Component Carrier (De)Activation
in Communication Systems using
Carrier Aggregation
FIELD OF THE INVENTION
This invention relates to the proposal of component carrier (de)activation message that is
allowing an activation or deactivation of one or more component carriers in the uplink or
downlink. Furthermore, the invention relates to the use of the new component carrier
(de)activation message in methods for (de)activation of downlink component carrier(s)
configured for a mobile terminal, a base station and a mobile terminal.
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). 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 multiple-input multiple-output (MIMO) channel
transmission techniques, and a highly efficient control signaling structure is achieved in
LTE (Release 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 eNodeB, providing the
E-UTRA user plane (PDCP/RLC/MAC/PHY) and control plane (RRC) protocol
terminations towards the user equipment (UE). The eNodeB (eNB) hosts the Physical
(PHY), Medium Access Control (MAC), Radio Link Control (RLC), and Packet Data
Control Protocol (PDCP) layers that include the functionality of user-plane headercompression
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 Quality of
Service (QoS), cell information broadcast, ciphering/deciphering of user and control
plane data, and compression/decompression of downlink/uplink user plane packet
headers. The eNodeBs are interconnected with each other by means of the X2 interface.
The eNodeBs 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 eNodeBs. The
SGW routes and forwards user data packets, while also acting as the mobility anchor for
the user plane during inter-eNodeB handovers and as the anchor for mobility between
LTE and other 3GPP technologies (terminating S4 interface and relaying the traffic
between 2G/3G systems and PDN GW). For idle state user equipments, the SGW
terminates the downlink data path and triggers paging when downlink data arrives for the
user equipment. It manages and stores user equipment contexts, e.g. parameters of the
IP bearer service, network internal routing information. It also performs replication of the
user traffic in case of lawful interception.
The MME is the key control-node for the LTE access-network. It is responsible for idle
mode user equipment tracking and paging procedure including retransmissions. It is
involved in the bearer activation/deactivation process and is also responsible for
choosing the SGW for a user equipment at the initial attach and at time of intra-LTE
handover involving Core Network (CN) node relocation. It is responsible for
authenticating the user (by interacting with the HSS). The Non-Access Stratum (NAS)
signaling terminates at the MME and it is also responsible for generation and allocation
of temporary identities to user equipments. It checks the authorization of the user
equipment to camp on the service provider's Public Land Mobile Network (PLMN) and
enforces user equipment roaming restrictions. The MME is the termination point in the
network for ciphering/integrity protection for NAS signaling and handles the security key
management. Lawful interception of signaling is also supported by the MME. The MME
also provides the control plane function for mobility between LTE and 2G/3G access
networks with the S3 interface terminating at the MME from the SGSN. The MME also
terminates the S6a interface towards the home HSS for roaming user equipments.
Component Carrier Structure in LTE (Release 8)
The downlink component carrier of a 3GPP LTE (Release 8) is subdivided in the timefrequency
domain in so-called sub-frames. In 3GPP LTE (Release 8) each sub-frame is
divided into two downlink slots as shown in Fig. 3, wherein the first downlink slot
comprises the control channel region (PDCCH region) within the first OFDM symbols.
Each sub-frame consists of a give number of OFDM symbols in the time domain (12 or
14 OFDM symbols in 3GPP LTE (Release e)), wherein each of OFDM symbol spans
over the entire bandwidth of the component carrier. The OFDM symbols are thus each
consists of a number of modulation symbols transmitted on respective
B N subcarriers as also shown in Fig. 4.
Assuming a multi-carrier communication system, e.g. employing OFDM, as for example
used in 3GPP Long Term Evolution (LTE), the smallest unit of resources that can be
assigned by the scheduler is one "resource block". A physical resource block is defined
as ¾ , consecutive OFDM symbols in the time domain and N consecutive
subcarriers in the frequency domain as exemplified in Fig. 4. In 3GPP LTE (Release 8), a
physical resource block thus consists of resource elements, corresponding to
one slot in the time domain and 180 kHz in the frequency domain (for further details on
the downlink resource grid, see for example 3GPP TS 36.21 1, "Evolved Universal
Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation (Release 8)",
version 8.9.0 or 9.0.0, section 6.2, available at http://www.3gpp.org and incorporated
herein by reference).
Layer 1/Layer 2 (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 information, transmit power control (TPC)
commands), L1/L2 control signaling is transmitted on the downlink along with the data.
L1/L2 control signaling is multiplexed with the downlink data in a sub-frame, assuming
that the user allocation can change from sub-frame to sub-frame. 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, 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 in 3GPP LTE, assignments for uplink data
transmissions, also referred to as uplink scheduling grants or uplink resource
assignments, are also transmitted on the PDCCH.
With respect to scheduling grants, the information sent on the L1/L2 control signaling
may be separated into the following two categories.
Shared Control Information (SCI) carrying Cat 1information
The shared control information part of the L1/L2 control signaling contains information
related to the resource allocation (indication). The shared control information typically
contains the following information:
- A user identity indicating the user(s) that is/are allocated the resources.
- RB allocation information for indicating the resources (Resource Blocks (RBs)) on
which a user(s) is/are allocated. The number of allocated resource blocks can be
dynamic.
- The 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 Downlink Control
Information (DCI) - see below - the shared control information may additionally contain
information such as ACK/NACK for uplink transmission, uplink scheduling information,
information on the DCI (resource, MCS, etc.).
Downlink Control Information (DCI) carrying Cat 2/3 information
The downlink control information part of the L1/L2 control signaling contains information
related to the transmission format (Cat 2 information) of the data transmitted to a
scheduled user indicated by the Cat 1 information. Moreover, in case of using (Hybrid)
ARQ as a retransmission protocol, the Cat 2 information carries HARQ (Cat 3)
information. The downlink control information needs only to be decoded by the user
scheduled according to Cat 1. The downlink control information typically contains
information on:
- Cat 2 information: Modulation scheme, transport-block (payload) size or coding rate,
MIMO (Multiple Input Multiple Output)-related information, etc. 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 resource blocks)
- Cat 3 information: HARQ related information, e.g. hybrid ARQ process number,
redundancy version, retransmission sequence number
Downlink control information occurs in several formats that differ in overall size and also
in the information contained in its fields. The different DCI formats that are currently
defined for LTE Release 8/9 (3GPP LTE) are described in detail in 3GPP TS 36.212,
"Multiplexing and channel coding (Release 9)", version 8.8.0 or 9.0.0, section 5.3.3.1
(available at http://www.3gpp.org and incorporated herein by reference).
Downlink & Uplink Data Transmission
Regarding downlink data transmission, L1/L2 control signaling is transmitted on a
separate physical channel (PDCCH), along with the downlink packet data transmission.
This L1/L2 control signaling typically contains information on:
- The physical 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 UE (receiver) to identify the resources on which the data is transmitted.
- When user equipment is configured to have a Carrier Indication Field (CIF) in the
L1/L2 control signaling this information identifies the component carrier for which the
specific control signaling information is intended. This enables assignments to be sent
on one component carrier which are intended for another component carrier ("crosscarrier
scheduling"). This other, cross-scheduled component carrier could be for
example a PDCCH-less component carrier, i.e. the cross-scheduled component
carrier does not carry any L1/L2 control signaling.
- 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 (e.g. the number of resource blocks
assigned to the user equipment)) 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. The modulation
scheme may be signaled explicitly.
- Hybrid ARQ (HARQ) information:
■ HARQ process number: Allows the user equipment to identify the hybrid ARQ
process on which the data is mapped.
■ Sequence number or new data indicator (NDI): Allows the user equipment to
identify if the transmission is a new packet or a retransmitted packet. If soft
combining is implemented in the HARQ protocol, the sequence number or new
data indicator together with the HARQ process number enables soft-combining
of the transmissions for a PDU prior to decoding.
■ 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).
- UE Identity (UE 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.
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 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).
- When user equipment is configured to have a Carrier Indication Field (CIF) in the
L1/L2 control signaling this information identifies the component carrier for which the
specific control signaling information is intended. This enables assignments to be sent
on one component carrier which are intended for another component carrier. This
other, cross-scheduled component carrier may be for example a PDCCH-less
component carrier, i.e. the cross-scheduled component carrier does not carry any
L1/L2 control signaling.
- L1/L2 control signaling for uplink grants is sent on the DL component carrier that is
linked with the uplink component carrier or on one of the several DL component
carriers, if several DL component carriers link to the same UL component carrier.
- 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 (e.g. the number of
resource blocks assigned to the user equipment)) 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:
■ HARQ 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. If soft combining is implemented in the
HARQ protocol, the sequence number or new data indicator together with the
HARQ process number enables soft-combining of the transmissions for a
protocol data unit (PDU) prior to decoding.
• 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).
- UE Identity (UE 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 in uplink and downlink data transmission. Moreover, in uplink and
downlink, the L1/L2 control information may also contain additional information or may
omit some of the information. For example:
- HARQ process number may not be needed, i.e. is not signaled, in case of a
synchronous HARQ protocol.
- A redundancy and/or constellation version may not be needed, and thus not signaled,
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 (on the Physical Uplink Shared Channel (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 Transport Format (TF) respectively modulation and coding scheme (MCS) field
has for example a size of 5 bits, which corresponds to 32 entries. 3 TF/MCS table entries
are reserved for indicating redundancy versions (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. 3 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.
Physical Downlink Control Channel (PDCCH)
The physical downlink control channel (PDCCH) carries the L1/L2 control signaling, i.e.
transmit power control commands and the scheduling grants for allocating resources for
downlink or uplink data transmission. To be more precise, the downlink control channel
information (i.e. the DCI contents, respectively, the L1/L2 control signaling information) is
mapped to its corresponding physical channel, the PDCCH. This "mapping" includes the
determination of a CRC attachment for the downlink control channel information, which is
a CRC calculated on the downlink control channel information being masked with an
RNTI, as will explained below in more detail. The downlink control channel information
and its CRC attachment are then transmitted on the PDCCH (see 3GPP TS 36.212,
sections 4.2 and 5.3.3).
Each scheduling grant is defined based on Control Channel Elements (CCEs). Each
CCE corresponds to a set of Resource Elements (REs). In 3GPP LTE, one CCE consists
of 9 Resource Element Groups (REGs), where one REG consists of four REs.
The PDCCH is transmitted on the first one to three OFDM symbols within a sub-frame.
For a downlink grant on the physical downlink shared channel (PDSCH), the PDCCH
assigns a PDSCH resource for (user) data within the same sub-frame. The PDCCH
control channel region within a sub-frame consists of a set of CCE where the total
number of CCEs in the control region of sub-frame is distributed throughout time and
frequency control resource. Multiple CCEs can be combined to effectively reduce the
coding rate of the control channel. CCEs are combined in a predetermined manner using
a tree structure to achieve different coding rate.
In 3GPP LTE (Release 8/9), a PDCCH can aggregate 1, 2, 4 or 8 CCEs. The number of
CCEs available for control channel assignment is a function of several factors, including
carrier bandwidth, number of transmit antennas, number of OFDM symbols used for
control and the CCE size, etc. Multiple PDCCHs can be transmitted in a sub-frame.
Downlink control channel information in form of DCI transports downlink or uplink
scheduling information, requests for aperiodic CQI reports, or uplink power control
commands for one RNTI (Radio Network Terminal Identifier). The RNTI is a unique
identifier commonly used in 3GPP systems like 3GPP LTE (Release 8/9) for destining
data or information to a specific user equipment. The RNTI is implicitly included in the
PDCCH by masking a CRC calculated on the DCI with the RNTI - the result of this
operation is the CRC attachment mentioned above. On the user equipment side, if
decoding of the payload size of data is successful, the user equipment detects the DCI to
be destined to the user equipment by checking whether the CRC on the decoded
payload data using the "unmasked" CRC (i.e. after removing the masking using the
RNTI) is successful. The masking of the CRC code is for example performed by
scrambling the CRC with the RNTI.
In 3GPP LTE (Release 8) the following different DCI formats are defined:
- Uplink DCI formats:
Format 0 used for transmission of UL SCH assignments
Format 3 is used for transmission of TPC commands for PUCCH and PUSCH
with 2 bit power adjustments (multiple UEs are addressed)
■ Format 3A is used for transmission of TPC commands for PUCCH and
PUSCH with single bit power adjustments (multiple UEs are addressed)
- Downlink DCI formats:
■ Format 1 used for transmission of DL SCH assignments for SIMO operation
Format 1A used for compact transmission of DL SCH assignments for SIMO
operation
■ Format 1B used to support closed loop single rank transmission with possibly
contiguous resource allocation
■ Format 1C is for downlink transmission of paging, RACH response and
dynamic BCCH scheduling
■ Format 1D is used for compact scheduling of one PDSCH codeword with
precoding and power offset information
■ Format 2 is used for transmission of DL-SCH assignments for closed-loop
MIMO operation
■ Format 2A is used for transmission of DL-SCH assignments for open-loop
MIMO operation
For further information on the LTE physical channel structure in downlink and the
PDSCH and PDCCH format, see Stefania Sesia et al., "LTE - The UMTS Long Term
Evolution", Wiley & Sons Ltd., ISBN 978-0-47069716-0, April 2009 , sections 6 and 9.
Blind Decoding of PDCCHs at the User Equipment
In 3GPP LTE (Release 8/9), the user equipment attempts to detect the DCI within the
PDCCH using so-called "blind decoding" (sometimes also referred to as "blind
detection") . This means that there is no associated control signaling that would indicate
the CCE aggregation size or modulation and coding scheme for the PDCCHs signaled in
the downlink, but the user equipment tests for all possible combinations of CCE
aggregation sizes and modulation and coding schemes, and confirms that successful
decoding of a PDCCH based on the RNTI. To further limit complexity a common and
dedicated search space in the control signaling region of the LTE component carrier is
defined in which the user equipment searches for PDCCHs.
In 3GPP LTE (Release 8/9) the PDCCH payload size is detected in one blind decoding
attempt. The user equipment attempts to decode two different payload sizes for any
configured transmission mode, as highlighted in Table 1 below. Table 1 shows that
payload size X of DCI formats 0,1 A, 3, and 3A is identical irrespective of the transmission
mode configuration. The payload size of the other DCI format depends on the
transmission mode.
DCI Formats
payload size transmission
payload size X different from X mode
broadcast/ unicast/
1C paging /power
control
1 Mode 1
1 Mode 2
2A Mode 3
2 Mode 4 DL TX modes
0 / 1A / 3 / 3A 1B Mode 5
1D Mode 6
1 Mode 7
1 Mode 1
1 Mode 2
2A Mode 3 SPS-Modes
2 Mode 4
1 Mode 7
Table 1
Accordingly, the user equipment can check in a first blind decoding attempt the payload
size of the DCI. Furthermore, the user equipment is further configured to only search for
a given subset of the DCI formats in order to avoid too high processing demands.
Medium Access Layer (MAC)
The MAC layer is one of the sub-layers of the the Layer 2 in the 3GPP LTE radio
protocol stack. The MAC layer performs (de)multiplexing between logical channels and
transport channels by (de)constructing MAC PDUs (Protocol Data Units), also known as
transport blocks. MAC PDUs are constructed out of MAC SDUs (Service Data Units)
received through one or more logical channels in the transmitter. On the receiver side the
MAC PDUs are reconstructed out of the received MAC PDUs.
The transport block (MAC PDU) consists of a header and a payload. Apart from MAC
SDUs the payload can consist of MAC Control Elements and padding.
MAC Control Elements
For peer to peer signaling on MAC level MAC Control Elements (CEs) are used. MAC
Control Elements can be part of a MAC PDU's payload as described above and are
identified by a specific Logical Channel ID (LCID) in the MAC header.
There are several types of MAC CEs. Some of them are only included in uplink transport
blocks for signaling from user equipment to eNodeB, others only in downlink transport
blocks for signaling from eNodeB to user equipment. The special LCIDs and the
corresponding MAC Control Elements transmitted on the downlink are listed in Table 2.
LCID value MAC Control Element used for
11100 UE Contention Resolution Identity
11101 Timing Advance Command
11110 DRX Command
Table 2
The special LCIDs and the corresponding MAC Control Elements transmitted on the
uplink are listed in Table 3.
LCID value MAC Control Element used for
11010 Power Headroom Report
1101 1 C-RNTI
11100 Truncated Buffer Status Report (BSR)
11101 Short BSR
11110 Long BSR
Table 3
Sounding Reference Signals (SRS)
Sounding reference signals are send in the uplink. Together with the Demodulation
Reference Signals (DM RS) they are included in the uplink to enable channel estimation
for coherent demodulation as well as channel quality estimation for uplink scheduling.
While DM RSs are associated with the transmission of uplink data, the SRSs are not
associated with data transmission and primarily used for channel quality estimation to
enable frequency-selective scheduling by the scheduling eNodeB. Furthermore SRSs
can be used to enhance power control or to support the eNodeB in deciding on initial
Modulation and Coding Scheme (MCS) for data transmission. If configured by higher
layer signaling, the SRSs are transmitted in the last SC-FDMA symbol in a uplink subframe.
The sub-frame in which SRSs are to be transmitted by the user equipment is
indicated by cell-specific broadcast signaling and is selected out of a set of 15 possible
sub-frames within a radio frame. Data transmission on the Physical Uplink Shared
CHannel (PUSCH) is not allowed in the sub-frame designated for transmitting SRSs,
which sets the SRS overhead to 7% when all possible sub-frames are configured for
SRS transmission. As mentioned above, SRS configuration is done by the eNodeB using
higher layer signaling. The configuration inter alia determines amongst other parameters
duration and periodicity of the SRSs.
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 in the 3GPP. The study item covers technology components to be considered
for the evolution of E-UTRA, e.g. to fulfill the requirements on IMT-Advanced. Two major
technology components which are currently under consideration for LTE-A are described
in the following.
Carrier Aggregation in LTE-Afor support of wider bandwidth
In Carrier Aggregation (CA), two or more Component Carriers (CCs) are aggregated in
order to support wider transmission bandwidths up to 100 MHz. All component carriers
can be configured to be 3GPP LTE (Release 8/9) compatible, at least when the
aggregated numbers of component carriers in the uplink and the downlink are the same.
This does not necessarily mean that all component carriers need to be compatible to
3GPP LTE (Release 8/9).
A user equipment may simultaneously receive or transmit on one or multiple component
carriers. On how many component carriers simultaneous reception/transmission is
possible, is depending on the capabilities of a user equipment.
A 3GPP LTE (Release 8/9) compatible user equipment can receive and transmit on a
single CC only, provided that the structure of the CC follows the 3GPP LTE (Release
8/9) specifications, while a 3GPP LTE-A (Release 10) compatible user equipment with
reception and/or transmission capabilities for carrier aggregation can simultaneously
receive and/or transmit on multiple component carriers.
Carrier aggregation is supported for both contiguous and non-contiguous component
carriers with each component carrier limited to a maximum of 110 Resource Blocks in
the frequency domain using the 3GPP LTE (Release 8/9) numerology.
It is possible to configure a 3GPP LTE-A (Release 10) compatible user equipment to
aggregate a different number of component carriers originating from the same eNodeB
(base station) and of possibly different bandwidths in the uplink and the downlink. In a
typical TDD deployment, the number of component carriers and the bandwidth of each
component carrier in uplink and downlink is the same. Component carriers originating
from the same eNodeB need not to provide the same coverage.
The spacing between centre frequencies of contiguously aggregated component carriers
shall be a multiple of 300 kHz. This is in order to be compatible with the 100 kHz
frequency raster of 3GPP LTE (Release 8/9) and at the same time preserve
orthogonality of the subcarriers with 15 kHz spacing. Depending on the aggregation
scenario, the n x 300 kHz spacing can be facilitated by insertion of a low number of
unused subcarriers between contiguous component carriers.
The nature of the aggregation of multiple carriers is only exposed up to the MAC layer.
For both uplink and downlink there is one HARQ entity required in MAC for each
aggregated component carrier. There is (in the absence of SU-MIMO for uplink) at most
one transport block per component carrier. A transport block and its potential HARQ
retransmissions need to be mapped on the same component carrier.
The Layer 2 structure with activated carrier aggregation is shown in Fig. 5 and Fig. 6 for
the downlink and uplink respectively.
When carrier aggregation is configured, the user equipment only has one Radio
Resource Control (RRC) connection with the network. One cell - the "special cell" -
provides the security input and the Non-Access Stratum (NAS) mobility information (e.g.
TAI). There is only one special cell per user equipment in connected mode.
After RRC connection establishment to the special cell, the reconfiguration, addition and
removal of component carriers can be performed by RRC. At intra-LTE handover, RRC
can also add, remove, or reconfigure component carriers for usage in the target cell.
When adding a new component carrier, dedicated RRC signaling is used for sending
component carriers' system information which is necessary for component carrier
transmission / reception, similar to a handover in 3GPP LTE (Release 8/9).
When a user equipment is configured with carrier aggregation there is one pair of uplink
and downlink component carriers that is always activate. The downlink component
carrier of that pair might be also referred to as 'DL anchor carrier'. Same applies also for
the uplink.
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.
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. Fig. 7 and Fig. 8
exemplarily show possible linkages between downlink and uplink component carriers.
While in Fig. 7 all downlink component carriers are linked to the same uplink component
carrier, in Fig. 8 downlink component carriers 1 and 2 are linked to uplink component
carrier 1 and downlink component carrier 3 is linked to uplink component carrier 2.
DRX and Carrier Aggregation
In order to provide reasonable battery consumption of user equipment 3GPP LTE
(Release 8/9) as well as 3GPP LTE-A (Release 10) provides a concept of discontinuous
reception (DRX).
For this concept the following terms describe the user equipment's state in terms of DRX.
- on-duration: duration in downlink sub-frames that the user equipment waits for, after
waking up from DRX, to receive PDCCHs. If the user equipment successfully decodes
a PDCCH, the user equipment stays awake and starts the inactivity timer;
- inactivity-timer: duration in downlink sub-frames that the user equipment waits to
successfully decode a PDCCH, from the last successful decoding of a PDCCH, failing
which it re-enters DRX. The user equipment shall restart the inactivity timer following a
single successful decoding of a PDCCH for a first transmission only (i.e. not for
retransmissions).
- active-time: total duration that the user equipment is awake. This includes the "onduration"
of the DRX cycle, the time user equipment is performing continuous
reception while the inactivity timer has not expired and the time user equipment is
performing continuous reception while waiting for a downlink retransmission after one
HARQ RTT (Round Trip Time). Based on the above the minimum active time is of
length equal to on-duration, and the maximum is undefined (infinite);
There is only one DRX cycle per user equipment. All aggregated component carriers
follow this DRX pattern.
In order to allow for further battery saving optimization, a further step of
activation/deactivation of component carriers is introduced. Essentially a downlink
component carrier could be in one of the following three states: non-configured,
configured but deactivated and active. When a downlink component carrier is configured
but deactivated, the user equipment does not need to receive the corresponding PDCCH
or PDSCH, nor is it required to perform CQI measurements. Conversely, when a
downlink component carrier is active, the user equipment shall receive PDSCH and
PDCCH (if present), and is expected to be able to perform CQI measurements. After
configuration of component carriers in order to have PDCCH and PDSCH reception on a
downlink component as described above, the downlink component carrier needs to be
transitioned from configured but deactivated to active state.
In the uplink however, a user equipment is always required to be able to transmit on
PUSCH on any configured uplink component carrier when scheduled on the
corresponding PDCCH (i.e. there is no explicit activation of uplink component carriers).
For user equipment power-saving purposes, it's crucial that additional component
carriers can be de-activated and activated in an efficient and fast way. With bursty datatransmission,
it is imperative that additional component carriers can be activated and de¬
activated quickly, such that both the gains of high bit-rates can be utilized, and battery
preservation can be supported. As described before user equipments will not perform
and report CQI measurements on configured but deactivated downlink component
carriers but only radio resource management related measurements like RSRP
(Reference Signal Received Power) and RSRQ (Reference Signal Received Quality)
measurements. Hence when activating a downlink component carrier, it's important that
eNodeB acquires quickly CQI information for the newly activated component carrier(s) in
order to being able to select an appropriate MCS for efficient downlink scheduling.
Without CQI information eNodeB doesn't have knowledge about user equipment's
downlink channel state and might only select a rather conservative MCS for downlink
data transmission which would in turn lead to some resource utilization inefficiency.
In order to acquire CQI information quickly, eNodeB can schedule an aperiodic CQI by
means of an uplink scheduling grant. The aperiodic CQI would be transmitted on the
physical uplink shared channel (PUSCH). Therefore in order to activate a configured
downlink component carrier, eNodeB would need to issue essentially two grants
(PDCCH) to the UE, one downlink PDCCH in order to indicate the activation of a
downlink component carrier and one uplink PDCCH which schedules uplink resources
for the transmission of the aperiodic CQI. Furthermore both PDCCH has to be sent
respectively received in the same TTI in order to ensure, that user equipment measures
and reports CQI information for the correct downlink component carrier, i.e. the downlink
component carrier which will be activated.
The correct reception of the aperiodic CQI can serve as an acknowledgement for the
downlink activation command, i.e. when aperiodic CQI has been received eNodeB
assumes that user equipment has activated the downlink component carrier indicated in
the downlink PDCCH.
As it becomes apparent, the main drawback of the above described component carrier
activation method is, that two PDCCHs are required in order to activate a downlink
component carrier. Furthermore due to the fact that the two PDCCHs need to be
received/sent simultaneously, certain error cases may occur in the presence of PDCCH
loss.
In case only the downlink "activation" PDCCH is lost, user equipment will not activate the
downlink component carrier. However based on received CQI information eNB
erroneously assumes downlink activation has succeeded.
In the second error case when only the uplink PDCCH which requests the aperiodic CQI
is lost, eNodeB doesn't acquire CQI and erroneously assumes that downlink activation
has failed.
SUMMARY OF THE INVENTION
One object of the invention is to overcome at least one of the described problems.
Furthermore, it is another object of the invention to enable efficient and robust
(de)activation of component carriers.
The object is solved by the subject matter of the independent claims. Advantageous
embodiments of the invention are subject to the dependent claims.
A first aspect of the invention is the provision of a signaling format for communicating a
component carrier (de)activation message for controlling the activation state of at least
one component carrier. The proposed format comprises an identifier of the intended
recipient of the component carrier (de)activation message, e.g. by including a mobile
terminal identifier (ID). This mobile terminal ID (also referred to as a UE ID) may be for
example explicitly signaled in a field of the component carrier (de)activation message. In
view of the component carrier (de)activation message indicating the intended recipient
for the component carrier (de)activation message, a CRC that is calculated based on the
component carrier (de)activation message can be scrambled with a component carrierspecific
or cell-specific radio network temporary identifier. As will be outlined below in
further detail, this has the advantage that not as many radio network temporary
identifiers (the total number of which is limited by the number of bits spent for the radio
network temporary identifier) in comparison to a solution, where a radio network
temporary identifier for component carrier (de)activation is assigned to the mobile
terminals on a per-mobile terminal basis.
Furthermore, the component carrier (de)activation message format may be considered a
new format of downlink control channel information that is mapped to the physical
downlink control channel (PDCCH). The use of the component carrier-specific or cellspecific
radio network temporary identifiers therefore indicate the format of the downlink
control channel information being a component carrier (de)activation message.
Furthermore, in case of using component carrier-specific radio network temporary
identifier(s) that is/are linked to a respective component carrier, carrier-specific radio
network temporary identifier(s) also indicate(s) a component carrier to be activated or
deactivated. Hence, the component carrier (de)activation message as well as the CRC
attachment (i.e. the CRC for the component carrier (de)activation message scrambled
with a given radio network temporary identifier) indicate to the mobile terminal the
activation state of the component carriers, i.e. indicate which of them is/are to be
(de)activated.
Another, second of the invention is to propose a mechanism for (de)activating downlink
component carriers configured by a mobile terminal by means of a component carrier
(de)activation message that is transmitted on a physical downlink shared channel as part
of a transport block. According to this aspect of the invention, the component carrier
(de)activation message comprises (de)activation information that indicates for the
respective downlink component carriers configured by the mobile terminal, the activation
state of the respective component carriers. This way, the mobile terminal can recognize
a change in the activation state of the respective downlink component carriers and may
activate or deactivate them accordingly. In one exemplary implementation, the
(de)activation information for the component carriers may be provided in a MAC control
element, i.e. by means of MAC signaling.
Furthermore, still in line with this second aspect of the invention, the (de)activation
information may be provided in form of a bitmap, the individual bits of which indicate the
activation state of a respective configured downlink component carrier associated to a
respective bit of the bitmap.
It should be noted that - in line with the first and second aspect of the invention - in
cases where there is a downlink component carrier configured for the mobile terminal
that is always active, the (de)activation information does not need to indicate the
activation state for such "always active" component carrier - the "always active" downlink
component carrier is also referred to as the downlink primary component carrier (PCC)
herein.
A further aspect of the invention is to trigger the signaling of sounding reference signals
(SRSs) in the uplink. For this purpose, a SRS (de)activation message is defined which is
reusing the different structures and mechanisms for transmitting the component carrier
(de)activation message according to the various embodiments described herein. For
example, the SRS (de)activation message may also comprise SRS (de)activation
information that indicated the activation state of the SRS transmission for the uplink
component carriers configured for the mobile terminal. This SRS (de)activation
information may be provided in form of a bitmap, the individual bits of which indicate the
activation state SRS signaling on the respective configured uplink component carrier
associated to a respective bit of the bitmap. Please note that alternatively the bits of the
bitmap in the SRS (de)activation message may also be considered associated to
respective configured downlink component carriers, and the logical values of the
individual bits of the bitmap indicate the activation state of SRS signaling on the uplink
component carrier linked to the respective downlink component carrier associated to the
given bit in the bitmap. The SRS (de)activation message may be signaled as part of a
transport block on the physical uplink shared channel or may be signaled as a new
format of downlink control channel information that is mapped to the physical downlink
control channel (PDCCH) as described herein in line with the first aspect of the invention.
Moreover, the SRS (de)activation information may also be sent together with
(de)activation information for activating/deactivating configured downlink component
carriers within a single message. For example, the SRS (de)activation information and
the component carrier (de)activation information may be signaled in a single MAC control
element as part of a transport block of the physical downlink shared channel, or may be
signaled together in a new format of downlink control channel information that is mapped
to the physical downlink control channel (PDCCH) as described herein in line with the
first aspect of the invention.
According to one exemplary embodiment of the invention, a method for (de)activating
configured component carriers in communication system using component carrier
aggregation is provided. According to this method a mobile terminal receives on a
physical downlink shared channel a transport block comprising a component carrier
(de)activation message. Component carrier (de)activation message comprises
(de)activation information in form of a bitmap consisting of a number of bits. Each of the
bits of the bitmap is associated to a respective one of the configured downlink
component carriers, wherein logical value of each bit is indicating whether the associated
downlink component carrier is to be activated or deactivated. Furthermore, the mobile
terminal activates or deactivates the configured component carriers according to
(de)activation information obtained from the component carrier (de)activation message.
In one exemplary implementation according to another embodiment of the invention, the
component carrier (de)activation message is a MAC control element.
Optionally, the component carrier (de)activation message may be multiplexed to the
transport block together with other logical channel data to be transmitted to the mobile
terminal.
In another embodiment of the invention, one of the plurality of configured downlink
component carriers is a downlink primary component carrier. This which primary
component carrier cannot be activated or deactivated by the component carrier
(de)activation message. Accordingly, the (de)activation information of the component
carrier (de)activation message do not need to comprise an indication of the activation
state of the primary component carrier of the mobile terminal.
In one exemplary implementation, the base station may ensure that the transport block
comprising a component carrier (de)activation message is received by the mobile
terminal on the downlink primary component carrier of the mobile terminal.
Optionally, the component carrier (de)activation message may further comprise SRS
information allowing the base station to request the mobile terminal to start sending a
sounding reference signal (SRS) on at least one of the uplink component carriers
respectively linked to the configured downlink component carriers. In a more detailed
implementation, the SRS information is provided in form of a bitmap consisting of a
number of bits. Each of the bits of the bitmap within the SRS information is associated to
a respective one of uplink component carriers and the logical value of each bit of the
bitmap is indicating whether SRS should be transmitted on the associated uplink
component carrier by the mobile terminal.
Another embodiment of the invention is providing a method for (de)activating configured
component carriers in communication system using component carrier aggregation.
According to this method the mobile terminal receives a sub-frame from a base station,
and performs a blind detection blind decoding within a control signaling region on one of
the configured downlink component carriers within the received sub-frame to obtain a
component carrier (de)activation message and a CRC attachment thereof. The
component carrier (de)activation message and its CRC attachment may be considered a
PDCCH. The CRC attachment comprises a CRC of the component carrier (de)activation
message, wherein the CRC is scrambled with a component carrier-specific or cellspecific
radio network temporary identifier (RNTI) used for signaling the activation state
of the target component carrier(s).
The mobile terminal checks the CRC of the CRC attachment using the component
carrier-specific or radio cell-specific radio network temporary identifier. This may be for
example realized by the mobile terminal descrambling the CRC with the component
carrier-specific or radio cell-specific radio network temporary identifier, and subsequently
comparing the resultant descrambled CRC with the locally generated CRC from the
received and decoded downlink control channel information (without CRC).
In case of a match, i.e. if the CRC check passes, the mobile terminal determines a
mobile terminal identifier (e.g. a UE ID or a mobile terminal-specific RNTI) from the
component carrier (de)activation message. Based on the mobile terminal identifier the
mobile terminal verifies whether the component carrier (de)activation message is
destined to the mobile terminal. If the component carrier (de)activation message is
destined to the mobile terminal, the mobile terminal activates or deactivates the
configured component carriers according to (de)activation information obtained from the
component carrier (de)activation message and/or implicit to the use of the radio network
temporary identifier for scrambling the CRC attachment.
Furthermore, according to another embodiment of the invention, another method for
(de)activating configured component carriers in communication system using component
carrier aggregation is employed. According to this method the base station transmits a
sub-frame to the mobile terminal. The sub-frame comprises within a control signaling
region on one of the configured downlink component carriers a component carrier
(de)activation message and a CRC attachment thereof (i.e. a PDCCH). The component
carrier (de)activation message indicates at least a mobile terminal identifier to address
the message to its intended receiver (mobile terminal). The CRC attachment comprises a
CRC of the component carrier (de)activation message that has been calculated on the
component carrier (de)activation message by a processor of the base station and has
been subsequently scrambled with a component carrier-specific or cell-specific radio
network temporary identifier (RNTI) used for signaling the activation state of the target
component carrier(s).
In a further embodiment of the invention, the component carrier (de)activation message
indicates which of the plurality of configured downlink component carriers is/are to be
activated, respectively deactivated. Hence, in this embodiment of the invention the
indication of the configured component carrier to be (de)activated may be comprised in a
carrier indication field of the component carrier (de)activation message.
Furthermore, in another exemplary embodiment, the state of the indicated component
carrier is implicit to the RNTI used for scrambling the CRC. In this embodiment, there
may be two radio cell-specific radio network temporary identifiers used for signaling the
activation state of the downlink component carriers. One of the radio network temporary
identifiers is indicating the activation of at least one of the configured downlink
component carriers indicated in the component carrier (de)activation message and the
other radio network temporary identifier is indicating the deactivation of at least one of
the configured downlink component carriers indicated in the component carrier
(de)activation message.
In an alternative implementation according to another embodiment of the invention, the
component carrier to be (de)activated is implicit to the RNTI used for scrambling the
CRC. In this embodiment, it can be assumed that each configured downlink component
carrier is linked to a component carrier-specific radio network temporary identifier. The
component carrier-specific radio network temporary identifier used for scrambling the
CRC thus implicitly indicates at least the configured downlink component carrier to be
activated or deactivated.
In a variation of this embodiment, the component carrier (de)activation message
indicates whether the configured downlink component carrier to be activated or
deactivated linked to the component carrier-specific radio network temporary identifier
used for scrambling the CRC is to be activated or deactivated.
In a further variation of this embodiment, each configured downlink component carrier
may be linked to two component carrier-specific radio network temporary identifiers, and
the component carrier-specific radio network temporary identifier used for scrambling the
CRC indicates at least the configured downlink component carrier and whether it is to be
activated or deactivated. Hence, in this variation the indication of the component carrier
and its activation state are implicit to the RNTI used for scrambling the CRC.
In another embodiment of the invention, the component carrier (de)activation message
comprises an activation flag that requests the mobile terminal to activate, respectively
deactivate an indicated configured downlink component carrier.
In one further exemplary embodiment, the component carrier (de)activation message
received within the control signaling region of a sub-frame is received on a downlink
primary component carrier of the mobile terminal.
In another embodiment of the invention, the activation of a downlink component carrier
triggers the transmission of a power headroom report by the mobile terminal for the
uplink component carrier linked to the downlink component carrier being activated. For
example the mobile terminal may transmit, in response to the activation of a downlink
component carrier, a power headroom report for the for the uplink component carrier
linked to the downlink component carrier being activated. The power headroom report is
transmitted by the mobile terminal on the linked uplink component carrier on resources
assigned on the linked uplink component carrier assigned to the mobile terminal by the
next uplink resource assignment for the linked uplink component carrier.
In a further embodiment of the invention, the mobile terminal deactivates the indicated
component carrier in case the component carrier (de)activation message indicates the
deactivation of a downlink component carrier. This deactivation is however not performed
immediately, but
- upon a HARQ protocol used for transmitting transport blocks is acknowledging
successful decoding of a transport block pending for transmission on the downlink
component carrier to be deactivated at the time of receiving the component carrier
(de)activation message, or
- upon reaching a maximum number of retransmissions of the HARQ protocol for the
transport block pending for transmission on the downlink component carrier to be
deactivated.
In this context the transport block pending for transmission is referring to one or more
transport blocks transmitted in individual HARQ processes on the downlink component
carrier to be deactivated and that are currently transmitted (retransmission of the
transportr block is pending) at the time of receiving the deactivation command for the
downlink component carrier.
In addition thereto, or alternatively, according to another embodiment of the invention,
the component carrier (de)activation message comprises a SRS flag that, when set,
requests the mobile terminal to start sending a sounding reference signal (SRS) on the
uplink component carrier linked to the indicated configured downlink component carrier.
Optionally, the SRS flag, when not set, may request the mobile terminal to stop sending
a sounding reference signal (SRS) on the uplink component carrier linked to the
indicated configured downlink component carrier.
In addition to at least one of the activation flag and the SRS flag, or alternatively thereto,
the component carrier (de)activation message according to a further embodiment of the
invention comprises a CQI request flag that, when set, requests channel quality feedback
for the one or more indicated configured downlink component carriers.
In a variation of this embodiment, in case the mobile terminal is requested to send
channel quality feedback for an indicated downlink component carrier, the mobile
terminal performs a channel quality measurement for each downlink component carrier
indicated by the component carrier (de)activation message, and transmits the channel
quality feedback for the one or more indicated downlink component carriers to the base
station.
The channel quality feedback may be for example transmitted on pre-configured uplink
resources on a physical uplink shared channel (PUSCH) or a physical uplink control
channel (PUCCH), or alternatively on uplink resources on the physical uplink control
channel (PUCCH) configured by RRC for periodic channel quality feedback.
In one exemplary implementation the channel quality feedback is transmitted 4 subframes
or 4 ms after having received the sub-frame comprising the component carrier
(de)activation message.
In the examples given above, the channel quality feedback may be an aperiodic channel
quality feedback. In addition or as an alternative to triggering such aperiodic channel
quality feedback or alternatively thereto, the CQI flag may be used to trigger the mobile
terminal to start sending periodic channel quality feedback. Accordingly, in case the
mobile terminal is requested to send channel quality feedback for an indicated downlink
component carrier the mobile terminal may periodically perform a channel quality
measurement for each downlink component carrier indicated by the component carrier
(de)activation message, and may periodically transmit the channel quality feedback for
the one or more indicated downlink component carriers to the base station on uplink
resources for example on the physical uplink control channel configured by RRC for
periodic channel quality feedback.
Furthermore, in order not to increase the blind decoding attempts of the mobile terminal
to detect the format of the control channel information signaled on the PDCCH of the
received sub-frame, in another embodiment of the invention, the component carrier
(de)activation message format (which can be considered a DCI format) has the same
size (number of bits) as at least one other downlink control information format defined in
the mobile communication system. For example, when implementing the invention in a
3GPP LTE-A (Release 10) system or its successors, the component carrier
(de)activation message format may have the same size as DCI formats 0/1 A in 3GPP
LTE (Release 8/9) or 3GPP LTE-A (Release 10). Moreover, the size of the component
carrier (de)activation message format may optionally depend on the component carrier
bandwidth. The component carrier bandwidth may be for example the bandwidth of the
component carrier the activation state of which is signaled by the component carrier
(de)activation message and/or its CRC attachment, or the bandwidth of the component
carrier on which the component carrier (de)activation message is signaled.
In another embodiment of the invention, the reception of the component carrier
(de)activation message is acknowledged by the mobile terminal. This may be for
example realized by signaling an ACK/NACK in the uplink at a given timing relative to the
transmission of the component carrier (de)activation message. Alternatively, the
acknowledgment may also be sent in form of channel quality feedback on the indicated
downlink component carrier(s). This latter option may for example be useful, if a CQI flag
in the component carrier (de)activation message is triggering channel quality feedback
from the mobile terminal.
A further aspect of the invention is the implementation of the different methods for
(de)activating configured component carriers in communication system using component
carrier aggregation in hardware and/or software. In this respect, different apparatuses
that perform or participate in the performance of such methods are provided.
One embodiment of the invention thus provides a mobile terminal for (de)activating
configured component carriers in communication system using component carrier
aggregation. The mobile terminal comprises a receiver for receiving on a physical
downlink shared channel a transport block comprising a component carrier (de)activation
message, wherein the component carrier (de)activation message comprises
(de)activation information indicating which of a plurality of configured downlink
component carriers is/are to be activated, respectively deactivated by the mobile
terminal, and a processor for activating or deactivating the configured component
carriers according to (de)activation information obtained from the component carrier
(de)activation message.
Furthermore, according to an embodiment of the invention, the mobile terminal is
adapted to/comprises means to perform the method for (de)activating configured
component carriers in communication system using component carrier aggregation
according to one of the various embodiments described herein, where the component
carrier (de)activation message is sent as part of a transport block on the physical
downlink shared channel.
Another embodiment of the invention provides a mobile terminal for use in a
communication system using component carrier aggregation. The mobile terminal
comprises a receiver for receiving a sub-frame from a base station, and a processing
means for performing a blind detection blind decoding within a control signaling region on
one of the configured downlink component carriers within the received sub-frame to
obtain a component carrier (de)activation message and a CRC attachment thereof,
wherein the CRC attachment comprises a CRC of the component carrier (de)activation
message, the CRC being scrambled with a component carrier-specific or cell-specific
radio network temporary identifier (RNTI) used for signaling the activation state of the
target component carrier(s). The blind detectionblind decoding may for example also
involve the operations of a decoder and a demodulator of the mobile terminal.
The mobile terminal's processor further checks the CRC of the CRC attachment using
the component carrier-specific or radio cell-specific radio network temporary identifier. As
mentioned above, this check of the CRC may be for example implemented by
descrambling the CRC of the CRC attachment using the component carrier-specific or
radio cell-specific radio network temporary identifier, and subsequently comparing the
descrambled CRC with the a CRC (locally) generated by the processor of the mobile
terminal from the received and decoded downlink control channel.
In case of a match, i.e. in case the CRC check passes, the mobile terminal determines a
mobile terminal identifier from the component carrier (de)activation message.
Furthermore, the processor verifies based on the mobile terminal identifier whether the
component carrier (de)activation message is destined to the mobile terminal.
Accordingly, the mobile terminal can activate or deactivate the configured component
carriers according to (de)activation information obtained from the component carrier
(de)activation message and/or implicit to the use of the radio network temporary identifier
for scrambling the CRC attachment, if the component carrier (de)activation message is
destined to the mobile terminal.
In another embodiment of the invention, a base station for (de)activating configured
component carriers of a mobile terminal in communication system using component
carrier aggregation is provided. The base station comprises a processor for generating a
component carrier (de)activation message comprising at least a mobile terminal identifier
of the mobile terminal. The processor further determines a CRC for the component
carrier (de)activation message, and scrambles the CRC with a component carrierspecific
or cell-specific radio network temporary identifier (RNTI) used for signaling the
activation state of the target component carrier(s), to thereby obtain a CRC attachment of
the component carrier (de)activation message. Moreover, the base station also includes
a transmitter for transmitting the component carrier (de)activation message and its CRC
attachment within the control signaling region of a downlink component carrier within a
sub-frame to the mobile terminal.
The invention further relates the implementation of the methods for (de)activating
configured component carriers in communication system using component carrier
aggregation described herein in software. One further embodiment of the invention is
therefore providing a computer-readable medium storing instructions that, when
executed by a processor of a mobile terminal, cause the mobile terminal to (de)activate
configured component carriers in communication system using component carrier
aggregation, by receiving on a physical downlink shared channel a transport block
comprising a component carrier (de)activation message, wherein the component carrier
(de)activation message comprises (de)activation information indicating which of a
plurality of configured downlink component carriers is/are to be activated, respectively
deactivated by the mobile terminal, and activating or deactivating the configured
component carriers according to (de)activation information obtained from the component
carrier (de)activation message.
A further embodiment of the invention relates to a computer-readable medium that is
storing instructions that, when executed by a processor of a mobile terminal, cause the
mobile terminal to perform one of the different methods for (de)activating configured
component carriers in communication system using component carrier aggregation. In
one example, the mobile terminal may be for example caused to receive a sub-frame
from a base station, and to perform a blind detectionblind decoding within a control
signaling region on one of the configured downlink component carriers within the
received sub-frame to obtain a component carrier (de)activation message and a CRC
attachment thereof. The CRC attachment comprises a CRC of the component carrier
(de)activation message, wherein the CRC is scrambled with a component carrier-specific
or cell-specific radio network temporary identifier (RNTI) used for signaling the activation
state of the target component carrier(s).
The mobile terminal may be further caused by the executed instructions to check the
CRC of the CRC attachment using the component carrier-specific or radio cell-specific
radio network temporary identifier. In case the CRC check passes, the mobile terminal is
caused to determine a mobile terminal identifier (e.g. a UE ID or a mobile terminalspecific
RNTI) from the component carrier (de)activation message. Moreover, the
instructions, when executed by the mobile terminal's processor, cause the mobile
terminal to verify based on the mobile terminal identifier whether the component carrier
(de)activation message is destined to the mobile terminal., and If the component carrier
(de)activation message is destined to the mobile terminal, to activate or deactivates the
configured component carriers according to (de)activation information obtained from the
component carrier (de)activation message and/or implicit to the use of the radio network
temporary identifier for scrambling the CRC attachment.
Another embodiment therefore relates to a computer-readable medium that is storing
instructions that, when executed by a processor of a base station, cause the base station
to perform one of the different methods for (de)activating configured component carriers
in communication system using component carrier aggregation. In one example, the
base station may be for example caused to generate a component carrier (de)activation
message comprising at least a mobile terminal identifier of the mobile terminal. The
execution of the instructions by the processor of the base station may further cause the
base station to determine a CRC for the component carrier (de)activation message, and
to scramble the CRC with a component carrier-specific or cell-specific radio network
temporary identifier (RNTI) used for signaling the activation state of the target component
carrier(s), for thereby obtaining a CRC attachment of the component carrier
(de)activation message. Moreover, the base station is also caused by the execution of
the instructions by its processor to transmit the component carrier (de)activation
message and its CRC attachment within the control signaling region of a downlink
component carrier within a sub-frame to the mobile terminal.
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
3GPP LTE,
Fig. 3 shows an exemplary sub-frame structure on a downlink component
carrier as defined for 3GPP LTE (Release 8/9),
Fig. 4 shows an exemplary downlink resource grid of a downlink slot as defined
for 3GPP LTE (Release 8/9),
Figs. 5 & 6 show the 3GPP LTE-A (Release 10) Layer 2 structure with activated
carrier aggregation for the downlink and uplink, respectively,
Figs. 7 & 8 show exemplarily linkages between downlink and uplink component
carriers in 3GPP LTE-A (Release 10),
Fig. 9 exemplarily shows the dependence of the size of the component carrier
(de)activation message from the bandwidth of a component carrier
according to an embodiment of the invention and in relation to DCI format
0/1 A,
Figs. 10 to 19 show different formats of the component carrier (de)activation message
according to different embodiments of the invention,
Figs. 20 to 23 show different exemplary scenarios related to acknowledging the
component carrier (de)activation message and the triggering of CQI
reporting from the mobile terminal in accordance with different
embodiments of the invention,
Fig. 24 shows a MAC control element according to an exemplary embodiment of
the invention for simultaneously (de)activating one or more downlink
component carriers and (de)activating SRS transmissions on one or more
(linked) uplink component carriers of the user equipment, and
Figs. 25 &_an4-26 show different formats of the component carrier (de)activation
message according to different embodiments 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 single-carrier uplink radio access scheme according to 3GPP LTE (Release
8) and LTE-A (Release 10) mobile communication systems 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 3GPP LTE
(Release 8) and LTE-A (Release 10) communication systems 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 3GPP LTE (Release 8) and LTE-A (Release 10) 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.
One possible implementation to indicate a component carrier in the downlink that is to be
activated is the use of the CIF field in the downlink DCI formats of 3GPP LTE-A (Release
10). In case that the CIF field points to a configured but deactivated downlink component
carrier, this downlink component carrier is activated. However this approach cannot be
used in a straightforward fashion to deactivate a component carrier. Furthermore, the
CIF field may not be a mandatory part of the DCI formats.
Another solution for (de)activating configured downlink component carriers is to employ a
mechanism similar to the 3GPP LTE (Release 8/9) semi-persistent scheduling (SPS)
activation and deactivation. Each user equipment is assigned a UE-specific RNTI (SPSC-
RNTI). In case that the DCI CRC is scrambled with the SPS-C-RNTI, this DCI is
interpreted as activation or deactivation message. This mechanism could also be used
fro the activation and deactivation of the downlink component carriers. However, this
may have a drawback that for each user equipment for which a carrier aggregation is
configured, a new separate RNTI would be required. As the total number of RNTIs is
limited to 65536, many of these are required for non-carrier-aggregation purposes (e.g.
C-RNTI, SPS-C-RNTI, etc) and the number of user equipments in carrier activation
should support a large peak number, it would be beneficial to find other methods which
do not impose such a requirement.
Another solution for (de)activating configured downlink component carriers and in line
with a first aspect of the invention, a signaling format for communicating a component
carrier (de)activation message for controlling the activation state of at least one
component carrier is provided. The proposed new format of a component carrier
(de)activation message allows for an explicit identification of the intended recipient of the
component carrier (de)activation message. For example, this identification can be
realized by including a mobile terminal identifier (ID) to the component carrier
(de)activation message. This mobile terminal ID (also referred to as a UE ID) is for
example signaled in a mobile terminal identifier field of the component carrier
(de)activation message. In one exemplary implementation the mobile terminal ID
indicated in the component carrier (de)activation message is a mobile terminal-specific
identifier, such as for example a C-RNTI of the mobile terminal.
In view of the component carrier (de)activation message indicating the intended recipient
for the component carrier (de)activation message, it is not longer necessary to
unambiguously identify the intended recipient of the component carrier (de)activation
message by means of scrambling the CRC of the component carrier (de)activation
message with a mobile terminal-specific identifier. The component carrier (de)activation
message format can be considered a downlink control information (DCI) format. In the
physical layer, the component carrier (de)activation message is downlink control channel
information that is mapped to the physical downlink control channel (PDCCH) for
transmission to the mobile terminal.
In line with the first aspect of the invention, a CRC is calculated based on the component
carrier (de)activation message and is scrambled at the base station. The scrambling is
performed at the base station using a component carrier-specific or cell-specific radio
network temporary identifier. As indicated above, this implies a significantly reduced
number of radio network temporary identifier(s) that need to be reserved for controlling
the (de)activation state of the configured component carriers.
As mentioned in the previous paragraph, the component carrier (de)activation message
format may be considered a new format of downlink control channel information that is
mapped to the physical downlink control channel (PDCCH). The component carrierspecific
or cell-specific radio network temporary identifier(s) used for scrambling the CRC
of a component carrier (de)activation message thus indicate the format of the downlink
control channel information being a component carrier (de)activation message.
Furthermore, in case of using component carrier-specific radio network temporary
identifier(s) that is/are linked to a respective component carrier, carrier-specific radio
network temporary identifier(s) also indicate(s) a component carrier to be activated or
deactivated. Hence, the component carrier (de)activation message as well as the CRC
attachment (i.e. the CRC for the component carrier (de)activation message scrambled
with a given radio network temporary identifier) indicate to the mobile terminal the
desired activation state of the component carriers, i.e. indicate which of them is/are to be
(de)activated.
A further solution for (de)activating configured downlink component carriers and in line
with a second aspect of the invention, the component carrier (de)activation message is
provided within a transport block in the physical downlink shared channel (PDSCH). The
transport block is thus transmitted as (part of) a scheduled transmission on the PDSCH
to the mobile terminal. The component carrier (de)activation message may be
multiplexed with other data of logical channels to the transport block. Furthermore, the
component carrier (de)activation message may be optionally assigned a logical channel
identifier (LCID).
Similar to the solutions in line with the first aspect of the invention, the component carrier
(de)activation message comprises (de)activation information that indicate for the
respective downlink component carriers configured by the mobile terminal, the activation
state of the respective component carriers and which allow the mobile terminal recognize
a change in the activation state of the respective downlink component carriers. The
detection of such change of the activation state for one or more downlink component
carriers will cause the mobile terminal to activate or deactivate the effected configured
downlink component carrier(s) accordingly. In one exemplary implementation, the
(de)activation information for the component carriers may be provided in a MAC control
element, i.e. by means of MAC signaling.
Furthermore, still in line with this second aspect of the invention, the (de)activation
information may be provided in form of a bitmap. The individual bits of the bitmap
indicate the activation state of a respective configured downlink component carrier
associated to a respective bit of the bitmap.
A further aspect of the invention is to trigger the signaling of sounding reference signals
(SRSs) in the uplink. This may be done by means of an individual signaling message or
together with the (de)activation of configured component carriers. In case of using an
individual signaling message, a SRS (de)activation message may be defined. This SRS
(de)activation message may reuse the different structures and mechanisms for
transmitting the component carrier (de)activation message according to the various
embodiments described herein. For example, the SRS (de)activation message may
comprise SRS (de)activation information that indicated the activation state of the SRS
transmission for the uplink component carriers configured for the mobile terminal.
This SRS (de)activation information may be structured similarly to the component carrier
(de)activation information. For example, the SRS (de)activation information may be
provided in form of a bitmap. The individual bits of this bitmap may indicate the activation
state SRS signaling on the respective configured uplink component carrier associated to
a respective bit of the bitmap. Alternatively the bits of the bitmap in the SRS
(de)activation message may also be considered associated to respective configured
downlink component carriers, and the logical values of the individual bits of the bitmap
indicate the activation state of SRS signaling on the uplink component carrier linked to
the respective downlink component carrier associated to the given bit in the bitmap.
The SRS (de)activation message may be signaled as part of a transport block on the
physical uplink shared channel as described herein in the embodiment in line with the
second aspect of this invention) or may be signaled as a new format of downlink control
channel information that is mapped to the physical downlink control channel (PDCCH) as
described herein in the embodiment in line with the first aspect of the invention.
Moreover, the SRS (de)activation information may also be sent together with
(de)activation information for activating/deactivating configured downlink component
carriers within a single message. In one exemplary embodiment of the invention, the
SRS (de)activation information and the component carrier (de)activation information are
signaled in a MAC control element as part of a transport block of the physical downlink
shared channel. In a further exemplary embodiment, the SRS (de)activation information
and the component carrier (de)activation information are signaled together in a new
format of downlink control channel information that is mapped to the physical downlink
control channel (PDCCH) as described herein in line with the first aspect of the invention.
Please note that the principles for component carrier (de)activation may be applied for
the activation and deactivation of downlink and uplink component carriers. In this respect
it should be further noted that it is assumed in the exemplary embodiments and
implementations of the invention, that a component carrier could be defined to be in one
of the following three activation states: non-configured, configured but deactivated and
active. Moreover, it is also important to notice that In cases where there is a downlink
(and/or uplink) component carrier configured for the mobile terminal that is always active,
the(de)activation information does not need to indicate the activation state for such
"always active" component carrier - an "always active" component carrier is also referred
to as the primary component carrier (PCC) herein.
Exemplarily considering downlink component carriers, when a downlink component
carrier is configured but deactivated, the user equipment does not need to receive the
corresponding PDCCH or PDSCH, nor is it required to perform CQI measurements.
Conversely, when a downlink component carrier is active, the user equipment shall
receive PDSCH and PDCCH (if present), and is expected to be able to perform CQI
measurements. After configuration of component carrier(s) same is/are in configured but
deactivated state. In order to enable PDCCH and PDSCH reception on a downlink
component carrier, the downlink component carrier needs to be transitioned from
configured but deactivated state to active state. The configuration of a component carrier
may alternatively implicitly or explicitly activate the component carrier, in which case the
component carrier needs to be transitioned from active ("configured and active") state to
configured but deactivated state in order to save processing resources and/or signaling.
When an uplink component carrier is configured and activated, it is assumed to be
eligible for transmission of signals and channels such as ACK/NACK, sounding reference
symbols, scheduling request, and periodic CQI reports. Conversely, when the downlink
component carrier is in configured but deactivated state, the uplink component carrier is
assumed to be completely muted and not eligible for transmission of uplink signals and
channels such as the above.
The new proposed component carrier (de)activation according to the various
embodiments of the invention described herein may therefore be used for indicating state
transitions between configured but deactivated state and active state ("configured and
activated").
As outlined above, one aspect of the invention is the proposal of a new component
carrier (de)activation message for (de)activating one or more uplink or downlink
component carriers. According to one embodiment of the invention related to the
implementation of the concepts of this invention in a 3GPP based system using carrier
aggregation in downlink and/or uplink, the format for the new component carrier
(de)activation message is a DCI format. The new component carrier (de)activation
message contains at least a target UE ID, such as for example the C-RNTI of the user
equipment to which the new component carrier (de)activation message is destined.
Furthermore, in case the component carrier(s) to which the new component carrier
(de)activation message pertains is/are not implicit to the RNTI used for scrambling the
CRC of the new component carrier (de)activation message, the new component carrier
(de)activation message further contains a target component carrier ID. An example for a
component carrier (de)activation message according to one embodiment of the invention
including a CQI request flag is shown in Fig. 16. The remaining bits available in the
component carrier (de)activation message may be used to signal further information or
requests to the mobile terminal as will be discussed below, or may be filled with padding
or reserved bits.
This target component carrier ID may be for example signaled in a field of the new
component carrier (de)activation message, which has a size of bits, given
that there is one always-active component carrier in the downlink/uplink, the so-called
anchor carrier, which cannot be activated/deactivated by this message, and where N is
the number of configured downlink/uplink component carriers and is the ceiling
function, i.e. the smallest integer number that is larger than or equal to x . Hence, for a
typical downlink scenario, one can assume that there are up to N = 5 configured
downlink component carriers, one of them being defined as the anchor carrier, so that a
total of 2 bits would be needed for the target component carrier ID in the component
carrier (de)activation message.
Furthermore, according to a further aspect and embodiment of the invention, no user
equipment-specific RNTI is used to scramble the CRC for the component carrier
(de)activation message, when mapping the component carrier (de)activation message as
downlink control channel information to the PDCCH. This becomes possible since the
target UE ID is part of the payload of the component carrier (de)activation message.
Instead, the RNTI(s) used for signaling messages related to the (de)activation of
component carriers, such as the component carrier (de)activation message, is either a
cell-specific RNTI or a component carrier-specific RNTI.
If the scrambling of the CRC is using a single cell-specific RNTI defined for the signaling
of messages relates to the (de)activation of component carriers, such as the component
carrier (de)activation message, the component carrier (de)activation message's payload
further includes information for which component carrier the (de)activation command
should be applied. For this purpose, the component carrier (de)activation message may
comprise one or more target component carrier IDs to indicate one or more component
carriers in the downlink or uplink, which should be activated or deactivated. The base
station may indicate the cell-specific RNTI for component carrier (de)activation to the
mobile terminal by RRC signaling, e.g. as part of a component carrier configuration
message.
In case the one or all component carriers indicated in the component carrier
(de)activation message should be (simultaneously) activated or deactivated, the
component carrier (de)activation message may comprise an additional
activation/deactivation flag to indicate whether the one or more component carriers are to
be activated or deactivated. Another example for a component carrier (de)activation
message according to a further embodiment of the invention including multiple target
component carrier IDs and a single activation/deactivation flag is shown in Fig. 11.
In an alternative implementation according to a further embodiment, the component
carrier (de)activation message comprises an activation/deactivation flag for each target
component carrier ID indicated in the target component carrier IDs. This way, the base
station can control the mobile terminal to individually activate or deactivate the respective
component carrier(s) indicated by the target component carrier ID(s). Please note that it
is a matter of definition of whether the target component carrier ID and a corresponding
activation/deactivation flag is considered two fields of the component carrier
(de)activation message or whether the two information is provided in a single signaling
component carrier activation/deactivation field. An example for a component carrier
(de)activation message according to one embodiment of the invention including multiple
target component carrier IDs and activation/deactivation flags is shown in Fig. 12.
Furthermore, in another embodiment of the invention, there are two cell-specific RNTIs
defined for the signaling of messages relates to the (de)activation of component carriers,
such as the component carrier (de)activation message. In this case one of the two RNTIs
(Activation RNTI) can be used to indicate the activation of the component carrier(s)
indicated by means of one or more target component carrier IDs in the component carrier
(de)activation message. Likewise, the other one of the two RNTIs (Deactivation RNTI)
can be used to indicate the deactivation of the component carrier(s) indicated by means
of one or more target component carrier IDs in the component carrier (de)activation
message. Therefore, no additional activation/deactivation flag is needed in the payload of
the component carrier (de)activation message in this exemplary implementation. The
base station may indicate the Activation RNTI and Deactivation RNTI for component
carrier (de)activation and their respective function (activation/deactivation) to the mobile
terminal by means of RRC signaling, e.g. as part of a component carrier configuration
message. An example for a component carrier (de)activation message according to an
embodiment of the invention including a target component carrier ID but no
activation/deactivation flags is shown in Fig. 13.
In another embodiment of the invention, one or two cell-specific RNTIs may be used as
described above. Instead of indicating individual component carrier to be activated by
means of the target component carrier IDs (and using respective activation/deactivation
flags), a bit-mask is signaled in the component carrier (de)activation message to indicate
the activation state of each configured downlink/uplink component carrier. An example
for a component carrier (de)activation message for the (de)activation of downlink/uplink
component carriers is shown in Fig. 18. The bit-mask is comprises in the CC bit-mask
field. The bit-mask consists of N - l bits, where N is the number of configured
downlink/uplink component carriers. If there are N = 5 configured component carriers,
the bit-mask has a size of 4 bits. Please note that only N - l bits are required, if
assuming that there is always one active downlink component carrier in the uplink and
downlink for a mobile terminal in connected mode. Each of the bits in the bit-mask is
linked to a corresponding configured component carrier in the downlink/uplink. The
logical value 1 of a bit of the bit-mask may indicate the configured downlink component
carrier associated to the bit being active, while the logical value 0 of a bit of the bit-mask
may indicate the corresponding configured downlink component carrier associated to the
bit being configured but deactivated (or vice versa). The use of the (de)activation
message according to this embodiment of the invention has the benefit that a single DCI
payload can activate and deactivate several component carriers simultaneously.
The association between the respective association between the bits of the bit-mask (or
the codepoints of the bit-maks field) and a component carrier may be for example
configured for each mobile terminal a higher layer, e.g. RRC, configuration message.
In accordance with a further embodiment of the invention a component carrier-specific
RNTI is used for scrambling the CRC. In this embodiment, each of the configured
component carriers in the downlink or uplink is assigned a specific RNTI. The component
carrier-specific RNTIs may also be defined per-cell, so that they can be considered a
sub-class of the cell-specific RNTIs. Please note that the anchor carrier may also be
assigned a component carrier-specific RNTI, as different mobile terminals may have
different anchor carriers in a cell controlled by a base station.
The mobile terminal may be informed by the base station on the correspondence of
component carrier-RNTIs and component carriers. The correspondence information may
for example be signaled to the mobile terminal via RRC signaling, e.g. as part of the
component carrier configuration message. One benefit of the use of component carrierspecific
RNTI(s) is that a mobile node that is not configured to monitor component
carrier-specific RNTI(s) for the (de)activation of component carriers, cannot falsely
(de)activate a component carrier in case of a corrupted DCI message. Furthermore, in
addition to the component carrier-specific RNTI(s) also the target UE ID in the
(de)activation message has to match, so that a false (de)activation of a component
carrier is less likely.
In this case, the component carrier-specific RNTI used by the base station for scrambling
the CRC of the component carrier (de)activation message already indicates to the mobile
terminal the component carrier to which the (de)activation command of the component
carrier (de)activation message pertains. Hence, the component carrier (de)activation
message may not include a target component carrier ID in this case. Nevertheless, the
component carrier (de)activation message may still include the activation/deactivation
flag to indicate the activation state to be set for the component carrier indicated by the
component carrier-specific RNTI. An example for a component carrier (de)activation
message according to an embodiment of the invention an activation/deactivation flag for
the downlink component carrier implicit to the component carrier-specific RNTI used for
scrambling the CRC is shown in Fig. 14.
In another alternative embodiment, there are two components carrier-specific RNTIs
defined for each component carrier for scrambling the CRC of component carrier
(de)activation related messages, such as the proposed component carrier (de)activation
message. Similar to the example above, one of the two component carrier-specific
RNTIs (Activation RNTI) is indicating to activate the component carrier linked to the
component carrier-specific RNTI, while the other one of the two component carrierspecific
RNTIs (Deactivation RNTI) is indicating to deactivate the component carrier
linked to the component carrier-specific RNTI. This way, the component carrier
(de)activation message may only need to signal the UE ID to destine the component
carrier (de)activation related message to the correct recipient (user equipment), while the
component carrier to be (de)activated is implicit to the use of the RNTI for scrambling the
CRC of the component carrier (de)activation related message. Please note that also in
this case the base station may indicate the correspondence of Activation RNTIs and
Deactivation RNTIs for the different component carriers by means of RRC signaling, e.g.
as part of a component carrier configuration message. An example for a component
carrier (de)activation message according to an embodiment of the invention only
comprising the target UE ID and optionally further information and request (Extended
Usage) is shown in Fig. 15.
Irrespective of whether (a) cell-specific or component carrier-specific RNTI(s) are used,
these RNTIs may be signaled to the mobile terminals by means of RRC signaling or
other means of sending control information related to the carrier aggregation mode. In
particular, when configuring the terminal to which component carrier(s) it should consider
as being "configured", the mobile terminal is also notified which RNTI(s) to use for one or
more such configured component carriers.
Furthermore, in a 3GPP based communication system using OFDM on the downlink, it
can be assumed that the component carrier (de)activation message is forming the
payload (DCI) of a PDCCH transmitted within a sub-frame on a downlink component
carrier to one or more user equipments and the user equipments perform a blind
decoding on the different DCI formats signaled in a sub-frame on PDCCH. Using the
same size as at least one other DCI format defined in the communication system for the
component carrier (de)activation message format, and using an implicit this format by
means of the cell-specific or component carrier specific RNTI(s), it is possible not to
increase the blind decoding efforts of a mobile terminal.
As the format of the component carrier (de)activation message is thus assumed to have
a given size, the remaining bits not needed to signal the UE ID and the component
carrier (de)activation related information such as target component carrier ID(s) and
activation flag(s) may be for example used to signal further information or requests to the
mobile terminals. Please note that in the different examples described above explaining
how cell-specific or component carrier specific RNTI(s) can be used, some allow to avoid
the signaling of target component carrier ID(s) and/or activation/deactivation flag(s), so
that the size of the component carrier (de)activation related information may be
minimized (or even avoided). Moreover, the size of the component carrier (de)activation
message format may be either constant (fixed) or may depend on the component carrier
bandwidth, e.g. the bandwidth of the (de)activated component carrier, the bandwidth of
the component carrier in the downlink on which the component carrier (de)activation
message is signaled, or the linked uplink component carrier of the downlink on which the
component carrier (de)activation message is signaled.
In one exemplary implementation, the size of the component carrier (de)activation
message format is corresponding to the size of DCI formats 0/1 A in 3GPP LTE (Release
8/9) or 3GPP LTE-A (Release 10). The format size may optionally depend on the
component carrier bandwidth.
In this context, Table 4 illustrates the sizes of formats 0/1 A in 3GPP LTE (Release 8/9)
(as known from 3GPP TS 36.212 mentioned previously herein) depending on the
component carrier bandwidth:
Table 4
If a CIF field is added these formats 0/1 A, as defined in 3GPP LTE-A (Release 10), the
size of formats 0/1 A in 3GPP LTE-A (Release 10) has additional three bits more to
account for the CIF field.
Hence, as apparent from the different examples given above, the minimum information
that needs to be signaled in the component carrier (de)activation message is the target
UE ID to identify the intended recipient of the component carrier (de)activation message.
If the target UE ID is a C-RNTI of the destined user equipment, this means that 16 bits
are required for the target UE ID. For each target component carrier ID, additional
log (N - l ) bits are required. Each activation/deactivation flag requires one additional
bit.
For example, in case of using one single cell-specific RNTI for identifying the DCI format,
assuming that there are N = 5 configured component carriers, of which N - l = 4 need
to be indicated in the target component carrier ID field (the anchor carrier is always in
active state) and that the activation state for one component carrier is to be signaled
only, this would imply that the DCI payload of the component carrier (de)activation
message requires 16 bits for the cell-specific RNTI (target UE ID), 2 bits for the indication
of the target component carrier (target component carrier ID) and one bit of the
activation/deactivation flag ((De)Act flag), which is 19 bits in total. Hence, assuming the
smallest component carrier bandwidth of 1.4 MHz at least two "extra" bits are available
for further use. If the activation/flag can be omitted due to using two cell-specific RNTI for
identifying the DCI format and the activation state, even three additional bits would be
unused for the smallest component carrier bandwidth of 1.4 MHz.
In another embodiment of the invention, and in accordance with the second aspect of
this invention, the component carrier (de)activation message is provided within a
transport block on the physical downlink shared channel (PDSCH). For example, the
component carrier (de)activation message may be a MAC signaling message for
activating and deactivating downlink component carriers. In one exemplary
implementation, the component carrier (de)activation message is provided in form of a
new MAC control element identified by a specific LCID. This new MAC control element
carries the (de)activation information of which configured downlink component carrier(s)
of the mobile terminal shall be activated and/or deactivated.
The MAC control element for the component carrier (de)activation message may be octet
aligned, i.e. consist of a multiple of 8 bits ( 1 byte). The actually size of the MAC control
element for the component carrier (de)activation may be determined by the number of
downlink component carriers that can be configured in the user equipment. If there is a
a n always active primary component carrier provided, as for example in an 3GPP LTE-A
(Release 10) system, this number of downlink component carriers is the number of
secondary component carriers that can be configured in the user equipment.
In one exemplary embodiment, the (de)activation information within the component
carrier (de)activation message is provided a s a bitmap. Each bit of the bitmap represents
a n activation/deactivation flag for one of the downlink component carriers (or secondary
component carriers, if a primary component carrier is provided). For example, a bit set to
0 could mean that the corresponding component carrier is to be deactivated and the bit
set to 1 could mean the activation of the component carrier, or vice versa.
Alternatively, the bits of the bitmap may also indicate the activation state of the
component carriers associated to the respective bits. For example, a bit set to 0 could
mean that the activation state of the corresponding component carrier is the configured
but deactivated state and the bit set to 1 could mean the activation state of the
component carrier is active state ("configured and activated"), or vice versa. In this case,
the mobile terminal would determine whether there is a change of the activation state for
a component carrier and activates or deactivates the respective component carrier
accordingly. If the number of downlink component carriers that need to be distinguished
in the is lower than nine, only one octet of payload is needed for signaling the bitmap.
For example currently in 3GPP standardization with respect to 3GPP LTE-A (Release
10), it is assumed that a maximum of five component carriers in the downlink can be
aggregated. One of these five downlink component carrier is designated as the downlink
primary component carrier, which is always active and hence cannot be activated or
deactivated. This would leaves four additional downlink secondary component carriers
(SCCs) in the downlink that can be configured in a user equipment and thus can be
activated/ deactivated. Hence, in one exemplary embodiment of the invention, the bitmap
has a size of four bits corresponding to the maximum of four downlink secondary
component carriers. This leaves four additional bits for further signaling in the MAC
control element that may be used for triggering the transmission of SRSs and/or power
headroom reports (PHRs) by the user equipment.
An exemplary component carrier (de)activation message that is defining a new DCI
format for transmission on the PDCCH and for use in a 3GPP LTE-A (Release 10) is
shown in Fig. 25. Similar to the other DCI exemplary formats proposed herein, the
messages comprises ain identification of the target user equipment. Furthermore, there
are 4 flags provided that form the bitmap. Each of the flags is associated to a respective
downlink component carrier and is used for (de)activation thereof as outlined above.
Please note that this 4 bit-bitmap may also form the payload of a MAC control element
that is used to implement the component carrier (de)activation message.
Furthermore, it may be advantageous to ensure that there is a one to one mapping
between each bit of the bitmap and the corresponding component carrier it refers. This
type of correspondence may be for example realized by using the component carrier
index (CI) used in component carrier configuration message transmitted via RRC. For
instance, the highest bit (first bit) of the bitmap could refer to the highest (or lowest)
component carrier index, the second highest (second bit) of the bitmap could refer to the
second highest (second lowest) component carrier index, etc. This way a one-to-one
correspondence between the individual bit positions in the bitmap and the component
carriers they refer to can be established.
As mentioned above, component carrier (de)activation message, e.g. in form of an MAC
control elements, is included in the transport block in the PDSCH of one of the downlink
component carriers. Hence, for reception of the component carrier (de)activation
message, the user equipment needs to successfully decode the transport block in order
to "obtain" the (de)activation information. The transport block containing the component
carrier (de)activation message (as well as other transport blocks on the PDSCH) may be
transmitted using an HARQ protocol in order to ensure its successful delivery and
decoding at the user equipment. If the transport block is not decoded successfully by the
user equipment's decoder, HARQ retransmissions for a transport block (including the
component carrier (de)activation message) increase the time between actual issuing of a
(de)activation command by the eNodeB and the reception of the (de)activation command
at the user equipment. In the case of using a MAC control element for component carrier
(de)activation this could mean delayed activation and deactivation with possible negative
effects on scheduling and power saving of the user equipment.
In order to minimize the possibility of retransmissions, and thus avoiding the possible
negative effects mentioned above, the transmission of the component carrier
(de)activation message may be for example restricted to the most reliable of the
downlink component carriers. In actual deployments this most reliable component carrier
may be - in most cases - the primary component carrier (PCC) of the user equipment.
The PCC is also associated with Radio Link Failure (RLF), therefore it needs to be a
reliable component carrier since otherwise the user equipment could not establish a
reliable connection to the network. Furthermore, it is the only component carrier that is
always active, i.e. cannot be deactivated or activated. Hence, in one implementation
example, the component carrier (de)activation message is transmitted by the eNodeB on
the user equipment's PCC to the user equipment. Hence, if the component carrier
(de)activation message is implemented as a MAC control element, the transmission of
the MAC control element for component carrier (de)activation to the PCC reduces the
chances of delayed activation and deactivation of the secondary component carriers of
the user equipment.
In the sections above (de)activation of configured downlink component carriers using
either L 1 signaling (i.e. a new DCI format on the PDCCH) or L2 signaling (i.e. signaling
the component carrier (de)activation message in a transport block on the PDSCH, e.g. in
form of a MAC control element) have been described. The following considerations apply
to both aspects of this invention.
When eNodeB is deactivating a configured downlink component carrier, the user
equipment may deactivate the indicated component carriers immediately after reception
of the deactivation command (component carrier deactivation message). If the user
equipment receives a deactivation message for a configured component carrier where
the transmission of a transport block using the HARQ protocol (i.e. one of the HARQ
processes is (re)transmitting a transport block on the PDSCH when receiving the
deactivation command) is not finished, i.e. retransmissions are still pending for the
transport block, the immediate deactivation of the component carrier would stop HARQ
retransmission and the transport block would be lost.
As the HARQ protocol of Layer 2 is also terminated in the eNodeB, the eNodeB is aware
of the ongoing HARQ retransmissions of the user equipment on the configured downlink
component carrier and may thus not deactivate a component carrier, where a transport
block has not yet successfully received by the user equipment, i.e. not yet (positively)
acknowledged by the user equipment. This would have however imply that the eNodeB
may need to send an individual deactivation messages for each component carrier, even
though when deactivation would be possible to be sent within one signaling message,
since the HARQ operation on the different downlink component carriers and HARQ
processes of the HARQ protocol may not be aligned.
Therefore, in another embodiment of the invention, in order to allow eNodeB to combine
several deactivation commands within one signaling message without causing loss of
transport blocks, the user equipment is not deactivating a component carrier right after
receiving a deactivation command for the given configured component carrier. Instead,
the user equipment determines the HARQ protocol status for the component carrier (i.e.
determines whether there are still any retransmission(s) of a transport block(s) pending)
and deactivates the component carrier upon a pending transmission having been
successfully finished (i.e. having been (positively) acknowledged by the user equipment
or the maximum number of retransmissions has been reached for the pending
transmission.
This operation of the downlink component carrier deactivation is also advantageous in
terms of the eNodeB not needing to wait for an acknowledgement on each of the
transmissions ongoing on the component carriers to be deactivated, so that the actual
deactivation command for a component carrier can occur several sub-frames (TTIs)
earlier since the user equipment does not need to wait for the acknowledgement of the
last transmission.
Especially when (de)activation signaling is done by MAC signaling this is beneficial for
power saving at the user equipment.
In the following paragraphs, different exemplary implementations and embodiments
regarding the design of the component carrier (de)activation message format will be
discussed in further detail.
In one exemplary implementation of the component carrier (de)activation message
format (i.e. the DCI format) is used for controlling the activation state of one downlink
component carrier configured by a mobile terminal. In this embodiment, one of the
"Extra" bits/flags as for example shown in Fig. 9 or Fig. 10 is used to request the mobile
terminal to send channel quality feedback for the controlled downlink component carrier.
This may be especially suitable in situations where the downlink component carrier is
activated (configured but activated state ® active state). For this purpose the
component carrier (de)activation message comprises in its payload a "CQI request flag",
that when set triggers the provision of channel quality feedback for the downlink
component carrier activated by the component carrier (de)activation message. An
example for a component carrier (de)activation message according to one embodiment
of the invention including a CQI request flag is shown in Fig. 16.
In one more detailed implementation example according to an embodiment of the
invention, the channel quality feedback in form of CQI, PMI (Precoding Matrix Indicator)
or Rl (Rank Indicator) could be transmitted on resources of a physical uplink control
channel (PUCCH). If considering an implementation in a 3GPP based system, like 3GPP
LTE-A (Release 10), the possible PUCCH payload may be quite restricted since a single
resource block shares PUCCHs from multiple user equipments. Therefore, the channel
quality feedback may for example signal a wideband CQI/PMI assuming a Rank=1
transmission.
The transmission of the channel quality feedback message can further be considered by
the base station as an acknowledgement for the mobile terminal having successfully
received the component carrier (de)activation message, respectively for the mobile
terminal having executed the activation command comprised in the component carrier
(de)activation message.
Furthermore, the channel quality feedback (e.g. the CQI/PMI) may be sent by the mobile
terminal a known time interval (e.g. 4 ms) after having received the sub-frame (PDCCH)
containing the component carrier (de)activation message. In 3GPP LTE (Release 8/9) in
FDD mode, the time span between reception of a sub-frame (PDCCH) and a
corresponding uplink transmission is 4 ms (for TDD the time span determination as more
complicated). The time span between reception of the sub-frame (PDCCH) containing
the component carrier (de)activation message and the transmission of channel quality
feedback in uplink may alternatively be configured by RRC signaling. For instance, it may
be desirable to give the mobile terminal more than 4 ms (e.g. 8 ms or 12 ms) to send the
channel quality feedback, in order to allow the mobile terminal to perform an accurate
channel quality measurement to obtain an adequate accuracy of the CQI/PMI after
activating the respective downlink component carrier(s).
As to the uplink resources for the transmission of the channel quality feedback, the
resource on the PUCCH may be for example the same PUCCH resource that is given to
the mobile terminal for the periodic CQI reporting. This PUCCH resource may be
configured by the base station via RRC signaling when configuring the downlink/uplink
component carrier.
Alternatively, the channel quality feedback may also be transmitted on a PUCCH or
PUSCH resource that is predetermined by the base station, e.g. as part of the RRC
component carrier configuration message. A further alternative is that the uplink resource
for transmitting the channel quality feedback is indicated by one or more of the "extra"
bits that are available in the payload of the component carrier (de)activation message.
This implementation can be beneficially exploited in case of a large component carrier
bandwidth (as discussed above with respect to Fig. 9 and Table 4), where several bits
may be unused and available to specify the feedback resources in the uplink. The two
latter alternatives may also be combined in that the RRC component carrier configuration
message configures a set of uplink resources for the channel quality feedback
(CQI/PMI/RI), and the (de)activation message comprises a feedback resource field that
selects one out of the available configured uplink resources. An example for an extended
component carrier (de)activation message including a CQI request flag and a CQI
feedback resource field is shown in Fig. 17.
Moreover, in case that the uplink resource for the channel quality feedback is signaled or
pre-configured, the channel quality feedback is preferably determined according to the
configured aperiodic CQI mode and/or the configured downlink transmission mode of the
downlink component carrier that is indicated by the component carrier (de)activation
message.
Furthermore, in another embodiment, channel quality feedback may also be multiplexed
with further physical layer messages or signals, such as HARQ feedback (ACK/NACK),
SR or SRS, on the assigned uplink resource. In case only physical layer messages but
no transport block data is signaled on the uplink resource, no HARQ process (HARQ
protocol) needs to be employed for the transmission, so that HARQ related control
information (such as NDI, HARQ process ID, etc.) may not need to be signaled for the
transmission.
In another embodiment of the invention, the component carrier (de)activation message
may be used to trigger/activate periodic channel quality feedback (periodic CQI/PMI/RI
transmission) with respect to the sub-frame where the component carrier (de)activation
message for the action of the downlink component carrier is received.
In this embodiment of the invention, procedure as known from 3GPP LTE (Release 8/9)
is reused. Accordingly periodic CQI/PMI/RI is basically transmitted in sub-frames having
a sub-frame number satisfying the condition:
Subframe ~ ^OFFSET, CQI m N Periodici!y = 0
where
= + 2 (3)
and where nf is the system frame number, and ns = {0,1,..., 19} is the slot index within
the frame. It should be noted that the relation here is a simplified mechanism to explain
the timing principle, however there are special cases that render the timing slightly more
complicated (see also 3GPP TS 36.213, "Physical layer procedures", version 8.8.0
(Release 8) or 9.0.1 (Release 9), section 7.2.2 for further details, the documents being
available at http://www.3gpp.org and the sections being incorporated herein by
reference).
In one embodiment of the invention, in case the component carrier (de)activation
message from the base station comprises a CQI flag being set, the mobile terminal is
providing a single (aperiodic) CQI report (One-time CQI) at a given offset of k subframes
relative to the sub-frame of the (de)activation message and starts signaling
periodic CQI reports in the sub-frames and on the PUCCH resources that have been
configured for the component carrier activated by the component carrier (de)activation
message. An exemplary scenario according to this embodiment of the invention for
visualizing this procedure is shown in Fig. 22, where after the activation of downlink (DL)
component carrier (CC) 2 (DL CC2) by means of the CC activation message, a CQI
report (One-time CQI for DL CC2) is sent after k = 4 sub-frames after having received
the CC activation message for DL CC2 in which a CQI request flag is included and set,
while the subsequent CQI reports for DL CC2 are signaled in the sub-frame number
indicated by the parameter N OFFSET CQI on the uplink resources and with the periodicity
^periodicity configured for periodic CQI reporting. Furthermore, upon the base station
signaling a CC deactivation message for DL CC2 in which a CQI request flag included
and not set, the mobile terminal deactivates DL CC2 again and stops periodic CQI
reporting.
In another embodiment of the invention, a new way of calculating N O FSE CQI is employed
so that the first periodic CQI report of the mobile terminal is transmitted at a given offset
k relative to the component carrier activation message. In the periodic CQI reporting
procedure of 3GPP LTE (Release 8/9) indicated above, the transmission of the
CQI/PMI/RI thus depends on the system-wide sub-frame number, irrespective of the subframe
number of the sub-frame comprising the component carrier (de)activation
message. In order to start the periodic CQI/PMI/RI report as early as possible, in this
embodiment the condition is modified as follows. Periodic CQI/PMI/RI is transmitted in a
sub-frame the sub-frame number of which is satisfying the (updated) conditions (2) and
(3) above as known from 3GPP TS 36.213, however changing the definition of the offset
N 0FFSEr CQ,so that it doesn't refer to sub-frame number 0, but to the sub-frame number in
which the component carrier (de)activation message has been received, i.e.
N ,OFFSET, CQI Subframe ,Activation + k , N Subframe,Max (4)
where NSubframe A iv t n
is the sub-frame number of the sub-frame in which the component
carrier (de)activation message triggering (activating) CQI/PMI/RI reporting for the
activated downlink component carrier, and NSuhframeMax
is largest sub-frame index. In
3GPP LTE (Release 8/9), the system frame number ranges from 0 to 1023, each system
frame comprises slot 0 to 19; consequently NSubfmmeMax = xnf Max + 2J or
subf ne = 10239 . In the condition (4), the offset k added to iVJ „ ta may be for
example configurable or static.
In one example, k=4 so as to ensure that the earliest channel quality feedback
transmission occurs 4 sub-frames after the sub-frame number of the sub-frame in which
the component carrier (de)activation message triggering (activating) CQI/PMI/RI
reporting for the activated downlink component carrier(s). However, if the channel quality
feedback is to be provided with a larger offset (i.e. later), it can be necessary to increase
the parameter k, as mentioned before. For example, k {4, 6, 8, 10, 12} .
Fig. 23 is exemplarily highlighting the mobile terminal's behavior according to this
embodiment of the invention in response to the reception of a component carrier
(de)activation message comprising a CQI request flag being set using the updated
periodic CQI reporting procedure. Upon the base station activating DL CC2 by means of
the CC activation message received in sub-frame number NSubframe A iva ion , the offset
OFFSET,cQi s assumed to be set according to condition (4) and sends the CQI report for
DL CC2 ksub-frames later, which is here 4 sub-frames, respectively 4 ms, after having
received the CC activation message on the PUCCH resources configured for periodic
CQI reporting. Subsequently, the mobile terminal provides periodic CQI reports for DL
CC2 with periodicity NPeriodicity configured for periodic CQI reporting, until the CC
deactivation message of the base station deactivates DL CC2.
The benefit of the modified periodic CQI/PMI/RI reporting procedure discussed in the
previous paragraphs is that the first CQI/PMI/RI report is received very early after having
activated the downlink component carrier, which may be helpful for the scheduler of the
base station to schedule transmission on the activated downlink component carrier, and
that subsequent CQI reports are transmitted according to the configured periodicity.
Since depending on the configuration of the periodic CQI/PMI/RI report it can happen
that it is unclear what kind of transmission rank (the transmission rank determines the
precoder matrix dimension for MIMO transmissions) is used, preferably the first such
periodic CQI/PMI report consists of a wideband CQI/PMI report assuming Rank=1 .
Alternatively, the first CQI/PMI/RI report after activation of the downlink component
carrier(s) consists of a Rank indicator (Rl), followed by the CQI/PMI in the next report
transmitted according to the periodic CQI/PMI/RI configuration as discussed in the
preceding paragraphs.
The cases where the periodic CQI/PMI/RI report is configured as at least wideband
CQI/PMI and sub-band CQI as per 3GPP TS 36.213, section 7.2.2 can be treated
applying the above mentioned timing offset and first CQI/PMI/RI report content principles
mutatis mutandis. Particularly, it should be avoided to send a subband CQI as the first
CQI report after activation.
In addition to the CQI request flag or alternatively thereto, the unused bits (extended use)
of the component carrier (de)activation message may also be used to trigger the
transmission of sounding reference symbols (SRS) in the uplink or a power headroom
report (PHR).
In a further embodiment of the invention a "SRS request" flag may be included in the
component carrier (de)activation message as shown in Fig. 19. The SRS request flag
when set by the base station, requests the mobile terminal to start transmission of
sounding reference symbols (SRS) on the linked uplink component carrier(s) that is/are
linked to the downlink component carrier(s) activated by the component carrier
(de)activation message. If the component carrier (de)activation message is activating
uplink component carrier(s), the mobile terminal starts sending sounding reference
symbols (SRS) on the activated uplink component carrier(s). Triggering SRS instead of
CQI may be particularly beneficial in case of time division duplex (TDD) systems where
the channel can be assumed to be reciprocal, so that the channel estimation for the
uplink based on SRS can be used for the channel estimation for the downlink as well.
Similar to the inclusion of a CQI request flag, the inclusion of the SRS request flag is
advantageously included in component carrier (de)activation messages that indicate a
component carrier activation. In case of deactivation, the bits for the either flag can be
reserved for other signaling. Alternatively, SRS request flag (or an SRS field having more
than one bit) may also be present in component carrier (de)activation messages that
deactivated a component carrier, and may be used to point to a new component carrier
where the mobile terminal should subsequently expect or transmit signals that so far
have been transmitted on the component carrier that is being deactivated.
In a further alternative implementation the bits for the SRS request flag and the CQI
request flag within a component carrier (de)activation message could be used to indicate
a time offset between the reception of the (de)activation command and the execution of
the (de)activation command. Alternative uses of extra bits are to signal whether the
reception of the command should be acknowledged by the receiver (explained below).
The signalling of SRS enabling/disabling as described above can also be realized in
accordance with the second and third aspect of the invention: Using MAC signaling. SRS
information that indicates for which component carriers(s) in the uplink SRS(s) should be
transmitted by the user equipment. For example, the SRS information that indicate the
(de)activation of the SRS(s) may be for example provided in a new MAC control element,
similar as described for the component carrier (de)activation message. This MAC control
element contains a bitmap similar to the MAC control element for the downlink
component carrier (de)activation as described above. Each bit in the bitmap refers to one
uplink component carrier of the user equipment for which the SRS transmission should
be started/stopped. Alternatively, one can consider the bits of the bitmap associated to
respective ones of the configured downlink component carriers. In this case the bit for a
given downlink component carrier indicating the (de)activation of SRS will cause the user
equipment to (de)activate the transmission of SRS on the uplink component carrier
linked to the given downlink component carrier. For example, a bit of the bitmap being
set to 0 may indicates not to transmit periodic SRS on the associated (linked) uplink
component carrier, respectively to stop transmitting periodic SRS; while a bit set to 1
would indicate to activate periodic SRS transmission on the associated (linked) uplink
component carrier (or vice versa).
If there are enough bits unused in the MAC control element for downlink component
carrier (de)activation these bits can be used for the SRS (de)activation as described
above. In the example given above, assuming that there are five downlink component
carriers aggregated in th downlink, of which four downlink component carriers can be
activated or deactivated (i.e. one PCC and four SCCs are provided), four bits are needed
for the (de)activation of the downlink secondary component carriers. Considering the
MAC control element to have the size of one octet, this leaves additional four bits that
are not used which can be used for the bitmap to signal SRS (de)activation as described
above.
An exemplary MAC control element which allows simultaneous (de)activation of downlink
component carriers and deactivation of SRS transmissions by the user equipment is
shown in Fig. 24. The first four bits of the octet define the bitmap for downlink component
carrier (de)activation, while the second four bits thereof define the bitmap for the
(de)activation of SRS transmission by the user equipment. An advantage of combining
both bitmaps for (de)activation of SCCs and (de)activation of SRS transmission within
one MAC control element may be that periodic SRS transmission on the linked uplink
component carrier(s) can start simultaneous with downlink SCC activation. This avoids
possible delays that could occur when both functions are signalled in separate MAC
control elements and reduces overhead. It should be noticed that both component carrier
(de)activation and SRS enabling/disabling can be still signalled independently even when
they are signalled in the same MAC control element. Fig. 26 shows another exemplary
implementation of a component carrier (de)activation message in form of a new DCI
format that allows simultaneous (de)activation of downlink component carriers and
deactivation of SRS transmissions by the user equipment. Basically, the bitmask as
shown in Fig. 24 is signaled in this component carrier (de)activation message together
with an indication of the user equipment which is to receive the component carrier
(de)activation message.
In another embodiment of the invention in case a downlink component carrier is activated
by the base station, the activation of the downlink component carrier triggers a power
headroom report (PHR) by the mobile terminal. The mobile terminal may send the
triggered PHR report on the resources assigned by a next uplink grant for this linked
uplink component carrier to the base station. This may ensure that the base station is
informed on the path-loss situation for the linked uplink component carrier in the next
uplink transmission of the mobile terminal on the linked uplink component carrier. This
may be beneficial since the linked uplink component carrier has most likely not been
used at least for a longer time period prior to the activation of the linked downlink
component carrier. The power headroom reports from the mobile terminal enable the
base station to improve scheduling decisions.
Alternatively, in another embodiment of the invention, the detailed CQI reporting, SRS
transmission, PHR reporting etc. in response to a component carrier (de)activation may
also be configured by the base station using RRC signaling or may use a pre-determined
configuration (known to base station and mobile terminal).
Upon successful detection of a (de)activation command, the mobile station may confirm
the execution of the (de)activation command by sending a confirmation message
(acknowledgement) in uplink. In one embodiment of the invention, the following method
is used to acknowledge the successful decoding of the component carrier (de)activation
message, respectively the execution of the (de)activation command:
- Sending an acknowledgement (also referred to as "HARQ-ACK" in the 3GPP
terminology) in case of deactivation of a component carrier, where the resource for
the acknowledgement transmission follows the principles of 3GPP LTE (Release 8/9)
for sending HARQ-ACK in case of a downlink data transmission (PDSCH) as defined
in 3GPP TS 36.213, section 10. In brief, the PUCCH resource for the HARQ-ACK is
determined according to the PDCCH resource where the (de)activation message is
transmitted. In this case, the eNodeB can do a power detection to check whether
HARQ-ACK was transmitted on the expected resource or not.
- Sending an acknowledgement (also referred to as "HARQ-ACK" in the 3GPP
terminology) in case of activation of a component carrier without requesting a quick
CQI, where the resource for the acknowledgement transmission follows the
procedure of 3GPP LTE (Release 8/9) for sending HARQ-ACK in case of a downlink
data transmission as defined in 3GPP TS 36.213, section 10. In this case, the eNB
can do a power detection to check whether HARQ-ACK was transmitted on the
expected resource or not.
- Sending the CQI report in case of activation of a component carrier and CQI request
flag being set in the component carrier (de)activation message. In this case, the
eNodeB can do a power detection to check whether CQI report was transmitted on
the expected resource or not.
- Triggering a PHR in case of activation of a component carrier.
- As indicated above, PUCCH feedback resources for the acknowledgement may be
for example determined by the mobile terminal in the same fashion as provided I the
3GPP LTE (Release 8/9) procedure, as if the component carrier (de)activation
message schedules a PDSCH transmission, e.g. by DCI format 1A (which is may
have the same size as the component carrier (de)activation message). Furthermore,
as eNodeB is aware of whether the user equipment will send an acknowledgement
(HARQ-ACK) or a CQI report, the eNodeB can monitor the respective uplink
resources on which the acknowledgement or CQI report is expected from the user
equipment.
Optionally, the user equipment may also send a NACK (HARQ NACK) in case of not
having decoded the component carrier (de)activation message procedure of 3GPP LTE
(Release 8/9) for sending HARQ-NACK in case of a downlink data transmission as
defined in 3GPP TS 36.213, section 10.
Fig. 20 shows an exemplary scenario according to an exemplary embodiment of the
invention, where an Activation and a Deactivation RNTI are configured for the activation,
respectively deactivation of component carriers. In this example, upon activation of one
of the component carriers by the CC activation message (Activation RNTI), the user
equipment synchronously signals an HARQ-ACK to the eNodeB to acknowledge the
successful decoding of the CC activation message. The HARQ-ACK is sent with a given
offset to the CC activation message (i.e. PDCCH containing same), for example after 4
ms. Similarly, upon the base station deactivating the component carrier again by means
of the CC deactivation message (Deactivation RNTI), the user equipment again
acknowledges the deactivation by means of a HARQ-ACK that is again synchronously
sent in the uplink after 4 ms.
Fig. 2 1 shows another exemplary scenario according to a further exemplary embodiment
of the invention, where an Activation and a Deactivation RNTI are configured for the
activation, respectively deactivation of component carriers. Furthermore, the activation of
one of the component carriers by the CC activation message (Activation RNTI) is further
requesting the user equipment to signal channel quality feedback for the activated
downlink component carrier (CQI request flag being set in the CC activation message).
Accordingly, the user equipment signals at a known timing relative to the CC activation
message, here 4 ms after receiving same, an CWI report to the eNodeB thereby
acknowledging the successful decoding of the CC activation message. Upon the base
station deactivating the component carrier again by means of the CC deactivation
message (Deactivation RNTI), the user equipment again acknowledges the deactivation
by means of a HARQ-ACK that is synchronously sent in the uplink after 4 ms.
In case the eNodeB intents to increase uplink and downlink capacity at the same time, in
a further embodiment of the invention, the base station may further activate a downlink
component carrier that is linked to an uplink component carrier that is currently not used
for uplink transmissions. There is no information as to channel quality for an inactive or
configured but deactivated uplink component carrier available at the eNodeB.
Consequently in this embodiment of the invention, the activation of a downlink
component carrier is further triggering sounding reference signal (SRS) transmission on
the uplink component carrier(s) linked to the activated downlink component carriers(s). In
this case no additional SRS request flag may be needed, but the start of signaling SRS
on the uplink component carrier linked to a downlink component carrier activated by
component carrier (de)activation message may be a default behavior of the mobile
terminal in response to the activation of the downlink component carrier.
Similarly as for the CQI reporting, also the transmission of SRS is not in all cases
beneficial/required. Therefore it should be possible that eNodeB enables/disables SRS
transmission when activating downlink component(s). This could be achieved by
including a flag in the (de)activation message which indicates whether user equipment is
required to send SRS. It may be further configured or specified or signaled whether such
an SRS should be one-time only, or periodic. In either case, further "extra" bits can be
used to define one or more of the SRS parameters such as bandwidth, comb, etc (refer
to 3GPP LTE (Release 8/9) SRS parameters).
Of course, the component carrier (de)activation message may also be designed to allow
the simultaneous transmission of a CQI request flag, triggering a PHR and/or a SRS
request flag.
When user equipment monitors the PDCCH, there is always a certain probability (false
alarm rate) that the mobile terminal falsely detects a PDCCH: the CRC check of the
PDCCH may be correct even though the PDCCH was not intended for this user
equipment, i.e. CRC passes even though there is a RNTI mismatch (unintended user).
This so called false alarm might happen, if the two effects of transmission errors caused
by the radio channel and RNTI mismatch cancel each other. The probability of a falsely
positive decoded PDCCH depends on the CRC length. The longer the CRC length, the
lower the probability that a CRC-protected message is falsely correct decoded. With the
CRC size of 16 bit the false alarm probability would be 1.5 10 5 .
In case a user equipment falsely detects a PDCCH with a downlink component carrier
(de)activation message indicating the deactivation of certain downlink component
carrier(s) the user equipment would stop monitoring PDCCH/PDSCH for those indicated
downlink component carrier(s) and also stops reporting CQI measurements. Given the
severe consequences of such user equipment behavior, it is therefore desirable to
decrease the false alarm probability.
Each bit of virtual CRC can be assumed to halve the false alarm risk. On the other hand,
each additional RNTI that is used increases the false alarm risk linearly. For example, in
case of employing four component carrier-specific activation-RNTIs and four component
carrier-specific deactivation-RNTIs, the false alarm risk is eight times higher than for the
case of a single CC-RNTI. On the other hand, using the altogether eight CC-RNTIs does
not require the inclusion of a target CC ID field in the DCI payload nor that of an
Activation/Deactivation field. In most of the exemplary implementations that have been
discussed above, the largest target component carrier ID size is four bits. Consequently,
the usage of eight component carrier-RNTIs without target component carrier ID field
results in a false alarm risk of — = 0.5 times compared to the risk when a single CCRNTI
with a four-bit target component carrier ID field is employed. The drawback is the
increased cost of RNTI, and the restriction that multiple (de)activation messages are
required to (de)activate multiple component carriers at the same time.
In one embodiment of the invention, it is therefore proposed that the downlink component
carrier (de)activation message comprises one or more extra bits (in a CRC field) can be
used as a virtual CRC to reduce the false alarm risk. These additional bit(s) are set to a
known, predefined value which is to be verified by the mobile terminal.
Another embodiment of the invention relates to the implementation of the above
described various embodiments using hardware and software. It is recognized that the
various embodiments of the invention may be implemented or performed using
computing devices (processors). A computing device or processor may for example be
general purpose processors, digital signal processors (DSP), application specific
integrated circuits (ASIC), field programmable gate arrays (FPGA) or other
programmable logic devices, etc. The various embodiments of the invention may also be
performed or embodied by a combination of these devices.
Further, the various embodiments of the invention may also be implemented by means of
software modules, which are executed by a processor or directly in hardware. Also a
combination of software modules and a hardware implementation may be possible. The
software modules may be stored on any kind of computer readable storage media, for
example RAM, EPROM, EEPROM, flash memory, registers, hard disks, CD-ROM, DVD,
etc.
It should be further noted that the individual features of the different embodiments of the
invention may individually or in arbitrary combination be subject matter to another
invention.
It would be appreciated by a person skilled in the art that numerous variations and/or
modifications may be made to the present invention as shown in the specific
embodiments without departing from the spirit or scope of the invention as broadly
described. The present embodiments are, therefore, to be considered in all respects to
be illustrative and not restrictive.
CLAIMS
1. A method for (de)activating configured component carriers in communication
system using component carrier aggregation, the method comprising the
following steps performed by a terminal:
receiving on a physical downlink shared channel a transport block comprising
a component carrier (de)activation message, wherein the component carrier
(de)activation message comprises (de)activation information in form of a
bitmap consisting of a number of bits, wherein each of the bits of the bitmap is
associated to a respective one of the configured downlink component
carriers, wherein logical value of each bit is indicating whether the associated
downlink component carrier is to be activated or deactivated, and
activating or deactivating the configured component carriers according to
(de)activation information obtained from the component carrier (de)activation
message.
2. The method according to claim 1, wherein the component carrier
(de)activation message is a MAC control element.
3. The method according to claim 1 or 2, wherein the component carrier
(de)activation message multiplexed to the transport block together with other
logical channel data to be transmitted to the mobile terminal.
4. The method according to one of claims 1 to 3, wherein one of the plurality of
configured downlink component carriers is a downlink primary component
carrier which cannot be activated or deactivated by the component carrier
(de)activation message and the component carrier(de)activation message is
received by the mobile terminal on the downlink primary component carrier.
5. The method according to one of claims 1 to 4, wherein the transport block
comprising a component carrier (de)activation message is received on a
downlink primary component carrier of the mobile terminal.
6. The method according to one of claims 1 to 5, wherein the component carrier
(de)activation message is further comprises SRS information allowing to
request the mobile terminal to start sending a sounding reference signal
(SRS) on at least one of the uplink component carriers respectively linked to
the configured downlink component carriers.
7. The method according to claim 6, wherein the SRS information is provided in
form of a bitmap consisting of a number of bits, wherein each of the bits of the
bitmap is associated to a respective one of uplink component carriers,
wherein logical value of each bit of the bitmap is indicating whether SRS
should be transmitted on the associated uplink component carrier.
8. A method for (de)activating configured component carriers in communication
system using component carrier aggregation, the method comprising the
following steps performed by a terminal:
receiving a sub-frame from a base station,
performing a blind detoction blind decoding within a control signaling region on
one of the configured downlink component carriers within the received subframe
to obtain a component carrier (de)activation message and a CRC
attachment thereof, wherein the CRC attachment comprises a CRC of the
component carrier (de)activation message, the CRC being scrambled with a
component carrier-specific or cell-specific radio network temporary identifier
(RNTI) used for signaling the activation state of the target component
carrier(s), and
checking the CRC of the CRC attachment using the component carrierspecific
or radio cell-specific radio network temporary identifier,
wherein the mobile terminal further performs the following steps if the CRC
check passes:
determining a mobile terminal identifier from the component carrier
(de)activation message,
verifying based on the mobile terminal identifier whether the component
carrier (de)activation message is destined to the mobile terminal, and
activating or deactivating the configured component carriers according to
(de)activation information obtained from the component carrier (de)activation
message and/or implicit to the use of the radio network temporary identifier
for scrambling the CRC attachment, if the component carrier (de)activation
message is destined to the mobile terminal.
9. A method for (de)activating configured component carriers of a mobile
terminal in communication system using component carrier aggregation, the
method comprising the following steps performed by a base station:
generating a component carrier (de)activation message comprising at least a
mobile terminal identifier of the mobile terminal,
determining a CRC for the component carrier (de)activation message,
scrambling the CRC with a component carrier-specific or cell-specific radio
network temporary identifier (RNTI) used for signaling the activation state of
the target component carrier(s), to thereby obtain a CRC attachment of the
component carrier (de)activation message,
transmitting the component carrier (de)activation message and its CRC
attachment within the control signaling region of a downlink component carrier
within a sub-frame to the mobile terminal.
10. The method according to claim 8 or 9, wherein the component carrier
(de)activation message indicates which of the plurality of configured downlink
component carriers is/are to be activated, respectively deactivated.
11. The method according to one of claims 8 to 10, wherein there are two radio
cell-specific radio network temporary identifiers used for signaling the
activation state of the downlink component carriers,
wherein one of the radio network temporary identifiers is indicating the
activation of at least one of the configured downlink component carrier
indicated in the component carrier (de)activation message and the other radio
network temporary identifier is indicating the deactivation of at least one of the
configured downlink component carrier indicated in the component carrier
(de)activation message.
12. The method according to one of claims 8 to 10, wherein each configured
downlink component carrier is linked to a component carrier-specific radio
network temporary identifier, and
wherein the component carrier-specific radio network temporary identifier
used for scrambling the CRC indicates at least the configured downlink
component carrier to be activated or deactivated.
13. The method according to claim 12, wherein each configured downlink
component carrier is linked to two component carrier-specific radio network
temporary identifiers, and
wherein the component carrier-specific radio network temporary identifier
used for scrambling the CRC indicates at least the configured downlink
component carrier and whether it is to be activated or deactivated.
14. The method according to one of claims 8, 9, 10, or 12, wherein the
component carrier (de)activation message comprises an activation flag that
requests the mobile terminal to activate, respectively deactivate an indicated
configured downlink component carrier.
15. The method according to one of claims 8 to 14, wherein the component
carrier (de)activation message format has the same number of bits as at least
one other downlink control information format defined in the mobile
communication system.
16. The method according to one of claims 8 to 15, wherein one of the plurality of
configured downlink component carriers is a downlink primary component
carrier which cannot be activated or deactivated by the component carrier
(de)activation message and the component carrier (de)activation message is
received on a downlink primary component carrier of the mobile terminal.
17. The method according to one of claims 1 to 16, wherein the activation of a
downlink component carrier triggers the transmission of a power headroom
report by the mobile terminal for the uplink component carrier linked to the
downlink component carrier being activated.
18. The method according to claim 17, further comprising the step of transmitting
in response to the activation of a downlink component carrier a power
headroom report for the for the uplink component carrier linked to the
downlink component carrier being activated, wherein the power headroom
report is transmitted by the mobile terminal on the linked uplink component
carrier on resources assigned on the linked uplink component carrier
assigned to the mobile terminal by the next uplink resource assignment for
the linked uplink component carrier.
The method according to one of claims 1 to 18, wherein in case the
component carrier (de)activation message indicates the deactivation of a
downlink component carrier, the mobile terminal deactivates the indicated
component carrier when all HARQ processes protocol entities of the HARQ
protocol te r-transmittinq transport blocks f- on that-the indicated component
carrier upon reception of the component carrier (de)activation message either
a. acknowledge successful decoding of the respective a-transport block(s)
pending for transmission on the downlink component carrier to be
deactivated after the time of receiving the component carrier (de)activation
message, or
b. upon reaching a maximum number of retransmissions of the HARQ
protocol for the transport block pending for transmission on the downlink
component carrier to be deactivated.
The method according to one of claim 1 to 19, wherein the component carrier
(de)activation message comprises a SRS flag that, when set, requests the
mobile terminal to start sending a sounding reference signal (SRS) on the
uplink component carrier linked to the indicated configured downlink
component carrier.
The method according to one of claim 1 to 20, wherein the component carrier
(de)activation message comprises a CQI request flag that, when set, requests
channel quality feedback for the one or more indicated configured downlink
component carriers.
The method according to claim 2 1, further comprising the following steps
performed by the mobile terminal in case the mobile terminal is requested to
send channel quality feedback for an indicated downlink component carrier:
performing a channel quality measurement for each downlink component
carrier indicated by the component carrier (de)activation message, and
transmitting the channel quality feedback for the one or more indicated
downlink component carriers to the base station.
23. The method according to one of claims 2 1 or 22, further comprising the
following steps performed by the mobile terminal in case the mobile terminal
is requested to send channel quality feedback for an indicated downlink
component carrier:
periodically performing a channel quality measurement for each downlink
component carrier indicated by the component carrier (de)activation
message, and
periodically transmitting the channel quality feedback for the one or more
indicated downlink component carriers to the base station on uplink resources
on the physical uplink control channel configured by RRC for periodic channel
quality feedback.
24. The method according to one of claims 1 to 23, further comprising the step of
acknowledging reception of the component carrier (de)activation message.
25. A mobile terminal for (de)activating configured component carriers in
communication system using component carrier aggregation, the mobile
terminal comprising:
a receiver for receiving on a physical downlink shared channel a transport
block comprising a component carrier (de)activation message, wherein the
component carrier (de)activation message comprises (de)activation
information indicating which of a plurality of configured downlink component
carriers is/are to be activated, respectively deactivated by the mobile terminal,
and
a processor for activating or deactivating the configured component carriers
according to (de)activation information obtained from the component carrier
(de)activation message.
26. A mobile terminal for use in a communication system using component carrier
aggregation, the mobile terminal comprising:
a receiver for receiving a sub-frame from a base station,
a processor for performing a blind dotoctionblind decoding within a control
signaling region on one of the configured downlink component carriers within
the received sub-frame to obtain a component carrier (de)activation message
and a CRC attachment thereof, wherein the CRC attachment comprises a
CRC of the component carrier (de)activation message, the CRC being
scrambled with a component carrier-specific or cell-specific radio network
temporary identifier (RNTI) used for signaling the activation state of the target
component carrier(s),
wherein the processor is adapted to check the CRC of the CRC attachment
using the component carrier-specific or radio cell-specific radio network
temporary identifier, and to determine a mobile terminal identifier from the
component carrier (de)activation message, if the CRC check passes,
wherein the processor is adapted to verify based on the mobile terminal
identifier whether the component carrier (de)activation message is destined to
the mobile terminal, and to activate or deactivate the configured component
carriers according to (de)activation information obtained from the component
carrier (de)activation message and/or implicit to the use of the radio network
temporary identifier for scrambling the CRC attachment, if the component
carrier (de)activation message is destined to the mobile terminal.
A base station for (de)activating configured component carriers of a mobile
terminal in communication system using component carrier aggregation, the
base station comprising:
a processor for generating a component carrier (de)activation message
comprising at least a mobile terminal identifier of the mobile terminal,
wherein the processor is adapted to determine a CRC for the component
carrier (de)activation message, and to scramble the CRC with a component
carrier-specific or cell-specific radio network temporary identifier (RNTI) used
for signaling the activation state of the target component carrier(s), to thereby
obtain a CRC attachment of the component carrier (de)activation message,
and
a transmitter for transmitting the component carrier (de)activation message
and its CRC attachment within the control signaling region of a downlink
component carrier within a sub-frame to the mobile terminal.
A computer-readable medium storing instructions that, when executed by a
processor of a mobile terminal, cause the mobile terminal to (de)activate
configured component carriers in communication system using component
carrier aggregation, by:
receiving on a physical downlink shared channel a transport block comprising
a component carrier (de)activation message, wherein the component carrier
(de)activation message comprises (de)activation information indicating which
of a plurality of configured downlink component carriers is/are to be activated,
respectively deactivated by the mobile terminal, and
activating or deactivating the configured component carriers according to
(de)activation information obtained from the component carrier (de)activation
message.