WO2012124552A1

WO2012124552A1 - Channel state information feedback method, user equipment and base station

Info

Publication number: WO2012124552A1
Application number: PCT/JP2012/055732
Authority: WO
Inventors: Zeng YANG; Lei Huang; Ming Ding; Renmao Liu
Original assignee: Sharp Kabushiki Kaisha
Priority date: 2011-03-11
Filing date: 2012-02-29
Publication date: 2012-09-20
Also published as: CN102684850A; CN102684850B

Abstract

A Channel State Information (CSI) feedback method of a User Equipment (UE) is provided, which includes the following steps of: receiving from a Base Station (BS) a Channel State Information-Reference Signal (CSI-RS) measurement set configuration signal which contains an indication of a CSI-RS measurement set configured for a UE; measuring a CSI-RS in the CSI-RS measurement set based on the indication of the CSI-RS measurement set to obtain metric information corresponding to a CSI-RS pattern in the CSI-RS measurement set; obtaining a CSI-RS report set which is selected from the CSI-RS measurement set based on the metric information; determining a CSI feedback resource corresponding to a CSI-RS pattern in the CSI-RS report set; and feeding back CSI corresponding to the CSI-RS pattern in the CSI-RS report set to the BS over the determined CSI feedback resource. Corresponding UE and BS are also provided.

Description

DESCRIPTION

TITLE OF INVENTION:

CHANNEL STATE INFORMATION FEEDBACK METHOD,

USER EQUIPMENT AND BASE STATION TECHNICAL FIELD

The invention relates to communication technology, and more particularly, to a Channel State Information (CSI) feedback method, a User Equipment (UE) and a Base Station (BS) especially applicable in a Coordinated Multi-Point (CoMP) transmission scenario .

BACKGROUND ART

The 3^rd Generation Partnership Proj ect (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, also referred to as LTE Rel-8) project for designing Evolved Universal Terrestrial Radio Access (EUTRA) and Evolved Universal Terrestrial Radio Access Network (EUTRAN) . 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 or LTE Rel- 10) . In the LTE-A system, a concept known as Coordinated Multi-Point (CoMP) gets extensive attention and support. The core idea of CoMP is to solve the problem of downlink inter-cell interference by dynamic coordination between a plurality of geographically separate transmission points, thereby providing improved data transmission rate and user experience for a UE located at the edge of a cell.

Some concepts and fundamental terminologies for CoMP scenario are defined in 3GPP TR 36.8 14 V9.0.0 , Evolved Universal Terrestrial Radio Access (E-UTRA) ; Further advancements for E-UTRA physical layer aspects, 3GPP.

A serving cell refers to a single cell transmitting Physical Downlink Control CHannel (PDCCH) information, which is a concept already present in LTE .

In general, the CoMP transmission schemes can be divided into two categories : Joint Processing (JP) and Coordinated Scheduling/ Beamforming (CS / CB) . In the JP scheme , data are distributed over all transmission points in a CoMP coordination set. The JP scheme can be sub-divided into Joint Transmission (JT) and Dynamic Cell Selection (DCS) . The difference between JT and DCS lies in whether the Physical Downlink Shared CHannel (PDSCH) transmission is carried out on multiple or single transmission point in the coordination set. In the CS / CB scheme, data are only present in the serving cell while the scheduling of UE and the decision on beamforming are conducted based on the coordination between transmission points in the CoMP coordination set.

In the CoMP transmission, a UE needs to measure channel state/ statistical information of a link between the UE and a BS in each of a set of cells. This set of cells is referred to as a CoMP measurement set. The set of cells for which the UE actually performs information feedback can be a subset of the measurement set and is referred to as a report set. Here, the report set can be the same as the CoMP coordination set in which the BS in each of the cells participates in PDSCH transmission for the UE, either directly or indirectly. The coordination set may be or may be not transparent to the UE. For a UE configured into the CoMP mode, information feedback is mainly carried out separately for each cell and is transmitted over the uplink resources of the serving cell.

In 3GPP RAN Meeting #50, the research contents for LTE Rel-11 CoMP are further modified (cf. RP- 101425, Revised SID Proposal: Coordinated Multi-point Operation for LTE, Samsung). In order to expand the applicable scope, some non-traditional deployment scenarios, such as heterogeneous network and/or Distributed Remote Radio Heads within cell (also referred to as RRHs or RRUs), are also incorporated into the research goal of CoMP. According to the conclusion of 3GPP RANI Meeting #63bis, the research of CoMP will be directed to the following four deployment scenarios:

-Scenario 1 : Intra- Station CoMP,

- Scenario 2 : Inter-Station CoMP,

- Scenario 3 : Multi-Cell ID , in which all transmission points covered by a macro cell have different cell IDs, and

-Scenario 4 : Shared Cell ID , in which all transmission points covered by a macro cell share a single cell ID .

A common assumption in all of the above scenarios is that the communication between transmission points has low delay and infinite capacity, which is the most straightforward benefit from the use of distributed RRHs since the medium connecting between the transmission points is typically optical fiber such that the constraints on transmission delay and bandwidth are substantially relaxed.

According to R l - 1 1046 1 , Baseline Schemes and Focus of

CoMP Studies, Ericsson, ST-Ericsson and R l - 1 10649 , Aspects on Distributed RRUs with Shared Cell-ID for Heterogeneous Deployments, Ericsson, ST-Ericsson, in the above CoMP scenarios, regardless of whether cell ID is shared among transmission points, each transmission point needs an individual Channel State Information-Reference Signal (CSI-RS) pattern such that the effective CSI feedback for each transmission point can be obtained. The contents of the CSI-RS pattern include : 1 ) sequence of CSI-RS; 2) number of ports; 3) time-frequency location of CSI-RS in a sub-frame, period and sub-frame offset of CSI-RS; and 4) ratio of data to CSI Energy Per Resource Element (EPRE) , each CSI-RS pattern which requires PDSCH muting, including time-frequency location of the CSI-RS in a sub-frame, period and sub-frame offset of the CSI-RS , etc. In this regard, reference can be made to CSI-RS-Config definition in Section 6. 10.5 of TS 36.2 1 1 , V I O .0.0 , Physical channels and modulation, 3GPP or Section 6.3.2 of TS 36.33 1 , V I O .0.0 , Radio Resource Control (RRC) ; Protocol specification, 3GPP. A set of transmission points for which each UE measures and feeds back CSI and thus the configuration of CSI-RS pattern should be UE specific . Based on uplink signals received from the UE, such as measurements of channel Sounding Reference Signal (SRS) , Physical Uplink Control CHannel (PUCCH) signal and Physical Uplink Shared CHannel (PUSCH) signal, the BS configures a set of CSI-RS patterns required to be measured by the UE, referred to as CSI-RS measurement set. The transmission points corresponding to this CSI-RS measurement set constitute the originally defined CoMP measurement set and have a set size configured via Radio Resource Control (RRC) signaling. A CSI-RS report set, corresponding to the originally defined CoMP report set, can be a subset of the CSI-RS measurement set and also has a set size configured via RRC signaling.

In the current standardization discussion, there is no specific approach for selecting a subset of the CSI-RS measurement set as the CSI-RS report set and transmitting signaling related to such selection between the BS and the UE. This problem constitutes the maj or research content of the present invention .

SUMMARY OF INVENTION

It is an object of the present invention to solve the problem of how to select a subset of a CSI-RS measurement set as a CSI-RS report set by providing a novel CSI feedback method, a UE and a B S particularly applicable to the CoMP transmission scenario .

According to the first aspect of the present invention, a Channel State Information (CSI) feedback method of a User Equipment (UE) is provided, which includes the following steps of: receiving from a Base Station (BS) a Channel State Information-Reference Signal (CSI-RS) measurement set configuration signal which contains an indication of a CSI-RS measurement set configured for a UE; measuring a CSI-RS in the CSI-RS measurement set based on the indication of the CSI-RS measurement set to obtain metric information corresponding to a CSI-RS pattern in the CSI-RS measurement set; obtaining a CSI-RS report set which is selected from the CSI-RS measurement set based on the metric information; determining a CSI feedback resource corresponding to a CSI-RS pattern in the CSI-RS report set; and feeding back CSI corresponding to the CSI-RS pattern in the CSI-RS report set to the BS over the determined CSI feedback resource .

Preferably, the metric information includes at least one of (i) Channel Quality Indicator (CQI) , (ii) Pre-coding Matrix Indicator (PMI) , (iii) Reference Signal Reception Power (RSRP) and (iv) Reference Signal Reception Quality (RSRQ) .

Preferably, the step of obtaining CSI-RS report set includes: transmitting the metric information to the BS ; and receiving from the BS a CSI-RS report set configuration signal and obtaining the CSI-RS report set based on the CSI-RS report set configuration signal, wherein the CSI-RS report set configuration signal contains an indication of a CSI-RS pattern in the CSI-RS report set selected by the BS based on the metric information.

More preferably, the step of determining CSI feedback resource includes: receiving from the BS a CSI feedback resource configuration signal which contains an indication of a CSI feedback resource corresponding to the CSI-RS pattern in the CSI-RS report set; determining the CSI feedback resource based on the received CSI feedback resource configuration signal. Preferably, the step of obtaining CSI-RS report set includes : selecting the CSI-RS report set from the CSI-RS measurement set based on the metric information. More preferably, the step of determining CSI feedback resource includes : transmitting to the BS a CSI-RS report set notification signal which contains an indication of the CSI-RS report set selected by the UE; receiving from the BS a CSI feedback resource configuration signal which contains an indication of a CSI feedback resource corresponding to the CSI-RS pattern in the CSI-RS report set; and determining the CSI feedback resource based on the received CSI feedback resource configuration signal. Preferably, the CSI-RS measurement set configuration signal further contains an indication of available CSI feedback resources.

More preferably, the step of determining CSI feedback resource includes: determining the CSI feedback resource corresponding to the CSI-RS pattern in the CSI-RS report set based on the indication of available CSI feedback resources; the method further includes: transmitting to the BS a CSI feedback resource notification signal which contains an indication of the determined CSI feedback resource. According to the second aspect of the present invention, a User Equipment (UE) is provided, which includes: a receiving unit configured for receiving from a Base Station (BS) a Channel State Information-Reference Signal (CSI-RS) measurement set configuration signal which contains an indication of a CSI-RS measurement set configured for the User Equipment (UE) ; a measuring unit configured for measuring a CSI-RS in the CSI-RS measurement set based on the indication of the CSI-RS measurement set received by the receiving unit, to obtain metric information corresponding to a CSI-RS pattern in the CSI-RS measurement set; a report set obtaining unit configured for obtaining a CSI-RS report set which is selected from the CSI-RS measurement set based on the metric information; a feedback resource determining unit configured for determining a CSI feedback resource corresponding to a CSI-RS pattern in the CSI-RS report set obtained by the report set obtaining unit; and a transmitting unit configured for feeding back CSI corresponding to the CSI-RS pattern in the CSI-RS report set to the BS over the CSI feedback resource determined by the feedback resource determining unit.

Preferably, the transmitting unit is further configured for transmitting the metric information to the BS ; the receiving unit is further configured for receiving from the BS a CSI-RS report set configuration signal; and the report set obtaining unit is further configured for obtaining the C SI-RS report set based on the CSI-RS report set configuration signal received by the receiving unit, wherein the CSI-RS report set configuration signal contains an indication of a CSI-RS pattern in the CSI-RS report set selected by the BS based on the metric information .

More preferably, the receiving unit is further configured for receiving from the BS a CSI feedback resource configuration signal which contains an indication of a CSI feedback resource corresponding to the CSI-RS pattern in the CSI-RS report set; the feedback resource determining unit is configured for determining the CSI feedback resource based on the CSI feedback resource configuration signal received by the receiving unit.

Preferably, the report set obtaining unit is configured for selecting the CSI-RS report set from the CSI-RS measurement set based on the metric information . More preferably, the transmitting unit is further configured for transmitting to the BS a CSI-RS report set notification signal which contains an indication of the CSI-RS report set selected by the UE; the receiving unit is further configured for receiving from the BS a CSI feedback resource configuration signal which contains an indication of a CSI feedback resource corresponding to the CSI-RS pattern in the CSI-RS report set; and the feedback resource determining unit is configured for determining the CSI feedback resource based on the CSI feedback resource configuration signal received by the receiving unit.

Preferably, the CSI-RS measurement set configuration signal further contains an indication of available CSI feedback resources .

More preferably, the feedback resource determining unit is configured for determining the CSI feedback resource corresponding to the CSI-RS pattern in the CSI-RS report set based on the indication of available CSI feedback resources; the transmitting unit is further configured for transmitting to the BS a CSI feedback resource notification signal which contains an indication of the CSI feedback resource determined by the feedback resource determining unit. According to the third aspect of the present invention, a Channel State Information (CSI) feedback method of a Base Station (BS) is provided, which includes the following steps of: configuring, for a User Equipment (UE) , a Channel State Information-Reference Signal (CSI-RS) measurement set which contains a CSI-RS pattern to be measured by the UE; transmitting to the UE a CSI-RS measurement set configuration signal which contains an indication of a configured CSI-RS measurement set; obtaining a CSI-RS report set which is selected from the CSI-RS measurement set based on metric information obtained by measuring at the UE a CSI-RS in the CSI-RS measurement set; determining a CSI feedback resource corresponding to a CSI-RS pattern in the CSI-RS report set; and receiving CSI corresponding to the CSI-RS pattern in the CSI-RS report set fed back from the UE .

Preferably, the step of obtaining CSI-RS report set includes: receiving the metric information from the UE; and selecting the CSI-RS report set from the CSI-RS measurement set based on the metric information; the method further includes: transmitting to the UE a CSI-RS report set configuration signal, wherein the CSI-RS report set configuration signal contains an indication of a CSI-RS pattern in the selected CSI-RS report set.

Preferably, the step of obtaining CSI-RS report set includes: receiving from the UE a CSI-RS report set notification signal which contains an indication of a CSI-RS report set selected by the UE from the CSI-RS measurement set based on the metric information; and obtaining the CSI-RS report set based on the CSI-RS report set notification signal.

Preferably, the step of determining CSI-RS feedback resource includes: determining a CSI feedback resource corresponding to a CSI-RS pattern in the CSI-RS report set; the method further includes: transmitting to the UE a CSI feedback resource configuration signal which contains an indication of the determined CSI feedback resource . Preferably, the CSI-RS measurement set configuration signal further includes an indication of available CSI feedback resources.

More preferably, the step of determining CSI-RS feedback resource includes: receiving from the UE a CSI feedback resource notification signal which contains an indication of a CSI feedback resource corresponding to the CSI-RS pattern in the CSI-RS report set, the CSI feedback resource being determined by the UE based on the indication of available CSI feedback resources; determining the CSI feedback resource based on the CSI feedback resource notification signal.

According to the fourth aspect of the present invention, a Base Station (BS) is provided, which includes : a measurement set configuring unit configured for configuring, for a User Equipment (UE) , a Channel State Information-Reference Signal (CSI-RS) measurement set which contains a CSI-RS pattern to be measured by the UE; a transmitting unit configured for transmitting to the UE a CSI-RS measurement set configuration signal which contains an indication of a CSI-RS measurement set configured by the measurement set configuring unit; a report set obtaining unit configured for obtaining a CSI-RS report set which is selected from the CSI-RS measurement set based on metric information obtained by measuring at the UE a CSI-RS in the CSI-RS measurement set; a feedback resource determining unit configured for determining a CSI feedback resource corresponding to a CSI-RS pattern in the CSI-RS report set obtained by the report set obtaining unit; and a receiving unit configured for receiving CSI corresponding to the CSI-RS pattern in the CSI-RS report set fed back from the UE. Preferably, the metric information includes at least one of (i) Channel Quality Indicator (CQI) , (ii) Pre-coding Matrix Indicator (PMI) , (iii) Reference Signal Reception Power (RSRP) and (iv) Reference Signal Reception Quality (RSRQ) .

Preferably, the receiving unit is further configured for receiving the metric information from the UE; the report set obtaining unit is configured for selecting the CSI-RS report set from the CSI-RS measurement set based on the metric information; and the transmitting unit is further configured for transmitting to the UE a CSI-RS report set configuration signal, wherein the CSI-RS report set configuration signal contains an indication of a CSI-RS pattern in the CSI-RS report set selected by the report set obtaining unit.

Preferably, the receiving unit is further configured for receiving from the UE a CSI-RS report set notification signal which contains an indication of a CSI-RS report set selected by the UE from the CSI-RS measurement set based on the metric information; and the report set obtaining unit is configured for obtaining the CSI-RS report set based on the CSI-RS report set notification signal received by the receiving unit. Preferably, the feedback resource determining unit is configured for determining a CSI feedback resource corresponding to a CSI-RS pattern in the CSI-RS report set; the transmitting unit is further configured for transmitting to the UE a CSI feedback resource configuration signal which contains an indication of the CSI feedback resource determined by the feedback resource determining unit.

Preferably, the CSI-RS measurement set configuration signal further includes an indication of available CSI feedback resources.

More preferably, the receiving unit is further configured for receiving from the UE a CSI feedback resource notification signal which contains an indication of a CSI feedback resource corresponding to the CSI-RS pattern in the CSI-RS report set, the CSI feedback resource being determined by the UE based on the indication of available CSI feedback resources; the feedback resource determining unit is configured for determining the CSI feedback resource based on the CSI feedback resource notification signal received by the receiving unit.

BRIEF DESCRIPTION OF DRAWINGS

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 an exemplary scenario in which the present invention can be applied;

Fig. 2 is a block diagram of a UE according to the present invention;

Fig. 3 is a block diagram of a BS according to the present invention;

Fig. 4 is a flowchart illustrating a CSI feedback method of a UE according to an embodiment of the present invention; and

Fig. 5 is a flowchart illustrating a CSI feedback method of a BS according to another embodiment of the present invention .

DESCRIPTION OF EMBODIMENTS

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 examples applicable to the LTE-A (Rel- 10 , Rel- 1 1 and subsequent releases) 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.

Fig. 1 shows an example of Scenario 4 in an LTE Rel- 1 1 network in which the present invention can be applied . It can be appreciated by those skilled in the art that the application scenario of the present invention is not limited to Scenario 4 , but includes all scenarios within the CoMP technical scope , including a degraded CoMP scenario as described later. In Scenario 4 , there are three distributed RRH s within the coverage of a macro cell BS 10 1 , denoted as RRH 102 , RRH 103 and RRH 104 , respectively. The four transmission points, i .e . , the macro cell BS 10 1 , RRH 102 , RRH 103 and RRH 104 , have the same cell ID but are configured with different CSI-RS patterns, i. e . , CSI-RS Pattern 0 , CSI-RS Pattern 1 , CSI-RS Pattern 2 and CSI-RS Pattern 3 , respectively. While Fig. 1 shows an example in which different transmission points are configured with different CSI-RS patterns, in an actual communication process, different transmission points may have the same CSI-RS pattern. In this regard, there are two typical situations . In one situation, RRH transmission points which are physically well-separated (thus signals of the transmission points will not interfere with each other) can reuse the same CSI-RS pattern, so as to reduce the occupation of CSI-RS patterns, in which case the antennas of different transmission points may correspond to the same CSI-RS port. In the other situation, RRH transmission points which are physically closely-located (thus signals of the transmission points will interfere with each other) can also use the same CSI-RS pattern, in which case the antennas of different transmission points may correspond to the same or different CSI-RS port(s) . When the antennas of different transmission points correspond to the same CSI-RS port, the number of transmission points visible to a UE can be decreased, such that the network complexity can be reduced while improving the coverage effect of Single Frequency Network (SFN) . When the antennas of different transmission points correspond to different CSI-RS ports, these antennas can be combined into a transmission point having a large number of antennas, so as to increase spatial freedom. As an example, if two transmission points each have 4 antennas, use the same CSI-RS pattern, but occupy CSI-RS ports 1 -4 and 5-8 , respectively, these two transmission points can be combined into a logic transmission point having 8 antennas which can communicate with a UE by means of a larger MIMO (Multiple Input Multiple Output) , referred to as network MIMO transmission approach . The following discussions are applicable to the above situations .

For example , a UE 105 can be configured to use CSI-RS Pattern 0, i. e . , only served by the macro cell BS 10 1 . If the UE is a UE prior to LTE Rel- 1 1 (exclusive) , there are the following three basic approaches for an LTE Rel- 1 1 BS to communicate with the UE. First, assuming that the UE is a Rel- 10 UE, the BS can configure the UE to use Transmission Mode 9 , i. e . , 8-layer transmission mode . In this transmission mode , the BS can determine a transmission point (macro cell BS transmission point or RRH transmission point) associated with the UE based on a measurement result of an uplink signal of the UE and configure a CSI-RS pattern corresponding to the transmission point to the UE. The UE measures the CSI-RS and feeds back the CSI corresponding to the transmission point to the. BS . The BS transmits downlink allocation information to the UE over a PDCCH to be demodulated based on Cell-specific Reference Signal (CRS) (this information will be transmitted through all transmission points in an SFN manner) . Then, the UE obtains the allocation information by downlink SFN soft combination . The BS transmits a PDSCH to be demodulated based on DeModulation Reference Signal (DM-RS) to the UE through the associated transmission point. A spatial reuse gain can be obtained with this communication approach.

The second communication approach is an LTE Rel-8 / 9 compatible communication approach. That is, all downlink control signals to be demodulated based on CRS , including Physical Control Format Indicator CHannel (PCFICH) , Physical Hybrid ARQ Indicator CHannel (PHICH) , PDCCH and the CRS itself, are transmitted through all transmission points in an SFN-like manner. Then, the UE receives the control signals by SFN soft combination and measures the CRS to feed back CSI . The BS transmits a PDSCH to be demodulated based on CRS to the UE in the same way as the transmission of the above control signals. No spatial reuse gain can be obtained with this communication approach .

The third communication approach is LTE Rel-8 / 9 compatible and employs UE specific DM-RS, such as Rel-8 Transmission Mode 7 , Rel-9 Transmission Mode 8 , etc. This approach lies between the above two approaches, with the difference from the first approach in that the CSI can only be obtained based on CRS and the different from the second approach in that DM-RS can be used in PDSCH transmission. Thus, a spatial reuse gain can be obtained.

In these three communication approaches, the BS obtains a signal transmitted from the UE by soft combining uplink signals received through all transmission points.

A new CoMP communication scheme, which is different from the above communication approaches, is introduced in the LTE system after Rel- 1 1 (inclusive) . Taking a Rel- 1 1 UE 107 employing the CoMP communication scheme in Fig. 1 as an example , the uplink signal from the UE can be received by four transmission points including the BS 10 1 and the RRHs 102 , 103 and 104. Thus, the BS 10 1 can configure the CSI-RS measurement set for the UE 107 to contain CSI-RS Patterns 0-3. The details of the UE 107 and its communication approach with the network side will be discussed later. Details irrelevant to the present invention will not be described, including components of the UE 107 which are irrelevant to the concept of the present invention, an initial access process and a communication process carried out in an LTE Rel-8 / 9 / 10 compatible mode after the initial access, etc .

Fig. 2 shows a block diagram of the UE (e . g. , UE 107) according to the present invention. The UE includes : a receiving unit 2 10 , a measuring unit 220 , a report set obtaining unit 230, a feedback resource determining unit 240 and a transmitting unit 250. It can be appreciated by those skilled in the art that the UE may further include other functional units necessary for achieving its functionality, such as various processors and memories.

Fig. 3 shows a block diagram of the BS (e . g. , BS 10 1 ) according to the present invention . The BS includes : a transmitting unit 3 10 , a measurement set determining unit 320 , a report set obtaining unit 330, a feedback resource determining unit 340 and a receiving unit 350. It can be appreciated by those skilled in the art that the BS may further include other functional units necessary for achieving its functionality, such as various processors and memories.

In the following, the detailed functions and operations of the respective components of the UE and the BS according to the present invention will be described in the following with reference to Fig. 2 and Fig. 3.

The measurement set configuring unit 320 of the BS is configured for configuring, for the UE, a Channel State Information-Reference Signal (CSI-RS) measurement set which contains a CSI-RS pattern to be measured by the UE.

In an embodiment, the measurement set configuring unit 320 of the BS can configure the CSI-RS measurement set for the UE based on a measurement result of an uplink signal transmitted from the UE and transmit to the UE a CSI-RS measurement set configuration signal which contains an indication of the CSI-RS measurement set configured for the UE via the transmitting unit 3 10. In particular, the macro cell BS and the distributed RRHs can calculate the strengths of various uplink signals (such as PUCCH , SRS, PUSCH and the like) transmitted from the UE and received via their respective antennas . The measurement set configuring unit 320 of the BS processes such information and transmits to the UE information on a CSI-RS pattern of a transmission point (macro cell BS and/ or RRH device, possibly logic transmission point) required to be measured by the UE via the transmitting unit 3 10 by using a UE specific RRC signaling (i . e . , CSI-RS measurement set configuration signal) .

In particular, the measurement set configuring unit 320 of the BS can be configured for determining a transmission point required to be measured by the UE; determining a transmission mode which can be provided to the UE through the transmission point as well as a corresponding feedback mode; and determining a CSI-RS pattern of the transmission point.

The measurement set configuring unit 320 can determine a transmission point required to be measured by the UE based on the strengths of uplink signals received by different transmission points from the UE . By setting a lower limit threshold of signal strength, some transmission points with very low reception signal strengths can be excluded first, so as to reduce the measurement workload of the UE. The remaining transmission points with sufficiently high reception signal strengths form an initially selected measurement set.

If the uplink signal from the UE can accurately reflect the condition of the UE's downlink channel, a finely selected measurement set can be further determined based on the initially selected measurement set. As an example, if it is found that only the BS or a particular RRH can receive a strong uplink signal from the UE, or if the BS or a particular RRH can receive a much stronger uplink signal from the UE than any other transmission points, the finely selected measurement set should only contain the BS or the particular RRH . As another example , if there is more than one transmission point that can receive strong uplink signals from the UE, the finely selected measurement set should contain these transmission points .

Next, the measurement set configuring unit 320 can determine a transmission mode which can be provided to the UE by the above determined transmission point(s) as well as a corresponding feedback mode. If the finely selected measurement set contains only one transmission point, the UE can be configured into non-CoMP transmission mode . If the transmission point is the BS, the transmission mode of the UE can be configured according to the communication approach of the UE 105 as described above . On the other hand, if the transmission point is a RRH , the UE can be configured to employ Transmission Mode 9.

If the finely selected measurement set contains more than one transmission point, the measurement set configuring unit 320 can compare the strengths of uplink signals received by different transmission points from the UE . If there is a small difference between the uplink signal strengths, these transmission points can be combined into a logic transmission point employing the network MIMO transmission mode and the UE can be configured to employ Transmission Mode 9. If there is a large difference between the uplink signal strengths, the UE can be configured to employ a transmission mode corresponding to the CoMP transmission scheme (however, the UE can also be configured to employ Transmission Mode 9 since the Transmission Mode 9 itself also supports the CoMP transmission scheme) .

More importantly, the difference between the network MIMO and CoMP transmission schemes lies in feedback mode . The network MIMO has the same feedback mode as the above-mentioned single transmission point scenario , with CSI corresponding to only one transmission point to be fed back. The CoMP transmission, however, needs to feed back CSI corresponding to a number of transmission points.

Then, the measurement set configuring unit 320 determines the CSI-RS pattern(s) of the above determined transmission point(s) . If the finely selected measurement set contains only one transmission point which is the BS , the CSI-RS pattern of the transmission point is the CSI-RS pattern by which the BS serves the Rel- 10 UE . If the finely selected measurement set contains only one transmission point which is a RRH , the CSI-RS pattern of the transmission point is the CSI-RS pattern specific to the transmission point. If the finely selected measurement set contains more than one transmission point, the CSI-RS patterns are determined based on their corresponding configured transmission schemes. If the transmission scheme is the network MIMO, there is only one CSI-RS pattern. In this case , antenna interfaces of different transmission points correspond to different CSI-RS ports of the CSI-RS pattern, which can be flexibly configured. As an example, if there are two transmission points each having four antennas, the configured CSI-RS pattern can have eight CSI-RS ports 1 -8 in which ports 1 -4 are allocated to one transmission point and ports 5-8 are allocated to the other transmission point. Of course, it is also possible to configure the CSI-RS pattern to have four CSI-RS ports 1 -4 in which ports 1 -2 are allocated to one transmission point and ports 3 -4 are allocated to the other transmission point. However, this allocation process is transparent to the UE. Thus, from the UE's perspective, there is no difference between the network MIMO transmission scheme and the single transmission point scheme. On the other hand, if the transmission scheme is CoMP, different transmission points may have their respective transmission point specific CSI-RS patterns. The number of CSI-RS ports may or may not vary from one transmission point to another.

Then, the transmitting unit 3 10 of the BS can transmit to the UE the above CSI-RS measurement set determined by the measurement set configuring unit 320 along with corresponding parameters.

The transmitting unit 3 10 of the BS is configured for transmitting to the UE the CSI-RS measurement set configuration signal which contains an indication of the CSI-RS measurement set configured by the measurement set configuring unit 320. Accordingly, the receiving unit 2 10 of the

UE is configured for receiving from the BS the CSI-RS measurement set configuration signal.

Specifically, the CSI-RS measurement set configuration signal is used to configure the CSI-RS measurement set of the UE and may contain one or more of the following:

-the number N of the CSI-RS patterns contained in the CSI-RS measurement set;

-the number M of the CSI-RS patterns contained in the

CSI-RS report set;

-each CSI-RS pattern to be measured, including: 1 ) sequence of CSI-RS; 2) number of ports; 3) time-frequency location of CSI-RS in a sub-frame, period and sub-frame offset of CSI-RS ; and 4) ratio of data to CSI Energy Per Resource Element (EPRE) , each CSI-RS pattern which requires PDSCH muting, including time-frequency location of the CSI-RS in a sub-frame, period and sub-frame offset of the CSI-RS , etc;

-transmission power of the RRH device corresponding to the CSI-RS and the CRS EPRE ratio of the RRH device corresponding to the CSI-RS ; and

-association offset of the transmission point corresponding to the CSI-RS , etc .

Here , a CSI-RS requiring PDSCH muting corresponds to a CSI-RS pattern used by other transmission points . The PDSCH of the UE needs to be null at these CSI-RS locations in order to avoid interference of data on reference signals. The last three items as described above can be used to facilitate accurate uplink power control and report set selection. Herein, the association offset is used to determine the coverage of a transmission point, which is similar to the prior art cell range expansion offset (cf. R l - 1 008 10, Cell association analysis in outdoor Hotzone of heterogeneous networks, Huawei) .

Of course, all or part of the above CSI-RS measurement set configuration signal can be transmitted to the UE via RRC signaling, Layer- 1 signaling, Layer-2 signaling or any combination thereof.

In addition, the following information can be transmitted by the transmitting unit 3 10 of the BS to the UE and received by the receiving unit 2 10 of the UE along with, or as a part of, the CSI-RS measurement set configuration signal:

-transmission mode and feedback mode used by the UE; and

-an indication of available CSI feedback resources, such as resource indication information for periodic PUCCH resources or resource indication information for aperiodic PUSCH resources (the amount of available CSI feedback resources may be equal to N or M) , etc .

It is to be noted that there are two situations in which a subset needs to be down-selected from the CSI-RS measurement set as the CSI-RS report set: if the measurement set configuring unit 320 cannot obtain a finely selected measurement set to be used as the CSI-RS report set based on the uplink signal from the UE; and if the measurement set configuring unit 320 cannot obtain a finely selected measurement small enough to be used as the CSI-RS report set. In these cases, an additional down-selection process is required. In this process, it is assumed that the measurement set configuring unit 320 has determined CSI-RS patterns of N transmission points and notified them to the UE, and that each CSI-RS pattern in the CSI-RS measurement set corresponds to one transmission point (possibly logic transmission point) . Due to the one-to-one correspondence between a transmission point and a CSI-RS pattern, in the following description, the transmission point and the CSI-RS pattern corresponding to the transmission point can sometimes be used synonymously as appropriate . Further, since the additional down-selection process is required, there is no need to configure transmission mode, feedback mode and feedback resource in the operation of the measurement set configuring unit 320. Thus, if the follow description involves configuration of transmission mode , feedback mode and feedback resource, it is assumed that the respective item has not been configured by the measurement set configuring unit previously.

Herein, the CSI-RS report set can be the same as the

CSI-RS measurement set (i. e . , M = N) . At this time, the order in which the UE reports CSI can be determined based on the order in which the CSI-RSs are notified in the measurement set. However, in a typical situation where the CSI-RS report set is a subset of the CSI-RS measurement set (i. e. , M< N) , a signaling interaction between the UE and the BS is required to select the report set, which will be detailed in the following.

As noted above, the receiving unit 2 10 of the UE receives from the BS the CSI-RS measurement set configuration signal and provides it to the measuring unit 220 for further processing.

The measuring unit 220 of the UE is configured for measuring a CSI-RS in the CSI-RS measurement set based on the indication of the CSI-RS measurement set received by the receiving unit 2 10, to obtain metric information corresponding to a CSI-RS pattern in the CSI-RS measurement set.

In an embodiment, the metric information obtained by the measuring unit 220 may include short term information and statistical information. It can be appreciated by those skilled in the art that other metric information than these two types of metric information can also be used. The short term information includes Channel Quality Indicator (CQI) and Pre-coding Matrix Indicator (PMI) calculated from a channel measured based on a particular CSI-RS under a close loop spatial reuse assumption as well as Reference Signal Reception Power (RSRP) and Reference Signal Reception Quality (RSRQ) calculated from a particular CSI-RS measurement. The calculation of RSRP/ RSRQ is similar to the calculation of the RSPR/ RSRQ in handover as known in the art, except that the original measured signal CRS is replaced with the CSI-RS and appropriately scaled . The statistical information can be obtained by performing multiple measurements on the CSI-RS at different times . The statistical CQI and PMI can be obtained by calculating the averaged channel matrices obtained from the multiple measurements under the close loop spatial reuse assumption . The RSRP and RSRQ obtained from the multiple measurements can employ a measurement model similar to the E-UTRAN measurement model described in Section 10. 6 of TS 36.300 V I O .0.0 , Overall description, Stage 2 , 3GPP, so as to obtain the Layer- 1 and Layer-3 filtered statistical RSRQ and RSRQ .

Next, the UE and the BS obtain the CSI-RS report set by performing a sequence of operations and signaling interactions. The CSI-RS report set is selected from the CSI-RS measurement set based on the above metric information. Additionally, the UE and the BS determine CSI feedback resources corresponding to the CSI-RS patterns in the obtained CSI-RS report set by performing a sequence of operations and signaling interactions. These operations are achieved by the report set obtaining unit 230 and the feedback resource determining unit 240 of the UE as well as the report set obtaining unit 330 and the feedback resource determining unit 340. In the following, specific examples will be given to explain the detailed operations of these units and the signaling interactions between the UE and the BS . (Example 1 )

In this example, the report set obtaining unit 230 of the UE can obtain the CSI-RS report set by cooperating with the receiving unit 2 10 and the transmitting unit 250. In this case, the transmitting unit 250 of the UE can be configured for transmitting the metric information obtained by the measuring unit 220 to the BS . Accordingly, the receiving unit 350 of the BS can be configured for receiving the metric information from the UE .

In particular, the transmitting unit 250 of the UE can transmit the metric information to the BS via PUCCH or aperiodic PUSCH at Layer 1 , MAC signaling at Layer 2 , RRC signaling at Layer 3 or any combination thereof. The metric information corresponding to a number of CSI-RS patterns can be concatenated in the order in which it is notified in the measurement set, and then j ointly coded into a data block reported to the BS . Alternatively, the metric information corresponding to each CSI-RS pattern can be added with individual indicator information , individually coded and reported to the BS on demand . The former applies to aperiodic PUSCH , MAC and RRC signaling, while the latter applies to aperiodic PUSCH , PUCCH , MAC and RRC signaling. If the metric information is transmitted over the aperiodic PUSCH , the aperiodic PUSCH resource can be allocated by the BS via RRC signaling or via dynamically scheduled uplink allocation . Such allocation is received by the receiving unit. If the metric information is transmitted via MAC or RRC signaling, the transmission of such signaling can be performed periodically or triggered based on a threshold defined in advance via RRC signaling. For example, when a RSRP of a particular CSI-RS pattern exceeds a threshold, the UE can notify the metric information associated with the CSI-RS pattern to the BS via the transmitting unit 250.

In the case where M< N, preferably the transmitting unit 250 can only feed back the metric information corresponding to the M best CSI-RS patterns to the BS . The "best" as used herein may refer to the best in terms of signal strength or the best in terms of spatial channel orthogonality (i.e . , the measured PMIs of the M CSI-RSs have the best orthogonality) .

It is to be noted that the transmission of the above metric information can be omitted in the TDD system. In the TDD system, the BS and the RRH s can obtain downlink CSI from the received uplink SRS based on channel reciprocity, so as to determine the CSI-RS report set.

The report set obtaining unit 330 of the BS can be configured for determining the transmission points which can finally serve the UE (i. e . , the transmission points for which the UE needs to feed back CSI) based on the metric information corresponding to the CSI-RS patterns in the CSI-RS measurement set as transmitted from the UE, possibly in combination with the scheduling statuses of the BS and/ or RRHs corresponding to the respective CSI-RS patterns.

In this case , the operation of the report set obtaining unit 330 is similar to the operation of the measurement set determining unit 320. In particular, the report set obtaining unit 330 can be configured for: determining a transmission point for which the UE needs to report CSI ; determining a transmission mode which can be provided to the UE through the transmission point as well as a corresponding feedback mode; and determining a CSI-RS pattern for which the UE needs to report CSI .

In particular, the report set obtaining unit 330 can determine the transmission point(s) for which the UE needs to report CSI , based on the metric information of different transmission points as reported from the UE. For example , if it is found that only the metric information (RSRP/ RSRQ or CQI) obtained by measuring the CSI-RS pattern corresponding to the BS or a particular RRH is strong enough, or that the metric information (RSRP/ RSRQ or CQI) obtained by measuring the CSI-RS pattern corresponding to the BS or a particular RRH is much stronger than that of any other transmission points, the report set should only contain the BS or this RRH . If there is more than one transmission point having strong metric information (RSRP/ RSRQ or CQI) , in another example, the report set should contain these transmission points. As still another example , it is possible to select a set of transmission points having the best PMI orthogonalities from the above transmission points having strong metric information (RSRP/ RSRQ or CQI) , as the report set. As a further example, based on the above selection, a transmission point having heavy traffic load can be removed from the report set according to the scheduling statuses of the BS and/ or the RRHs.

The above determination on whether the metric information (RSRP/ RSRQ or CQI) is strong enough can be made by comparing the metric information with a predetermined threshold (similar to the handover process in the prior art) . In this process, the above mentioned cell range expansion offset can also be taken into consideration (similar to the handover process in heterogeneous network environment in the prior art) .

Next, the report set obtaining unit 330 can determine a transmission mode which can be provided to the UE by the above determined transmission point(s) as well as a corresponding feedback mode . If the report set contains only one transmission point, the UE can be configured into non-CoMP transmission mode . If the transmission point is the BS , the transmission mode of the UE can be configured according to the communication approach of the UE 105 as described above . On the other hand, if the transmission point is a RRH , the UE can be configured to employ Transmission Mode 9. If the report set contains more than one transmission point, the report set obtaining unit 330 can compare the strengths of the metric information (RSRP/ RSRQ or CQI) of different transmission points. If there is a small difference between the strengths, these transmission points can be combined into a logic transmission point employing the network MIMO transmission mode and the UE can be configured to employ Transmission Mode 9. If there is a large difference between the strengths, the UE can be configured to employ a transmission mode corresponding to the CoMP transmission scheme (however, the UE can also be configured to employ Transmission Mode 9 since the Transmission Mode 9 itself also supports the CoMP transmission scheme) .

More importantly, the difference between the network MIMO and CoMP transmission schemes lies in feedback mode . The network MIMO has the same feedback mode as the above-mentioned single transmission point scenario , with CSI corresponding to only one transmission point to be fed back. The CoMP transmission , however, needs to feed back CSI corresponding to a number of transmission points .

Then, the report set obtaining unit 320 determines the CSI-RS pattern(s) for which the UE needs to report CSI . If the report set contains only one transmission point which is the BS, the CSI-RS pattern of the transmission point is the CSI-RS pattern by which the BS serves the Rel- 10 UE . If the report set contains only one transmission point which is a RRH, the CSI-RS pattern of the transmission point is the CSI- RS pattern specific to the transmission point. If the report set contains more than one transmission point, the CSI-RS patterns are determined based on their corresponding configured transmission schemes. If the transmission scheme is the network MIMO, there is only one CSI-RS pattern . In this case, antenna interfaces of different transmission points correspond to different CSI-RS ports of the CSI-RS pattern, which can be flexibly configured. As an example , if there are two transmission points each having four antennas, the configured CSI-RS pattern can have eight CSI- RS ports 1 -8 in which ports 1 -4 are allocated to one transmission point and ports 5-8 are allocated to the other transmission point. Of course, it is also possible to configure the CSI-RS pattern to have four CSI-RS ports 1 -4 in which ports 1 -2 are allocated to one transmission point and ports 3-4 are allocated to the other transmission points. However, this allocation process is transparent to the UE. Thus, from the UE's perspective, there is no difference between the network MIMO transmission scheme and the single transmission point scheme. On the other hand, if the transmission scheme is CoMP, different transmission points may have their respective transmission point specific CSI-RS patterns. The number of CSI-RS ports may or may not vary from one transmission point to another. It can be seen that the CSI-RS patterns configured for the UE in the CSI-RS measurement set and the CSI-RS patterns configured for the UE in the CSI-RS report set may be different. The correspondence between the CSI-RS patterns and the transmission points may also be different. This can be achieved by the BS flexibly configuring the CSI-RS pattern of the logic transmission point. From the UE's perspective, only the CSI-RS pattern required to be measured or measured and reported is visible while the transmission point is invisible .

In other words, the report set obtaining unit 330 of the BS is configured for selecting the CSI-RS report set from the CSI-RS measurement set based on the received metric information. Then, the transmitting unit 3 10 of the BS transmits to the UE a CSI-RS report set configuration signal which contains an indication of a CSI-RS pattern in the CSI-RS report set selected by the report set obtaining unit 330.

The contents of the CSI-RS report set configuration signal contain one or more of the following:

-the number M' of the CSI-RS patterns in the report set (M' may be or may not be the same as the M indicated in the CSI-RS measurement set configuration signal such that the number of CSI-RS patterns for which the UE needs to feed back CSI can be indicated more flexibly and accurately) ; and

-information on M' CSI-RS patterns (if these patterns already exist in the measurement set indicated by the CSI-RS measurement set configuration signal, they can be indicated using their sequence numbers in the measurement set; if there is a newly added CSI-RS pattern, which may be a CSI-RS pattern of a transmission point acquired by the UE in another way or a CSI-RS pattern changed with the setting of logic transmission point, the specific pattern of such CSI-RS pattern needs to be indicated) .

In addition, the following information can be transmitted by the transmitting unit 3 10 of the BS to the UE and received by the receiving unit 2 10 of the UE along with, or as a part of, the CSI-RS report set configuration signal:

-transmission mode and feedback mode used by the UE; and

Accordingly, the receiving unit 2 10 of the UE can be configured for receiving from the BS the CSI-RS report set configuration signal which contains an indication of a CSI-RS pattern in the CSI-RS report set selected by the BS based on the metric information.

Then, the report set obtaining unit 230 of the UE can obtain the CSI-RS report set based on the CSI-RS report set configuration signal received by the receiving unit 2 10. In other words, the report set obtaining unit 230 can obtain the CSI-RS report set based on the signaling indication transmitted from the transmitting unit 3 10 of the BS.

Further, in this example, the feedback resource determining unit 340 of the BS can be configured for determining the CSI feedback resource corresponding to a CSI-RS pattern in the CSI-RS report set. The transmitting unit 3 10 of the BS is further configured for transmitting to the UE a CSI feedback resource configuration signal which contains an indication of the CSI feedback resource determined by the feedback resource determining unit 340.

Accordingly, the feedback resource determining unit 240 of the UE can determine the CSI feedback resource by cooperating with the receiving unit 2 10. In this case, the receiving unit 2 10 is further configured for receiving from the BS the CSI feedback resource configuration signal which contains an indication of a CSI feedback resource corresponding to the CSI-RS pattern in the CSI-RS report set.

In particular, the CSI feedback resource configuration signal can contain: CSI feedback resource configuration information corresponding to the number M' of the CSI-RS patterns in the report set, such as resource indication information for M ' periodic PUCCH resources or resource indication information for one periodic or aperiodic PUSCH resource; correspondence between CSI obtained by measuring the M' CSI-RS patterns and the CSI feedback resources; and, if jointly coded CSI is transmitted over PUSCH, an indication of the order in which the CSI obtained by measuring different CSI-RS patterns is j ointly coded.

Accordingly, the feedback resource determining unit 240 of the UE is configured for determining the CSI feedback resource based on the CSI feedback resource configuration signal received by the receiving unit 2 10.

It is to be noted here that the above CSI-RS report set configuration signal and the CSI feedback resource configuration signal are preferably implemented using RRC signaling. However, they can also be implemented by using Layer- 1 and / or Layer-2 signaling or using signaling at different layers jointly. In practice, the above CSI-RS report set configuration signal and the CSI feedback resource configuration signal can be implemented by the same or different RRC signaling, Layer- 1 signaling, Layer-2 signaling or any combination thereof. For example, if the CSI-RS measurement set configuration signal contains an indication of available CSI feedback resources, the CSI-RS report set configuration signal and the CSI feedback resource configuration signal can be implemented using a Layer-2 MAC COMMAND to indicate information on the M ' CSI-RS patterns and a sequence number of the resource for CSI feedback corresponding to each CSI-RS pattern in the above indication of available CSI feedback resources. As another example , the CSI-RS report set configuration signal can be implemented using a Layer-2 MAC COMMAND to indicate for example information on the M' CSI-RS patterns while the CSI-RS feedback resource configuration signal can be implemented using Layer 3 RRC signaling to indicate for example information on CSI feedback resources corresponding to the M' CSI-RS patterns.

In addition, one implementation of the above MAC

COMMAND is to reuse the carrier activation and deactivation signals currently present in the LTE Rel- 10 carrier aggregation, by replacing the members of these signals with CSI-RS patterns.

(Example 2)

In this example, the report set obtaining unit 230 of the UE can autonomously determine the CSI-RS report set. In this case , the report set obtaining unit 230 is configured for selecting the CSI- RS report set from the CSI-RS measurement set based on the metric information.

In particular, the report set obtaining unit 230 determines the CSI-RS report set based on the metric information obtained by the measuring unit 220. The specific approach for determining the CSI-RS report set is similar to the approach by which the report set obtaining unit 330 of the BS determines the CSI-RS report set in Example 1 , except that the CSI-RS report set is determined at the UE.

Accordingly, the report set obtaining unit 330 of the BS can determine the CSI-RS report set by cooperating with the receiving unit 350. In this case, the receiving unit 350 of the BS is further configured for receiving from the UE a CSI-RS report set notification signal which contains an indication of a CSI-RS report set selected by the UE from the CSI-RS measurement set based on the metric information. Then, the report set obtaining unit 340 of the BS is configured for obtaining the CSI-RS report set based on the CSI-RS report set notification signal received by the receiving unit 350.

In this example, the feedback resource determining unit 240 of the UE can determine the CSI feedback resource by cooperating with the receiving unit 2 1 0 and the transmitting unit 250. In this case , the transmitting unit 250 of the UE can be configured for transmitting to the BS a CSI-RS report set notification signal which contains an indication of the CSI-RS report set selected by the UE. Accordingly, the receiving unit 350 of the BS is further configured for receiving the CSI-RS report set notification signal from the UE.

Specifically, the transmitting unit 250 of the UE transmits an indication of the determined CSI-RS report set to the BS by using the CSI-RS report set notification signal. The CSI-RS report set notification signal may contain one or more of the following:

-the number M ' of the CSI-RS patterns in the report set (M' may be or may not be the same-as the M indicated in the CSI-RS measurement set configuration signal) ; and

-information on M ' CSI-RS patterns (if these patterns already exist in the measurement set indicated by the CSI-RS measurement set configuration signal, they can be indicated using their sequence numbers in the measurement set; if there is a newly added CSI-RS pattern, the specific pattern of such CSI-RS pattern needs to be indicated) .

Preferably, the CSI-RS report set notification signal can be implemented using RRC signaling. However, Layer- 1 and/ or Layer 2 signaling can also be used . For example, an approach similar to the carrier activation and deactivation operations currently present in the LTE Rel- 10 carrier aggregation can be used and the selection and de-selection of the report set can be implemented using MAC COMMAND .

Preferably, the CSI-RS report set notification signal can be implemented using Layer-2 MAC COMMAND . Particularly, the carrier activation and deactivation in the carrier aggregation can be used . Of course , the CSI-RS report set notification signal can also be implemented by using Layer- 1 and / or Layer-3 RRC signaling or using joint notification of the individual layers . For example , if it is implemented using Layer- 1 PUCCH signaling, one possibility is to load sequence numbers of the CSI-RS patterns from the CSI-RS report set in the CSI-RS measurement set into the content or signal fed back over a particular CSI feedback resource in any of the following ways such that the notification of the CIS-RS report set can be achieved indirectly by detection at the BS : j ointly coding a sequence of sequence numbers of the CSI-RS patterns with all or part of CSI feedback contents; scrambling a sequence of sequence numbers of the CSI-RS patterns together with all or part of coded CSI feedback contents; and feeding back the sequence numbers of the CSI-RS patterns as a part of CSI feedback contents. For example, a sequence number of a CSI-RS pattern can be jointly coded with a RI of a non-serving cell, or the sequence number of the CSI-RS pattern can be fed back to the BS instead of the RI of the non- serving cell. The transmitting unit 250 can be configured to achieve the signaling and feedback as described above .

At the BS , the report set obtaining unit 330 is configured for obtaining the CSI-RS report set based on the CSI-RS report set notification signal received by the receiving unit 350. Then, as discussed above, the feedback resource determining unit 340 of the BS can determine the CSI feedback resource corresponding to the CSI-RS pattern in the CSI-RS report set. The transmitting unit 3 10 of the BS is further configured for transmitting to the UE a CSI feedback resource configuration signal which contains an indication of the CSI feedback resource determined by the feedback resource determining unit 340.

Accordingly, the receiving unit 2 10 of the UE can be configured for receiving from the BS the CSI feedback resource configuration signal which contains an indication of the CSI feedback resource corresponding to the CSI-RS pattern in the CSI-RS report set. In particular, as described above with respect to Example 1 , the CSI feedback resource configuration signal can contain: CSI feedback resource configuration information corresponding to the number M ' of the CSI-RS patterns in the report set, such as resource indication information for M' periodic PUCCH resources or resource indication information for one periodic or aperiodic PUSCH resource ; correspondence between CSI obtained by measuring the M ' CSI-RS patterns and the CSI feedback resources; and, if jointly coded CSI is transmitted over PUSCH , an indication of the order in which the CSI obtained by measuring different CSI-RS patterns is jointly coded .

Accordingly, the feedback resource determining unit 240 of the UE is configured for determining the CSI feedback resource corresponding to the CSI-RS pattern in the CSI-RS report set based on the CSI feedback resource configuration signal received by the receiving unit 2 1 0. (Example 3) This example differs from the above Example 2 in that, in this example, the feedback resource determining unit 240 of the UE autonomously determines the desired CSI feedback resource .

In this example, as explained above, the CSI-RS measurement set configuration signal, which is transmitted from the transmitting unit 3 10 of the BS and received by the receiving unit 2 10 of the UE, contains an indication of available CSI feedback resources.

Thus, the feedback resource determining unit 240 of the

UE can be configured for determining the CSI feedback resource corresponding to the CSI-RS pattern in the CSI-RS report set based on the indication of available CSI feedback resources .

In this case, the transmitting unit 250 of the UE is further configured for transmitting to the BS a CSI feedback resource notification signal which contains an indication of the CSI feedback resource determined by the feedback resource determining unit.

In particular, the CSI feedback resource notification signal may contain a sequence number of the CSI feedback resource corresponding to each CSI-RS pattern from the CSI-RS report set in the indication of available CSI feedback resources of the CSI-RS measurement set configuration signal.

If the available CSI feedback resources indicated in the CSI-RS measurement set configuration signal is sufficient, e . g. , the amount of the resources equals to N, a correspondence between the CSI feedback resources and the sequence numbers of the CSI-RS patterns in the CSI-RS measurement set can be established directly. The BS can obtain the CSI-RS report set by detecting the CSI feedback resources used by the UE.

Accordingly, the receiving unit 350 of the BS is configured for receiving from the UE a CSI feedback resource notification signal which contains an indication of a CSI feedback resource corresponding to the CSI-RS pattern in the CSI-RS report set, the CSI feedback resource being determined by the UE based on the indication of available CSI feedback resources . Then, the feedback resource determining unit 340 of the BS is configured for determining the CSI feedback resource based on the CSI feedback resource notification signal received by the receiving unit 350.

The transmitting unit 250 of the UE is configured for feeding back CSI corresponding to the CSI-RS pattern, in the CSI-RS report set to the BS over the CSI feedback resource determined by the feedback resource determining unit 240. In particular, the UE (e. g. , the measuring unit 220) measures the CSI of each CSI-RS pattern in the CSI-RS report set and feeds back the measured CSI over the CSI feedback resource determined by the feedback resource determining unit 240. Accordingly, the receiving unit 350 of the BS receives the CSI corresponding to the CSI-RS pattern in the CSI-RS report set fed back from the UE.

While the foregoing description relates to functions and operations of a UE operating in CoMP transmission mode , as noted above, the UE of the present invention is not limited to operation in CoMP transmission mode, but also applicable in a degraded CoMP scenario (such as single point transmission) . For example, the UE 106 is covered by the BS 10 1 and the RRH 102 jointly. The UE 106 differs from the UE 105 in that it is an LTE Rel- 1 1 UE and differs from the UE 107 in that it does not employ the CoMP transmission scheme . Since the UE 106 does not employ the CoMP transmission scheme, it needs to select a transmission point corresponding to a CSI-RS pattern from the CSI-RS measurement set, as an actual transmission point for data channels and UE specific control channels, or referred to as associated transmission point. In this case, the operations of the UE 106 are the same as the operations of the above UE 107 , except that the CSI-RS report set obtained by the report set obtaining unit 230 of the UE 106 contains only the CSI-RS pattern corresponding to the associated transmission point and the feedback resource determining unit 240 only determines the feedback resources for feeding back CSI corresponding to the CSI-RS pattern. Thus, the UE 106 can be implemented as a special case of the UE according to the present invention in which the size M of the CSI-RS report set is 1 .

While the UE according to the present invention has been described above taking the communication system corresponding to Scenario 4 as an example, the present invention is not limited thereto . The LTE Rel- 1 1 and subsequent releases may be deployed in Scenario 1 , 2 or 3 , which differs from Scenario 4 in that each transmission point has an independent cell ID . However, as for CSI-RS pattern, an independent cell ID inherently corresponds to an independent CSI-RS pattern . Thus, it can be appreciated by those skilled in the art that the concept of the present invention depends on CSI-RS pattern, regardless of whether the transmission points corresponding to CSI-RS patterns have the same cell ID . Therefore, the UE of the present invention also applies to the communication system corresponding to the above Scenario 1 , 2 or 3.

Also , it is to be noted that since the UE can move in the cell, the measurement set detected by the BS may change . Thus, in the CSI-RS measurement set configuration signal, the CSI-RS patterns to be measured can be added, removed or changed dynamically for the UE. Also, in the CSI-RS report set configuration signal and the CSI-RS report set notification signal, the CSI-RS patterns to be reported can be added, removed or changed dynamically.

The signaling of the present invention includes basic formats of the existing signaling in the LTE technology, including Layer- 1 PUCCH or aperiodic PUSCH , Layer-2 MAC signaling or Layer-3 RRC signaling. The contents of the signals described herein can be loaded into the existing signaling formats as payload for transmission between the BS and the UE, so as to implement the functions of the present invention.

In the following, the embodiments of the CSI feedback method according to the present invention will be described with reference to flowcharts . In the following description, the method will be described in connection with the above embodiments of the UE and the BS for the purpose of clarity. However, it can be appreciated by those skilled in the art that it is illustrative only to describe the method of present invention in connection with the specific functional units of the UE and the BS . In the case where the method is implemented in computer program, for example, such definitions of the functional units and components are unnecessary, the UE or the BS can act as a whole to implement the method of the present invention .

Fig. 4 is a flowchart illustrating an embodiment of the CSI feedback method 400 of a UE according to the present invention . The CSI feedback method of this embodiment can be performed at the UE. The method includes the following steps .

At step 40 1 , the receiving unit 2 10 of the UE receives from a Base Station (BS) a Channel State Information-Reference Signal (CSI-RS) measurement set configuration signal which contains an indication of a CSI-RS measurement set configured for the UE .

At step 402 , the measuring unit 220 of the UE measures a CSI-RS in the CSI-RS measurement set based on the indication of the CSI-RS measurement set to obtain metric information corresponding to a CSI-RS pattern in the CSI-RS measurement set.

At step 403 , the report set obtaining unit 230 of the UE obtains a CSI-RS report set which is selected from the CSI-RS measurement set based on the metric information .

At step 404 , the feedback resource determining unit 240 of the UE determines a CSI feedback resource corresponding to a CSI-RS pattern in the CSI-RS report set.

At step 405 , the transmitting unit 250 of the UE feeds back CSI corresponding to the CSI-RS pattern in the CSI-RS report set to the BS over the determined CSI feedback resource .

Preferably, the step 403 of obtaining CSI-RS report set includes : the transmitting unit 250 of the UE transmitting the metric information to the BS; and the receiving unit 2 10 of the UE receiving from the BS a CSI-RS report set configuration signal and obtaining the CSI-RS report set based on the CSI-RS report set configuration signal. The CSI-RS report set configuration signal contains an indication of a CSI-RS pattern in the CSI-RS report set selected by the BS based on the metric information.

Preferably, the step 404 of determining CSI feedback resource includes : the receiving unit 2 10 of the UE receiving from the BS a CSI feedback resource configuration signal which contains an indication of a CSI feedback resource corresponding to the CSI-RS pattern in the CSI-RS report set; and the feedback resource determining unit 240 of the UE determining the CSI feedback resource based on the received CSI feedback resource configuration signal.

Preferably, the step 403 of obtaining CSI-RS report set includes : the report set obtaining unit 230 selecting the CSI-RS report set from the CSI-RS measurement set based on the metric information.

Preferably, the step 404 of determining CSI feedback resource includes : the transmitting unit 250 of the UE transmitting to the BS a CSI-RS report set notification signal which contains an indication of the CSI-RS report set selected by the UE; the receiving unit 2 10 of the UE receiving from the BS a CSI feedback resource configuration signal which contains an indication of a CSI feedback resource corresponding to the CSI-RS pattern in the CSI-RS report set; and the feedback resource determining unit 240 of the UE determining the CSI feedback resource based on the received CSI feedback resource configuration signal.

Preferably, in step 4 10 , the CSI-RS measurement set configuration signal further contains an indication of available CSI feedback resources.

Preferably, the step 404 of determining CSI feedback resource includes : the feedback resource determining unit 240 of the UE determining the CSI feedback resource corresponding to the CSI-RS pattern in the CSI-RS report set based on the indication of available CSI feedback resources. The method further includes: the transmitting unit 250 of the UE transmitting to the BS a CSI feedback resource notification signal which contains an indication of the determined CSI feedback resource .

Fig. 5 is a flowchart illustrating an embodiment of the CSI feedback method 500 of a BS according to the present invention. The CSI feedback method of this embodiment can be performed at the BS . The method includes the following steps .

At step 50 1 , the measurement set configuring unit 320 of the BS configures, for a User Equipment (UE) , a Channel State Information-Reference Signal (CSI-RS) measurement set which contains a CSI-RS pattern to be measured by the UE.

At step 502 , the transmitting unit 3 10 of the BS transmits to the UE a CSI-RS measurement set configuration signal which contains an indication of a configured CSI-RS measurement set which is configured for the UE by the measurement set configuring unit 320.

At step 503 , the report set obtaining unit 330 of the BS obtains a CSI-RS report set which is selected from the CSI-RS measurement set based on metric information obtained by measuring at the UE a CSI-RS in the CSI-RS measurement set.

At step 504 , the feedback resource determining unit 340 of the BS determines a CSI feedback resource corresponding to a CSI-RS pattern in the CSI-RS report set.

At step 505, the receiving unit 350 of the BS receives CSI corresponding to the CSI-RS pattern in the CSI-RS report set fed back from the UE.

Preferably, the step 503 of obtaining CSI-RS report set includes: the receiving unit 350 of the BS receiving the metric information from the UE; and the report set obtaining unit 330 of the BS selecting the CSI-RS report set from the CSI-RS measurement set based on the metric information . The method further includes: the transmitting unit 3 10 of the BS transmitting to the UE a CSI-RS report set configuration signal, wherein the CSI-RS report set configuration signal contains an indication of a CSI-RS pattern in the selected CSI-RS report set.

Preferably, the step 503 of obtaining CSI-RS report set includes: the receiving unit 350 of the BS receiving from the UE a CSI-RS report set notification signal which contains an indication of a CSI-RS report set selected by the UE from the CSI-RS measurement set based on the metric information ; and the report set obtaining unit 330 of the BS obtaining the CSI-RS report set based on the CSI-RS report set notification signal.

Preferably, the step 504 of the feedback resource determining unit 340 of the BS determining CSI-RS feedback resource includes : determining a CSI feedback resource corresponding to a CSI-RS pattern in the CSI-RS report set. The method further includes : the transmitting unit 3 10 of the BS transmitting to the UE a CSI feedback resource configuration signal which contains an indication of the determined CSI feedback resource .

Preferably, in step 502 , the CSI -RS measurement set configuration signal further includes an indication of available CSI feedback resources.

Preferably, the step 504 of determining CSI-RS feedback resource includes : the receiving unit 350 of the BS receiving from the UE a CSI feedback resource notification signal which contains an indication of a CSI feedback resource corresponding to the CSI-RS pattern in the CSI-RS report set, the CSI feedback resource being determined by the UE based on the indication of available CSI feedback resources; and the feedback resource determining unit 340 of the BS determining the CSI feedback resource based on the CSI feedback resource notification signal.

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 .

A number of examples have been illustrated in the above description. While the inventor has tried to list the examples in association with each other, it does not imply that it is required for the listed examples to have such correspondence as described. A number of solutions can be achieved by selecting examples having no correspondence as long as the conditions underlying the selected examples do not conflict with each other. Such solutions are encompassed by the scope of the present invention.

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

1 . A Channel State Information (CSI) feedback method of a User Equipment (UE) , comprising the following steps of:

-receiving from a Base Station (BS) a Channel State

Information-Reference Signal (CSI-RS) measurement set configuration signal which contains an indication of a CSI-RS measurement set configured for the UE;

-measuring a CSI-RS in the CSI-RS measurement set based on the indication of the CSI-RS measurement set to obtain metric information corresponding to a CSI-RS pattern in the CSI-RS measurement set;

-obtaining a CSI-RS report set which is selected from the CSI-RS measurement set based on the metric information;

-determining a CSI feedback resource corresponding to a

CSI-RS pattern in the CSI-RS report set; and

-feeding back CSI corresponding to the CSI-RS pattern in the CSI-RS report set to the BS over the determined CSI feedback resource .

2. The CSI feedback method according to claim 1 , wherein the metric information comprises at least one of (i) Channel Quality Indicator (CQI) , (ii) Pre-coding Matrix Indicator (PMI) , (iii) Reference Signal Reception Power (RSRP) and (iv) Reference Signal Reception Quality (RSRQ) .

3. The CSI feedback method according to claim 1 , wherein the step of obtaining CSI-RS report set comprises:

-transmitting the metric information to the BS ; and -receiving from the BS a CSI-RS report set configuration signal and obtaining the CSI-RS report set based on the CSI-RS report set configuration signal,

wherein the CSI-RS report set configuration signal contains an indication of a CSI-RS pattern in the CSI-RS report set selected by the BS based on the metric information.

4. The CSI feedback method according to claim 3 , wherein the step of determining CSI feedback resource comprises :

-receiving from the BS a CSI feedback resource configuration signal which contains an indication of a CSI feedback resource corresponding to the CSI-RS pattern in the CSI-RS report set;

-determining the CSI feedback resource based on the received CSI feedback resource configuration signal.

5. The CSI feedback method according to claim 1 , wherein the step of obtaining CSI-RS report set comprises:

- selecting the CSI-RS report set from the CSI-RS measurement set based on the metric information.

6. The CSI feedback method according to claim 5, wherein the step of determining CSI feedback resource comprises:

-transmitting to the BS a CSI-RS report set notification signal which contains an indication of the CSI-RS report set selected by the UE;

-receiving from the BS a CSI feedback resource configuration signal which contains an indication of a CSI feedback resource corresponding to the CSI-RS pattern in the CSI-RS report set; and

-determining the CSI feedback resource based on the received CSI feedback resource configuration signal .

7. The CSI feedback method according to claim 1 , wherein the CSI-RS measurement set configuration signal further contains an indication of available CSI feedback resources .

8. The CSI feedback method according to claim 7, wherein the step of determining CSI feedback resource comprises:

-determining the CSI feedback resource corresponding to the CSI-RS pattern in the CSI-RS report set based on the indication of available CSI feedback resources;

the method further comprises:

-transmitting to the BS a CSI feedback resource notification signal which contains an indication of the determined CSI feedback resource .

9. A User Equipment (UE) , comprising:

-a receiving unit configured for receiving from a Base Station (BS) a Channel State Information-Reference Signal (CSI-RS) measurement set configuration signal which contains an indication of a CSI-RS measurement set configured for the UE;

-a measuring unit configured for measuring a CSI-RS in the CSI-RS measurement set based on the indication of the CSI-RS measurement set received by the receiving unit, to obtain metric information corresponding to a CSI-RS pattern in the CSI-RS measurement set;

-a report set obtaining unit configured for obtaining a

CSI-RS report set which is selected from the CSI-RS measurement set based on the metric information;

-a feedback resource determining unit configured for determining a CSI feedback resource corresponding to a CSI-RS pattern in the CSI-RS report set obtained by the report set obtaining unit; and

-a transmitting unit configured for feeding back CSI corresponding to the CSI-RS pattern in the CSI-RS report set to the BS over the CSI feedback resource determined by the feedback resource determining unit.

10. The UE according to claim 9 , wherein the metric information comprises at least one of (i) Channel Quality Indicator (CQI) , (ii) Pre-coding Matrix Indicator (PMI) , (iii) Reference Signal Reception Power (RSRP) and (iv) Reference Signal Reception Quality (RSRQ) .

1 1 . The UE according to claim 9 , wherein:

the transmitting unit is further configured for transmitting the metric information to the BS ;

the receiving unit is further configured for receiving from the BS a CSI-RS report set configuration signal; and

the report set obtaining unit is further configured for obtaining the CSI-RS report set based on the CSI-RS report set configuration signal received by the receiving unit,

12. The UE according to claim 1 1 , wherein:

the receiving unit is further configured for receiving from the BS a CSI feedback resource configuration signal which contains an indication of a CSI feedback resource corresponding to the CSI-RS pattern in the CSI-RS report set; the feedback resource determining unit is configured for determining the CSI feedback resource based on the CSI feedback resource configuration signal received by the receiving unit.

13. The UE according to claim 9 , wherein:

the report set obtaining unit is configured for selecting the CSI-RS report set from the CSI-RS measurement set based on the metric information.

14. The UE according to claim 13 , wherein :

the transmitting unit is further configured for transmitting to the BS a CSI-RS report set notification signal which contains an indication of the CSI-RS report set selected by the UE;

the receiving unit is further configured for receiving from the BS a CSI feedback resource configuration signal which contains an indication of a CSI feedback resource corresponding to the CSI-RS pattern in the CSI-RS report set; and

the feedback resource determining unit is configured for determining the CSI feedback resource based on the CSI feedback resource configuration signal received by the receiving unit.

15. The UE according to claim 9 , wherein the CSI-RS measurement set configuration signal further contains an indication of available CSI feedback resources.

16. The UE according to claim 15 , wherein:

the feedback resource determining unit is configured for determining the CSI feedback resource corresponding to the CSI-RS pattern in the CSI-RS report set based on the indication of available CSI feedback resources;

the transmitting unit is further configured for transmitting to the BS a CSI feedback resource notification signal which contains an indication of the CSI feedback resource determined by the feedback resource determining unit.

17. A Channel State Information (CSI) feedback method of a Base Station (BS) , comprising the following steps of:

-configuring, for a User Equipment (UE) , a Channel State

Information-Reference Signal (CSI-RS) measurement set which contains a CSI-RS pattern to be measured by the UE;

-transmitting to the UE a CSI-RS measurement set configuration signal which contains an indication of a configured CSI-RS measurement set;

-obtaining a CSI-RS report set which is selected from the CSI-RS measurement set based on metric information obtained by measuring at the UE a CSI-RS in the CSI-RS measurement set;

-determining a CSI feedback resource corresponding to a CSI-RS pattern in the CSI-RS report set; and

-receiving CSI corresponding to the CSI-RS pattern in the CSI-RS report set fed back from the UE .

18. The CSI feedback method according to claim 17 , wherein the metric information comprises at least one of (i) Channel Quality Indicator (CQI) , (ii) Pre-coding Matrix Indicator (PMI) , (iii) Reference Signal Reception Power (RSRP) and (iv) Reference Signal Reception Quality (RSRQ) .

19. The CSI feedback method according to claim 17 , wherein the step of obtaining CSI-RS report set comprises :

-receiving the metric information from the UE; and

- selecting the CSI-RS report set from the CSI-RS measurement set based on the metric information;

the method further comprises :

-transmitting to the UE a CSI-RS report set configuration signal,

wherein the CSI-RS report set configuration signal contains an indication of a CSI-RS pattern in the selected CSI-RS report set.

20. The CSI feedback method according to claim 17, wherein the step of obtaining CSI-RS report set comprises:

-receiving from the UE a CSI-RS report set notification signal which contains an indication of a CSI-RS report set selected by the UE from the CSI-RS measurement set based on the metric information; and

-obtaining the CSI-RS report set based on the CSI-RS report set notification signal.

2 1 . The CSI feedback method according to claim 17 , wherein the step of determining CSI-RS feedback resource comprises:

-determining a CSI feedback resource corresponding to a

CSI-RS pattern in the CSI-RS report set;

the method further comprises:

-transmitting to the UE a CSI feedback resource configuration signal which contains an indication of the . determined CSI feedback resource .

22. The CSI feedback method according to claim 17 , wherein the CSI-RS measurement set configuration signal further comprises an indication of available CSI feedback resource s.

23. The CSI feedback method according to claim 22 , wherein the step of determining CSI-RS feedback resource comprises:

-receiving from the UE a CSI feedback resource notification signal which contains an indication of a CSI feedback resource corresponding to the CSI-RS pattern in the CSI-RS report set, the CSI feedback resource being determined by the UE based on the indication of available CSI feedback resources;

-determining the CSI feedback resource based on the CSI feedback resource notification signal.

24. A Base Station (BS) , comprising:

-a measurement set configuring unit configured for configuring, for a User Equipment (UE) , a Channel State Information-Reference Signal (CSI-RS) measurement set which contains a CSI-RS pattern to be measured by the UE;

-a transmitting unit configured for transmitting to the UE a CSI-RS measurement set configuration signal which contains an indication of a CSI-RS measurement set configured by the measurement set configuring unit;

-a report set obtaining unit configured for obtaining a CSI-RS report set which is selected from the CSI-RS measurement set based on metric information obtained by measuring at the UE a CSI-RS in the CSI-RS measurement set;

-a feedback resource determining unit configured for determining a CSI feedback resource corresponding to a CSI-RS pattern in the CSI-RS report set obtained by the report set obtaining unit; and -a receiving unit configured for receiving CSI corresponding to the CSI-RS pattern in the CSI-RS report set fed back from the UE.

25. The BS according to claim 24 , wherein the metric information comprises at least one of (i) Channel Quality Indicator (CQI) , (ii) Pre-coding Matrix Indicator (PMI) , (iii) Reference Signal Reception Power (RSRP) and (iv) Reference Signal Reception Quality (RSRQ) .

26. The BS according to claim 24 , wherein :

the receiving unit is further configured for receiving the metric information from the UE;

the report set obtaining unit is configured for selecting the CSI-RS report set from the CSI-RS measurement set based on the metric information; and

the transmitting unit is further configured for transmitting to the UE a CSI-RS report set configuration signal, wherein the CSI-RS report set configuration signal contains an indication of a CSI-RS pattern in the CSI-RS report set selected by the report set obtaining unit.

27. The BS according to claim 24 , wherein :

the receiving unit is further configured for receiving from the UE a CSI-RS report set notification signal which contains an indication of a CSI-RS report set selected by the UE from the CSI-RS measurement set based on the metric information; and the report set obtaining unit is configured for obtaining the CSI-RS report set based on the CSI-RS report set notification signal received by the receiving unit.

28. The BS according to claim 24 , wherein:

the feedback resource determining unit is configured for determining a CSI feedback resource corresponding to a CSI-RS pattern in the CSI-RS report set;

the transmitting unit is further configured for transmitting to the UE a CSI feedback resource configuration signal which contains an indication of the CSI feedback resource determined by the feedback resource determining unit.

29. The BS according to claim 24 , wherein the CSI-RS measurement set configuration signal further comprises an indication of available CSI feedback resources.

30. The BS according to claim 29 , wherein:

the receiving unit is further configured for receiving from the UE a CSI feedback resource notification signal which contains an indication of a CSI feedback resource corresponding to the CSI-RS pattern in the CSI-RS report set, the CSI feedback resource being determined by the UE based on the indication of available CSI feedback resources;

the feedback resource determining unit is configured for determining the CSI feedback resource based on the CSI feedback resource notification signal received by the receiving unit.