WO2014122689A1

WO2014122689A1 - Communication control method and system for channel estimation based on demodulation reference signal

Info

Publication number: WO2014122689A1
Application number: PCT/JP2013/000666
Authority: WO
Inventors: Le LIU; Naoto Ishii; Yoshikazu Kakura
Original assignee: Nec Corporation
Priority date: 2013-02-07
Filing date: 2013-02-07
Publication date: 2014-08-14
Also published as: JP2016509761A

Abstract

A method and system which can achieve accurate channel estimation of the interfering precoded channel based on DM-RS is disclosed. A radio communication system has a network including multiple points which are capable of communicating with a user equipment (UE), wherein the network sends information related to an interfering UE to a target UE and a point involved in receiving state of the target UE to adjust relative power between a demodulation reference signal (RS) of the interfering UE and a data signal of the target UE, wherein the interfering UE is served by an interfering point which is selected for interference suppression or cancelation at the target UE.

Description

COMMUNICATION CONTROL METHOD AND SYSTEM FOR CHANNEL ESTIMATION BASED ON DEMODULATION REFERENCE SIGNAL

The present invention relates generally to a radio communication system and, more specifically, to techniques to improve channel estimation based on network-configured demodulation reference signal in coordinated multi-point (CoMP) transmission system.

In general, user equipments (UEs) close to cell-edge suffer from strong inter-cell interferences. For such UEs, CoMP transmission/reception has been employed in LTE (Long Term Evolution)-Advanced Release 11(Rel. 11) as a tool to improve the cell-edge throughput without loss of the system throughput (see Sect. 4 of NPL1). In LTE Rel. 12, 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, as shown in Fig. 1. As the number of LPNs increases, the inter-point interference becomes significant, resulting in performance degradation.

In NPL2, a set of 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 as a set of points about which channel state/statistical information (CSI) related to their link to a user equipment (UE) is measured and/or reported (see Sect. 5.1.4 of NPL1).

As illustrated in Fig. 2, it is assumed that Macro eNB and low power nodes LPN1 and LPN2, connected by optical fiber (backhaul link), are grouped into a CoMP cooperating set for centralized scheduling at Macro eNB. Fig. 1 shows a case where UE1's CMS includes its serving point LPN1 and neighbor point Macro eNB; while UE2's CoMP measurement set includes only its serving point LPN2.

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. 3, only the neighbor point satisfying that the difference between serving cell's RSRP, RSRP_serv, and neighbor cell's RSRP, RSRP_neigh, is smaller than a pre-defined threshold TH_RSRP, will be included in the CRMS, i.e., RSRP_serv - RSRP_neigh < TH_RSRP. 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.

In NPL4, for RRC-related aspects of the agreements reached in LTE RAN1 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 association of channel part, one non-zero power CSI-RS resource in the CMS, and interference part, one Interference Measurement Resource (CSI-IM) which occupies 4 REs that can be configured as a single zero power CSI-RS configuration. For a CoMP candidate UE with more than one configured CSI process, 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.

Based on the feedback CSI, CoMP schemes such as joint transmission (JT), dynamic point selection (DPS), and coordinated scheduling/coordinated beamforming (CS/CB) can be scheduled as described in the Sect. 5.1.3 of NPL1. 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.

In order to achieve the accurate measurement of the CoMP candidate UEs' CSI, the transmission power at the resources of multiple non-zero-power CSI-RSs are muted off and the rate matching for the UEs' data over PDSCH is mandatorily implemented at the UE side. In addition, a power boosting factor is configured to indicate the relative power of the CSI-RS against the data over PDSCH (physical data shared channel). To increase the power boosting factor can further improve the channel measurement of the CSI.

Instead of employing CoMP at the transmitter, an advanced receiver with interference suppression (IS) or interference cancellation (IC) has been proposed to improve the performance. The interference suppression (IS) is made by using interference rejection combining (IRC) in NPL5 and the interference cancellation (IC) is made by generating interference replica in NPL6. The advanced receiver with IS or IC can further improve the received SINR, which requires the information of demodulation reference signal (DM-RS) to estimate the channel of the interfering point selected for IS/IC.

DM-RS is used for channel estimation of the precoded channel since DM-RS is precoded in the same manner at the data signals. Different from the CSI-RS, the same power of the DM-RS and the PDSCH data is assumed for conventional data reception. Assuming a transmission point with highest received signal power is selected, the received power of the target UE's data is higher than the interfering power. The same power of the DM-RS and the PDSCH data, assumed for conventional data reception, may not result in severe channel estimation error.

3GPP TR 36.819 v11.0.0, Coordinated multi-point operation for LTE physical layer aspects (Release 11). http://www.3gpp.org/ftp/Specs/archive/36_series/36.819/.

R1-123077, LS on CSI-RSRP and CoMP Resource Management Set, (http://www.3gpp.org/ftp/tsg_ran/WG1_RL1/TSGR1_69/Docs/)

3GPP TR 36.214 v11.0.0, 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/.

R1-124669, RRC Parameters for Downlink CoMP

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.

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,

Summary

However, in order to suppress and further cancel the interference from the neighbor cell, the channel from the interfering point is required to be estimated based on the DM-RS of the interfering UE. Since the target UE's data conflicts with the DM-RS of the interfering UE in the allocated resource block, the lower received power of the interfering UE's DM-RS may result in very poor channel estimation of the interfering channel. In conventional system, there is no way to improve the channel estimation of the interfering precoded channel based on DS-RS sent from the selected interfering point.

An object of the present invention is to provide a method and system which can achieve accurate channel estimation of the interfering precoded channel based on DM-RS.

According to the present invention, a radio communication system has a network including multiple points which are capable of communicating with a user equipment (UE), wherein the network sends information related to an interfering UE to a target UE and a point involved in receiving state of the target UE to adjust relative power between a demodulation reference signal (RS) of the interfering UE and a data signal of the target UE, wherein the interfering UE is served by an interfering point which is selected for interference suppression or cancelation at the target UE.

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 receiving information related to an interfering user equipment (UE), wherein relative power between a demodulation reference signal (RS) of the interfering UE and a data signal received from a transmission point is adjusted based on the information related to the interfering UE; an interfering channel measurement section for estimating an interfering channel of the data signal based on the demodulation RS of the interfering UE; and a receiver having an interference suppression or cancelation function using the interfering channel estimated by the interfering channel measurement section.

According to the present invention, a scheduler in a radio communication system comprising a network including multiple points which are capable of communicating with a user equipment (UE), includes: an information configuration section for configuring information related to an interfering UE; and a communication section for sending the information related to the interfering UE to a target UE and a point involved in receiving state of the target UE to adjust relative power between the demodulation RS of the interfering UE and a data signal of the target UE, wherein the interfering UE is served by an interfering point which is selected for interference suppression or cancelation at the target UE.

According to the present invention, a communication control method in a radio communication system comprising a network including multiple points which are capable of communicating with a user equipment (UE), includes the steps of: at the network, sending information related to an interfering UE to a target UE and a point involved in receiving state of the target UE ; at the target UE and the point involved in receiving state of the target UE, adjusting relative power between a demodulation reference signal (RS) of the interfering UE and a data signal of the target UE based on the information related to an interfering UE, wherein the interfering UE is served by an interfering point which is selected for interference suppression or cancelation at the target UE.

According to the present invention, information related to an interfering UE is sent from the network to the target UE or a point involved in the receiving state of the target UE to adjust relative power between a demodulation reference signal (RS) of the interfering UE and a data signal of the target UE, resulting in accurate channel estimation of the interfering precoded channel based on the demodulation RS.

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 accompanying drawings, in which like reference numerals represent like parts:

Fig. 1 is a schematic diagram illustrating interference variations in a conventional radio communication system. Fig. 2 is a schematic diagram illustrating a radio communication system for explanation of CoMP cooperating set and CoMP measurement set. Fig. 3 is a diagram illustrating RSRP for each cell for explanation of RSRP-based decision of CoMP measurement set. Fig. 4 is a schematic diagram illustrating a radio communication system according to a first embodiment of the present invention. Fig. 5(A) is a diagram illustrating resources allocated to a target UE at a transmission point and Fig. 5(B) is a diagram illustrating resources allocated to a interfering UE at a selected interfering point according to the first embodiment, and Fig. 5(C) is a diagram illustrating the average received power of data signals and DM-RSs at target UE and interfering UE according to the first embodiment. Fig. 6 is a schematic diagram illustrating a radio communication system according to a second embodiment of the present invention. Fig. 7(A) is a diagram illustrating resources allocated to a target UE at a transmission point and Fig. 7(B) is a diagram illustrating resources allocated to a interfering UE at a selected interfering point according to the second embodiment, and Fig. 7(C) is a diagram illustrating the average received power of data signals and DM-RSs at target UE and interfering UE according to the second embodiment. Fig. 8 is a schematic diagram illustrating a radio communication system with centralized scheduling scheme according to the first or second embodiment of the present invention. Fig. 9 is a schematic diagram illustrating a radio communication system with distributed scheduling scheme according to the first or second embodiment of the present invention. Fig. 10 is a schematic diagram illustrating a radio communication system according to the first or second embodiment of the present invention. Fig. 11(A) is a function block diagram illustrating the advanced receiver with IS function and Fig. 11(B) is a function block diagram illustrating the advanced receiver with IC function in the radio communication system according to an example of the first or second exemplary embodiment of the present invention. Fig. 12 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 second exemplary embodiment of the present invention. Fig. 13(A) and Fig. 13(B) are diagrams illustrating a table of PQL states and a table of PQI which are used in the signaling as shown in Fig. 12. Fig. 14(A) and Fig. 14(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. 12. 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. 12.

Detailed Description

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 interpreted as serving cell, cooperating cell and neighbor point, respectively.

According to exemplary embodiments of the present invention, a system adjusts the relative power between the demodulation reference signal (DM-RS) sent from an interfering point and the data signal sent from a transmission point and the network informs a target UE and the interfering/transmission point of the information related to the DM-RS sent from an interfering point. Accordingly, the channel estimation for the interfering point based on the DM-RS can be improved, resulting in the improved performance of the advanced receiver with IS/IC to detect the target UE's data and the improved performance of receiving the interfering UE's data. Hereafter, first and second exemplary embodiments of the present invention will be described with references to Figs. 4-7.

1. First exemplary embodiment (Power boosting for DM-RS)
According to the first exemplary embodiment, a power boosting factor for DM-RS is signaled to the interfering point and the target UE, improving channel estimation for the interfering point at the target UE.

As illustrated in Fig. 4, a network provides a CoMP transmission system which includes a plurality of nodes or base stations (hereinafter, referred to as points) and a scheduler 100a. The scheduler 100a may be provided in a single point for centralized scheduling or may be distributed among a plurality of points for distributed scheduling. In Fig. 4, it is assumed that points 20_0 and 20_1 belong to the CoMP measurement set (CMS) of a target user equipment (UE) 30 for joint transmission, where point 20_0 is the target UE 30's serving point. A point 20_2 is an interfering point which serves an interfering UE 40 and transmits data signals at the radio resource overlapped with radio resource for the data transmission of the points 20_0 and 20_1 to the target UE 30.

A user equipment (target UE 30 in Fig. 4) is provided with function blocks including a radio transceiver 31, an advanced receiver 32 and an interfering channel measurement section 33. The radio transceiver 31 is used to communicate with the points 20_0 and 20_1. The advanced receiver 32 has IS/IC function assisted by the interfering channel measurement section 33 which measures channel estimation for the interfering point based on the DM-RS of the interfering UE 40.

The scheduler 100 notifies the interfering point 20_2 and the target UE 30 of information related to the interfering UE 40 which indicates the power boosting factor for the DM-RS of the interfering UE 40. In other words, according to the first exemplary embodiment, a new DM-RS configuration function is provided in the scheduler 100 to configure the power boosting factor PBF for the DM-RS. The target UE can estimate the interfering channel of the selected interfering point for IS/IC, e.g., the interfering point 20_2, based on the informed interfering UE 40's DM-RS information, including the configured DM-RS's initial value of scrambling sequence, the port number, resource position as well as the newly configured power boosting factor. Such a power boosting factor configuration is also required for the interfering UE's own DM-RS-based channel estimation.

Referring to Fig. 5, how to set the power boosting factor will be described in the case where the target UE 30 has the transmission point 20_0 (serving point) and the interfering point 20_2. As shown in Fig. 5(A) and Fig. 5(B), the DM-RS 20_21 at the interfering point 20_2 is conflicted with the target UE's data 20_02 in the same resource block. Without power boosting, the data's transmission power is the same as that of DM-RS. Therefore, as shown in Fig. 5(C), the interfering UE's DM-RS at the interfering point 20_2 is received at the target UE 30 with lower average received power than that of the data at the transmission point 20_0, resulting in poor channel estimation of the interfering UE 40 for the target UE's data detection with IS/IC.

The power boosting factor is defined as the relative power between the received average power of target UE's data (target UE's reported RSRP of the transmission point) and that of the interfering UE's DM-RS (target UE's reported RSRP of the interfering point). Assuming the transmission power for DM-RS without power boosting is the same as that of PDSCH data, the power boosting power for the DM-RS at the interfering point 20_2 can be set as the difference between the RSRP of the transmission point 20_0 and the interfering point 20_2, which is also used for the CRMS and CMS decision. According to the network-informed power boosting factor, the interfering pint 20_2 generates the power boosted DM-RS and sends it to the interfering UE 40. As shown in Fig. 5(C), the received power of the DM-RS from the interfering point 20_2 is increased, comparable to that of the DM-RS from the transmission point 20_0.

The DM-RS power boosting factor is required to be informed to the target UE 30 as the RRC signaling over PDSCH. With the knowledge of the interfering UE's DM-RS power boosting factor, the target UE 30 can accurately estimate the interfering channel of the data by using the DM-RS-based channel power measurement obtained by the interfering channel measurement section 33. Thereafter, the channel estimation based on the power-boosted DM-RS of the interfering UE 40 is improved and the advanced receiver 32 uses the measured channel estimation for the target UE's data detection with IS/IC.

Also for the data reception of the interfering UE 40, the data channel estimation is carried out at the interfering UE 40 itself. Accordingly, the channel estimation of the interfering UE itself is also beneficial from the power-boosted DM-RS, resulting in the improved received SINR of interfering UE.

2. Second exemplary embodiment (Data rate matching on DM-RS resources)
According to the second exemplary embodiment, the conventional DM-RS configuration is used at the interfering point 20_2 to decide the DM-RS's port number and resource position, without the above-mentioned power boosting for DM-RS. A scheduler 100b notifies the transmission point 20_0 and the target UE 30 of information related to the interfering UE 40 which indicates the resource position of DM-RS of the interfering UE 40. Based on the resource position of DM-RS of the interfering UE 40, the transmission point 20_0 disables the data transmission to the target UE 30 at the resource elements of the interfering UE's DM-RS and the target UE 30 measures the channel of the interfering UE's based on the DM-RS sent from the interfering point 20_2 without data from the transmission point 20_0. Accordingly, the DM-RS-based channel estimation for the interfering point 20_2 can also be improved.

As shown in Fig. 7(A) and Fig. 7(B), the data transmission at the transmission point 20_0 of the target UE 30 is disabled at the DM-RS resource element 20_21 of the interfering point 20_2. With the knowledge of the DM-RS resource position 20_21 of the interfering point 20_2, the target UE 30 is required to implement PDSCH resource element rate matching around the informed DM-RS resource elements, which is defined as a new UE behavior. Accordingly, the DM-RS of the interfering point 20_2 does not suffer from any interference from the target UE's transmission point 20_0, allowing the channel estimation based on the interference-free DM-RS to be improved at the price of the disabled resource elements for data transmission, beneficial for the data receiving with IS/IC at the target UE side as well as the data receiving for the interfering UE itself.

The coordinated scheduling according to the first and second exemplary embodiments can be implemented in a centralized scheduling system as shown in Fig. 8 or a distributed scheduling system as shown in Fig. 9. In other words, the functions of the centralized scheduling can also be distributed into multiple nodes.

<Centralized scheduling>
Referring to Fig. 8, 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) respectively 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 cooperating set. The Macro eNB is provided with a centralized scheduler 100, which performs the CRMS and CMS decision, reference signal (RS), PQL and DM-RS configurations 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.

<Distributed scheduling>
Referring to Fig. 9, 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 backhaul links and N2-N4 are also connected to each other through backhaul links. 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 are 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 distributed scheduler at the Macro eNB performs control for CRMS and CMS decision for UE1, RS, PQL and DM-RS configurations as well as resource allocation coordinated among the neighbor nodes (here, N3) in the UE1's CMS. Similarly, the distributed scheduler at the node N2 performs control for CRMS and CMS decision for UE2, RS, PQL and DM-RS configurations 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.

Hereafter, an example of the present invention will be explained in the case of the centralized scheduling. As described above, the functions of the centralized scheduling can also be implemented in the distributed scheduling system.

3. Example
An example of the exemplary embodiment is used to suppress/cancelation interference from an interfering point inside or outside the CMS. A system according to the example is shown in Figs. 10 and 11 and its operation is illustrated in Fig. 12. The

scheduler

100a or 100b as mentioned above can be applied to a centralized scheduler 100 according to the present example.

3.1) System structure
As illustrated in Fig. 10, a centralized scheduler 100 is located in Macro eNB 10 to control all the LPNs, LPN0-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/IC configuration section 105, a DM-RS configuration section 106, and a controller 107. All those blocks 101-106 are connected to the controller 107. 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 UE's CSI feedback. The PQL configuration 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 estimation based on quasi-co-location information.

The DM-RS configuration section 106 configures DM-RS, which is precoded in the same manner as the data signals, to estimate the precoded channel for data demodulation at the UE side. The system as shown in Fig. 10 can use two types of DM-RS configuration as follows:
1) Conventional DM-RS configuration is composed of the initial value configuration of scrambling sequence and the port and resource element configuration; and
2) New DM-RS configuration is composed of the initial value configuration of scrambling sequence, the port and resource element configuration, and the power boosting configuration.
The new DM-RS configuration is used for the scheduler 100a according to the first exemplary embodiment and the conventional DM-RS configuration is used for the scheduler 100b according to the second exemplary embodiment.

The configured RS and PQL states as well as the scheduling results are sent from a backhaul TX/RX section 108 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 signal and reference signal (RS) are generated by a data generation section 202 and a RS generation section 203, respectively and transmitted from the RF TX/RS section 204 to the UE 30.

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) / Cancelation (IC) 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 data is received by using the estimated channel matrix at the advanced receiver 303 assisted by the interfering channel measurement section 304.

Referring to Fig. 11(A), the advanced receiver 303a with IS 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 W_s ^MMSE-IRC according to the following equation (1):

Math.1

the average noise and the average interferences except the interference from the interfering point. In the equation (1), H^~ _I 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, H^~ _I with reality, the MMSE-IRC receiver 303a requires the information of reference signal for the interfering point.

Referring to Fig. 11(B), the advanced receiver 303b with IC generates a replica X^~ _I-replica, of the interfering data and outputs the interference-canceled signal data X^{~^} _s which is estimated according to the following procedure.

Firstly, the interfering channel measurement section 304 estimates the interfering channel matrix of an interfering point as H^~ _I based on the DM-RS configuration. Using the same method as described above, the signal data X^~ _s is estimated by using the MMSE-IRC weight W_s ^MMSE-IRC according to the equation (1).

Next, the interfering data is firstly estimated by using the MMSE weight according to the following equation (2):

Math.2

Thereafter, the interfering data X^~ _I can be detected by using the maximum likelihood detection (MLD) with the knowledge of the modulation scheme. The replica X^~ _I-replica is then generated by re-modulation using the same modulated scheme. Finally, the advanced receiver 303b estimates the signal data X^{~^} _s after cancelling the replica X^~ _I-replica according to the following equation (3):

Math.3

the average noise and the average interferences except the interference from the interfering point.

As described in the first and second exemplary embodiments, the interfering channel measurement section 304 performs accurate channel estimation of the interfering precoded channel based on the DM-RS configuration, allowing the advanced receiver 303 to receive data reliably. Inaccurate channel estimation may degrade the performance, even worse than the conventional CoMP performance without IS/IC.

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 LPN0 to decide the new DCI signaling for IS. However, in case of distributed scheduling, the serving point LPN0 should inform the interfering point to trigger or stop the reporting of the dynamic scheduling results for IS.

3.2) Operation
Referring to Fig. 12, at the Macro eNB 10, the RS generation section 109 generates the cell-specific RS (CRS) and sends it to the target UE 30 through the RF RX/TX section 111. Similarly, at each of the LPN0-LPN3, the RS generation section 203 generates the cell-specific RS (CRS) and sends through the RF RX/TX section 204 (Operation S401).

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, LPN0, through the RF TX/RX section 301 (Operation S403). The feedback [RSRP] is transferred from the serving cell, LPN0, 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).

Base on the RSRP ranking, the CRMS and CMS decision section 101 decides the UE's CRMS and CMS (Operation S406). Assuming RSRP_LPN0> RSRP_LPN1> RSRP_LPN2> RSRP_LPN3> RSRP_Macro and five points with RSRP_serv-RSRP_point<TH_RSRP are selected into CRMS, maximum 3 points among the five points can be selected into the UE's CMS. In this example, the target UE 30 has the CMS of LPN0 (serving point), LPN1 and LPN2 with RSRP_LPN0> RSRP_LPN1> RSRP_LPN2. The LPN3 and Macro eNB10 belong to the CRMS but outside the CMS with RSRP_LPN2> RSRP_LPN3> RSRP_Macro. Therefore, the target UE 30 is regarded as a CoMP candidate UE.

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 port and resource element configuration and, in the case of the first exemplary embodiment, the power boosting configuration as described before. 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 UE's CMS through the backhaul links (Operations S409, S410).

In addition, the PQL configuration section 104 and the IS/IC configuration section 105 of the Macro eNB 10 configure PQL together with IS/IC states (PQL/IS/IC) and send the PQL and IS/IC configurations to the serving cell, LPN0, through the backhaul TX/RX section 107 (Operation S411). Details of the PQL and IS/IC states and corresponding PQL indicator (PQI), which is used to trigger a PQL and IS/IC state, will be described later.

The serving point LPN0 is in charge of informing the target UE 30 of the CSI-RS and DM-RS configurations and PQL/PQI and IS/IC configurations over RRC signaling semi-statically (e.g., every 100ms) (Operations S412-S414).

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). Accordingly, 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).

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 allocation 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).

When receiving the dynamic scheduling results from the Macro eNB 10, the serving cell, LPN0, informs the UE 30 of the corresponding PQL/ISIC state indicated according to the PQI in the downlink control information (DCI), e.g. DCI format 2D or a newly defined 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 LPN0 and LPN1 are both selected for synchronized joint transmitting the data of the target UE 30 over PDSCH (physical downlink shared channel). As shown in Fig. 13, the corresponding PQL/ISIC state, e.g., PQL state 3 and IS/IC state 2, are indicated according to the PQI of '11' in the DCI over the control channel. Besides, the other scheduling results for target UE 30, e.g., MCS, allocated resource blocks and dynamically selected DM-RS initialization value, are also dynamically indicated in the DCI for PDSCH reception.

Accordingly, the advanced receiver 303 can receive data on PDSCH from JT points, LPN0 and LPN1, according to the PQL state while suppressing/canceling interference from the selected point for IS/IC according to the IS/IC state, LPN2 inside the CMS, or LPN3 outside the CMS, which is accurately estimated by the interfering channel measurement section 304 based on the indicated DM-RS configuration in the IS/IC state,. Also, the interfering channel measurement section 304 can further estimate the un-precoded channel from the interfering point by using the CRS and NZP-CSI-RS configuration indicated in the PQL/ISIC state (Operation S422).

As described above, by using the new RRC signaling and DCI signaling to obtain the configured IS/IC information, the network-assisted IS/IC is implemented at the receiver side provided with the advanced receiver 303 together with interfering channel measurement section 304.

Hereafter, the dynamic IS/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.

3.3) 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 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. The four PQL states are newly defined as Table I shown in Fig. 13(A). Referring to Fig. 11(A), each PQL state in Rel.11 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 LPN0 (serving point), LPN1 and LPN2 with RSRP_LPN0>RSRP_LPN0>RSRP_LPN2, 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 LPN0 and LPN1 are both selected for joint transmission.

As described before, new RRC signaling is needed for suppressing/canceling 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 NZP-CSI-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. 13(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. Accordingly, 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.

The PQI, conventionally used for indicating the selected TP, is newly defined as Table II of Fig. 13(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_LPN0>RSRP_LPN1>RSRP_LPN2, the PQL state = State0 in PQI '00' indicates that LPN0 is selected as the TP and the IS state = State1 in PQI '00' represents that the interference from LPN1 is selected for IS. In case of PQI = '11', the PQL state 3 is triggered to indicate LPN0 and LPN1 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.

The newly defined PQL states including the information for PQL and IS as well as the newly defined PQI table are firstly transferred from Macro eNB 10 to the serving point LPN0 through the backhaul link and then sent from the LPN0 to the target UE 30 over RRC signaling semi-statically (e.g., every 100ms) in PDSCH.

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 to estimate the precoded channel from the interfering point by using the DM-RS configuration.

On the other hand, the initialization value of DM-RS scrambling sequence can be dynamically 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. 14(A) may be needed in the DCI to indicate the dynamically 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.

In addition, another bit, defined as the layer indicator in Table IV as shown in Fig. 14(B), may be required in the DCI per RBG to inform the UE the strongest one or two layers for IS. 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 additional 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.

With the network assistance of the new RRC signaling, e.g., PQL/IS states and PQI table (see Fig. 13), as well as the new DCI signaling, e.g., DM-RS indicator and layer indicator (see Fig. 14), 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.

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 W_s ^MMSE-IRC according to the equation (1) with

Math.4

is the average noise and the average interferences except the interference from LPN2.

3.4) 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. 12. For such a point, the new RRC signaling is needed to indicate the information of LPN3, including the configuration 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 configuration.

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 W_s ^MMSE-IRC according to the equation (1) with

Math.5

is the average noise and the average interferences except the interference from LPN3.

3.5) Cancellation of interference from a point inside CMS
Besides the estimation of the interfering channel by using the IS information described in 3.3) of IS case, 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 IS case, 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.

Firstly, the interfering channel measurement section 304 estimates the interfering channel matrix of LPN2 as H^~ _I = H^{^} ₂. Using the method in the IS case, the signal data can be firstly estimated by using the MMSE-IRC weight according to the following equation (1) with

Math.6

is the average noise and average interferences except the interference from LPN2.

Next, the interfering data is firstly estimated by using the MMSE weight according to the following equation (2).

Thereafter, the interfering data X^~ _I can be detected by using the maximum likelihood detection (MLD) with the knowledge of the modulation scheme. The replica X^~ _I-replica is then generated by re-modulation using the same modulated scheme. Finally, the advanced receiver 303 estimates the signal data X^{~^} _s after cancelling the replica X^~ _I-replica according to the equation (2).

3.6) 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 3.3), 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.

Firstly, the interfering channel measurement section 304 estimates the interfering channel matrix of LPN3 as H^~ _I = H^{^} ₃. Using the method described in 3.3) of the first example, the signal data can be firstly estimated by using the MMSE-IRC weight according to the equation (1) with

Math.7

Thereafter, the interfering data X^~ _I can be detected by using the maximum likelihood detection (MLD) with the knowledge of the modulation scheme. The replica X^~ _I-replica is then generated by re-modulation using the same modulated scheme. Finally, the advanced receiver 303 estimates the signal data X^{~^} _s after cancelling the replica X^~ _I-replica according to the following equation (3).

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 (UE), wherein the network sends information related to an interfering UE to a target UE and a point involved in receiving state of the target UE to adjust relative power between a demodulation reference signal (RS) of the interfering UE and a data signal of the target UE, wherein the interfering UE is served by an interfering point which is selected for interference suppression or cancelation at the target UE.
The radio communication system according to claim 1, wherein the network signals the target UE and the interfering point of the information related to the interfering UE which includes a power boosting factor for the demodulation RS of the interfering UE, wherein the power boosting factor is determined depending on a received power difference between the data signal transmitted by a transmission point to the target UE and the demodulation RS transmitted by the interfering point.
The radio communication system according to claim 1, wherein the network signals the target UE and a transmission point to the target UE of the information related to the interfering UE which includes a resource position of the demodulation RS, based on which transmission of the data signal is disabled at the transmission point.
The radio communication system according to one of claims 1-3, wherein the target UE comprises:
an interfering channel measurement section for estimating an interfering channel of the data signal based on the demodulation RS of the interfering UE; and
a receiver having an interference suppression or cancelation function using the interfering channel estimated by the interfering channel measurement section.
The radio communication system according to one of claims 1-4, wherein the network also signals the target UE of information related to the interfering point for interference suppression or cancelation at the target UE, wherein the interfering point is a candidate for a coordinated multi-point measurement set of the target UE but not selected for any coordinated multi-point scheme.
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 receiving information related to an interfering user equipment, wherein relative power between a demodulation reference signal (RS) of the interfering user equipment and a data signal received from a transmission point is adjusted based on the information related to the interfering user equipment;
an interfering channel measurement section for estimating an interfering channel of the data signal based on the demodulation RS of the interfering user equipment; and
a receiver having an interference suppression or cancelation function using the interfering channel estimated by the interfering channel measurement section.
The user equipment according to claim 6, wherein the radio transceiver receives the information related to the interfering user equipment which includes a power boosting factor for the demodulation RS of the interfering user equipment, wherein the power boosting factor is determined depending on a received power difference between the data signal transmitted by the transmission point and the demodulation RS transmitted by the interfering point.
The user equipment according to claim 6, wherein the radio transceiver receives the information related to the interfering user equipment which includes a resource position of the demodulation RS, based on which transmission of the data signal is disabled at the transmission point, wherein the interfering channel measurement section estimates an interfering channel of the data signal based on the demodulation RS of the interfering UE.
The user equipment according to one of claims 6-8, wherein the radio transceiver further receives information related to the interfering point, based on which the receiver receives the data signal from the transmission point with interference suppression or cancelation, wherein the interfering point is a candidate for a coordinated multi-point measurement set of the target user equipment but not selected for any coordinated multi-point scheme.
A scheduler in a radio communication system comprising a network including multiple points which are capable of communicating with a user equipment (UE), comprising:
an information configuration section for configuring information related to an interference UE; and
a communication section for sending the information related to the interfering UE to a target UE and a point involved in receiving state of the target UE to adjust relative power between the demodulation RS of the interfering UE and a data signal of the target UE, wherein the interfering UE is served by an interfering point which is selected for interference suppression or cancelation at the target UE.
The scheduler according to claim 10, wherein the communication section sends the target UE and the interfering point of the information related to the interfering UE which includes a power boosting factor for the demodulation RS of the interfering UE, wherein the power boosting factor is determined depending on a received power difference between the data signal transmitted by a transmission point to the target UE and the demodulation RS transmitted by the interfering point.
The scheduler according to claim 10, wherein the communication section sends the target UE and a transmission point to the target UE of the information related to the interfering UE which includes a resource position of the demodulation RS, based on which transmission of the data signal is disabled at the transmission point.
The scheduler according to claim 10, wherein the communication section also signals the target UE of information related to the interfering point for interference suppression or cancelation at the target UE, wherein the interfering point is a candidate for a coordinated multi-point measurement set of the target UE but not selected for any coordinated multi-point scheme.
A communication control method in a radio communication system comprising a network including multiple points which are capable of communicating with a user equipment (UE), comprising:
at the network, sending information related to an interfering UE to a target UE and a point involved in receiving state of the target UE ;
at the target UE and the point involved in receiving state of the target UE, adjusting relative power between a demodulation reference signal (RS) of the interfering UE and a data signal of the target UE based on the information related to an interfering UE, wherein the interfering UE is served by an interfering point which is selected for interference suppression or cancelation at the target UE.
The communication control method according to claim 14, wherein the information related to the interfering UE is sent to the target UE and the interfering point, which includes a power boosting factor for the demodulation RS of the interfering UE, wherein the power boosting factor is determined depending on a received power difference between the data signal transmitted by a transmission point to the target UE and the demodulation RS transmitted by the interfering point.
The communication control method according to claim 14, wherein the information related to the interfering UE is sent to the target UE and a transmission point to the target UE, which includes a resource position of the demodulation RS, based on which transmission of the data signal is disabled at the transmission point.
The communication control method according to one of claims 14-16, wherein at the target UE,
estimating an interfering channel of the data signal based on the demodulation RS of the interfering UE; and
performing interference suppression or cancelation using the interfering channel estimated.
The communication control method according to one of claims 14-17, wherein information related to the interfering point is also sent to the target UE for interference suppression or cancelation at the target UE, wherein the interfering point is a candidate for a coordinated multi-point measurement set of the target UE but not selected for any coordinated multi-point scheme.
A method of interference suppression or cancelation of a user equipment (UE) in a network including multiple points wherein the user equipment is capable of communicating with the multiple points, comprising:
receiving information related to an interference UE from the network, wherein relative power between a demodulation reference signal (RS) of the interfering UE and a data signal received from a transmission point is adjusted based on the information related to the interfering UE;
estimating an interfering channel of the data signal based on the demodulation RS of the interfering UE; and
performing interference suppression or cancelation using the interfering channel estimated.
A scheduling method of a scheduler in a radio communication system comprising a network including multiple points which are capable of communicating with a user equipment (UE), comprising:
configuring information related to an interference UE; and
sending the information related to the interfering UE to a target UE and a point involved in receiving state of the target UE to adjust relative power between the demodulation RS of the interfering UE and a data signal of the target UE, wherein the interfering UE is served by an interfering point which is selected for interference suppression or cancelation at the target UE.