KR20130125058A - Method and apparatus for channel information feedback - Google Patents

Abstract

The present invention relates to a method and apparatus for feeding back channel information. The method for feeding back channel information according to the present invention includes channel quality per CSI-RS resource based on received CSI-RS (Channel State Information-Reference Signal). Indicator) and estimating aggregate CQI across a plurality of CSI-RS resources and transmitting CSI feedback including aggregate CQI information about the aggregate CQI.

Description

Channel information feedback method and apparatus {METHOD AND APPARATUS FOR CHANNEL INFORMATION FEEDBACK}

The present invention relates to wireless communication, and more particularly, to a method and apparatus for transmitting a feedback signal for a reference signal in a wireless communication system.

Multi-cell (or point) cooperation has been introduced to increase the performance and communication capacity of wireless communication systems. Multi-cell (or point) cooperative transmission and reception is also referred to as Cooperative Multiple Point (CoMP) transmission and reception.

CoMP includes a beam avoidance technique in which adjacent cells (or points) cooperate to mitigate interference to a user at a cell (or point) boundary, and a joint transmission technique in which adjacent cells cooperate to transmit the same data. .

In a next generation wireless communication system such as IEEE (Institute of Electrical and Electronics Engineers) 802.16m or 3GPP (Long Term Evolution) -Advanced, performance of users Is one of the main requirements, and CoMP can be considered to solve this problem. CoMP can be performed based on various scenarios.

Meanwhile, the base station transmits a reference signal to the terminal to check the downlink channel state. The terminal receives the reference signal, performs a measurement on the channel state based on the transmission state of the reference signal, and feeds back the result of the measurement to the base station. The base station may estimate the state of the downlink channel based on the feedback measurement result.

Similarly, in the CoMP environment, the channel state can be estimated by transmitting the reference signal in downlink. In this case, a specific method for how the UE transmits feedback on a reference signal transmitted from each transmission point constituting a CoMP cooperation set is required.

An object of the present invention is to provide a feedback method for an aggregate CQI and an apparatus using the same in a CoMP system.

Another object of the present invention is to provide a method and apparatus for reducing the number of bits of CQI feedback and increasing transmission efficiency in a CoMP system.

An object of the present invention is to provide a method and apparatus for effectively selecting and controlling a mode of CoMP transmission in a CoMP system.

(1) An embodiment of the present invention is a CSI feedback method, which provides a CQI (Channel Quality Indicator) and a plurality of CSI-RS resources based on a received CSI-RS (Channel State Information-Reference Signal). Estimating the aggregated aggregate CQI and transmitting CSI feedback comprising aggregated CQI information about the aggregated CQI.

(2) In (1), the aggregate CQI information may be 1-bit or 2-bit difference information indicating an offset level between the aggregate CQI and the CSI-RS CQI.

(3) In (2), the offset level corresponds to a value obtained by subtracting the CSI-RS from the aggregation CQI and may be greater than or equal to zero.

(4) In (1), in the case where the rank is greater than 1, the difference information is the first difference information and the codeword 1 indicating the offset level between the aggregation CQI and the CSI-RS CQI with respect to codeword 0. The second difference information indicating the offset level between the aggregation CQI and the CSI-RS CQI may be included.

(5) In (4), the CSI feedback may be transmitted using Physical Uplink Control Channel (PUCCH) Report Type 4.

(6) In (1), the aggregate CQI information may be divided and fed back according to the number of CSI-RS resources corresponding to the aggregate CQI.

(7) In (6), the divided aggregate CQI information may be distributed and transmitted in feedback of CQI per CSI-RS resource for the CSI-RS resource corresponding to the aggregate CQI, respectively.

(8) In (6), the CSI-RS resource corresponding to the aggregate CQI is a first CSI-RS resource and a second CSI-RS resource,

Most Significant Bits (MSB) of the Aggregated CQI are fed back together with CQI per CSI-RS resource for the first CSI-RS resource, and Least Significant Bits (LSB) of the Aggregated CQI are the second CSI-RS It can be fed back with CQI per CSI-RS resource for the resource.

(9) In (1), the aggregate CQI information may be fed back based on a PUCCH report type separate from the CQI per CSI-RS resource.

(10) In (9), if there are two CSI-RS resources corresponding to the aggregate CQI and the rank is greater than 1, the aggregate CQI information is aggregated CQI for codeword 0 and for codeword 0. It may include a difference value of the aggregate CQI and the aggregate CQI for codeword 1.

(11) In (9), when there are three CSI-RS resources corresponding to the aggregation CQI and the rank is 1, the aggregation CQI information is for each aggregation CQI, and the CSI-RS corresponding to each aggregation CQI. The difference information may indicate an offset level based on the CQI per CSI-RS resource for any one resource.

(12) In (9), when there are three CSI-RS resources corresponding to the aggregate CQI and the rank is 2, the aggregate CQI information is for each aggregate CQI, and the CSI-RS corresponding to each aggregate CQI. Difference information indicating an offset level based on the CQI per CSI-RS resource for any one resource may be included for each codeword.

(13) In (1), the CSI feedback is transmitted in PUCCH format 3, and the aggregate CQI information may be transmitted together with the CQI per corresponding CSI-RS resource.

(14) Another embodiment of the present invention is a CoMP control method, comprising: receiving a channel quality indicator (CQI) feedback, a plurality of CQIs per channel state information-reference signal (CSI-RS) resource included in the CQI feedback and a plurality of CQI feedback; Comparing the size of the aggregated CQI across the CSI-RS resources, and determining the CoMP (Coordinated Multi Points) transmission mode according to the comparison result.

(15) In (14), the aggregate CQI information may be 1-bit or 2-bit difference information indicating an offset level between the aggregate CQI and the CSI-RS CQI.

(16) In (14), the aggregate CQI information may be fed back based on a PUCCH report type separate from the CQI per CSI-RS resource.

(17) In (14), the aggregate CQI information may be fed back based on a PUCCH report type separate from the CQI per CSI-RS resource.

(18) In (14), the CQI feedback may be transmitted in PUCCH format 3, and the aggregate CQI information may be transmitted together with the CQI per corresponding CSI-RS resource.

(19) In (14), in the CoMP transmission mode determination step, if the aggregate CQI is larger than the CQI per CSI-RS resource, JT (Joint Transmission) CoMP may be performed.

(20) In (19), the size of the aggregate CQI may be compared with the CQI per CSI-RS resource for at least one CSI-RS resource among the CSI-RS resources corresponding to the aggregate CQI.

According to the present invention, in the CoMP system, it is possible to effectively perform feedback on the aggregated CQI. Based on this, the eNB can effectively control the transmission mode of the CoMP system. In addition, according to the present invention, it is possible to reduce the number of bits of CQI feedback and to increase transmission efficiency.

1 is a block diagram showing a wireless communication system to which the present invention is applied.
2 is a diagram schematically illustrating an example of a method in which JT CoMP is performed.
3 is a diagram schematically illustrating a method of dividing an aggregated CQI into CQIs per two or more CSI-RS resources and transmitting the same together according to the present invention.
4 is a diagram schematically illustrating a case of separately transmitting information about an aggregate CQI according to the present invention.
5 is a flowchart schematically illustrating an operation performed by a UE to transmit information about aggregate CQI according to the present invention.
6 is a flowchart schematically illustrating an operation of an eNB that receives information on an aggregate CQI according to the present invention.
7 is a block diagram schematically illustrating a structure of a UE that performs CQI feedback in a system to which the present invention is applied.
8 is a block diagram schematically illustrating the structure of an eNB in a system according to the present invention.

Hereinafter, some embodiments will be described in detail with reference to exemplary drawings. It should be noted that, in adding reference numerals to the constituent elements of the drawings, the same constituent elements are denoted by the same reference symbols as possible even if they are shown in different drawings. In the following description of the embodiments of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present disclosure rather unclear.

The present specification describes a communication network, and the work performed in the communication network is performed in the process of controlling the network and transmitting data in a system (for example, a base station) that manages the communication network, or a terminal linked to the network. Work can be done in

1 is a block diagram showing a wireless communication system to which the present invention is applied.

Referring to FIG. 1, a wireless communication system 10 is widely deployed to provide various communication services such as voice, packet data, and the like. The wireless communication system 10 includes at least one base station (BS) 11. Each base station 11 provides a communication service for a specific geographic area or frequency area and may be called a site. The site may be divided into a plurality of regions 15a, 15b, and 15c, which may be called sectors, and the sectors may have different cell IDs.

A terminal 12 may be fixed or mobile and may be a user equipment (UE), a mobile terminal (MT), a user terminal (UT), a subscriber station (SS), a wireless device, a PDA (personal digital assistant), a wireless modem, a handheld device, and the like. The base station 11 generally refers to a station that communicates with the terminal 12 and includes an evolved Node B (eNodeB), a base transceiver system (BTS), an access point, a femto base station (Femto eNodeB) (Home eNodeB: HeNodeB), a relay, a remote radio head (RRH), and the like. Cells 15a, 15b and 15c should be interpreted in a generic sense to denote a partial area covered by the base station 11 and include all coverage areas such as megacell, macrocell, microcell, picocell, femtocell It means.

Hereinafter, downlink refers to a communication or communication path from the base station 11 to the terminal 12, and uplink refers to a communication or communication path from the terminal 12 to the base station 11. . In the downlink, the transmitter may be part of the base station 11, and the receiver may be part of the terminal 12. In the uplink, the transmitter may be part of the terminal 12, and the receiver may be part of the base station 11.

There is no limitation on the multiple access scheme applied to the wireless communication system 10. (CDMA), Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), Orthogonal Frequency Division Multiple Access (OFDMA), Single Carrier-FDMA , OFDM-CDMA, and the like.

These modulation techniques increase the capacity of the communication system by demodulating signals received from multiple users of the communication system. The uplink transmission and the downlink transmission may use a time division duplex (TDD) scheme transmitted using different times or a frequency division duplex (FDD) scheme transmitted using different frequencies.

The wireless communication system 10 may be a Coordinated Multi Point (CoMP) system. The CoMP system refers to a communication system that supports CoMP or a communication system to which CoMP is applied. CoMP is a technique for adjusting or combining signals transmitted or received by multiple transmission / reception points (Tx / Rx). CoMP can increase data throughput and provide high quality.

The transmission / reception point may be defined as an element carrier or a cell or a base station (macro cell, Pico eNodeB, Femto eNodeB, or the like), or a remote radio head (RRH). The transmission / reception point may also be defined as a set of antenna ports. The transmitting / receiving point may transmit information on the set of antenna ports to the terminal through radio resource control (RRC) signaling. Therefore, a plurality of transmission points (TPs) in one cell can be defined as a set of antenna ports.

Each base station or cell may comprise multiple transmit and receive points. For example, multiple transmit and receive points may be macro cells forming a homogeneous network. In addition, the multiple transmission / reception points may be macro cells and RRHs having high transmission power. In addition, the multiple transmit / receive points may be RRHs with low transmit power in macrocell and macrocell regions.

The CoMP system can selectively apply CoMP. A mode in which a CoMP system communicates using CoMP is called a CoMP mode, and a mode other than the CoMP system is called a normal mode or a non-CoMP mode.

The terminal 12 may be a CoMP terminal. The CoMP terminal is a component of the CoMP system, and performs communication with the CoMP Cooperating Set. Like the CoMP system, the CoMP terminal can operate in the CoMP mode or in the normal mode. The CoMP cooperative set is a set of transmit / receive points that directly / indirectly participate in data transmission in a certain time-frequency resource for CoMP terminals.

Direct participation in data transmission or reception means that the transmission / reception points actually transmit data to or receive data from the CoMP terminal in the corresponding time-frequency resource. Indirect participation in data transmission or reception implies that the transmission / reception points do not actually transmit data to or from the CoMP terminal in the corresponding time-frequency resource, but contribute to making decisions about user scheduling / beamforming .

CoMP terminals can simultaneously receive signals from a CoMP cooperative set or simultaneously transmit signals to a CoMP cooperative set. In this case, the CoMP system minimizes the interference influence among CoMP cooperative sets considering the channel environment of each cell constituting CoMP cooperative set.

Various scenarios are possible when operating the CoMP system. The first CoMP scenario may be referred to as intra-site CoMP, with CoMP being homogeneous among a number of cells in one base station. The second CoMP scenario is a CoMP consisting of one macrocell and a homogeneous network for one or more High-Power RRHs. The third CoMP scenario and the fourth CoMP scenario are CoMPs consisting of one macro cell and one heterogeneous network for one or more low-power RRHs in the macro cell region. In this case, if the physical cell ID of the RRHs is not the same as the physical cell ID of the macro cell, the third CoMP scenario corresponds to the fourth cell CoMP scenario.

The CoMP is classified into Joint Processing (JP) and Coordinated Scheduling / Beamforming (CS / CB), and JP And CS / CB can be mixed.

In the case of the JP, the data for the terminal is available at at least one send / receive point of the CoMP cooperative set at some time-frequency resource. JP includes Joint Transmission (JT, hereinafter referred to as 'JT') and Dynamic Point Selection (DPS, hereinafter referred to as 'DPS').

JT refers to the simultaneous transmission of data from multiple transmission / reception points (multi-points) belonging to CoMP cooperation set to one terminal or a plurality of terminals in a time-frequency resource. In the case of JT, multiple cells (data transmission / reception points) transmitting data to one terminal perform transmission using the same time / frequency resource.

In the case of DPS, data transmission is performed from one transmission / reception point of the CoMP cooperative set in the time-frequency resource. The transmission and reception point may be changed for each subframe in consideration of interference. The data to be transmitted is available at a plurality of transmission / reception points simultaneously. DPS includes Dynamic Cell Selection (DCS).

In the case of CS, data is transmitted from one of the transmit and receive points in the CoMP cooperative set for time-frequency resources, where user scheduling is determined by coordination between the transmit and receive points of the CoMP cooperative set.

The CB is also determined by cooperation between the sending and receiving points of the CoMP cooperation set. Coordinated Beamforming (CB) can avoid interference with neighboring cell terminals.

The CS / CB may include an SSPS (Semi-Static Point Selection) which can change the transmission / reception point by semi-static selection.

As described above, it is also possible to mix JP and CS / CB. For example, some transmit / receive points within the CoMP cooperative set may transmit data to the target station according to the JP, and other transmit and receive points within the CoMP cooperative set may perform CS / CB.

The transmission / reception point to which the present invention is applied may include a base station, a cell or an RRH. That is, the base station or the RRH may be a transmission / reception point. On the other hand, a plurality of base stations may be multiplex transmission / reception points, and a plurality of RRHs may be multiplex transmission / reception points. Of course, the operations of all base stations or RRHs described in the present invention can be similarly applied to other types of transmission / reception points.

Meanwhile, a multi-input multi-output (MIMO) system, also called a multi-antenna system, improves transmission and reception data transmission efficiency by using a multi-transmission antenna and a multi-reception antenna.

In the data transmission / reception process performed in the MIMO system, the base station may receive data from N users and output K streams to be transmitted at one time. In a MIMO system, a base station may determine a terminal and a transmission rate to transmit to an available radio resource by using channel information transmitted to or from each terminal. For example, a code rate is extracted by extracting channel information from feedback information. , Modulation and Coding Scheme (MCS) may be selected.

Channel State Information (CSI) reporting information fed back from the UE to the eNB for the operation of the MIMO system may include a Channel Quality Indicator (CQI), a Rank Indicator (RI), a Pre-coding Matrix Indicator (PMI), and the like. .

The CQI provides the eNB with information about link adaptation parameters that the UE can support. In this case, the UE may consider the transmission mode, the type of the UE, the number of antennas, an interference state, and the like. CQI may be defined to indicate specific Modulation and Coding Schemes (MCS) on a given table. Table 1 briefly illustrates an example of a table defining a CQI (hereinafter, referred to as a CQI table for convenience of description).

TABLE 1

As shown in Table 1, CQI may indicate a predetermined modulation method and coding rate, that is, MCS, respectively.

The RI is the number of layers recommended by the UE, that is, the number of streams used in spatial multiplexing. RI is reported when the UE operates in MIMO mode with spatial multiplexing. The RI may have a value of 1 or 2 in the 2x2 antenna configuration and may have a value of 1 to 4 in the 4x4 antenna configuration. The RI may be associated with one or more CQI reports, where the reported CQI is assuming a value of a specific RI. Because the rank changes slower than the CQI, it may not be reported as often as the CQI.

PMI provides information about a preferred precoding matrix in codebook based precoding. Like the RI, the PMI is one piece of information provided under the MIMO operation. MIMO involving PMI feedback is called closed loop MIMO. PMI feedback may be made only in certain transmission modes. The number of precoding matrices of the codebook may be determined according to the number of antenna ports of the eNB, the number of antenna ports and performance of the UE. The PMI report (feedback) may be for a wide band or for a frequency selective subband, depending on the CSI feedback mode. The UE can estimate the channel, select a precoding matrix that maximizes channel performance, and report the PMI for the selected precoding matrix. The eNB may select a precoding matrix indicated by the fed back PMI from the codebook and use it for data transmission.

Meanwhile, in a wireless communication system, it is necessary to estimate an uplink channel or a downlink channel for data transmission / reception, system synchronization acquisition, channel information feedback, etc., and compensates for signal distortion caused by a sudden change in environment. The process of restoring the signal is called channel estimation. It is also necessary to measure the channel state of the cell or other cell to which the terminal belongs. Generally, a transceiver uses a reference signal (RS) known to each other for channel estimation or channel state measurement.

Since the receiver knows the information of the reference signal, the receiver can estimate the channel based on the reference signal of the received signal and compensate the channel value to accurately obtain the data sent from the transmitter. If p is the reference signal transmitted from the transmitter, channel information that the reference signal undergoes during transmission, h is thermal noise generated at the receiver, and n is the signal received at the receiver, it can be expressed as y = h + p + n . . In this case, since the reference signal p is already known to the receiver, when the LS (Least Square) method is used, channel information (

) Can be estimated.

<Formula 1>

Here, the channel estimation value estimated using the reference signal p

The

Value, so for accurate estimation of the h value

It is necessary to converge to zero. By using a large number of reference signals

It is possible to estimate the channel by minimizing the influence of the channel.

Reference signals are generally transmitted in sequence. The reference signal sequence may be any sequence without any particular limitation. The reference signal sequence may use a PSK-based computer generated sequence (PSK) -based computer. Examples of PSKs include Binary Phase Shift Keying (BPSK) and Quadrature Phase Shift Keying (QPSK). Alternatively, the reference signal sequence may use a Constant Amplitude Zero Auto-Correlation (CAZAC) sequence. Examples of the CAZAC sequence include a ZC-based sequence, a ZC sequence with a cyclic extension, a truncation ZC sequence (ZC sequence with truncation), and the like . Alternatively, the reference signal sequence may use a PN (pseudo-random) sequence. Examples of PN sequences include m-sequences, computer generated sequences, Gold sequences, and Kasami sequences. Also, the reference signal sequence may use a cyclically shifted sequence.

The downlink reference signal includes a cell-specific RS (CRS), an MBSFN reference signal, a UE-specific RS, a positioning reference signal (PRS), and channel state information (CSI). And a reference signal (CSI-RS).

In a multi-antenna system, resource elements used for reference signals of one antenna are not used for reference signals of other antennas in order not to interfere with the antennas.

The CSI-RS of the downlink reference signal may be used for estimation of channel state information. The CSI-RS is located in the frequency domain or the time domain, and channel quality indicator (CQI), precoding matrix indicator (PMI) and A rank indicator (RI) and the like may be reported from the UE as channel state information.

The CSI-RS may be transmitted on one or more antenna ports. For example, the CSI-RS may be transmitted using not only one antenna port but also two antenna ports, four antenna ports, eight antenna ports or the like under MIMO operation.

In the CoMP system, a plurality of cells or transmission / reception points can transmit a reference signal, for example, a CSI-RS to a UE. In the CoMP system, the reference signal sequence may be cell-specific determined. In particular, in a CoMP environment in which a cell ID of a transmission / reception point (for example, RRHs) cooperating with a specific transmission / reception point (for example, a macro cell) is equal to each other, A sequence may be used to generate the reference signal. This means that all the transmission / reception points (for example, RRHs) belonging to the same cooperative set as the macro cell transmit reference signals using the same reference signal sequence.

The time and frequency resources available to the UE for CSI reporting or CSI-RS feedback including CQI, PMI, PTI and / or RI may be controlled by the eNB. For example, the eNB may indicate the resource to be used by the UE through higher layer signaling and may control by specifying a transmission location on time and frequency of the CSI-RS.

CSI reporting may be performed periodically or aperiodicly. If there is more than one serving cell, the UE sends CSI to the activated serving cell.

If the UE is not configured to simultaneously perform Physical Uplink Shared Channel (PUSCH) transmission and Physical Uplink Control Channel (PUCCH) transmission, the UE may transmit periodic CSI report on the PUCCH or PUSCH.

The UE may send an aperiodic CSI report on the PUSCH under certain conditions.

Meanwhile, in the CoMP system, multiple CQIs based on different interference measurement resources may be transmitted from the UE to the eNB.

In this regard, aggregated CQI may be supported in the CoMP system. In this case, multiple CQIs can be used for the same band type (wideband or subband). Hereinafter, a method of supporting multiple CQIs for the same band type will be described with reference to the drawings and tables.

Four feedback modes are used for periodic CSI reporting (feedback). Table 2 shows PUCCH CSI reporting modes for periodic feedback according to the CQI feedback type and the PMI feedback type.

<Table 2>

Referring to Table 2, in the CSI report, the CQI feedback type is a wideband CQI (wideband CQI), the mode 1-0, the CQI feedback type is a wideband CQI (wideband CQI), and the PMI feedback type is In case of single PMI, mode 1-1, CQI feedback type is subband CQI, and in case of no PMI, mode 2-0, CQI feedback type is subband CQI, and PMI feedback type is single. The case of PMI is called mode 2-1.

For the PUCCH report mode defined in Table 2, the payload sizes of the PUCCH report type and the PUCCH report type may be determined.

Table 3 shows the PUCCH report mode and the PUCCH report type payload size for each mode state.

<Table 3>

Table 3 shows the mode state according to the PUCCH reporting type, the reported content, and the payload size according to the PUCCH reporting mode defined in Table 2.

The mode state may be determined according to the RI value, the number of antenna ports, the number of spatial multiplexing layers, and the like.

The added bit L is a subband index indicating which part of the entire band is used for feedback (reporting) and may be defined as shown in Equation 2.

<Formula 2>

In Equation 2, values of N ^DL _RB , k, and J may be defined as shown in Table 4 below.

TABLE 4

Referring to Table 3, it is possible to determine the bit amount of information transmitted in the periodic CSI report. For example, in the case of PUCCH report type 1, what is reported is the subband CQI, and if RI is 1 as the mode state, mode 1-0 and mode 1-1 are not available (NA), and mode 2 In -0 and mode 2-1, 4 bits and an additional L bit are transmitted.

In case of periodic CSI reporting, for the wideband CQI, if the rank is 1, one wideband CQI is fed back from the UE to the eNB with 4 bits when referring to Table 3.

In the case of periodic CSI reporting, if the rank is greater than 1, a 3-bit spatial differential CQI value may be used. The differential CQI value indicates an offset level value between the CQI indexes for each codeword. Therefore, the CQI index may be determined using a differential CQI value indicating an offset level as shown in Table 5.

Table 5 is an example of a table that maps offset levels and differential CQI values for CQI.

<Table 5>

If the rank is 2 or more and two codewords (Codeword 0 and Codeword 1) are transmitted, the offset level of Codeword 1 is the CQI index for Codeword 0 and the CQI for Codeword 1, as shown in Equation 3. Defined as the difference value of the index.

<Formula 3>

Codeword 1 offset level = CQI index for codeword 0-CQI index for codeword 1

Therefore, when the CQI index for codeword 0 is transmitted, the UE may indicate the CQI index for codeword 1 by transmitting a differential CQI value having a smaller number of bits than the CQI index. The transmitted CQI index indicates an offset level between the CQI index for codeword 0 and the CQI index for codeword 1 on a predetermined table as shown in Table 5, and the CQI index for codeword 1 may be derived as shown in Equation 4. Can be.

<Equation 4>

CQI index for codeword 1 = CQI index for codeword 0-codeword 1 offset level

For example, when the rank is greater than 1, a 3-bit wideband differential CQI value based on the codeword 1 offset level of Table 5 may be used to transmit the wideband CQI of codeword 1. FIG. That is, the codeword 1 offset level indicated by the wideband differential CQI value is obtained by subtracting the wideband CQI index for codeword 1 from the wideband CQI index for codeword 0.

The same method can be applied to the subbands. For example, when the rank is greater than 1, the codeword 1 offset level indicated by the subband differential CQI value is obtained by subtracting the subband CQI index for codeword 1 from the subband CQI index for codeword 0.

One CQI may be fed back for one codeword. As described above, a differential CQI based on the CQI for another codeword may be used to transmit the CQI for one codeword between two different codewords of the MIMO operation.

If no differential CQI is used, four bits are required for the original CQI feedback. As described above, in a CSI report including a plurality of CQIs, when differential CQIs are applied between a plurality of CQIs, CQI feedback may be performed even with fewer than 4 bits in at least one or more CQI feedbacks.

As described in Table 1, the transmitted CQI may indicate the MCS level.

Meanwhile, in the CoMP system, as described above, multiple CQIs based on different interference measurement resources may be transmitted from the UE to the eNB. Multiple CQI may consist of CQI per CSI-RSs and Aggregated CQIs for the same type (wideband CQI or subband CQI).

Aggregate CQI is for Joint Transmission (JT).

1 is a diagram schematically illustrating a method of performing a non-JT CoMP (Non-JT CoMP) as a general downlink transmission method.

Referring to FIG. 1, a transmission point TP1 transmits information including a CSI-RS to UE1 belonging to its own cell 110. The transmission point TP2 also transmits information including the CSI-RS to UE2 belonging to its cell 120, and the transmission point TS3 also transmits information including the CSI-RS to UE3 belonging to its own cell 130.

As described above, in the case of Non-JT CoMP, at least one of the transmission points TP1, TP2, and TP3 and / or at least one of the UEs UE1, UE2, and UE3 may support CoMP, but JT is not performed. Does not. Therefore, CSI-RSs using different resources are not transmitted from two or more transmission points to one UE.

In contrast, in the case of JT CoMP, CSI-RS using different resources may be transmitted to different terminals from different transmission points.

2 is a diagram schematically illustrating an example of a method in which JT CoMP is performed.

In the example of FIG. 2, a transmission point TP1, which is responsible for transmission in cell 1 210, and a transmission point TP2, which is responsible for transmission in cell 2 220, of the different cells 210, 220, and 230 support CoMP. The CSI-RS is transmitted to 240. CSI-RS1 250 transmitted from TP1 and CSI-RS2 260 transmitted from TP2 are transmitted using different CSI-RS resources.

For CSI-RSs using different resources, a channel on which CSI-RS1 250 is transmitted is called H1, and a channel on which CSI-RS2 260 is transmitted is called H2.

In the case of Non-JT CoMP illustrated in FIG. 1, CQI per CSI-RS resource may be determined as shown in Equation 5. CQI1 is a CQI per CSI-RS resource for CSI-RS1, and CQI2 is a CQI per CSI-RS resource for CSI-RS2.

&Lt; EMI ID =

Here, W1 and W2 each represent a precoding matrix for the corresponding channel. In addition, I represents the interference value from the exterior.

On the other hand, when the JT CoMP as described in Figure 2 is performed, the value of the aggregate CQI is as shown in Equation 6 in consideration of both the CSI-RS1 transmitted from TP1 through H1 and the CSI-RS2 transmitted through H2 from TP2 Can be determined.

&Lt; EMI ID =

As shown in Equation 6, the value of the aggregate CQI is different from the value of the CQI per CSI-RS resource and is calculated across two different CSI-RS resources.

Therefore, in addition to the method of transmitting CQI per CSI-RS resource as shown in Tables 2 and 3, a method of effectively transmitting the aggregated CQI needs to be considered. In addition, CSI feedback transmitted on PUCCH needs to be considered in relation to which PUCCH format is used.

PUCCH may support multiple formats. That is, uplink control information having different numbers of bits per subframe may be transmitted according to a modulation scheme.

Table 6 is a table schematically describing the PUCCH format.

<Table 6>

CQI information may be transmitted using PUCCH format 2 and PUCCH format 3 among PUCCH formats.

In the PUCCH format 2, a QPSK () modulation scheme is used, and 20 bits of encoding information can be transmitted using the PUCCH format 2. CQI information may be transmitted up to 11 bits using PUCCH format 2.

In the case of PUCCH format 3, a QPSK () modulation scheme is used, and 48 bits of encoding information can be transmitted using PUCCH format 3. CQI information may be transmitted up to 20 bits using PUCCH format 3.

Hereinafter, a method of periodically performing CQI feedback on aggregate CQI in a system where JT CoMP is performed will be described in detail considering the PUCCH format.

Specifically, Method 1 to Method 3, which will be described later, relate to the case of using the PUCCH format 2. Method 4 relates to the case of using the PUCCH format 3.

<Method 1-Single direction differential CQI feedback>

As described above, the aggregated CQI is for Joint Transmission (JT) CoMP. Considering that JT will be used only when a single transmission from each transmission point to the UE, i.e., when non-JT is performed, the aggregate CQI can be said to be greater than the CQI per CSI-RS resource.

Therefore, the case where the aggregated CQI is larger than the CQI per CSI-RS resource and the case where the aggregated CQI is larger than the CQI per CSI-RS resource may be given priority or mainly. Since the difference between the aggregated CQI and the CQI per CSI-RS resource is mainly considered a direction larger than zero among directions larger than zero and smaller than zero, the method may be referred to as a unidirectional differential CQI feedback method.

Since we consider the case where the aggregated CQI is greater than the CQI per CSI-RS resource, we do not consider both cases where the differential CQI value is greater than or equal to zero and less than zero, as shown in Table 5. Only in the same case, the differential CQI can be transmitted with a smaller number of bits.

For example, the UE may transmit differential CQI between the aggregate CQI and the CQI per CSI-RS resource using 2 bits, and the eNB may derive the aggregate CQI based on the received differential CQI and the CQI per CSI-RS resource.

In addition, the UE may transmit a differential CQI between the aggregate CQI and the CQI per CSI-RS resource using 1 bit, and the eNB may derive the aggregate CQI based on the received differential CQI and the CQI per CSI-RS resource.

Table 7 shows an example of a table for mapping a 2-bit differential CQI value with an offset level according to the present invention.

<Table 7>

Table 7 is an example of a table that maps 2-bit differential CQI values only for offset levels greater than or equal to zero. In the example of Table 6, the difference CQI value of 2 bits is mapped to only offset levels greater than or equal to 0 in Table 3.

Meanwhile, although Table 7 shows an example of mapping 2-bit differential CQI to successive offset levels, the present invention is not limited thereto, and 2-bit differential CQI may be mapped to offset levels having a predetermined interval.

Table 8 shows another example of a table for mapping a 2-bit differential CQI value with an offset level according to the present invention.

<Table 8>

Table 8 is an example of a table that maps a 2-bit differential CQI value to offset levels greater than or equal to 0 having a predetermined interval. Table 8 shows an example of mapping a 2-bit differential CQI value to discrete offset levels having a spacing of two when the offset level is 1 or more. However, the interval between offset levels may be 3 or 4 irrespective of this. And a larger number that reflects the state of the system.

It is also possible to set the spacing between offset levels irregularly.

Table 9 shows another example of a table for mapping a 2-bit differential CQI value with an offset level according to the present invention.

<Table 9>

Table 9 shows an example of setting aperiodic or irregular intervals between offset levels greater than or equal to zero and matching two-bit differential CQI values.

In Table 9, an example of using offset levels spaced between 0 and 2 is described as an example, but the present invention is not limited thereto, and the offset levels may be used in various ways.

On the other hand, in consideration of the total number of bits allocated to the CSI-RS report, instead of the two-bit differential CQI described above, one-bit differential CQI may be used.

Table 10 shows an example of a table for mapping a 1-bit differential CQI value with an offset level according to the present invention.

<Table 10>

Referring to Table 10, the differential CQI value 0 indicates an offset level equal to or less than 0, and the differential CQI value 1 indicates an offset level greater than or equal to 3. On the other hand, a value between 0 and 3 of the offset level may be variably processed according to the implementation of the terminal. In other words, it is regarded as a terminal implementation issue.

Here, one bit differential CQI value (0 or 1) is used to indicate an offset level equal to or less than 0 and an offset level greater than or equal to 3, but the offset level indicated by the differential CQI having a value of 0 or 1 is shown in the table. It is not limited to the example of 9, but can be variously set. For example, one differential CQI of a difference CQI value of 0 or 1 may indicate one offset level, and the other differential CQI may indicate a range of offset levels. It is also possible for all of the difference CQI values of 0 or 1 to indicate an offset level of a specific value rather than a specific range of offset levels.

As described above, the difference CQI value indicates an offset level corresponding to the difference between the aggregated CQI and the CQI per CSI-RS resource.

Even if the rank is large, a difference CQI indicating the offset level between the CQI per CSI-RS resource and the aggregate CQI can be obtained based on the CQI per CSI-RS resource for the same codeword. For example, even if the rank is high, the offset level indicated by the differential CQI for the aggregate CQI may be obtained based on the CQI per CSI-RS resource of the corresponding codeword.

Specifically, for codeword 0, the relationship between the offset level indicated by the differential CQI and the aggregated CQI and the CQI per CSI-RS resource may be determined as shown in Equation 7.

Equation (7)

Codeword 0 offset level

= Wideband / subband aggregate CQI index for codeword 0-CQI index per wideband / subband CSI-RS resource for codeword 0

As shown in Equation 7, a method of transmitting aggregate CQI information using differential CQI may be equally applied to a wideband case and a subband case among PUCCH CQI feedback types. When the rank is 2 or more, not only codeword 0 but also codeword 1 can be considered. In this case, for codeword 1, the relationship between the offset level indicated by the differential CQI and the aggregate CQI and the CQI per CSI-RS resource may be determined as shown in Equation 8.

CQI that is a reference when the aggregate CQI is calculated. For example, when two CQIs are considered to obtain the aggregate CQI, the CQI on which the aggregate CQI is calculated may be CQI1 (from CSI-RS1), or CQI2 ( CSI-RS2). In another method, CQI reporting (CQI1 or CQI2) in which the aggregated CQI is carried out may be a reference, or may be max {CQI1, CQI2}.

<Formula 8>

Codeword 1 offset level = for codeword 1 Wide band / Subband aggregation CQI  Index-for codeword 1 Wide band Subband CSI - RS  Per resource CQI  index

Like Equation 7, the method of Equation 8 may be applied to the case of wideband and subband in the PUCCH CQI feedback type.

The correct value of the offset level for codeword 0 in Equation 7 and the correct value of the offset level for codeword 1 in Equation 8 may be determined using a table that maps the transmitted differential CQI and the off-cell level. Tables 7-10 are examples of tables that map differential CQI and offset levels in accordance with the present invention.

Bits related to aggregate CQI (also referred to as 'aggregated CQI bits' for convenience of description) are added to CQI feedback (reporting) per CSI-RS resource in such a way as to use differential CQI of 2 bits or 1 bit as described above. Or may be attached. Thus, there is no need to define a separate format or method for feeding back the aggregate CQI.

Meanwhile, referring to Table 3, in the case of PUCCH Reporting Type 4, since there are enough bits to transmit information, a format for transmitting aggregate CQI may be configured as shown in Table 11.

Table 11 is a table schematically illustrating an example of aggregate CQI in PUCCH report (feedback) type 4 according to the present invention.

<Table 11>

Referring to Table 11, in case of using 2 antenna ports in PUCCH report type 4, if the rank is 1, 4 bits are used to transmit CQI per CSI-RS resource, and aggregate CQI is used for CQI per CSI-RS resource. It is transmitted in the form of a difference value of 2 bits as a base line. Therefore, in this case, the information actually transmitted with respect to the aggregate CQI in Table 11 may be the difference CQI as described above. The differential CQI indicates an offset level for deriving an aggregate CQI based on the CQI per CSI-RS resource on the mapping table as shown in Tables 7 to 9.

In addition, in the example of Table 11, when using two antenna ports, if the rank is 2, 4 bits are used for the first codeword to transmit CQI per CSI-RS resource and the first codeword for the second codeword. The differential CQI of 3 bits is transmitted on the basis of. In this case, the 3-bit differential CQI may indicate an offset level for deriving the second codeword based on the first codeword on the mapping table as shown in Table 5. Aggregated CQI is transmitted in the form of a 2-bit difference value based on the CQI per CSI-RS resource.

In addition, when using two antenna ports, if the rank is 1, the differential CQI based on the CQI per CSI-RS resource may be transmitted as information on the aggregated CQI. Accordingly, in Table 11, when two antenna ports are used, information actually transmitted as an aggregate CQI may be a differential CQI based on CQI per CSI-RS resource, and the differential CQI is 2 as shown in the examples of Tables 7 to 9. The offset level can be indicated as the value of the bit. The eNB may derive the aggregate CQI based on the CQI per CSI-RS resource and using the offset level indicated by the differential CQI.

In addition, when using two antenna ports, if the rank is 2, two bits of differential CQI based on the CQI per CSI-RS resource for the first codeword as the information about the aggregate CQI can be transmitted for the first codeword. have. For a second codeword, a CQI per CSI-RS resource for a second codeword or a 2-bit differential CQI for a 3-bit differential CQI based on the first codeword may be transmitted. In this case, the difference CQI for each codeword may be calculated using Equations 7 and 8.

Even in the case of using four antenna ports in Table 11, the above-described information may be applied to the case of using two antenna ports in the same manner.

On the other hand, when using the aggregated CQI, there may be more than one CQI per CSI-RS resource, information about the aggregated CQI is to be transmitted with the CQI per CSI-RS resource used as a base line for calculating the differential CQI Can be.

For example, assume that CSI-RS1 CQI and CSI-RS2 CQI exist as CQI per CSI-RS resource using two different resources. In this case, the differential CQI between the aggregate CQI and the CSI-RS1 CQI may be transmitted together with the CSI-RS1 CQI, and the differential CQI between the aggregate CQI and the CSI-RS2 CQI may be transmitted together with the CSI-RS2 CQI. Since the CQIs per reference CSI-RS resource are different, the value of the differential CQI transmitted may be different, but the value of the derived aggregate CQI may be the same.

Among the PUCCH report types for transmitting the CQI, for the types except for the PUCCH report type 4 described above, information about the aggregate CQI may be added or appended to the CQI per CSI-RS resource and transmitted. In this case, the information on the aggregate CQI may be the above-described two-bit difference CQI. The eNB may derive an aggregate CQI based on the offset level indicated by the received 2-bit differential CQI and the CQI per CSI-RS resource transmitted with the differential CQI.

Table 12 schematically illustrates a method of transmitting information on the aggregate CQI (differential CQI) for the types except for the PUCCH report type 4 among the PUCCH report types for transmitting the CQI according to the present invention.

<Table 12>

Comparing Table 12 and Table 3, it can be seen that information on the aggregate CQI (differential CQI of 2 bits or 1 bit) is attached to the CQI per CSI-RS resource and transmitted. Aggregated CQI may be derived using Equation 7 and / or Equation 8 based on the offset level indicated by the differential CQI and the CQI per CSI-RS resource transmitted together with the differential CQI.

Since the number of bits allocated for CSI reporting is limited, the information on the aggregated CQI may be transmitted in consideration of the amount of information such as CQI, RI, or PMI per transmitted CSI-RS resource. In Table 12, an example in which 11 bits are allocated to the CSI report on the PUCCH and 4 bits are allocated to the aggregate CQI itself is described as an example. In Table 12, '(X)' means that a method of transmitting information on the aggregate CQI (differential CQI) by additional bits is not supported. In Table 12, (*) indicates that an additional bit for deriving an aggregate CQI with one bit differential CQI is supported instead of a two bit differential CQI.

Meanwhile, a table (eg, Tables 5 or 7 to 10, etc.) for mapping the difference CQI and the offset level may be shared in advance between the UE and the eNB or transmitted from the eNB to the UE through higher layer signaling.

<Method 2-Divided Aggregate CQI by CSI-RS Resource Feedback>

Aggregated CQI is associated with at least two CSI-RS resources. Using this, the aggregated CQI bits can be divided into several parts and transmitted. For example, different parts of the aggregated CQI may be fed back using a feedback process for different CSI-RS resources.

Basically, if the difference method described above is not used, all bits of the aggregate CQI are the transmission targets. For example, if the differential scheme is not used, the aggregated CQI to be transmitted may have 4 bits.

The bits of the aggregated CQI may be composed of Most Significant Bits (MSB) and Least Significant Bits (LSB). For example, if the aggregate CQI has 4 bits, the 4 bits may have an MSB and an LSB.

In this case, the MSB of the aggregate CQI is transmitted together with the CQI per CSI-RS resource having a lower index among the CQIs per two CSI-RS resources associated with the aggregate CQI, and the CQI of the aggregate CQI together with the CQI per CSI-RS resource having the high index. The LSB can be transmitted.

In addition, the MSB of the aggregated CQI is transmitted along with the CQI per CSI-RS resource having a higher index among the CQIs per two or more CSI-RS resources associated with the aggregated CQI, and the CQI of the aggregated CQI together with the CQI per CSI-RS resource having the low index. The LSB may be transmitted.

3 is a diagram schematically illustrating a method of dividing an aggregated CQI into CQIs per two or more CSI-RS resources and transmitting the same together according to the present invention.

3 illustrates a method of dividing and attaching bits of an aggregated CQI to CQIs of two CSI-RSs using two different resources (CSI-RS resource 1 and CSI-RS resource 2).

Let CQI per CSI-RS resource 1 for CSI-RS resource 1 be CQI 1 and CQI per CSI-RS resource for CSI-RS resource 2 be CQI 2. In this case, CQI 3 represents the aggregated CQI across CSI-RS resource 1 and CSI-RS resource 2.

Referring to FIG. 3, feedback information 310 for CSI-RS resource 1 may be composed of MSBs of CQI 1 and CQI 3. In addition, the feedback information 320 for the CSI-RS resource 2 may be composed of LSBs of CQI 2 and CQI 3.

At this time, whether the CQI having the lower index and the MSB of the aggregated CQI are transmitted together and the CQI having the higher index and the LSB of the aggregated CQI are transmitted together or aggregated together with the CQI having the higher index. Whether the MSB of the CQI is transmitted together and the LSB of the aggregated CQI and the CQI having the lower index are transmitted together may be determined in advance between the UE and the eNB or may be transmitted through higher layer signaling.

Although FIG. 3 illustrates that the bits of the aggregate CQI are transmitted together by transmitting the CQIs per two CSI-RS resources, the present invention is not limited thereto. For example, the aggregated CQIs may be distributed and transmitted together with more CQIs per CSI-RS resource than CQIs per two CSI-RS resources. For example, if there are four CQIs per CSI-RS resource, the MSB of the aggregated CQI may be divided into CQIs per two CSI-RS resources, and the LSBs of the aggregated CQIs may be divided into two different CQIs per two CSI-RS resources. have.

Meanwhile, in the case of PUCCH Reporting Type 4, since there are enough bits to transmit information, there is no problem in transmitting the aggregate CQI in the format shown in FIG. 3. In this regard, the aggregate CQI may be reported in a manner of dividing and attaching bits of the aggregate CQI to the report of the CQI for each CSI-RS resource even for types except for the PUCCH report type 4 among the PUCCH report types including the CQI.

Table 13 schematically illustrates a method for reporting aggregate CQI in types other than PUCCH report type 4 among PUCCH report types including CQI according to the present invention.

<Table 13>

Table 13 illustrates an example in which 11 bits are allocated to the CSI report on the PUCCH and an aggregate CQI is reported using 4 bits as an example.

Referring to Table 13, bits of an aggregate CQI are transmitted along with CQI per CSI-RS resource or CQI and PMI per CSI-RS resource. For example, with CQI per CSI-RS resource (CQI1) for CSI-RS resource 1 and CQI per CSI-RS resource (CQI2) for CSI-RS resource 2, CSI-RS resource 1 and CSI-RS resource 2 If the 4-bit aggregate CQI is transmitted, 2 bits of the 4 bits constituting the aggregate CQI may be transmitted together with the CQI1, and the remaining 2 bits constituting the aggregate CQI may be transmitted together with the CQI2.

In this case, two bits transmitted together with the CQI1 may be the MSB or the LSB of the aggregated CQI. In addition, two bits transmitted with the CQI2 may be the MSB or the LSB of the aggregated CQI. Which CQI and MSB of CQI1 and CQI2 are transmitted, and which CQI and LSB are transmitted may be predetermined between the UE and the eNB or may be delivered through higher layer signaling.

In Table 13, when the rank is greater than 4 in the case of PUCCH report type 2b and the rank is 8 in the case of PUCCH report type 2c, considering the maximum number of bits of the CSI report, the bits of the aggregated CQI are divided into 4 bits. Can transmit

Meanwhile, a method of using the differential CQI described above for the aggregate CQI may be considered, and a method of dividing the differential CQI as described above and transmitting the same with the corresponding CQI per CSI-RS resource may be considered. In this case, the number of transmission bits can be further reduced, and a larger bit number of differential CQI can be used without using one bit of differential CQI.

Table 14 is a table schematically illustrating a method of dividing a differential CQI and transmitting the same with the corresponding CQI per CSI-RS resource according to the present invention.

TABLE 14

Table 14 illustrates an example in which 11 bits are allocated to the CSI report on the PUCCH and an aggregate CQI is reported using 4 bits as an example.

Referring to the case of PUCCH report type 1 as an example, in the case of rank 1, in PUCCH report modes 2-1 and 2-0, the difference for aggregate CQI together with 4 bits of CQI per CSI-RS resource for a subband. CQI is sent.

The differential CQI is composed of 2 bits, as described in Tables 7-9. The eNB may derive an aggregate CQI from the offset level indicated by the differential CQI transmitted by the UE and the CQI per CSI-RS resource that is equivalent to the differential CQI.

In the PUCCH report type 1 having a rank of 1, two bits of differential CQI are divided by one bit and transmitted along with the CQI per CSI-RS resource. For example, CQI per CSI-RS resource (CQI1) for CSI-RS resource 1 and CQI per CSI-RS resource (CQI2) for CSI-RS resource 2 are sent, and aggregate CQI Assume that it spans CSI-RS resource 2. In this case, the differential CQI may be a 2-bit signal indicating an offset level based on either CQI1 or CQI2. One bit of the differential CQI is transmitted as shown in Table 14 with CQI1, and the other 1 bit of the differential CQI is transmitted as shown in Table 14 with CQI2.

In PUCCH report type 1 with rank 2, the UE divides the 2-bit differential CQI (differential CQI0) for codeword 0 by 1 bit and transmits the CQI per CSI-RS resource with 2 bits for codeword 1. The differential CQI (differential CQI1) is divided by 1 bit and transmitted along with the CQI per CSI-RS resource. For example, CQI per CSI-RS resource (CQI1) for CSI-RS resource 1 and CQI per CSI-RS resource (CQI2) for CSI-RS resource 2 are sent, and aggregate CQI Assume that it spans CSI-RS resource 2. In this case, the difference CQI0 may be a 2-bit signal indicating an offset level based on either CQI1 or CQI2 for the codeword 0. The differential CQI1 may be a 2-bit signal indicating an offset level based on either CQI1 or CQI2 for codeword 1.

One bit of the differential CQI0 is transmitted as shown in Table 14, with CQI1 for codeword 0, and the other 1 bit of the differential CQI is transmitted as shown in Table 14, with CQI2 for codeword 0. One bit of the differential CQI1 is transmitted as shown in Table 14 with CQI1 for codeword 1, and the other 1 bit of the differential CQI is transmitted as shown in Table 14 with CQI2 for codeword 1. Accordingly, two bits of differential CQI may be transmitted together with CQI1, and two bits of differential CQI may be transmitted together with CQI2.

Although the case of the PUCCH report type 1 has been described as an example, information on the aggregate CQI (differential CQI) may be transmitted in the same manner with respect to other PUCCH report types.

On the other hand, also in method 2, when using differential CQI, a table (e.g., Tables 5 or 7 to 10, etc.) for mapping the differential CQI and the offset level is shared in advance between the UE and the eNB, or via the higher layer signaling from the eNB. Can be sent to.

Method 3-Separate Transfer of Aggregated CQI Information

In consideration of the total number of bits allocated for CSI reporting on PUCCH, it may be difficult to add information on aggregate CQI, for example, split bits or differential CQI of aggregate CQI, to CQI per CSI-RS resource and to transmit. have.

Therefore, a method of separately transmitting only the information of the aggregate CQI may be considered by adding a new report type to the PUCCH report type of Table 3.

According to the method, the information of the aggregate CQI may be transmitted separately from the CQI per CSI-RS resource. In addition, in order to reduce the number of transmission bits, information on the aggregate CQI may be calculated and transmitted. In this case, the CQI per CQI-RS resource, which is a reference of the offset level indicated by the differential CQI, may be transmitted through a separate PUCCH report type.

4 is a diagram schematically illustrating a case of separately transmitting information about an aggregate CQI according to the present invention.

Referring to FIG. 4, information on aggregate CQIs may be transmitted through a separate PUCCH report type.

In FIG. 4, aggregate CQIs may be defined according to which CSI-RSs are aggregated. For example, if three CSI-RS resources are used for CSI-RS transmission, aggregate CQI1 aggregates CQI across the CSI-RS resource 1 and the CSI-RS resource 2. Aggregate CQI2 is the aggregate CQI over CSI-RS resource 1 and CSI-RS resource 3, CQI3 is the aggregate CQI over CSI-RS resource 2 and CSI-RS resource 3, and CQI4 is CSI-RS resource 1, CSI It may be an aggregate CQI over -RS resource 2 and CSI-RS resource 3.

On the other hand, in order to reduce the transmission bit, the information of the aggregate CQI can be calculated and transmitted to the differential CQI.

In this case, in FIG. 4, aggregate CQI1 is CQI per CSI-RS resource (CQI1) for CSI-RS resource 1 or CQI per CSI-RS resource (CQI2) and CSI-RS resource 1 and It may be a differential CQI indicating an offset level between the aggregated CQIs over two. Aggregate CQI2 is the difference between CQI per CSI-RS resource (CQI1) for CSI-RS resource 1 (CQI1) or CQI per CSI-RS resource for CSI-RS resource 3 (CQI3) and aggregate CQI across CSI-RS resources 1 and 3 It may be a differential CQI indicating an offset level. Aggregate CQI3 is the value between CQI per CSI-RS resource (CQI1) for CSI-RS resource 1 (CQI1) or CQI per CSI-RS resource for CSI-RS resource 3 (CQI3) and aggregate CQI across CSI-RS resources 1 and 3 It may be a differential CQI indicating an offset level. In addition, aggregate CQI4 is CQI per CSI-RS resource (CQI1) for CSI-RS resource 1, CQI per CSI-RS resource (CQI2) for CSI-RS resource 2, or CSI-RS resource for CSI-RS resource 3 It may be a differential CQI indicating an offset level between the party CQI (CQI3) and the aggregated CQI across CSI-RS resources 1, 2, and 3. Here, the case in which CSI-RS transmission is performed using three CSI-RS resources is described, but the same may be considered when more or less CSI-RS resources are used.

In addition, if the rank is greater than 1 and in the case of two codeword transmissions, in FIG. 4, the aggregation CQI1 may be an aggregation CQI for codeword 0, and CQI2 may be an aggregation CQI for codeword 0 and aggregation for codeword 1. It may be a differential CQI between CQIs. At this time, the differential CQI represents the difference between the aggregation CQI for codeword 0 and the aggregation CQI for codeword 1.

For example, when performing CSI feedback on two CSI-RS resources, information on the aggregate CQI across these CSI-RS resources may be considered for each codeword and transmitted. For example, when only one codeword is transmitted (rank = 1), only an aggregate CQI for the corresponding codeword may be transmitted. When two codewords are transmitted (rank 2 or more), the aggregate CQI for the first codeword (codeword 0) may be transmitted, and the aggregate CQI related information for the second codeword may be transmitted as a differential CQI. In this case, the differential CQI becomes a difference between the aggregate CQI for the first codeword and the aggregate CQI for the second codeword.

Table 15 is a table schematically illustrating a method of separately transmitting an aggregated CQI across two CSI-RS resources.

<Table 15>

In Table 15, the case where 4 bits are allocated to the aggregate CQI is described as an example.

In the case of using two antenna ports in Table 15 as an example, when the rank is 1, only the aggregate CQI for one codeword is transmitted using 4 bits. If the rank is 2, the aggregate CQI for one codeword (codeword 0) is transmitted in 4 bits, and the aggregate CQI for the other codeword (codeword 1) is transmitted in a 3-bit differential CQI. In this case, the difference CQI is a difference between the aggregation CQI for codeword 0 and the aggregation CQI for codeword 1. FIG.

In the same way, even for the 4-port antenna, when the rank is 1, only the aggregate CQI for one codeword is transmitted using 4 bits. If the rank is greater than 1, the aggregate CQI for one codeword (codeword 0) is transmitted in 4 bits, and the aggregate CQI for the other codeword (codeword 1) is transmitted in 3 bits of differential CQI. In this case, the difference CQI is a difference between the aggregation CQI for codeword 0 and the aggregation CQI for codeword 1. FIG.

Meanwhile, when performing CSI feedback on three CSI-RS resources, information on each aggregate CQI may be transmitted separately from the CQI per CSI-RS resource by transmitting a differential CQI for the aggregate CQI.

For example, CSI feedback is performed on three CSI-RS resources (CSI-RS resource 1, CSI-RS resource 2, and CSI-RS resource 3), and two CSI-RS resources of three CSI-RS resources are performed. If aggregation occurs across, there are three aggregate CQIs. That is, aggregate CQI1 over CSI-RS resource 1 and CSI-RS resource 2, aggregate CQI2 over CSI-RS resource 1 and CSI-RS resource 3, and aggregate CQI3 over CSI-RS resource 2 and CSI-RS resource 3 Information of can be transmitted.

In this case, in consideration of all bits allocated to the CSI feedback (reporting), the information on the aggregated CQI may be transmitted as difference information.

Table 16 is a table schematically illustrating a format that can be used when separately transmitting the information on the aggregated CQI according to the present invention.

<Table 16>

Table 16 describes an example in which a total of 11 bits are allocated for CSI reporting and 4 bits are allocated to an aggregate CQI.

Aggregate CQI1 spans CSI-RS resource 1 and CSI-RS resource 2, Aggregate CQI2 spans CSI-RS resource 1 and CSI-RS resource 3, and Aggregate CQI3 spans CSI-RS resource 2 and CSI-RS resource 3 .

The differential CQI1 is a differential CQI indicating an offset level at which aggregation CQI1 can be derived based on the CQI per CSI-RS resource for CSI-RS resource 1 or the CQI per CSI-RS resource for CSI-RS resource 2.

The differential CQI2 is a differential CQI indicating an offset level capable of inducing aggregation CQI2 based on the CQI per CSI-RS resource for CSI-RS resource 1 or the CQI per CSI-RS resource for CSI-RS resource 3.

The differential CQI3 is a differential CQI indicating an offset level at which aggregation CQI3 can be derived based on the CQI per CSI-RS resource for CSI-RS resource 2 or the CQI per CSI-RS resource for CSI-RS resource 3.

The difference CQI1, difference CQI2, and difference CQI3 may be composed of two bits of information, as described with reference to Tables 7 to 9 above. Here, the relationship between the aggregate CQI, the CQI per CSI-RS resource, and the offset level is shown in Equation 9.

Equation (9)

Offset Level = Aggregate CQI-CQI per CSI-RS Resource

CQI per CSI-RS resource, which is a criterion for deriving aggregate CQI using differential CQI, is transmitted separately using another PUCCH report type.

Referring to Table 16, when using a two-port antenna and the rank is 1, each differential CQI for the aggregated CQI is composed of 2 bits, respectively, and is transmitted separately from the CQI per CSI-RS resource.

When using a two-port antenna and rank 2, the differential CQI1, differential CQI2, and differential CQI3 consist of two bits of differential CQI for codeword 0 and two bits of differential CQI for codeword 1, respectively, CSI-RS It is sent separately from the CQI per resource.

However, when the total number of bits allocated for CSI reporting (feedback) is insufficient, the difference CQI for the aggregation CQI3 may be configured as a difference value of 1 bit as described in Table 9. For example, if only 11 bits are allocated for CSI reporting, differential CQI3 may consist of one bit differential CQI for codeword 0 and one bit differential CQI for codeword 1.

In the case of using the 4-port antenna, the differential CQI for each aggregation CQI may be transmitted separately from the CQI per CSI-RS resource as described above. In case of using 4 port antenna and rank is 1, each differential CQI for aggregate CQI is composed of 2 bits each and transmitted separately from CQI per CSI-RS resource.

If a 4-port antenna is used and the rank is 2 or more, the differential CQI1, the differential CQI2, and the differential CQI3 each consist of a 2-bit differential CQI for codeword 0 and a 2-bit differential CQI for codeword 1, respectively, and the CSI-RS It is sent separately from the CQI per resource. Even in this case, when the total number of bits allocated for CSI reporting (feedback) is insufficient, the difference CQI for the aggregation CQI3 may be configured with a difference value of 1 bit as described in Table 9. For example, if only 11 bits are allocated for CSI reporting, differential CQI3 may consist of one bit differential CQI for codeword 0 and one bit differential CQI for codeword 1.

Herein, a case where aggregation is performed over two CSI-RS resources among three CSI-RS resources is described. However, aggregation may be performed over all three CSI-RS resources. For example, aggregate CQI1 over CSI-RS resource 1 and CSI-RS resource 2, aggregate CQI2 over CSI-RS resource 1 and CSI-RS resource 3, and CSI-RS resource 1, CSI-RS resource 2 and CSI-RS Information of aggregation CQI3 over resource 3 may be transmitted.

Also in this case, in consideration of the total bits allocated to the CSI feedback (reporting), the information on the aggregated CQI can be transmitted as difference information. Also in this case, Table 15 can be used as it is.

In this case, however, the difference CQI3 in Table 16 is CQI per CSI-RS resource for CSI-RS resource 1, CQI per CSI-RS resource for CSI-RS resource 2, or CSI-RS resource for CSI-RS resource 3 It indicates the offset level from which the aggregate CQI can be derived based on the sugar CQI.

The difference CQI1, difference CQI2, and difference CQI3 may be composed of two bits of information, as described above with respect to Tables 7 to 9, and the relationship between the aggregated CQI, the CQI per CSI-RS resource, and the offset level is also expressed in Equation 9 and same. In addition, the number of bits for each differential CQI may be allocated according to the number of antenna ports and the rank value as described above.

Meanwhile, the method of defining and transmitting information on the aggregate CQI by defining a type separate from the PUCCH report type through which the CQI per CSI-RS resource is transmitted may also be used in the definition of multiple CQIs because of multiple IMRs.

On the other hand, also in method 3, when using differential CQI, a table for mapping the differential CQI and the offset level (for example, Tables 5 or 7 to 10, etc.) is shared in advance between the UE and the eNB, or the UE through higher layer signaling from the eNB. Can be sent to.

Method 4-Aggregated CQI Feedback using PUCCH Format 3

Meanwhile,

Among the PUCCH formats, PUCCH format 2 is used for transmission of CQI and can be allocated for CSI feedback transmission up to 11 bits in one subframe through the QPSK modulation scheme.

As described above, Method 1 to Method 3 correspond to a method using PUCCH format 2 as described above.

In contrast, PUCCH format 3 is a PUCCH format to which Discrete Fourier Transform-Spreading-Orthogonal Frequency-Division Multiplexing (DFT-S-OFDM) is applied, and can be allocated to CSI feedback transmission up to 20 bits using PUCCH format 3.

Therefore, even if the method of differential CQI is not used, the PUCCH format 3 can transmit information on the aggregate CQI on the PUCCH.

Table 17 is a table schematically illustrating a method of transmitting differential CQI information using PUCCH format 3.

<Table 17>

Referring to Table 17, in the available PUCCH report mode of each PUCCH report type, a 4-bit aggregate CQI is transmitted along with the CQI per CSI-RS resource.

For example, in PUCCH report mode 2-1 of PUCCH report type 1a, 4-bit aggregate CQI is transmitted along with 9-bit CQI per CSI-RS resource. In PUCCH report modes 1-1 and 2-1 of PUCCH report type 2, 4-bit aggregate CQI is transmitted along with 11-bit CQI per CSI-RS resource.

Meanwhile, the number of bits allocated to information transmitted in a new PUCCH report type may be newly defined using the PUCCH format 3. That is, when using the PUCCH format 3, which can be assigned a large number of bits, the number of bits can be allocated so that the entire information can be transmitted without using a difference value or the like. Accordingly, by using the PUCCH format 3, the aggregate CQI can be transmitted together with the CQI per CSI-RS resource without splitting the aggregate CQI in all or some PUCCH report types or using differential CQI for the aggregate CQI.

Table 18 schematically illustrates an example of newly defining bit allocation of a PUCCH report type according to the present invention.

<Table 18>

Table 18 describes an example in which report type 2c of the PUCCH report type is performed using PUCCH format 3 as an example.

Referring to Table 18, in the case of PUCCH report type 2c, the reported content is RI, wideband CQI, first PMI, and second PMI. In this case, the wideband CQI includes a CQI and an aggregate CQI per CSI-RS resource for the wideband.

In the case of the PUCCH report type 2c, since the PMI is transmitted as wideband, referring to Table 2, it can be seen that reporting is performed only in the mode 1-1.

Accordingly, the total number of bits allocated for CSI feedback is bits for RI, bits for CQI per CSI-RS resource, bits for aggregate CQI, bits for first PMI and second PMI.

Since 8 antenna ports are used, 3 bits are allocated to the RI, 2 bits are allocated to indicate the first PMI, and 2 bits are allocated to indicate the second PMI.

In Table 18, when RI = 1, 4 bits are allocated to CQI per CSI-RS resource. The aggregation CQI will be described here by allocating 2 bits using the difference, but 4 bits may be allocated to transmit the aggregate CQI as it is.

If 1 <RI≤4, 4 bits are allocated to CQI per CSI-RS resource for codeword 0, CQI per CSI-RS resource for codeword 0 and CQI per CSI-RS resource for codeword 1 3 bits are allocated to the difference between them. For the aggregate CQI, two bits are allocated for each codeword using the difference. In addition, 4 bits may be allocated for each codeword in order to transmit the aggregate CQI.

If 4 <RI≤7, 4 bits are allocated to CQI per CSI-RS resource for codeword 0, CQI per CSI-RS resource for codeword 0 and CQI per CSI-RS resource for codeword 1 3 bits are allocated to the difference between them. For the aggregate CQI, two bits are allocated for each codeword using the difference. In addition, 4 bits may be allocated for each codeword in order to transmit the aggregate CQI. However, since the codebook size for the second PMI is 1, only the first PMI is transmitted in 2 bits without transmitting the second PMI.

If RI = 8, 4 bits are allocated to CQI per CSI-RS resource for codeword 0, and the difference between CQI per CSI-RS resource for codeword 0 and CQI per CSI-RS resource for codeword 1 3 bits are allocated. For the aggregate CQI, two bits are allocated for each codeword using the difference. In addition, 4 bits may be allocated for each codeword in order to transmit the aggregate CQI. In this case, since the codebook sizes for the first PMI and the second PMI are both 1, there is no need to transmit PMI information separately.

5 is a flowchart schematically illustrating an operation performed by a UE to transmit information about aggregate CQI according to the present invention.

Referring to FIG. 5, based on the received CSI-RSs, the UE estimates CQI per CSI-RS resource (S510). In a system supporting CoMP, the CSI-RS may be transmitted from each transmission point.

The UE estimates the aggregate CSI (S520). In the case where the CoMP system supports JT, as shown in FIG. 2, aggregate CQI may be estimated over resources of different CSI-RSs transmitted from different transmission points.

In this example, the CQI per CSI-RS resource is estimated and then the aggregate CQI is estimated. However, the CQI per CSI-RS resource and the aggregate CQI can be estimated simultaneously. It can also be estimated first.

The UE feeds back the aggregate CQI to the eNB (S530). As described above, the feedback of the aggregate CQI may be transmitted together with the CQI per CSI-RS resource or separately from the CQI per CSI-RS resource in consideration of the CQI per CSI-RS resource.

In this case, the UE may transmit the differential CQI or the differential CQI indicating the offset level so that the aggregate CQI may be derived from the CQI per CSI-RS resource without transmitting the aggregate CQI as it is.

The UE may periodically perform the feedback described with reference to FIG. 5.

6 is a flowchart schematically illustrating an operation of an eNB that receives information on an aggregate CQI according to the present invention.

The eNB receives the CQI feedback from the UE (S510). The CQI feedback may be included in the CSI and transmitted from the UE. The CSI may include RI, PMI, etc. in addition to the CQI. The CQI included in the CSI and transmitted is estimated to the UE based on the CSI-RS transmitted from each transmission point in the CoMP system, and may include a CQI per CSI-RS resource and an aggregate CQI across the CSI-RS resources. In this case, instead of transmitting the aggregate CQI as it is, a differential CQI or a differential CQI capable of inducing the aggregate CQI may be transmitted as described above.

The eNB compares the sizes of the aggregate CQI and the CQI per CSI-RS resource, and determines whether the difference between the aggregate CQI and the CQI per CSI-RS resource exceeds a predetermined reference value (S620). In case the differential CQI or differential CQI is transmitted instead of the aggregate CQI, the eNB derives the aggregate CQI necessary for the determination.

The eNB may compare the size of the CQI per CSI-RS resource for at least one CSI-RS resource among the aggregate CQI and the CSI-RS resources corresponding to the aggregate CQI.

The predetermined reference value may be predetermined between the UE and the eNB, or may be transmitted through higher layer signaling. If the rank is greater than 1, the aggregated CQI and the size of the CQI per CSI-RS resource are compared only for the same codeword.

As described above, JT CoMP is effective when the value of the aggregate CQI is larger than the CQI per CSI-RS resource. Accordingly, the eNB may determine the CoMP transmission mode by comparing the size of the aggregate CQI and the CQI per CSI-RS resource. In other words, the eNB compares the size of the aggregated CQI and the CQI per CSI-RS resource to determine whether to perform JT CoMP.

As a result of the determination, when the aggregated CQI is larger than the CQI per CSI-RS resource by more than a predetermined reference value, the eNB performs JT CoMP transmission (S630). The eNB may compare the size of the CQI per CSI-RS resource for at least one CSI-RS resource among the aggregate CQI and the CSI-RS resources corresponding to the aggregate CQI. Accordingly, the eNB may perform JT CoMP when ① aggregate CQI is larger than a CQI per CSI-RS resource for one CSI-RS resource by a predetermined reference value, and ② is applied to all CSI-RS resources corresponding to aggregate CQI. JT CoMP may be performed when the CQIs per CSI-RS resource are larger than the CQIs for each CSI-RS resource, and ③ are larger than the average of the CQIs per CSI-RS resource for all the CSI-RS resources corresponding to the aggregate CQIs. In this case, JT CoMP may be performed. ④ JT CoMP is greater than a predetermined number of CQIs per CSI-RS resource among CQIs per CSI-RS resource for all CSI-RS resources corresponding to the aggregate CQI. You can also do Which method of ① to ④ may be determined in advance or may be determined when applying step S620 in consideration of the state of the system.

As a result of the determination, when the aggregate CQI is not large enough to exceed a predetermined reference value than the CQI per CSI-RS resource, the eNB performs Non-JT CoMP transmission (S640).

7 is a block diagram schematically illustrating a structure of a UE that performs CQI feedback in a system to which the present invention is applied.

Referring to FIG. 7, the UE 700 includes an RF unit 710, a memory 720, and a processor 730.

The UE 700 transmits and receives necessary information or signals through the RF unit 710.

The memory 720 stores information necessary for the UE 700 to communicate. For example, the memory 720 may store the table information regarding the PUCCH report mode as described above, the table information regarding the PUUCH report type, the table information for mapping the offset level and the differential CQI, and the like.

Processor 730 performs the functions and controls necessary to implement the features of the present invention as described above. The processor 730 may include a measurement unit 740 and a CQI configuration unit 750.

The measurement unit 740 may estimate the CQI for each CSI-RS resource or the CQI over the plurality of CSI-RS resources based on the CSI-RS received from each transmission point in the CoMP system.

The CQI configuration unit 750 configures information for feeding back the estimated CQI to the eNB. For example, the CQI configuration unit 750 may configure the information to be transmitted about the aggregate CQI by any of the above methods 1 to 4 in consideration of the current system or UE status, the amount of information of the CSI report to be transmitted on the PUCCH, and the like. . In the case of using the method 1, the CQI configuration unit 750 configures the differential CQI to transmit, and in the case of using the method 2, the CQI configuration unit 750 splits the bits of the aggregated CQI and assigns the CQI to each CSI-RS resource. Can be attached separately.

The processor 730 transmits the configured CQI to the eNB on the PUCCH through the RF unit 710.

8 is a block diagram schematically illustrating the structure of an eNB in a system according to the present invention.

Referring to FIG. 8, the eNB 800 includes an RF unit 810, a memory 820, and a processor 830.

The eNB 800 transmits and receives necessary information or signals through the RF unit 810.

The memory 820 stores information necessary for the eNB 800 to perform communication. For example, the memory 820 may store the table information regarding the PUCCH report mode as described above, the table information regarding the PUUCH report type, the table information for mapping the offset level and the differential CQI, and the like.

Processor 830 performs the functions and controls necessary to implement the features of the present invention as described above. The processor 830 may include a CSI-RS configuration unit 840, a CQI processing unit 850, and a CoMP control unit 860.

The CSI-RS configuration unit 840 configures the CSI-RS to be transmitted to the UE. The CSI-RS configuration unit 840 may determine the CSI-RS pattern, resources, transmission power, etc. for each transmission point in the CoMP system. Here, although the CSI-RS is described as configured in the eNB, the CSI-RS may be configured / transmitted at each transmission point such as the RRH in the CoMP system.

The CSI processor 850 processes information in the CSI fed back from the UE. The CSI includes information such as RI, CQI, and PMI. In this case, the CQI may include a CQI per CSI-RS resource and an aggregate CQI across CSI-RS resources. In addition, instead of transmitting the aggregate CQI as it is, a differential CQI or a differential CQI capable of deriving the aggregate CQI may be transmitted as described above.

The CSI processor 850 may obtain information such as RI, PMI, CQI per CSI-RS resource, aggregate CQI, and the like from the CSI. When the differential CQI or differential CQI is transmitted, the CSI processing unit 850 may derive the aggregation CQI based on the offset CQI or the offset level indicated by the differential CQI, as described above.

The CoMP control unit 860 may control the operation of each transmission point or reception point in the CoMP system. For example, the CoMP controller 860 may determine whether to perform JT CoMP by comparing the aggregated CQI obtained by the CSI processor 850 with the size of CQI per CSI-RS resource.

The CoMP control unit 860 performs JT CoMP transmission when the aggregate CQI is larger than the CQI per CSI-RS resource, and is not larger than the CQI per CSI-RS resource. JT CoMP transmission can be performed.

In the present specification, when the aggregate CQI is for predetermined CSI-RS resources, the expression aggregate CQI that spans the predetermined CSI-RS resources is used. In the same sense, the expression CSI-RS resource corresponding to the aggregate CQI is used for the predetermined CSI-RS resources.

In the exemplary system described above, although the methods are described on the basis of a flowchart as a series of steps or blocks, the present invention is not limited to the order of the steps, and some steps may occur in different orders or simultaneously . In addition, the above-described embodiments include examples of various aspects. For example, the above-described embodiments may be implemented in combination with each other, which also belongs to the embodiments according to the present invention. The invention includes various modifications and changes in accordance with the spirit of the invention within the scope of the claims.

Claims (20)

Estimating a channel quality indicator (CQI) per CSI-RS resource and an aggregate CQI across a plurality of CSI-RS resources based on the received CSI-RS (Channel State Information-Reference Signal); And
And transmitting CSI feedback including aggregate CQI information about the aggregate CQI. The method of claim 1, wherein the aggregate CQI information,
CSI feedback method characterized in that the difference information of one or two bits indicating the offset level between the aggregate CQI and the CSI-RS CQI. The CSI feedback method of claim 2, wherein the offset level corresponds to a value obtained by subtracting the CSI-RS from the aggregate CQI and is greater than or equal to zero. The method of claim 1, wherein when the rank is greater than 1, the difference information is
First difference information indicating an offset level between the aggregation CQI and the CSI-RS CQI with respect to codeword 0; And
And second difference information indicating an offset level between the aggregation CQI and the CSI-RS CQI with respect to codeword 1. The method of claim 4, wherein the CSI feedback is transmitted using a Physical Uplink Control Channel (PUCCH) report type 4. The method of claim 1, wherein the aggregated CQI information is divided and fed back according to the number of CSI-RS resources corresponding to the aggregated CQI. The method of claim 6, wherein the divided aggregate CQI information,
CSI feedback method, characterized in that the CSI feedback is distributed to each CSI-RS resource feedback for the CSI-RS resources corresponding to the aggregated CQI. The method of claim 6, wherein the CSI-RS resources corresponding to the aggregate CQI are first CSI-RS resources and second CSI-RS resources.
Most Significant Bits (MSBs) of the aggregated CQI are fed back together with CQI per CSI-RS resource for the first CSI-RS resource,
Least Significant Bits (LSBs) of the aggregated CQI are fed back together with CQI per CSI-RS resource for the second CSI-RS resource. The CSI feedback method of claim 1, wherein the aggregated CQI information is fed back based on a PUCCH report type separate from the CQI per CSI-RS resource. 10. The method of claim 9, wherein when there are two CSI-RS resources corresponding to the aggregate CQI and the rank is greater than 1,
The aggregate CQI information,
Aggregation CQI for codeword 0; And
And a difference value between the aggregate CQI for codeword 0 and the aggregate CQI for codeword 1. 10. The method of claim 9, wherein when there are three CSI-RS resources corresponding to the aggregate CQI and the rank is 1,
The aggregate CQI information is differential information indicating, for each aggregate CQI, an offset level based on a CQI per CSI-RS resource for any one of the CSI-RS resources corresponding to each aggregate CQI. Feedback method. 10. The method of claim 9, wherein when there are three CSI-RS resources corresponding to the aggregate CQI and the rank is 2,
The aggregate CQI information includes, for each aggregate CQI, differential information indicating the offset level based on the CQI per CSI-RS resource for any one of the CSI-RS resources corresponding to each aggregate CQI, for each codeword. CSI feedback method, characterized in that. The method of claim 1, wherein the CSI feedback is transmitted in PUCCH format 3.
The aggregate CQI information is transmitted with a CQI per corresponding CSI-RS resource. Receiving channel quality indicator (CQI) feedback;
Comparing CQIs per Channel State Information-Reference Signal (CSI-RS) resources included in the CQI feedback with aggregate CQIs spanning a plurality of CSI-RS resources; And
And determining a CoMP (Coordinated Multi Points) transmission mode according to the comparison result. The method of claim 14, wherein the aggregate CQI information,
And 1 bit or 2 bit difference information indicating an offset level between the aggregate CQI and the CSI-RS CQI. 15. The method of claim 14, wherein the aggregated CQI information is fed back based on a PUCCH report type separate from the CQI per CSI-RS resource. 15. The method of claim 14, wherein the aggregated CQI information is fed back based on a PUCCH report type separate from the CQI per CSI-RS resource. The method of claim 14, wherein the CQI feedback is transmitted in PUCCH format 3
The aggregate CQI information is transmitted with a CQI per corresponding CSI-RS resource. The method of claim 14, wherein in the step of determining the CoMP transmission mode,
And if the aggregated CQI is larger than the CQI per CSI-RS resource, Cot Control (JT) CoMP. 20. The method of claim 19, wherein the size of the aggregate CQI is compared with a CQI per CSI-RS resource for at least one CSI-RS resource among the CSI-RS resources corresponding to the aggregate CQI.

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