WO2013022266A2

WO2013022266A2 - Method and apparatus for transmitting and receiving channel state information

Info

Publication number: WO2013022266A2
Application number: PCT/KR2012/006282
Authority: WO
Inventors: Jian Jun Li; Kyoung Min PARK
Original assignee: Pantech Co., Ltd.
Priority date: 2011-08-08
Filing date: 2012-08-08
Publication date: 2013-02-14
Also published as: WO2013022266A3; KR20130016701A

Abstract

Disclosed are a method and apparatus for transmitting and receiving channel state information. The method of transmitting channel state information includes receiving downlink control information including information field requesting aperiodic channel state information feedback, and transmitting channel state information configured according to the information field, wherein the information field is a channel state information request field, and each field value of the channel state information request field indicates a CoMP category as a target of triggering channel state information feedback. Channel state information can be effectively transmitted in a CoMP environment and overhead required for transmitting channel state information can be reduced.

Description

METHOD AND APPARATUS FOR TRANSMITTING AND RECEIVING CHANNEL STATE INFORMATION

The present invention relates to a MIMO (Multi Input Multi Output) in a wireless communication system and, more particularly, to a CoMP (Coordinated Multi-Points) system using a closed loop MIMO.

High speed large quantity data transmissions have been made by using a multi-antenna system. In line with this, a CoMP technique based on MIMO (Multi-Input Multi-Output) has been discussed.

CoMP is a technique of coordinating or combining signals transmitted from multiple points, and by applying CoMP, a data transfer rate can be increased and high quality and high throughput can be obtained.

In case of a CoMP applied terminal (hereinafter, referred to as a ‘terminal operating in a CoMP mode’) in a CoMP environment (hereinafter, a system supporting CoMP or employing CoMP will be referred to as a ‘CoMP environment’) to which CoMP is applied, the terminal aims at receiving data simultaneously from a CoMP cooperated set in consideration of a channel environment of each cell constituting the CoMP cooperated set or aims at receiving data by minimizing an interference influence among the CoMP cooperation set, so it is required to measure channel information regarding each cell and reported to a serving cell of the corresponding cell. The CoMP cooperated set is a set of points which directly/indirectly participate in a data transmission (and geographically separated) in a certain time-frequency domain with respect to a single user equipment (UE). Here, directly participating in a data transmission refers to that the points actually transmit data to the UE in a corresponding time-frequency resource, and indirectly participating in a data transmission refers to that the points do not actually transmit data in the corresponding time-frequency resource but contribute to determining regarding user scheduling/beamforming.

Meanwhile, it is required to determine reference information, e.g., a reference signal, for generating channel information in a CoMP cooperated set including various cells, and pertinent information is required to be shared between a terminal and a base station.

Therefore, an object of the present invention is to provide a method for effectively transmitting channel state information in a CoMP environment.

Another object of the present invention is to provide a method for reducing overhead required for transmitting channel state information of a user equipment (UE) in a CoMP environment.

Another object of the present invention is to provide a method for specifying a CoMP category and/or a cell to which channel state information is to be transmitted in a CoMP environment.

Another object of the present invention is to provide a method for reducing the number of bits of channel state information transmitted in a CoMP environment.

Another object of the present invention is to provide a method for reducing the number of bits of a channel quality indicator in channel state information transmitted in a CoMP environment.

(1) According to an aspect of the present invention, there is provided a method for receiving channel state information, including: transmitting downlink control information including information field requesting aperiodic channel state information feedback; and receiving aperiodic channel state information feedback according to the request, wherein the information field may be a channel state information request field, and each field value of the channel state information request field may indicate a CoMP category as a target of triggering channel state information feedback.

(2) In (1), the channel state information request field may be 2-bit information field.

(3) In (1), the field values of the channel state information request field may indicate not triggering feedback of aperiodic channel state information, triggering aperiodic channel state information feedback with respect to dynamic cell selection and/or coordinate scheduling/coordinated beamforming among CoMP categories, and triggering aperiodic channel state information feedback with respect to a joint transmission among the CoMP categories, respectively.

(4) In (3), a field value indicating triggering aperiodic channel stage feedback with respect to dynamic cell selection, among the field values of the channel state information request field may indicate a particular cell as a target of aperiodic channel state feedback.

(5) In (1), when a field value of the channel state information request field triggers feedback of channel state information with respect to joint transmission among CoMP categories, it may discriminately indicate whether a target of channel state information feedback to be triggered relates to coherent joint transmission or non-coherent joint transmission.

(6) In (1), when a field value of the channel state information request field indicates channel state information feedback with respect to joint transmission among the CoMP categories, the downlink control information may include joint transmission combination information indicating a particular combination of serving cells as targets of the channel state information feedback among combinations of serving cells that perform joint transmission.

(7) In (6), the joint transmission combination information may be index information indicating a particular combination of serving cells or a bit map indicating a particular combination of serving cells.

(8) According to another aspect of the present invention, there is provided a method of transmitting channel state information, including: receiving downlink control information including information field requesting aperiodic channel state information feedback; and transmitting channel state information configured according to the information field, wherein the information field may be a channel state information request field, and each field value of the channel state information request field may indicate a CoMP category as a target of triggering channel state information feedback.

(9) In (8), the field values of the channel state information request field may indicate not triggering feedback of aperiodic channel state information, triggering aperiodic channel state information feedback with respect to dynamic cell selection and/or coordinate scheduling/coordinated beamforming among CoMP categories, and triggering aperiodic channel state information feedback with respect to a joint transmission among the CoMP categories, respectively, and in the transmitting of the channel state information, channel state information generated with respect to a CoMP category in which a field value of the channel state information request field may indicate triggering channel state information feedback.

(10) In (9), a field value indicating triggering aperiodic channel stage feedback with respect to dynamic cell selection, among the field values of the channel state information request field may indicate a particular cell as a target of aperiodic channel state feedback, and in the transmitting of the channel state information, channel state information generated with respect to the particular cell may be transmitted.

(11) In (8), when a field value for triggering feedback of channel state information with respect to joint transmission of CoMP category among field values of the channels state information request field may discriminately indicate whether a target of channel state information feedback to be triggered relates to coherent joint transmission or non-coherent joint transmission, and in case of transmitting channel state information regarding joint transmission in the transmitting of the channel state information, channel state information generated with respect to coherent joint transmission or non-coherent joint transmission may be transmitted according to a field value of the channel state information request field.

(12) In (8), the downlink control information may include joint transmission combination information indicating a particular combination of serving cells as targets of the channel state information feedback among combinations of serving cells that perform joint transmission, and when the field value of the channel state information request filed indicates channel state information feedback with respect to joint transmission among CoMP categories, in the transmitting of the channel state information, channel state information may be transmitted with respect to a particular combination of serving cells indicated by the joint transmission combination information.

(13) In (12), the joint transmission combination information may be index information indicating a particular combination of serving cells or a bit map indicating a particular combination of serving cells.

(14) In (8), in case of transmitting channel state information with respect to joint transmission in the transmitting of the channel state information, a difference value between a channel quality indicator with respect to dynamic cell selection and a channel quality indicator with respect to joint transmission, instead of a value of a channel quality indicator with respect to joint transmission, may be included in the channel state information and transmitted.

(15) In (8), the downlink control information may include joint transmission combination information indicating a particular combination of serving cells as targets of the channel state information feedback among combinations of serving cells that perform joint transmission, and when a field value of the channel state information request field indicates channel state information feedback with respect to joint transmission among CoMP categories, in the transmitting of the channel state information, channel state information may be transmitted with respect to a particular combination of serving cells indicated by the joint transmission combination information, and a difference value between a channel quality indicator with respect to dynamic cell selection and a channel quality indicator with respect to joint transmission, instead of a value of a channel quality indicator with respect to joint transmission, may be included in the channel state information and transmitted.

According to embodiments of the present invention, channel state information can be effectively transmitted in a CoMP environment, and overhead required for transmitting channel state information may be reduced.

According to embodiments of the present invention, overhead with respect to a transmission of channel state information can be reduced by specifying a CoMP category and/or a cell to which channel state information is to be transmitted in a CoMP environment.

According to embodiments of the present invention, overhead with respect to a transmission of channel state information can be reduced by reducing the number of bits of channel state information transmitted in a CoMP environment.

According to embodiments of the present invention, overhead with respect to a transmission of channel state information can be reduced by reducing the number of bits of a channel quality indicator of channel state information transmitted in a CoMP environment.

FIG. 1 is a view schematically showing an example of a downlink radio frame structure in a 3GPP LTE.

FIG. 2 is a schematic flow chart illustrating an example of data processing between an eNodeB and a UE in a multi-antenna system.

FIG. 3 is a view schematically showing an example in which CRSs are mapped to an RE in case of a normal CP.

FIG. 4 is a view schematically showing an example in which CRSs are mapped to an RE in case of an extended CP.

FIG. 5 is a view schematically showing a first CoMP scenario.

FIG. 6 is a view schematically showing a second CoMP scenario.

FIG. 7 is a view schematically showing third and fourth CoMP scenarios.

FIG. 8 is a conceptual view schematically showing an example of zero power CSI-RS configuration.

FIG. 9 is a view schematically showing a method of performing CSI feedback in a system to which the present invention is applied.

FIG. 10 is a flow chart illustrating a CSI receiving method performed by a primary cell of a CoMP system in a system to which the present invention is applied.

FIG. 11 is a flow chart illustrating a method of performing aperiodic CSI feedback by a UE in a system to which the present invention is applied.

FIG. 12 is a view schematically showing a configuration of a UE in a system to which the present invention is applied.

FIG. 13 is a view schematically illustrating a configuration of an eNB in a system to which the present invention is applied.

The embodiments of the present invention will now be described with reference to the accompanying drawings, in which like numbers refer to like elements throughout although the embodiments are different, and a description of the like elements a first embodiment will be used for those of the different embodiment. In describing the present invention, if a detailed explanation for a related known function or construction is considered to unnecessarily divert the gist of the present invention, such explanation has been omitted but would be understood by those skilled in the art.

A wireless communication network will be described, and an operation performed in a wireless communication network may be performed in a process of controlling a network and transmitting data by a system (e.g., a base station) that administers a corresponding wireless communication network or a terminal coupled to the corresponding wireless network.

A user equipment (UE) may be fixed or mobile, and may be called by other names such as MS (mobile station), MT (mobile terminal), UT (user terminal), SS (subscriber station), wireless device, PDA (personal digital assistant), wireless modem, handheld device, or the like.

A base station (BS) generally refers to a fixed station communicating with a UE, and may be called by other names such as eNodeB (evolved-NodeB), BTS (Base Transceiver System), access point, or the like.

Each BS provides a communication service to a particular geographical area (which is generally called a cell). A BS may be divided into a plurality of regions (which is called sectors). Also, a plurality of transmitters may constitute a single cell.

FIG. 1 schematically shows an example of a radio frame structure in a system to which the present invention is applied. One radio frame includes 20 slots (#0~#19). One subframe includes two slots. A time (length) during which a single subframe is transmitted is called a TTI (transmission time interval). With reference to FIG. 1, for example, it can be seen that a length of one subframe is 1ms, and a length of one slot is 0.5 ms.

One slot may include a plurality of symbols in a time domain. For example, when OFDMA (Orthogonal Frequency Division Multiple Access) is used in downlink (DL), the symbol may be an OFDM (Orthogonal Frequency Division Multiplexing) symbol. Meanwhile, an expression of a symbol period in a time domain is not limited to a multi-access scheme or name. For example, besides the OFDM symbols, a plurality of symbols may be SC-FDMA (Single Carrier-Frequency Division Multiple Access) symbols, symbol period, or the like.

The number of symbols included in one slot may vary according to a length of a cyclic prefix (CP). For example, in case of a normal CP, one slot includes seven symbols, an in case of an extended CP, one slot may include six or three symbols.

A resource block (RB), a resource allocation unit, is defined in time-frequency domain, being expressed by one slot in the time domain and by a plurality of subcarriers corresponding to 180 KHz in the frequency domain. For example, when one slot includes seven symbols in the time domain and the plurality of subcarriers corresponding to 180 KHz totals 12 in the frequency domain, one resource block may include 84 (=7x12) resource elements (RE).

‘RE’ (Resource element) is the smallest frequency-time unit too which a modulation symbol of a data channel or a modulation symbol of a control channel is mapped. When there are M number of subcarriers on one symbol and one slot includes N number of symbols, one symbol includes MxN number of REs.

A downlink subframe may be divided into a control region and a data region in the time domain. The control region may include a maximum of four front OFDM symbols in the first slot of the subframe. The number of OFDM symbols included in the control region may vary. A control channel such as a PDCCH, or the like, is allocated to the control region, and a data transmission channel such as a PDSCH is allocated to the data region.

The PCFICH transmitted in the first OFDM symbol of the subframe carries a CFI (Control Format Indicator) indicating the number of OFDM symbols (i.e., the size of the control region) used to transmit control channels within the subframe. For example, a UE may first receive the CFI on the PCFICH and monitor the PDCCH. The PCFICH may be transmitted through a fixed PCFICH resource of the subframe.

A PHICH (Physical Hybrid ARQ Indicator CHannel) carries an ACK (positive-acknowledgement)/NACK (negative-acknowledgement) signal for an uplink HARQ (Hybrid Automatic Repeat reQuest).

A PBCH (Physical Broadcast Channel) is transmitted front four OFDM symbols of a second slot of the first subframe. The PBCH carries system information essential for the UE to communicate with a base station (BS). System information transmitted via the PBCH is called an MIB (Master Information Block). Meanwhile, system information transmitted on the PDSCH indicated by the PDCCH is called an SIB (System Information Block).

Control information transmitted via the PDCCH is called downlink control information (DCI). DCI may include a resource allocation (this is also called a downlink grant) of a PDSCH, a resource allocation (this is also called an uplink grant) of a PUSCH, a set of transmission power control commands with respect to individual UEs of a certain UE group and/or an activation of VoIP (Voice over Internet Protocol).

The control region of the subframe includes a plurality of CCEs (control channel elements). The CCE is a logical allocation unit used to provide a coding rate according to a state of a radio channel to the PDCCH. The CCEs correspond to a plurality of REGs (resource element groups). The format of the PDCCH and the number of bits of the PDCCH are determined according to correlation between the number of CCEs and the coding rate provided by the CCEs.

A plurality of PDCCHs may be transmitted in a single subframe. A UE monitors a plurality of PDCCHs in every subframe. Here, monitoring refers to that a UE attempts to decode by the UE according to a format of a target PDCCH.

Meanwhile, a MIMO (Multi-Input Multi-Output) system, also called a multi-antenna system, enhances transmission/reception data transmission efficiency by using multiple transmission antennas and multiple reception antennas.

A MIMO technique includes transmit diversity, spatial multiplexing, beamforming, and the like.

The transmit diversity is a technique that transmits the same data from respective antennas constituting multiple transmission antennas to thus enhance a transmission reliability.

Spatial multiplexing is a technique that simultaneously transmits different data from multiple transmission antennas to thus transmit high speed data without increasing a bandwidth of a system.

Beamforming is used to increase a signal to interference plus noise ratio (SINR) of a signal by adding a weight value according to a channel state at multiple antennas. In this case, the weight value may be represented by a weight vector or a weight matrix, and it is called a precoding vector or a precoding matrix. An example of precoding schemes is codebook-based precoding. The codebook-based precoding scheme is a scheme of preprocessing data by using a precoding matrix most similar to a MIMO channel among previously determined precoding matrices. When the codebook-based precoding scheme is used, a PMI (Precoding Matrix Indicator) can be transmitted as feedback data, reducing overhead. A codebook is comprised of a codebook set that may represent a spatial channel. In order to enhance a data transfer rate, the number of antennas is required to be increased, and here, as the number of antennas is increased, the codebook should include more codebook sets.

Spatial multiplexing includes spatial multiplexing for a single user and spatial multiplexing for multiple users. The spatial multiplexing for a single user is called a single user MIMO (SU-MIMO), and the spatial multiplexing for multiple users is called spatial division multiple access (SDMA) or multi-user MIMO (MU-MIMO).

Meanwhile, the capacity of a MIMO channel increases in proportion to the number of antennas. The MIMO channel may be disintegrated into independent channels. If the number of transmission antennas is Nt and the number of reception antennas is Nr, the number of independent channels Ni is Ni ≤ min{Nt, Nr}. Each independent channel may be a spatial layer. A rank is the number of non-zero eigen value of the MIMO channel, which may be defined as the number of spatial streams that can be multiplexed.

FIG. 2 is a schematic flow chart illustrating an example of data processing between an eNB and a UE in a multi-antenna system.

With reference to FIG. 2, an eNB transmits data to a UE (S210). The eNodeB may perform precoding on input symbols by using a precoding matrix including a plurality of rows and columns and transmit the precoded symbols, namely, data. Here, the eNodeB may select a precoding matrix by using a codebook including at least one precoding matrix.

The UE may receive data transmitted from the eNB through Nr (Nr>1) number of reception antennas, and transmit feedback with respect to the received data (S220).

In the data transmission/reception process performed in the MIMO system of FIG. 2, the eNB may receive data from N number of users and output K number of streams to be transmitted at a time. In the MIMO system, the eNB may determine a user to which transmission is made with available radio resource by using channel information regarding each user or transmitted from each user, and a transfer rate. For example, the eNB may extract channel information from feedback information and select a code rate, a modulation and coding scheme (MCS), or the like.

For an operation of the MIMO system, the feedback information may include control information such as CQI (Channel Quality Indicator), CSI (Channel State Information), CCM (Channel Covariance Matrix), PW (Precoding Weight), CR (Channel Rank), and the like.

The CSI may include a channel matrix, a channel correlation matrix, a quantized channel matrix, or a quantized channel correlation matrix, a PMI, and the like, between a transmitter and a receiver. The CQI may be a signal-to-noise ratio (SNR), a signal-to-interference and noise ratio (SINR), or the like between a transmitter and a receiver.

The UE may estimate a channel, select a precoding matrix that maximizes channel performance, and report a precoding matrix indicator (PMI) with respect to the selected precoding matrix. The eNB may select the precoding matrix indicated by the feedback PMI from the codebook and use the same for a data transmission.

A MIMO scheme of using a precoding weight according to a channel state is called a CL (Closed-Loop) MIMO scheme, and a MIMO scheme of using a precoding weight irrespective of a channel state is called an OL (Open-Loop) MIMO scheme. In the CL MIMO scheme, a transmitter, e.g., the eNB copes with a channel situation by utilizing channel state information (CSI) as feedback information transmitted from a receiver, e.g., the UE. The CSI may include the PMI and be transmitted.

Meanwhile, in the wireless communication system, an uplink channel or a downlink channel is required to be estimated for a data transmission/reception, system synchronization acquirement, channel information feedback, or the like. A process of compensating for distortion of a signal caused by a rapid change in an environment to restore a transmission signal is called a channel estimation. Also, a channel state with respect to a cell to which the UE belongs or a different cell may also be required to be measured. In general, in order to estimate a channel or measure a channel state, a reference signal (RS) known by a transmitter and receiver is used.

Since the receiver knows the information regarding a reference signal, the receiver may estimate a channel based on the reference signal of the received signal and compensate for a channel value to accurately obtain data transmitted from the transmitter. When the reference signal transmitted by the transmitter is p, channel information undergone by the reference signal during a transmission is h, thermal noise generated from the receiver is n, and a signal received by the receiver is y, it may be expressed such that y = h·p + n. Here, since the receiver already knows the reference signal p, when an LS (Least Square) scheme is used, the channel information

can be estimated.

[Equation 1]

Here, the channel estimation value

estimated by using the reference signal P relies on the value

, so in order to accurately estiamed the h value,

is required to be converged on 0.

In the OFDM system, there are a scheme of allocating the reference signal to every subcarrier and a scheme of allocating the reference signal between data subcarriers transmitting data. In the scheme of allocating the reference signal to every subcarrier, a signal comprised of only the reference signal, like a preamble signal, is used in order to obtain a gain of channel estimation performance. In the case of the scheme of allocating the reference signal between data subcarriers, an amount of data transmission can be increased.

A reference signal is generally transmitted as a sequence. A reference signal sequence is not particularly limited and a certain sequence may be used as the reference signal sequence. As the reference signal sequence, a sequence generated through a computer based on PSK (Phase Shift Keying) (i.e., a PSK-based computer generated sequence) may be used. The PSK may include, for example, BPSK (Binary Phase Shift Keying), QPSK (Quadrature Phase Shift Keying), and the like. Or, as the reference signal sequence, a CAZAC (Constant Amplitude Zero Auto-Correlation) may be used. The CAZAC sequence may include, for example, a ZC (Zadoff-Chu)-based sequence, a ZC sequence with cyclic extension, a ZC sequence with truncation, and the like. Also, as the reference signal sequence, a PN (pseudo-random) sequence may be used. The PN sequence may include, for example, an m-sequence, a sequence generated through a computer, a gold sequence, a Kasami sequence, and the like. Also, a cyclically shifted sequence may be used as the reference signal sequence.

Downlink references signal include a cell-specific reference signal (CRS), an MBSFN (Multimedia Broadcast and multicast Single Frequency Network) reference signal, a UE-specific RS, a positioning RS, a channel state information reference signal (CSI-RS), and the like.

In the multi-antenna system, a resource element used for a reference signal of an antenna is not used for a reference signal of a different antenna. This is not to cause interference between antennas. For example, only one reference signal per antenna may be transmitted.

The CRS, a reference signal transmitted to every UE within a cell, is used to estimate a channel. The CRS may be transmitted in every downlink subframe within a cell supporting a PDSCH transmission.

The UE-specific RS is a reference signal received by a particular UE or a particular UE group within a cell. Since the UE-specific RS is largely used for data modulation of a particular UE or a particular UE group, it may also be called a DM-RS (Demodulation RS).

The MBSFN RS, a reference signal for providing an MBMS (Multimedia Broadcast Multicast Service), may be transmitted in a subframe allocated for an MBSFN transmission. The MBSFN reference signal may be defined only in the extended CP structure.

The PRS may be used to measure a location of a UE. The PRS may be transmitted only through a resource block within a downlink subframe allocated to transmit the PRS.

The CSI-RS may be used to estimate channel state information. The CSI-RS is disposed in a frequency domain or a time domain, and through an estimation of a channel state using the CSI-RS, a CQI (Channel Quality Indicator), a PMI (Precoding Matrix Indicator), and an RI ( Rank Indicator), or the like, may be reported as channel state information from the UE when necessary.

A reference signal sequence

used for generating a CRS is defined as shwon in Equation 3 below.

[Equation 2]

Here, n_s is the number of slots within a radio frame, and 1 is the number of OFDM symbols within a slot. Also,

indicates a maximum number of downlink resource blocks.

In Equation 2, c(i) is a pseudo-random sequence defined by a length-31 gold sequence, which is initialized at the start of each OFDM symbol as shown in Equation 3 below.

[Equation 3]

Here, N_CP has a value 1 in the case of a normal CP (Cyclic Prefix) and has a value 0 in the case of an extended CP. Also, N^cell _ID indicates a cell ID in a physical layer (physical layer cell ID).

In a subframe configured with respect to a CSI-RS transmission, a reference signal sequence

is mapped to

used as a reference symbol in an antenna port p, and

is a modulation symbol having a complex value. Here, a mapping relationship bewteen

and

is as shwon in Equation 4 below.

[Equation 4]

Here, values w, k, l, l", and m' may be obtained as shown in Equation 5 below.

[Equation 5]

Here, k’ and l’ for determining the resource elements k and l may be determined according to a configuration of the CSI-RS. As for CSI-RS configuration, in case of normal CPs, certain configurations, e.g., CSI-RS configurations 0~19 are determined for TDD and FDD, and certain configurations, e.g., configurations 20~31 are determined for TDD. Similarly, in case of an extended CPs, certain CSI-RS configurations are determined for TDD and FDD, and certain CSI-RS configurations are determined for TDD.

FIG. 3 is a view schematically showing an example in which CSI-RSs are mapped to REs in case of the normal CP according to the foregoing description. The CSI-RS mapping illustrated in FIG. 3 is examples regarding CSI configuration 0 with respect to the normal CP, in which R_p is an RE used for a CSI-RS transmission in an antenna port p. Also, FIG. 4 is a view schematically showing an example in which CSI-RSs are mapped to REs in case of an extended CP. The CSI-RS mapping illustrated in FIG. 4 are examples regarding CSI configuration 0 with respect to the extended CSI. As shown in FIGS. 3 and 4, the CSI-RSs may be mapped to REs in a certain pattern according to an antenna port through which CSI-RSs are transmitted.

Meanwhile, in the MIMO system, a transmission and reception may be performed between a UE and a multi-cell and/or multi-points by employing a CoMP (Coordinated Multi-Point) scheme. A CoMP system is also called a cooperation type multi-transmission and reception system.

In a CoMP system employing CoMP, points are a set of geographically co-located transmission antennas. Sectors may correspond to different points although they are sectors of the same site.

A serving point is a point through which a UE receives a PBCH. A plurality of serving points may exist. When a plurality of serving points exists, they may form an aggregation. The serving point may include a concept of a serving cell. A control signaling point is a point through which a UE receives a UE-specific control signal, and a plurality of control signaling points may exist. When a plurality of control signaling points exists, they may form an aggregation. The control signaling point also includes a concept of a serving cell. Points used for transmitting a PDSCH to a particular UE may be serving points of a UE and/or control signaling points.

Meanwhile, in the CoMP system, a primary cell is a transmission/reception point that transmits system information and/or control information to a UE and receives CSI feedback from the UE. Any one of transmission points constituting a CoMP cooperated set is determined as a primary cell and perform handover between transmission points, e.g., an eNB and an RRH.

CoMP scenarios include first to fourth CoMP scenarios as follows.

FIG. 5 is a view schematically showing a first CoMP scenario. The first CoMP scenario relates to a homogeneous network with intra-site CoMP. For example, in the first CoMP scenario, a CoMP cooperated set is configured among three different cells (or sectors) configured by an eNB.

The CoMP cooperated set refers to a set of (geographically separated) points that directly/indirectly participating in a data transmission with respect to a certain UE in a certain time-frequency resource. The CoMP cooperated set may be transparent or not with respect to a corresponding UE. Here, directly participating in a data transmission refers to that a corresponding point actually transmits data in a corresponding time-frequency resource. Indirectly participating in a data transmission refers to that corresponding point, as a candidate point with respect to a data transmission, does not actually transmit data in the corresponding time-frequency resource but contributes to determining scheduling/beamforming, or the like.

With reference to FIG. 5, with respect to a cooperated region 501 to which CoMP is applied, three

sectors

503, 504, and 505 configured by one eNB 402 forms a CoMP cooperated set.

FIG. 6 is a view schematically showing a second CoMP scenario. The second CoMP scenario relates to a homogeneous network with high Tx Power RRH (Remote Radio Head). The RRH is a device configured to have only an RF (Radio Frequency) part by dividing eNB equipment into the RF part and a baseband part. Thus, the RRH may include an A/D converter (Analog to Digital Converter), an up/down converter, in addition to an RF circuitry. Since the RRH has a small size by having only the RF part, it can extend coverage without an installation of a base station. The RRH may be connected to the eNB through an optical fiber, or the like.

In the second CoMP scenario, for example, a CoMP cooperated set is configured between eNBs, and the eNBs may share data required for operating the CoMP system through a wired/wireless network (e.g., an optical fiber) connecting the eNBs. Here, eNBs are taken as an example for the convenience of explanation, but points constituting a CoMP cooperated set in the second CoMP scenario may also include RRHs as well as eNBs. With reference to FIG. 6, a wired network is established between the eNB and the RRHs, and information required for operating the CoMP system may be s hared through the wired network.

FIG. 7 is a view schematically showing third and fourth CoMP scenarios.

The third CoMP scenario relates to a heterogeneous network with low power RRHs within the macro cell coverage. Here, the transmission/reception points generated by the RRHs have cell IDs different from that of a macro cell. The fourth CoMP scenario also relates to a heterogeneous network with low power RRHs within the macro cell coverage, but unlike the third CoMP scenario, transmission/reception points generated by RRHs have the same cell ID as that of a macro cell. Here, the CoMP transmission point(s) refers to a point or a set of points transmitting data to a certain UE, and the CoMP reception point(s) refers to a point or a set of points receiving data from a certain UE.

A category of the CoMP includes joint processing (JP) and coordinated scheduling/beamforming (CS/CB), and here, JP and CS/CB may be mixed.

In the case of JP, data with respect to a UE is available in at least one point of a CoMP cooperated set in a certain time-frequency resource. JP includes a joint transmission (JT) and dynamic point selection (DPS).

JT refers to performing a data transmission from multi-point belonging to a CoMP to one UE or a plurality of UEs in a time-frequency resource. In the case of JT, multiple cells (multiple points) that transmit data with respect to one UE perform a transmission by using the same time/frequency resource.

In the case of DPS, a data transmission is performed from one point of a CoMP cooperated set in a time-domain resource. A transmission point may be changed in every subframe in consideration of interference, and it includes a transmission point changing over a resource block pair within a subframe. Transmitted data may be simultaneously used in a plurality of points. DPS includes a dynamic cell selection (DCS).

In the case of CS, data is transmitted from one point of a CoMP cooperated set with respect to a time-frequency resource. User scheduling is determined through coordination between points of a corresponding CoMP cooperated set. Here, a used point is dynamically or semi-statically. In case of dynamically selecting a point, a transmission is performed from one point at a time, and here, a transmission point may be changed in every subframe and it includes a transmission points changing over an RB pair within a subframe. In case of selecting a point semi-statically, a transmission is performed from only one point at a time and a transmission point may be changed only in a semi-static manner.

In the case of CB, CB is determined through coordination between points of a corresponding CoMP cooperated set. By CB (Coordinated Beamforming), interference generated between UEs of neighbor cells can be avoided.

As mentioned above, JP and CS/CB may be mixed. For example, some points of a CoMP cooperated set may transmit data to a target UE according to JP, while the other points of the CoMP cooperated set may perform CS/CB.

Meanwhile, with respect to the DCS, a CQI (Channel Quality Indicator) value may be derived by zero power CSI-RS configuration.

FIG. 8 is a conceptual view schematically showing an example of zero power CSI-RS configuration. In FIG. 8, a case in which CoMP is performed through three

transmission points

810, 820, and 830 is illustrated.

With reference to FIG. 8, the three

transmission points

810, 820, and 830 transmit a CSI-RS in an #n OFDM symbol of #k subframe, respectively. Here, transmissions in the #k subframe in the same manner from the three

transmission points

810, 820, and 830 means that transmissions to a UE 840 are performed during the same period of time (the same TTI). The UE 840 combines the data transmitted from the respective transmission points in the #k subframes to obtain downlink data transmitted in the #k subframes.

Here, as can be seen in Equation 2 to Equation 4, when cell IDs of the respective transmission points 810, 820, and 830 are different, CSI-

RSs

850, 860, and 870 transmitted in the #n OFDM symbols of the #k subframes may be disposed in a different pattern.

In the case of zero power CSI-RS configuration, a PDSCH is not mapped to an OFDM symbol in which the CSI-RS is positioned or an RE in which the CSI-RS is positioned, and one CSI-RS is transmitted from one cell, and interference of CSI-RS does not occur between different cells.

Thus, in the case of the zero power CSI-RS configuration, only interference from the outside of the CoMP cooperated set performing CoMP is made on the CSI-RSs transmitted from the respective cells (transmission points).

Meanwhile, the CQI value calculated for the DCS may also be approximately applied also to the case of CS/CB. In the case of JT, the value of CQI may vary according to a combination of serving cells performing JT CoMP, and may also vary according to whether or not the serving cells constituting the combination are coherent.

In the case of JT CoMP, when a cell A and a cell B constituting a CoMP cooperated set are coherent, the cell A and the cell B transmit the same symbols in the same REs by the same MCS (Modulation and Coding Scheme) to the same UE. Thus, when the cell A and the cell B are coherent, interference does not occur between a transmission from the cell A and a transmission from the cell B.

Meanwhile, even when CoMP is applied, per cell-based CSI feedback is performed. Thus, with respect to each CoMP scheme, the UE transmits CSI feedback including CQI values measured for each cell. Here, as described above, the CQI value may vary according to a CoMP scheme, and in the case of JP CoMP, the CQI value may vary according to which serving cells are combined to perform CoMP or according to whether or not the serving cells are coherent.

Table 1 below shows an example of CQI values calculated in the case of DCS and CS/CB.

[Table 1]

With reference to Table 1, when a cell constituting a CoMP cooperated set is a third cell among first to third cells, three CQI values are calculated for each cell that can be selected according to the results of DCS. In Table 1, S1, S2, and S3 indicate PDSCH symbol power or CSI-RS power of the first cell, the second cell, and the third cell, and I_OUT is interference made from the outside other than the cells constituting the CoMP cooperated set. In this case, I_OUT may have the same physical dimension, namely, power dimension, as that of power of the CSI-RS or PDSCH symbol power, and have the common value with respect to the cells constituting the CoMP cooperated set.

Table 2 below shows an example of CQI values calculated in case of coherent JP.

[Table 2]

When a CoMP cooperated set is comprised of three cells, available JT transmission combinations are four cases as shown in Table 2. With reference to Table 2, in case of coherent JP, it can be seen that CQI values are different according to combinations of serving cells performing JT CoMP. Here, the CQI values are the same in serving cells belonging to the same serving cell combination.

Table 3 below shows an example of CQI values calculated in case of non-coherent JP.

[Table 3]

In this case, when we calculate the CQI, for the interference part, the DL signal of other cells can be taken into account.

When a CoMP cooperated set is comprised of three cells, available transmission combinations are four cases as shown in Table 2. However, with reference to Table 3, in the case of non-coherent JT, the CQI values are different according to the combinations of serving cells performing JT CoMP and serving cells belonging to the same serving cells have different CQI values. Thus, even in the case that the serving cells belong to the same serving cells combination, the CQI values reported by each cell are different.

Table 1 to Table 3 show the cases in which the cells constituting the CoMP cooperated sets are three cells, but the foregoing content may also be applied in the same manner when cells constituting a CoMP cooperated set is more than 3 or less than 3.

CSI feedback may be divided into periodic CSI feedback and aperiodic CSI feedback. In the CoMP environment, the periodic CSI feedback is performed in the case of DCS. Also, the periodic CSI feedback may be performed in the case of CS/CB. In comparison, the aperiodic CSI feedback is performed according to a request from a primary cell, and may be performed with respect to JT CoMP, DSC, or CS/CB.

Also, in the case of CoMP, CSI feedback is performed in each cell. Thus, in the case of the periodic CSI feedback, a UE may report a CQI value by cells with respect to DCS, but in the case of the aperiodic CSI feedback, the UE reports a CQI with respect to each available CoMP scheme by cells. For example, in the case of the aperiodic CSI feedback the CoMP-applied UE should report CQIs measured for each cell with respect to CS/CB or DCS, CQIs measured for each cell with respect to coherent JT, and CQIs measured for each cell with respect to non-coherent JT, among CoMP schemes, through CSI feedback. The CSI feedback is transferred to the primary cell as described above.

In this manner, reporting the CQIs calculated for each cell with respect to all the CoMP schemes drastically increases overhead of CSI feedback. The present invention proposes a method of performing CSI feedback by reducing overhead in a CoMP environment.

Designation of CSI feedback target using CSI request field

In an embodiment of the present invention, in case of aperiodic CSI feedback, a primary cell requesting CSI feedback specifically indicates a target of CSI feedback, thus considerably reducing overhead of CSI feedback. For example, when requesting aperiodic CSI feedback, the primary cell may specifically indicate whether or not it is request for CSI feedback regarding DCS or CS/CB or whether or not it is request for CSI feedback regarding JT. Also, the primary cell may specifically indicate whether or not it is request for CSI feedback regarding coherent JT or whether or not it is request for CSI feedback regarding non-coherent JT. Also, in case of the DCS or CS/CB, the primary cell may request CSI feedback with respect to a particular cell, and in case of the JT, the primary cell may request CSI feedback with respect to a particular serving cell combination.

A request for aperiodic CSI feedback is included in downlink control information (DCI) transferred on a control channel to the UE.

Table 4 below schematically shows an example of CSI request fields transferred in DCI in a carrier aggregation (CA) environment.

[Table 4]

Carrier aggregation (CA) follows a scheme of configuring carriers by combining a plurality of bands over downlink and uplink with respect to FDD, and extending an existing single band or carrier allocated to the entire uplink and downlink with respect to TDD. Through CA, communication quality and channel capacity can be increased. In the CA environment, the CSI request fields as shown in Table 4 are transmitted in DCI to thus request aperiodic CSI feedback from the UE. For example, the CSI request field may be included in a DCI format 0, a DCI format 4, or the like, so as to be transmitted to the UE.

Meanwhile, unlike the CA environment, in a CoMP environment, respective transmission points constituting a CoMP cooperated set performs transmission in the same band. In this case, aperiodic CSI feedback may be requested from the UE in the CoMP environment by allowing the CSI request field included in the DCI to indicate each category of CoMP. The UE performs CSI feedback with respect to a CoMP category indicated by the CSI request field value. Here, the CSI request field value indicating JT among CoMP categories may discriminately indicate whether a target of aperiodic CSI feedback is coherent JT or non-coherent JT. Also, a CSI request field value indicating CS/DB or DCS among the CoMP categories may specifically indicate a cell as a target of CSI feedback. For example, the primary cell may request aperiodic CSI feedback from the UE by setting 2-bit CSI request field as shown in Table 5 in the CoMP environment.

[Table 5]

With respect to the 2-bit CSI request field as shown in the example of Table 5, the UE, which has received the CSI request field values (01, 10, 11) triggering a report, may decode an uplink DCI format including the corresponding CSI request fields or a random access response grant, and after the lapse of certain time (subframe), the UE may report CSI on a PUSCH.

With respect to the 2-bit CSI request field as shown in the example of Table 5, when the received CSI request field value is 00, the UE does not trigger aperiodic CSI feedback. Also, in this case, the UE may perform periodic CSI feedback with respect to DCS or CS/CB.

With respect to the 2-bit CSI request field as shown in the example of Table 5, when the received CSI request field value is 01, the UE triggers CSI feedback with respect to DCS or CS/CB. In this case, the CSI request field value may be allowed to indicate transmission of all the CQI values for serving cells constituting a CoMP cooperated set with respect to DCS or CS/CB category, or may be allowed to indicate transmission of a CQI value only for a corresponding serving cell upon being specified as a target of a CSI report.

With respect to the 2-bit CSI request field as shown in the example of Table 5, when the received CSI request field value is 10 or 11, the UE triggers CSI feedback with respect to JT. In this case, the CSI field value may discriminately indicate whether JT as a target of CSI feedback is coherent JT or non-coherent JT. For example, in the example of Table 5, when the CSI request value is 10, the UE may trigger CSI feedback with respect to coherent JT, and when the CSI request value is 11, the UE may trigger CSI feedback with respect to non-coherent JT.

With reference to FIG. 9, periodic CSI feedback is performed only on DCS or CS/CB in a CoMP environment. As described above, CSI feedback is performed per cell-based CSI feedback. As described above, a CQI included in a CSI and reported may be obtained from zero power CSI-RS configuration with respect to DCS, and may also be applied to CS/CB.

Also, in the CoMP environment, aperiodic CSI feedback may be performed every CoMP category. For example, aperiodic CSI feedback may be performed even in case of JP, as well as DCS or CS/CB. Here, as described above, triggering of aperiodic CSI feedback may be made by a CSI request field included in DCI. In case in which the CSI request field is as shown in Table 5, when a value of the CSI request field is 00, and CSI feedback of the UE is not triggered, when the field value is 01, CSI feedback with respect to DCS or CS/CB is triggered. In this case, the field value 01 may be determined to indicate CSI feedback with respect to any one of DCS and CS/CB. When a value of the CSI request field is 10 or 11, CSI feedback with respect to JT is triggered. In case of 10, CSI feedback with respect to coherent JT may be triggered, and in case of 11, CSI feedback with respect to non-coherent JT may be triggered.

As shown in Table 5, in the per cell-based CSI feedback, overhead of CSI feedback can be considerably reduced by designating a target of CSI feedback through the CSI request field included in DCI.

Meanwhile, in Table 5, CQIs with respect to DCS or CS/CB can be easily obtained for each cell from zero power CSI/RS configuration as described above regarding Table 1.

Also, in Table 5, CQIs with respect to coherent JT and non-coherent JT can be obtained as shown in Table 2 and Table 3. In the case of JT, as described above, the CQI value varies according to a combination of serving cells, and even in case of the combination of the same serving cells, the CQI varies according to whether or not the combination is a combination of coherent serving cells or a combination of non-coherent serving cells.

Since per cell-based CSI feedback is performed, in the case of JT, although performing of CSI feedback is indicated by differentiating the coherent JT and non-coherent JT, there may be a great amount of CQI values to be reported by the UE. For example, like the case of Table 5, when three cells constitute a CoMP cooperated set, CQI values should be reported for four types of JTs, and in case of non-coherent JT, nine types of values should be reported. When four cells constitute a CoMP cooperated set, 11 types of JTs are generated, and in case of the non-coherent JT, the number of CQI values to be reported is significantly increased. In this manner, the increase in the number of cells constituting a CoMP cooperated set leads to an increase in CQI values to be reported for JT and an increase in overhead of CSI report in the per cell-based CSI feedback.

Thus, in the case of JT CoMP, the use of a method of reducing the number of bits of CQI values to be reported or further limiting combinations of serving cells to be reported may be considered along with the use of the foregoing Table 5.

Method of reducing number of bits of CQI values

With respect to JT CoMP, overhead of CSI feedback may be reduced by transmitting a differential value of CQI. Here, the differential value of CQI may be a difference value between an original CQI value with respect to JT and a CQI value with respect to DCS or CS/CB.

In this case, an example of the CQI value (DCS CQI) reported as CSI feedback with respect to DCS and the CQI value (JT CQI) reported as CSI feedback with respect to JT is as shown in Table 6 below.

[Table 6]

Table 6 shows an example of a CQI value with respect to DCS, as a CQI value with respect to DCS or CS/CB. The CQI value with respect to DCS may be equal to that of CS/CB, or the CQI value with respect to DCS may be used as a CQI value with respect to CS/CB.

In the example of Table 6, CQI_DCS is a CQI value measured with respect to DCS, and a differential value (△CQI_JT) obtained by subtracting the CQI value (CQI_DCS) with respect to DCS from a CQI value (CQI_JT) originally calculated for JT is reported as a CQI value with respect to JT through CSI feedback. In the example of Table 6, it is described that the value obtained by subtracting CQI_DCS from CQI_JT is reported as a CQI value with respect to JT, but a value obtained by subtracting CQI_JT from CQI_DCS may be reported as a CQI value with respect to JT.

Meanwhile, the CQI_DCS value is periodically reported as a CQI value with respect to DCS or CS/CB to a primary cell of the CoMP system through periodic CSI feedback. Thus, when the primary cell receives aperiodic CSI feedback from the UE, it can obtain the original CQI_JT based on the differential value (△CQI_JT) between CQI_JT and CQI_DCS and the periodically received CQI_DCS value.

Also, the UE may transmit the differential value (△CQI_JT), rather than CQI_JT, through CSI feedback, thus reducing overhead of CSI feedback.

Method of limiting targets of CSI feedback

Overhead of CSI feedback may be reduced by introducing a new field indicating a combination of serving cells as targets of CSI feedback, as a combination of serving cells performing JT in DCI transmitted via a downlink control channel.

Hereinafter, a new field indicating a combination of serving cells as targets of CSI feedback will be referred to as ‘JT combination index’ for the convenience of explanation. The JT field index may specifically indicate a combination of serving cells as targets of CSI feedback when a CSI request field in Table 5 indicates CSI feedback with respect to JT.

Table 7 below shows an example of combinations of serving cells performing JT and JT combination indices indicating the combinations when three cells (first, second, third cells) constitute a CoMP cooperated set.

[Table 7]

A primary cell of a CoMP system may transmit DCI including a JT combination index along with a CSI feedback request field to a UE. When three cells constitute a CoMP cooperated set, the JT combination index may be transmitted by two bits as shown in Table 7. When the CSI request field value is a value triggering CSI feedback with respect to JT, the UE may perform CSI feedback with respect to a particular serving cell combination indicated by the JT combination index.

For example, when the CSI request field indicates CSI feedback with respect to JT (e.g., when the CSI request field value is 10 or 11 in Table 5), if a JT combination index is 0, the UE may obtain a CQI value of the first cell and that of the second cell and report the same through CSI feedback with respect to a case in which the first and second cells perform JT. Here, whether to report with respect to coherent JT or non-coherent JT may be indicated by the CSI request field as shown in Table 5, and the JT combination index may indicate a serving cell combination reflecting it.

Table 8 below shows an example of combinations of serving cells performing JT and JT combination indices indicating the combinations in case in which four cells (first, second, third, and fourth cells) constitute a CoMP cooperated set.

[Table 8]

With reference to Table 8, in case in which four cells constitute a CoMP cooperated set, when the CSI request field as shown in Table 5 indicates CSI feedback with respect to JT, the UE calculates CQIs for each cell with respect to combinations of the serving cells indicated by the JT combination indices, and report the same to the primary cell through CSI feedback. Here, whether to report CSI with respect to coherent JT or whether to report CSI with respect to non-coherent JT is indicated by the CSI request field, and the JT combination index may indicate a serving cell combination reflecting it.

For example, in the example of Table 5, when the CSI request field value is 10 and the JT combination index is 6, the UE may calculate CQI values of each cell of the combination of the first, second, and third cells with respect to the coherent JT, and report the same through feedback.

Also, in the example of Table 5, when the CSI request field value is 11 and the JT combination index is 7, the UE may calculate CQI values of each cell of the combination of the first, second, and fourth cells with respect to non-coherent JT, and report the same through CSI feedback.

Meanwhile, a combination serving cells performing JT may be indicated by a bit map, rather than by the index as shown in Table 7 and Table 8. Table 9 shows an example of indicating a combination of serving cells performing JT by a bit map.

[Table 9]

In the example of Table 9, among combinations of serving cells that may be indicated by a bit map, a combination comprised of first, fourth, and sixth cells and a combination comprised of first, third, fourth, sixth, and eighth cells are indicated by bit maps

In this manner, in the system to which the present invention is applied, when CSI feedback with respect to JT (coherent JT or non-coherent JT) is requested through a CSI request field, a combination of specific cells as targets of CSI feedback may be indicated through a bit map.

For example, in the case of Table 9, when a CSI request field requests CSI feedback with respect to coherent JT and a bit map indicating a combination of serving cells performing JT is 10010100, the UE may calculate a CQI value for coherent JT with respect to the combination comprised of first, fourth, and sixth cells and report the same through CSI feedback. Also, in the case of Table 9, when a CSI request field requests CSI feedback for non-coherent JT and a bit map indicating a combination of serving cells is 10110101, the UE may calculate a CQI value for non-coherent JT with respect to the combination comprised of first, third, fourth, sixth, and eighth cells and report the same through CSI feedback.

Limitation of target of CSI feedback and reduction in number of bits of CQI report value

Meanwhile, overhead may be reduced by using both the method of limiting a target of CSI feedback and the method of reducing the number of bits of a reported CQI value. For example, in case that a CoMP category as a target of CSI feedback is designated through a CSI request field as shown in Table 8 and the CSI request field indicates CSI feedback with respect to JT, the primary cell of the CoMP system may specifically designate a combination as a target of CSI feedback among serving cell combinations performing JT CoMP through an information field included in DCI as shown in Table 7 and Table 8, and the UE may report a differential value with the CQI value with respect to DCS like the case of Table 6, as a CQI value reported through CSI feedback.

With reference to FIG. 10, a primary cell of the CoMP system requests aperiodic CSI feedback from a UE (S1010).

Whether or not the aperiodic CSI feedback is required may be determined by the primary cell, or may be determined among cells constituting a CoMP cooperated set. As described above, the cells constituting the CoMP cooperated set are connected through a wired/wireless network.

The aperiodic CSI feedback request transmitted by the primary cell may be included in DCI (Downlink Control Information) transmitted via a control channel, so as to be transferred to the UE. Here, the aperiodic CSI feedback request may be made by using a CSI request field. For example, the CSI request field may be included in a DCI format 0, a DCI format 4, or the like, and transmitted to the UE. Here, the CSI request field value may specifically indicate a CoMP category as a target of the CSI feedback to thereby specify the CoMP category as a target of the CSI feedback and reduce overhead. A detailed method using the CSI request field is the same as described above.

Here, the primary cell of the CoMP system may further include a JT combination index in the DCI and transfer the same to the UE. The JT combination index specifically indicates a combination of serving cells performing JP CoMP. Thus, when CSI feedback with respect to (coherent or non-coherent) JT is requested with the CSI request field, serving cells (the combination of serving cells) as targets of the CSI feedback may be specified through the JT combination index, and thus, the targets of the CSI feedback may be further limited. Here, a bit map indicating a particular JT combination (a combination of serving cells performing JT CoMP) may also be used instead of a JT combination index. What the JT combination index or the bit map indicating the JT combination indicates may be previously determined between the UE and the CoMP cooperated set or may be transferred to the UE from the primary cell of the CoMP system through a higher layer message. A detailed method using a JT combination index or a bit map indicating a JT combination is the same as described above.

The primary cell of the CoMP system receives CSI feedback from the UE (S1020). The CSI feedback includes CSI (Channel State Information). The CSI is fed back based on a cell unit from the UE, and includes a CQI of each cell as a target of the CSI feedback. Here, when a CQI value is a CQI value with respect to JT, a differential value between a CQI value with respect to DCS and an original value with respect to JT, instead of the original CQI value measured for each cell with respect to JT, may be included in the CSI. In this case, the primary cell may calculate the original CQI value with respect to JT by using the CQI value with respect to DCS reported through periodic CSI feedback.

With reference to FIG. 11, the UE receives a request for aperiodic CSI feedback from the primary cell of the CoMP system (S1110). As described above, the request for aperiodic CSI feedback may be made by using a CSI request field of DCI transmitted on a downlink control channel. Also, the DCI received by the UE may include a JT combination index indicating a serving cell performing JT CoMP. When the target of the CSI feedback indicated by the CSI request field is (coherent or non-coherent) JT, the UE may include the CSI with respect to the combination of the serving cells indicated by the JT combination index in the CSI feedback and report the same. Meanwhile, the UE may receive a bit map indicating a particular combination of serving cells instead of the JT combination index. Here, when there is an aperiodic CSI request with respect to (coherent or non-coherent) JT, the UE may perform CSI feedback with respect to the combination of the serving cells indicated by the received bit map.

The UE transmits aperiodic CSI feedback according to the request from the primary cell of the CoMP system (S1120). The transmitted CSI includes a CQI with respect to serving cell(s) as a target(s) of the CSI feedback. Here, when the CQI value is a CQI value with respect to JT, the UE may include a differential value between the CQI value with respect to DCS and the original value with respect to the JT, instead of the original CQI value measured for each cell with respect to JT, in the CSI.

FIG. 12 is a view schematically showing a configuration of a UE in a system to which the present invention is applied. With reference to FIG. 12, a UE 1200 includes an RF unit 1210, a memory 1220, and a processor 1230.

The UE 1200 transmits and receives data through the RF unit 1210. The RF unit 1210 may include multiple antennas.

The memory 1220 stores information required for performing communication. For example, the memory 1220 may store information regarding a CSI request field value, information regarding a JT combination index, information regarding a bit map indicating a JT combination, a measurement value (e.g., a CQI value) with respect to a channel state, and the like.

The processor 1230 implements the function, process and/or method proposed in the present disclosure. For example, as described above, the processor 1230 may perform an operation of receiving a request for aperiodic CSI feedback, configuring a corresponding CSI, and reporting the same to the primary cell.

The processor 1230 may include a CoMP controller 1240, a CSI generating unit 1250, a measurement unit 1260, and the like. The CoMP controller 1240 controls an operation of the UE required for performing transmission and reception in a CoMP environment. The CSI generating unit 1250 may generate periodic or aperiodic CSI and transmit the same to the primary cell through the RF unit 1210. When the CSI generating unit 1250 generates aperiodic CSI, it may generate CSI with respect to a target of CSI feedback indicated through DCI. The measurement unit 1260 may measure a channel state to be reported as the CSI feedback, or the like, as channel information along with the CQI, or the like. Measurement results of the measurement unit 1260 may be stored in the memory 1230 or may be used to generate CSI in the CSI generating unit 1250.

FIG. 13 is a view schematically illustrating a configuration of an eNB in a system to which the present invention is applied. In FIG. 13, eNB may be a primary cell of a CoMP system. With reference to FIG. 13, the eNB 1300 may include a communication unit 1310, a memory 1320, and a processor 1330.

The eNB 1300 may perform communication through the communication unit 1310. The communication unit 1310 may include multiple antennas and may be connected to cells constituting a CoMP cooperated set or a different eNB through a wired/wireless network.

The memory 1320 may store information required for communication. For example, the memory 1320 may store information regarding a CSI request field value, information regarding a JT combination index, information regarding a bit map indicating a JT combination, information included in a CSI (e.g., a CQI value, or the like) received by a UE, and the like.

The processor 1330 implements the function, process and/or method proposed in the present disclosure. For example, as described above, the processor 1330 may determine whether or not aperiodic CSI feedback is required, request aperiodic CSI feedback from a UE, and perform a controlling operation including scheduling based on the received CSI.

The processor 1330 may include a DCI generating unit 1340, a CoMP controller 1350, and the like. The DCI generating unit 1340 may generate a DCI including an indication regarding aperiodic CSI request. The DCI including a CSI request may be the same as described above, and may include a JT combination index, or the like, along with a CSI request field.

The CoMP controller 1350 may perform a controlling operation to perform CoMP. The CoMP controller 1350 may determine whether to request aperiodic CSI feedback and specify a target of CSI feedback. The DCI generating unit 1340 may generate a DCI indicating a target of the specified CSI feedback. Also, the CoMP controller 1350 may perform controlling required for CoMP to be effectively performed between CoMP categories based on the CSI received from a UE.

In the exemplary system as described above, the methods are described based on the flow chart by sequential steps or blocks, but the present invention is not limited to the order of the steps, and a step may be performed in different order from another step as described above or simultaneously performed. It would be understood by a skilled person in the art that the steps are not exclusive, a different step may be included, or one or more of the steps of the flow chart may be deleted without affecting the scope of the present invention.

The embodiments of the present invention have been described with reference to the accompanying drawings, and it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope of the invention. Thus, the technical idea of the present invention should be interpreted to embrace all such alterations, modifications, and variations in addition to the accompanying drawings.

Claims

A method of receiving channel state information, the method comprising:
transmitting downlink control information including information field requesting aperiodic channel state information feedback; and
receiving aperiodic channel state information feedback according to the request,
wherein the information field is a channel state information request field, and each field value of the channel state information request field indicates a CoMP category as a target of triggering channel state information feedback.
The method of claim 1, wherein the channel state information request field is 2-bit information field.
The method of claim 1, wherein the field values of the channel state information request field indicate not triggering feedback of aperiodic channel state information, triggering aperiodic channel state information feedback with respect to dynamic cell selection and/or coordinate scheduling/coordinated beamforming among CoMP categories, and triggering aperiodic channel state information feedback with respect to a joint transmission among the CoMP categories, respectively.
The method of claim 1, wherein when a field value of the channel state information request field indicates channel state information feedback with respect to joint transmission among the CoMP categories, the downlink control information includes joint transmission combination information indicating a particular combination of serving cells as targets of the channel state information feedback among combinations of serving cells that perform joint transmission.
The method of claim 4, wherein the joint transmission combination information is index information indicating a particular combination of serving cells.
The method of claim 4, wherein the joint transmission combination information is a bit map indicating a particular combination of serving cells.
A method of transmitting channel state information, the method comprising:
receiving downlink control information including information field requesting aperiodic channel state information feedback; and
transmitting channel state information configured according to the information field,
wherein the information field is a channel state information request field, and each field value of the channel state information request field indicates a CoMP category as a target of triggering channel state information feedback.
The method of claim 7, wherein each of the field values of the channel state information request field indicate not triggering feedback of aperiodic channel state information, triggering aperiodic channel state information feedback with respect to dynamic cell selection and/or coordinate scheduling/coordinated beamforming among CoMP categories, and triggering aperiodic channel state information feedback with respect to a joint transmission among the CoMP categories, respectively.
The method of claim 7, wherein the downlink control information includes joint transmission combination information indicating a particular combination of serving cells as targets of the channel state information feedback among combinations of serving cells that perform joint transmission, and
when the field value of the channel state information request filed indicates channel state information feedback with respect to joint transmission among CoMP categories, in the transmitting of the channel state information, channel state information is transmitted with respect to a particular combination of serving cells indicated by the joint transmission combination information.
The method of claim 9, wherein the joint transmission combination information is index information indicating a particular combination of serving cells.
The method of claim 9, wherein the joint transmission combination information is a bit map indicating a particular combination of serving cells.
The method of claim 7, wherein in case of transmitting channel state information with respect to joint transmission in the transmitting of the channel state information,
a difference value between a channel quality indicator with respect to dynamic cell selection and a channel quality indicator with respect to joint transmission, instead of a value of a channel quality indicator with respect to joint transmission, is included in the channel state information and transmitted.
The method of claim 7, wherein the downlink control information includes joint transmission combination information indicating a particular combination of serving cells as targets of the channel state information feedback among combinations of serving cells that perform joint transmission, and
when a field value of the channel state information request field indicates channel state information feedback with respect to joint transmission among CoMP categories, in the transmitting of the channel state information,
channel state information is transmitted with respect to a particular combination of serving cells indicated by the joint transmission combination information, and
a difference value between a channel quality indicator with respect to dynamic cell selection and a channel quality indicator with respect to joint transmission, instead of a value of a channel quality indicator with respect to joint transmission, is included in the channel state information and transmitted.
An apparatus of receiving channel state information (CSI), the apparatus comprising:
a processor determining whether aperiodic CSI feedback is required, requesting aperiodic CSI feedback from a User Equipment (UE), and performing a controlling operation including scheduling based on the received CSI; and
a radio frequency (RF) unit transmitting downlink control information including information field requesting aperiodic CSI feedback and receiving aperiodic CSI feedback as a response for the requesting aperiodic CSI feedback,
wherein the information field is a CSI request field, and each field value of the CSI request field indicates a CoMP category in which the aperiodic CSI feedback to be triggered.
An apparatus of transmitting channel state information (CSI), the apparatus comprising:
a radio frequency (RF) unit receiving downlink control information including information field requesting aperiodic CSI feedback and transmitting CSI configured according to the information field; and,
a processor configuring CSI according to the information field,
wherein the information field is a CSI request field, and each field value of the CSI request field indicates a CoMP category in which the aperiodic CSI feedback to be triggered.