METHOD AND SYSTEM FOR NETWORKASSISTED
INTERFERENCE SUPPRESSION/CANCELATION
Technical Field
[0001] The present invention relates generally to a radio communication system and, more
specifically, to techniques of interference suppression/cancellation in downlink co
ordinated multi-point (CoMP) transmission.
Background Art
[0002] Coordinated multi-point transmission/reception is considered in LTE (Long Term
Evolution)-Advanced Release 1l(Rel. 11) as a tool to improve the coverage of high
data rates, the cell-edge throughput, and also to increase the system throughput as
described in the Sect. 4 of NPLl.
[0003] The CoMP schemes, joint transmission (JT), dynamic point selection (DPS), and co
ordinated scheduling/coordinated beamforming (CS/CB) have been agreed to be
supported as described in the Sect. 5.1.3 of NPLl. For JT, multiple transmission points
(TPs) are selected for simultaneous data transmission and the interference comes from
the points other than the selected TPs. For DPS, only one TP is dynamically selected
and the interference comes from the points other than the only selected TP. While, for
CB/CS, the serving point is the only TP to transmit data but the strong interference
from the neighbor cell is reduced significantly.
[0004] In NPL2, a set of channel state/statistical information-reference signal (CSI-RS)
resources is defined as a CoMP resource management set (CRMS), for which CSI-RS
received signal measurement can be made and reported. Within the CRMS, a CoMP
measurement set (CMS) is defined in the Sect. 5.1.4 of NPLl as a set of points about
which CSI related to their link to a user equipment (UE) is measured and/or reported.
[0005] As illustrated in Fig. 1, it is assumed that Macro eNB and low power nodes LPN1
and LPN2, connected by optical fiber (backhaul), are grouped into a CoMP co
operating set for centralized scheduling at Macro eNB. Fig. 1 shows a case where
UEl's CMS includes its serving point LPN1 and neighbor point Macro eNB; while
UE2's CoMP measurement set includes only its serving point LPN2.
[0006] For the CRMS and CMS decision, the long-term measurements of received reference
signals are made and reported by UE to its serving cell. For example, the reference
signal received power (RSRP) defined in Sect. 5.1.1 of NPL3, is used for the CRMS
and CMS decision. For example, as shown in Fig. 2, only the neighbor point satisfying
that the difference between serving cell's RSRP, RSRPse , and neighbor cell's RSRP,
RSRP e g , is smaller than a pre-defined threshold THRS will be included in the
CRMS, i.e., RSRPse - RSRP e < THRS . From the CRMS, the maximum 3 top points
in the RSRP ranking list are selected in the CMS for downlink CoMP in LTE Rel. 11.
[0007] In NPL4, for RRC-related aspects of the agreements reached in LTE RANI for
downlink CoMP in LTE Rel. 11, a Rel. 11 UE can be configured to report one or more
CSI processes per component carrier. Each CSI process is configured by the a s
sociation of channel part, one non-zero power CSI-RS resource in the CMS, and in
terference part, one Interference Measurement Resource (CSI-IM) which occupies 4
REs that can be configured as a single zero power CSI-RS configuration. For CoMP,
the CSI processes considering the interference power with or without muting on
different cells in the CMS need to be estimated at UE side. The obtained channel state
information (CSI), such as precoding vector index (PMI), rank index (RI) and channel
quality index (CQI), is used for channel-dependent scheduling to support the variable
CoMP schemes among multiple coordinated points in the CMS. In the present speci
fication, a point for coordinated multi-point transmission/reception can be used as a
technical term including a cell, base station, Node-B, eNB, remote radio equipment
(RRE), distributed antenna, and the likes.
[0008] In LTE Rel. 11, besides the CSI-process configuration for CSI measurement and
reporting, it was also agreed that the specification would provide signaling to indicate
the cell-specific reference signal (CRS) position of at least one cell from which
PDSCH transmission may occur, as well as the quasi-co-location assumption on
DMRS. Up to 4 sets (states) per CC of PDSCH RE mapping and quasi-co-location
(PQL) parameters can be configured using RRC signaling and indicated by downlink
control information (DCI) format 2D. Each set that can be signaled in DCI format 2D
for TM10 corresponds to a higher- layer list of the parameters listed in Table 5 in
NPL4.
[0009] As illustrated in Fig. 3, the dense small cell scenarios in Heterogeneous Network
(HetNet) are considered with large number of low power nodes (LPNs) and/or smaller
inter-point distance in LTE Rel. 12. As the number of LPNs increases, the inter-point
interference becomes significant, resulting in performance degradation.
[0010] As mentioned before, the maximum 3 points in the CRMS can be included in the
CMS if their RSRP satisfying RSRPse - RSRP e < THRS . Within the CMS, the
limited number of points can be selected as transmission points (TPs) or CS/CB points
to improve the spectrum efficiency at the transmitter side. For example, 2 TPs are
selected for JT; one TP is selected for DPS; and one point is selected for CS/CB.
[001 1] However, as illustrated in Fig. 4, strong precoded interferences from the following
two types of points may result in significant degradation of user throughput:
Type_l: A point in the CMS, which is not selected as a TP or a CS/CB point, may
dynamically result in strong interference to a CoMP UE, e.g., Point 2 in the CMS of
Points 0, 1 and 2 in Fig. 4; and
Type_2: A point outside the CMS, which has high RSRP, may dynamically result in
strong interference to a CoMP UE, e.g., Point 3 outside the CMS of Points 0, 1 and 2
in Fig. 4.
[0012] In Fig. 4, assuming that Points 0 and 1 are both selected for synchronized joint
transmitting the data of the target UEO, the UE 30 receives the data based on minimum
mean square error (MMSE) criterion by using the estimated channel matrix as follows.
Assuming Xs is the transmit data signal to the target UEO in the frequency domain, X
is the frequency-domain interfering data signal of the other UE, the received
frequency-domain signal Y can be written by the following equation (1):
Math.l
[0013]
Y (H + + H . C . + N -- ( 1) .
i ¹ , l
Hereafter, H-circumflex ( ) as in the above equation (1) is denoted by FT for con
venience in writing. In the equation (1), F is the precoded channel matrix at the point
i and N is Additive White Gaussian Noise (AWGN). The signal data X~
s can be
estimated by using the MMSE weight WS
MMSE according to the following equation (2):
Math.2
[0014] ~ MMSE
wherein s + is
the average noise and interference. Hereafter, X-tilde, H-tilde (~) as in the above
equation (2) are respectively denoted by X~ , H~ for convenience in writing. In the
equation (2), H~
s is the estimated equivalent channel which is nearly equal to H 0 + H
[0015] At this moment, Point 2 in the CMS is not selected (type_l point) and therefore, the
transmission of the other UE's data at Point 2 may result in the strong interference to
the target UEO. Also the interference from Point 3, which has high RSRP but not
included the CMS (type_2 point) may also reduce the SINR of the target UE.
Citation List
Patent Literature
[0016] NPL 1: 3GPP TR 36.819 v l 1.0.0, Coordinated multi-point operation for LTE physical
layer aspects (Release 11). http://www.3gpp.org/ftp/Specs/archive/36_series/36.819/.
[0017] NPL 2: Rl-123077, LS on CSI-RSRP and CoMP Resource Management Set,
(http://www.3gpp.org/ftp/tsg_ranAVGl_RLl/TSGRl_69/Docs/)
[0018] NPL 3: 3GPP TR 36.214 vl 1.0.0, Physical Channels and Modulation of Evolved
Universal Terrestrial Radio Access (E-UTRA); Physical layer; Measurements (Release
11). http://www.3gpp.org/ftp/Specs/archive/36_series/36.214/.
[0019] NPL 4: Rl-124669, RRC Parameters for Downlink CoMP
[0020] NPL 5: Ohwatari, Y., Miki, N., and et. al., "Performance of Advanced Receiver
Employing Interference Rejection Combining to Suppress Inter-Cell Interference in
LTE-Advanced Downlink", IEEE VTC-Fall, 2011.
[0021] NPL 6: Hui, A.L.C.; Letaief, K.B., "Successive interference cancellation for multiuser
asynchronous DS/CDMA detectors in multiplath fading links", IEEE Transaction on,
Page, 384-391, vol. 46, Issue 3, 1998.
Summary
Technical Problem
[0022] To combat with the interference from the point of the above-mentioned type_l, that
is, a point inside CMS, a simple solution is to increase the number of selected TPs for
JT or CS/CB points to improve the user throughput of the CoMP UE. However, the
improvement for the CoMP UE costs the resources at such a point for other UEs,
resulting in the degradation of the other UEs' user throughput.
[0023] To consider the interference from the point of the above-mentioned type_2, that is, a
point outside CMS, a simple solution is to increase the number of points in the CMS.
The dynamic channel state information (CSI) of such a point with high RSRP can be
measured and reported from UE to the network to be considered for CoMP scheduling.
However, for the CMS with larger number of points, the corresponding reference
signals needs complicated network configuration as well as large signaling overhead.
Also it is harder to handle the coordinated scheduling for a CMS with a larger size.
[0024] Instead of employing CoMP at the transmitter, an advanced receiver with in
terference suppression (IS) or interference cancellation (IC) has been proposed to
improve the performance. The interference suppression (IS) is made by using in
terference rejection combining (IRC) in NPL5 and the interference cancellation (IC) is
made by generating interference replica in NPL6. In NPL6, the channel estimation of
the interfering signals is assumed ideally known to achieve good IC performance. In
NPL5, without the knowledge of the interfering channel, the correlation of the overall
interferences plus AWGN is directly calculated by using the received data and the
target UE's DM-RS. However, the performance of IRC receiver in NPL5 is evaluated
assuming the Gaussian-distributed inter-cell interference and the channel estimation
error may severely degrade the performance due to the limited average number of
samples. In the real environment, the inter-cell interference may not follow Gaussian
distribution, especially from the point close to the transmission point. Therefore,
without the knowledge of the strong interference from the specific point, such as the
point of type_l or type_2, the performance improvement by IS/IC is limited.
Solution to Problem
[0025] An object of the present invention is to provide a method and system which can
achieve effective interference suppression/cancelation in downlink coordinated multi
point (CoMP) transmission.
[0026] According to the present invention, a radio communication system has a network
including multiple points which is capable of communicating with a user equipment,
wherein the network signals the user equipment of information related to an interfering
point for interference suppression or cancelation at the user equipment, wherein the in
terfering point is a candidate for a coordinated multi-point measurement set of the user
equipment but not selected for any coordinated multi-point scheme.
According to the present invention, a user equipment in a network including multiple
points wherein the user equipment is capable of communicating with the multiple
points, includes: a radio transceiver for communicating with at least one of the multiple
points; and a receiver for receiving data from the network with suppressing or
canceling interference from an interfering point based on information related to the in
terfering point, wherein the interfering point is a candidate for a coordinated multi
point measurement set of the user equipment but not selected for any coordinated
multi-point scheme.
According to the present invention, a scheduler in a radio communication system
comprising a network including multiple points which is capable of communicating
with a user equipment, includes: an interference information configuring section for
configuring information related to an interfering point which is a candidate for a co
ordinated multi-point measurement set of the user equipment but not selected for any
coordinated multi-point scheme; and a communication section for sending the in
formation related to the interfering point to the user equipment for interference sup
pression or cancelation at the user equipment.
According to the present invention, a communication control method in a radio com
munication system comprising a network including multiple points which is capable of
communicating with a user equipment, includes the steps of: selecting an interfering
point as a candidate for a coordinated multi-point measurement set of the user
equipment but not selected for any coordinated multi-point scheme; and signaling from
the network to the user equipment information related to the interfering point for in
terference suppression or cancelation at the user equipment.
Advantageous Effects of Invention
[0027] According to the present invention, effective interference suppression/cancelation at
a user equipment can be made in downlink coordinated multi-point (CoMP)
transmission.
[0028] For a more complete understanding of the present disclosure and its advantages,
reference is now made to the following description taken in conjunction with the ac
companying drawings, in which like reference numerals represent like parts:
Brief Description of Drawings
[0029] [fig. 1]Fig. 1 is a schematic diagram illustrating a radio communication system for ex
planation of CoMP cooperating set and CoMP measurement set.
[fig.2]Fig. 2 is a diagram illustrating RSRP for each cell for explanation of RSRPbased
decision of CoMP measurement set.
[fig.3]Fig. 3 is a schematic diagram illustrating interference variations in a con
ventional radio communication system.
[fig.4]Fig. 4 is a schematic diagram illustrating interferences from transmission points
inside CMS and outside CMS in a conventional radio communication system.
[fig.5]Fig. 5 is a diagram illustrating a sequence of interference suppression/can
celation in a radio communication system according to an embodiment of the present
invention.
[fig.6]Fig. 6 is a schematic diagram illustrating a radio communication system with
centralized scheduling scheme according to an embodiment of the present invention.
[fig.7]Fig. 7 is a schematic diagram illustrating a radio communication system with
distributed scheduling scheme according to an embodiment of the present invention.
[fig.8]Fig. 8 is a schematic diagram illustrating a radio communication system
according to a first exemplary embodiment of the present invention.
[fig.9]Fig. 9 is a function block diagram illustrating the advanced receiver with IS
function in the radio communication system according to the first exemplary em
bodiment of the present invention.
[fig. 10] Fig. 10 is a diagram illustrating a sequence of the signaling for dynamic
network-assisted interference suppression or cancellation (IS/IC) at the UE receiver
according to the first or the second example of the present invention.
[fig. 1l]Fig. 11(A) and Fig. 11(B) are diagrams illustrating a table of PQL states and a
table of PQI which are used in the signaling as shown in Fig. 9.
[fig.l2]Fig. 12(A) and Fig. 12(B) are diagrams illustrating a table of DM-RS indicator
per RBG and a table of layer indicator per RBG which may be used in the signaling as
shown in Fig. 10.
[fig.l3]Fig. 13 is a schematic diagram illustrating a radio communication system
according to a second exemplary embodiment of the present invention.
[fig. 14] Fig. 14 is a function block diagram illustrating the advanced receiver with IC
function in the radio communication system according to the second exemplary em
bodiment of the present invention.
[fig.l5]Fig. 15 is a diagram illustrating a table of modulation indicator per RBG which
is used in the signaling of the system as shown in Fig. 13.
Detailed Description
[0030] Embodiments and examples of the present invention will be explained by making
references to the accompanied drawings. The embodiments and examples are used to
describe the principles of the present invention by way of illustration only and should
not be construed in any way to limit the scope of the disclosure. Those skilled in the art
will understand that the principles of the present disclosure may be implemented in any
suitably arranged wireless network. In this technical area, a point and a cell may have
same meaning, so serving point, cooperating point and neighbor point can be in
terpreted as serving cell, cooperating cell and neighbor cell, respectively.
[0031] 1. Exemplary embodiment
Assuming the case of a network composed of a plurality of transmission points
where interferences from some transmission points occur at a user equipment (UE) as
shown in Fig. 4, network-assisted interference suppression/cancelation according to an
exemplary embodiment of the present invention will be described by referring to Fig.
5.
[0032] In Fig. 5, the network decides which transmission point within the CRMS belongs to
a CMS of the UE based on reception power information (e.g. RSRP) received from the
UE as a response to each cell-specific RS (Operation S_A). For the point(s) in CMS,
the network sends the information for the CSI feedback (Operation S_B). Based on the
UE CSI feedback, the network performs the coordinated scheduling (Operation S_C).
According to the results of CMRS/CMS decision or coordinated resource allocation,
the network can select an interfering point which is included in the CRMS but not
selected for any CoMP scheme, e.g., JT, DPS, or CS/CB (Operation S_D). Thereafter,
the network sends information related to the reference signal used by the selected in
terfering point to the UE (Operation S_E). The UE detects data sent from a
transmission point selected for a CoMP scheme with suppressing/canceling inter
ferences from the selected interfering point (Operation S_F).
[0033] Specifically, the network provides the signaling to indicate the reference signal used
at a selected interfering point, which is included in the CRMS but neither selected for
data transmission nor CS/CB. The reference signal used at the selected interfering
point is used for dynamic network-assisted interference suppression or cancellation
(IS/IC) at the UE receiver. In the case of interference-limited dense small cell
scenarios, the spectrum efficiency can be improved at the price of small signaling
overhead.
[0034] The coordinated scheduling according to the exemplary embodiment can be im
plemented in a centralized scheduling system as shown in Fig. 6 or a distributed
scheduling system as shown in Fig. 7. In other words, the functions of the centralized
scheduling can also be distributed into multiple nodes.
[0035]
Referring to Fig. 6, it is assumed for simplicity that the centralized scheduling system
includes a predetermined radio node (Macro eNB) and multiple radio nodes (N2-N4).
Here, the Macro eNB is connected to nodes N2-N4 through backhaul links (BLs) re
spectively and user equipments UE1-UE4 are served by the Macro eNB and the nodes
N2-N4, respectively. The Macro eNB plus nodes N2-N4 are regarded as a CoMP co
operating set. The Macro eNB is provided with a centralized scheduler, which
performs the CRMS and CMS decision, reference signal (RS) and PQL configuration
as well as coordinated resource allocation for all UEs in the CoMP cooperating set.
The details of the coordinated scheduling in the centralized scheduling system will be
described later.
[0036]
Referring to Fig. 7, it is also assumed for simplicity that the distributed scheduling
system includes multiple radio nodes (Macro eNB, nodes N2-N4). Here, the Macro
eNB is connected to nodes N2-N4 through BLs and N2-N4 are also connected to each
other through BLs. The user equipments UE1-UE4 are served by the Macro eNB and
the nodes N2-N4, respectively. In the distributed scheduling system, not only the
Macro eNB but also each of the nodes N2-N4 is provided with a distributed scheduler,
which is capable of communicating with other distributed schedulers. Each distributed
scheduler performs the coordinated scheduling for its serving UE. For instance, the dis
tributed scheduler at the Macro eNB performs control for CRMS and CMS decision
for UE1, RS configuration as well as resource allocation coordinated among the
neighbor nodes (here, N3) in the UEl's CMS. Similarly, the distributed scheduler at
the node N2 performs control for CRMS and CMS decision for UE2, RS and PQL con
figuration as well as resource allocation coordinated among the neighbor nodes. The
coordinated information among the serving node N2 and the point Macro eNB in the
UE2's CMS is exchanged over backhaul link. A backhaul link can be optical fiber,
DSL, X2 backhaul or wireless link, such as LOS or NLOS microwave.
[0037] Hereafter, several examples of the present invention will be explained taking as an
example the case of the centralized scheduling. As described above, the functions of
the centralized scheduling can also be implemented in the distributed scheduling
system.
[0038] 1. First Example
A first example of the exemplary embodiment is used to suppress interference from a
point inside or outside the CMS. A system according to the first example is shown in
Figs. 8 and 9. An operation of the present example is illustrated in Fig. 10.
[0039] 1.1) System structure
As illustrated in Fig. 8, a centralized scheduler 100 is located in Macro eNB 10 to
control all the LPNs, LPNO-LPNn, which are connected to the Macro eNB 10 through
respective backhaul link (BL). The centralized scheduler 100 includes a CRMS and
CMS decision section 101, a RS configuration section 102, a resource allocation
section 103, a PQL configuration section 104, a IS configuration section 105, and a
controller 106. The CRMS and CMS decision section 101 is in charge of deciding on
which point is included in the CRMS and CMS respectively based on the UE reported
RSRP. In RS configuration section 102, the CSI-RS and DM-RS are respectively
configured for the channel estimation and data demodulation for each UE in the CoMP
cooperating set. The resource allocation section 103 is used to allocate each resource
block for each point to the UE based on the UEs' CSI feedback. The PQL con
figuration section 104 is used to configure several states for a CoMP candidate UE to
correctly implement PDSCH resource element rate matching as well as channel e s
timation based on quasi-co-location information. All those blocks are connected to the
controller 106.
[0040] The configured RS and PQL states as well as the scheduling results are sent from a
backhaul TX/RX section 107 of the Macro eNB 10 to the backhaul TX/RX section 201
of each LPN through a corresponding backhaul link. At the serving point LPN0 of the
target UE 30, data and reference signals (RS) are generated by a data and RS
generation section 202 and 203, respectively and transmitted from the RF TX/RS
section 204 to the UE 30.
[0041] The UE 30 is composed of a RF TX/RX section 301, a channel measurement and
feedback controller 302, an advanced receiver 303 which has Interference Suppression
(IS) function, and an interfering channel measurement section 304. The signal channel
matrix between each transmission point and the UE 30 is estimated by the channel
measurement and feedback controller 302 based on the RS received at RF TX/RX
section 301. While, the interfering channel matrix between the interfering point and the
UE 30 is estimated by the interfering channel measurement section 304. Based on the
estimated signal and interfering channel matrixes, the data is received by using the
estimated channel matrix at the advanced receiver 303 based on minimum mean square
error with interference rejection combining (MMSE-IRC).
[0042] Referring to Fig. 9, the advanced receiver 303 receives the frequency-domain signal
Y at the RF TX/RX section 301 to output the signal data X~
s which is estimated by
using the MMSE-IRC weight WS
MMSE IRC according to the following equation (3):
Math.3
[0043] - _ - MMSE - IRC
H
with s = — — --· ( 3 ) ,
+ H + s +!
wherein s N+ , is
the average noise and average interferences except the interference from the in
terfering point.
[0044] In the equation (3), is the precoded channel of an interfering point and H~
s is the
precoded channel of a signal transmission point. In order to estimate the precoded
channel of the interfering point, with reality, the MMSE-IRC receiver 303 requires
the information of reference signal for the interfering point.
[0045] In case of centralized scheduling, the centralized scheduler 100 only needs to send
the dynamic scheduling results of the interfering point over backhaul links to the
serving point LPNO to decide the new DCI signaling for IS. However, in case of dis
tributed scheduling, the serving point LPNO should inform the interfering point to
trigger or stop the reporting of the dynamic scheduling results for IS.
[0046] 1.2) Operation
Referring to Fig. 10, at the Macro eNB 10, the RS generation section 108 generates
the cell-specific RS (CRS) and sends it to the target UE 30 through the RF RX/TX
section 110. Similarly, at each of the LPN0-LPN3, the RS generation section 203
generates the cell-specific RS (CRS) and sends it through the RF RX/TX section 204
(Operation S401).
[0047] At the UE 30, the channel measurement and feedback controller 302 performs RSRP
measurement of CRSs received from different points (the Macro eNB 10 and the
LPN0-LPN3) (Operation S402) and reports the estimated [RSRP] of the different
points to its serving cell, LPNO, through the RF TX/RX section 301 (Operation S403).
The feedback [RSRP] is transferred from the serving cell, LPNO, to the centralized
scheduler 100 of the Macro eNB 10 (Operation S404). Similarly, the LPN3 receives
the feedback [RSRP] from other UEs and transfers them to the centralized scheduler
100 of the Macro eNB 10 (Operation S405).
[0048] Base on the RSRP ranking, the CRMS and CMS decision section 101 decides the
UE's CRMS and CMS (Operation S406). Assuming RSRPLPN0> RSRPLPN1> RSRPLPN2>
RSRP LPN3> RSRPM ro and five points with RSRP se -RSRPp o t RSRPLPN1> RSRPLPN2. The LPN3 and Macro eNB 10 belong to
the CRMS but outside the CMS with RSRPLPN2> RSRPLPN3> RSRPM ro- Therefore, the
target UE 30 is regarded as a CoMP candidate UE.
[0049] For such a CoMP candidate UE, the multiple NZP-CSI-RSs and ZP-CSI-RSs are
configured for the measurement of required CSI processes in the RS configuration
section 102. Also the DM-RSs of corresponding points are also configured with two
candidate initialization values of the DM-RS scrambling sequence for each point. The
CSI-RS configuration and DM-RS configuration are sent from the Macro eNB 10 to
each point in the target UE's CMS through the backhaul links (Operations S407, S408).
Also, the CSI-RS configuration and DM-RS configuration for the other UEs are sent
from the Macro eNB 10 to the other point in the other UEs' CMS through the backhaul
links (Operations S409, S410). In addition, the PQL configuration section 104 and the
IS configuration section 105 of the Macro eNB 10 configure PQL together with IS
states (PQL/IS states) and send the PQL/IS configurations to the serving cell, LPN0,
through the backhaul TX/RX section 107 (Operation S411). Details of the PQL/IS
states and corresponding PQL indicator (PQI), which is used to trigger a PQL/IS state,
will be described later.
[0050] The serving point LPN0 is in charge of informing the target UE 30 of the CSI-RS
and DM-RS configurations and PQL IS and PQI configurations over RRC signaling
semi-statically (e.g., every 100ms) (Operations S412-S414).
[0051] Base on the CSI-RS configuration, each LPN in the target UE's CMS generates and
sends the NZP-CSI-RS and/or mutes the resources of ZP-CSI-RS to the target UE 30
through the RF RX/TX section 204 periodically (e.g., every 5ms or 10ms). With the
knowledge of the CSI-RS, the channel measurement and feedback controller 302 of the
UE 30 can measure CSIs for signal and interference estimation (Operation S415). Ac
cordingly, the short-term channel state information (CSI), represented by e.g., rank
index (RI), precoding matrix index (PMI), channel quality index (CQI), are calculated
and reported to its serving point LPN0 over wireless channel, e.g., PUCCH (physical
uplink control channel) or PUSCH (physical uplink shared channel) (Operation S416).
[0052] The reported CSI is transferred from the serving point LPN0 to the Macro eNB 10
over the backhaul link for centralized scheduling (Operation S417). The resource a l
location section 103 of the centralized scheduler 100 dynamically selects the resource
blocks at each point in the CMS and allocates the selected resource blocks to the target
UE 30 (Operation S418). The dynamic scheduling results, including the selected
points, the allocated resource blocks, the selected MCS (Modulation and Coding Set),
selected initialization value of the DM-RS scrambling sequence, etc., are informed to
the LPN0-LPN3 over respective backhaul links (Operations S419, S420).
[0053] When receiving the dynamic scheduling results from the Macro eNB 10, the serving
cell, LPN0, informs the UE 30 of the corresponding PQL/IS state indicated according
to the PQI in the DCI, e.g. DCI format 2D or a new DCI format, over the control
channel, e.g., PDCCH (physical downlink control channel) or EPDCCH (enhanced
PDCCH) (Operation S421). In the present example as shown in Fig. 10, the LPNO and
LPNl are both selected for synchronized joint transmitting the data of the target UE 30
over PDSCH (physical downlink shared channel). As shown in Fig. 11, the corre
sponding PQL/IS states, e.g., PQL state 3 and IS state 2, are indicated simultaneously
according to the PQI of Ί G in the DCI over the control channel. Besides, the other
scheduling results for target UE 30, e.g., MCS, allocated resource blocks and dy
namically selected DM-RS initialization value, are also dynamically indicated in the
DCI for PDSCH reception.
[0054] Accordingly, the advanced receiver 303 can receive data on PDSCH from JT points,
LPNO and LPNl, according to the PQL state; while suppressing interference from the
selected point for IS according to the IS state, LPN2 inside the CMS or LPN3 outside
the CMS. For IS, the interfering channel is estimated by the interfering channel mea
surement section 304 based on the indicated DM-RS configuration in the IS state
(Operation S422). Also, the interfering channel measurement section 304 can further
improve the estimation of the un-precoded channel power delay profile from the in
terfering point by using the CRS and NZP-CSI-RS configuration indicated by the
PQL/IS configuration.
[0055] As described above, by using the new RRC signaling and DCI signaling to obtain the
configured IS information, the network-assisted IS is implemented at the receiver side
provided with the advanced receiver 303 together with interfering channel mea
surement section 304.
[0056] Hereafter, the dynamic IS operations in the cases of an interfering point inside the
UE's CMS and an interfering point outside the UE's CMS will be described in more
detail.
[0057] 1.3) Suppression of interference from a point inside CMS
As described above, for correct channel estimation and reception of the CoMP
candidate UE's PDSCH data, several states are configured at the PQL configuration
section 104 to correctly implement PDSCH resource element rate matching as well as
channel estimation based on QCL information for possible selected transmission
point(s). In LTE Release 11, four PQL states are required to support dynamic point
selection in a maximum 3-point CMS. Correspondingly, a 2-bit PQI is required in the
DCI, e.g., DCI format 2D, to dynamically indicate one of the four PQL states.
Referring to Fig. 11(A), each PQL state in Rel.l 1 includes the information of a
selected TP's cell ID, CRS 's port number, zero-power CSI-RS for PDSCH rate
matching, NZP CSI-RS for quasi-co-location. For example, assuming the target UE
has a CMS of LPNO (serving point), LPNl and LPN2 with RSRP LPNO>RSRP LPNO
>RSRPLPN2, the PQL state i, i=0, 1, 2, is configured assuming LPNi is the selected TP
and the PQL state 3 is configured for a case of JT, for instance, that LPNO and LPNl
are both selected for joint transmission.
[0058] As described before, new RRC signaling is needed for suppressing the interference
from the point inside the CMS. In order to save the RRC signaling overhead, the
available four PQL states and two PQI bits are reused by adding the information for IS.
For IS, the information of the DM-RS is also required besides the CRS and NZPCSI-
RS. To generate a PQL/IS state, the DM-RS configuration for LPNi is added in
the PQL state i with i=0, 1, 2, which includes the DM-RS port number, frequency shift
as well as the two candidate initialization values of DM-RS scrambling sequence. As
illustrated in Table I of Fig. 11(A), a combined PQL/IS state i, i=0, 1, 2, is configured
assuming LPNi is the selected TP or the selected IS point for the target UE. Ac
cordingly, by selecting one of the four states 0-3, a point for the selected CoMP
scheme or an interfering point for IS can be determined.
[0059] The PQI, conventionally used for indicating the selected TP, is newly defined as
Table II of Fig. 11(B) to simultaneously indicate a PQL state for the dynamically
selected point and a IS state for the dynamically selected interfering point, where the
non-selected point with strongest RSRP among the non-selected TPs inside the CMS is
chosen as the point for IS at the advanced receiver 303. For example, considering
RSRP LPNO>RSRPLPNI>RSRPLPN2, the PQL state = StateO in PQI ΌO' indicates that LPNO
is selected as the TP and the IS state = State 1 in PQI '00' represents that the in
terference from LPNl is selected for IS. In case of PQI = Ί G, the PQL state 3 is
triggered to indicate LPNO and LPNl are both selected for joint transmission as shown
in Fig. 10; while, the IS state = State2 is simultaneously triggered which indicates the
information of LPN2 in Table I as the interfering point.
[0060] The newly defined PQL/IS states as well as the newly defined PQI table are firstly
transferred from Macro eNB 10 to the serving point LPNO through the backhaul link
and then sent from the LPNO to the target UE 30 over RRC signaling semi-statically
(e.g., every 100ms) in PDSCH.
[0061] The interfering channel measurement section 304 of the UE 30 can use the newly
defined PQL/IS sate to estimate the un-precoded channel from the interfering point by
using the CRS and NZP-CSI-RS configuration and also to estimate the precoded
channel from the interfering point by using the DM-RS configuration.
[0062] On the other hand, the initialization value of DM-RS scrambling sequence can be dy
namically selected for different interfering UE on different resource block group
(RBG) allocated for the target UE 30. Therefore, a new bit of DM-RS indicator per
RBG in Table III as shown in Fig. 12(A) may be needed in the DCI to indicate the dy
namically selected initialization value of DM-RS scrambling sequence for different interfering
UE. Since the default value of DM-RS scrambling sequence is the cell ID,
which is used by most UEs with SU-MIMO or UEs without CoMP, the DM-RS
indicator bit is not needed for suppressing or cancelling the interference from such
UEs. For further overhead reduction, it is possible that the DM-RS indicator per RBG
is not added in the DCI.
[0063] In addition, another bit, defined as the layer indicator in Table IV as shown in Fig.
12(B), may be required in the DCI per RBG to inform the UE the strongest one or two
layers for IS/IC. Although more than 2 layers may be precoded at the transmitter, the
strongest two layers are selected here for IS to achieve most gain with minimum ad
ditional bit in the new defined DCI. Accordingly, the overhead of DCI is reduced
without too much performance loss. Further overhead reduction with no layer indicator
is also possible by detecting the strongest layer of the interfering channel by default.
[0064] With the network assistance of the new RRC signaling, e.g., PQL/IS states and PQI
table (see Fig. 11), as well as the new DCI signaling, e.g., DM-RS indicator and layer
indicator (see Fig. 12), the UE 30 is able to estimate the interfering channel from LPN2
and suppress the interference inside the CMS by using the MMSE with interference
rejection combining (MMSE-IRC) at the advanced receiver 303.
[0065] Assuming the interfering channel matrix of LPN2 is estimated as H~i = H 2, the
advanced receiver 303 receives the frequency-domain signal Y at the RF TX/RX
section 301 to output the signal data X~
s which is estimated by using the MMSE-IRC
weight WS
MMSE I according to the equation (3) with
Math.4
[0066]
s N + r
is the average noise and the average interferences except the interference from LPN2.
[0067] 1.4) Suppression of interference from a point outside CMS
Based on the ranking of RSRP, the point with highest RSRP outside the CMS is
semi-statically selected for IS, e.g., LPN3 as illustrated in Fig. 10. For such a point, the
new RRC signaling is needed to indicate the information of LPN3, including the con
figuration of CRS, NZP-CSI-RS, and DM-RS, etc.. As described before, the interfering
channel measurement section 304 of the UE 30 can estimate the un-precoded channel
from the interfering point LPN3 by using the CRS and NZP-CSI-RS configuration as
well as the precoded channel from the interfering point by using the DM-RS con
figuration.
[0068] Assuming the interfering channel matrix of LPN3 is estimated as H~i = H 3, the
advanced receiver 303 receives the frequency-domain signal Y at the RF TX/RX
section 301 to output the signal data X~
s which is estimated by using the MMSE-IRC
weight s
MMSE I according to the equation (3) with
Math.5
[0069] _ 2
N + G
is the average noise and the average interferences except the interference from LPN3.
[0070] 2. Second Example
A second example of the exemplary embodiment is used to cancel interference from
a point inside or outside the CMS. A system according to the second example is shown
in Figs. 13 and 14. An operation of the present example is illustrated in Fig. 10.
[007 1] 2.1) System structure
Referring to Fig. 13, the system structure of the second example is basically identical
to that of the first example as shown in Fig. 8 except that the Macro eNB 10 is
provided with an IC configuration section 120 replacing the IS configuration section
105 of the first example and the UE 30 is provided with an advanced receiver 323
which has an IC function replacing the advanced receiver 303, an interfering channel
measurement section 324 replacing the interfering channel measurement section 304
and an interfering data replica generation section 325. Accordingly, other blocks
similar to those previously described with reference to Fig. 8 are denoted by the same
reference numerals and details are omitted.
[0072] According to the second example, the new RRC signaling and new DCI signaling are
used to obtain the configured IC information, allowing the network-assisted IC to be
implemented at the receiver side by the advanced receiver 323, the interfering channel
measurement section 324 and the interfering data replica generation section 325.
[0073] Referring to Fig. 14, the advanced receiver 323 generates a replica X~i- p ca , of the in
terfering data and outputs the interference-canceled signal data X~ which is estimated
according to the following procedure.
[0074] Firstly, the interfering channel measurement section 324 estimates the interfering
channel matrix of an interfering point as H^. Using the same method as described in
1.3) of the first example, the signal data X~
s is estimated by using the MMSE-IRC
weight MMSE I according to the equation (3).
[0075] Next, the interfering data replica generation section 325 firstly estimates the in
terfering data by using the MMSE weight according to the following equation (4):
Math.6
[0076]
X = (Y
Thereafter, the interfering data X~ can be detected by using the maximum likelihood
detection (MLD) with the knowledge of the modulation scheme. The replica X~i-rep iica is
then generated by re-modulation using the same modulated scheme. Finally, the
advanced receiver 323 estimates the signal data X~ after cancelling the replica X~i-rep iica
according to the following equation (5):
Math.7
[0078]
= s (Y - - replica )
ith , = s — 5 ,
H + s N+I ,
wherein j +
the average noise and the average interferences except the interference from the in
terfering point.
[0079] 2.2) Operation
The operation of the second example has the same sequence as the first example as
shown in Fig. 10 except that IS is replaced with IC in the operations S41 1, S414 and
S422. Accordingly, hereinafter, based on the system shown in Fig. 13, how to
configure and signaling the information for the network-assisted IC of interference
inside or outside the CMS are illustrated by referring to Figs. 10, 13 and 15.
[0080] Accordingly, the advanced receiver 323 can receive data on PDSCH from JT points,
LPNO and LPNl, according to the PQL/IS state while canceling interference from the
selected point for IC, LPN2 inside the CMS, or LPN3 outside the CMS. The in
terfering channel is estimated by the interfering channel measurement section 324
based on the DM-RS configuration in the IC state, wherein the PQL/IC state is
triggered by the PQI IC in the DCI (Operation S422). Besides, the scheduling results
for target UE 30 are also dynamically indicated in the DCI format 2D for PDSCH
reception.
[0081] As described above, by using the new RRC signaling and new DCI signaling to
obtain the configured IC information, the network- assisted IC is implemented at the
receiver side provided with the advanced receiver 323 together with interfering
channel measurement section 324 and the interfering data replica generation section
325.
[0082] Hereafter, the dynamic IC operations in the cases of an interfering point inside the
UE's CMS and an interfering point outside the UE's CMS will be described in more
detail.
[0083] 2.3) Cancellation of interference from a point inside CMS
Besides the estimation of the interfering channel by using the IS information
described in 1.3) of the first example, the replica generation of the interfering data is
required for further canceling the interference data of LPN2 inside the CMS.
Therefore, besides the above signaling of the first example, new DCI bits to indicate
the dynamic modulation and coding scheme are required for different interfering UE
allocated on the same RBG. For example, two DCI bits of Modulation indicator per
RBG are illustrated in Table V as shown in Fig. 15. In the presence of the modulation
scheme, the received interfering can be demodulated and the replica of the modulated
interfering data can be generated.
[0084] Firstly, the interfering channel measurement section 324 estimates the interfering
channel matrix of LPN2 as = F 2. Using the method in the first example, the signal
data can be firstly estimated by using the MMSE-IRC weight according to the equation
(3) with
Math.8
[0085]
s N +
is the average noise and average interferences except the interference from LPN2.
[0086] Next, the interfering data replica generation section 325 firstly estimates the in
terfering data by using the MMSE weight according to the equation (4).
[0087] Thereafter, the interfering data X~ can be detected by using the maximum likelihood
detection (MLD) with the knowledge of the modulation scheme. The replica X~i-rep ca is
then generated by re-modulation using the same modulated scheme. Finally, the
advanced receiver 323 estimates the signal data X~ after cancelling the replica X~i-rep ca
according to the equation (5).
[0088] 2.4) Cancellation of interference from a point outside CMS
Besides the estimation of the interfering channel by using the IS information
described above, the replica generation of the interfering data is required for further
canceling the interference data of LPN3. Therefore, besides the above RRC and DCI
signaling described in 2.3), new DCI bits to indicate the dynamic modulation and
coding scheme are required for different interfering UE allocated on the same RBG.
For example, two DCI bits of Modulation indicator per RBG are illustrated in Table V
as shown in Fig. 15. In the presence of the modulation scheme, the received interfering
can be demodulated and the replica of the modulated interfering data can be generated.
[0089] Firstly, the interfering channel measurement section 324 estimates the interfering
channel matrix of LPN3 as = F 3. Using the method described in 1.3) of the first
example, the signal data can be firstly estimated by using the MMSE-IRC weight
according to the following equation (3) with
Math.9
[0090]
2
s N +
is the average noise and the average interferences except the interference from LPN3.
[0091] Next, the interfering data replica generation section 325 firstly estimates the in
terfering data by using the MMSE weight according to the equation (4).
[0092] Thereafter, the interfering data X~ can be detected by using the maximum likelihood
detection (MLD) with the knowledge of the modulation scheme. The replica X~i-rep ca is
then generated by re-modulation using the same modulated scheme. Finally, the
advanced receiver 323 estimates the signal data X~ after cancelling the replica X~i-rep C
according to the equation (5).
Industrial Applicability
[0093] The present invention can be applied to a mobile communications system employing
coordinated scheduling among multiple TPs.

Claims
A radio communication system comprising a network including
multiple points which are capable of communicating with a user
equipment, wherein the network sends information related to an in
terfering point to the user equipment for interference suppression or
cancelation at the user equipment, wherein the interfering point is a
candidate for a coordinated multi-point measurement set of the user
equipment but not selected for any coordinated multi-point scheme.
The radio communication system according to claim 1, wherein the in
formation related to the interfering point includes reference signal con
figuration used by the interfering point.
The radio communication system according to claim 1 or 2, wherein
the user equipment comprises a receiver having an interference sup
pression function based on the information related to the interfering
point.
The radio communication system according to claim 1 or 2, wherein
the user equipment comprises a receiver having an interference can
celation function based on the information related to the interfering
point.
The radio communication system according to one of claims 1-4,
wherein when the interfering point is a point included in the co
ordinated multi-point measurement set, the network sends first in
formation on possible point selection within the coordinated multi
point measurement set to the user equipment.
The radio communication system according to claim 5, wherein the
network sends second information for triggering a single point selection
from the first information to the user equipment.
The radio communication system according to claim 5 or 6, wherein
the first information includes a predetermined number of states, each of
which indicates a different point selection to which the information
related to the interfering point is added.
The radio communication system according to one of claims 1-4,
wherein when the interfering point is a point out of the coordinated
multi-point measurement set, the network sends the information related
to at least one interfering point to the user equipment, wherein said at
least one interfering point is selected in descending ranking of received
power at the user equipment.
PCT7JP2013/000665
A user equipment in a network including multiple points wherein the
user equipment is capable of communicating with the multiple points,
comprising:
a radio transceiver for communicating with at least one of the multiple
points; and
a receiver for receiving data from the network with suppressing or
canceling interference from an interfering point based on information
related to the interfering point,
wherein the interfering point is a candidate for a coordinated multi
point measurement set of the user equipment but not selected for any
coordinated multi-point scheme.
The user equipment according to claim 9, wherein the information
related to the interfering point includes reference signal configuration
used by the interfering point.
The user equipment according to claim 9 or 10, wherein when the in
terfering point is a point included in the coordinated multi-point mea
surement set, the radio transceiver receives from the network first in
formation on possible point selection within the coordinated multi
point measurement set.
The user equipment according to claim 11, wherein the radio
transceiver receives from the network second information for triggering
a single point selection from the first information.
The user equipment according to claim 1 1 or 12, wherein the first in
formation includes a predetermined number of states, each of which
indicates a different point selection to which the information related to
the interfering point is added.
The user equipment according to claim 9 or 10, wherein when the in
terfering point is a point out of the coordinated multi-point mea
surement set, the radio transceiver receives from the network the in
formation related to at least one interfering point which is selected in
descending ranking of received power at the user equipment.
A scheduler in a radio communication system comprising a network
including multiple points which are capable of communicating with a
user equipment, comprising:
an interference information configuring section for configuring in
formation related to an interfering point which is a candidate for a co
ordinated multi-point measurement set of the user equipment but not
selected for any coordinated multi-point scheme; and
PCT7JP2013/000665
a communication section for sending the information related to the in
terfering point to the user equipment for interference suppression or
cancelation at the user equipment.
The scheduler according to claim 15, wherein the information related to
the interfering point includes reference signal configuration used by the
interfering point.
The scheduler according to claim 15 or 16, wherein when the in
terfering point is a point included in the coordinated multi-point mea
surement set, the interference information configuring section signals
the user equipment of first information on possible point selection
within the coordinated multi-point measurement set.
The scheduler according to claim 17, wherein the interference in
formation configuring section signals the user equipment of second in
formation for triggering a single point selection from the first in
formation.
The scheduler according to claim 17 or 18, wherein the first in
formation includes a predetermined number of states, each of which
indicates a different point selection to which the information related to
the interfering point is added.
The scheduler according to claim 15 or 16, wherein when the in
terfering point is a point out of the coordinated multi-point mea
surement set, the interference information configuring section signals
the user equipment of the information related to at least one interfering
point which is selected in descending ranking of received power at the
user equipment.
The scheduler according to one of claims 15-20, wherein the scheduler
performs centralized scheduling in a macro base station included in the
network.
The scheduler according to one of claims 15-20, wherein the scheduler
performs distributed scheduling among a plurality of points included in
the network.
A communication control method in a radio communication system
comprising a network including multiple points which are capable of
communicating with a user equipment, comprising:
selecting an interfering point as a candidate for a coordinated multi
point measurement set of the user equipment but not selected for any
coordinated multi-point scheme; and
signaling from the network to the user equipment information related to
PCT7JP2013/000665
the interfering point for interference suppression or cancelation at the
user equipment.
The communication control method according to claim 23, wherein the
information related to the interfering point includes reference signal
configuration used by the interfering point.
The communication control method according to claim 23 or 24,
further comprising: at the user equipment, suppressing interference
based on the information related to the interfering point.
The communication control method according to claim 23 or 24,
further comprising: at the user equipment, canceling interference based
on the information related to the interfering point.
The communication control method according to one of claims 23-26,
further comprising: when the interfering point is a point included in the
coordinated multi-point measurement set, signaling the user equipment
of first information on possible point selection within the coordinated
multi-point measurement set.
The communication control method according to claim 27, further
comprising: signaling the user equipment of second information for
triggering a single point selection from the first information.
The communication control method according to claim 27 or 28,
wherein the first information includes a predetermined number of
states, each of which indicates a different point selection to which the
information related to the interfering point is added.
The communication control method according to one of claims 23-26,
further comprising: when the interfering point is a point out of the co
ordinated multi-point measurement set, signaling the user equipment of
the information related to at least one interfering point which is selected
in descending ranking of received power at the user equipment.
A receiving method in a user equipment of a network including
multiple points wherein the user equipment is capable of commu
nicating with the multiple points, comprising:
communicating with at least one of the multiple points; and
receiving data from the network with suppressing or canceling in
terference from an interfering point based on information related to the
interfering point, wherein the interfering point is a candidate for a co
ordinated multi-point measurement set of the user equipment but not
selected for any coordinated multi-point scheme.
A communication control method in a network including multiple
WO 2014/122688 PCT7JP2013/000665
points which are capable of communicating with a user equipment,
comprising:
configuring information related to an interfering point which is a
candidate for a coordinated multi-point measurement set of the user
equipment but not selected for any coordinated multi-point scheme; and
signaling the information related to the interfering point to the user
equipment for interference suppression or cancelation at the user
equipment.
[Claim 33] The radio communication system according to claim 1, wherein for the
interfering point, which is configured for coordinated CSI measurement
of coordinated mutlipoint transmission, the information related to such
a point is indicated by
firstly, reusing the sets with each set defined for data rate matching and
quasi-co-location for one of the mentioned points, with additional in
formation of the demodulation reference signal configuration at the cor
responding point for network-assisted interference suppression/can
cellation; and
secondly, sending signaling to trigger one of the above sets to select a
point for network-assisted interference suppression/cancellation.
[Claim 34] The radio communication system according to claim 1, wherein for the
interfering point, which is not configured for coordinated CSI mea
surement of coordinated mutlipoint transmission, the information
related to such a point is indicated by
sending signaling to inform reference signal configuration for networkassisted
interference suppression/cancellation.