Signalling in Coordinated Multi-Point Transmission and Reception (CoMP)
[0001] This application claims the benefit of
U.S. Provisional Application No. 62/055,381, entitled "Signalling for Inter-eNB CoMP," filed on
September 25, 2014,
U.S. Provisional Application No. 62/056,095, entitled "Signalling for Inter-eNB CoMP," filed on
September 26, 2014,
U.S. Provisional Application No. 62/076,221, entitled "CSI Exchange for Inter-eNB CoMP," filed on
November 6, 2014,
U.S. Provisional Application No. 62/076,873, entitled "CSI Exchange for Inter-eNB CoMP," filed on
November 7, 2014,
U.S. Provisional Application No. 62/1 10,006, entitled "CSI Exchange for Inter-eNB CoMP," filed on
January 30, 2015,
U.S. Provisional Application No. 62/145,251, entitled "Efficient CSI and e-RNTP Exchange for
Inter-eNB CoMP," filed on April 9, 2015,
U.S. Provisional Application No. 62/145,580, entitled "Efficient CSI and e-RNTP Exchange for
Inter-eNB CoMP," filed on April 10, 2015,
U.S. Provisional Application No. 62/150,178, entitled "CSI Exchange for Inter-eNB CoMP," filed on
April 20, 2015,
U.S. Provisional Application No. 62/151,796, entitled "Subband Definitions and eRNTP enhancements,"
filed on April 23, 2015,
U.S. Provisional Application No. 62/161,804, entitled "On the Subband Definition in CSI Signaling,"
filed on May 14, 2015,
U.S. Provisional Application No. 62/162,285, entitled "eRNTP Signalling for Inter-eNB CoMP," filed
on May 15, 2015,
U.S. Provisional Application No. 62/204,541, entitled "Subband definition in CSI Signaling," filed on
August 13, 2015,
the contents of all of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to coordinated multi-point transmission and reception (CoMP) in
wireless or mobile communications and, more particularly, to signalling in inter-eNB (E-UTRAN
NodeB or eNodeB) CoMP.
[0003] Referring now to FIG. 1, a CoMP mobile communications system 400 comprising a CoMP
coordination zone or area or CoMP cooperating set 402 in which the embodiments may be implemented
is illustrated. One or more user equipments (UEs) 410 are served by one or more TPs or cells 404 to 408.
TPs 404 to 408 can be base stations or eNBs. Each of the user equipments includes e.g. a transmitter and
a receiver, and each of the base stations or eNBs 104 includes e.g. a transmitter and a receiver.
[0004] Transmission layers are sometimes called "transmit layers" or "layers." The number of
transmission layers is known as "transmission rank" or "rank." A codebook is a set of precoding
matrices or precoders. A precoding matrix is also known as a codeword.
[0005] Reference
[0006] [1] RP-141032, "New Work Item on Enhanced Signaling for Inter-eNB CoMP," June 2014.
[0007] [2] R3-142582, "Way forward on WI: Enhanced signalling for inter-eNB CoMP," October 2014.
[0008] [3] Rl-141206, "Signaling Considerations for Inter-eNB CoMP", NEC, March 2014.
[0009] [4] R3-151209, Change Request, May 2015.
BRIEF SUMMARY OF THE INVENTION
[0010] An objective of the present invention is to provide efficient channel state information (CSI)
and/or relative narrowband Tx (transmit) power (RNTP) exchanges between eNBs.
[001 1] An aspect of the present invention includes, in a wireless communications system including a
first base station and a second base station, a wireless communications method implemented in the first
base station supporting coordinated multi-point transmission and reception (CoMP). The wireless
communications method comprises, for a given user equipment (UE) identification (ID) and a given
channel state information (CSI) process, receiving from the second base station a plurality of CSI reports
each of which comprises a rank indication (RI) and a channel quality indicator (CQI), wherein the
second base station receives from one or more user equipments (UEs) RI and CQI information.
[0012] Another aspect of the present invention includes, in a wireless communications system including
a first base station and a second base station, a wireless communications method implemented in the
second base station supporting coordinated multi-point transmission and reception (CoMP). The
wireless communications method comprises receiving from one or more user equipments (UEs) rank
indication (RI) and channel quality indicator (CQI) information, and for a given user equipment (UE)
identification (ID) and a given channel state information (CSI) process, transmitting to the first base
station a plurality of CSI reports each of which comprises an RI and a CQI.
[0013] Still another aspect of the present invention includes a first base station supporting coordinated
multi-point transmission and reception (CoMP) and used in a wireless communications system. The first
base station comprises a receiver to receive from a second base station, for a given user equipment (UE)
identification (ID) and a given channel state information (CSI) process, a plurality of CSI reports each of
which comprises a rank indication (RI) and a channel quality indicator (CQI), wherein the second base
station receives from one or more user equipments (UEs) RI and CQI information.
[0014] Still another aspect of the present invention includes a second base station supporting
coordinated multi-point transmission and reception (CoMP) and used in a wireless communications
system. The second base station comprises a receiver to receive from one or more user equipments
(UEs) rank indication (RI) and channel quality indicator (CQI) information, and a transmitter to transmit
to a first base station, for a given user equipment (UE) identification (ID) and a given channel state
information (CSI) process, a plurality of CSI reports each of which comprises an RI and a CQI.
[0015] Still another aspect of the present invention includes a wireless communications method
implemented in a wireless communications system supporting coordinated multi-point transmission and
reception (CoMP) and including a first base station and a second base station. The wireless
communications comprises transmitting from one or more user equipments (UEs) to the second base
station rank indication (RI) and channel quality indicator (CQI) information, and for a given user
equipment (UE) identification (ID) and a given channel state information (CSI) process, transmitting
from the second base station to the first base station a plurality of CSI reports each of which comprises
an RI and a CQI.
[0016] Still another aspect of the present invention includes a wireless communications system
supporting coordinated multi-point transmission and reception (CoMP). The wireless communications
system comprises a first base station, a second base station transmitting to the first base station, for a
given user equipment (UE) identification (ID) and a given channel state information (CSI) process, a
plurality of CSI reports each of which comprises a rank indication (RI) and a channel quality indicator
(CQI), and one or more user equipments (UEs) transmitting to the second base station RI and CQI
information.
[0017] An aspect of the present invention includes, in a wireless communications system including a
first base station and a second base station, a wireless communications method implemented in the first
base station supporting coordinated multi-point transmission and reception (CoMP). The wireless
communications method comprises receiving from the second base station an information element (IE)
indicating multiple relative narrowband Tx (transmit) power (RNTP) thresholds, and performing
interference aware scheduling.
[0018] Another aspect of the present invention includes, in a wireless communications system including
a first base station and a second base station, a wireless communications method implemented in the
second base station supporting coordinated multi-point transmission and reception (CoMP). The
wireless communications method comprises transmitting to the first base station an information element
(IE) indicating multiple relative narrowband Tx (transmit) power (RNTP) thresholds, wherein the first
base station performs interference aware scheduling.
[0019] Still another aspect of the present invention includes a first base station supporting coordinated
multi-point transmission and reception (CoMP) and used in a wireless communications system. The first
base station comprises a receiver to receive from the second base station an information element (IE)
indicating multiple relative narrowband Tx (transmit) power (RNTP) thresholds, and a controller to
perform interference aware scheduling.
[0020] Still another aspect of the present invention includes a second base station supporting
coordinated multi-point transmission and reception (CoMP) and used in a wireless communications
system. The second base station comprises a transmitter to transmit to the first base station an
information element (IE) indicating multiple relative narrowband Tx (transmit) power (RNTP)
thresholds, wherein the first base station performs interference aware scheduling.
[0021] Still another aspect of the present invention includes a wireless communications method
implemented in a wireless communications system supporting coordinated multi-point transmission and
reception (CoMP) and including a first base station and a second base station. The wireless
communications comprises transmitting from the second base station to the first base station an
information element (IE) indicating multiple relative narrowband Tx (transmit) power (RNTP)
thresholds, and performing at the first base station interference aware scheduling.
[0022] Still another aspect of the present invention includes a wireless communications system
supporting coordinated multi-point transmission and reception (CoMP). The wireless communications
system comprises a first base station, and a second base station transmitting to the first base station an
information element (IE) indicating multiple relative narrowband Tx (transmit) power (RNTP)
thresholds, wherein the first base station performs interference aware scheduling.
[0023] An aspect of the present invention includes, in a wireless communications system including a
first base station and a second base station, a wireless communications method implemented in the first
base station supporting coordinated multi-point transmission and reception (CoMP). The wireless
communications method comprises receiving, from the second base station, a user equipment (UE)
identification (ID) for a UE in a reference signal received power (RSRP) report, and using the UE ID to
link the RSRP report with another measurement result for the UE.
[0024] Another aspect of the present invention includes, in a wireless communications system including
a first base station and a second base station, a wireless communications method implemented in the
second base station supporting coordinated multi-point transmission and reception (CoMP). The
wireless communications method comprises transmitting, to the first base station, a user equipment (UE)
identification (ID) for a UE in a reference signal received power (RSRP) report, wherein the first base
station uses the UE ID to link the RSRP report with another measurement result for the UE.
[0025] Still another aspect of the present invention includes a first base station supporting coordinated
multi-point transmission and reception (CoMP) and used in a wireless communications system. The first
base station comprises a receiver to receive, from the second base station, a user equipment (UE)
identification (ID) for a UE in a reference signal received power (RSRP) report, and a controller to use
the UE ID to link the RSRP report with another measurement result for the UE.
[0026] Still another aspect of the present invention includes a second base station supporting
coordinated multi-point transmission and reception (CoMP) and used in a wireless communications
system. The second base station comprises a transmitter to transmit to the first base station, a user
equipment (UE) identification (ID) for a UE in a reference signal received power (RSRP) report,
wherein the first base station uses the UE ID to link the RSRP report with another measurement result
for the UE.
[0027] Still another aspect of the present invention includes a wireless communications method
implemented in a wireless communications system supporting coordinated multi-point transmission and
reception (CoMP) and including a first base station and a second base station. The wireless
communications comprises transmitting, from the second base station to the first base station, a user
equipment (UE) identification (ID) for a UE in a reference signal received power (RSRP) report, and
using at the first base station the UE ID to link the RSRP report with another measurement result for the
UE.
[0028] Still another aspect of the present invention includes a wireless communications system
supporting coordinated multi-point transmission and reception (CoMP). The wireless communications
system comprises a first base station, and a second base station transmitting to the first base station, a
user equipment (UE) identification (ID) for a UE in a reference signal received power (RSRP) report,
wherein the first base station uses the UE ID to link the RSRP report with another measurement result
for the UE.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] FIG. 1 depicts a block diagram of a CoMP system.
DETAILED DESCRIPTION
[0030] Embodiment A
[0031] Al. Introduction
[0032] In the following we provide our views on channel state information (CSI) and enhanced relative
narrowband Tx (transmit) power (eRNTP) exchange as well as proposals containing the required
message structure.
[0033] A2. Discussion
[0034] A2.1 CSI exchange
[0035] One eNB can send CSI report pertaining to one or more of its users to a neighboring eNB.
[0036] For each UE the CSI that the eNB sends can comprise:
[0037] CQI (channel quality indication): up-to 2 CQIs, each including a wideband CQI or component
and possible sub-band differential CQIs or components
[0038] RI: wideband component
[0039] We note that the PMI was excluded from the CSI exchange report. The justification for this
exclusion was to minimize the overhead and the fact that PMI can depend on fast changing channel
information, thus reducing its utility over non ideal backhaul with a higher latency. However, in the
absence of PMI the use of RI is limited. Indeed, any rank greater than 1 will convey only 2 CQIs, one
for each of the two codewords. No further information about the (average) spatial directions seen by that
user can be deduced by the eNB receiving the report. As a result, reporting the RI should be made
optional. Moreover, the eNB requesting the CSI report should be able to able to specify whether or not it
would like to receive RI reports. This can be achieved by setting a bit (for instance in the CSI
Measurement Report type field) to be 0 if rank is not requested and 1 otherwise. Similarly, the eNB
requesting the CSI reports should be able to specify whether or not it requires subband specific CQI
reports. Another bit can be set to 0 if subband CQIs are not requested and 1 otherwise. The response of
the eNB receiving the request can be mandated to comply with this request, i.e., that eNB can decide to
include a rank indication in its response only if it is requested in the CSI measurement report type field of
the corresponding request. Further, the subband specific CQI can be included only if they are requested in
the CSI measurement report type field of the corresponding request.
[0040] In this context, we note that a CSI process can be defined to be the reference process for another
one. In that case the latter process will reuse the rank determined for its reference process. It can be
beneficial to exploit reference rank in the X2 signalling as well. One way to achieve this is to include
another bit in the CSI Measurement Report type field which specifies whether or not a single rank is
requested. In particular, this bit can be set to 1 only if the rank request bit is also set to 1. In that case the
eNB receiving the request should understand that the requesting eNB is requesting CSI reports where only
one rank is reported for each user. The response of the eNB receiving the request can be mandated to
comply with this request, i.e., if the eNB decides to include a rank indication in its response then it has to
be one indication per user.
[0041] Alternatively, no such mandate can be enforced, in which case it is up-to the eNB whether or not to
include a rank indication in the CSI corresponding to each CSI-process of each user and the ranks
indicated for a particular user need not be identical.
[0042] One of the goals of CSI exchange was to facilitate centralized RRM. In a scenario with
centralized RRM, the central node receiving the CSI reports should be able to keep track of the CSI
information received for each particular UE, over all the received CSI reports. This can be achieved by
including a UE identifier in each CSI report for each UE whose CSI is conveyed in that report.
[0043] Moreover, for each CSI in the report, the CSI process configuration information should be
included in order to convey the conditions under which the CSI was measured by the UE. This
configuration information includes non-zero power CSI-RS information and IMR information
(including, for example, the subframe indices and zero-power CSI-RS information). Since this
configuration is anyway informed to the UE via higher layer signaling, for instance CSI-RS in tables
7.2.6 of TS36.213, and tables 6.10.5.2-1, 6.10.5.2-2 of TS36.21 1 and subframe indices in tables 7.2.6 of
TS36.213, and table 6.10.5.3-1 of TS36.21 1, the same signaling can be reused to convey the
configuration to the neighboring eNB. Another way of conveying this configuration information is
through a look-up-table. A look-up-table mapping an index to each distinct applied CSI process
configuration can be constructed for each eNB. Here, by an applied CSI process we mean a process that
is used by at-least one served UE to measure its CSI. Such a table can be conveyed beforehand by it to
eNBl, and then each report can include an index which will inform. Such a table can also be exchanged
among neighbor eNBs first, and then the configuration information can be exchanged via indices.
[0044] We note that the period specified in the request by eNBl to a neighboring eNB2 (via the
Reporting Periodicity of CSI Measurement Report field) can be different from the periodicity with which
the CSI is measured by a UE as per a CSI process, and then reported (over the air) to eNB2. To address
such scenarios, eNB2 can either subsample (for example select the most recently received CSI) or average
(over all CSIs received after those considered while determining the previous response) and send its
response to eNBl, for example, about the CSI process configuration information. Note that the averaging
can be done over the CQIs for a given codeword, given rank and given subband. The most recent received
rank can be used for averaging.
[0045] A2.2 eRNTP exchange
[0046] Our view on eRNTP exchange is captured in a corresponding proposal.
[0047] We note that the RNTP for the first subframe is always conveyed. If no information about the
downlink (DL) power restriction on any subsequent subframe is conveyed, then the one conveyed for
the first subframe can be assumed to remain static (i.e., applicable over subsequent subframes).
[0048] A3. Conclusion
[0049] We discussed the necessary X2 message to support CSI and eRNTP exchange for inter-eNB
CoMP and presented corresponding proposals.
[0050] Proposals
[0051] 9.1.2.1 LOAD INFORMATION
[0052] This message is sent by an eNB to neighbouring eNBs to transfer load and interference
co-ordination information.
[0053] Direction: eNBi ® eNB2.
TableAl
»lntended 0 ENUMER One of the YES ignore
UL-DL ATED UL-DL
Configuration (saO, sal , configuration
sa2, sa3, s defined in
sa4, sa5, TS 36.21 1
sa6, ...) [ 10]. The UL
subframe(s)
in the
indicated
configuration
is subset of
those in
SIB 1 UL-DL
configuration
This IE
applies to
TDD only.
»Extended UL 0 9.2.67 This IE YES ignore
Interference applies to
Overload Info TDD only.
»Enhanced 0 9.2.X2 YES ignore
Relative
Narrowband Tx
Power (eRNTP)
[0054] 9.1.2. 11 RESOURCE STATUS REQUEST
[0055] This message is sent by an eNBi to a neighbouring eNB2 to initiate the requested measurement
according to the parameters given in the message.
[0056] Direction: eNBi ® eNB2.
TableA2
1,
Fifth Bit = ABS
Status Periodic,
Xth Bit = UE-CSI
Periodic.
Other bits shall be
ignored by the
eNB2 .
Cell To Report 1 Cell ID list for YES ignore
which
measurement is
needed
>Cell To Report 1 .. EACH ignore
Item
»Cell ID M ECGI
9.2. 14
Reporting Periodicity 0 ENUMERA YES ignore
TED(1 000
ms,
2000ms,
5000ms, 10
000ms, ...)
Partial Success 0 ENUMERA Included if partial YES ignore
Indicator TED(partia success is allowed
I success
allowed, ...
)
CSI Measurement 0 BITSTRIN Each position in YES ignore
Report type G the bitmap
(SIZE(2)) indicates the type
of CSI
measurement to
report.
First bit=Rank,
Second
bit=subband CQI .
Reporting Periodicity 0 ENUMERA Periodicity for CSI YES ignore
of CSI Measurement TED(5ms, Measurement
Report 10ms, Report Periodic
20ms,40m
s , 80ms,
aperiodic, .
)
[0057] 9.1.2.14 RESOURCE STATUS UPDATE
[0058] This message is sent by eNB2 to neighbouring eNBi to report the results of the requested
measurements.
[0059] Direction: eNB2 ® eNBi.
TableA3
[0060] 9.2.xl UE-CSI Report
[0061] This information element (IE) provides UE-CSI information for a subset or set of UEs served by
eNB2.
TableA4
(2))
»UE-CSI process M INTEGER(0..3 CSI process
Configuration information 1) or FFS configuration
information.
[0062] maxUEsubsetCSIReport can alternatively be set to 16, 20, 30, 35, or 40.
[0063] 9.2.x2 Enhanced Relative Narrowband Tx Power (E-RNTP)
[0064] This IE (infromation element) provides an indication on DL power restriction per PRB (physical
resource block) per subframe in a cell and other information needed by to a neighbour eNB for
interference aware scheduling.
Table A5
IE/Group Presence Range IE type and Semantics Criticality Assigned
Name reference description Criticality
RNTP Per M BIT STRING Each position
PRB (6. .110 , ...) in the bitmap
represents a
n value
(i.e. first
bit=PRB 0
and so on),
for which the
bit value
represents
RNTP (n PRB) ,
defined in TS
36.2 13 [ 1 1] .
Value 0
indicates "Tx
not
exceeding
RNTP
threshold".
Value 1
indicates "no
promise on
the Tx power
is given".
This IE is
used to
indicate DL
power
restriction per
PRB for the
first
subframe. In
case the DL
power
restriction is
static, the
indicated DL
power
restriction is
maintained
over the
subsequent
subframes.
RNTP M ENUMERAT RNTPthreshold
Threshold ED (-¥, - 11, is defined in
- 10 , -9, -8, TS 36.21 3
-7, -6, -5, -4, [ 1 1] .
-3, -2, - 1, 0 ,
1, 2 , 3 , ...)
Number Of M ENUMERAT P (number of
Cell-specifi ED ( 1 , 2 , 4 , antenna ports
c Antenna ) for
Ports cell-specific
reference
signals)
defined in TS
36.2 11 [ 10]
P_B M INTEGER PB is defined
(0. .3, ...) in TS 36.21 3
[ 1 1] .
PDCCH M INTEGER Measured by
Interferenc (0. .4, ...) Predicted
e Impact Number Of
Occupied
PDCCH
9 :>i 78
OFDM
Symbols (see
TS 36.21 1
[ 10]).
Value 0
means "no
prediction is
available".
Starting M INTEGER Number of
SFN (0. .1023, ...) the first
system frame
from which
the RNTP
Per PRB Per
Subframe IE
is valid.
Starting M INTEGER Index of the
Subframe (0. .9, ...) first subframe
Index from which
the RNTP
Per PRB Per
Subframe IE
is valid.
RNTP List 0 2 .. The first item
to the second
subframe, the
second to the
third
subframe,
and so on.
The DL
power
restrictions
conveyed for
the first
subframe and
the ones
conveyed for
the
subsequent
subframes in
the list, are
together
applied
repeatedly.
>RNTP M BIT STRING Each position
Per PRB (6. .110 , ...) in the bitmap
Subframe represents a
-Specific n value
(i.e. first
bit=PRB 0
and so on),
for which the
bit value
represents
RNTP (n PRB) ,
defined in TS
36.2 13 [ 1 1] .
Value 0
indicates "Tx
not
exceeding
RNTP
threshold".
Value 1
indicates "no
promise on
the Tx power
is given".
This IE is
used to
indicate DL
power
restriction per
PRB for the
correspondin
g subframe.
[0065] Embodiment B
[0066] Bl. Introduction
[0067] In the following we provide our views on CSI and eRNTP exchange, as well as proposals
containing the required message structures.
[0068] B2. Discussion
[0069] B2.1 CSI exchange: Configuring CSI processes
[0070] The concept of CSI processes was defined in Rel.l 1 to enable CSI feedback from a UE to its
serving eNB. The CSI feedback is determined for each CSI process according to the serving TP and
interference hypothesis configured in that process. . Each CSI process that is configured for a UE,
comprises a set of resource elements on which non-zero power CSI-RSs are sent and a channel estimate
is obtained by that UE using observations received on those resource elements.
[0071] In addition, a set of resource elements is also indicated by the CSI process (referred to as
interference measurement resources (IMRs)) on which the UE estimates the covariance of the
interference it observes. The channel and covariance estimates are together used by the UE to determine
and send its feedback report corresponding to that CSI process. Multiple such CSI processes (up-to 4)
can be configured for a UE, each process corresponding to a different choice of signal or interference
hypothesis. Moreover, in the scenario in which fast switching of the serving TP is not possible, different
CSI processes that are configured for any given UE typically correspond to different choices of
interference hypothesis.
[0072] Note from the brief discussion above that in the event the interference hypothesis of a configured
CSI process presumes muting from a TP (that is a dominant interferer for the UE of interest) which is
controlled by the neighboring eNB, coordination among the eNBs is required in order to ensure that the
interference estimated by the UE on the constituent IMRs is consistent with the assumed hypothesis.
Another similar event that requires coordination is if the non-zero power CSI-RSs indicated in the CSI
process must be interference protected in order to ensure reliable channel estimation at the UE. In both
these events, the dominant interferer that is controlled by the neighboring eNB must be muted on certain
resource elements. Thus, a mechanism (with appropriate signaling) should be available to share the
CSI-RS (comprising non-zero power CSI-RSs and IMRs) configurations between eNBs, which would
facilitate configuration of CSI processes across multiple eNBs.
[0073] Once the CSI processes are configured, the CSI exchanged among eNBs over the backhaul
should include the respective CSI process configuration information, in order to convey the conditions
under which the CSI was measured by the UE. This configuration information includes non-zero power
CSI-RS information and IMR information (comprising the subframe indices and zero-power CSI-RS
information). Since this configuration is anyway informed to the UE via RRC (or higher layer)
signaling, the same information can be reused as a container to convey the configuration to the
neighboring eNB.
[0074] Another way of conveying this configuration information is through a look-up-table. A
look-up-table mapping an index to one or more distinct applied CSI process configurations can be
constructed for each eNB. Here, by an applied CSI process we mean a process that is used by at-least
one UE served by that eNB to measure its CSI. Such a table can be exchanged among neighbors first
and from then on the configuration information can be exchanged via indices. The total number of
configurations in the table can be limited in order to limit signaling overhead.
[0075] Suitable values for the number of configurations in this table are either 8 or 16 or 32.
[0076] B2.2 CSI exchange: Contents
[0077] One eNB can send CSI report pertaining to one or more of UEs to a neighboring
eNB. For each UE, the CSI that the eNB sends to a neighbor can comprise:
[0078] (i) CQI: up-to 2 CQIs, each including a wideband component and possible
sub-band differential components
[0079] (ii) RI (rank indicator): one wideband component
[0080] We note that the PMI was excluded from the CSI exchange report [1]. The
justification for this exclusion was to minimize the overhead and the fact that PMI can
depend on fast changing channel information, thus reducing its utility over non ideal
backhaul with a higher latency. However, in the absence of PMI the use of RI is limited.
Indeed, any rank greater than 1 will convey only 2 CQI(s), one for each of the two
codewords. No further information about the (average) spatial directions seen by that UE
can be deduced by the eNB receiving the report. As a result, reporting the RI should be
made optional. Moreover, the eNB requesting the CSI report should be able to specify
whether or not it would like to receive RI reports. Similarly, the eNB requesting the CSI
reports should be able to specify whether or not it requires subband specific CQI reports.
This can be achieved by setting a bit (in the measurement request) to be 0 if rank is not
requested and 1 otherwise. Another bit can be set to 0 if subband CQIs are not requested
and 1 otherwise.
[0081] Processing (filtering or subsampling) of the short-term CSI (received via
over-the-air signaling) at an eNB prior to exchange should be permitted.
[0082] One use case for this is when the periodicity of the CSI report that is requested by
eNBl to its neighbor eNB2, is larger than the over-the-air CSI signaling periodicity
configured by eNB2. In this case eNB2 has to do some processing (such as subsampling
or averaging) of the reports it receives before it sends it to eNBl . In this context, we note
that the subsampling employed by eNB2 should be understood by eNBl (if needed
additional signaling can be added to ensure this). One possible way this can be
accomplished (without any signaling overhead) is for eNB2 to use the subsampling factor
determined by a pre-determined rule (known to or configured for all eNBs in advance)
that outputs a subsampling factor, given the requested periodicity and CSI process
configuration as inputs. On the other hand, averaging or scaling or filtering employed by
eNB2 can be transparent to the receiving eNB 1.
[0083] One of the goals of CSI exchange is to facilitate centralized RRM [3]. In a scenario
with centralized RRM, the central node receiving the CSI reports should be able to keep
track of the CSI information received for each particular UE, over all the received CSI
reports. This can be achieved by including a UE identifier in each CSI report for each UE
whose CSI is conveyed in that report. We want to include a unique ID (identification or
identifier) for each user so that the receiving node knows which ones among all the
reports that it receives, belong that user. This will be useful for RRM. Otherwise the
receiving eNB will regard each received report as belonging to a distinct user. This can
lead to sub-optimal resource allocation.
[0084] B2.3 eRNTP exchange
[0085] Our view on eRNTP exchange is captured in a corresponding proposal attached in
the end of this embodiment.
[0086] We note that the RNTP (i.e., downlink (DL) power restriction) for the first
subframe is always conveyed. If no information about the DL power restriction on any
subsequent subframe is conveyed, then the one conveyed for the first subframe can be
assumed to remain static (i.e., applicable over subsequent subframes).
[0087] We also present several variations, one of which includes the use of multiple
thresholds
[0088] B3. Conclusion
[0089] We discussed the necessary X2 message to support CSI and eRNTP exchange for
inter-eNB CoMP and presented corresponding proposals.
[0090] Proposals
[0091] 9.1.2.1 1 RESOURCE STATUS REQUEST
[0092] This message is sent by an eNBi to a neighbouring eNB2 to initiate the requested measurement
according to the parameters given in the message.
[0093] Direction: eNBi ® eNB2.
Table Bl
IE/Group Name Presenc Range IE type Semantics Criticalit Assigned
e and description y Criticality
referenc
e
Message Type M 9.2. 13 YES reject
eNB 1 M INTEGE Allocated by YES reject
Measurement ID R eNB -
( 1..4095,
)
eNB2 C-ifRegi INTEGE Allocated by YES ignore
Measurement ID strationR R eNB2
equestSt ( 1..4095,
op )
Registration M ENUME A value set to YES reject
Request RATED( "stop",
start, indicates a
stop, request to
) stop all cells
measuremen
ts.
Report 0 BITSTRI Each position YES reject
Characteristics NG in the bitmap
(SIZE(32 indicates
)) measuremen
t object the
eNB2 is
requested to
report.
First Bit =
PRB
Periodic,
Second Bit =
TNL load Ind
Periodic,
Third Bit =
HW Load Ind
Periodic,
Fourth Bit =
Composite
Available
Capacity
Periodic, this
bit should be
set to 1 if at
least one of
the First,
Second or
Third bits is
set to 1,
Fifth Bit =
ABS Status
Periodic, Xth
Bit = UE-CSI
Periodic.
Other bits
shall be
ignored by
the eNB2.
Cell To Report 1 Cell ID list for YES ignore
which
measuremen
t is needed
>Cell To 1 .. EACH ignore
Report Item
»Cell ID M ECGI
9.2. 14
Reporting 0 ENUME YES ignore
Periodicity RATED(
1000ms,
2000ms,
5000ms,
10000ms
, . . . )
Partial Success 0 ENUME Included if YES ignore
Indicator RATED( partial
partial success is
success allowed
allowed,
)
CSI 0 BITSTRI Each position YES ignore
Measurement NG in the bitmap
Report type (SIZE(2)) indicates the
type of CSI
measuremen
t to report.
First
bit=Rank,
Second
bit=subband
CQI .
((Reporting 0 ENUME Periodicity YES ignore
Periodicity of CSI RATED( for CSI
Measurement 5ms, Measuremen
Report 10ms, t Report
20ms,40 Periodic
ms,
80ms,
aperiodic
, . ..)
Range bound Explanation
maxCellineNB Maximum no. cells that can be served by an eNB. Value is
256.
Condition Explanation
ifRegistrationRequestStop This IE shall be present if the Registration Request IE is
set to the value "stop".
[0094] 9.1.2.14 RESOURCE STATUS UPDATE
[0095] This message is sent by eNB2 to neighbouring eNBl to report the results of the requested
measurements.
[0096] Direction: eNB2 ® e Bi .
Table B2
IE/Group Name Presen Range IE type Semantics Criticality Assigned
ce and description Criticality
reference
Message Type M 9.2. 13 YES ignore
eNB 1 M INTEGER Allocated by YES reject
Measurement ID ( 1..4095, . . . eNB -
)
eNB2 M INTEGER Allocated by YES reject
Measurement ID ( 1..4095, . . . eNB2
)
Cell 1 YES ignore
Measurement
Result
>Cell 1 .. EACH ignore
Measurement
»Cell ID M ECGI
9.2. 14
»Hardware 0 9.2.34
Load Indicator
»S1 TNL 0 9.2.35
Load Indicator
» Radio 0 9.2.37
Resource
Status
»Composite 0 9.2.44 YES ignore
Available
Capacity Group
»ABS Status 0 9.2.58 YES ignore
» UE-CSI 0 9.2.X1 YES ignore
Report
Range bound Explanation
maxCellineNB Maximum no. cells that can be served by an eNB. Value
is 256.
[0097] 9.2.xl UE-CSI Report
[0098] This IE provides UE-CSI information for a set of UEs served by eNB2.
Table B3
IE/Group Name Presence Range IE type and Semantics
reference description
UE subset CSI 1 ..
Report
>(C-RNTI) UE ID M BIT STRING (SIZE ID of the UE served by
( 16)) the cell in eNB2 .
Defined in TS 36.331 .
>UE-CSI process 1 ..
information
»Rank 0 BIT STRING (SIZE The rank indicator IE is
Indicator (3)) present only if it is
requested in the
associated request. In
that case Cf. TS 36.21 3
[7.2.3].
»Wideband M BIT STRING (SIZE Cf. TS 36.21 3 [7.2.3].
CQI For (4))
Codeword 0
»Wideband 0 BIT STRING (SIZE Cf. TS 36.21 3 [7.2.3].
CQI For (4))
Codeword 1
»Subband CQI 0.. CQI, which is always
chosen if associated
request does not want
subband CQI, or this IE
is present only if
associated request
wants subband CQI
»>Subband 0 BIT STRING (SIZE Cf. TS 36.21 3 [7.2.3].
CQI for (2))
codeword 0
»>Subband 0 BIT STRING (SIZE Cf. TS 36.21 3 [7.2.3].
CQI for (2))
codeword 1
»UE-CSI M FFS CSI process
process configuration
Configuration information.
information
[0099] Alternatively, the parameter maxUEsubsetCSIReport can be 8, 16, 32, 48, 64, or 256. Further,
optionally, the UE-ID can have a more compact representation using say 8bits or 6bits or 5 bits
(equivalently 256 or 64 or 32 possible indices from a configurable table).
[00100] Next, we consider the case when subband indices have to be indicated. This is important
to accommodate feedback modes that involve UE selected subband feedback.
Table B4
IE/Group Name Presence Range IE type and Semantics
reference description
UE subset CSI Report 1 ..

>C-RNTI M BIT STRING ID of the UE served by
(SIZE ( 16)) the cell in eNB2.
Defined in TS 36.331 .
>UE-CSI process 1 ..
information
»Rank Indicator 0 BIT STRING The rank indicator IE is
(SIZE (3)) present only if it is
requested in the
associated request. In
that case Cf. TS
36.21 3 [7.2.3].
»Wideband CQI For M BIT STRING
Codeword 0 (SIZE (4))
»Wideband CQI For 0 BIT STRING
Codeword 1 (SIZE (4))
»Subband CQI List .. if associated request
wants subband CQI
»>Subband CQI 0 BIT STRING
for codeword 0 (SIZE (4))
»>Subband CQI 0 BIT STRING
for codeword 1 (SIZE (4))
»>Subband index O INTEGER Included in case of UE
(0. .27, ...) selected subband CQI
reporting.

[00101] Note that as an alternative in the above tables, for each CQI the bit string field of 4 bits (2
bits) can be replaced by INTEGER (0.. 15, . ..) (INTEGER (0..7, . ..)).
[00102] In another alternative the sub band indices can be conveyed by means of a combinatorial
index which is described next.
[00103] The idea here is that depending on the number of PRBs (or RBs (resource blocks) for
short) in the downlink available at sending eNB2 (a parameter which is known or conveyed separately to
the receiving eNBl) , the set of all possible subband selections that can be made together with the
subband size, for all feedback modes, can be deduced by eNBl.
[00104] For example when 110 RBs are available at eNB2 (and this number is conveyed to
eNBl) eNBl can deduce that for a UE configured under:
[00105] Aperiodic, Mode 2-*: 6 UE selected subband indices
[00106] A subframe is composed of 28 subbands. Among 28 subbands, 6 subbands are selected
by the UE. The number of PRBs in the subbands is 4 except for the last one; the number of PRBs in the
last subband is 2 (4*27 + 2 = 110).
[00107] For Aperiodic, Mode 3-* : 14 higher layer-configured sub bands
[00108] A subframe is composed of 14 subbands. The number of PRBs in the subband is 8 except
for the last one; the number of PRBs in the last subband is 6 (8*13 + 6 = 110).
[00109] For Periodic, Mode 2-*: 4 UE selected subband indices (with an additional constraint on
choosing one sub band per bandwidth portion or part)
[001 10] A subframe is composed of 14 subbands. Among 14 subbands, 4 subbands are selected
by the UE. The number of PRBs in the subbands is 8 except for the last one; the number of PRBs in the
last subband is 6 (8*13 + 6 = 110).
[001 11] Then, considering all possible feasible subband selections under all the aforementioned
feedback modes, it is possible to assign a unique label to each distinct feasible selection of sub bands.
All possible such labels together decide the range of a combinatorial index R. As a result, knowing the
value of R the receiving eNBl can deduce the subband selection. The associated CQIs (one for each
subband in the indicated selection) can be ordered in the increasing order of the frequency range
represented by the indicated subbands. Each such CQI can be conveyed using full representation (i.e.,
using 16 possibilities) which can then be directly used by the receiving eNBl .
Table B5
IE/Group Name Presence Range IE type and Semantics
reference description
UE subset CSI Report 1 ..

>C-RNTI M BIT STRING ID of the UE
(SIZE ( 16)) served by the cell
in eNB2.
Defined in TS
36.331 .
>UE-CSI process 1 ..
information
»Rank Indicator 0 BIT STRING The rank indicator
(SIZE (3)) IE is present only if
it is requested in
the associated
request. In that
case Cf. TS 36.21 3
[7.2.3].
»Wideband CQI For M BIT STRING
Codeword 0 (SIZE (4))
»Wideband CQI For 0 BIT STRING
Codeword 1 (SIZE (4))
» combinatorial O Integer FFS This IE is present
index only if associated
request wants
subband CQI
»>Subband CQI List 0.. subbands in the list
as well as their
respective indices
and sizes are
deduced from the
combinatorial index.
»»Subband CQI M BIT STRING
for codeword 0 (SIZE (4))
»»Subband CQI 0 BIT STRING
for codeword 1 (SIZE (4))
»UE-CSI process M FFS CSI process
Configuration configuration
information information.
[001 12] UE configuration independent coding structure
[001 13] A coding structure for signaling CSI over X2 in a UE-configuration independent way is
shown in Table I I . In this structure, a subband is defined as a set of contiguous PRBs having the same CQI
value. The subband partitioning is left to the sending eNB2 implementation, and is not restricted by the
UE's CSI reporting configuration. Each indicated CQI follows the definition of a 4 bit CQI (Cf. TS
36.213). This allows for the sending eNB2 to process the CSI it receives from the UE in any manner as
long as each indicated CQI is consistent with the basic CQI definition. The receiving eNBl can directly
use these CQIs while being agnostic to how they were procured and processed by eNBl .
Table B6 UE configuration independent coding structure
IE/Group Name Presence Range IE type and Semantics description
reference
CSI per UE 1..
>C-RNTI M BIT STRING
(SIZE ( 16))
>CSI per Interference 1..
»lnterference Hypothesis M [FFS]
Information
»Wideband CQI for M INTEGER(0..1 5,
Codeword 0 ...)
»Wideband CQI for O INTEGER(0..1 5,
Codeword 1 ...)
»Rank Indication M INTEGER(1 ..8,..) Defined in TS 36.21 3 [ 1 1] .
»Subband CQI List 0.. Subbands are listed in the
frequency.
»>Subband Start O INTEGER(0.. 109 PRB number of the first
, ...) PRB in the subband. If this
IE is not present, the
subband is contiguous with
the previous subband in the
list, or starts with PRB 0 if
this is the first subband in
the list.
»>Subband Size O INTEGER(1 ..110 Number of contiguous
, ...) PRBs in the subband. If this
IE is not present, the value
is the same as the previous
subband in the list.
»>Subband CQI for M INTEGER(0..1 5,
Codeword 0 ...)
»>Subband CQI for O INTEGER(0.. 15,
[001 14] We note here that reporting full (complete) CQI (with 16 possibilities) for each indicated
subband CQI instead of differential CQI is useful since otherwise the receiving eNBl may not know how
to combine a corresponding wideband CQI and differential sub-band CQI (with fewer than 16
possibilities) in order to obtain the full CQI for that subband, for instance, in the case that the precise
feedback mode configured for the UE of interest under that CSI process is not conveyed to the receiving
eNBl .We note here also that it might be desirable to not impose restrictions on sending eNB2 on how it
combines reports from multiple different feedback modes configured for that UE under the same CSI
process. Then, note that when aperiodic feedback mode 3-1 is configured for the UE (by eNB2), the UE
reported sub band CQI is encoded differentially with respect to the corresponding wideband CQI using 2
bits representing differential values {-2, 0, 1, 2}. On the other hand, in the case of aperiodic feedback
mode 2-0 or 2-2, only the best M-average is reported by the UE by differentially encoding it with respect
to a corresponding wideband CQI using 2 bits representing differential values {1, 2, 3, 4 }. Further, in case
of periodic feedback mode 2-1 the CQI corresponding to codeword- 1 for each UE selected subband within
a bandwidth part can itself be of 4 bits, whereas that of codeword-2 (when RI>1) is differentially encoded
with respect to CQI of codeword- 1 using 3 bits.
[001 15] It becomes apparent from the above discussion that a transparent way of conveying CQI
(without having to convey all details regarding to one or more feedback modes configured under that CSI
process for that UE) is to allow for full (complete) CQI for each indicated subband.
[001 16] Another issue that is important, is to ensure that the RI and CQIs conveyed by eNB2 to
eNBl in a UE CSI report are mutually consistent, i.e., all the reported CQIs are computed by the UE for
the same RI (which is identical to the one in the Rank Indication IE when the latter is present). This issue
is important to address because under certain feedback modes (such as periodic mode 2-1) the RI and the
wideband CQI(s) as well as the subband CQI(s) for one or more bandwidth portions can be reported by the
UE on different subframes. Thus, depending on the periodicity defined by eNBl in its CSI request, it can
happen that the latest RI available for the UE under the CSI process, can be different from the one for
which the most recent CQI(s) are computed. In such a case, the sending eNB2 should ensure that its CSI
report is consistent, for instance by using the RI value for which the most recently available CQI(s) have
been computed.
[001 17] The variation (which allows the requesting eNB to specify whether or not it wants to
receive subband CQI(s) or Rank Indication is provided below. In this context, we note that since the
requesting eNBl has no control over how eNB2 configures CSI processes (and constituent feedback
modes) for its users, it should be in any case able to exploit different type of CSI reports (wideband only or
wideband and subband).
Table B7
IE/Group Name Presence Range IE type and Semantics description
reference
CSI per UE 1..
>C-RNTI M BIT STRING
(SIZE ( 16))
>CSI per Interference 1..
»lnterference M [FFS]
Hypothesis Information
»Wideband CQI for M INTEGER(0. .1
Codeword 0 5 ,...)
»Wideband CQI for 0 INTEGER(0. .1
Codeword 1 5 ,...)
»Rank Indication 0 INTEGER(1 ..8 The rank indication IE is
) present only if it is
requested in the
associated request. In
that case it follows the
definition in TS 36.21 3
[ 1 11-
»Subband CQI List 0.. This IE is present only if
wants subband CQI . In
that case subbands are
listed in the order of
increasing frequency.
»>Subband Start 0 INTEGER(0.. 1 PRB number of the first
09, ...) PRB in the subband. If
this IE is not present,
the subband is
contiguous with the
previous subband in the
list, or starts with PRB 0
if this is the first
subband in the list.
»>Subband Size 0 INTEGER(1 ..1 Number of contiguous
10 , ...) PRBs in the subband. If
this IE is not present,
the value is the same as
the previous subband in
the list.
»>Subband CQI for M INTEGER(0. .1
Codeword 0 5 , ...)
»>Subband CQI for 0 INTEGER(0. .1
Codeword 1 5 , ...)
[00 118] Another variation which allows for further simplification at the expense of not being bit
efficient is as follows. Here the full CQIs for all possible subbands (which can be determined by the
number of PRBs in the downlink available at eNB2) are always conveyed for a UE under the CSI
process. In case the sub band CQI is not reported by a UE under the configured feedback mode for a
subband, the sending eNB2 simply uses the corresponding wideband CQI value for that subband. Then,
note that there is no need to include the wideband CQI(s) in case the associated request wants subband
CQI.
[00 119] 9.2. 19 Relative Narrowband Tx Power (RNTP)
[00120] This IE provides an indication on DL power restriction per PRB in a cell and other
information needed by a neighbour eNB for interference aware scheduling.
Table B8
IE/Group Presence Range IE type Semantics Criticality Assigned
Name and description Criticality
reference
RNTP Per M BIT Each position in
PRB STRING the bitmap
(6. .110 , represents a nPRB
) value (i.e. first
bit=PRB 0 and so
on), for which the
bit value
represents RNTP
(npRB), defined in
TS 36.21 3 [ 1 1] .
Value 0 indicates
"Tx not exceeding
RNTP threshold".
Value 1 indicates
"no promise on the
Tx power is
given".
This IE is used to
indicate DL power
restriction per
PRB for the first
subframe. In case
the DL power
restriction is static,
the indicated DL
power restriction
is maintained over
the subsequent
subframes.
RNTP M ENUMER RNTPthreshold s
Threshold ATED (-¥, defined in TS
- 11, - 10 , 36.2 13 [ 1 1] .
-9, -8, -7,
-6, -5, -4,
-3, -2, - 1,
0 , 1, 2 , 3 ,
)
Number Of M ENUMER P (number of
Cell-specific ATED ( 1 , antenna ports for
Antenna 2 , 4 , ...) cell-specific
Ports reference signals)
defined in TS
36.2 11 [ 10]
P_B M INTEGER PB is defined in TS
(0..3, ...) 36.2 13 [ 1 1] .
PDCCH M INTEGER Measured by
Interference (0..4, ...) Predicted Number
Impact Of Occupied
PDCCH OFDM
Symbols (see TS
36.2 11 [ 10]).
Value 0 means
"no prediction is
available".
Extended M or O BIT Each position in
RNTP Per STRING the bitmap
PRB (6. .4290, represents a PRB
) in a subframe, for
which value " 1"
indicates
'interference
protected
resource' or 'no
promise on the Tx
power is given'
and value "0"
indicates
'resource with no
utilization
constraints' or 'Tx
not exceeding
RNTP threshold.'
The first bit
corresponds to
PRB 0 of the
second or first
subframe for
which the
extended RNTP
per PRB IE is
valid , the second
bit corresponds to
PRB 1 of the
second or first
subframe for
which the
extended RNTP
per PRB IE is
valid, and so on.
The length of the
bit string is an
integer (maximum
39) multiple of
Nm is
defined in TS
36.2 11 [ 10].
The bit string may
span across
multiple
contiguous
subframes.
The pattern
across contiguous
subframes
(formed by RNTP
per PRB and
extended RNTP
per PRB) is
continuously
repeated.
RNTP per 0.. 1
PRB start
time
>Starting M or 0 INTEGE Number of the first
SFN R system frame from
(0. .1023, which the RNTP Per
) PRB {PerSubframe)
IE is valid or SFN
of the radio frame
containing the first
subframe when the
RNTP Per PRB IE is
valid.
>Starting M or 0 INTEGE Index of the first
Subframe R (0..9, subframe from
Index ) which the RNTP Per
PRB {PerSubframe)
IE is valid or
Subframe number,
within the radio
frame indicated by
the Start SFN IE, of
the first subframe
when the RNTP Per
PRB IE is valid.
121] An alternate Table for RNTP enhancement is given below.

What is claimed is:
1. In a wireless communications system including a first base station and a second
base station, a wireless communications method implemented in the first base station
supporting coordinated multi-point transmission and reception (CoMP), the wireless
communications method comprising:
for a given user equipment (UE) identification (ID) and a given channel state
information (CSI) process, receiving from the second base station a plurality of CSI reports
each of which comprises a rank indication (RI) and a channel quality indicator (CQI),
wherein the second base station receives from one or more user equipments (UEs)
RI and CQI information.
2. The wireless communications method as in claim 1, further comprising:
performing resource allocation based on the RI and the CQI.
3. In a wireless communications system including a first base station and a second
base station, a wireless communications method implemented in the second base station
supporting coordinated multi-point transmission and reception (CoMP), the wireless
communications method comprising:
receiving from one or more user equipments (UEs) rank indication (RI) and channel
quality indicator (CQI) information; and
for a given user equipment (UE) identification (ID) and a given channel state
information (CSI) process, transmitting to the first base station a plurality of CSI reports
each of which comprises an RI and a CQI.
4. The wireless communications method as in claim 1 or 3,
wherein the number of the plurality of CSI reports is up to 2.
5. The wireless communications method as in claim 1 or 3,
wherein each of the RI and the CQI can be different for the plurality of CSI reports.
6. The wireless communications method as in claim 1 or 3,
wherein, for each CSI report, the RI corresponds to the CQI being reported.
7. The wireless communications method as in claim 1 or 3,
wherein, in each CSI report, the RI and the CQI are mutually consistent.
8. The wireless communications method as in claim 1 or 3,
wherein each of the plurality of CSI reports further comprises a subband index.
9. The wireless communications method as in claim 8,
wherein a maximum number of subbands is 14 and the subband index takes an
integer of 0 to 27.
10. The wireless communications method as in claim 1 or 3,
wherein the plurality of CSI reports further comprises a subband CQI consisting of
4-bits for codeword 1.
11. The wireless communications method as in claim 1 or 3,
wherein the plurality of CSI reports are transmitted according to an information
element (IE) comprising:
and
12. A first base station supporting coordinated multi-point transmission and reception
(CoMP) and used in a wireless communications system, the first base station comprising:
a receiver to receive from a second base station, for a given user equipment (UE)
identification (ID) and a given channel state information (CSI) process, a plurality of CSI
reports each of which comprises a rank indication (RI) and a channel quality indicator
(CQI),
wherein the second base station receives from one or more user equipments (UEs)
RI and CQI information.
13. The first base station as in claim 12, further comprising:
a controller to perform resource allocation based on the RI and the CQI.
14. A second base station supporting coordinated multi-point transmission and
reception (CoMP) and used in a wireless communications system, the second base station
comprising:
a receiver to receive from one or more user equipments (UEs) rank indication (RI)
and channel quality indicator (CQI) information; and
a transmitter to transmit to a first base station, for a given user equipment (UE)
identification (ID) and a given channel state information (CSI) process, a plurality of CSI
reports each of which comprises an RI and a CQI.
15. The second base station as in claim 14,
wherein the number of the plurality of CSI reports is up to 2.
16. The second base station as in claim 14,
wherein each of the RI and the CQI can be different for the plurality of CSI reports.
17. The second base station as in claim 14,
wherein, for each CSI report, the RI corresponds to the CQI being reported.
18. The second base station as in claim 14,
wherein, in each CSI report, the RI and the CQI are mutually consistent.
19. The second base station as in claim 14,
wherein each of the plurality of CSI reports further comprises a subband index.
20. The second base station as in claim 19,
wherein a maximum number of subbands is 14 and the subband index takes an
integer of 0 to 27.
2 1. The second base station as in claim 14,
wherein the plurality of CSI reports further comprises a subband CQI consisting of
4-bits for codeword 1.
22. The second base station as in claim 14,
wherein the plurality of CSI reports are transmitted according to an information
element (IE) comprising:
and
23. A wireless communications method implemented in a wireless communications
system supporting coordinated multi-point transmission and reception (CoMP) and
including a first base station and a second base station, the wireless communications
comprising:
transmitting from one or more user equipments (UEs) to the second base station
rank indication (RI) and channel quality indicator (CQI) information; and
for a given user equipment (UE) identification (ID) and a given channel state
information (CSI) process, transmitting from the second base station to the first base station
a plurality of CSI reports each of which comprises an RI and a CQI.
24. A wireless communications system supporting coordinated multi-point transmission
and reception (CoMP), the wireless communications system comprising:
a first base station;
a second base station transmitting to the first base station, for a given user
equipment (UE) identification (ID) and a given channel state information (CSI) process, a
plurality of CSI reports each of which comprises a rank indication (RI) and a channel
quality indicator (CQI); and
one or more user equipments (UEs) transmitting to the second base station RI and
CQI information.