WO2013038601A1

WO2013038601A1 - Channel state information feedback method and user equipment

Info

Publication number: WO2013038601A1
Application number: PCT/JP2012/005297
Authority: WO
Inventors: Ming Ding; Zeng YANG; Lei Huang
Original assignee: Sharp Kabushiki Kaisha
Priority date: 2011-09-13
Filing date: 2012-08-23
Publication date: 2013-03-21
Also published as: CN103001679A

Abstract

A method and a user equipment (UE) for feeding back Channel State Information (CSI) in a multi-Base station (multi-BS) coordination mode are provided. The CSI feedback method comprises: acquiring a set of Transmission Points (TPs) participating in multi-antenna multi-BS coordination from a serving BS; selecting a TP from the set of TPs; and feeding back the CSI to the serving BS, wherein the CSI contains index information identifying the selected TP. The CSI feedback method and user equipment according to the present invention have the advantages of dynamically supporting JT and DCS transmission, simple implementation and high system throughput.

Description

CHANNEL STATE INFORMATION FEEDBACK METHOD AND USER EQUIPMENT

The present invention relates to communication technology, and more particularly, to a method for feeding back Channel State Information (CSI) in a multi-Base station (multi-BS) coordination mode and a user equipment corresponding thereto.

Multiple Input Multiple Output (MIMO) wireless transmission technique can achieve spatial multiplex gain and spatial diversity gain by deploying a plurality of antennas at both the transmitter and the receiver and utilizing the spatial resources in wireless transmission. Researches on information theory have shown that the capacity of a MIMO system grows linearly with the minimum of the number of transmitting antennas and the number of receiving antennas. Fig. 1 shows a schematic diagram of a MIMO system. As shown in Fig. 1, a plurality of antennas at the transmitter and a plurality of antennas at each of the receivers constitute a multi-antenna wireless channel containing spatial domain information. Further, Orthogonal Frequency Division Multiplexing (OFDM) technique has a strong anti-fading capability and high frequency utilization and is thus suitable for high speed data transmission in a multi-path and fading environment. The MIMO-OFDM technique, in which MIMO and OFDM are combined, has become a core technique for a new generation of mobile communication.

For instance, the 3^rd Generation Partnership Project (3GPP) organization is an international organization in mobile communication field and plays an important role in standardization of 3G cellular communication technologies. Since the second half of the year 2004, the 3GPP organization has initiated a so-called Long Term Evolution (LTE) project for designing Evolved UMTS Terrestrial Radio Access (EUTRA) and Evolved UMTS Terrestrial Radio Access Network (EUTRAN). The MIMO-OFDM technique is employed in the downlink of the LTE system. In a conference held in Shenzhen, China in April 2008, the 3GPP organization started a discussion on the standardization of 4G cellular communication systems (currently referred to as LTE-A systems). In this conference, a concept known as "multi-antenna multi-BS coordination" gets extensive attention and support. Its core idea is that multiple BSs can provide communication services for one or more user equipments (UEs) simultaneously, so as to improve data transmission rate for a UE located at the edge of a cell.

With regard to the multi-antenna multi-BS coordination, fundamental agreements are mainly available from the following standard document by March, 2010: 3GPP TR 36.814 V9.0.0 (2010-03), "Further advancements for E-UTRA physical layer aspects (Release 9)" ,which can be outlined as follows:

(1) In a multi-antenna multi-BS service, a UE needs to report channel state/statistical information of a link between the UE and each BS/cell in a set of cells. This set of cells is referred to as a measurement set for multi-antenna multi-BS transmission.

(2) The set of BSs/cells for which the UE actually performs information feedback can be a subset of the measurement set and is referred to as a coordination set for multi-antenna multi-BS transmission. Obviously, the coordination set for multi-antenna multi-BS transmission can be the same as the measurement set for multi-antenna multi-BS transmission.

(3) A BS/cell in the coordination set for multi-antenna multi-BS transmission participates in Physical Downlink Shared Channel (PDSCH) transmission for the UE, either directly or indirectly. The Physical Downlink Shared Channel is the data channel of the UE.

(4) The scheme in which multiple BSs directly participate in coordination transmission is referred to as Joint Processing (JP). The JP scheme needs to share PDSCH signal of the UE among the multiple BSs participating the coordination and can be divided into two approaches. One is referred to as Joint Transmission (JT) in which the multiples BSs transmit their PDSCH signals to the UE simultaneously. The other one is referred to as Dynamic Cell Selection (DCS) in which at any time instance, only one of the BSs which has the strongest signal link is selected to transmit its PDSCH signal to the UE. It should be noted that, with the advance of the standardization process, the DCS shall be understood in an extended sense of "Transmission Point" (TP), rather than in a limited sense of "cell". The term transmission point refers to a set of a plurality of transmission ports corresponding to a downlink Reference Signal pattern (CSI-RS Pattern).

(5) The scheme in which multiple BSs indirectly participate in coordination transmission is referred to as Coordinated Beamforming/Coordinated Scheduling (CB/CS). In this CB/CS scheme, instead of sharing PDSCH signal of the UE among the multiple BSs participating in the coordination, the beams/resources for transmission of PDSCHs for different UEs are coordinated among the multiple BSs to suppress the interference between each other.

(6) For a UE operating in the multi-antenna multi-BS coordinated transmission environment, information feedback is mainly carried out separately for each BS and is transmitted over the uplink resources of the serving BS.

As used herein, the term "information feedback" mainly refers to a process in which a UE feeds back CSI to a BS such that the BS can perform corresponding operations such as radio resource management. There are primarily the following three CSI feedback approaches in the prior art.

Complete CSI Feedback: The UE quantizes all elements in a transceiver channel matrix and feeds back each of the elements to the BS. Alternatively, the UE can analogously modulate all elements in the transceiver channel matrix and feeds back them to the BS. Alternatively, the UE can obtain a transient covariance matrix for the transceiver channel matrix, quantizes all elements in the covariance matrix and feeds back each of the elements to the BS. Thus, the BS can reconstruct an accurate channel from the channel quantization information fed back from the UE. This approach is described in detail in non-patent document 1: 3GPP R1-093720, "CoMP email summary", Qualcomm and its implementation is illustrated in Fig. 2.

Statistic-Based CSI Feedback: The UE applies a statistical process on a transceiver channel matrix, e.g., calculating a covariance matrix thereof, quantizes the statistical information and then feeds back it to the BS. Thus, the BS can obtain statistical state information of the channel based on the feedback from the UE. This approach is described in detail in non-patent document 1: 3GPP R1-093720, "CoMP email summary", Qualcomm and its implementation is illustrated in Fig. 3.

CSI Feedback Based on Codebook Space Search: A finite set of CSI is predefined by the UE and the BS (i.e., codebook space, common codebook spaces including channel rank and/or pre-coding matrix and/or channel quality indication, etc.). Upon detection of a transceiver channel matrix, the UE searches in the codebook space for an element best matching the CSI of the current channel matrix and feeds back the index of the element to the BS. Thus, the BS looks up the predefined codebook space based on the index to obtain rough CSI. This approach is described in detail in non-patent document 2: 3GPP, R1-083546, "Per-cell precoding methods for downlink joint processing CoMP", ETRI, and its implementation is illustrated in Fig. 4.

Among the above three approaches, the complete CSI feedback has the best performance, but is impractical to be applied to actual system due to the highest feedback overhead. In particular, in the multi-antenna multi-BS coordination system, its feedback overhead grows in proportional to the increase of the number of BSs and it is even more impractical. The CSI feedback based on codebook space search has the lowest feedback overhead, but is worst in terms of performance since it cannot accurately describe the channel state such that the transmitter cannot make full use of channel characteristics and cannot perform transmission accordingly. However, it is extremely simple to implement and can typically accomplish feedback with a few bits. Hence, it is widely applied in actual systems. In comparison, the statistic-based CSI feedback achieves a good tradeoff between these two approaches. When the channel state has significant statistical information, this approach can accurately describe the channel state with a relatively small amount of feedback, thereby achieving a relatively ideal performance.

Currently, in the LTE and the LTE-A systems, in consideration of factors for practical system implementation, the CSI feedback based on codebook space search is employed in a single cell transmission mode. In the multi-BS/cell coordination mode in the LTE-A system, it is expected that this CSI feedback based on codebook space search will continue to be used.

For the CSI feedback based on codebook space search, there are two feedback channels in the LTE system, namely, a Physical Uplink Control CHannel (PUCCH) and a Physical Uplink Shared CHannel (PUSCH). In general, the PUCCH is configured for transmission of periodic, basic CSI with low payload; while PUSCH is configured for transmission of bursty, extended CSI with high payload. For the PUCCH, a complete CSI is composed of various feedback contents which are transmitted in different sub-frames. For the PUSCH, on the other hand, a complete CSI is transmitted within one sub-frame. Such design principles remain applicable in the LTE-A system.

The feedback contents can be divided into three categories: Channel Quality Index (CQI), Pre-coding Matrix Index (PMI) and Rank Index (RI), all of which are bit quantized feedbacks. The CQI typically corresponds to a transmission format having a packet error rate no more than 0.1.

In the LTE system, the following eight types of MIMO transmission approaches for downlink data are defined:

1) Single antenna transmission. This is used for signal transmission at a single antenna BS. This approach is a special instance of MIMO system and can only transmit a single layer of data.

2) Transmission diversity. In a MIMO system, diversity effects of time and/or frequency can be utilized to transmit signals, so as to improve the reception quality of the signals. This approach can only transmit a single layer of data.

3) Open-loop space division multiplexing. This is a space division multiplexing without the need for PMI feedback from UE.

4) Closed-loop space division multiplexing. This is a space division multiplexing in which PMI feedback from UE is required.

5) Multi-user MIMO. There are multiple UEs simultaneously participating in the downlink communication of the MIMO system on the same frequecy.

6) Closed-loop single layer pre-coding. Only one single layer of data is transmitted using the MIMO system. The PMI feedback from UE is required.

7) Beam forming transmission. The beam forming technique is employed in the MIMO system. A dedicated reference signal is used for data demodulation at UE. Only one single layer of data is transmitted using the MIMO system. The PMI feedback from UE is not required.

8) Two-layer beam forming transmission. The UE can be configured to feed back PMI and RI, or not to feed back PMI and RI. In the LTE-A system, the above eight types of transmission approaches may be retained and/or cancelled.

Optionally, a new type of transmission approach, type 9) dynamic MIMO switching, can be added, by which the BS can dynamically adjust the MIMO mode in which the UE operates.

In order to support the above MIMO transmission approaches, a variety of CSI feedback modes are defined in the LTE system. Each MIMO transmission approach corresponds to a number of CSI feedback modes, as detailed in the following.

There are four CSI feedback modes for the PUCCH, namely, Mode 1-0, Mode 1-1, Mode 2-0 and Mode 2-1. These modes are combination of four types of feedbacks, including:

1) Type 1: one preferred sub-band location in a Band Part (BP, which is a subset of the set of communication spectrum resources S and has its size dependent on the size of the Set S) and a CQI for the sub-band. The respective overheads are L bits for the sub-band location, 4 bits for the CQI of the first codeword and 3 bits for the CQI of the possible second codeword which is differentially coded with respect to the CQI of the first codeword.

2) Type 2: wideband CQI and PMI. The respective overheads are 4 bits for the CQI of the first codeword, 3 bits for the CQI of the possible second codeword which is differentially coded with respect to the CQI of the first codeword and 1, 2 or 4 bits for PMI depending on the antenna configuration at BS.

3) Type 3: RI. The overhead for RI is 1 bit for two antennas, or 2 bits for four antennas, depending on the antenna configuration at BS.

4) Type 4: wideband CQI. The overhead is constantly 4 bits.

The UE feeds back different information to the BS in correspondence with the above different types.

The Mode 1-0 is a combination of Type 3 and Type 4. That is, the feedbacks of Type 3 and Type 4 are carried out at different periods and/or with different sub-frame offsets, which means that the wideband CQI of the first codeword in the Set S and possibly the RI information are fed back.

The Mode 1-1 is a combination of Type 3 and Type 2. That is, the feedbacks of Type 3 and Type 2 are carried out at different periods and/or with different sub-frame offsets, which means that the wideband PMI of the Set S, the wideband CQIs for the individual codewords and possibly the RI information are fed back.

The Mode 2-0 is a combination of Type 3, Type 4 and Type 1. That is, the feedbacks of Type 3, Type 4 and Type 1 are carried out at different periods and/or with different sub-frame offsets, which means that the wideband CQI of the first codeword in the Set S, possibly the RI information as well as one preferred sub-band location in the BP and the CQI for the sub-band are fed back.

The Mode 2-1 is a combination of Type 3, Type 2 and Type 1. That is, the feedbacks of Type 3, Type 2 and Type 1 are carried out at different periods and/or with different sub-frame offsets, which means that the wideband PMI of the Set S, the wideband CQIs for the individual codewords and possibly the RI information, as well as one preferred sub-band location in the BP and the CQI for the sub-band are fed back.

There are thus the following correspondences between the MIMO transmission approaches and the CSI feedback modes:
MIMO transmission approach 1): Mode 1-0 and Mode 2-0;
MIMO transmission approach 2): Mode 1-0 and Mode 2-0;
MIMO transmission approach 3): Mode 1-0 and Mode 2-0;
MIMO transmission approach 4): Mode 1-1 and Mode 2-1;
MIMO transmission approach 5): Mode 1-1 and Mode 2-1;
MIMO transmission approach 6): Mode 1-1 and Mode 2-1;
MIMO transmission approach 7): Mode 1-0 and Mode 2-0;
MIMO transmission approach 8): Mode 1-1 and Mode 2-1, with PMI/RI feedback from UE; or Mode 1-0 and Mode 2-0, without PMI/RI feedback from UE.

Still, CQI, PMI and RI are primary feedback contents in the single BS transmission approach of the LTE-A system. In order to keep the feedback modes for a UE consistent with those corresponding to the transmission approaches 4) and 8) and to enable the new transmission approach 9), the Mode 1-1 and Mode 2-1 in the LTE-A system are optimized for a scenario where a BS is equipped with 8 transmission antennas. That is, a PMI is collectively determined from two channel pre-coding matrix indices, W1 and W2, where W1 represents wideband/long-term channel characteristics and W2 represents sub-band/short-term channel characteristics. For transmission of W1 and W2 over PUCCH, Mode 1-1 is sub-divided into two sub-modes: Mode 1-1 (sub-mode 1) and Mode 1-1 (sub-mode 2). Also, the original Mode 2-1 is modified.

In order to support the newly defined feedback modes, several types of feedbacks are newly defined in the LTE-A system as follows:

Type 1a: one preferred sub-band location in a Band Part (BP, which is a subset of the set of communication spectrum resources S and has its size dependent on the size of the Set S) and a CQI for the sub-band, as well as a W2 for another sub-band. The overhead for the sub-band location is L bits, and the total overhead for the CQI and the W2 is 8 bits (if RI=1), 9 bits (if 1<RI<5), or 7 bits (if RI>4).

Type 2a: W1. The overhead for the W1 is 4 bits (if RI<3), 2 bits (if 2<RI<8), or 0 bits (if RI=8).

Type 2b: wideband W2 and wideband CQI. The total overhead for the wideband W2 and the wideband CQI is 8 bits (if RI=1), 11 bits (if 1<RI<4), 10 bits (if RI=4), or 7 bits (if RI>4).

Type 2c: wideband CQI, W1 and wideband W2. The total overhead for the wideband CQI, the W1 and the wideband W2 is 8 bits (if RI=1), 11 bits (if 1<RI<4), 9 bits (if RI=4), or 7 bits (if RI>4). It is to be noted that, in order to limit the feedback overhead, the W1 and the wideband W2 take values from an incomplete set (i.e., subset) of values, which is obtained by down-sampling all possible values of the W1 and the wideband W2.

Type 5: RI and W1. The total overhead for the RI and the WI is 4 bits (in the case of 8 antennae and 2-layer data multiplexing) or 5 bits (in the case of 8 antennae and 4/8-layer data multiplexing). Also, it is to be noted that, in order to limit the feedback overhead, the W1 takes values from an incomplete set (i.e., subset) of values, which is obtained by down-sampling all possible values of the W1.

Type 6: RI and Precoding Type Indicator (PTI). The overhead for PTI is 1 bit, indicating the type of precoding. The total overhead for the RI and the PTI is 2 bits (in the case of 8 antennae and 2-layer data multiplexing), 3 bits (in the case of 8 antennae and 3-layer data multiplexing), or 4 bits (in the case of 8 antennae and 8-layer data multiplexing).

In the description, "W2" when used alone refers to "sub-band W2", while "wideband W2" is referred to in their full expressions.

The mode-type relationships between the Mode 1-1 (sub-mode 1), the Mode 1-1 (sub-mode 1) and the Mode 2-1 and the original and the above new types of feedbacks are as follows:

(1) the Mode 1-1 (sub-mode 1) is a combination of Type 5 and Claim 2b. That is, the feedbacks of Type 5 and Type 2b are carried out at different periods and/or with different sub-frame offsets.

(2) the Mode 1-1 (sub-mode 2) is a combination of Type 3 and Type 2/2c,

(2.1) when the MIMO transmission approach is of type 4) or 8), the Mode 1-1 (sub-mode 2) is composed of Type 3 and Type 2. That is, the feedbacks of Type 3 and Type 2 are carried out at different periods and/or with different sub-frame offsets.

(2.2) when the MIMO transmission approach is of type 9), the Mode 1-1 (sub-mode 2) is composed of Type 3 and Type 2c. That is, the feedbacks of Type 3 and Type 2c are carried out at different periods and/or with different sub-frame offsets.

(3) the new Mode 2-1 is specific to the MIMO transmission approach of type 9), and is a combination of Type 6, Type 2b and Type 2a/1a,

(3.1) when the PTI of Type 6 is 0, the new Mode 2-1 is composed of Type 6, Type 2b and Type 2a. That is, the feedbacks of Type 6, Type 2b and Type 2a are carried out at different periods and/or with different sub-frame offsets.

(3.2) when the PTI of Type 6 is 1, the new Mode 2-1 is composed of Type 6, Type 2b and Type 1a. That is, the feedbacks of Type 6, Type 2b and Type 1a are carried out at different periods and/or with different sub-frame offsets.

Further, it is to be noted that the typical scenario for researching multi-antenna multi-BS coordination in the LTE-A system is where a macro BS is connected to a plurality of low-power Remote Radio Heads (RRHs) with cell IDs which are the same as or different from the BS' cell ID, according to the minutes of the 3GPP TSG-RAN WG1 meeting #63bis held in Dublin, Ireland in January 2011.

In summary, as for the CSI feedback for multi-antenna multi-BS coordination in the LTE-A system, the general concept is that the feedback contents involve CSI based on codebook space search, such as CQI, PMI and RI, and the information feedback is mainly carried out separately to each BS. In this architecture, there are still a number of issues to be researched. In particular, in the typical scenario for researching multi-antenna multi-BS coordination, it is an important topic on how to feed back CSI for the multi-BS coordination environment to organically combine JT and DCS operations.

In view of the lack of CSI feedback approaches dynamically supporting JT and DCS transmission in the prior art, it is an object of the present invention to provide a novel CSI feedback method and user equipment to fill this gap.

Specifically, according to a first aspect of the present invention, a User Equipment (UE) is provided, which comprises: a Transmission Point (TP) set acquiring unit configured to acquire a set of TPs participating in multi-antenna multi-BS coordination from a serving Base Station (BS); a TP selecting unit configured to select a TP from the set of TPs; and a Channel State Information (CSI) feedback unit configured to feed back CSI to the serving BS, wherein the CSI contains index information identifying the selected TP.

Preferably, the set of TPs are determined by the serving BS, and semi-statically configured to the UE via Radio Resource Control (RRC) signalings or Media Access Control (MAC) layer signallings.

Preferably, the number of TPs in the set of TPs is an integer more than 1 and less than 9. The set of TPs contains TPs corresponding to a Dynamic Cell Selection (DCS) transmission approach and/or TPs corresponding to a Joint Transmission (JT) transmission approach. A TP is composed of transmission ports of one or more BSs, and TPs have the same number or different numbers of transmission ports. The same set of transmission ports is permuted in different order to constitute different TPs.

Preferably, the CSI feedback unit may feed back the CSI containing the index information to the serving BS in a periodic feedback manner, wherein the index information is a Point Selection Index (PSI).

Preferably, in an LTE-A system, feedback of PSI is defined as a type of feedback whose feedback period is an integer multiple of the feedback period of feedback Type 5 and whose feedback time slot offset is the same as that of the feedback Type 5. If the defined type of feedback conflicts with the feedback Type 5, only the PSI is fed back.

Preferably, in an LTE-A system, feedback of PSI is defined as a type of feedback whose feedback period is an integer multiple of the feedback period of feedback Type 3 and whose feedback time slot offset is the same as that of the feedback Type 3. If the defined type of feedback conflicts with the feedback Type 3, only the PSI is fed back.

Preferably, in an LTE-A system, feedback of PSI is defined as a type of feedback whose feedback period is an integer multiple of the feedback period of feedback Type 6 and whose feedback time slot offset is the same as that of the feedback Type 6. If the defined type of feedback conflicts with the feedback Type 6, only the PSI is fed back.

Preferably, the CSI feedback unit may also feed back the CSI containing the index information to the serving BS in a triggered feedback manner, wherein one Flag bit is contained in the CSI to dynamically indicate whether the index information changes and the index information is a PSI.

Preferably, in an LTE-A system, if the PSI changes, feedback of PSI will be carried out using a combination of the following types of feedbacks: a feedback type for feeding back the Flag bit and the PSI; and a feedback Type 5.

Preferably, in an LTE-A system, if the PSI changes, feedback of PSI will be carried out using a combination of the following types of feedbacks: a feedback type for feeding back the Flag bit, the PSI and Rank Index (RI); and a feedback Type 2.

Preferably, in an LTE-A system, if the Flag bit contained in the CSI indicates that the PSI changes, feedback of PSI will be carried out using a combination of the following types of feedbacks: a feedback type for feeding back the Flag bit and the PSI; and a feedback Type 3.

Preferably, in an LTE-A system, if the Flag bit contained in the CSI indicates that the PSI changes, feedback of PSI will be carried out using a combination of the following types of feedbacks: a feedback type for feeding back the Flag bit and the PSI; a feedback Type 5; and a feedback Type 2b.

Preferably, in an LTE-A system, if the Flag bit contained in the CSI indicates that the PSI changes, feedback of PSI will be carried out using a combination of the following types of feedbacks: a feedback type for feeding back the Flag bit and the PSI; a feedback Type 3; and a feedback Type 2c.

Preferably, in an LTE-A system, if the Flag bit contained in the CSI indicates that the PSI changes, feedback of PSI will be carried out using a combination of the following types of feedbacks: a feedback type for feeding back the Flag bit, the PSI and RI; a feedback Type 2a; and a feedback Type 2b.

Preferably, the type of feedback used to feed back the Flag bit and the PSI further contains padding bits.

Preferably, the index information is a PSI, and the UE may be configured to update the PSI according to RRC signallings and MAC layer signallings transmitted from the serving BS.

According to a second aspect of the present invention, a User Equipment (UE) is provided, a CSI feedback is provided, which comprises: acquiring a set of Transmission Points (TPs) participating in multi-antenna multi-BS coordination from a serving BS; selecting a TP from the set of TPs; and feeding back the CSI to the serving Base Station (BS), wherein the CSI contains index information identifying the selected TP.

The CSI feedback method and user equipment according to the present invention have the advantages of dynamically supporting JT and DCS transmission, simple implementation and high system throughput.

The above and other objects, features and advantages of the present invention will be more apparent from the following preferred embodiments illustrated with reference to the figures, in which:
Fig. 1 is a schematic diagram of a MIMO system; Fig. 2 is a schematic diagram of complete CSI feedback; Fig. 3 is a schematic diagram of statistic-based CSI feedback; Fig. 4 is a schematic diagram of CSI feedback based on codebook space search; Fig. 5 is a schematic diagram of a multi-cell cellular communication system; Fig. 6 is a flowchart illustrating a CSI feedback method according to the present invention; Fig. 7 is a schematic block diagram of a UE according to the present invention; Fig. 8 is a schematic diagram illustrating example 1 of periodic feedback; Fig. 9 is a schematic diagram illustrating example 2 of the periodic feedback; Fig. 10 is a schematic diagram illustrating example 3 of the periodic feedback; Fig. 11 is a schematic diagram illustrating example 1 of triggered feedback; Fig. 12 is a schematic block diagram illustrating example 2 of the triggered feedback; and Fig. 13 is a schematic block diagram illustrating example 3 of the triggered feedback.

Preferred embodiments of the present invention will be detailed with reference to the drawings. In the following description, details and functions unnecessary to the present invention are omitted so as not to obscure the concept of the invention. For clear and detailed explanation of the implementation steps of the present invention, some specific embodiments applicable to the downlink of the LTE-A cellular communication system are given below. Herein, it is to be noted that the present invention is not limited to the application exemplified in the embodiments. Rather, it is applicable to other communication systems, such as the future 5G system.

Also, it is to be noted that, among the terms "serving BS", "coordinated BS" and "coordinated BS set" used herein, the term "serving BS", as commonly used by those skilled in the art, refers to a BS which can transmit control signallings directly to a MS. However, for clearly distinguishing between different concepts, the term "coordinated BS" is used in a manner different from that familiar to those skilled in the art. Specifically, although those skilled in the art commonly use the term to refer to all BSs participating in coordination transmission, the term "coordinated BS" used herein refers in particular to other BSs participating in the coordination transmission than the serving BS. The term "coordinated BS set" refers to a set of such "coordinated BSs". Obviously, there is no "serving BS" included in the coordinated BS set.

Fig. 5 is a schematic diagram of a multi-cell cellular communication system. The cellular system divides a service coverage area into a number of adjacent wireless coverage areas, i.e., cells. In Fig. 5, the entire service area is formed by

cells

100, 102 and 104, each being illustratively shown as a hexagon. Base Stations (BSs) 200, 202 and 204 are associated with the

cells

100, 102 and 104, respectively. As known to those skilled in the art, each of the BSs 200-204 includes at least a transmitter and a receiver. Herein, it is to be noted that a BS, which is generally a serving node in a cell, can be an independent BS having a function of resource scheduling, a transmitting node belonging to an independent BS, a relay node (which is generally configured for further enlarging the coverage of a cell), or the like. As illustratively shown in Fig. 5, each of the BSs 200-204 is located in a particular area of the corresponding one of the cells 100-104 and is equipped with an omni-directional antenna. It is to be noted that, however, in a cell arrangement for the cellular communication system, each of the BSs 200-204 can also be equipped with a directional antenna for directionally covering a partial area of the corresponding one of the cells 100-104, which is commonly referred to as a sector. Thus, the diagram of the multi-cell cellular communication system as shown in Fig. 5 is illustrative only and does not imply that the implementation of the cellular system according to the present invention is limited to the above particular constraints.

As shown in Fig. 5, the

BSs

200, 202 and 204 are connected with each other via X2 interfaces 300, 302 and 304. In an LTE-A system, a three-layer node network architecture including base station, radio network control unit and core network is simplified into a two-layer node architecture in which the function of the radio network control unit is assigned to the base station and a wired interface named "X2" is defined for coordination and communication between base stations.

In Fig. 5, the

BSs

200, 202 and 204 are also connected with each other via air interfaces, A1 interfaces, 310, 312 and 314. In a future communication system, it is possible to introduce a concept of relay node. Relay nodes are connected with each other via wireless interfaces and a base station can be considered as a special relay node. Thus, a wireless interface named "A1" can then be used for coordination and communication between base stations.

Additionally, an upper layer entity 220 of the

BSs

200, 202 and 204 is also shown in Fig. 5, which can be a gateway or another network entity such as mobility management entity. The upper layer entity 220 is connected to the

BSs

200, 202 and 204 via S1 interfaces 320, 322 and 324, respectively. In an LTE-A system, a wired interface named "S1" is defined for coordination and communication between the upper layer entity and the base station.

A number of User Equipments (UEs) 400 and 402 to 430 are distributed over the

cells

100, 102 and 104, as shown in Fig. 5. As known to those skilled in the art, each of the UEs 400-430 includes a transmitter, a receiver and a mobile terminal control unit. Each of the UEs can access the cellular communication system via its serving BS (one of the

BSs

200, 202 and 204). It should be understood that while only 16 UEs are illustratively shown in Fig. 5, there may be a large number of UEs in practice. In this sense, the description of the UEs in Fig. 5 is also for illustrative purpose only. Each of the UEs can access the cellular communication network via its serving BS. The BS transmitting control signallings directly to a certain UE is referred to as the serving BS of that UE, while other BSs are referred to non-serving BSs of that UE. The non-serving BSs can function as coordinated BSs of the serving BS and provide communication service to the UE along with the serving BS.

For explanation of specific embodiments of the present invention, the UE 416 is considered. The UE 416 operates in a multi-BS coordination mode, has BS 202 as its serving BS and has

BSs

200 and 204 as its coordinated BSs. It is to be noted that this embodiment focuses on the UE 416, which does not imply that the present invention is only applicable to one UE scenario. Rather, the present invention is fully applicable to multi-UE scenario. For example, the inventive method can be applied to the

UEs

408, 410, 430 and the like as shown in Fig. 5. In an exemplary scenario, there is one serving BS and two coordinated BSs. However, the present invention is not limited to this. In fact, the present invention is not limited to any specific number of serving BS(s) or coordinated BS(s).

In the following, a CSI feedback method 600 according to the present invention will be described with reference to Fig. 6. In description of specific embodiments, the following scenario of multi-BS coordination is assumed:

As an example for illustrative purpose only, the UE 416 operates in a multi-BS coordination mode, has BS 202 as its serving BS, and has

BSs

200 and 204 as its coordinated BSs (non-serving BSs). For the UE's multi-antenna multi-BS coordination transmission, each of the BS 200 and the BS 202 is equipped with 8 transmitting antennae and uses 8 transmission ports, and the BS 204 is equipped with 4 transmitting antennae and uses 4 transmission ports. The UE 416 can be a single antenna or multi-antenna device. For any other UE (e.g., any of UEs 400-430) operable in the multi-BS coordination mode, there are also serving and coordinated BSs prescribed.

It is to be noted that the transmitting antennae and the transmission ports of a BS are not necessarily in one-to-one correspondence, although generally the number of the BS's transmitting antennae is equal to the number of transmission ports. In practical implementation, a plurality of transmitting antennae of a BS can be mapped to a single transmission port by combining the plurality of transmitting antennae in a weighted manner (see non-patent document: 3GPP, R1-092427, "CSI-RS Design for Virtualized LTE Antenna in LTE-A System", Fujitsu).

Further, it is to be noted that the specific transmission port numbers according to the inconsistent transmission port configurations used in the above scenario are just for illustrative purpose only. The application of the present invention is by no means limited to these numbers. Rather, having regard to embodiments of the present invention, those skilled in the art will appreciate that the present invention is widely applicable to any transmission port configuration.

As shown in Fig. 6, the CSI feedback method 600 according to the present invention begins with step S601. In step S601, a UE acquires a set of TPs participating in multi-antenna multi-BS coordination from a serving BS.

As a non-limited implementation of this step, the UE (e.g., UE 416) may periodically report to the serving BS (e.g., serving BS 202) path loss information of paths from the UE to its adjacent BSs. Accordingly, the serving BS can estimate the geographic location of the UE from the report, determine the set of TPs participating in the multi-antenna multi-BS coordination based on the estimated geographic location, and semi-statically configure the set of TPs for the UE via upper layer signallings, such as Radio Resource Control (RRC) signallings, or Media Acccess Control (MAC) layer signallings.

In the following, 7 non-limited examples of the TP set will be given for cases wherein the TP set includes 2 to 8 TPs, respectively.

Example 1: The TP set which the serving BS 202 configures for the UE 416 includes 2 TPs, so that the UE 416 can use 1 bit to feed back the result of choosing one from two opinions. The 2 TPs may include: 1) a TP composed of a total of 8 ports, including ports 0 to 7 of the BS 202; and 2) a TP composed of a total of 8 ports, including ports 0 to 3 of the BS 202,

ports

0 and 1 of the BS 200, and

ports

2 and 3 of the BS 204.

Example 2: The TP set which the serving BS 202 configures for the UE 416 includes 3 TPs, so that the UE 416 can use 2 bit to feed back the result of choosing one from three opinions. The 3 TPs may include: 1) a TP composed of a total of 8 ports, including ports 0 to 7 of the BS 202; 2) a TP composed of a total of 8 ports, including ports 0 to 3 of the BS 202,

ports

0 and 1 of the BS 200, and

ports

2 and 3 of the BS 204; and 3) a TP composed of a total of 8 ports, including ports 0 to 3 of the BS 202, ports 3 and 4 of the BS 200, and

ports

0 and 1 of the BS 204.

Example 3: The TP set which the serving BS 202 configures for the UE 416 includes 4 TPs, so that the UE 416 can use 2 bit to feed back the result of choosing one from four opinions. The 4 TPs may include: 1) a TP composed of a total of 8 ports, including ports 0 to 7 of the BS 202; 2) a TP composed of a total of 8 ports, including ports 0 to 3 of the BS 202,

ports

0 and 1 of the BS 200, and

ports

2 and 3 of the BS 204; 3) a TP composed of a total of 8 ports, including ports 0 to 3 of the BS 202, ports 3 and 4 of the BS 200, and

ports

0 and 1 of the BS 204; and 4) a TP composed of a total of 4 ports, including ports 0 to 3 of the BS 204. It is to be noted that, if the UE chooses the fourth TP, the UE chooses the entire BS 204 equivalently. That is, the DCS transmission approach is implemented. Herein, such a TP corresponding to the DCS transmission approach may be involved in all illustrative configurations of the set of TPs participating in the multi-antenna multi-BS coordination.

Example 4: The TP set which the serving BS 202 configures for the UE 416 includes 5 TPs, so that the UE 416 can use 3 bit to feed back the result of choosing one from five opinions. The 5 TPs may include: 1) a TP composed of a total of 8 ports, including ports 0 to 7 of the BS 202; 2) a TP composed of a total of 8 ports, including ports 0 to 3 of the BS 202,

ports

0 and 1 of the BS 200, and

ports

0 and 1 of the BS 204; 4) a TP composed of a total of 4 ports, including ports 0 to 3 of the BS 204; and 5) a TP composed of a total of 4 ports, including ports 4 to 7 of the BS 200. Note that, in practical implementation, it is possible for the number of ports of the fourth and fifth TPs to be different from that of the first three TPs, because different TPs have configurations independent of each other. Herein, such TPs having different numbers of ports may be involved in all illustrative configurations of the set of APs participating in the multi-antenna multi-BS coordination.

Example 5: The TP set which the serving BS 202 configures for the UE 416 includes 6 TPs, so that the UE 416 can use 3 bit to feed back the result of choosing one from six opinions. The 6 TPs may include: 1) a TP composed of a total of 8 ports, including ports 0 to 7 of the BS 202; 2) a TP composed of a total of 8 ports, including ports 0 to 3 of the BS 202,

ports

0 and 1 of the BS 200, and

ports

0 and 1 of the BS 204; 4) a TP composed of a total of 4 ports, including ports 0 to 3 of the BS 204; 5) a TP composed of a total of 4 ports, including ports 4 to 7 of the BS 200; and 6) a TP composed of a total of 6 ports, including ports 0 to 3 of the BS 204, and ports 7 and 8 of the BS 200. It is to be noted that, the sixth TP is composed of all ports of the BS 204 as well as part (or all) of the ports of another BS. This corresponds to the JT transmission approach. Herein, such a TP may be involved in all illustrative configurations of the set of APs participating in the multi-antenna multi-BS coordination.

Example 6: The TP set which the serving BS 202 configures for the UE 416 includes 7 TPs, so that the UE 416 can use 3 bit to feed back the result of choosing one from seven opinions. The 7 TPs may include: 1) a TP composed of a total of 8 ports, including ports 0 to 7 of the BS 202; 2) a TP composed of a total of 8 ports, including ports 0 to 3 of the BS 202,

ports

0 and 1 of the BS 200, and

ports

0 and 1 of the BS 204; 4) a TP composed of a total of 4 ports, including ports 0 to 3 of the BS 204; 5) a TP composed of a total of 4 ports, including ports 4 to 7 of the BS 200; 6) a TP composed of a total of 6 ports, including ports 0 to 3 of the BS 204, and ports 7 and 8 of the BS 200; and 7) a TP composed of a total of 8 ports, including ports 0 to 7 of the BS 200.

Example 7: The TP set which the serving BS 202 configures for the UE 416 includes 8 TPs, so that the UE 416 can use 3 bit to feed back the result of choosing one from eight opinions. The 8 TPs may include: 1) a TP composed of a total of 8 ports, including ports 0 to 7 of the BS 202; 2) a TP composed of a total of 8 ports, including ports 0 to 3 of the BS 202,

ports

0 and 1 of the BS 200, and

ports

0 and 1 of the BS 204; 4) a TP composed of a total of 4 ports, including ports 0 to 3 of the BS 204; 5) a TP composed of a total of 4 ports, including ports 4 to 7 of the BS 200; 6) a TP composed of a total of 6 ports, including ports 0 to 3 of the BS 204, and ports 7 and 8 of the BS 200; 7) a TP composed of a total of 8 ports, including ports 0 to 7 of the BS 200; and 8) a TP composed of a total of ports 3 and 4 of the BS 200, ports 0 to 3 of the BS 202, and

ports

0 and 1 of the BS 204. Note that, in practical implementation, it is possible for the eighth TP and the third TP to have the same set of 8 ports ordered differently, because TPs with different port orders shall be regarded as different TPs.

Subsequently, the method proceeds to step S602 and then to step S603. At step S602, the UE selects a TP from the set of TPs. At step S603, the UE feeds back CSI containing index information identifying the TP selected at step S602, to the serving BS.

In the following, specific manners in which the UE may feed back CSI containing index information to the serving BS will be set forth, with respect to a periodic feedback manner and a triggered feedback manner respectively. For the period feedback manner and the triggered feedback manner respectively, three examples are given to illustrate the feedback operations of the UE to the serving BS.

Periodic feedback

(Example 1) where the serving BS 202 configures the feedback mode of the UE 416 as Mode 1-1 (sub-mode 1).

A new type (Type 7) of feedback containing dynamic TP selection information, referred to as Point Selection Index (PSI), is defined for feedback to the serving BS 202. Depending on the size of the set of TPs configured by the serving BS at step S601, the PSI uses 1, 2 or 3 bits to indicate the TP selected by the UE from the set of TPs.

The feedback period of Type 7 is an integer multiple of the feedback period of Type 5, and the time slot offset of Type 7 is the same as that of Type 5. The technical principle behind such a design is that: among all CSI information of Mode 1-1 (sub-mode 1), the dynamic TP selection information changes most slowly, and thus shall has the longest feed period. When there is a conflict between Type 7 and Type 5 (i.e., when both the feedback of Type 7 and the feedback of Type 5 are scheduled in the same Transmission Time Interval, TTI), the feedback of Type 7 is carried out while the feedback of claim 5 is not carried out. Example 1 of the periodic feedback is illustratively shown in Fig. 8.

(Example 2) where the serving BS 202 configures the feedback mode of the UE 416 as Mode 1-1 (sub-mode 2).

A new type (Type 7) of feedback containing PSI is defined for feedback to the serving BS 202. Depending on the size of the set of TPs configured by the serving BS at step S601, the PSI uses 1, 2 or 3 bits to indicate the TP selected by the UE from the set of TPs.

The feedback period of Type 7 is an integer multiple of the feedback period of Type 3, and the time slot offset of Type 7 is the same as that of Type 3. The technical principle behind such a design is that: among all CSI information of Mode 1-1 (sub-mode 2), the dynamic TP selection information changes most slowly, and thus shall has the longest feed period. When there is a conflict between Type 7 and Type 3, the feedback of Type 7 is carried out while the feedback of Type 3 is not carried out. Example 2 of the periodic feedback is illustratively shown in Fig. 9.

(Example 3) where the serving BS 202 configures the feedback mode of the UE 416 as Mode 2-1.

The feedback period of Type 7 is an integer multiple of the feedback period of Type 6, and the time slot offset of Type 7 is the same as that of Type 6. The technical principle behind such a design is that: among all CSI information of Mode 2-1, the dynamic TP selection information changes most slowly, and thus shall has the longest feed period. When there is a conflict between Type 7 and Type 6, the feedback of Type 7 is carried out while the feedback of Type 6 is not carried out. Example 3 of the periodic feedback is illustratively shown in Fig. 10.

Triggered feedback

A new type of feedback containing an indication referred to as Flag bit is defined for feedback to the serving BS 202. The Flag bit contains one bit dynamically indicating whether PSI changes. In the following, two illustrative triggered feedback schemes are given with respect to Mode 1-1 (sub-mode 1).

Scheme 1:
When Flag=0, indicating that the PSI does not change,
in the first part of Mode 1-1 (sub-mode 1), which corresponds to the former Type 5, the feedback of RI and W1 following the Flag bit remains unchanged, and
in the second part of Mode 1-1 (sub-mode 1), which corresponds to Type 2b, the feedback of wideband W2 and wideband CQI remains unchanged.

When Flag=1, indicating that the PSI changes,
the first part of Mode 1-1 (sub-mode 1) changes into a type composed of one Flag bit followed by PSI (containing 1, 2 or 3 bits) and possibly padding bits, wherein the possible padding bits can make the length of the first part of the Mode 1-1 (sub-mode 1) when Flag=1 equal to the length of the first part of the Mode 1-1 (sub-mode 1) when Flag=0, and
the second part of Mode 1-1 (sub-mode 1) changes from Type 2b into Type 5, for transmitting RI and WI corresponding to the new PSI.

Scheme 2:
As an alternative, when Flag=0, indicating the PSI does not change,
in the first part of Mode 1-1 (sub-mode 1), which corresponds to the former Type 5, the feedback of RI and W1 following the Flag bit and possibly followed by padding bits remains unchanged, wherein the possible padding bits can make the length of the first part of the Mode 1-1 (sub-mode 1) when Flag=0 equal to the length of the first part of the Mode 1-1 (sub-mode 1) when Flag=1 so as to facilitate detection at the BS, and
in the second part of Mode 1-1 (sub-mode 1), which corresponds to Type 2b, the feedback of wideband W2 and wideband CQI remains unchanged.

When Flag=1, indicating that the PSI changes,
the first part of Mode 1-1 (sub-mode 1) changes into a type composed of one Flag bit, followed by PSI (containing 1, 2 or 3 bits) and RI, and
the second part of Mode 1-1 (sub-mode 1) changes from Type 2b into Type 2c, for transmitting W1, wideband W2 and wideband CQI corresponding to the new PSI.

It is to be noted that the above described correspondence between the value of the Flag bit and its indication is for illustrative purpose only. In practical implementation, Flag=0 may either indicate that the PSI changes or that the PSI does not change.

The above two schemes of Example 1 of the triggered feedback are illustratively shown in Fig. 11.

A new type of feedback containing an indication, referred to as Flag bit, is defined for feedback to the serving BS 202. The Flag bit contains one bit dynamically indicating whether the PSI changes. In the following, one illustrative triggered feedback scheme is given with respect to Mode 1-1 (sub-mode 2).

When Flag=0, indicating that the PSI does not change,
in the first part of Mode 1-1 (sub-mode 2), which corresponds to the former Type 3, the feedback of RI following the Flag bit remains unchanged, and
in the second part of Mode 1-1 (sub-mode 1), which corresponds to Type 2c, the feedback of W1, wideband W2 and wideband CQI remains unchanged.

When Flag=1, indicating that the PSI changes,
the first part of Mode 1-1 (sub-mode 2) changes into a type composed of one Flag bit, followed by PSI (containing 1, 2 or 3 bits) and possibly padding bits, wherein the possible padding bits can make the length of the first part of the Mode 1-1 (sub-mode 2) when Flag=1 equal to the length of the first part of the Mode 1-1 (sub-mode 2) when Flag=0 so as to facilitate detection at the BS, and
the second part of Mode 1-1 (sub-mode 2) changes from Type 2c into Type 3, for transmitting RI corresponding to the new PSI.

Also, it is to be noted that the above correspondence between the value of the Flag bit and its indication is for illustrative purpose only. In practical implementation, Flag=0 may either indicate that the PSI changes or that the PSI does not change.

The above scheme of Example 2 of the triggered feedback is illustratively shown in Fig. 12.

(Example 3) where the serving BS 202 configures the feedback mode of the UE 416 as a new Mode 2-1.

A new type of feedback containing an indication, referred to as Flag bit, is defined for feedback to the serving BS 202. The Flag bit contains one bit dynamically indicating whether the PSI changes. In the following, three illustrative triggered feedback schemes are given with respect to the new Mode 2-1.

Scheme 1:
When Flag=0, indicating that the PSI does not change,
in the first part of Mode 2-1, which corresponds to the former Type 6, the feedback of RI and PTI following the Flag bit remains unchanged,
in the second part of Mode 2-1, which corresponds to Type 2a if PTI=0 or corresponds to Type 2b if PTI=1, the feedback remains unchanged, and
in the third part of Mode 2-1, which corresponds to Type 2b if PTI=0 or corresponds to type 1a if PTI=1, the feedback remains unchanged.

When Flag=1, indicating that the PSI changes,
the first part of Mode 2-1 changes into a type composed of one Flag bit, followed by PSI (containing 1, 2 or 3 bits) and possibly padding bits, wherein the possible padding bits can make the length of the first part of the Mode 2-1 when Flag=1 equal to the length of the first part of the Mode 2-1 when Flag=0 so as to facilitate detection at the BS,
the second part of Mode 2-1 changes from the former type into Type 5, for transmitting RI and W1 corresponding to the new PSI, and
the third part of Mode 2-1 changes from the former type into Type 2b, for transmitting wideband W2 and wideband CQI corresponding to the new PSI.

Scheme 2:
As an alternative, when Flag=0, indicating the PSI does not change,
in the first part of Mode 2-1, which corresponds to the former Type 6, the feedback of RI and PTI following the Flag bit remains unchanged,
in the second part of Mode 2-1, which corresponds to Type 2a if PTI=0 or corresponds to Type 2b if PTI=1, the feedback remains unchanged, and
in the third part of Mode 2-1, which corresponds to Type 2b if PTI=0 or corresponds to Type 1a if PTI=1, the feedback remains unchanged.

When Flag=1, indicating that the PSI changes,
the first part of Mode 2-1 changes into a type composed of one Flag bit, followed by PSI (containing 1, 2 or 3 bits) and possibly padding bits, wherein the padding bits can make the length of the first part of the Mode 2-1 when Flag=1 equal to the length of the first part of the Mode 2-1 when Flag=0 so as to facilitate detection at the BS,
the second part of Mode 2-1 changes from the former type into Type 3, for transmitting RI corresponding to the new PSI, and
the third part of Mode 2-1 changes from the former type into Type 2c, for transmitting W1, wideband W2 and wideband CQI corresponding to the new PSI.

Scheme 3:
As another alternative, when Flag=0, indicating the PSI does not change,
in the first part of Mode 2-1, which corresponds to the former Type 6, the feedback of RI and W1 following the Flag bit and possibly followed by padding bits remains unchanged, wherein the padding bits can make the length of the first part of the Mode 2-1 when Flag=0 equal to the length of the first part of the Mode 2-1 when Flag=1 so as to facilitate detection at the BS,
in the second part of Mode 2-1, which corresponds to Type 2a if PTI=0 or corresponds to Type 2b if PTI=1, the feedback remains unchanged, and
in the third part of Mode 2-1, which corresponds to Type 2b if PTI=0 or corresponds to Type 1a if PTI=1, the feedback remains unchanged.

When Flag=1, indicating that the PSI changes,
the first part of Mode 2-1 changes into a type composed of one Flag bit, followed by PSI (containing 1, 2 or 3 bits) and RI,
the second part of Mode 2-1 changes from the former type into Type 2a, for transmitting W1 corresponding to the new PSI, and
the third part of Mode 2-1 changes from the former type into Type 2b, for transmitting wideband W2 and wideband CQI corresponding to the new PSI.

The above three schemes of Example 3 of the triggered feedback are illustratively shown in Fig. 13.

It should be appreciated that the serving BS may also semi-statically configure the UE to or not to update the PSI using upper signallings or MAC layer signallings. As such, the BS may flexibly instruct the UE to or not to update the PSI, according to backhaul connection state, traffic load, UE's QoS, and/or connection/handover state of UE. In addition, one bit of feedback overhead can be saved, because of the omission of the Flag bit.

Here, a UE 700 enabling the implementation of the above CSI feedback methods is also provided. Fig. 7 is a schematic block diagram of the UE 700 according to the present invention.

As shown in Fig. 7, the UE 700 according to the present invention comprises: a TP set acquiring unit 710 configured to acquire a set of TPs from a serving BS; a TP selecting unit 720 configured to select a TP from the set of TPs; and a CSI feedback unit 730 configured to feed back CSI to the serving BS, wherein the CSI contains index information identifying the selected TP.

It should be noted that the solution of the present invention has been described above by a way of example only. However, the present invention is not limited to the above steps and element structures. It is possible to adjust, add and remove the steps and elements structures depending on actual requirements. Thus, some of the steps and elements are not essential for achieving the general inventive concept of the present invention. Therefore, the features necessary for the present invention is only limited to a minimum requirement for achieving the general inventive concept of the present invention, rather than the above specific examples.

The present invention has been described above with reference to the preferred embodiments thereof. It should be understood that various modifications, alternations and additions can be made by those skilled in the art without departing from the spirits and scope of the present invention. Therefore, the scope of the present invention is not limited to the above particular embodiments but only defined by the claims as attached.

Claims

A User Equipment (UE), comprising:
a Transmission Point (TP) set acquiring unit configured to acquire a set of TPs participating in multi-antenna multi-BS coordination from a serving Base Station (BS);
a TP selecting unit configured to select a TP from the set of TPs; and
a Channel State Information (CSI) feedback unit configured to feed back CSI to the serving BS, wherein the CSI contains index information identifying the selected TP.
The UE according to claim 1, wherein the set of TPs are determined by the serving BS, and semi-statically configured to the UE via Radio Resource Control (RRC) signalings or Media Access Control (MAC) layer signallings.
The UE according to claim 1 or 2, wherein the number of TPs in the set of TPs is an integer more than 1 and less than 9.
The UE according to any of claims 1-3, wherein the set of TPs contains TPs corresponding to a Dynamic Cell Selection (DCS) transmission approach and/or TPs corresponding to a Joint Transmission (JT) transmission approach.
The UE according to any of claims 1-4, wherein a TP is composed of transmission ports of one or more BSs, and TPs have the same number or different numbers of transmission ports.
The UE according to claim 5, wherein the same set of transmission ports is permuted in different order to constitute different TPs.
The UE according to any of claims 1-6, wherein the CSI feedback unit feeds back the CSI containing the index information to the serving BS in a periodic feedback manner, wherein the index information is a Point Selection Index (PSI).
The UE according to claims 7, wherein, in an LTE-A system, feedback of PSI is defined as a type of feedback whose feedback period is an integer multiple of the feedback period of feedback Type 5 and whose feedback time slot offset is the same as that of the feedback Type 5.
The UE according to claim 8, wherein if the defined type of feedback conflicts with the feedback Type 5, only the PSI is fed back.
The UE according to claim 7, wherein, in an LTE-A system, feedback of PSI is defined as a type of feedback whose feedback period is an integer multiple of the feedback period of feedback Type 3 and whose feedback time slot offset is the same as that of the feedback Type 3.
The UE according to claim 10, wherein if the defined type of feedback conflicts with the feedback Type 3, only the PSI is fed back.
The UE according to claim 7, wherein, in an LTE-A system, feedback of PSI is defined as a type of feedback whose feedback period is an integer multiple of the feedback period of feedback Type 6 and whose feedback time slot offset is the same as that of the feedback Type 6.
The UE according to claim 12, wherein if the defined type of feedback conflicts with the feedback Type 6, only the PSI is fed back.
The UE according to any of claims 1-6, wherein the CSI feedback unit feeds back the CSI containing the index information to the serving BS in a triggered feedback manner, wherein one Flag bit is contained in the CSI to dynamically indicate whether the index information changes and the index information is a PSI.
The UE according to claim 14, wherein, in an LTE-A system, if the Flag bit contained in the CSI indicates that the PSI changes, feedback of PSI will be carried out using a combination of the following types of feedbacks:
a feedback type for feeding back the Flag bit and the PSI; and
a feedback Type 5.
The UE according to claim 14, wherein, in an LTE-A system, if the Flag bit contained in the CSI indicates that the PSI changes, feedback of PSI will be carried out using a combination of the following types of feedbacks:
a feedback type for feeding back the Flag bit, the PSI and Rank Index (RI); and
a feedback Type 2c.
The UE according to claim 14, wherein, in an LTE-A system, if the Flag bit contained in the CSI indicates that the PSI changes, feedback of PSI will be carried out using a combination of the following types of feedbacks:
a feedback type for feeding back the Flag bit and the PSI; and
a feedback Type 3.
The UE according to claim 14, wherein, in an LTE-A system, if the Flag bit contained in the CSI indicates that the PSI changes, feedback of PSI will be carried out using a combination of the following types of feedbacks:
a feedback type for feeding back the Flag bit and the PSI;
a feedback Type 5; and
a feedback Type 2b.
The UE according to claim 14, wherein, in an LTE-A system, if the Flag bit contained in the CSI indicates that the PSI changes, feedback of PSI will be carried out using a combination of the following types of feedbacks:
a feedback type for feeding back the Flag bit and the PSI;
a feedback Type 3; and
a feedback Type 2c.
The UE according to claim 14, wherein, in an LTE-A system, if the Flag bit contained in the CSI indicates that the PSI changes, feedback of PSI will be carried out using a combination of the following types of feedbacks:
a feedback type for feeding back the Flag bit, the PSI and RI;
a feedback Type 2a; and
a feedback Type 2b.
The UE according to any of claims 15, and 17 through 19, wherein the type of feedback used to feed back the Flag bit and the PSI further contains padding bits.
The UE according to any of claims 1-6, wherein the index information is a PSI, and the UE is configured to update the PSI according to RRC signallings or MAC layer signallings transmitted from the serving BS.
A CSI feedback method, comprising:
acquiring a set of Transmission Points (TPs) participating in multi-antenna multi-BS coordination from a serving Base Station (BS);
selecting a TP from the set of TPs; and
feeding back the CSI to the serving BS, wherein the CSI contains index information identifying the selected TP.