KR20130049561A - Communicating method with transceiver and terminal, transceiver thereof and terminal thereof in coordinated multi-point transmission/reception system - Google Patents

Abstract

PURPOSE: A communication method of a transmission and reception point, a communication method, and a terminal thereof are provided to reduce overhead by selectively giving feedback on channel information for cooperative transmission and reception points. CONSTITUTION: A terminal processor(1210) measures the strength of a signal received from two or more transmission and reception points. The terminal processor searches for one or more transmission and reception points. A terminal RF(Radio Frequency) unit(1205) transmits the chance information of the searched transmission and reception point. The strength of the signal is an RSSI(Received Signal Strength Indicator). [Reference numerals] (1205) Terminal RF unit; (1210) Terminal processor; (1212) RSSI measurement unit; (1214) Transceiving point selection unit; (1216) Antenna group selection unit; (1218) Channel information generation unit; (1255) Transceiving point RF unit; (1260) Transceiving point processor; (1262) Threshold value generation unit; (1264) Transceiving point number determination unit; (1266) Antenna group generation unit; (AA) Reference signal; (BB) RRC signaling; (CC) Channel information; (DD) Data transmission

Description

TECHNICAL FIELD The communication method of a transmission / reception point, the transmission / reception point, the communication method of a terminal, and the terminal thereof in a cooperative multi-cell communication system, and the terminal method in a coordinated multi-point transmission / reception system.

The present invention relates to a cooperative multi-cell communication system in which two or more transmission / reception points cooperate to transmit a signal, and wherein one or more transmission / reception points receive channel information from a terminal to perform cooperative communication. It is about.

In order to improve transmission efficiency in a multi-antenna-based wireless communication system, techniques such as a closed-loop precoding transmission method, an adaptive modulation and coding (AMC) method, and a channel sensitive scheduling method are described. I use it.

The closed loop precoding transmission method improves the gain of the received signal by adjusting the phase of the multiple antenna channels experienced by the received signal. The AMC method allows the transmitter to adjust the amount of data to be transmitted according to the channel condition. have. Using the channel sensitive scheduling resource management method, the transmitter selectively services a user having a good channel condition among several users, thereby increasing system capacity compared to allocating and serving a channel to one user.

For example, a closed loop precoding transmission method, an ACM method, and a channel sensitive scheduling method are methods of applying appropriate precoding, modulation, and coding schemes at a time when it is determined to be the most efficient by receiving channel information from a receiver.

In a wireless communication system using Orthogonal Frequency Division Multiple Access (OFDMA), one of various reasons for achieving capacity increase in the OFDMA scheme is that scheduling on the frequency axis can be performed. Just as the channel gains capacity gains through channel-sensitive scheduling as the channel changes over time, more capacity gains can be achieved if the channel utilizes different characteristics depending on frequency.

The aforementioned closed loop precoding transmission method, the ACM method, and the channel sensitive scheduling method are techniques capable of improving transmission efficiency in a state where a transmitter acquires sufficient information about a transmission channel. When the transmitter cannot infer the state of the transmission channel through the reception channel as in the frequency division duplex (FDD) scheme, the receiver is designed to report information on the transmission channel to the transmitter. However, in the wireless communication system environment, since the state of the channel changes with time, the effectiveness of the closed loop precoding transmission method, the ACM method, and the channel sensitive scheduling method may be degraded when the channel state report is delayed.

The wireless communication system uses a method of maintaining a call in such a manner that one base station manages a user in a certain area of coverage and hands over to another base station when the user moves out of coverage.

In such a wireless communication system, a user located outside of cell coverage suffers from interference from a signal transmitted from another base station, and thus the state of a channel is relatively poor. Therefore, the closer the user is to the base station, the higher the rate of service, and the users located at the cell coverage boundary receive the lower rate of service. In order to improve this problem, it is expected that in the 4G mobile communication system which is recently discussed, several base stations adopt a cooperative transmission that transmits a signal for a user located at a cell coverage boundary.

The present invention provides an apparatus and method for selectively feeding back channel information on cooperative transmission / reception points in order to reduce feedback feedback overhead required when supporting cooperative communication between transmission / reception points.

In an embodiment, in a wireless communication system in which a terminal is cooperatively communicating with two or more transmission / reception points, measuring the strength of a signal received from the two or more transmission / reception points; Searching for one or more transmission / reception points whose measured signal strength is greater than a predetermined threshold; And transmitting the channel information of the searched transmission / reception point to the terminal.

Another embodiment of the present invention provides a wireless communication system in which a terminal communicates with two or more transmission and reception points, the method comprising: transmitting a threshold value of a signal strength to the terminal; Receiving channel information of at least one transmission / reception point from which the signal strength is greater than a predetermined threshold from the terminal; And transmitting a signal to the terminal based on channel information of the transmission and reception point.

In another embodiment, in a wireless communication system in which a terminal is in cooperative communication with two or more transmission and reception points, receiving the strength of the signal measured for the two or more transmission and reception points from the terminal; Determining a threshold of the strength of the signal using the average of the received strengths of the signal; And transmitting the threshold value of the determined strength of the signal to the terminal.

In another embodiment, in a wireless communication system in which a terminal is in cooperative communication with two or more transmission and reception points, receiving the strength of the signal measured for the two or more transmission and reception points from the terminal; Determining a threshold of the strength of the signal using the standard deviation of the strengths of the received signal; And transmitting the threshold value of the determined strength of the signal to the terminal.

According to another embodiment, in a wireless communication system in which a terminal cooperates with two or more transmission / reception points, the strength of a signal received from the two or more transmission / reception points is measured, and the measured signal strength is greater than a predetermined threshold. A processor for searching for one or more transmission / reception points; And an FR unit for transmitting the channel information of the found transmission / reception point to the terminal.

In another embodiment, in a wireless communication system in which a terminal cooperates with two or more transmission / reception points, the terminal transmits a threshold value of a signal strength to the terminal, and the signal strength of the signal is greater than a predetermined threshold. An RF unit for receiving channel information of the terminal from the terminal and transmitting a signal to the terminal based on the channel information of the transmission / reception point; And it provides a transmission and reception point comprising a processor for generating the threshold.

Another embodiment, in a wireless communication system in which the terminal is a cooperative communication with two or more transmission and reception points, RF unit for receiving the strength of the signal measured for the two or more transmission and reception points from the terminal; And a processor configured to determine a threshold value of the signal strength using the average of the received signal strengths, wherein the RF unit transmits a threshold value of the determined signal strength to the terminal. to provide.

Another embodiment, in a wireless communication system in which the terminal is a cooperative communication with two or more transmission and reception points, RF unit for receiving the strength of the signal measured for the two or more transmission and reception points from the terminal; And a processor configured to determine a threshold value of the signal strength using the standard deviation of the received signal strengths, wherein the RF unit transmits the threshold value of the determined signal strength to the terminal. To provide.

The channel information feedback apparatus and method according to the embodiment may reduce the feedback overhead while minimizing the gain reduction obtained from the cooperative transmission between the transmission and reception points by feeding back only channel information that is likely to be substantially used in data scheduling.

1 is a block diagram showing a wireless communication system to which the present invention is applied.
2 is a conceptual diagram of a CoMP system according to an embodiment of the present invention.
FIG. 3 illustrates one transmission / reception point and an antenna array structure of a terminal and a propagation channel according to the CoMP system of FIG. 1 or 2.
4 is a structural diagram of a CoMP system according to an embodiment.
5 is a flowchart illustrating a cooperative communication method of transmission / reception points of a terminal and a CoMP system according to another embodiment.
6 to 8 are flowcharts of a channel information feedback method in a CoMP system according to another embodiment.
9A shows an example of antenna grouping into two groups for four single array transmit antennas.
9B shows an example of antenna grouping into two groups in the case of a transmit antenna of eight dual polarized antenna arrays.
10 is a flowchart illustrating a method of determining a relative threshold value using an average RSSI of cooperative transmission / reception points in a CoMP system and transmitting the same to a terminal.
11 is a flowchart illustrating a method of determining and transmitting a relative threshold value using a standard deviation of RSSI of cooperative transmission / reception points in a CoMP system according to another embodiment.
12 is a block diagram illustrating a terminal and a transmission / reception point according to another embodiment.

Hereinafter, some embodiments of the present invention will be described in detail with reference to exemplary drawings. In adding reference numerals to the components of each drawing, it should be noted that the same reference numerals are used to refer to the same components as much as possible even if displayed on different drawings. In the following description 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 invention 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, the wireless communication system 100 is widely deployed to provide various communication services such as voice and packet data.

The wireless communication system 100 includes at least one transmission / reception point 110. Each transmit / receive point 110 provides a communication service for a specific geographic area or frequency area and may be called a site. A site may be divided into a plurality of regions 150a, 150b, and 150c, which may be called sectors, and the sectors may have different cell IDs.

The user equipment (UE) 120 may be fixed or mobile, and may include a user equipment (UE), a mobile terminal (MT), a user terminal (UT), a subscriber station (SS), a wireless device, and a PDA. (personal digital assistant), wireless modem (wireless modem), a handheld device (handheld device) may be called other terms.

The transmission / reception point 110 generally refers to a station communicating with the terminal 120, and may include a component carrier or cell, an evolved-NodeB (eNodeB), a base transceiver system (BTS), an access point, and a femto base station. (Femto eNodeB), Home eNodeB (HeNodeB), Relay, Pico eNodeB, Remote radio head (hereinafter referred to as “RRH”), or Hot Spot Can be defined. Alternatively, the transmission / reception point 110 may be defined as a set of antenna ports. Information about the set of antenna ports of the transmission and reception points may be transmitted to the terminal through radio resource control (RRC) signaling. Therefore, a plurality of transmission / reception points in one cell may be defined as a set of antenna ports. The intersection between the set of antenna ports is always empty.

Cells 150a, 150b, and 150c should be interpreted in a comprehensive sense to indicate some areas covered by the transmit / receive points 110 and cover all of the various coverage areas such as megacells, macrocells, microcells, picocells, femtocells, and the like. It means. The transmission / reception point 110 may refer to a transmission point for transmitting a signal to provide a communication service, and may receive a signal from the terminal 120 to provide a communication service.

In this specification, the transmission and reception point 110 and the terminal 120 are two transmission / reception subjects used to implement the technology or technical idea described in this specification, and are used in a comprehensive sense and are not limited by the terms or words specifically referred to. .

Hereinafter, downlink (downlink) means a communication or communication path from the transmission and reception point 110 to the terminal 120, uplink (uplink) indicates a communication or communication path from the terminal 120 to the transmission and reception point 110. it means. In downlink, the transmitter may be part of the transmission / reception point 110 and the receiver may be part of the terminal 120. In uplink, the transmitter may be part of the terminal 120 and the receiver may be part of the transmission / reception point 110.

There is no limitation on the multiple access scheme applied to the wireless communication system 100. Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), Orthogonal Frequency Division Multiple Access (OFDMA), Single Carrier-FDMA (SC-FDMA), OFDM-FDMA, OFDM-TDMA For example, various multiple access schemes such as OFDM-CDMA may be used. These modulation techniques demodulate signals received from multiple users of a communication system to increase the capacity 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.

One embodiment of the present invention provides asynchronous wireless communication that evolves into Long Term Evolution (LTE) and LTE-advanced through GSM, WCDMA, HSPA, and synchronous wireless communication that evolves into CDMA, CDMA-2000 and UMB). Applicable to resource allocation. The present invention should not be construed as being limited or limited to a specific wireless communication field, but should be construed as including all technical fields to which the spirit of the present invention can be applied.

The wireless communication system 100 to which the embodiments are applied includes a coordinated multi-point transmission / reception system (CoMP system) or a cooperative multi-antenna transmission scheme in which two or more transmission / reception points cooperate to transmit a signal. coordinated multi-antenna transmission system), a cooperative multi-cell communication system.

The CoMP system refers to a communication system supporting CoMP or a communication system to which CoMP is applied. CoMP is a technique for adjusting or combining signals transmitted or received by multi transmission / reception (Tx / Rx) points. CoMP can increase data throughput and provide high quality.

In this CoMP system, transmission / reception points may provide a service by allocating the same frequency resource at the same time when attempting cooperative transmission / reception to one user terminal 120. That is, the transmission / reception points selected as the cooperative transmission / reception points at the same time may transmit and receive data with one user terminal 120 using the same frequency resource.

Each transmit / receive point or cells may constitute multiple transmit / receive points. For example, the multiple transmit / receive points may be macro cells forming a homogeneous network. In addition, the multiple transmission / reception points may be RRHs having a macro cell and high transmission power. In addition, the multiple transmission / reception points may be RRHs having low transmission power in the macro cell and the macro cell region.

The CoMP system may 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 120 may be a CoMP terminal. The CoMP terminal is a component of the CoMP system and performs communication with a CoMP cooperating set or a CoMP set. Like the CoMP system, the CoMP terminal may operate in the CoMP mode or in the normal mode. The CoMP set is a set of transmission / reception points that directly or indirectly participate in data transmission in a time-frequency resource for a CoMP terminal. In addition, the CoMP terminal may apply a multi-user multi-antenna (MU-MIMO) scheme as well as a single-user multi-antenna (SU-MIMO) scheme. Although the terminal 120 receives data from the transmission and reception points, respectively, since the frequency bands for receiving the association data are the same, the terminal 120 may be regarded as receiving data from one transmission point.

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

The CoMP terminal may simultaneously receive signals from the CoMP set or transmit signals to the CoMP set at the same time. At this time, the CoMP system minimizes the interference effect between the CoMP sets in consideration of the channel environment of each cell constituting the CoMP set.

When operating a CoMP system, various scenarios are possible. The first CoMP scenario is CoMP, which is composed of a homogeneous network among a plurality of cells in one transmission / reception point, and may be referred to as intra-site CoMP. The second CoMP scenario is CoMP, which consists of a homogeneous network for one macro cell and one or more high-power RRHs. The third CoMP scenario and the fourth CoMP scenario are CoMPs that consist of a heterogeneous network for one macro cell and one or more low-power RRHs in the macro cell region. In this case, when the physical cell IDs of the RRHs are not the same as the physical cell IDs of the macro cells, they correspond to the third CoMP scenario and the same cases correspond to the fourth CoMP scenario.

CoMP's category includes Joint Processing (JP) and Coordinated Scheduling / Beamforming (CS / CB). It is also possible to mix CS and CB.

In the case of JP, data for the terminal is available at at least one transmit / receive point of the CoMP set in some time-frequency resource. JP stands for Joint Transmission (JT), Dynamic Point Selection (DPS), or Dynamic Point Scheduling / Dynamic. point blanking, DPS / DPB).

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

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

In the case of CS, data is sent from one transmit / receive point in a CoMP set for time-frequency resources, and user scheduling is determined by coordination between the points in that CoMP set.

In the case of CB, it is also determined by cooperation between the transmission and reception points of the CoMP set. By the CB (Coordinated Beamforming) it is possible to avoid the interference occurring between the terminals of the neighbor cell.

The CS / CB may include a semi-static point selection (SSPS) that can be changed by selecting a transmission / reception point semi-statically.

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

The transmission and reception points to which the present invention is applied may include a base station (macro base station or micro base station (local base station)), a cell, or an RRH. That is, the base station or the RRH may be a transmission / reception point. Meanwhile, the plurality of base stations may be multiple transmission / reception points, and the plurality of RRHs may be multiple transmission / reception points. Of course, the operation of all base stations or RRH described in the present invention can be equally applied to other types of transmission and reception points.

There is a radio interface protocol between a terminal and a transmission / reception point. Of course, the operation of all base stations or RRH described in the present invention can be equally applied to other types of transmission and reception points.

Layers of a radio interface protocol between a terminal and a transmission / reception point are based on the lower three layers of the Open System Interconnection (OSI) model, which is well known in a communication system. It may be divided into a second layer L2 and a third layer L3. Among them, the physical layer belonging to the first layer provides an information transfer service using a physical channel.

There are several physical channels used in the physical layer. The physical downlink control channel (PDCCH) includes a resource allocation and transmission format of a downlink shared channel (DL-SCH), a resource of an uplink shared channel (UL-SCH) Resource allocation of an upper layer control message such as allocation information, a random access response transmitted on a physical downlink shared channel (PDSCH), transmission power control for individual terminals in an arbitrary terminal group : TPC) commands, and so on. A plurality of PDCCHs can be transmitted in the control domain, and the UE can monitor a plurality of PDCCHs.

The control information of the physical layer mapped to the PDCCH is referred to as downlink control information (DCI). That is, the DCI is transmitted on the PDCCH. The DCI may include an uplink or downlink resource allocation field, an uplink transmission power control command field, a control field for paging, a control field for indicating a random access response (RA response), and the like.

DCI has different uses according to its format, and fields defined in DCI are also different. Table 1 shows DCIs according to various formats.

 Referring to Table 1, DCI format 0 is uplink scheduling information, format 1 for scheduling one PDSCH codeword, format 1A for compact scheduling of one PDSCH codeword, and very simple of DL-SCH. Format 1C for scheduling, format 2 for PDSCH scheduling in closed-loop spatial multiplexing mode, format 2A for PDSCH scheduling in open-loop spatial multiplexing mode, and uplink channel Formats 3 and 3A for transmission of a transmission power control (TPC) command.

Each field of the DCI is sequentially mapped to n information bits a0 to an-1. For example, suppose that DCI is mapped to information bits having a total length of 44 bits, each DCI field is sequentially mapped to a0 to a43. DCI formats 0, 1A, 3, and 3A may all have the same payload size. DCI format 0 may be called an uplink grant.

A radio frame includes 10 subframes. One subframe includes two slots. The time (length) of transmitting one subframe is called a transmission time interval (TTI). For example, one subframe may have a length of 1 ms, and one slot may have a length of 0.5 ms.

One slot may include a plurality of symbols in the time domain. For example, in a wireless system using orthogonal frequency division multiple access (OFDMA) in downlink (DL), the symbol may be an orthogonal frequency division multiplexing (OFDM) symbol. Meanwhile, the representation of the symbol period in the time domain is not limited by the multiple access scheme or the name. For example, the plurality of symbols in the time domain may be a Single Carrier-Frequency Division Multiple Access (SCFDMA) symbol, a symbol interval, etc. in addition to the OFDM symbol.

The number of OFDM symbols included in one slot may vary depending on the length of a cyclic prefix (CP). For example, in case of a normal CP, one slot may include 7 OFDM symbols, and in case of an extended CP, one slot may include 6 OFDM symbols.

A resource block (RB) is a resource allocation unit and includes a time-frequency resource corresponding to one slot on the time axis and 180 kHz on the frequency axis. For example, if one slot includes seven symbols on the time axis and 180 kHz on the frequency axis includes 12 subcarriers, one resource block may include 7 × 12 resource elements (REs). Can be.

The resource element represents the smallest time-frequency unit to which a modulation symbol of a data channel or a modulation channel of a control channel is mapped.

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, and the like. The process of restoring a transmission signal by compensating for distortion of a signal caused by a sudden change in channel environment is called channel estimation. It is also necessary to measure the channel state of the cell or other cell to which the terminal belongs. In general, a reference signal (RS) that is known between a terminal and a transmission / reception point is used for channel estimation or channel state measurement.

Since the UE knows the information of the reference signal, the terminal can estimate the channel based on the received reference signal and compensate the channel value to accurately obtain the data sent from the transmission / reception point. If p is the reference signal transmitted from the transmission / reception point, h is channel information experienced by the reference signal during transmission, n is thermal noise generated at the terminal, and y is the signal received at the terminal, such that y = h · p + n. have. In this case, since the reference signal p is already known by the terminal, when the LS (Least Square) method is used, channel information (

) Can be estimated.

[Equation 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.

The reference signal is generally transmitted by generating a signal from a sequence of reference signals. In the reference signal sequence, one or more of various sequences having excellent correlation characteristics may be used. For example, Zadoff-Chu (ZC) sequences, Constant Amplitude Zero Auto-Correlation (CAZAC) sequences, or pseudo-noise (PN) sequences such as m-sequences, Gold sequences, and Kasami sequences. It may be used as a sequence of reference signals, and various other sequences having excellent correlation characteristics may be used depending on the system situation. In addition, the reference signal sequence may be used by cyclic extension or truncation to adjust the length of the sequence, and may be various forms such as binary phase shift keying (BPSK) or quadrature phase shift keying (QPSK). May be modulated and mapped to a resource element (RE).

The downlink reference signal includes a cell-specific RS (CRS), a Multimedia Broadcast and Multicast Single Frequency Network (MBSFN) reference signal, a UE-specific RS (UE) -specific RS, and a positioning reference signal (PRS) RS and Channel State Information (CSI) reference signals (CSI-RS).

The CRS is a reference signal transmitted to all terminals in a cell and used for channel estimation. The CRS may be transmitted in all downlink subframes in a cell supporting PDSCH transmission.

The UE-specific reference signal is a reference signal received by a specific terminal or a specific terminal group in a cell, and may be called a demodulation RS (DM-RS) because it is mainly used for data demodulation of a specific terminal or a specific terminal group. have.

The MBSFN reference signal is a reference signal for providing a multimedia broadcast multicast service (MBMS), and the PRS may be used as a reference signal for position measurement of the terminal.

CSI-RS may be used for estimation of channel information. The CSI-RS is arranged in the frequency domain or the time domain. Channel quality indicator (CQI), precoding matrix indicator (PMI), rank indicator (RI), etc. may be used as channel information when necessary through channel state estimation using CSI-RS. It may be reported from the terminal. The CSI-RS may be transmitted on one or more antenna ports.

The uplink data channel (hereinafter referred to as "PUSCH") is transmitted in a region excluding the PUCCH and SRS regions of the system band. PUCCH includes ACK (Acknowledge) / NACK (Negative ACK) for HARQ (Hybrid Automatic Repeat reQuest) operation, RI (Rank Indicator), channel status information for downlink data scheduling, Precoding Matrix Indicator (PMI), and Channel Quality (CQI). Indication) information, and the like, and the SRS is a signal for acquiring uplink channel information for each user and adjusting uplink transmission timing for the entire system.

The feedback method of the channel state information includes a method of periodically transmitting using a PUCCH and a method of periodically transmitting using a PUSCH allocated for feedback according to a request of a transmission / reception point.

In the CoMP system, a plurality of cells or transmission / reception points may transmit a reference signal to the terminal.

As one example, the reference signal sequence in the CoMP system may be determined cell-specific. In particular, in a fourth scenario, in a CoMP environment in which the cell IDs of the transmission / reception points (eg, RRHs) that are set together with a specific transmission / reception point (eg, macro cells) are the same, within one macro cell, The same reference signal sequence is used for generation of the reference signal. This means that all of the transmit / receive points (eg, RRHs) belonging to the same set as the macro cell transmit the reference signal using the same reference signal sequence.

2 is a conceptual diagram of a CoMP system according to an embodiment of the present invention.

Referring to FIG. 2, the serving cells (or points) for the UE0 200, the UE1 205, the UE2 210, and the UE3 215 are the macro cell 220, the RRH1 225, and the RRH2 230, respectively. RRH3 (235). In addition, the bandwidth allocated for each UE in the UE0 200, the UE1 205, the UE2 210, and the UE3 215 overlaps each other in frequency with some or all of the bandwidth allocated for other UEs.

FIG. 3 illustrates one transmission / reception point and an antenna array structure of a terminal and a propagation channel according to the CoMP system of FIG. 1 or 2.

Referring to FIG. 3, each of the transmission / reception points illustrated in FIGS. 1 and 2, for example, the transmission / reception point 310 may include an antenna array 312 including two or more antennas. Although the transmission / reception point 310 is described as an example, other macro or micro base stations described with reference to FIGS. 1 and 2 may be the same. Likewise, the terminal 320 illustrated in FIGS. 1 and 2 may also include an antenna array 322 including two or more antennas.

In this case, the antenna arrays 310 may use a dual polarized antenna array in which two antennas having different polarizations are alternately installed to arrange more antennas in a limited space in a communication system. Antennas equally polarized in one polarity (direction) among the antennas included in the antenna arrays 312 are referred to as a first domain or a first antenna group 312a of a transmission / reception point (hereinafter referred to as a “first antenna group at a transmission / reception point”). Antennas equally polarized in the other polarity (direction) may be called a second domain or a second antenna group (312b, hereinafter referred to as a 'second antenna group of a transmit / receive point') of a transmit / receive point. But is not limited to these terms. In this case, the first antenna group 312a of the transmission / reception point and the second antenna group 312b of the transmission / reception point may be orthogonal, but are not limited thereto.

Similarly, the antenna arrays 322 included in the terminal 320 are dual polarized antenna arrays in which two antennas having different polarizations are alternately installed to arrange more antennas in a limited space in a communication system. ) Can be used. Antennas equally polarized in one direction among the antennas included in the antenna arrays 322 may be referred to as a first domain or a first antenna group 322a (hereinafter, referred to as a 'first antenna group of a terminal') of the terminal. And the same polarized antennas in the other direction may be referred to as a second domain or a second antenna group 322b (hereinafter, referred to as a “second antenna group of a terminal”) of the terminal, but is not limited thereto. At this time, the first antenna group 322a of the terminal and the second antenna group 322b of the terminal may be orthogonal, but are not limited thereto.

In the above embodiment, a dual polarization antenna array has been described as an example, but the present invention is not limited thereto. For example, it may be a multi-polarized antenna array such as a triple polarized wave or a quadrupole polarized antenna array. In addition, the transmitting and receiving point and the terminal is not limited to including a multi-polarized antenna array such as a single polarized antenna, and may include two or more multi-polarized antenna arrays, a single array antenna (linear array antenna), a combination thereof. In this case, the transmitting and receiving point and the terminal may use all of two or more multipolarization antenna arrays, or some of them may be selectively used.

Meanwhile, the transmission / reception point 310 may perform dual structure precoding as described later in downlink transmission. In this structure, W ₁ and W ₂ constituting the precoding matrix may be transferred from the terminal 320 to the transmit / receive point 310 through PMI1 or PMI2 which are different precoding matrix indicators, respectively. Can be.

W ₁ may be a precoder matrix selected for the entire system bandwidth. On the other hand, W ₂ is selected as one precoding matrix for the entire system bandwidth or one precoding matrix for each subband, which is a subset of the system band. ) May be selected.

In other words, W ₁ is a precoating matrix determined by receiving feedback of channel information applied to the entire OFDMA band in a long cycle for each terminal, and means a transmission direction from a transmission / reception point to a corresponding terminal. Changing the transmission direction of the transmission / reception point according to the movement of the terminal does not occur frequently in a short time, and thus performance deterioration is small even when fed back at a long period. W2 is a precoding matrix determined by feeding back subbands of several resource blocks (RBs) in a short cycle with more detailed channel information. That is, W ₁ selects and co-phasses codewords to feed back channel information regardless of a uniform linear array antenna (ULA) or cross-polarized antenna (CPA) structure.

In other words, the terminal 320 may report one W ₁ and a plurality of W ₂ generally within a reporting period, and one digital index indicating W ₁ for all bands to which the terminal 320 intends to receive a signal. Report PMI1 to the transmit / receive point 310 and divide the entire band into several subbands, and then transmit / receive the digital factor values PMI2 determined to be suitable for use as W ₂ in each subband. You can report to The reason for using this method is to perform precoding using a different precoder matrix for each subband. In order to use a different precoder matrix for each subband, W ₁ and W ₂ may have a structure as follows.

&Quot; (2) "

W = W ₁ * W ₂

In Equation 1, W ₁ is [X _n 0; 0 x _n ] block diagonal matrix. W ₂ is a matrix that performs beam selection and performs co-phasing to correct for phase mismatch between antenna groups.

For example, when performing rank 1 and 2 transmissions, the precoding matrix W ₁ indicated by the digital index n may be as follows.

&Quot; (3) "

In this case, W ₁ ^(K) is a block diagonal matrix as follows.

&Quot; (4) "

At this time

Where X ^(K) is

to be.

X ^(K) divides 360 ° into 32 directions and includes four direction information (UE-selected codebook) among them.

Therefore, the precoding matrix W ₁ indicated by the digital index n may be as follows.

[Equation 5]

In this case, b _n is beam forming vectors that perform beam forming, and may perform beam forming according to a signal transmission and reception direction.

Is a column vector of zeros and the same size as b _n .

In particular, adjacent overlapping beams at b _n of W ₁ , for example four adjacent beams, can be used to reduce the edge effect in frequency selective procoding. For convenience, in the present specification, a case _where the size of b _n is 4 will be described as an example. The size of b _n is not limited to four.

That is, in the case of rank 1 and rank 2, the codebook is an index for selecting four adjacent beam forming vectors, and the codebook is expressed as an index of the beamforming vector selected according to PMI1 of the codebook.

Therefore, 16 W ₁ matrices for each rank are expressed only by the indices of the beams, so that a total of 16 (4 bits) in which two direction information superimpose different beamforming vectors, that is, [0, 1, 2, 3], [ 2,3,4,5], [4,5,6,7], ..., [28,29,30,31], [30,31,0,1]. In this case, although the beams are described as being adjacent, the present invention is not limited thereto, and the W ₁ matrix may be formed of non-adjacent beams.

Meanwhile, in the W ₁ matrices, two beamforming vectors may overlap each other. For example, [2,3] overlaps with [0,1,2,3] and [2,3,4,5].

In this case, W ₁ may coincide with the spatial covariance of the dual polarized antenna array polarized at a constant distance.

In this case, b _n are beam forming vectors that perform beam forming, and may be expressed as in the following equation.

[Equation 6]

the magnitude of b _n as a simple example of less than 4, in the form of W ₁ according to the PMI1 = n = 2 to refer to the precoder matrix W ₁ may be set as follows.

[Equation 7]

That is, each element of the codebook for reporting W ₁ may be composed of a combination of a plurality of beam forming vectors.

In the case of a transmission stage including 8 antennas, if 32 beamforming vectors are represented by beam indices n of 0 to 31, they are converted into column vectors.

May be the same as

W ₂ simultaneously performs a process of selecting r of a plurality of beam forming vectors included in W ₁ ^(K) and a co-phasing operation. In other words, the codebook of W ₂ (in the case of rank 1 transmission), one of the vectors of four beamforming selection by W ₁ or 2 for repeated selection (in the case of Rank 2 transmission) performs the task of, and at the same time each Determines the co-phase element applied to the beamforming vectors to be used for the transmit antenna group (or domain).

When performing rank 1 transmission, W ₂ may be defined as in the following equation.

&Quot; (8) "

In this case, Y is a beam selection vector for performing beam selection.

Is a co-phase element that performs a phase matching operation, and may be, for example, 1 or -1, j, -j.

That is, when performing rank 1 transmission, W ₂ is

For example, 1 or -1, j, -j can be defined as the following equation.

&Quot; (9) "

At this time

Is a 4 × 1 selection vector with a value of 1 for the nth component and a value of 1 for the remaining components.

Therefore, Y can be defined as follows.

&Quot; (10) "

In case of performing rank 2 transmission, W ₂ may be defined as follows.

[Equation 11]

That is, when performing rank 2 transmission, W ₂ is

For example, 1 or -1, j, -j can be defined as the following equation.

[Equation 12]

In this case, Y ₁ and Y ₂ are beam selection vectors for performing beam selection.

Is a phase matching element value for performing the phase matching operation, and may be, for example, 1 or -1, j, -j.

At this time, Y ₁ selects a beamforming vector to be used for the first layer transmission when the value of PMI2 indicating W ₂ is a from 4 beamforming vectors selected by W ₁ , and Y ₂ is W. _When the value of PMI2 indicating ₂ is a, a beamforming vector to be used for the second layer transmission is selected from four beamforming vectors selected by W ₁ .

Y ₁ and Y ₂ may be defined as follows.

&Quot; (13) "

That is, Y ₁ , Y ₂ are column vectors of length 4 with one value equal to 1 and the other equal to zero.

In other words, for rank 2

When the beamforming vector selected through W ₁ and Y ₁ is applied to the transmitting antenna group (domain), the phase matching element value and the beam forming vector determined by W ₁ and Y ₂ are transmitted antenna group Z _1. And a phase match element value to be used when applied to Z ₂ , for example, from (1, j).

[Equation 14]

Therefore, when performing rank 1 transmission, W may have the following structure.

[Equation 15]

In the following equations, the relationship between the terminal and the nth transmission / reception point is represented by a superscript n. For example, the relationship between the terminal and the first transmission / reception point is represented by superscript 1, and the relationship between the terminal and the second transmission / reception point is represented by superscript 2.

In case of performing rank 2 transmission, W may have a structure as follows.

[Equation 16]

On the other hand, the channel matrix or the propagation channel between the transmission and reception point 310 and the terminal 320

Let's say. Where the precoding matrix is rank1

Precode using to

When transmitted to the horse 320, the signal received from the terminal 320 is

.

On the other hand, the precoding matrix with rank 2 or higher, for example rank 2

Precode the signal to

When transmitting to the terminal 320, the signal received at the terminal may be as follows.

[Equation 17]

In this case, R _b means a signal received by the first antenna group 322a of the terminal, and R _r means a signal received by the second antenna group 322b of the terminal.

In the case of rank 3 and 4 transmission, the W ₁ codebook divides 360 ° into 16 directions and includes 8 direction information among them. In the case of rank 3 and 4 transmission, the W ₁ codebook is summarized as follows.

Equation 18

The transmission and reception points described above with reference to FIG. 3, for example, the transmission and reception point 310 and the terminal 320 each include an antenna array 312 and an antenna array 322 including two or more antennas, and an antenna array 312. And the antenna array 322 have been described as using a multi-polarized antenna array, for example, a dual polarized antenna array, provided by crossing two antennas having different polarizations. Also, the transmit / receive point 310 and the terminal 320 may include two or more multipolarized antenna arrays and a single array antenna, without being limited to including a multipolarized antenna array such as one dual polarized antenna. have.

The transmission / reception point 110 may use a linear array antenna using four transmission antennas, and the terminal 120 may use a linear array antenna using two transmission antennas. At this time, the transmission and reception point 110 may perform a single precoding (W).

In this structure, W, which constitutes a precoding matrix, is transmitted and received from the terminal 320 through PMI, which is a precoding matrix indicator of the codebook of Table 2.

May be delivered to the insert 310.

Meanwhile, in a wireless communication system, channel resources for feedback of channel information are limited in consideration of limited uplink resources. Table 1 shows a codebook of limited PMI for downlink data scheduling for four transmission antennas.

Meanwhile, the transmission / reception point may be an RRH using four polarized antennas. In this case, in the case of rank 1 and 2 transmission, W ₁ may divide 360 ° into eight directions as shown in FIG. 8 and include four direction information (four beamforming vectors) among them. In this case, a total of four codebooks in which two direction information (two beamforming vectors) are superposed between the codebooks of each W ₁ may exist as in the following equation.

[Equation 19]

However, the above-described codebooks designed for a single transmission / reception point are not sufficient for precoding that cooperative transmission / reception points must be used in an integrated cooperative transmission method between high transmission and reception points.

That is, when only the codebook for one transmission / reception point described in the above equations or Table 1 is used, coherent coupling of channels between transmission / reception points is impossible in cooperative transmission between transmission / reception points, thereby improving performance of a reception signal. You can limit it. In addition, the gain of the received signal may vary depending on how the codebook is used for the cooperative transmission / reception points.

Accordingly, various extended codebook designs and utilization methods for improving the gain of the received signal of the cooperative transmission between the transmission and reception points can be considered, but at this time, additional feedback information for the cooperative transmission between the transmission and reception points can be transmitted. As such, there is a need to reduce an increase in feedback overhead of channel information involved for cooperative transmission between transmission and reception points.

By limiting user's indiscriminate use of the CQI channel, collision between adjacent cells is reduced, thereby reducing multicarrier-to-interference-plus-noise ratio (CINR) attenuation of the CQI channel, thereby obtaining multi-user diversity gain.

In this case, the channel information feedback method according to the embodiments described below may limit a user's channel information reporting by setting a specific channel quality threshold or channel quality threshold (CQT) in order to obtain a multi-user diversity gain. That is, the CQI channel may be used for channel information reporting only when the channel quality value of the user is greater than or equal to the CQT.

4 is a conceptual diagram of cooperative communication of each transmission / reception point in a CoMP system according to an embodiment.

Referring to FIG. 4, in the cooperative multi-cell communication system 400 according to an exemplary embodiment, as shown in FIGS. 2 and 3, transmission / reception points 410, 412, 414, and 416 and a terminal perform cooperative communication. Can be done. In this case, only transmission / reception points 410, 412, 414, and 416 are described as transmission / reception points participating in cooperative communication. However, as described above, two, three, five or more transmission / reception points may be used for cooperative communication with the terminal. You can also participate.

Each of the transmit / receive points 410, 412, 414, 416 may include antenna arrays including antennas polarized into two antenna groups as described with reference to FIG. 3, or may include a linear polarized array.

The transmit / receive points 410, 412, 414, and 416 precode data symbols using their precoding matrix and transmit 2n precoded data symbols (n is 1 or a natural number greater than 1) through the antenna array. Can propagate into the air.

Meanwhile, the transmit / receive points 410, 412, 414, and 416 may use a dual structure precoding (precoder) matrix represented by W = W ₁ * W ₂ , or a single structure precoding (precoder) matrix. It may be. In this case, the transmission / reception points 410, 412, 414, and 416 precode data symbols using their precoding matrix using channel information received from the UE, for example, CQI / PMI / RI. 2n precoded data symbols (n is 1 or a natural number greater than 1) may propagate into the air through the antenna array.

5 is a flowchart illustrating a cooperative communication method of transmission / reception points of a terminal and a CoMP system according to another embodiment.

Referring to FIG. 5, in the cooperative communication method of transmitting / receiving points with a terminal of a CoMP system according to another embodiment, the terminal 420 transmits signals transmitted from each of the transmitting and receiving points 410, 412, 414, and 416. For example, reference signals may be received (S510, S512, S514, and S516). As described below, signal strength of each transmit / receive point 410, 412, 414, 416 is measured by using reference signals transmitted from the transmit / receive points 410, 412, 414, and 416. However, the present invention is not limited thereto and may use any signal transmitted from each transmit / receive point 410, 412, 414, 416 to measure the strength of the signal at each transmit / receive point 410, 412, 414, 416. have.

In this case, the CoMP system according to another embodiment is a cooperative multi-cell communication system 400 described with reference to FIG. 4, but is not limited thereto. Of course, the transmission and reception points participating in the cooperative communication may be four as shown in FIG. 5, but the present disclosure is not limited thereto and may be two, three, five, or more. However, for convenience of description, transmission and reception points participating in the cooperative communication will be described as the first to fourth transmission and reception points 410, 412, 414, and 416 as shown in FIG. 5.

In the cooperative transmission method between transmission and reception points, the terminal 420 transmits and receives point selection measurement values with all transmission and reception points 410, 412, 414, and 416 in a CoMP set of cooperative transmission / reception points using the aforementioned reference signals, For example, an instantaneous received signal strength or a received signal strength indicator (hereinafter referred to as “RSSI”) is measured (S518). RSSI is a measure of the power present in the received unsigned signal. In this case, the transmission and reception point selection measurement values are described as searching and selecting transmission and reception points to feed back channel information by using received signal strength, but are not limited to the reception signal strength. You can also use the form of measurement information. For example, the transmission / reception point selection measurement may search for and select transmission / reception points for feeding back channel information based on SNR or SINR from transmission / reception points. The aforementioned transmission / reception point selection measurement value may refer to channel quality such as carrier-to-interference-plus-noise ratio (CINR) of the channel.

One of the transmission / reception points 410, 412, 414, and 416, for example, the serving transmission / reception point 410 may set a relative threshold limiting the feedback of channel information for cooperative transmission. It may transmit to the terminal 420 through the control channel. This relative threshold may be the same or different for each terminal.

Using the instantaneous RSSI (Received Signal Strength Indicator, Received Signal Strength or Received Field Strength) with all the transmit and receive points (410, 412, 414, 416), select the transmit / receive point that provides the highest RSSI and refer to the highest RSSI. In operation S519, transmission and reception points, for example, first and second transmission and reception points 410 and 412, which provide RSSI within a predetermined threshold are selected. In operation S519, transmission / reception points may be selected in consideration of a threshold value, which will be described below in detail with reference to FIG. 7. In other words, at least one transmission / reception point channel information providing a channel quality value within a threshold value based on the largest size among channel quality values (signal strength) received from the cooperative transmission / reception points is fed back.

In addition, the serving transmission / reception point 410 may further transmit the maximum feedback possible transmission / reception point number to the terminal 420 through the RRC signaling and the downlink control channel together with the threshold value. The number of feedback points available for transmission and reception may be the same or different for each terminal. In operation S519, transmission and reception points may be selected in consideration of the maximum number of transmission and reception points that can be fed back together with a threshold, which will be described in detail below with reference to FIG. 8.

In addition, the serving transmission / reception point 410 transmits the preset antenna grouping information together with the threshold value to the terminal 420 through the RRC signaling and the downlink control channel. Antenna grouping may be the same for each terminal or may be different. In operation S519, transmission and reception points may be selected in consideration of antenna grouping information together with a threshold, which will be described in detail with reference to FIG. 9.

Thereafter, the terminal 420 may estimate channel states or channel matrixes for each antenna of the selected first and second transmission and reception points 410 and 412 using the received reference signals (S520). For example, the terminal 420 may estimate the downlink channel during downlink transmission. In particular, when transmitting an OFDM or Orthogonal Frequency Division Multiple Access (OFDMA) signal, the UE 420 may estimate a channel of each subband.

Thereafter, the terminal 420 grasps each channel state or channel matrix of the selected first and second transmission and reception points 410 and 412, and then directly or indirectly obtains channel information or channel state information related thereto. It feeds back to the first transmission and reception point 410 corresponding to the serving transmission and reception point or the main transmission and reception point (S530).

The first transmission / reception point 410 that receives the channel information from the terminal 420 may transfer channel information of another transmission / reception point to a corresponding transmission / reception point through a specific interface, for example, an X2 interface (S532). When the first transmission / reception point 410 and the second transmission / reception point 412 are the macro base station and the RRH, the first transmission / reception point 410 which is the macro base station may manage the information of the second transmission / reception point.

In addition, it is possible to feed back instantaneous channel information for a particular antenna group of the multiple transmit antennas of the selected cooperative first and second transmit / receive points 410 and 412. That is, the terminal 420 may only feed back channel information for the designated antenna group in each of the selected cooperative first and second transmission / reception points 410 and 412.

In this case, the channel information CSI1 and CSI2 may be a propagation channel or indicators or indexes indicating factors suitable for the propagation channel, as shown in FIG. 4, for example, PMI1 and PMI2. The channel information may be a Channel Quality Indicator (CQI) or a Rank Index (RI).

The first transmission / reception point 410 or higher layer which received the feedback of the channel information selects transmission / reception points showing good channel performance to form a cooperative transmission / reception point set or a CoMP set, and includes them in the cooperative transmission / reception point set or a CoMP set. At least one transmit / receive point, for example, the second transmit / receive point 412, may be selected.

The feedback method of channel information includes a method of periodically transmitting using a PUCCH and a method of periodically transmitting using a PUSCH allocated for feedback according to a request of a transmission / reception point.

Thereafter, the first transmission / reception point 410 and the second transmission / reception point 412 may perform cooperative communication with the terminal 420 (S540 and S542). When the number of transmission / reception points participating in the cooperative communication is three or more, the three or more transmission / reception points and the terminal 420 perform the cooperative MIMO communication.

However, in the cooperative multi-cell communication method described with reference to FIG. 5, even if two or more transmission / reception points (S410 and 412) for transmitting signals are transmitted to or received from the terminal, the transmission / reception point is transmitted to the serving transmission / reception point or the main transmission / reception point. There may be one corresponding first transmission / reception point 410.

6 is a flowchart of a channel information feedback method in a CoMP system according to another embodiment.

Referring to FIG. 6, the channel information feedback method 600 in a CoMP system according to another embodiment feeds back channel information using a relative threshold value of a maximum RSSI criterion in a cooperative transmission method between transmission and reception points.

Referring to FIG. 6, first, the terminal 420 obtains a relative threshold limiting feedback of channel information for cooperative transmission from at least one of transmission / reception points, for example, the serving transmission / reception point 410 (S610). . In operation S610, the terminal 420 may receive the relative threshold value from the serving transmission / reception point 410 to obtain the relative threshold value.

Here, the relative threshold may be in dB unit. The serving transmission / reception point 410 may transmit a relative threshold limiting feedback of channel information for cooperative transmission to the terminal 420 through an RRC signaling and a downlink control channel. This relative threshold may be the same or different for each terminal.

Next, the terminal 420 acquires the RSSI for all cooperative transmission / reception points 410, 412, 414, and 416 and searches for a transmission / reception point providing the maximum RSSI value and the maximum RSSI (S620). For example, the transmission / reception point providing the maximum RSSI may be the first transmission / reception point 410 serving as the serving transmission / reception point or the second transmission / reception point 412 which is the RRH nearest to the terminal.

Next, the terminal 420 searches for cooperative transmission / reception points in which the ratio of the maximum RSSI to the RSSI of each cooperative transmission / reception point is larger than the relative threshold (S630). For example, the RSSIs of all cooperative transmit / receive points 410, 412, 414, and 416 search for transmit / receive points larger than a threshold obtained at S610, for example, first and second transmit / receive points 410 and 412. can do.

Next, the terminal 420 periodically or non-receives the information of the selected cooperative transmission / reception points 410 and 412 and the channel information about the selected cooperative transmission / reception points 410 and 412, for example, RI, PMI, and CQI information. Periodically, transmission is performed on an uplink channel of one subframe, for example, PUCCH or PUSCH, or is distributed and transmitted on uplink channels of a plurality of subframes, for example, PUCCH or PUSCH (S640).

In step S640, the terminal 420 feeds the information and channel information of the cooperative transmission / reception points selected to the serving transmission / reception point 410 and the total number of bits used for the channel information to the index and channel information of the cooperative transmission / reception points. For example, 11 bits may be represented, and indexes and channel information of selected cooperative transmission / reception points may be separately expressed. In the latter case, the reserved value of the existing field may be utilized or the cell ID may be expressed in a map form.

Meanwhile, although the channel information of the selected transmission / reception points may be separately fed back, two or more transmission / reception points may be combined to form one channel information, and the combined channel information may be fed back to the serving transmission / reception point 410. have. For example, when the number of ranks of the first transmission / reception point 410 is two and the number of ranks of the second transmission / reception point 412 is two, the precoding matrix of the optimal rank 4 is selected and the precoding matrix index of the rank 4 (combined PMI). ) May be fed back to the serving transmit / receive point.

7 is a flowchart of a channel information feedback method in a CoMP system according to another embodiment.

Referring to FIG. 7, in the CoMP system according to another embodiment, the channel information feedback method 700 feeds back channel information by using a relative threshold value of the maximum RSSI criterion and the maximum number of transmit / receive points that can be feedback in a cooperative transmission method between transmit / receive points. .

Referring to FIG. 7, first, a terminal 420 may determine a relative threshold limiting channel information feedback for cooperative transmission from transmission / reception points 410, 412, 414, and 416 and a maximum number of feedback transmission / reception points N. Acquire (S710). In operation S710, the terminal 420 may receive the relative threshold value and the maximum number of transmission / reception points N from the serving transmission / reception point 410 to obtain this relative threshold.

Here, the relative threshold may be in dB unit. As described above, the relative threshold value and / or the maximum number N of feedback points that can be fed back may be the same or different for each terminal.

Next, the terminal 420 acquires the RSSI for all cooperative transmission / reception points 410, 412, 414, and 416 and searches for a transmission / reception point providing the maximum RSSI value and the maximum RSSI (S720).

Next, the terminal 420 searches for cooperative transmission / reception points having a ratio of the maximum RSSI to the RSSI of each cooperative transmission / reception point greater than a relative threshold (S730). For example, the RSSIs of all cooperative transmit / receive points 410, 412, 414, and 416 search for transmit / receive points larger than a threshold obtained at S710, for example, first and second transmit / receive points 410 and 412. can do.

Next, the terminal 420 compares the selected number of cooperative transmission / reception points with the maximum number of feedback transmission / reception points (N) (S732).

If the number of cooperative transmission / reception points selected in step S730 is greater than the maximum number of feedback possible transmission / reception points (N, N is a natural number greater than 1), the terminal 420 may transmit N cooperative transmission / reception points among the selected transmission / reception points. Select (S734). In step S734, the terminal 420 may select N cooperative transmission / reception points providing a relatively high RSSI among the selected transmission / reception points. For example, if the number of cooperative transmit / receive points selected in step S730 is three and the maximum number of feedback possible transmit / receive points (N) obtained in step S710 is two, the terminal 420 provides two relatively high RSSIs among the selected transmit / receive points. Cooperative transmission and reception point can be selected.

In this case, when the terminal 420 selects the N cooperative transmission / reception points, in step S730, since the ratio of the maximum RSSI to the RSSI is selected as the transmission / reception points larger than the relative threshold, the terminal 420 does not select the N cooperative transmission / reception points in the order of the high RSSI, or randomly or differently. N cooperative transmission / reception points may be selected as a reference.

Then, the terminal transmits channel information, for example, RI, PMI, CQI information for the selected N cooperative transmission and reception points on an uplink channel of one subframe, for example, PUCCH or PUSCH periodically or aperiodically. In operation S740a, the uplink channels of the plurality of subframes are distributed to, for example, PUCCH or PUSCH.

If the number of selected cooperative transmit / receive points is smaller than the maximum number of feedback transmit / receive points (N), the terminal 420 may periodically or aperiodically perform an uplink channel of one subframe for all selected cooperative transmit / receive points, for example. The transmission is performed on the PUCCH or the PUSCH, or transmitted in uplink channels of a plurality of subframes, for example, in the PUCCH or the PUSCHs (S740b).

In step S740a or step S740b, the terminal 420 feeds back information and channel information of the cooperative transmission / reception points selected to the serving transmission / reception point 410 may be the same as operation S640 described with reference to FIG. 6.

8 is a flowchart of a channel information feedback method in a CoMP system according to another embodiment.

Referring to FIG. 8, in the CoMP system according to another embodiment, the channel information feedback method feeds back channel information by using a relative threshold value of the maximum RSSI criterion and antenna grouping in a cooperative transmission method between transmission and reception points.

Referring to FIG. 8, first, a terminal acquires a relative threshold value and antenna grouping information for limiting channel state feedback for cooperative transmission from a transmission / reception point (S810). In operation S810, the terminal 420 may receive the relative threshold value and the antenna grouping information from the serving transmission / reception point 410 to obtain the relative threshold value and the antenna grouping information. Here, the relative threshold may be in dB unit.

9A illustrates an example of antenna grouping into two groups for four single arrays of transmit antennas. 9A shows antennas 1 and 2 as one group, and antennas 3 and 4 are set as different groups. In FIG. 9A (b), antennas 1 and 3 are set as one group, and antennas 2 and 4 are set as another group. In FIG. 9A (c), antennas 1 and 4 are set as one group, and antennas 2 and 3 are set as another group.

9B shows an example of antenna grouping into two groups in the case of a transmit antenna of eight dual polarized antenna arrays. FIG. 9B shows four antennas of the same polarization as one group and four antennas of the same polarization as the other group. (B) of FIG. 9B sets two neighboring polarized pair antennas into one group and sets two other neighboring polarized pair antennas into another group. In this case, two non-neighboring polarization pair antennas may configure one group. In the case of a transmission antenna of four dual polarization antenna arrays, antenna groups may be set as shown in FIG. 9B.

As such, the preset grouping information is transmitted to the UE through the RRC signaling and the downlink control channel. Antenna grouping may be the same for each terminal or may be different.

Meanwhile, when the terminal 420 includes two or more antennas, the terminal 420 may also perform antenna grouping in the same manner as the transmission and reception points. Therefore, the relationship between the antenna group of the transmission and reception point and the terminal below should be understood to include the relationship between the antenna group of the transmission and reception point and the antenna group of the terminal.

Next, the terminal 420 acquires RSSI for each antenna group with all cooperative transmission / reception points, and then searches for transmission / reception points and antenna groups providing the maximum RSSI value and the maximum RSSI (S820).

Next, the terminal 420 searches for a cooperative transmission / reception point and an antenna group in which the ratio of the maximum RSSI to the RSSI of each cooperative transmission / reception point is larger than the relative threshold (S830). For example, the RSSIs of the antenna groups of all cooperative transmit / receive points 410, 412, 414, and 416 are larger than the antenna groups of transmit / receive points larger than the threshold obtained in S810, for example, the group of the first transmit / receive point 410. Group 2 of the first and second transmission and reception points 412 may be searched.

Next, the terminal 420 periodically or aperiodically transmits the antenna group indicator and channel information, for example, RI, PMI, and CQI information, for all selected cooperative transmission / reception points, for example, an uplink channel, for example. The transmission is performed on the PUCCH or the PUSCH, or distributed in uplink channels of a plurality of subframes, for example, on the PUCCH or the PUSCH (S840).

The method of feeding back the grouping information and the channel information of the cooperative transmission / reception points selected by the terminal 420 to the serving transmission / reception point 410 in operation S840 may be the same as operation S640 described with reference to FIG. 6.

In the cooperative transmission method between the transmission and reception points described with reference to FIG. 8, the feedback method using the relative threshold value of the maximum RSSI reference and the antenna grouping may be used in combination with the feedback method using the maximum number of feedback possible transmission and reception points described with reference to FIG. 7. . In other words, the terminal may search for the number of antenna groups of the transmission / reception points using the maximum number of antenna groups of the transmission / reception points and transmit channel information of the antenna groups of the transmission / reception points to the serving transmission / reception point.

10 is a flowchart illustrating a method of determining a relative threshold value using an average RSSI of cooperative transmission / reception points in a CoMP system and transmitting the same to a terminal.

Referring to FIG. 10, the serving transmission / reception point receives RSSIs measured for the cooperative transmission / reception points including the serving transmission / reception point from the terminal 420 (S1010).

The transmission / reception point calculates an average RSSI for each transmission / reception point (serving transmission / reception point and cooperative transmission / reception point) from the received RSSIs. The difference between the maximum average RSSI and the minimum average RSSI among the average RSSIs is determined as a relative threshold value (S1020).

When the number of cooperative transmission / reception points is large, the number of cooperative transmission / reception points may be limited to N, and a relative threshold may be determined as a difference between the maximum average RSSI and the Nth largest average RSSI.

In addition, when the number of cooperative transmission / reception points and terminals increases or increases in the system, resulting in excessive feedback overhead, the feedback may be further limited by multiplying the relative threshold determined by the aforementioned feedback method by a weight of a value greater than 0 and less than 1. Can be. Here, the weight may be determined by the inverse of (number of cooperative transmission / reception points * number of users).

The transmission and reception point transmits the determined relative threshold value to the terminal 420 (S1030). This relative threshold may be used to search for transmission / reception points, which are objects to which the channel information described with reference to FIGS. 5 to 8 is fed back.

11 is a flowchart illustrating a method of determining and transmitting a relative threshold value using a standard deviation of RSSI of cooperative transmission / reception points in a CoMP system according to another embodiment.

Referring to FIG. 11, the serving transmission / reception point receives signal strengths, for example, RSSIs, measured for the cooperative transmission / reception points including the serving transmission / reception point from the terminal 420 (S1110).

The transmit / receive point calculates the standard deviation of RSSI for each transmit / receive point (serving transmit / receive point and cooperative transmit / receive point) from the RSSIs. The average standard deviation is calculated by dividing the sum of the standard deviations of the RSSI by the number of cooperative transmission / reception points. Then, the average standard deviation is determined as a relative threshold value (S1120).

Here, the standard deviation can be calculated from all RSSIs for all cooperative transmission / reception points and serving transmission / reception points without averaging the standard deviation for each transmission / reception point, and the standard deviation can be determined as a relative threshold.

When the number of cooperative transmission / reception points is large, the number of cooperative transmission / reception points may be limited to N. In this case, the serving transmission / reception point calculates an average RSSI for each transmission / reception point using the RSSI received from the terminal. Using the average RSSIs, the relative thresholds can be determined by arranging the transmit / receive points in order of the largest average RSSI and then calculating the standard deviation of the RSSI as described above by considering only the transmit / receive points providing the Nth largest average RSSI. have.

In addition, if the number of cooperative transmission / reception points and users in the system increases or increases, resulting in excessive feedback overhead, the feedback may be further limited by multiplying the relative threshold determined by the aforementioned method by a weight of a value greater than 0 and less than 1. have. Here, the weight may be determined by the inverse of (number of cooperative transmission / reception points * number of users).

On the other hand, using the RSSI received from the terminal, the transmission and reception point may determine the relative threshold by mixing and / or adjusting the above two methods. However, when the reception period of the RSSI received from the terminal is very long, the transmission / reception point may request transmission of the RSSI information from the terminal in order to determine or adjust the relative threshold. This may be the same as a method in which a transmission / reception point further requests channel information, for example, RI, PMI, and CQI.

In this method, when a transmitting / receiving point further requests channel information, for example, RI, PMI, and CQI information, the RI, PMI, and CQI information are mapped to the PUSCH region allocated by the transmitting / receiving point in a predetermined order and transmitted to the transmitting / receiving point. . As such, when the transmission / reception point requests additional RSSI information, the terminal may transmit the RSSI information to the allocated PUSCH region. In this case, the RSSI information may be transmitted together with RI, PMI, and CQI in the PUSCH region, and may be mapped to the region closest to the reference signal among regions except for the region where the RI, PMI, and CQI are mapped. This is to minimize the error of the channel estimate value used when decoding RSSI information.

12 is a block diagram illustrating a terminal and a transmission / reception point according to another embodiment.

Referring to FIG. 12, the terminal 1300 includes a terminal RF unit 1205 and a terminal processor 1210.

The terminal processor 1210 measures the RSSI with the cooperative transmission / reception point, searches for the RSSI in the threshold and the corresponding transmission / reception point, selects transmission / reception points in consideration of the number of transmission / reception points that can be fed back, and if necessary, an antenna group of transmission / reception points. Selects and generates channel information about a specified transmission / reception point and a specified antenna group in the terminal.

In more detail, the terminal processor 1210 may search for an RSSI measurement unit 1212 that measures RSSI with a cooperative transmission / reception point, a search for a maximum RSSI, a search for a maximum RSSI, a transmission / reception point, and search for and feedback a RSSI within a threshold and a corresponding transmission / reception point. A transmit / receive point selector 1214 that selects transmit / receive points in consideration of the number of transmit / receive points, an antenna group selector 1216 that selects an antenna group of transmit / receive points, a designated transmit / receive point at a terminal, and channel information about a designated antenna group, eg For example, all or part of the channel information generator 1218 generating at least one of RI, PMI, and CQI.

The method of selecting the transmit / receive point and antenna group by the transmit / receive point selector 1214 and the antenna group selector 1216 may be the same as those described above with reference to FIGS. 5 to 11.

The channel information generator 1218 identifies a reference signal specific to the terminal 1200 by using the obtained reference signal sequence, and performs downlink channel estimation based on the reference signal specific to the terminal 1200.

The terminal RF unit 1205 receives all information or signals, such as downlink control information, a reference signal, and a data signal, from the transmission / reception point 1250. The transmission / reception point 1250 may be a macro cell described with reference to FIGS. 1 and 2, or may be an RRH. The transmission / reception point 1250 may be an entity communicating with the terminal 1200 in a cooperative set with other transmission / reception points (not shown).

The terminal RF unit 1205 transmits channel information of the transmission / reception point and / or antenna group selected by the terminal processor 1210 to the transmission / reception point 1250.

The transmission / reception point 1250 includes a transmission / reception point RF unit 1255 and a transmission / reception point processor 1260.

The transmit / receive point processor 1260 generates a relative threshold value, generates a maximum feedback possible transmit / receive point number as needed, and generates antenna group information as needed.

The transmit / receive point processor 1260 may include a threshold value generator 1262 for generating a relative threshold value of the maximum RSSI reference, a transmit / receive point number determiner 1264 for generating the maximum number of transmittable / receivable points, and an antenna group for generating antenna group information. The generator 1268 includes all or part of the generator.

Each operation or operation of the threshold value generator 1262, the transmission / reception point number determination unit 1264, and the antenna group generation unit 1268 may constitute a part of the operation or operation of the terminal described with reference to FIGS. 5 to 11. Can be.

The transmission / reception point RF unit 1255 transmits all information or signals, such as downlink control information, RRC signaling, and data signals, to the terminal 1200. The transmit / receive point RF unit 1255 may transmit the relative threshold value and / or the maximum number of transmit / receive point and antenna group information generated by the transmit / receive point processor 1260 to the terminal 1200.

The method and apparatus for selectively feeding back channel information on cooperative transmission / reception points when supporting cooperative transmission between transmission / reception points described above may transmit and receive only channel information limited to cooperative transmission / reception points or antenna groups that are likely to be substantially used in data scheduling. Feedback overhead can be minimized while preserving the gains from point-to-point cooperative transmission. Therefore, it is possible to maximize the capacity increase effect obtained by the cooperative transmission between the transmission and reception points.

The foregoing description is merely illustrative of the technical idea of the present invention, and various changes and modifications may be made by those skilled in the art without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the scope of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The protection scope of the present invention should be interpreted by the following claims, and all technical ideas within the equivalent scope should be interpreted as being included in the scope of the present invention.

Claims (22)

In a wireless communication system in which two or more transmission and reception points and the terminal cooperative communication,
Measuring the strength of a signal received from the two or more transmission / reception points;
Searching for one or more transmission / reception points whose strength of the measured signal is greater than a predetermined threshold; And
And transmitting the channel information of the searched transmission / reception point to the terminal. The method of claim 1,
The signal strength is a feedback method of the channel information of the terminal, characterized in that the RSSI (Received Signal Strength Indicator). The method of claim 1,
And searching for at least one transmit / receive point providing an RSSI larger than a predetermined threshold value based on the highest RSSI in the search for the transmit / receive point. The method of claim 1,
Measuring the strength of the received signal, measuring the strength of a signal received from at least one antenna group of the two or more transmission / reception points,
Searching for one or more transmission / reception points, searching for an antenna group of one or more transmission / reception points whose measured signal strength is greater than a predetermined threshold,
In the step of transmitting to the terminal, the channel information feedback method of the terminal, characterized in that for transmitting the channel information of the antenna group of the searched transmission and reception points to the terminal. The method of claim 1,
Searching for transmission / reception points, if the number of searched transmission / reception points is greater than a predetermined number of transmission / reception points, search for transmission / reception points having a predetermined number of transmission / reception points,
In the step of transmitting to the terminal, the channel information feedback method of the terminal, characterized in that for transmitting the channel information of the transmission and reception points of a predetermined number of transmission and reception points to the terminal. The method of claim 1,
And receiving the predetermined threshold value from one of two or more transmission / reception points through an RRC signaling and a downlink control channel. 5. The method of claim 4,
The method of claim 1, wherein the predetermined number of transmission / reception points is received from one of two or more transmission / reception points through an RRC signaling and a downlink control channel. The method of claim 1,
The channel information is at least one of Channel Quality Indicator (CQI), Precoder Matrix Index (PMI), Rank Index (RI). In a wireless communication system in which two or more transmission and reception points and the terminal cooperative communication,
Transmitting a threshold value for a signal strength to the terminal;
Receiving channel information of at least one transmission / reception point from which the signal strength is greater than a predetermined threshold from the terminal; And
Transmitting and receiving point communication method comprising the step of transmitting a signal to the terminal based on the channel information of the transmission and reception point. 9. The method of claim 8,
In the step of transmitting to the terminal, transmitting at least one antenna group information of the two or more transmission and reception points to the terminal,
In the receiving of the channel information from the terminal, the communication method of the transmission and reception point, characterized in that for receiving the channel information of the antenna group of one or more transmission and reception point of the measured signal strength is greater than a predetermined threshold value from the terminal. 9. The method of claim 8,
In the step of transmitting to the terminal, and transmits a predetermined number of transmission and reception points to the terminal,
In the step of receiving channel information from the terminal, if the number of one or more transmission and reception points with a signal strength greater than a predetermined threshold value is greater than the predetermined number of transmission and reception points, the channel information of the transmission and reception points of the predetermined number of transmission and reception points; Communication method of the transmission and reception points, characterized in that received from the terminal. 9. The method of claim 8,
And transmitting the predetermined threshold value to the terminal through an RRC signaling and a downlink control channel. The method of claim 10,
And transmitting the predetermined number of transmission and reception points to the terminal through an RRC signaling and a downlink control channel. 9. The method of claim 8,
The channel information is a communication method of a transmission and reception point, characterized in that at least one of Channel Quality Indicator (CQI), Precoder Matrix Index (PMI), Rank Index (RI). In a wireless communication system in which two or more transmission and reception points and the terminal cooperative communication,
Receiving strengths of signals measured for the two or more transmission / reception points from the terminal;
Determining a threshold of the strength of the signal using the average of the received strengths of the signal; And
And transmitting the threshold value of the determined strength of the signal to the terminal. In a wireless communication system in which two or more transmission and reception points and the terminal cooperative communication,
Receiving strengths of signals measured for the two or more transmission / reception points from the terminal;
Determining a threshold of the strength of the signal using the standard deviation of the strengths of the received signal; And
And transmitting the threshold value of the determined strength of the signal to the terminal. 16. The method according to claim 14 or 15,
In the step of determining the threshold value, the threshold value transmission method of the transmission and reception point, characterized in that for determining the threshold value by multiplying the weight. In a wireless communication system in which two or more transmission and reception points and the terminal cooperative communication,
A processor for measuring the strength of a signal received from the two or more transmission / reception points, and searching for one or more transmission / reception points whose strength of the measured signal is greater than a predetermined threshold; And
And a FR unit for transmitting the channel information of the searched transmission / reception point to the terminal. In a wireless communication system in which two or more transmission and reception points and the terminal cooperative communication,
Transmits a threshold value of a signal strength to the terminal, receives channel information of at least one transmission / reception point from which the signal strength is greater than a predetermined threshold value, and transmits the channel information to the terminal based on the channel information of the transmission / reception point. RF unit for transmitting a signal; And
Sending and receiving point comprising a processor for generating the threshold. In a wireless communication system in which two or more transmission and reception points and the terminal cooperative communication,
RF unit for receiving the strength of the signal measured for the two or more transmission and reception points from the terminal; And
A processor for determining a threshold of the strength of the signal using the average of the strengths of the received signals;
The RF unit transmits and receives a threshold value of the strength of the determined signal to the terminal. In a wireless communication system in which two or more transmission and reception points and the terminal cooperative communication,
RF unit for receiving the strength of the signal measured for the two or more transmission and reception points from the terminal; And
A processor for determining a threshold of the strength of the signal using the standard deviation of the strengths of the received signal;
The RF unit transmits and receives a threshold value of the strength of the determined signal to the terminal. 22. The method according to claim 20 or 21,
And the processor determines the threshold value by multiplying a weight.

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