/L2 control signaling information for Uplink Data Transmission
To enable an uplink packet data transmission, L1/L2 control signaling is transmitted on the
downlink (PDCCH) to tell the user equipment about the transmission details. This L1/L2
control signaling typically contains information on:
- The physical channel resource(s) on which the user equipment should transmit the data
(e.g. subcarriers or subcarrier blocks in case of OFDM, codes in case of CDMA).
- The transport format, the user equipment should use for the transmission. This can be
the transport block size of the data (payload size, information bits size), the MCS
(Modulation and Coding Scheme) level, the Spectral Efficiency, the code rate, etc. This
information (usually together with the resource allocation) allows the user equipment
(transmitter) to pick the information bit size, the modulation scheme and the code rate in
order to start the modulation, the rate-matching and the encoding process. In some cases
the modulation scheme maybe signaled explicitly.
Hybrid ARQ information:
Process number: Tells the user equipment from which hybrid ARQ process it should
pick the data.
- Sequence number or new data indicator: Tells the user equipment to transmit a new
packet or to retransmit a packet.
Redundancy and/or constellation version: Tells the user equipment, which hybrid
ARQ redundancy version to use (required for rate-matching) and/or which modulation
constellation version to use (required for modulation).
- user equipment Identity (user equipment ID): Tells which user equipment should transmit
data. In typical implementations this information is used to mask the CRC of the L1/L2
control signaling in order to prevent other user equipments to read this information.
There are several different flavors how to exactly transmit the information pieces mentioned
above. Moreover, the L1/L2 control information may also contain additional information or
may omit some of the information. E.g.:
- HARQ process number may not be needed in case of a synchronous HARQ protocol.
- A redundancy and/or constellation version may not be needed if Chase Combining is
used (always the same redundancy and/or constellation version) or if the sequence of
redundancy and/or constellation versions is pre defined.
Power control information may be additionally included in the control signaling.
MIMO related control information, such as e.g. pre-coding, may be additionally included
in the control signaling.
- In case of multi-codeword MIMO transmission transport format and/or HARQ information
for multiple code words may be included.
For uplink resource assignments (PUSCH) signaled on PDCCH in LTE, the L1/L2 control
information does not contain a HARQ process number, since a synchronous HARQ protocol
is employed for LTE uplink. The HARQ process to be used for an uplink transmission is
given by the timing. Furthermore it should be noted that the redundancy version (RV)
information is jointly encoded with the transport format information, i.e. the RV info is
embedded in the transport format (TF) field. The TF respectively MCS field has for example
a size of 5 bits, which corresponds to 32 entries. 3 TF/MCS table entries are reserved for
indicating RVs 1, 2 or 3. The remaining MCS table entries are used to signal the MCS level
(TBS) implicitly indicating RVO. The size of the CRC field of the PDCCH is 16 bits.
For downlink assignments (PDSCH) signaled on PDCCH in LTE the Redundancy Version
(RV) is signaled separately in a two-bit field. Furthermore the modulation order information is
jointly encoded with the transport format information. Similar to the uplink case there is 5 bit
MCS field signaled on PDCCH. Three of the entries are reserved to signal an explicit
modulation order, providing no Transport format (Transport block) info. For the remaining 29
entries modulation order and Transport block size info are signaled.
Uplink Power Control
Uplink transmission power control in a mobile communication system serves an important
purpose: it balances the need for sufficient transmitted energy per bit to achieve the required
Quality-of-Service (QoS), against the needs to minimize interference to other users of the
system and to maximize the battery life of the mobile terminal. In achieving this purpose, the
role of the Power Control (PC) becomes decisive to provide the required SINR (Signal to
Interference 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, 3GPP has adopted
for LTE the use of Fractional Power Control (FPC). 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.
Detailed power control formulae are specified in LTE for the Physical Uplink Shared Channel
(PUSCH), Physical Uplink Control Channel (PUCCH) and the Sounding Reference Signals
(SRSs) (see section 5.1 of 3GPP TS 36.213, "Physical layer procedures (Release 8)",
version 8.6.0, available at http://www.3gpp.org). The respective power control formula for
each of these uplink signals follows the same basic principles. They can be considered as a
summation of two main terms: a basic open-loop operating point derived from static or semistatic
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 P , further comprised of a common
power level for all user equipments (UEs) in the cell (measured in dBm) and a 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 Modulation and Coding Scheme (MCS) and explicit
Transmitter Power Control (TPC) commands.
The MCS-dependent component (referred to in the LTE specifications as , where TF is
short for Transport Format) allows the transmitted power per RB 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).
For the PUSCH, the switch between these two modes is configured semi-statically for each
user equipment by RRC signaling - i.e. the mode cannot be changed dynamically. With the
accumulative TPC commands, each TPC command signals a power step relative to the
previous level.
Formula (1) below shows the user equipment transmit power in dBm for the PUSCH:
PUSCH ~ puscH + + + ( )
where:
p
X is the maximum available transmit power of the user equipment, which is
depending on the user equipment class and configuration by the network
is the number of allocated physical resource blocks (PRBs).
is the user equipment path loss derived at the UE-based on RSRP (Reference Signal
Received Power)measurement and signaled RS (Reference Symbol) eNodeB
transmission power.
S a Mcs-dependent power offset set by the eNodeB.
p
O_PUSCH jS a UE-specific parameter (partially broadcasted and partially signaled using
RRC).
is cell-specific parameter (broadcasted on BCH).
' are closed loop PC commands signaled from the eNodeB to the user equipment
function / ( ) indicates whether closed loop commands are relative accumulative or
absolute. The function / ( ) is signaled to the user equipment via higher layers.
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 IMTAdvanced.
Two major technology components which are currently under consideration for
LTE-Advanced (LTE-A for short) are described in the following.
LTE-A Support of wider bandwidth
Carrier aggregation, where two or more component carriers are aggregated, is considered
for LTE-A in order to support wider transmission bandwidths e.g. up to 100 MHz and for
spectrum aggregation.
A terminal may simultaneously receive or transmit on one or multiple component carriers
depending on its capabilities:
- An LTE-A terminal with reception and/or transmission capabilities for carrier aggregation
can simultaneously receive and/or transmit on multiple component carriers. There is one
Transport Block (in absence of spatial multiplexing) and one HARQ entity per component
carrier.
- An LTE Rel. 8 terminal can receive and transmit on a single component carrier only,
provided that the structure of the component carrier follows the Rel. 8 specifications.
It shall be possible to configure all component carriers LTE Rel. 8 compatible, at least when
the aggregated numbers of component carriers in the uplink and the downlink are same.
Consideration of non-backward-compatible configurations of LTE-A component carriers is
not precluded
At present, LTE-A supports carrier aggregation for both contiguous and non-contiguous
component carriers with each component carrier limited to a maximum of 110 Resource
Blocks (RBs) in the frequency domain, using the LTE Rel. 8 numerology. It is possible to
configure a user equipment to aggregate a different number of component carriers
originating from the same eNodeB. Please note that component carriers originating from the
same eNodeB do no necessarily need to provide the same coverage.
Furthermore, a user equipment may be configured with 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.
The spacing between centre frequencies of contiguously aggregated component carriers is a
multiple of 300 kHz. This is in order to be compatible with the 100 kHz frequency raster of
LTE Rel. 8 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
uplink and for downlink there is one HARQ entity required in MAC for each aggregated
component carrier. There is (in the absence of Single User - Multiple Input Multiple Output
(SU-MIMO) 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 configured carrier aggregation is shown in Fig. 5 and Fig. 6 for the
downlink and uplink respectively.
When carrier aggregation is configured, the user equipment has only 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 (NAS)
mobility information (e.g. tracking area identifier (TAI)), similar to LTE Rel. 8. After RRC
connection establishment/re-establishment, the component carrier corresponding to that cell
is referred to as the Downlink Primary Component Carrier (DL PCC) in the downlink. There is
always only one DL PCC and one UL PCC configured per user equipment in connected
mode. Within the configured set of component carriers, other component carriers are referred
to as Secondary Component Carriers (SCCs).
The characteristics of the DL PCC and UL PCC are:
- The UL PCC is used for transmission of Layer 1 (L1) uplink control information;
- The DL PCC cannot be de-activated;
- Re-establishment of the DL PCC is triggered when the DL PCC experiences Radio Link
Failure (RLF), but not when DL SCCs experience RLF;
- The DL PCC cell can change with handover;
- NAS information is taken from the DL PCC cell.
The reconfiguration, addition and removal of component carriers can be performed by RRC
signaling. 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 carrier's system information which is necessary for
component carrier transmission / reception (similarly as in LTE Rel.8 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 shall be
ongoing at any time. Cross-carrier scheduling allows the PDCCH of a component carrier to
schedule resources on another component carrier. For this purpose a component carrier
identification field is introduced in the respective DCI formats (called "CIF"). 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 DRX operation applies. In other cases, the same DRX operation applies
to all configured and activated component carriers (i.e. identical active time for PDCCH
monitoring). When in active time, any component carrier may always schedule PDSCH on
any other configured and activated component carrier.
To enable reasonable UE battery consumption when carrier aggregation is configured, a
component carrier activation/deactivation mechanism for downlink SCCs is introduced (i.e.
activation/deactivation does not apply to the PCC). When a downlink SCC is not active, the
UE does not need to receive the corresponding PDCCH or PDSCH, nor is it required to
perform CQI measurements. Conversely, when a downlink SCC is active, the user
equipment should receive the 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 the 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 SCCs are:
- Explicit activation of DL SCCs is done by MAC signaling;
- Explicit deactivation of DL SCCs is done by MAC signaling;
- Implicit deactivation of DL SCCs is also possible;
- DL SCCs can be activated and deactivated individually, and a single
activation/deactivation command can activate/deactivate a subset of the configured DL
SCCs;
- SCCs added to the set of configured CCs are initially "deactivated".
Timing Advance
As already mentioned above, for the uplink transmission scheme of 3GPP LTE single-carrier
frequency division multiple access (SC-FDMA) was chosen to achieve an orthogonal
multiple-access in time and frequency between the different user equipments transmitting in
the uplink.
Uplink orthogonality is maintained by ensuring that the transmissions from different user
equipments in a cell are time-aligned at the receiver of the eNodeB. This avoids intra-cell
interference occurring, both between user equipments assigned to transmit in consecutive
sub-frames and between user equipments transmitting on adjacent subcarriers. Time
alignment of the uplink transmissions is achieved by applying a timing advance at the user
equipment's transmitter, relative to the received downlink timing as exemplified in Fig. 7. The
main role of this is to counteract differing propagation delays between different user
equipments.
Initial Timing Advance Procedure
When user equipment is synchronized to the downlink transmissions received from eNodeB,
the initial timing advance is set by means of the random access procedure as described
below. The user equipment transmits a random access preamble based on which the
eNodeB can estimate the uplink timing. The eNodeB responds with an 1-bit initial timing
advance command contained within the Random Access Response (RAR) message. This
allows the timing advance to be configured by the eNodeB with a granularity of 0.52 s from
0 up to a maximum of 0.67 ms.
Additional information on the control of the uplink timing and timing advance on 3GPP LTE
(Release 8/9) can be found in chapter 20.2 of Stefania Sesia, Issam Toufik and Matthew
Baker, "LTE - The UMTS Long Term Evolution: From Theory to Practice", John Wiley &
Sons, Ltd. 2009, which is incorporated herein by reference.
Updates of the Timing Advance
Once the timing advance has been first set for each user equipment, the timing advance is
updated from time to time to counteract changes in the arrival time of the uplink signals at the
eNodeB. In deriving the timing advance update commands, the eNodeB may measure any
uplink signal which is useful. The details of the uplink timing measurements at the eNodeB
are not specified, but left to the implementation of the eNodeB.
The timing advance update commands are generated at the Medium Access Control (MAC)
layer in the eNodeB and transmitted to the user equipment as MAC control elements which
may be multiplexed together with data on the Physical Downlink Shared Channel (PDSCH).
Like the initial timing advance command in the response to the Random Access Channel
(RACH) preamble, the update commands have a granularity of 0.52 ps. The range of the
update commands is ±16 ps, allowing a step change in uplink timing equivalent to the length
of the extended cyclic prefix. They would typically not be sent more frequently than about
every 2 seconds. In practice, fast updates are unlikely to be necessary, as even for a user
equipment moving at 500 km/h the change in round-trip path length is not more than 278
m/s, corresponding to a change in round-trip time of 0.93 s/s.
The eNodeB balances the overhead of sending regular timing update commands to all the
UEs in the cell against a UE's ability to transmit quickly when data arrives in its transmit
buffer. The eNodeB therefore configures a timer for each user equipment, which the user
equipment restarts each time a timing advance update is received. In case the user
equipment does not receive another timing advance update before the timer expires, it must
then consider that it has lost uplink synchronization (see also section 5.2 of 3GPP TS
36.321, "Evolved Universal Terrestrial Radio Access (E-UTRA); Medium Access Control
(MAC) protocol specification", version 8.9.0, available at http://www.3gpp.org and
incorporated herein by reference).
In such a case, in order to avoid the risk of generating interference to uplink transmissions
from other user equipments, the UE is not permitted to make another uplink transmission of
any sort and needs to revert to the initial timing alignment procedure in order to restore the
uplink timing.
Random Access Procedure
A mobile terminal in LTE can only be scheduled for uplink transmission, if its uplink
transmission is time synchronized. Therefore the Random Access (RACH) procedure plays
an important role as an interface between non-synchronized mobile terminals (UEs) and the
orthogonal transmission of the uplink radio access.
Essentially the Random Access in LTE is used to achieve uplink time synchronization for a
user equipment which either has not yet acquired, or has lost, its uplink synchronization.
Once a user equipment has achieved uplink synchronization the eNodeB can schedule
uplink transmission resources for it. The following scenarios are therefore relevant for
random access:
- A user equipment in RRC_CONNECTED state, but not uplink-synchronized, wishing to
send new uplink data or control information
- A user equipment in RRC_CONNECTED state, but not uplink-synchronized, required to
receive downlink data, and therefore to transmit corresponding HARQ feedback, i.e.
ACK/NACK, in the uplink. This scenario is also referred to as Downlink data arrival
- A user equipment in RRC_CONNECTED state, handing over from its current serving cell
to a new target cell; in order to achieve uplink time-synchronization in the target cell
Random Access procedure is performed
- A transition from RRCJDLE state to RRC_CONNECTED, for example for initial access or
tracking area updates
- Recovering from radio link failure, i.e. RRC connection re-establishment
There is one more additional case, where user equipment performs random access
procedure, even though user equipment is time-synchronized. In this scenario the user
equipment uses the random access procedure in order to send a scheduling request, i.e.
uplink buffer status report, to its eNodeB, in case it does not have any other uplink resource
allocated in which to send the scheduling request, i.e. dedicated scheduling request (D-SR)
channel is not configured.
LTE offers two types of random access procedures that allow access to be either contention
based, i.e. implying an inherent risk of collision, or contention-free (non-contention based). It
should be noted that contention-based random access can be applied for all six scenarios
listed above, whereas a non-contention based random access procedure can only be applied
for the downlink data arrival and handover scenario.
In the following the contention based random access procedure is being described in more
detail with respect to Fig. 8. A detailed description of the random access procedure can be
also found in 3GPP 36.321 , section 5.1 .
Fig. 8 shows the contention based RACH procedure of LTE. This procedure consists of four
"steps". First, the user equipment transmits 801 a random access preamble on the Physical
Random Access Channel (PRACH) to the eNodeB. The preamble is selected by user
equipment from the set of available random access preambles reserved by eNodeB for
contention based access. In LTE, there are 64 preambles per cell which can be used for
contention-free as well as contention based random access. The set of contention based
preambles can be further subdivided into two groups, so that the choice of preamble can
carry one bit of information to indicate information relating to the amount of transmission
resources needed to transmit for the first scheduled transmission, which is referred to as
msg3 in TS36.321 (see step 703). The system information broadcasted in the cell contain the
information which signatures (preambles) are in each of the two subgroups as well as the
meaning of each subgroup. The user equipment randomly selects one preamble from the
subgroup corresponding to the size of transmission resource needed for message 3
transmission.
After eNodeB has detected a RACH preamble, it sends 802 a Random Access Response
(RAR) message on the PDSCH (Physical Downlink Shared Channel) addressed on the
PDCCH with the (Random Access) RA-RNTI identifying the time-frequency slot in which the
preamble was detected. If multiple user equipments transmitted the same RACH preamble in
the same PRACH resource, which is also referred to as collision, they would receive the
same random access response.
The RAR message conveys the detected RACH preamble, a timing alignment command (TA
command) for synchronization of subsequent uplink transmissions, an initial uplink resource
assignment (grant) for the transmission of the first scheduled transmission (see step 803)
and an assignment of a Temporary Cell Radio Network Temporary Identifier (T-CRNTI). This
T-CRNTI is used by eNodeB in order to address the mobile(s) whose RACH preamble were
detected until RACH procedure is finished, since the "real" identity of the mobile is at this
point not yet known by eNodeB.
Furthermore the RAR message can also contain a so-called back-off indicator, which the
eNodeB can set to instruct the user equipment to back off for a period of time before retrying
a random access attempt. The user equipment monitors the PDCCH for reception of random
access response within a given time window, which is configured by the eNodeB. In case
user equipment doesn't receive a random access response within the configured time
window, it retransmits the preamble at the next PRACH opportunity considering a potentially
back off period.
In response to the RAR message received from the eNodeB, the user equipment transmits
803 the first scheduled uplink transmission on the resources assigned by the grant within the
random access response. This scheduled uplink transmission conveys the actual random
access procedure message like for example RRC connection request, tracking area update
or buffer status report. Furthermore it includes either the C-RNTI for user equipments in
RRC_CONNECTED mode or the unique 48-bit user equipment identity if the user
equipments are in RRCJDLE mode. In case of a preamble collision having occurred, i.e.
multiple user equipments have sent the same preamble on the same PRACH resource, the
colliding user equipments will receive the same T-CRNTI within the random access response
and will also collide in the same uplink resources when transmitting 803 their scheduled
transmission. This may result in interference that no transmission from a colliding user
equipment can be decoded at the eNodeB, and the user equipments will restart the random
access procedure after having reached maximum number of retransmission for their
scheduled transmission. In case the scheduled transmission from one user equipment is
successfully decoded by eNodeB, the contention remains unsolved for the other user
equipments.
For resolution of this type of contention, the eNode B sends 804 a contention resolution
message addressed to the C-RNTI or Temporary C-RNTI, and, in the latter case, echoes the
48-bit user equipment identity contained the scheduled transmission. It supports HARQ. In
case of collision followed by a successful decoding of the message sent in step 803, the
HARQ feedback (ACK) is only transmitted by the user equipment which detects its own
identity, either C-RNTI or unique user equipment ID. Other UEs understand that there was a
collision at step 1 and can quickly exit the current RACH procedure and starts another one.
Fig. 9 is illustrating the contention-free random access procedure of 3GPP LTE Rel. 8/9. In
comparison to the contention based random access procedure, the contention-free random
access procedure is simplified. The eNodeB provides 901 the user equipment with the
preamble to use for random access so that there is no risk of collisions, i.e. multiple user
equipment transmitting the same preamble. Accordingly, the user equipment is sending 902
the preamble which was signaled by eNodeB in the uplink on a PRACH resource. Since the
case that multiple UEs are sending the same preamble is avoided for a contention-free
random access, no contention resolution is necessary, which in turn implies that step 804 of
the contention based procedure shown in Fig. 8 can be omitted. Essentially a contention-free
random access procedure is finished after having successfully received the random access
response.
Timing Advance and Component Carrier Aggregation in the Uplink
In currents specifications of the 3GPP standards the user equipment only maintains one
timing advance value and applies this to uplink transmissions on all aggregated component
carriers. When component carriers are aggregated from different bands, they can experience
different interference and coverage characteristics.
Furthermore the deployment of technologies like Frequency Selective Repeaters (FSR) as
shown for example in Fig. 1 and Remote Radio Heads (RRH) as shown for example in Fig.
12 will cause different interference and propagation scenarios for the aggregated component
carriers. This leads to the need of introducing more than one timing advance within one user
equipment.
This leads to the need of introducing more than one timing advance within one UE. There
might be a separate timing advance for each aggregated component carrier. Another option
is that component carriers that stem from the same location and hence all experience a
similar propagation delay are grouped into timing advance groups (TA groups). For each
group a separate timing advanced is maintained.
Discussions were already held in 3GPP on this problem but a single timing advance for all
aggregated uplink component carriers is regarded as sufficient, since current specifications
up to 3GPP LTE-A Rel. 10 support only carrier aggregation of carriers from the same
frequency band.
Accordingly, prioritization of different types of uplink transmissions on a plurality of
component carriers during a same transmission time interval (TTI) need to be considered.
For example when a user equipment (UE) is in power limited state, rules need to determine
which uplink transmission should receive the available power.
SUMMARY OF THE INVENTION
One object of the invention is to propose strategies how a mobile terminal utilizes the
transmit power available for uplink transmissions of plural transport blocks within a
transmission time interval in case a mobile terminal is power limited, i.e. the transmit power
that would be required for the transmission of the plural transport blocks within the
transmission time interval according to the uplink resources assignments is exceeding the
transmit power available for uplink transmissions within a transmission time interval.
Another object of the invention is to propose strategies and methods how a mobile terminal
utilizes the transmit power available for uplink transmissions within a transmission time
interval in power limited situations, i.e. in situations where the transmit power that would be
required for transmitting via the physical random access channel (PRACH) and the physical
uplink shared channel (PUSCH) / physical uplink control channel (PUCCH) is exceeding the
transmit power available for uplink transmissions within the given transmission time interval.
A further object of the invention is to propose strategies and methods how the delay imposed
by the RACH procedures for uplink component carriers to be time aligned can be reduced in
systems using carrier aggregation in the uplink.
At least one of these objects 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 the prioritization of the power allocation for individual
transport blocks corresponding to plural uplink resource assignments within power control.
This aspect is particularly applicable to situations where the mobile terminal is power limited.
According to this aspect of the invention, the order of processing the uplink resource
assignments (priority order) on the uplink component carriers is used to determine power
scaling for the power allocation of the individual transport blocks to be transmitted on the
respective component carriers in the uplink. In power limited situations, the mobile terminal
reduces the transmit power for the transmission of each of the transport blocks according to
the priority of the respective transport block given by the priority order, such that the total
transmit power spent for the transmissions of the transport blocks becomes smaller or equal
to a maximum transmit power available to the mobile terminal for transmitting the transport
blocks.
According to one exemplary implementation the transmit power scaling is reducing the
transmit power is taking into account the priority of the resource assignment of a respective
transport block /component carrier on which the respective transport block is to be
transmitted, as given by the priority/processing order in that transmission of transport blocks
having high priority should be least effected by the transmit power reduction.
Advantageously, the lower (higher) the priority of the resource assignment/component carrier
according to the priority order, the larger (smaller) the power reduction applied to the transmit
power for the transport block required by its corresponding uplink resource assignment.
Ideally, the transmission power of high priority transport blocks should not be reduced, if
possible, but rather the transmit power reduction to meet a maximum transmit power
available to the mobile terminal for transmitting the transport blocks should be first tried to be
obtained by limiting the transmit power for transmissions of low priority transport blocks.
A second aspect of the invention is the prioritization of the power allocation for simultaneous
uplink transmissions via different physical channels (i.e. there are multiple uplink
transmissions within the same transmission time interval). Examples for physical channels
allowing uplink transmissions are physical uplink shared channel (PUSCH), the physical
uplink control channel (PUCCH) and the physical random access channel (PRACH).
Prioritizing the power allocation for uplink transmission via different physical channels allows
assigning individual transmit powers. This power allocation may be independent from the
component carrier on which a respective uplink transmission is sent.
According to this second aspect different transmit power levels may be used for
simultaneous uplink transmissions via a physical random access channel (PRACH) and via a
physical uplink shared channel (PUSCH). Alternatively, the second aspect of the invention
can also be used to individually scale the transmit power for simultaneous uplink
transmissions via a physical random access channel (PRACH) and via a physical uplink
control channel (PUCCH). Scaling transmit power for uplink transmissions based on a
prioritization of the physical channels may be for example used to improve the SINR of the
respective uplink transmission via the prioritized physical channel. For instance, a reduction
of the transmit power for uplink transmissions based on the prioritization of the physical
channels may allow the mobile terminal to meet a given power constraint, if the mobile
terminal in a power limited situation.
In an exemplary embodiment of the invention that is in line with the second aspect of the
invention, the transmit power for physical uplink shared channel (PUSCH) transmissions
and/or physical random access channel (PRACH) transmissions is reduced according to a
respective prioritization of the corresponding the channels. In this context, either the transmit
power for physical uplink shared channel (PUSCH) transmissions is prioritized over the
transmit power for physical random access channel (PRACH) transmissions or vice versa.
Advantageously, the lower (higher) the priority of the physical channel transmission, the
larger (smaller) the power reduction applied to the transmit power for transmitting via the
physical channel. Ideally, in order to meet a transmit power constraint in a power limited
situation, it may be tried to first limit the transmit power for low priority physical channel
transmissions, and then - if the transmit power constraint is still not met - also the transmit
power for physical channel transmissions of higher priority may be limited.
A third aspect of the invention is to adjust the transmit power used for performing random
access (RACH) procedures based on the number of RACH procedures required for time
aligning plural uplink component carriers. Depending on the number of uplink component
carriers that are to be time aligned, a mobile terminal performs one or more RACH
procedures for time aligning the uplink component carriers. A RACH procedure requires
processing resources and introduces restrictions on uplink transmissions that can be
performed in parallel by a mobile terminal. It may be thus desirable to perform as few RACH
procedures as possible. Adjusting the transmit power based on the number of required
RACH procedures can improve the success probability of each of the required RACH
procedures. Due to a higher success probability of the RACH procedures, the delay
introduced by the RACH procedures for uplink component carriers to be time aligned is
reduced.
According to one exemplary embodiment, a user equipment could utilize the transmit power
of one or more RACH procedures that are not required (i.e. that are superfluous and thus not
performed) for adjusting the transmit power to perform only the required RACH procedures
for time aligning the plural uplink component carriers improves the success probability of
each of the required RACH procedures.
The first, second and third aspect of this invention can be readily combined with each other
and may use the same priority/processing order of the resource assignments in transport
block generation (logical channel prioritization) and of uplink transmission on a physical
random access channel (PRACH) and power scaling of the transmissions of the generated
transport blocks and of transmission on a physical random access channel (PRACH) in the
uplink.
According to one exemplary implementation of the invention in line with the first and second
aspect of the invention, a method for adjusting the transmit power utilized by a mobile
terminal for uplink transmissions is provided, wherein the mobile terminal is configured with
at least a first and a second uplink component carrier. The mobile terminal determines a
transmit power required for transmitting a transport block PPUSCH ( via a physical uplink
shared channel on the first uplink component carrier. Further, the mobile terminal determines
a transmit power required for transmitting a random access preamble P
PRACH ( via a
physical random access channel on the second uplink component carrier. Furthermore, the
mobile terminal reduces the determined transmit power for the physical uplink shared
channel transmission and/or the physical random access channel transmission according to
a prioritization between the transmit power for the physical uplink shared channel
transmission and the transmit power for the physical random access channel transmission
and transmits the transport block on the first uplink component carrier and the random
access preamble on the second uplink component carrier within a transmission time interval
, using the respective transmit powers.
In one exemplary implementation, the mobile terminal may further determine a transmit
power required for transmitting another transport block via an assigned physical uplink
shared channel on a third component carrier. The transmit powers for transmitting each
transport block P
PUSCHc ( e determined according to the corresponding uplink component
carrier c where the uplink component carriers have a priority order. Further, the mobile
terminal reduces the determined transmit power for transmitting each transport block
w P
PUSCHc ( according to the priority order, where wc [0,...,l]; and transmits each
transport block using the respective reduced transmit power.
In a more detailed implementation, the transmit power for transmitting via a physical uplink
shared channel is prioritized over the transmit power for transmitting via a physical random
access channel. In this case, the mobile terminal first reduces the determined transmit power
P
PRACH ( r transmitting the random access preamble via the physical random access
channel and then reduces the transmit power PUS cHC ) r transmitting each transport
c
block via the physical uplink shared channels on the uplink component carriers within the
transmission time interval .
Furthermore, in another exemplary embodiment of the invention, the transmit power of
physical random access channel transmissions is prioritized over the transmit power of
physical uplink shared channel transmissions. In this case, the mobile terminal reduces the
transmit power PFUSCHC ) 0 ' transmission via the physical uplink shared channels on the
c
uplink component carriers, uses the determined transmit power P
PRACH ( for transmission
via the physical random access channel and uses a non-reduced transmit power PPUCCH (0
for transmitting on a physical uplink control channel within the transmission time interval i .
In another exemplary embodiment of the invention, the mobile terminal reduces the
determined transmit powers such that the sum of the determined transmit powers is smaller
or equal to a maximum transmit power available PMAX to the mobile terminal for transmitting
on the uplink component carriers within the transmission time interval i .
In a further exemplary embodiment of the invention, the mobile terminal further determines a
transmit power required for transmitting another random access preamble via a physical
random access channel on a fourth uplink component carrier within the transmission time
interval i . The transmit powers for transmitting each random access preamble PPRACHC ( are
determined according to the corresponding uplink component carrier c , where the uplink
component carriers having a priority order. Further, the mobile terminal reduces the
determined transmit powers for transmitting each random access preamble wc ·RR A
')
according to the priority order, where w [0,...,l]; and transmits each random access
preamble using the respective reduced transmit power.
In another more detailed implementation, each uplink component carrier is assigned a cell
index and the mobile terminal reduces the determined transmit power for transmitting each
random access preamble w ·PPRACHC ( based on the priority order given by the cell indexes
of the uplink component carriers.
Furthermore, in another exemplary implementation of the invention, the mobile terminal is
configured with one uplink component carrier as the primary component carrier and with any
other uplink component carrier as a secondary component carrier. In this case, the mobile
terminal reduces the determined transmit power for transmitting each random access
preamble w PPRACHC ) . where the primary component carrier is prioritized over any other
secondary component carrier.
According to another implementation of the invention, the mobile terminal reduces the
transmit power for transmitting each random access preamble wc PPRACHC
') based on a
flag for each random access preamble. The flag indicates for each random access preamble
to be transmitted whether or not a request for transmitting the respective random access
preamble was previously received for the corresponding uplink component carrier by the
terminal.
In another embodiment of the invention, the mobile terminal determines the transmit power
for transmitting a random access preamble via a random access channel on each of the
second and the fourth component carrier by utilizing a first offset P0 PRACH , in case the uplink
component carrier to be time aligned and uplink component carriers already time aligned
belong to a same timing advance group; and a second, different offset Po_pRACH„, ,i , > case
the uplink component carrier to be time aligned and uplink component carriers already time
aligned belong to more than one timing advance groups.
In a more detailed implementation of the invention, the first offset P0_PRACH and the second
offset o_pRACH „ p
are signaled to the mobile terminal by a base station.
In a further exemplary embodiment, the mobile terminal determines the transmit power for
transmitting a random access preamble via a physical random access channel on an uplink
component carrier to be time aligned includes re-utilizing a previously determined power
ramping step N for the corresponding uplink component carrier or re-utilizing a different,
previously determined power ramping step N . for a different uplink component carrier The
mobile terminal uses the power ramping step N and/or . for ramping the transmit power
of consecutive transmissions of the random access preamble.
Furthermore, in a detailed implementation, the mobile terminal determines the transmit
power for transmitting a random access preamble via a physical random access channel on
an uplink component carrier by:
ACH (0 = m 0 _PRACH - P + (N - 1 )D RACH + D ft EAMBLE , PMAX } where N e {N , N^. } , in
case the uplink component carrier to be time aligned and uplink component carriers already
time aligned belong to a same timing advance group; and
PpRACH (0 = n
0 ACH m |tiple - P L (i) + (N - + e b le P MAX } Where N € N , } ,
in case the uplink component carrier to be time aligned and uplink component carriers
already time aligned belong to more than one timing advance groups.
In another embodiment of the invention, the mobile terminal adds a base station dependent
pre-scaling offset Aoffset that has been received by the mobile terminal form a base station
for an uplink component carrier c to adjust the transmit power for transmitting random
access preambles on the respective uplink component carrier.
Furthermore, in a detailed implementation of the invention, the mobile terminal determines
transmit power for transmitting a random access preamble via a physical random access
channel on an uplink component carrier by:
PpRACH (0 = m 0_PRACH - ( + (N - 1) RACH + D ,,, + Aoffset , PMAX jwhere
N {N ,N , in case the uplink component carrier to be time aligned and uplink
component carriers already time aligned belong to a same timing advance group, and
PRACH (0 = mi _P ACH MULTIPLE - i) + (N - 1) RACH + L M + Aoffset , PMAX jwhere
N G {N ,N^.}, in case the uplink component carrier to be time aligned and uplink
component carriers already time aligned belong to more than one timing advance groups.
According to another exemplary implementation of the invention in line with the second and
third aspect of the invention, a method for adjusting the transmit power used by a mobile
terminal for one or more RACH procedures is provided, where the mobile terminal is allowed
RACH access on plural uplink component carriers. The mobile terminal determines, for
uplink component carriers to be time aligned, the number of RACH procedures required for
time aligning the uplink component carriers. Further, the mobile terminal performs the
determined number of RACH procedures required for time aligning the uplink component
carriers, wherein a transmit power for all of the one or more RACH procedures is determined
according to the determined number of required RACH procedures.
In a more advanced implementation, the mobile terminal determines the transmit power for
all of the one or more RACH procedures utilizing a first offset P0_P CH , in case of
determining one required RACH procedure, and utilizing a second, different offset
P0 _pRACH m , i - n case ° determining more than one required RACH procedure, the second
offset P o_pRACH mu „p, having a higher value than the first offset P0 PRACH .
According to another alternative embodiment, the mobile terminal is configured with one
uplink component carrier as the primary component carrier and with any other uplink
component carrier as a secondary component carrier. The mobile terminal determines the
transmit power for RACH procedures utilizing a first offset P0 PRACH , in case a RACH
procedure is to be performed on the primary component carrier, and utilizing a second,
different offset P0 _pRACH„ W , >
n case one o r o re RACH procedures are to be performed on
the secondary component carrier, the second offset PO_PRACH,„ ,<, having a higher value than
the first offset P0_PRAC H
In a further implementation, the mobile terminal determines the number of required RACH
procedures based on a number of different timing advance groups to which said uplink
component carriers to be time aligned belong.
According to another implementation of the invention, each of the required one or more
RACH procedures is performed on uplink component carriers belonging to different timing
advance groups among the uplink component carriers to be time aligned.
In a further embodiment, the identified number of required RACH procedures is equal to the
number of different timing advance groups of the plurality of uplink component carriers to be
time aligned.
Furthermore, in another implementation, the uplink component carriers to be time aligned are
uplink component carriers activated at the mobile terminal.
In a more detailed implementation, the time alignment of the uplink component carriers
comprises configuring a timing advance value per timing advance group.
According to another exemplary embodiment of the invention, the number of required RACH
procedures corresponds to the number of timing advance groups to which the uplink
component carriers to be time aligned belong, excluding those timing advance groups for
which the mobile terminal is already time-aligned.
Furthermore, it should also be noted that of course the different criteria and rules outlined
above could be combined arbitrarily with each other to adjust the transmit power to be used
by the mobile terminal for uplink transmissions.
According to another exemplary implementation of the invention in line with the first and
second aspect of the invention, a mobile terminal for controlling the transmit power for uplink
transmissions is provided, wherein the mobile terminal is configured with at least a first and a
second uplink component carrier.
The mobile terminal comprises a processing unit for determining a transmit power required
for transmitting a transport block P
PUSCH ( via a physical uplink shared channel on the first
uplink component carrier, and for determining a transmit power required for transmitting a
random access preamble Pp
RACH ( v physical random access channel on the second
uplink component carrier. Further, the mobile terminal includes a power control unit for
reducing the determined transmit power for the physical uplink shared channel transmission
and/or the physical random access channel transmission according to a prioritization
between the transmit power for the physical uplink shared channel transmission and the
transmit power for the physical random access channel transmission. The mobile terminal
has also a transmitter for transmitting the transport block on the first uplink component carrier
and the random access preamble on the second uplink component carrier within a
transmission time interval i , using the respective transmit power.
According to a more detailed implementation of the invention, the mobile terminal further
comprises a processing unit adapted to determine a transmit power required for transmitting
another random access preamble via a physical random access channel on a fourth uplink
component carrier within the transmission time interval i , and the transmit powers for
transmitting each random access preamble a e determined according to the
corresponding uplink component carrier c , the uplink component carriers having a priority
order. The mobile terminal also has a power control unit adapted to reduce the determined
transmit powers further includes reducing the determined transmit powers for transmitting
each random access preamble w P PRACHc (i) according to the priority order, where
[q,. .,ΐ ] ; and wherein the transmitter is adapted to transmit each random access
preamble using the respective reduced transmit power.
Another embodiment of the invention, in line with the second and third aspect of the
invention, is providing a mobile terminal for adjusting the transmit power used by a mobile
terminal for one or more RACH procedures, the mobile terminal being allowed access on
plural uplink component carriers. The mobile terminal includes means for determining, for
uplink component carriers to be time aligned, the number of RACH procedures required for
time aligning the uplink component carriers. The mobile terminal further comprises means for
performing the determined number of RACH procedures required for time aligning the uplink
component carriers, wherein a transmit power for all of the one or more RACH procedures is
determined according to the determined number of required RACH procedures.
According to another embodiment of the invention, a base station for use with the mobile
terminal performing a method for adjusting the transmit power for transmitting random
access preambles via physical random access channels on uplink component carriers is
provided. The base station includes a power control unit configured to signal an offset
o_P ACHm
to n e mobile terminal, wherein the offset o_P ACH „p
s utilized by the mobile
terminal for determining a transmit power for transmitting a random access preamble in case
the uplink component carrier to be time aligned and uplink component carriers already time
aligned belong to more than one timing advance groups. The bases station also has a
receiving unit for receiving random access preambles on the uplink component carriers with
a transmit power that has been determined by the mobile terminal utilizing the offset
P 0_PRACH „W ,
In a exemplary detailed implementation, the base station further comprises a power control
unit is further configured to signal another offset P0_PRACH to the mobile terminal, wherein the
other offset P0 PRACH is utilized by the mobile terminal for determining a transmit power for a
random access preamble in case the uplink component carrier to be time aligned and uplink
component carriers already time aligned belong to a same timing advance group. The base
station also has a receiving unit is configured to receive random access preambles on the
uplink component carriers with a transmit power that has been determined by the mobile
terminal utilizing the other offset P0_PRACH
In a further exemplary embodiment of the invention, a base station for use with the mobile
terminal performing a method for adjusting the transmit power for transmitting random
access preambles via physical random access channels on uplink component carriers is
provided. The base station includes a power control unit for signaling a base station
dependent pre-scaling offset Aoffset for an uplink component carrier c to a mobile terminal
to be added by the mobile terminal for determining a transmit power for transmissions of
random access preambles on the uplink component carrier. Further, the base station
comprises a receiving unit for receiving random access preambles on the uplink component
carrier with a transmit power that has been determined by the mobile terminal adding the
base station dependent pre-scaling offset Aoffset for the uplink component carrier c .
Another exemplary embodiment of the invention in line with the first and second aspect of
this invention is related to a computer readable medium storing instructions that, when
executed by a processor of a mobile terminal, cause the mobile terminal to adjust the
transmit power utilized by the mobile terminal for uplink transmissions, wherein the mobile
terminal is configured with at least a first and a second uplink component carrier, by
determining a transmit power required for transmitting a transport block P
PUSCH ( via a
physical uplink shared channel on the first uplink component carrier, and determining a
transmit power required for transmitting a random access preamble P
PRACH ( via a physical
random access channel on the second uplink component carrier. Furthermore, the mobile
terminal is caused to reduce the determined transmit power for the physical uplink shared
channel transmission and/or the physical random access channel transmission according to
a prioritization between the transmit power for the physical uplink shared channel
transmission and the transmit power for the physical random access channel transmission,
and to transmit the transport block on the first uplink component carrier and the random
access preamble on the second uplink component carrier within a transmission time interval
i , using the respective transmit power.
In another embodiment of the invention, which is in line with the second and third aspect of
the invention, the execution of the instructions on the computer-readable medium by the
processor cause the mobile terminal to adjust the transmit power used for one or more
RACH procedures, the mobile terminal being allowed access on plural uplink component
carriers, by determining, for uplink component carriers to be time aligned, the number of
RACH procedures required for time aligning the uplink component carriers. The execution of
the instructions further cause the mobile terminal to perform the determined number of
RACH procedures required for time aligning the uplink component carriers, wherein a
transmit power for all of the one or more RACH procedures is determined according to the
determined number of required RACH procedures.
Another computer-readable medium according to a further embodiment of the invention
stores instructions that, when executed by a processor of a base station for use with the
mobile terminal performing a method for adjusting the transmit power for transmitting random
access preambles via physical random access channels on uplink component carriers, cause
the base station to signal an offset Po_pRACH,„„ ,
t0 n e mobile terminal, wherein the offset
o_PRACHm „ e
s utilized by the mobile terminal for determining a transmit power for a random
access preamble in case the uplink component carrier to be time aligned and uplink
component carriers already time aligned belong to a same timing advance group. Further,
the base station is caused to receive random access preambles on the uplink component
carriers with a transmit power that has been determined by the mobile terminal utilizing the
offset 0 _PRACH i , ip
■
A further computer-readable medium according to another embodiment of the invention
stores instructions that, when executed by a processor of a base station for use with the
mobile terminal performing a method for adjusting the transmit power for transmitting random
access preambles via physical random access channels on uplink component carriers, cause
the base station to signal a base station dependent pre-scaling offset Aoffset for an uplink
component carrier c to a mobile terminal to be added by the mobile terminal for determining
a transmit power for transmissions of random access preambles on the uplink component
carrier.
The execution of the instructions further cause the base station to receive random access
preambles on the uplink component carrier with a transmit power that has been determined
by the mobile terminal adding the base station dependent pre-scaling offset Aoffset for the
uplink component carrier .
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 & 4 show an exemplary localized allocation and distributed allocation of the uplink
bandwidth in a single carrier FDMA scheme,
Figs. 5 & 6 show the 3GPP LTE-A (Release 10) Layer 2 structure with activated carrier
aggregation for the downlink and uplink, respectively,
Fig. 7 exemplifies the time alignment of an uplink component carrier relative to a
downlink component carrier by means of a timing advance as defined for
3GPP LTE (Release 8/9),
Fig. 8 shows a RACH procedures as defined for 3GPP LTE (Release 8/9) in which
contentions may occur, and
Fig. 9 shows a contention-free RACH procedure as defined for 3GPP LTE
(Release 8/9),
Fig. 10 shows a flow chart of distributing a maximum available transmit power PkMAX
to the transport blocks to be transmitted within a T P according to an
exemplary embodiment of the invention,
Fig. 11 shows an exemplary scenario in which a user equipments aggregates two
radio cells, one radio cell originating from an eNodeB, and the other radio
cell originating from a Frequency Selective Repeater (FSR),
Fig. 12 shows an exemplary scenario in which a user equipments aggregates two
radio cells, one radio cell originating from an eNodeB, and the other radio
cell originating from a Remote Radio Head (RRH),
Fig. 13 exemplifies a different time alignment between a RACH and a PUSCH
transmission assuming a timing advance for the PUSCH transmission as
defined for 3GPP LTE (Release 8/9),
Fig. 14 exemplifies a RACH configuration of a user equipment setup with multiple
uplink component carriers, in case the uplink component carriers belong to a
same timing advance group,
Fig. 15 exemplifies a RACH configuration of a user equipment setup with multiple
uplink component carriers, in case the uplink component carriers belong to
two timing advance groups,
Fig. 16 shows a flow chart of a transmit power adjustment procedure for determining
transmit power for PRACH an PUSCH uplink transmissions according to
another embodiment of the invention,
Fig. 17 shows a flow chart of a transmit power adjustment procedure for multiple
RACH procedures according to yet another embodiment of the invention,
Fig. 18 shows a flow chart of a transmit power adjustment procedure for multiple
RACH procedures according to an exemplary implementation of the
embodiment of Fig. 17 of the invention.
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 singlecarrier
uplink radio access scheme according to the 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-A 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-A 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.
The invention aims to provide an efficient and tight QoS control for uplink transmissions by a
base station (eNodeB or Node B in the 3GPP context) in a scenario where a mobile terminal
(user equipment in the 3GPP context) is assigned multiple uplink resources in one
transmission time interval (e.g. one or more sub-frames). The invention also provides an
efficient utilization of the transmit power available to the mobile terminal for uplink
transmissions in a TTI, even in cases where the mobile terminal is power limited.
A consideration underlying this invention is to introduce a priority order for the uplink
resource assignments (respectively for the transport blocks corresponding thereto). This
priority order is considered by the mobile terminal when generating the transport blocks for
uplink transmission and/or in the distribution of the transmit power available to the mobile
terminal for uplink transmissions in a TTI to the respective transport blocks to be transmitted
within the TTI. The priority order is sometimes also referred to as the processing order. This
is - as will become more apparent from the following - because the priority order defined for
the uplink resource assignments (respectively for the transport blocks corresponding thereto)
is implying the order in which the uplink resource assignments (respectively for the transport
blocks corresponding thereto) are processed.
One aspect of the invention is the prioritization of the power allocation for individual transport
blocks corresponding to plural uplink resource assignments within power control. This aspect
is particularly applicable to situations where the mobile terminal is power limited and ensures
an efficient distribution of the available transmit power to the different transport blocks.
According to this aspect of the invention, the order of processing the uplink resource
assignments (priority order) on the uplink component carriers is used to determine power
scaling for the power allocation of the individual transport blocks to be transmitted on the
respective component carriers in the uplink. According to this aspect of the invention, a percomponent
carrier, respectively per- transport block or per-resource assignment, power
scaling is applied.
In power limited situations, the mobile terminal reduces the transmit power for the
transmission of each of the transport blocks according to the priority of the respective
transport block given by the priority order, such that the total transmit power spent for the
transmissions of the transport blocks becomes smaller or equal to a maximum transmit
power available to the mobile terminal for transmitting the transport blocks in the uplink within
a given TTI.
According to one exemplary implementation the transmit power scaling is reducing the
transmit power and is taking into account the priority of the resource assignment of a
respective transport block (or component carrier on which the respective transport block is to
be transmitted), as given by the priority order in that transmission of transport blocks having
high priority should be least effected by the transmit power reduction. Advantageously, the
lower (higher) the priority of the resource assignment/component carrier according to the
priority order, the larger (smaller) the power reduction applied to the transmit power for the
transport block required by its corresponding uplink resource assignment.
As mentioned before, the power scaling may be ideally configured such that the transmission
of high priority transport blocks should be not reduced where possible. Instead the transmit
power reduction to meet the a maximum transmit power available to the mobile terminal for
transmitting the transport blocks in the uplink within a given TTI should be first tried to be
obtained by limiting the transmit power of transmissions of low priority transport blocks.
Moreover, in a more advanced implementation, the power control mechanism in the mobile
terminal ensures that the control information to be signaled on a physical uplink control
channel, such as the PUCCH in LTE-A, do not undergo power scaling, but only
transmissions on the physical uplink shared channel, i.e. transport blocks, transmitted
concurrently to the control information, such as the PUCCH in LTE-A, within the same TTI is
subject to power scaling. In other words, the power control mechanism is designed to assign
the remainder of the difference between the transmit power available to the mobile terminal
for uplink transmissions within a TTI and the transmit power required for the signaling of
control information on the physical uplink control channel is distributed on a per-transport
block basis to the transport blocks on the physical uplink shared channel taking into account
the priority order of the transport blocks.
A second aspect of the invention is the prioritization of the power allocation for simultaneous
uplink transmissions via different physical channels (i.e. there are multiple uplink
transmissions within the same transmission time interval). Examples for physical channels
allowing uplink transmissions are physical uplink shared channel (PUSCH), the physical
uplink control channel (PUCCH) and the physical random access channel (PRACH).
Prioritizing the power allocation for uplink transmission via different physical channels allows
assigning individual transmit powers. This power allocation may be independent from the
component carrier on which a respective uplink transmission is sent.
According to this second aspect different transmit power levels may be used for
simultaneous uplink transmissions via a physical random access channel (PRACH) and via a
physical uplink shared channel (PUSCH). Alternatively, the second aspect of the invention
allows to to individually scale the transmit power of simultaneous uplink transmissions via a
physical random access channel (PRACH) and via a physical uplink control channel
(PUCCH). Scaling transmit power for uplink transmissions based on a prioritization of the
physical channels may be for example used to improve the SINR of the respective uplink
transmission via the prioritized physical channel. For instance, a reduction of the transmit
power for uplink transmissions based on the prioritization of the physical channels may allow
the mobile terminal to meet a given power constraint, if the mobile terminal in a power limited
situation.
In an exemplary embodiment of the invention that is in line with the second aspect of the
invention, the transmit power for physical uplink shared channel (PUSCH) transmissions
and/or physical random access channel (PRACH) transmissions is reduced according to a
respective prioritization of the corresponding the channels. In this context, either the transmit
power for physical uplink shared channel (PUSCH) transmissions is prioritized over the
transmit power for physical random access channel (PRACH) transmissions or vice versa.
Advantageously, the lower (higher) the priority of the physical channel transmission, the
larger (smaller) the power reduction applied to the transmit power for transmitting via the
physical channel.
Ideally, in order to meet a transmit power constraint in a power limited situation, it may be
tried to first limit the transmit power for low priority physical channel transmissions, and then
- if the transmit power constraint is still not met - also the transmit power for physical
channel transmissions of higher priority may be limited..
In an alternative embodiment of the invention, the prioritization of the power allocation for
simultaneous uplink transmissions via different physical channels can be advantageously
combined with the first aspect of the invention of prioritizing the power allocation for
individual transport blocks corresponding to plural uplink resource assignments within power
control.
When the user equipment is configured with multiple uplink component carriers belonging to
more than one timing advance group, the user equipment may be required to perform more
than one RACH procedure for time aligning the respective uplink component carriers within
the same transmission time interval. In other words, the user equipment may be required to
transmit more than one random access preamble via the PRACH channel within the same
TTI. Accordingly, in a further more advanced embodiment of the invention, a prioritization of
the power allocation for the transmission of RACH preamble of individual RACH procedures
is performed, in case multiple PRACH procedures are to be performed simultaneously.
In a further alternative embodiment of the invention, the priority order according to which the
user equipment is determining the transmit power of the RACH preambles for multiple RACH
procedures is linked to the indices assigned to the configured uplink component carriers.
Each component carrier may be assigned an individual cell index or carrier index (CI), and
the priority order may be defined according to the cell indices or carrier indices of the
component carriers on which the uplink resources are assigned.
In an exemplary and more advanced implementation, the eNodeB may assign the cell
indices or carrier indices, respectively, such that the higher/lower the priority of the
component carrier the higher/lower the cell index or component carrier index of the
component carrier. In this case, the user equipment should determine the transmit power for
transmissions of the RACH preambles for multiple RACH procedures in decreasing carrier
indicator order.
In a further alternative embodiment of the invention, the priority order for determining the
transmit power for RACH preamboles of multiple RACH procedures depends on the type of
component carrier. As described above there is one primary uplink component carrier (PCC)
configured per-user equipment and potentially multiple secondary uplink component carriers
(SCC). According to this embodiment a user equipment always assigns the transmit power
for transmitting the RACH preamble that is part of a RACH procedure for the PCC, before
assigning a transmit power of the RACH preamble of a RACH procedure to be performed on
any other uplink resource assignments within a TTI. Regarding the transmit power
assignments for the RACH preambles of the RACH procedures to be performed on SCC(s),
there are several options. For example, the assignment of transmit power for performing
RACH procedures on the SCC(s) could be left to user equipment implementation.
Alternatively the transmit power assignment for performing RACH procedures on the SCC(s)
could be treated in the order of the assigned cell indices or carrier indices.
A third aspect of the invention is to adjust the transmit power used for in random access
(RACH) procedures based on the number of RACH procedures required for time aligning
plural uplink component carriers. Depending on the number of uplink component carriers that
are to be time aligned, a mobile terminal performs one or more RACH procedures for time
aligning the uplink component carriers. A RACH procedure requires processing resources
and introduces restrictions on uplink transmissions that can be performed in parallel by a
mobile terminal. It may be thus desirable to perform as few RACH procedures as possible.
Adjusting the transmit power for the RACH preamble(s) based on the number of required
RACH procedures can improve the success probability of each of the required RACH
procedures. Due to a higher success probability of the RACH procedures, the delay
introduced by the RACH procedures for uplink component carriers to be time aligned is
reduced.
According to one exemplary embodiment of the invention, a user equipment could "reutilize"
the transmit power of one or more RACH procedures that are not required (i.e. that are
superfluous and thus not performed) for adjusting the transmit power to perform only the
required RACH procedures for time aligning the plural uplink component carriers improves
the success probability of each of the required RACH procedures.
In an alternative embodiment of the invention, the user equipment increases the transmit
power used for transmitting the RACH preambles, when plural RACH procedures are
required for time aligning the plural uplink component carriers. For example, the user
equipment uses a first offset P0_PRACH , in case there is only one RACH procedure to be
preformed, and utilizing a second, different offset Po_PRACH te > i n case tnere s r e n a
one RACH procedure to be performed. Advantageously, the second offset o_ ACH p
n s
a higher value than the first offset P0 PRACH , which may improve the success probability when
performing plural RACH procedures.
In a further, alternative embodiment of the invention, the user equipment may individually
increase the transmit power used for the RACH preambles in the RACH procedures
depending on the type of component carrier on which a respective one of the RACH
procedures is performed. It may be assumed for exemplary purposes that there is one
primary component carrier (PCC) configured per user equipment and optionally one or more
secondary component carriers (SCC). Accordingly, a user equipment would determine a
transmit power for the preamble of a RACH procedure utilizing a first offset P0 PRACH , case
the RACH procedure is to be performed on the PCC. The user equipment would utilize a
second, different offset O_PRACH ,„ „ , , , >
n case the RACH procedure is to be performed on a
secondary component carrier. As noted previously, the second offset Po_pRACH , te
a y
heave a higher value than the first offset P0 PRACH .
In an exemplary implementation of the third aspect of the invention, there are several options
for determining (or limiting) the number of required RACH procedures for plural uplink
component carriers to be time aligned. For example, the determination of the number of
required RACH procedures could be left to user equipment implementation. Another option
or alternative is that the user equipment determines the number of required RACH
procedures based on the number of timing advance groups to which the plural uplink
component carrier belong. As described above, an eNodeB may group component carriers
experiencing a similar propagation delay into the same timing advance group. Since the
propagation delay of all component carriers within a given timing advance group is equal,
only one single timing advance needs to be configures per timing advance group, which
means that only one RACH procedure is required per timing advance group for time aligning
all component carriers thereof. Accordingly, a user equipment obtaining information on the
timing advance groups determines the number of required RACH procedure by performing
only one RACH procedure per timing advance group.
Considering a situation where a RACH procedure is required for each timing advance group
to which at least one uplink component carrier to be time aligned belongs, the number of
required RACH procedures is equal to the number of different timing advance groups of the
plurality of uplink component carriers to be time aligned.
A user equipment may set the timing advance of each of the one or more uplink component
carriers to be time aligned and belonging to one timing advance group using a timing
advance value obtained from eNodeB after performing one single RACH procedure for one
of the uplink component carriers to be time aligned of the respective timing advance group.
Considering for exemplary purposes that the user equipment is configured with uplink
component carriers that are already time aligned (e.g. a RACH procedure was performed an
earlier point in time), a further RACH procedure for acquiring a timing advance value does
not need to be performed for those timing advance groups for which a timing advance value
is already configured, i.e. for those timing advance groups which comprise one of the already
time aligned uplink component carrier. Accordingly, the number of required RACH
corresponds to the number of timing advance groups for which no timing advance value is
configured, or in other words, the number of required RACH procedures is equal to the
number of timing advance groups not comprising an already time aligned uplink component
carrier. Regarding the component carriers to be time aligned and that belong to a timing
advance group for which a timing advance is already configured, the user equipment simply
configures the timing advance of each of the one or more uplink component carriers
according to the timing advance set for the respective timing advance group to which the
respective component carrier belongs.
As already indicated above, an aspect of the invention is the distribution of the transmit
power to the transmissions of the generated transport blocks on the assigned resources on
the uplink component carriers. In this context situations where the mobile terminal is power
limited are of particular interest. When implementing the invention in a communication
system using carrier aggregation in the uplink, like LTE-A, and assuming a per-component
carrier power control, another embodiment of the invention is proposing the prioritization of
the transmit power allocation on the physical uplink shared channel for the uplink component
carriers for cases where the mobile terminal is in a power limited situation. This proposed
prioritization of the transmit power available to the mobile terminal is capable of addressing
the different QoS of the data/uplink component carriers.
Power limitation denotes the situation where the total transmit power of the mobile terminal
that would be required for transmitting the transport blocks on uplink component carriers
within a single TTI according to the uplink resource assignments is exceeding the maximum
transmit power available to the mobile terminal for uplink transmissions PMAX . The maximum
transmit power available to the mobile terminal for uplink transmissions PMAX thereby
depends on the maximum power capabilities of the mobile terminal and the maximum
transmit power allowed by the network (i.e. configured by the eNodeB).
Fig. 10 shows a flow chart of distributing a maximum available transmit power PMAX to the
transport blocks to be transmitted within a TTI according to an exemplary embodiment of the
invention. In this exemplary embodiment and the following examples below a LTE-A based
communication system using carrier aggregation in the uplink, and assuming a percomponent
carrier power control will be assumed. Furthermore, it is also assumed that the
transmission power of the PUCCH (i.e. the control information) is prioritized over PUSCH
transmissions (i.e. the transport blocks generated according to the uplink resource
assignments), i.e. PUSCH transmit power is first scaled down in a power limited situation.
The mobile terminal first receives 1001 multiple uplink resource assignments for one TTI
using its receiver unit, and a processing unit of the mobile terminal determines 1002 their
priority order. The priority order of the uplink resource assignments may be determined
according to one of the various exemplary options discussed herein.
Furthermore, the mobile terminal's transport block generation unit generates 1003 the
transport blocks according to the uplink resource assignments. This transport block
generation may be again implemented according to one of the various exemplary options
outlined herein. Furthermore, in another alternative implementation, the transport block for
each component carrier may be generated according to the corresponding uplink resource
assignment by performing the known LTE Rel. 8 logical channel prioritization for each uplink
resource assignment, respectively uplink component carrier.
The mobile terminal's processing unit further determines 1004 for each of the generated
transport blocks the transmit power that would be required/implied by their respective uplink
resource assignments according to the power control, i.e. required transmission power is
given by power control formula. For example, the mobile terminal may use formula (1) as
provided in the Technical Background section to determine the transmit power that would be
implied for the transmission of each of the transport blocks on the uplink component carriers
by the corresponding uplink resource assignment. In this example, the mobile terminal is
considered power limited for the transmissions of the transport blocks within the given TTI.
The mobile terminal may for example determine its power limitation by comparing the sum of
the required transmit powers for the transport blocks to the maximum transmit power
available to the mobile terminal for uplink transmissions PMAX minus the transmit power
required for control signaling on the PUCCH PPUCCH in the same TTI, and determining
thereby that the sum of the required transmit powers for the transport blocks exceeds the
maximum transmit power available to the mobile terminal for uplink transmissions PMAX
minus the transmit power required for control signaling on the PUCCH PPUCCH in the same
TTI.
In order not to exceed the maximum transmit power available to the mobile terminal for
uplink transmissions PMAX minus the transmit power required for control signaling on the
PUCCH PPUCCH in the same TTI, the mobile terminal needs to reduce the uplink transmit
power for the transmission of all or some of the transport blocks. There are several options
how this power reduction, also referred to as power scaling, can be implemented done. In the
exemplary flow chart shown in Fig. 10, the mobile terminal determines 1005 next a power
reduction for each transmission of a respective transport block such that the sum of the
reduced transmit power for each transmission of the transport blocks (i.e. the transmit power
obtained for each respective transmission of a transport block when applying 1006 the
determined respective power reduction to the respective required transmit power as
determined in step 1004) becomes equal to or smaller than the maximum transmit power
available to the mobile terminal for uplink transmissions PMAX minus the transmit power
required for control signaling on the PUCCH PPUCCH in the same TTI. The transmit power
control unit of the mobile terminal applies 1006 the determined respective power reduction to
the respective required transmit power as determined in step 1004 and transmits 1007 the
transport blocks on the assigned uplink resources on the component carriers within the given
TTI using the reduced transmit power.
The power reduction or power scaling may be implemented as part of the transmit power
control functionality provided by the mobile terminal. The power control functionality may be
considered as a function of the physical layer of the mobile terminal. It may be assumed that
the physical layer has no idea about logical channel to transport block mapping, respectively
the logical channel to component carrier mapping, since the MAC layer of the mobile terminal
performs the multiplexing of the logical channel data for multiple component carriers.
However, power scaling of the transmissions of the transport blocks (i.e. of the PUSCH)
based on uplink component carrier priority (respectively the priority of the uplink resource
assignments assigning resources thereon) is desirable to be able to adequately support
delay sensitive traffic in a carrier aggregation setting.
More in particular, it is desirable that high QoS data within the transport blocks transmitted on
the PUSCH is scaled less compared to low QoS data which can tolerate more
retransmissions. Therefore according to one exemplary embodiment of the invention, the
power scaling of the transmissions of the transport blocks on the PUSCH (see steps 1005,
and 1006) advantageously considers the processing order of the uplink resource
assignments, which may be considered equivalent to the priority order of the component
carriers on which they assign resources. Since both the processing order of uplink resource
assignments as well as the power scaling has an impact on the transmission quality
experienced by logical channels, it is desirable to have some interaction between the
prioritization of the uplink resource assignments in the transport block generation in the MAC
layer of the mobile terminal (see for example step 1003) and the power scaling functionality
in the physical layer of the mobile terminal (see steps 1005 and 1006).
This interaction may be for example obtained by the power scaling function provided in the
physical layer using the same priority order of the uplink resource assignments for power
scaling of PUSCH transmissions as used in the MAC layer for determining the processing
order of the uplink resource assignments in the generation of the transport blocks. In one
exemplary implementation, the mobile terminal scales down the required transmit powers
(see step 1004) for the transport blocks on the PUSCH in the reverse processing order of the
uplink resource assignments. Basically the mobile terminal's power control unit starts scaling
down the required transmit power for the transmission of the transport block corresponding to
the lowest priority uplink resource assignment first, next the terminal's power control unit
scales down the required transmit power for the transmission of the transport block
corresponding to the second lowest priority uplink resource assignment, etc. If necessary the
transmit power of one or more transport blocks may be scaled down to zero, i.e. the mobile
terminal performs DTX on the given component carrier(s).
In one further exemplary implementation, the required transmit power for a transmission of
the transport block is scaled down to zero, before power scaling the next transport block.
Hence, power control unit starts scaling down the required transmit power for the
transmission of the transport block corresponding to the lowest priority uplink resource
assignment down to zero (if necessary), and if the transmit power needs to be further
reduced, the terminal's power control unit scales down the required transmit power for the
transmission of the transport block corresponding to the second lowest priority uplink
resource assignment again down to zero (if necessary), etc.
The power reduction/scaling of the transmit power may be for example implemented as
follows in a LTE-A system. In one exemplary implementation, the eNodeB signals a weight
factor for each component carrier c to user equipment that is applied to the PUSCH
transmission of a transport block on the respective component carrier. When the user
equipment is power limited, its power control unit scales the weighted sum of the transmit
power for all PUSCH transmissions on the component carriers on which resources have
been assigned. This may be realized by calculating a scaling factor s such that the
maximum transmit power available to the mobile terminal for uplink transmissions PMAX is
not exceed. The scaling factors can be determined from Formula (2):
PpUCCH + SSW c ' p SCHc ~ AX
(2)
where denotes the scaling factor and the weight factor for component carrier c .
uccH denotes the transmit power required for the control signaling on the PUCCH within
TTI i , and PPUSC Hc denotes the transmit power of a transport block to be transmitted on
the PUSCH of component carrier c within TTI i (see step 1004 and formula (1)). Apparently,
scaling factors can be determined as:
S < AX ~ ccH(0
' å W c - PpUSCHc W
c
The weight factor w of the component carriers may for example consider the QoS of the
data transmitted on a specific component carrier.
In one more advanced implementation, it may be assured that the transport block transmitted
on the PUSCH of the uplink PCC is not scaled. This may be for example realized by the
eNodeB defining the weight factor w for the uplink PCC to V . Alternatively, the following
relation may be used to determine the scaling factor s only for component carriers other
than the uplink PCC:
p CCH + USCH PCC ) + S c ' PpUSCH_SCC c AX
c (4)
so that:
AX " PpUCCH 0) " PpUSCH_PCC SW c ' PpUSCH_SCC
where PpUSCH_pcc s tne transmit power required for the transmission of the transport block
to be transmitted on the uplink PCC (see step 1004 and formula (1)), while PPUsCH_sccc ( ) s
the transmit power required for the transmission of the transport block to be transmitted on
other the uplink SCCs (see step 1004 and formula (1)).
In one further exemplary embodiment of the invention, when generating the transport blocks,
the user equipment may process the uplink resource assignments in decreasing order of the
weight factors wc . Hence, the priority order may be given by the weighting factors w . The
mobile terminal may start processing with the uplink resource assignment for an uplink
component carrier which is assigned the highest weight factor w . Essentially, the highest
weight factor w corresponds to highest priority uplink component carrier respectively uplink
resource assignment in this embodiment.
In case the same weight factor w is applied to multiple uplink component carriers, the
processing order may be left to user equipment implementation. Alternatively in case of
same weight factor wc , the processing order may also be determined based on the downlink
transmission timing of the uplink resource assignments (as discussed above) or based on
the carrier index (CI) of corresponding component carriers.
In another exemplary embodiment of the invention, the power scaling by the power control
unit of the mobile terminal depends on type of a component carrier on which the respective
transport block is to be transmitted. The power assignment to the PUSCH transmission of a
transport block on the uplink PCC which carries high priority traffic is prioritized over other
PUSCH transmissions on the uplink SCC(s). Power allocation, respectively, the amount of
power reduction/scaling on other uplink component carriers, i.e. uplink SCC(s), may be left to
user equipment implementation. For example, regarding the remaining uplink SCC(s), the
user equipment could multiplexes QoS sensitive data on a component carrier of its choice
and is allowed to prioritize power allocation of this component carrier relative to other uplink
SCC(s).
In a communication system using carrier aggregation, the mobile terminals may also be
allowed to perform random access on a component carrier, while transmitting scheduled data
(transport blocks) on other component carriers. For a 3GPP based system like LTE-A, it may
thus be possible to that the user equipment is performing a random access channel (RACH)
access on one component carrier, while transmitting PUSCH/PUCCH simultaneously on
other component carriers. The user equipment may thus transmit a RACH preamble, i.e. a
transmission on the physical random access channel (PRACH), and in the same TTI also
transmit data on the PUSCH and/or PUCCH. A potential use case for concurrent PRACH
and PUCCH/PUSCH transmission is the situation where user equipment is out-of sync on
one uplink component carrier, whereas it's still uplink synchronized on other uplink
component carrier. In order to regain uplink synchronization for the "out-of-sync component
carrier" the user equipment would make a RACH access, e.g. ordered by PDCCH.
Furthermore, also in cases where no dedicated scheduling request channel is configured for
a user equipment on the PUCCH, the user equipment may perform a RACH access in order
to request uplink resources, in case new data is arrived in the UE buffer.
In these cases, according to another embodiment of the invention, the transmit power for the
RACH access (i.e. the transmission of the RACH preamble on the PRACH) is not subject
power control by the access network. Nevertheless, in this embodiment the transmit power
for the PRACH transmission is considered when power scaling is applied by the mobile
terminal in power limited situations. Hence, in case of a concurrent PRACH transmission and
PUCCH / PUSCH transmission, the transmit powers for PRACH, PUSCH and PUCCH within
a TTI should fulfill the relation:
pUCCH + S p SCHc + PpRACH (0 — MA
(6)
where PPRACH ( the transmit power for the transmission on the PRACH in TTI i , while in
case of power scaling being necessary due to power limitation, the following relation may be
in one exemplary scenario to be met:
PpUCCH
+ SW c ' PpUSCHc + ^PRACH (0 — MA
c (7)
In a more detailed exemplary implementation, the initial preamble transmission power setting
(i.e. the setting of PPRACH
' ) ) ay be based on an user equipment's open-loop estimation
with full compensation of the path loss. This may ensure that the received power of the
RACH preambles is independent of the path-loss. The eNodeB may also configure an
additional power offset for the PRACH, depending for example on the desired received
SINR, the measured uplink interference and noise level in the time-frequency slots allocated
to RACH preambles, and possibly on the preamble format. Furthermore, the eNodeB may
optionally configure preamble power ramping so that the transmit power PPRACH ( r each
retransmitted preamble, i.e. in case the PRACH transmission attempt was not successfully,
is increased by a fixed step.
There are different alternatives for the power scaling for the case of concurrent PRACH and
PUCCH/PUSCH transmission. One option is that the PRACH transmission power PPRACH (
is prioritized over the PUSCH transmission power PPUScHC ' s m r to the PUCCH
c
transmit power PPUCCH (i) . This option is shown in relation (7) above.
Alternatively, another option is to prioritize the PUCCH/PUSCH transmissions over PRACH
transmissions. In this case the user equipment would first scale down the transmit power
PP ACH ) ° e PR CH and then subsequently scale down the transmit power PPUSCHC
c
of the PUSCH (if necessary).
In a third option, no concurrent transmission of PRACH and PUCCH/PUSCH is allowed.
Hence, in this case the user equipment drops either the PUCCH/PUSCH transmission or
PRACH transmission. Since the timing offset is different between PRACH and
PUCCH/PUSCH, the full utilization of the Power Amplifier (PA) is rather difficult.
In other words, a prioritization between the transmit power for a PUSCH transmission and a
transmit power for the PRACH transmission (i.e. the transmission of a RACH preamble)
defines how a user equipment performs power control when transmitting on different physical
channels within a same transmission time interval.
According to an embodiment of the invention, a user equipment uses different transmit power
levels for simultaneous uplink transmissions via a PRACH and via a PUSCH. By using
different power levels, the user equipment may meet a given power constraint, as will be
exemplarily illustrated below with reference to the flow chart of Fig. 16.
For adjusting the transmit power utilized by a user equipment for uplink transmissions, the
user equipment first determines a priority for PRACH and PUSCH transmissions (see step
1601). Further, the user equipment determines the transmit power for the PUSCH
transmission (see step 1602) and for the PRACH transmission (see step 1603) to be
performed in the same transmission time interval. In particular, these power levels may be
determined based on the uplink component carrier on which each of the transmission is to be
performed. It should be apparent that a PRACH and PUSCH transmission to occur in a same
sub-frame are to be performed on different uplink component carriers (i.e. by a user
equipment supporting carrier aggregation). This user equipment may be an LTE-A user
equipment.
Then, the user equipment reduces the determined transmit power for the PUSCH
transmission and/or the PRACH transmission (see step 1604). This power reduction is
performed according to a prioritization between the transmit power for the PUSCH
transmission and the transmit power for the PRACH transmission. By reducing the transmit
power according to the maximum available transmit power of the user equipment, the user
equipment may be adapted to meet a given power constraint in a power limited situation.
Thereafter, the user equipment applies the determine power reduction to determined PRACH
and PUSCH transmit power (see step 1605) and transmits the PRACH and PUSCH
transmission at the reduced transmit power on the respective uplink component carrier (see
step 1606).
A user equipment supporting carrier aggregation may simultaneously perform a RACH
access while transmitting PUSCH/PUCCH on other component carriers. In other words a
user equipment may encounter situations where it transmits a RACH preamble, i.e. PRACH
transmission, and in the same TTI also transmit PUSCH and/or PUCCH. Simultaneous
PRACH and PUCCH/PUSCH transmissions may for example occur in a situation where a
user equipment is uplink out-of sync on one component carrier, whereas it's still uplink
synchronized on other uplink component carrier. To regain uplink synchronization the user
equipment performs a RACH access, e.g. a contention-free RACH access ordered by
PDCCH for the component carrier being out-of sync. Furthermore when no dedicated
scheduling request channel is configured for a user equipment on PUCCH, the user
equipment may also initiate a RACH access in order to request uplink resource, for example
in case new data arrives in the user equipment buffer.
In LTE, uplink power control, as described in the Technical Background section herein, is
defined for the Physical Uplink Shared Channel (PUSCH), Physical Uplink Control Channel
(PUCCH) and the Sounding Reference Signals (SRSs) giving the impression that is not
applied for the Physical Uplink Shared Channel (PRACH). Nevertheless, it is necessary to
consider PRACH transmission when power scaling needs to be used due to power
limitations.
Conventionally, only PUCCH, PUSCH with multiplexed uplink control information (UCI) and
PUSCH are considered for the power limitation case, where PUCCH is given the highest
priority over PUSCH. A PUSCH transmission having multiplexed UCI is considered of higher
priority than a PUSCH transmission without (w/o) multiplexed UCI and is therefore prioritized.
This yields the following priority order:
PUCCH > PUSCH with UCI > PUSCH without UCI
Further, the initial power setting for transmission of a RACH preamble may be based on an
open-loop estimation with full compensation of the path loss. This would allow ensuring that
the received power of the RACH preamble at the eNodeB is independent from the path-loss.
According to a more detailed embodiment of the invention, the eNodeB configures for RACH
transmissions an additional power offset to be applied in addition to the power determined
from the conventional open-loop power control mechanism. Exemplary implementations for
determining the power offset for RACH transmissions may be based on the desired received
SI R, on the measured uplink interference and noise level in the time-frequency slots
allocated to RACH preambles, and on the preamble format.
According to another detailed embodiment of the invention, the eNodeB may reconfigure the
preamble power ramping so that the transmission for each retransmitted preamble, i.e. in
case the PRACH transmission attempt was not successfully, is increased by a fixed step.
In other words, there are different solutions to implement the aspect of the invention to
perform power scaling for the case of simultaneous PRACH and PUCCH/PUSCH
transmission.
According to one implementation of the invention, the PRACH transmission power is
prioritized over the PUSCH transmission power, similar to the PUCCH transmit power. This
yields the following priority order:
PUCCH > PRACH > PUSCH with UCI > PUSCH without UCI
A further implementation of the invention provides an additional advantage when prioritizing
PUSCH with multiplexed UCI over a PRACH transmission. PUSCH with multiplexed UCI
include viable time critical information. Accordingly, a respective priority order can be
implemented as follows:
PUCCH > PUSCH with UCI > PRACH > PUSCH without UCI
In yet another implementation of the invention PUCCH/PUSCH transmissions are prioritized
over PRACH. In this case the user equipment first scales down the transmit power for a
PRACH transmission and then subsequently scales down the transmit power for a PUSCH
transmission (if necessary). A priority order may be specified as follows:
PUCCH > PUSCH with UCI > PUSCH without UCI> PRACH
The above described implementations of the invention are compatible with different
configurations of user equipments. For example, a user equipment may be configured with
uplink component carriers belonging to more than one timing advance (TA) group, where the
user equipment has only one power amplifier (PA). Alternatively, the user equipment may be
configured with plural uplink component carriers belonging to more than one TA group,
where for each TA group of uplink component carriers a separate power amplifier (PA) is
provided.
In the exemplary configuration of a user equipment operating multiple uplink component
carriers belonging to more than one TA group with just one power amplifier (PA), the user
equipment has to ensure that no concurrent transmission of PRACH and PUCCH/PUSCH
occur. An implementation of such a user equipment would need to drop either
PUCCH/PUSCH or PRACH transmission. This is due to the fact that the timing offsets
between PRACH and PUCCH/PUSCH are different and, similar to HSUPA's HS-DPCCH and
DPCCH/DPDCH case, a full utilization of the Power Amplifier (PA) is rather difficult.
A further embodiment of the invention relates to the prioritization of multiple RACH
transmissions within one TTI.
An according implementation of the invention of is a user equipment deciding which of
several RACH transmissions is to prioritize based on an order according to the cell index of
the corresponding uplink component carriers on which the PRACH preamble shall be
transmitted. In this implementation, the highest priority may be assigned to the PRACH
transmission on the uplink component carrier with the lowest cell index.
Another implementation of the invention is a user equipment distinguishing between RACH
procedures initiated by the user equipment and RACH procedures that are ordered by
eNodeB with a PDCCH order (also referred to as contention-free RACH access). In this
implementation, RACH procedures ordered by an eNodeB are assigned higher priority than
those initiated by the user equipment.
Furthermore, both aforementioned implementations of priority schemes can be combined. In
this case the user equipment first ranks RACH procedures based on PDCCH order or UE
initiation and then ranks RACH procedures of both groups according to the cell index of
corresponding component carriers.
As indicated earlier, it is another detailed embodiment of the invention to reconfigures the
RACH preamble power ramping procedure performed by a user equipment so that the
transmission for each retransmitted preamble, i.e. in case the PRACH transmission attempt
was not successfully, is increased by a fixed step.
In case that user equipment aggregates plural uplink component carriers form more than a
single TA group where multiple RACH procedures become necessary. One example may be
a handover, where user equipment needs to apply carrier aggregation with activated carriers
in the target eNodeB. In this case part of the handover procedure is to time align all TA
groups with activated component carriers. If this is done consecutively this introduces
additional delay, but also simultaneous RACH procedures increase delay as most likely
RACH opportunities on different uplinks in secondary cells will be set slightly apart from
each other in order to allow the eNodeB to efficiently manage RACH preamble resources
and avoiding too many PRACH transmissions within one TTI.
Another situation where multiple (consecutive) RACH transmissions may occur is when a
user equipment is scheduled for data transmissions on several uplink component carriers
belonging to different TA groups that are not time aligned (this might be because of inactivity
over a longer period).
Furthermore, in another exemplary situation, a user equipment may be required to instantly
time align a component carrier upon activation. In this case, when a user equipment receives
an activation command for several component carriers belonging to more than one TA group
and these TA groups are currently not time aligned, the user equipment needs to perform
RACH procedures for all these TA groups simultaneously.
Therefore, according to an exemplary embodiment of the invention, the user equipment may
need to perform multiple RACH procedures simultaneously so that the additional delay that
would be induced by performing the RACH procedures consecutively is reduced. The aim is
to approach the delay time of a single RACH procedure, hence the delay caused by the
additional RACH procedures should be minimized.
According to an exemplary implementation, the user equipment increases a transmit power
for performing the RACH preamble transmission so as to minimize probability of
retransmission.
The PRACH power [dBm ] is determined by a user equipment as follows:
P
A C H (0 = m 0_PRACH - L (i) + (N - 1)A RACH + eambk ,PMAX }
For finding optimal power setting for PPRACH a user equipment has several options as
described below.
One implementation of the invention is to increase P0_PRACH when multiple uplink component
carriers with PRACH opportunity are aggregated by the user equipment, In this context it
may be advantageous, if the eNodeB signals different offset values, e.g. a first offset value
O_PRACH
anc ' a second offset value P0 PRACHMU; „ where the
primary component carrier is prioritized over any other secondary component
carrier.
9. The method according to claim 6, wherein the step of reducing the transmit
power for transmitting each random access preamble w ACH ( is based on
a flag for each random access preamble, the flag indicating for each random
access preamble to be transmitted whether or not a request for transmitting the
respective random access preamble was previously received for the
corresponding uplink component carrier by the terminal.
10. The method according to one of claims 6 to 9, wherein the transmit power for
transmitting a random access preamble via a random access channel on each of
the second and the fourth component carrier is determined by utilizing a first
offset P0 pRACH . in case the uplink component carrier to be time aligned and uplink
component carriers already time aligned belong to a same timing advance group;
and a second, different offset P0_PRACH„,„ „ , - n case n e uplink component carrier
to be time aligned and uplink component carriers already time aligned belong to
more than one timing advance groups.
11. The method according to claim to 10, wherein the first offset Po PRACH
ND TNE
second offset PQPRACH,,,^,,^ are signaled to the mobile terminal by a base station.
12. The method according to one of claims 0 to 11, wherein the step of determining
the transmit power for transmitting a random access preamble via a physical
random access channel on an uplink component carrier to be time aligned
includes re-utilizing a previously determined power ramping step N for the
corresponding uplink component carrier or re-utilizing a different, previously
determined power ramping step N for a different uplink component carrier, the
power ramping step N and being used for ramping the transmit power of
consecutive transmissions of the random access preamble.
13. The method according to claim 12, wherein the transmit power for transmitting a
random access preamble via a physical random access channel on an uplink
component carrier is determined by:
( ) = min{P 0 PRACH - PL(i) + (N - + eaM . MA where Ne {N^N }, in case the uplink component carrier to be time aligned and
uplink component carriers already time aligned belong to a same timing advance
group; and
PP RACH (0 = minfc . pRACH ,PMAX )
where N {N ,N^.}, in case the uplink component carrier to be time aligned
and uplink component carriers already time aligned belong to more than one
timing advance groups.
14. The method according to one of claims 0 to 12, wherein the step of determining
the transmit powers includes adding a base station dependent pre-scaling offset
Aoffset that has been received by the mobile terminal form a base station for an
uplink component carrier c to adjust the transmit power for transmitting random
access preambles on the respective uplink component carrier.
15. The method according to claim 14, wherein the transmit power for transmitting a
random access preamble via a physical random access channel on an uplink
component carrier is determined by:
PpRACH (0 = min{P 0 PRACH - PL(i) + (N - + eamble + Aoffset ,PMAX }
where N {N ,N^.}, in case the uplink component carrier to be time aligned and
uplink component carriers already time aligned belong to a same timing advance
group, and
( ) = min P0J>RACH - PL(i) + (N - 1) RACH + eamble + of set ,PMAX )
where N {N C,N_,C} , in case the uplink component carrier to be time aligned
and uplink component carriers already time aligned belong to more than one
timing advance groups.
16. A method for adjusting the transmit power used by a mobile terminal for one or
more RACH procedures, the mobile terminal being allowed RACH access on
plural uplink component carriers, the method comprising the steps of:
determining, for uplink component carriers to be time aligned, the number of
RACH procedures required for time aligning the uplink component carriers, and
performing the determined number of RACH procedures required for time
aligning the uplink component carriers, wherein a transmit power for all of the one
or more RACH procedures is determined according to the determined number of
required RACH procedures.
17. The method according to claim 16, wherein the transmit power for all of the one
or more RACH procedures is determined utilizing a first offset P0_PRACH , in case of
determining one required RACH procedure, and utilizing a second, different
offset o_P ACH > n case ° determining more than one required RACH
procedure, the second offset having a higher value than the first
offset P0 P ACH
18. The method according to claim 16, wherein one uplink component carrier is
configured with the mobile terminal as the primary component carrier and any
other uplink component carrier is configured with the mobile terminal as a
secondary component carrier, and wherein the transmit power for RACH
procedures is determined utilizing a first offset P0_PRACH > in case a RACH
procedure is to be performed on the primary component carrier, and utilizing a
second, different offset Po_pRACH i p >in case one o o e A CH procedures are
to be performed on the secondary component carrier, the second offset
p o_pRACHm W p h ing a higher value than the first offset P0 PRACH .
19. The method according to one of claims 16 to 18, wherein the number of required
RACH procedures is determined based on a number of different timing advance
groups to which said uplink component carriers to be time aligned belong.
20. The method according to claim 19, wherein each of the required one or more
RACH procedures is performed on uplink component carriers belonging to
different timing advance groups among the uplink component carriers to be time
aligned.
21. The method according to one of claims 16 to 20, wherein the identified number of
required RACH procedures is equal to the number of different timing advance
groups of the plurality of uplink component carriers to be time aligned.
22. The method according to one of claims 16 to 21, wherein the uplink component
carriers to be time aligned are uplink component carriers activated at the mobile
terminal.
23. The method according to one of claims 16 to 22, wherein the time alignment of
the uplink component carriers comprises configuring a timing advance value per
timing advance group.
24. The method according to claim 19 to 23, wherein the number of required RACH
procedures corresponds to the number of timing advance groups to which the
uplink component carriers to be time aligned belong, excluding those timing
advance groups for which the mobile terminal is already time-aligned.
The method according to one of claims 16 to 24, further comprising the steps of
the method according to one of claims 1 to 15.
26. A mobile terminal for controlling the transmit power for uplink transmissions,
wherein the mobile terminal is configured with at least a first and a second uplink
component carrier, the mobile terminal comprising:
a processing unit for determining a transmit power required for transmitting a
transport block PPUSCH ( via a physical uplink shared channel on the first uplink
component carrier, and for determining a transmit power required for transmitting
a random access preamble PPRACH ( v a a physical random access channel on
the second uplink component carrier;
a power control unit for reducing the determined transmit power for the physical
uplink shared channel transmission and/or the physical random access channel
transmission according to a prioritization between the transmit power for the
physical uplink shared channel transmission and the transmit power for the
physical random access channel transmission, and
a transmitter for transmitting the transport block on the first uplink component
carrier and the random access preamble on the second uplink component carrier
within a transmission time interval , using the respective transmit power.
27. The mobile terminal according to claim 26 further comprising means for
performing the steps according to one of claims 2 to 5.
28. The mobile terminal according to claim 26 or 27, wherein:
the processing unit is adapted to determine a transmit power required for
transmitting another random access preamble via a physical random access
channel on a fourth uplink component carrier within the transmission time interval
i , and the transmit powers for transmitting each random access preamble
PPRACHc
') are determined according to the corresponding uplink component
carrier c , the uplink component carriers having a priority order;
the power control unit is adapted to reduce the determined transmit powers
further includes reducing the determined transmit powers for transmitting each
random access preamble w c ' PpRACHc according to the priority order, where
wc e [0,...,l]; and wherein the transmitter is adapted to transmit each random
access preamble using the respective reduced transmit power.
29. The mobile terminal according to one of claims 26 to 28, further comprising
means for performing the steps according to one of claims 7 to 15.
30. A mobile terminal for adjusting the transmit power used by a mobile terminal for
one or more RACH procedures, the mobile terminal being allowed access on
plural uplink component carriers, the mobile terminal comprising:
means for determining, for uplink component carriers to be time aligned, the
number of RACH procedures required for time aligning the uplink component
carriers, and
means for performing the determined number of RACH procedures required for
time aligning the uplink component carriers, wherein a transmit power for all of
the one or more RACH procedures is determined according to the determined
number of required RACH procedures.
3 1. The mobile terminal according claim 30, further comprising means for performing
the steps according to one of claims 17 to 25.
32. A base station for use with the mobile terminal performing a method for adjusting
the transmit power for transmitting random access preambles via physical
random access channels on uplink component carriers; comprising:
a power control unit configured to signal an offset Po_PRACH , p te
0 tne mobile
terminal,
'
wherein the offset P
- R„
multiple
is utilized by the mobile terminal for
determining a transmit power for transmitting a random access preamble in case
the uplink component carrier to be time aligned and uplink component carriers
already time aligned belong to more than one timing advance groups ; and
a receiving unit for receiving random access preambles on the uplink component
carriers with a transmit power that has been determined by the mobile terminal
utilizing the offset 0 _ P RACH,„ , ·
33. The base station according to claim 32, wherein the power control unit is further
configured to signal another offset P0_PRACH to the mobile terminal, wherein the
other offset P0_pRACH
s utilized by the mobile terminal for determining a transmit
power for a random access preamble in case the uplink component carrier to be
time aligned and uplink component carriers already time aligned belong to a
same timing advance group ; and
and the receiving unit is configured to receive random access preambles on the
uplink component carriers with a transmit power that has been determined by the
mobile terminal utilizing the other offset P0_PRACH .
34. A base station for use with the mobile terminal performing a method for adjusting
the transmit power for transmitting random access preambles via physical
random access channels on uplink component carriers, comprising:
a power control unit for signaling a base station dependent pre-scaling offset
Aoffset for an uplink component carrier c to a mobile terminal to be added by
the mobile terminal for determining a transmit power for transmissions of random
access preambles on the uplink component carrier; and
a receiving unit for receiving random access preambles on the uplink component
carrier with a transmit power that has been determined by the mobile terminal
adding the base station dependent pre-scaling offset Aoffset for the uplink
component carrier c .
35. A computer readable medium storing instructions that, when executed by a
processor of a mobile terminal, cause the mobile terminal to adjusting the
transmit power utilized by the mobile terminal for uplink transmissions, wherein
the mobile terminal is configured with at least a first and a second uplink
component carrier, by:
determining a transmit power required for transmitting a transport block P
PUSCH (
via a physical uplink shared channel on the first uplink component carrier, and
determining a transmit power required for transmitting a random access preamble
P
PRACH ( via a physical random access channel on the second uplink component
carrier;
reducing the determined transmit power for the physical uplink shared channel
transmission and/or the physical random access channel transmission according
to a prioritization between the transmit power for the physical uplink shared
channel transmission and the transmit power for the physical random access
channel transmission,
transmitting the transport block on the first uplink component carrier and the
random access preamble on the second uplink component carrier within a
transmission time interval i , using the respective transmit power.
36. The computer readable medium according to claim 35, adapted to cause the
mobile terminal to perform the steps according to one of claims 2 to 15.
37. A computer readable medium storing instructions that, when executed by a
processor of a mobile terminal, cause the mobile terminal to adjust the transmit
power used for one or more RACH procedures, the mobile terminal being
allowed access on plural uplink component carriers, by:
determining, for uplink component carriers to be time aligned, the number of
RACH procedures required for time aligning the uplink component carriers, and
performing the determined number of RACH procedures required for time
aligning the uplink component carriers, wherein a transmit power for all of the one
or more RACH procedures is determined according to the determined number of
required RACH procedures.
38. The computer readable medium according to claim 35, adapted to cause the
mobile terminal to perform the steps according to one of claims 17 to 25.
39. A computer readable medium storing instructions that, when executed by a
processor of a base station for use with the mobile terminal performing a method
for adjusting the transmit power for transmitting random access preambles via
physical random access channels on uplink component carriers, cause the base
station performs the steps of:
signaling an offset PO_PRACH„,„ ,
0 tne mobile terminal, wherein the offset
o_pRACH,„ W ,,e
s utilized by the mobile terminal for determining a transmit power for
a random access preamble in case the uplink component carrier to be time
aligned and uplink component carriers already time aligned belong to a same
timing advance group; and
receiving random access preambles on the uplink component carriers with a
transmit power that has been determined by the mobile terminal utilizing the
offset P0_PRACH„, , ·
40. A computer readable medium storing instructions that, when executed by a
processor of a base station for use with the mobile terminal performing a method
for adjusting the transmit power for transmitting random access preambles via
physical random access channels on uplink component carriers, cause the base
station performs the steps of:
signaling a base station dependent pre-scaling offset Aoffset for an uplink
component carrier c to a mobile terminal to be added by the mobile terminal for
determining a transmit power for transmissions of random access preambles on
the uplink component carrier; and
receiving random access preambles on the uplink component carrier with a
transmit power that has been determined by the mobile terminal adding the base
station dependent pre-scaling offset Aoffset for the uplink component carrier c .