WO2014073846A1

WO2014073846A1 - Method and apparatus for transceiving channel information in wireless communication system

Info

Publication number: WO2014073846A1
Application number: PCT/KR2013/009991
Authority: WO
Inventors: 박경민; 리지안준; 박동현
Original assignee: 주식회사 팬택
Priority date: 2012-11-07
Filing date: 2013-11-06
Publication date: 2014-05-15

Abstract

The present invention relates to a method and apparatus for transceiving a reference signal and channel information in a wireless communication system. A base station can transmit precoded CSI-RS as the reference signal, and a terminal can measure reception power for the precoded CSI-RS and report, to the base station, exclusion indicator (ECI) or reference signal indicator (RSI) information as the channel information.

Description

Method and apparatus for transmitting and receiving channel information in wireless communication system

The present invention relates to a wireless communication system, and more particularly, to a method for transmitting and receiving channel information in a wireless communication system.

As communication systems have evolved, consumers, such as businesses and individuals, have used a wide variety of wireless terminals.

Currently, wireless communication systems such as 3GPP, Long Term Evolution (LTE), and LTE-A (LTE Advanced) are high-speed, high-capacity communication systems that can transmit and receive various data such as video and wireless data beyond voice-oriented services. In addition to the development of technology capable of transmitting large amounts of data comparable to wired communication networks, it was necessary to improve the system performance by minimizing the reduction of information loss and increasing the system transmission efficiency.

In order to solve the demand for high-speed information transmission, a modern communication system uses a transmission and reception technique using a multiple input multiple output antenna (MIMO) at both a transmitting and receiving end. The MIMO communication system has a structure in which each terminal receives or transmits a signal to one or more base stations connected thereto, and each terminal reports information on a forward channel to the base station to help the base station transmit information.

In this background, the present invention is to provide a method for transmitting and receiving channel information for MIMO in a system in which a multidimensional antenna array is used in a MIMO system.

In one aspect, the present invention provides a method for receiving a channel information in a base station in a wireless communication system, by transmitting a plurality of reference signals precoded in different matrices to different radio resources to transmit to the terminal step; And receiving, from the terminal, channel information including first information indicating one or more reference signals selected according to the received power strength among reference signals having a received power intensity greater than a reference value among the plurality of reference signals. It provides a channel information receiving method comprising. In another aspect, the present invention, in a method for transmitting channel information by a terminal in a wireless communication system, receiving a plurality of reference signals mapped to different radio resources and precoded in different matrices, respectively, from a base station Making; And first information for measuring received power strength with respect to each of the plurality of reference signals, and indicating one or more reference signals selected according to received power strength among reference signals having a received power strength greater than a reference value among the plurality of reference signals. It provides a channel information transmission method comprising the step of transmitting the channel information to the base station. In another aspect, the present invention, in a terminal for receiving a reference signal and transmitting channel information in a wireless communication system, a plurality of reference signals mapped to different radio resources and precoded in different matrices, respectively Receiving unit for receiving from the base station; A control unit measuring a received power intensity of each of the plurality of reference signals; And a transmitter configured to transmit channel information including first information indicating one or more reference signals selected according to the received power strength among reference signals having a received power intensity greater than a reference value among the plurality of reference signals. to provide.

In a system using a multidimensional antenna array in a MIMO system, channel information for MIMO can be transmitted and received with little overhead.

1 is a diagram schematically illustrating a wireless communication system to which embodiments are applied.

2 is a diagram illustrating a region where a strong electric field of an antenna is formed and a shaded region.

3 (a) and 3 (b) show an 8 × 4 antenna array and an 8 × 8 antenna array, respectively, as an example of a multidimensional antenna array.

4 is a diagram illustrating that the base station 120 transmits a reference signal 410 and receives channel information 420 including channel state information and channel quality information from the terminal 110.

5 is an exemplary diagram of CSI-RS antenna mapping in a two-dimensional antenna array where the base station 120 is used in 3D MIMO.

6 and 7 are flowcharts illustrating an example process in which the terminal 110 receives a CSI-RS and feeds back channel information through channel measurement.

FIG. 8 illustrates a channel information including a precoded CSI-RS for transmitting and receiving a precoded channel information estimation signal in a wireless communication system 100 and including a precoded CSI-RS index. Is a diagram showing that is fed back.

9 is a flowchart illustrating a process in which Precoded CSI-RS is transmitted and received and channel information including information indicating a maximum received power RS is transmitted and received in a wireless communication system according to an embodiment of the present invention.

FIG. 10 is a diagram illustrating an example of an information structure for transmitting and receiving a channel estimating RS and feeding back channel information according to 2D / 3D MIMO.

11 is a flowchart illustrating a process of feeding back information indicating a reference signal having a large received power strength by a terminal according to an embodiment of the present invention.

12 is a diagram illustrating an example in which channel estimation RS is mapped to an antenna array in 3D MIMO.

FIG. 13 is a diagram illustrating another example of an information structure for transmitting and receiving channel RS for channel estimation according to 2D / 3D MIMO.

14 shows an example of MU-MIMO in which a base station simultaneously transmits different information to two terminals using the same radio resource.

15 is an illustration of a channel information feedback first method for MAI avoidance.

16 is an illustration of a second method of channel information feedback for MAI avoidance.

17 is an illustration of a third method of channel information feedback for MAI avoidance.

18 is a diagram illustrating an AoD range in a horizontal domain and a vertical domain.

19 is an example of configuring an array using four antennas having a carrier wavelength X2 of antenna distances.

20 is a view illustrating waveforms of signal strength according to angles when beamforming is performed for AoD = -10.

21 shows an example of interference caused by side lobes.

22 shows an example of transmission of a precoded CSI-RS when the distance between transmission antennas is greater than wavelength / 2.

FIG. 23 illustrates an example in which a UE feeds back channel information when a precoded CSI-RS shown in FIG. 28 is transmitted.

24 illustrates a propagation path in the vertical domain.

FIG. 25 illustrates an example of channel information reported by a terminal when using the channel information feedback first method for avoiding MAI in a vertical direction domain.

26 is an illustration of a codebook for RSI.

27 shows an example of channel information sizes of types newly defined in relation to an ECI / RSI method.

28 is a flowchart illustrating a method for receiving channel information by a base station according to an embodiment of the present invention.

29 is a flowchart illustrating a method of transmitting channel information by a terminal according to an embodiment of the present invention.

30 is a block diagram of a base station according to an embodiment of the present invention.

31 is a block diagram of a terminal according to an embodiment of the present invention.

Hereinafter, some embodiments of the present invention will be described in detail through exemplary drawings. In adding reference numerals to the components of each drawing, it should be noted that the same reference numerals are assigned to the same components as much as possible even though they are shown in different drawings. In addition, in describing the present invention, when it is determined that the detailed description of the related well-known configuration or function may obscure the gist of the present invention, the detailed description thereof will be omitted.

In addition, in describing the component of this invention, terms, such as 1st, 2nd, A, B, (a), (b), can be used. These terms are only for distinguishing the components from other components, and the nature, order or order of the components are not limited by the terms. If a component is described as being "connected", "coupled" or "connected" to another component, that component may be directly connected to or connected to that other component, but there may be another configuration between each component. It is to be understood that the elements may be "connected", "coupled" or "connected".

The wireless communication system 100 is widely deployed to provide various communication services such as voice and packet data.

Referring to FIG. 1, the wireless communication system 100 includes a user equipment (UE) 110 and a base station 120 (BS).

In the present specification, the terminal 110 is a comprehensive concept of a user terminal in wireless communication, and includes a user equipment (WCDMA), a long term evolution (LTE), a long term evolution (LTE), a high speed packet access (HSPA), and the like. Equipment, of course, should be interpreted as including a mobile station (MS), a user terminal (UT), a subscriber station (SS), a wireless device, and the like in a global system for mobile communications (GSM). .

The terminal 110 may perform feedback of channel information described below, and provide an apparatus thereof.

The base station 120 or cell generally refers to a fixed station communicating with the terminal 110 and includes a Node-B, an evolved Node-B, and a Base Transceiver. It may be called other terms such as a System, an Access Point, a Relay Node, and the like.

The base station 120 may transmit a reference signal to the terminal 110, receive feedback of channel information from the terminal 110, and transmit data or signals using the channel information.

In the present specification, the terminal 110 and the base station 120 are two transmitting and receiving entities used to implement the technology or the technical idea described in the present specification and are used in a comprehensive sense and are not limited by the terms or words specifically referred to. .

There is no limitation on the multiple access scheme applied to the wireless communication system 100. Various multiple access techniques such as Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), Orthogonal Frequency Division Multiple Access (OFDMA), OFDM-FDMA, OFDM-TDMA, OFDM-CDMA Can be used.

The uplink transmission and the downlink transmission may use a time division duplex (TDD) scheme that is transmitted using different times, or may use a frequency division duplex (FDD) scheme that is transmitted using different frequencies.

One embodiment is applied to 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 Ultra Mobile Broadband (UMB). Can be. 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 may support uplink and / or downlink HARQ (HARID), and may use a channel quality indicator (CQI) for link adaptation. In addition, multiple access schemes for downlink and uplink transmission may be different from each other. For example, downlink uses Orthogonal Frequency Division Multiple Access (OFDMA), and uplink uses Single Carrier-Frequency Division Multiple Access (SC-FDMA). ) Is the same as can be used.

The wireless communication system 100 provides a single user multiple input multiple output (SU-MIMO) technique for transmitting information to a user through a specific band by using multiple antennas and high-speed information transmission to many users. To support this, it may be considered to selectively use a multiple user multiple input multiple output (MU-MIMO) technique that uses multiple antennas and simultaneously transmits information to multiple users through the same band. MU-MIMO allows two users to share a band when two or more user terminals have a high channel propagation gain for the same band, thus gaining channel propagation gain in addition to gaining more users using a wider band. It is possible to use this good band to improve the overall spectral efficiency.

In order to implement the present invention, a 3D MIMO (3 Dimensional Multiple Input Multiple Output) technique using a multidimensional antenna array may be used. Here, a 2D MIMO technique is used for the purpose of signal manipulation on a 2D plane using a 1D antenna array, and a 3D MIMO system is used to implement a MIMO system in a space including a vertical direction using a multidimensional antenna array. .

FIG. 2 is a diagram illustrating a region in which a strong electric field of an antenna is formed and a shaded region, and FIG. 3 is a diagram for describing vertical beamforming using a multiple antenna array and a multiple antenna array. 2 and 3 illustrate a problem in which shadowed areas appear according to propagation characteristics of an antenna and a method in which the wireless communication system 100 uses the 3D MIMO technique as an embodiment for solving the problem.

2 (a) shows the effective angle of the vertical strong field of the antenna in the wireless communication system. As can be seen with reference to (a) of FIG. 2, since the effective angle of the vertical strong electric field of the antenna is formed forward, a shaded area (shading area) may appear below and above the area where the antenna is installed. . In order to solve the problem of the shadow area due to the range of the effective angle of the vertical strong electric field of the antenna, it may be installed by tilting the antenna as shown in FIG. Figure 2 (b) is a view showing that the tilting the antenna is installed so that the range of the effective angle of the strong field of the antenna is directed downward (downward).

The antenna can be installed at a relatively high position (equivalent to 25 m from the ground) to have a wide propagation radius, and the antenna is placed inclined toward the ground to solve the problem of shadowed areas downward as described above (tilting) )can do. This antenna installation method is called physical antenna tilting.

By the way, the downward tilting of the antenna may partially solve the problem of occurrence of the shadow area in the lower part, but the problem of the occurrence of the shadow area in the upper part (high rise) may not be solved or may worsen. 2C is a diagram illustrating a strong electric field region and a shadowed region according to antenna tilting. As can be seen with reference to (c) of FIG. 2, the shaded area in the service area of the ground terminal 110 is narrowly formed, but the shaded area in the service area of the high-rise terminal 110 corresponding to the upper surface appears wide. Can be. This problem can cause serious problems that degrade communication capacity in urban areas where tall buildings are commonly present.

Another method for solving the above problem is that the wireless communication system 100 adopts a spatial division transmission scheme according to the altitude through soft tilting and multidimensional precoding using a multidimensional antenna array.

3 (c) is a diagram illustrating implementation of adaptive tilting or spatial division multiplexing (SDM) using such a multidimensional antenna array. In (c) of FIG. 3, when a signal is to be transmitted to the terminal 110 existing at a higher position than the antenna of the base station 120, the base station 120 performs a phase difference with the antennas arranged in the vertical domain. The signal processing is performed such that the subject signal supports strong electric field propagation in the upward direction. Such an operation may be defined by terms such as soft tilting in response to physical antenna tilting (physically changing the antenna direction). On the contrary, when the signal is to be transmitted to the terminal 110 existing at a lower position than the base station 120 antenna, the signal is provided to support the strong electric field propagation in the downward direction by giving a phase difference in a manner opposite to that described above. Processing can be performed. In addition, when a large enough number of transmit antennas are listed in the vertical direction to support high resolution, spatial division may be performed according to the height of the terminal 110.

As described with reference to FIG. 3, when the 3D MIMO technique is used, the tilting of the antenna can be performed in a vertical direction by transmitting a signal by giving a phase difference to the antennas arranged in the vertical direction, thereby physically tilting the antenna. In addition to solving the problem that the shadow area appears without, it is possible to partition the space according to the height of the terminal.

2 to 3, the wireless communication system 100 has been described using a 3D MIMO system. Hereinafter, a description will be given of transmitting and receiving a reference signal in the 3D MIMO system, and correspondingly transmitting and receiving channel information.

MIMO systems using multidimensional antenna arrays may form 3D or higher MIMO systems (eg, 4D MIMO systems). In the present invention, the 3D MIMO system refers to a MIMO system that performs precoding or beam forming using two or more phases defined independently of each other or defined on an orthogonal axis. When three or more phase components are used, this is defined as a 3D or higher MIMO system. Such a 3D or more MIMO system can implement all the characteristics according to an embodiment of the present invention to be described later, but will be described below based on the 3D MIMO system, but is not limited thereto.

A closed loop MIMO system may be used for the practice of the present invention.

The MIMO technique is an open loop MIMO technique in which the base station 120 can operate without acquiring prior information about a channel, and a closed loop in which the base station 120 acquires information about a channel and utilizes it. loop) It is divided into MIMO technique. The closed loop MIMO technique can perform more precise transmission control by using channel information, and thus, various loops cannot be obtained in the open loop MIMO technique such as acquisition of higher precoding gain and interference avoidance. It has the advantage of gaining benefits. On the other hand, a separate feedback overhead occurs in order for the terminal 110 to measure accurate channel information and report it to the base station 120, and to allow the terminal 110 to estimate a channel for each transmit antenna or antenna port. Reference signal overhead is generated.

The present invention provides a method for transmitting and receiving channel information. In order to transmit and receive channel information, the base station transmits a reference signal to the terminal, and the terminal can generate channel information using the reference signal and transmit the channel information to the base station. .

Different types of reference signals exist in downlink or uplink transmission, and new reference signals are defined and discussed for various purposes. For example, reference signals that may be used for uplink signal transmission include DM-RS (Demodulation RS) and SRS (Sounding RS). Reference signals that may be used for downlink signal transmission include CRS (Cell-specific RS), MBSFN RS, UE-specific RS, and the like. In addition, there is a channel state index-reference signal (CSI-RS) as a reference signal transmitted from the base station 120 to obtain channel state information (CSI) in the terminal 110 when transmitting a downlink signal. . The CSI-RS may be used to report a channel quality indicator (CQI) / precoder matrix indicator (PMI) / rank indicator (RI).

Referring back to FIG. 4, each terminal 110 receives a reference signal 410 and estimates a channel. Thereafter, each terminal 110 feeds back channel information 420 to the base station 120. In this case, the channel information may include channel state information, which is information on a propagation channel, and channel quality information, which is information on measured or calculated channel capacity or channel quality. Meanwhile, the channel information 420 may include a channel rank or RI (Rank Indicator) which is information on the number of layers used for downlink transmission to the terminal.

In this case, the channel state information may include information on a precoding of the UE suitable for the estimated channel, for example, a precoding matrix indicator (PMI) which is an index or identification information about the precoding matrix. For example, in the case of MIMO allowing simultaneous access of n terminals, each of the n terminals 110 may feed back channel state information, for example, PMI, to the base station 120.

Looking at the transmission of the channel information through the index, the terminal 110 measures the channel information, and then, after determining the channel information, the element which is determined to be the most suitable for representing the channel information among a plurality of elements included in the codebook (codebook) After the selection, the channel information report may be performed in a format in which an index indicating the element is transmitted to the base station 120.

If the MIMO scheme is to be used, the base station 120 maps and transmits a plurality of antenna ports to which different CRSs or CSI-RSs are mapped to different Tx antennas, and the terminal 110 transmits the CRSs or CRSs. Through the CSI-RS measurement, information about the MIMO channel generated by a plurality of Tx antennas and Rx antennas is acquired. After acquiring such information, the terminal 110 calculates a matrix most suitable for representing a channel matrix from a CSI feedback codebook, and calculates an index for the calculated matrix through a base station (RI and PMI). 120). In addition, the CQI may also be transmitted to the base station 120 as a report on channel quality. At this time, a wideband / subband CSI may be reported to the base station according to a feedback mode.

When performing closed loop MIMO in a wireless communication system 100 using a multi-dimensional antenna array that performs precise precoding using a plurality of transmission antennas or antenna ports, the MIMO scheme according to the accuracy of channel information reported by the terminal 110 The overall performance of is heavily dependent.

As described above, a closed loop 3D MIMO technique using a multi-dimensional antenna array may be used to implement the present invention. Also, as described with reference to FIG. 4, a reference signal transmitted from a base station and received from a terminal may be used. Channel information transmission and reception method for feeding back channel information may be used. An embodiment in which these two methods are applied together will be described.

In order to use the 3D MIMO scheme, first, as a reference signal transmission / reception step for channel measurement, the base station 120 assigns a plurality of antenna ports to which different CRSs or CSI-RSs are mapped to different Tx antennas. After mapping and transmitting, the terminal 110 acquires information on a MIMO channel generated by a plurality of Tx antennas and Rx antennas through CRS or CSI-RS measurement.

Next, as a step of transmitting and receiving channel information, the terminal 110 acquires the information on the above-described channel, and calculates, from the CSI feedback codebook, a matrix most suitable for representing a channel matrix. Channel information may be transmitted and received by reporting an index of the matrix to the base station 120 through RI and PMI.

More specifically, in the case of applying the CSI-RS based channel estimation scheme to 3D MIMO, a process of allocating and transmitting a reference signal to a resource will be described with reference to FIG. 5, and the UE receives the CSI-RS and measures the channel. An example process for feeding back channel information will be described with reference to FIGS. 6 and 7.

In the case of applying the CSI-RS based channel estimation scheme to 3D MIMO, in relation to a method of allocating a reference signal to a resource, the base station transmits a resource element for transmitting a reference signal (RS) to all transmission antennas or antenna ports. ) Or an antenna set for each domain (domain, vertical or horizontal direction) can be selected to allocate an RE for transmission of a reference signal.

FIG. 5 shows each transmission antenna (antenna port) when using the above two RE allocation schemes (a technique of allocating reference signals to all transmission antennas and a technique of selecting an antenna set for each domain and transmitting a reference signal). The method of allocating a reference signal for each) is an example of reusing a Rel-10 / 11 CSI-RS port. Based on the Rel-11 content, the terminal 110 may be allocated a plurality of CSI-RS resources, and each CSI-RS resource may include up to eight CSI-RS ports.

5 (a) is an example of a method of indicating reference signal mapping for nine or more transmit antennas (antenna ports) by reusing Rel-11 CSI-RS resources. In (a) of FIG. 5, after the CSI-RS port index (R #) is an index for each of a plurality of CSI-RS resources received by the terminal 110. If the CSI-RS port is not reused, CSI-RS port N (R0) of FIG. 5 (a) may be indicated as a new RS port N, and CSI-RS port N (Rm) is a new RS port 8m + N It can be written as

FIG. 5 (b) is a method of transmitting a reference signal through one representative antenna set for each domain of a multidimensional antenna array. When performing reference signal mapping and transmission by reusing Rel-11 CSI-RS resources, FIG. Two CSI-RS resources (R0 and R1 respectively in FIG. 4) that are in charge of the / horizontal / vertical domain may be defined in the same subframe or may be defined in different subframes. In addition, the CSI-RS resource may be defined on the same subframe in the time axis when the period or offset is defined by different subframes or the period and offset are defined by the same parameter when defined on the subframe. . Or it may be defined on another subframe. The terminal 110 may independently perform reception and channel estimation and CSI feedback on two domain RSs (two CSI-RS resources).

In the present invention, the CSI-RS resource refers to pattern information of an RE to which a CSI-RS is mapped to each PRB pair (physical resource block pair) in a subframe in which CSI-RS transmission is allowed. Or a combination of all the information necessary for performing CSI-RS reception including the information and information on a subframe in which the CSI-RS is transmitted, or part of the information.

When the terminal performs CSI measurement and reporting using the CSI-RS as shown in FIG. 5, the terminal 110 feeds back channel information according to whether to perform channel measurement independently for each domain and whether to use a codebook. The process may vary.

First, FIG. 6A is a flowchart of a first feedback scheme in which reference signals are transmitted through all transmission antennas (antenna ports), and the terminal 110 feeds back channel information through a matrix index. Referring to FIG. 6A, the terminal 110 receives a plurality of CSI-RSs (S602) and measures information on a multi-dimensional antenna array through the received plurality of CSI-RSs (S604). The terminal 110 may be a 3D channel matrix (when a 1D array is used for a receiving antenna) or a 4D channel matrix (when a 2D array is used for a receiving antenna) represented by a combination of a transmitting antenna and a receiving antenna (antenna antenna). A channel matrix suitable for expressing P is calculated in the codebook (S606), and an index (ie, a matrix index) indicating the calculated channel matrix is transmitted to the base station 120 (S608).

6 (b) is a flowchart of a second feedback scheme in which reference signals are transmitted through all transmission antennas (antenna ports) and the terminal 110 feeds back channel information through channel parameters. Referring to FIG. 5B, the terminal 110 receives a plurality of CSI-RSs (S652) and measures information on a multi-dimensional antenna array through the received plurality of CSI-RSs (S654). The terminal 110 calculates a channel parameter that can represent a 3D channel represented by a combination of a transmit antenna and a receive antenna (terminal antenna) (S656), and transmits the calculated channel parameter to the base station 120 (S658). ).

FIG. 7A is a flowchart of a third feedback scheme in which the base station 120 transmits an independent reference signal for each domain and the terminal 110 feeds back channel information through a matrix index for each domain. Referring to FIG. 7A, the terminal 110 independently receives a plurality of CSI-RSs for each domain (S702), and performs a horizontal domain antenna array and vertical through the received plurality of CSI-RSs. Information on a vertical domain antenna array is measured (S704). The terminal 110 calculates a channel matrix suitable for representing the channel matrix for each domain in the codebook (S706), and transmits an index indicating the calculated channel matrix to the base station 120 (S708).

7B is a flowchart of a fourth feedback scheme in which the base station 120 transmits an independent reference signal for each domain and the terminal 110 feeds back channel information through channel parameters for each domain. Referring to (b) of FIG. 7, the terminal 110 independently receives a plurality of CSI-RSs for each domain (S752), and performs a horizontal domain antenna array and vertical through the received plurality of CSI-RSs. Information on a vertical domain antenna array is measured (S754). The terminal 110 calculates a channel parameter suitable for representing a channel for each domain (S756), and transmits the calculated channel parameter to the base station 120 (S758).

In the case of the first feedback method in the wireless communication system 100 using the multi-dimensional antenna array, since a very complex and large codebook must be generated in consideration of various channel conditions when generating a codebook for CSI reporting, there is a large burden on the codebook design. In addition, there is no guarantee that a codebook suitable for representing such a complex channel can be designed.

In the case of the second feedback method, since the channel parameter having a very complicated form must be reported, the feedback overhead can be a big problem.

In case of the third feedback method, a method for independently measuring channel information for each domain is required, and a method for performing vertical domain channel measurement must be provided. In addition, a method of the fourth feedback method is required. In this case, there is a problem of feedback overhead of reporting complex channel parameters.

Other methods can be applied to solve the problems of the four feedback methods (first to fourth feedback methods) described above for the practice of the present invention.

A reference signal used in this other method may be defined as new CSI-RS to distinguish it from the existing CSI-RS. However, the present invention is not limited to these names.

Hereinafter, a method of estimating a channel and transmitting / receiving channel information using a precoded CSI-RS as a new CSI-RS will be described.

In FIG. 8, the base station 120 uses different radio blocks (REBs) or other subframes or the same REs when the reference signals are transmitted for estimating channel information. Precoding may be performed to have different propagation directivity with respect to a plurality of reference signals using the code division (RE and codes classified by code division). Each of the plurality of reference signals described above is precoded to have different propagation directions and propagated through a plurality of physical antennas of the transmitting end (base station 120).

Accordingly, when a reference signal propagated in a propagation direction preferred by the terminal 110 is mapped to a radio resource to which each reference signal is mapped, reception power is measured to be high and propagated in a propagation direction that the terminal 110 does not prefer. When the reference signal is mapped, the received power is low. In addition, the received power is not measured with respect to the reference signal propagated in the propagation direction in which the terminal 110 cannot receive the signal.

The terminal 110 may recognize a radio resource to which a reference signal mapped to a reference signal presenting a suitable direction to the terminal 110 by measuring and comparing the received power of each radio resource to which a reference signal propagated with different propagation directions is mapped. In addition, the index for the radio resource suitable for the terminal 110 is reported to the base station 120 so that the base station 120 can obtain the propagation direction or precoding information suitable for the terminal 110.

As one embodiment, referring to FIG. 8, when the base station 120 transmits a plurality of channel information estimation reference signals (new CSI-RS, precoded CSI-RS), each reference signal is transmitted in a vertical component. It is precoded to have different propagation directions and transmitted. In FIG. 8, the base station 120 transmits six

reference signals

810, 811, 812, 813, 814, and 815. As shown in FIG. 8, each Precoded CSI-RS propagates with a different propagation direction. do. Among these, the terminal 110 may measure the highest received power with respect to the precoded CSI-RS 3 813 which is propagated with the propagation direction most suitable for the terminal 110. In this case, the terminal 110 may measure the precoded CSI- The index for RS 3 may be reported to the base station 120. Through this process, the base station 120 may check the information on the most preferred channel or the most suitable propagation direction (precoding information) of the terminal 110.

The first to fourth feedback schemes described above with reference to FIGS. 6 to 7 must perform a complicated operation in which the terminal 110 measures a channel matrix, and in this operation, the terminal 110 uses a plurality of channels or channel matrices. Amplitude and phase measurements should be performed on each of the elements. In addition, codebook search must be performed to represent the measured channel matrix. In this case, precise CSI reporting may not be possible in some specific communication environments depending on the codebook configuration. This is because the codebook is finite in size, so that some similarities may not exist in the codebook.

On the other hand, in the feedback method using the Precoded CSI-RS described with reference to FIG. 8, the transmitting end is used for transmitting the reference signal in consideration of the communication environment in the area dedicated to each cell or each transmitting end (base station 120). Since the precoder can be arbitrarily selected, more various channel information can be measured.

In the present invention, the precoded CSI-RS is defined as an RS that has been precoded to be transmitted to perform channel information reporting, not for channel measurement, for PDSCH demodulation. The precoded CSI-RS means RS transmitted to a plurality of terminals after precoding. In a subframe and a resource block in which a precoded CSI-RS is transmitted, each UE can receive the precoded CSI-RS regardless of whether a PDSCH is received, and estimate channel information through the precoded CSI-RS. report.

In FIG. 8, the Precoded CSI-RS may transmit a plurality of reference signals that are precoded to form a strong electric field having different propagation directions in the vertical direction. Reference signals precoded to form strong electric fields with different propagation directions are generated using different radio resources (either different REs or the same REs, but sequenced to be divided into orthogonal codes, or a combination of both). May be mapped and transmitted.

9 is a flowchart illustrating a process in which a Precoded CSI-RS is transmitted and received and channel information including information indicating a maximum received power reference signal (RS) is transmitted and received in the wireless communication system 100 according to an embodiment of the present invention.

Referring to FIG. 9, the base station 120 precodes a plurality of reference signals in different matrices (S910), maps the plurality of precoded reference signals to different radio resources, and transmits them to the terminal 110 ( S920).

The terminal 120 receives a plurality of reference signals mapped to different radio resources from the base station 120 (S920), and measures received power strengths for each of the plurality of reference signals (S930).

In operation S920 and S930, the plurality of reference signals may be mapped to different radio resources in one resource block pair (PRB pair). This structure is a structure in which differently precoded reference signals are mapped in one PRB pair. In addition, the precoded CSI-RS may exist on all PRB pairs in a subframe in which transmission is configured, or may exist on some PRB pairs thereof. For example, a structure may exist only in an even PRB pair, or exist only in a PRB pair near a center frequency around a carrier frequency.

The terminal 120 transmits channel information including information indicating a reference signal having the largest received power strength among the plurality of received reference signals to the base station 120 or is determined according to the ascending or descending order of the received power strength. The channel information including the information indicating the reference signal is transmitted to the base station 120 (S940), and the base station 120 receives the received power strength of the terminal 110 among the plurality of reference signals transmitted to the terminal 110. The channel information including the information indicating the largest reference signal or the channel information including the information indicating one or more reference signals determined according to the ascending or descending order for the received power strength is received from the terminal 110 (S940). ).

The terminal 120 may transmit channel information including information indicating a reference signal having the largest received power intensity to the base station 120, but the terminal 120 further uses channel information in addition to the received power strength to provide channel information. In this case, channel information including information indicating a reference signal other than the reference signal having the largest received power strength may be transmitted to the base station 120. In the latter case, the terminal 120 sorts the reference signals in ascending or descending order according to the received power strength, and selects one preferred reference signal according to the above-mentioned other information for two or more reference signals in the order of the received power strength in the order of increasing. The channel information including the information indicating the selected reference signal may be transmitted to the base station 120.

In the wireless communication system 100, the base station 120 is a system using a multidimensional antenna array, and in step S920 in which the base station 120 transmits a reference signal, different matrices have a plurality of reference signals. It may be a beamforming matrix to be transmitted with different propagation directions in the vertical domain of the antenna array.

In the case of a communication system using MIMO, the channel characteristics between the transmitting end and the receiving end are largely determined by the physical position between the transmitting end and the receiving end and the distribution of reflectors generating multiple paths. However, when looking at the distribution of the transmitter / receiver physical location and the reflector separately in the horizontal direction and the vertical direction, the vertical direction has a narrower angle range than the horizontal direction, which causes reflection or disturbance of radio waves between the transmitter / receiver. There are relatively few scatters. For this reason, the channel information feedback through the Precoded CSI-RS according to the embodiment of the present invention can be used for the vertical channel information feedback without using the channel estimation information through the CSI-RS.

As a result, the base station 120 receives the channel information by using the precoded CSI-RS precoded to have different propagation directions in the vertical direction, and uses the same CRS (R) as used in Rel-10 / 11 in the horizontal direction. Rank indicator (RI), Precoder Matrix Indicator (PMI), and Channel Quality (CQI) as channel estimation information through a cell-specific reference signal (CSI-RS) or channel state information reference signal (CSI-RS) or similar cell-specific transmission RS. And channel information including at least one piece of information.

9, the base station 120 further adds a cell-specific reference signal (CRS) or a channel state information reference signal (CSI-RS) to the terminal 110 in step S920 of transmitting a reference signal. In step S940 of transmitting and receiving channel information, among the RI (Rank Indicator), PMI (Precoder Matrix Indicator), and CQI (Channel Quality Indicator) as horizontal domain channel estimation information through CRS or CSI-RS. Channel information further including at least one information may be received from the terminal 110.

The base station 120 may transmit a plurality of reference signals with the same power level between the reference signals in step S920. The terminal 110 may report the optimal propagation direction or precoding information by measuring the change in the intensity of the received power according to the propagation path. Alternatively, when the base station is specialized in signal propagation in a specific vertical direction, the base station may transmit a specific reference signal using a larger power than other reference signals. The terminal does not receive information on whether the base station uses a larger power than other reference signals with respect to a specific reference signal, and measures the received power of each reference signal.

The base station 120 may transmit a plurality of reference signals through some antenna sets of the vertical antenna sets constituting the antenna array in operation S920. This is a method for reducing the signaling overhead of the base station 120 transmitting a reference signal or the feedback overhead of the terminal 110 feeding back channel information in feeding back channel information for all antennas in the vertical direction.

The terminal 110 transmits the channel information to the base station 120 by including the index information of the reference signal in the channel information with respect to the one or more reference signals in the order of increasing the received power strength (S940). Index information of the radio resource to which the signal is mapped may be included in the channel information and transmitted to the base station 120.

If the terminal 110 receives the configuration information of the Precoded CSI-RS from the base station 120 and can identify the indexes of the reference signals precoded with different matrices, the terminal 110 may feed back the corresponding indexes. If the configuration information is not received or the index of the reference signal cannot be determined for another reason, a method of feeding back the index of the radio resource to which the reference signal is mapped may be used.

The terminal 110 may transmit channel information including information indicating one reference signal having the largest received power strength to the base station 120, and at least one (for example, order of magnitude of the received power strength). Channel information including information indicating the upper three) reference signals may be transmitted to the base station 120. When the base station 120 receives information indicating the top three reference signals in order of received power strength, the base station 120 may select and use information indicating one reference signal. When the information indicating the plurality of reference signals is transmitted to the base station as described above, the terminal may also report the information in a bitmap format.

In the wireless communication system 100 according to an exemplary embodiment of the present invention described with reference to FIG. 9, some operations are described with reference to a transmitting end or a receiving end, but the base station 120 and the terminal 110 operate as a transmitting end or a receiving end, respectively. As such, the reverse of the described operation may be performed at the receiving end or transmitting end.

The wireless communication system base station 120 may use a 2D MIMO or 3D MIMO technique in the downlink. Accordingly, the base station 120 may transmit a reference signal for 2D MIMO channel measurement or a reference signal for 3D MIMO channel measurement so that the terminal 110 may measure and report channel information necessary for using each MIMO scheme. In addition, the terminal 110 may notify the terminal 110 of the setting information for transmitting the reference signal so that the terminal 110 may receive the reference signal.

Referring to FIG. 10, the base station 120 may include reference signal information 1010 for 2D MIMO and reference signal information 1020 for 3D MIMO as fields of configuration information.

Base station 120 performs a single or multiple CSI-RS transmission for 2D MIMO channel measurement, and also for 3D MIMO channel measurement, 3D CSI-RS and vertical direction (for horizontal domain channel measurement) vertical domain) precoded CSI-RS transmission for channel measurement. Accordingly, the reference signal information 1030 for 3D MIMO may include 3D CSI-RS information 1022 for horizontal channel measurement and precoded CSI-RS information 1024 for vertical channel measurement.

In addition, the base station 120 may arbitrarily select whether the technique applied in 2D / 3D MIMO, or both techniques is used, and transmit the random access to the terminal 110 in the form of a transmission mode. For example, in FIG. 10, when the transmission mode (Tx mode) 1030 corresponds to 1 to N (a natural number of 1 or more), it indicates that MIMO is not used. When the transmission mode 1030 is N + 1, 2D MIMO is used. If the transmission mode is N + 2, it may indicate that 3D MIMO is used or any one of 2D / 3D MIMO is used. Such transmission mode information may be transmitted from the base station 120 to the terminal 110.

In addition to the information on the transmission mode, the base station 120 may request the aperiodic CSI report to the terminal 110, this request information may be included in the aperiodic CSI report field 1040 and transmitted to the terminal 110. have.

The terminal 110 extracts the CSI information through the channel estimation reference signal according to the

reference signal information

1010 and 1020 and the transmission mode information 1030 for 2D / 3D MIMO described above and reports the same to the base station 120. .

The base station 120 transmits a reference signal for 2D MIMO channel estimation and a reference signal for 3D MIMO channel estimation as separate reference signals, and the terminal 110 performs 2D or 3D MIMO channel estimation through each reference signal. 2D MIMO channel estimation is performed according to the Rel-10 / 11 method. For 3D channel estimation, RI, PMI, and CQI are measured using a reference signal for horizontal CSI estimation, and a precoded CSI-RS, a vertical component reference signal, is measured. Estimate the vertical CSI through.

11 is a flowchart illustrating a process of feeding back information indicating a reference signal having a large received power strength by the terminal 110 according to an embodiment of the present invention.

Referring to FIG. 11, the UE 110 measures received power for a plurality of radio resources (S1102) (UE measures Rc power On 6 physical resources), and then precoded CSI- mapped to the radio resource having the largest received power. The RS may be recognized as a precoded reference signal through a precoding matrix suitable for the terminal 110 or as a reference signal passed through a virtual channel suitable for the terminal 110. In this manner, the terminal 110 calculates appropriate vertical precoding information based on the received power (UE detect highest Rx power at physical resource 3) (S1104).

When the terminal 110 does not recognize the order or method (RS to resource mapping rule) in which each precoded CSI-RS is mapped to a radio resource (no at S1106), the terminal 110 is mapped with a suitable precoded CSI-RS. When an index indicating a radio resource is reported to the base station 120 (UE reports physical resource index) (S1108), and the terminal 110 recognizes the order or method of mapping each precoded CSI-RS to the radio resource ( Yes in S1106), the terminal 110 reports an index indicating a suitable precoded CSI-RS to the base station 120 (UE reports precoded CSI-RS index) (S1110).

12 (a) shows a reference signal (CRS or CSI-RS) for horizontal channel CSI measurement and a reference signal (Precoded CSI) for vertical channel measurement using all antennas that the base station 120 configures in the antenna array. (RS) is transmitted (using New RS ports 0 to 7), and FIG. 12 (b) shows a reference signal (CRS or CSI-RS) for horizontal channel CSI measurement using all antennas. Transmit and transmit a reference signal (Precoded CSI-RS) for vertical channel measurement using the first vertical antenna set of the antenna array. 12C illustrates reference signals CRS or CSI-RS for horizontal channel CSI measurement and precoded CSI-RS for vertical channel measurement using some antenna sets constituting the antenna array. Indicates to send.

The example of FIG. 12 is a method suitable for use when the number of ports used by the base station 120 for precoded CSI-RS transmission is determined, and all precoded CSI-RSs are allocated by assigning each precoded CSI-RS port to each transmit antenna. To be transmitted at the same transmit power.

FIG. 13 is a diagram illustrating another example of an information structure for transmitting and receiving a channel estimating RS and feeding back channel information according to 2D / 3D MIMO.

Comparing the example of the information structure of FIG. 13 with the example of the information structure of FIG. 8, whether the reference signal CSI-RS is used for horizontal channel CSI measurement for 3D MIMO in reference signal information 1310 for 2D MIMO. A subfield 1312 indicating whether or not is further included, and the reference signal information 1320 for 3D MIMO further includes information 1324 indicating a reference signal used for horizontal channel CSI measurement for 2D MIMO. have.

Since the horizontal channel CSI estimation in 3D MIMO may use the same method as 2D MIMO, the embodiment of FIG. 13 illustrates a method of displaying information about a reference signal that can be commonly used in 2D and 3D MIMO.

Referring to FIG. 13, information about reference signals usable for 3D MIMO horizontal channel CSI measurement among a plurality of 2D MIMO channel CSI measurement signals (CRS or CSI-RS) may be referred to as reference signal information for 2D MIMO. 1310 may be transmitted together through a subfield corresponding to reference number 1312 (a subfield 1312 indicating whether the 3D MIMO horizontal channel CSI is used for measurement).

Or information on a reference signal (precoded CSI-RS) for 3D MIMO vertical channel measurement (location of a radio resource to which a precoded CSI-RS is mapped, and information on a subframe in which a precoded CSI-RS is transmitted). ) Information indicating the reference signal (CRS or CSI-RS) to be used together for 3D MIMO horizontal channel CSI measurement (for example, how many times of the CSI-RS the UE is configured to receive) May be included in a subfield corresponding to reference number 1324 (information 1324 indicating a reference signal used for horizontal channel CSI measurement for 2D MIMO) and transmitted to the terminal 110 together.

Further details regarding reference signal precoding at the base station 120 will be described.

In order to support the free use of precoded CSI-RS at base station 120, a scheme may be considered in which base station 120 transmits a precode CSI-RS in any number. In this case, the base station 120 may define precoded CSI-RS ports less than the number of antennas constituting the vertical array and perform precoding when mapping each RS port to the antenna. In this case, the base station 120 may transmit precoded CSI-RS in any number (the number of antenna ports) regardless of the number of physical antennas.

When performing precoding on the reference signal, the base station 120 may use any precoder or select some of the precoder having the following characteristics to configure the precoding matrix of Equation 1 below.

[Equation 1]

As a more general example, it may be expressed as Equation 2 below.

[Equation 2]

In the foregoing precoder example, mapping rules between m and n may be separately defined. Also depending on the number of antenna ports or antennas used, the length K of v is determined.

In the case of allocating radio resources used for the new precoded CSI-RS transmission described above, in order to solve an RS collision problem occurring in another UE that does not perform reference signal reception, the existing zero power CSI-RS or non-zero power CSI-RS resource allocation scheme may be reused.

On the other hand, MU-MIMO can be used to practice the present invention.

As described above, the MU-MIMO uses multiple antennas to simultaneously transmit information to multiple users through the same band by using multiple antennas to support high-speed information transmission to many users. MU-MIMO). MU-MIMO allows two users to share a band when two or more user terminals have a high channel propagation gain for the same band, thus gaining channel propagation gain in addition to gaining more users using a wider band. It is possible to use this good band to improve the overall spectral efficiency.

MAI (Multiple Access Interference) may occur in the MU-MIMO. The MAI in the MU-MIMO will be described.

14 shows an example of MU-MIMO in which a base station simultaneously transmits different information to two terminals using the same radio resource. In FIG. 14, when the virtual channels H ₀ C ₀ and H ₀ C ₁ of two signals propagated to the terminal U0 are orthogonal to each other, the interference component H by the filter F ₀ designed for receiving the virtual channel H ₀ C _0. ₀ C ₁ X ₁ is erased so that the UE U0 can receive a signal without MAI. Similarly, when orthogonality is established between two virtual channels H ₁ C ₀ and H ₁ C ₁ , the interference component H ₁ C ₀ X ₀ received by U1 is removed by the filter F ₁ , so that the UE U1 can also communicate without MAI. Do. In order to perform the above operation, two terminal selection and precoder selection should be performed such that H ₀ C ₀ and H ₀ C ₁ are orthogonal and H ₁ C ₀ and H ₁ C ₁ are orthogonal. The base station should receive channel information or channel characteristic information necessary for performing the operation from the terminal.

In order to generate two orthogonal virtual channels as described above, accurate information about two channels H ₀ and H ₁ is required, but delivering precise information about these channels to a base station can require a very large CSI feedback overhead. Therefore, instead of reporting precise information about the channel, the terminal may report limited information that may be used for MAI control. This limited information is as follows.

(Channel information feedback first method for avoiding MAI) When precoder Cn is used in UE Un, if used together, a method for reporting index information on precoder Cm in which the UE cannot perform signal reception.

(Second method for channel information feedback for MAI avoidance) A method for reporting information or indexes of a plurality of precoding vectors that may cause interference to UE Un.

15 is an illustration of a channel information feedback first method for MAI avoidance. Each terminal reports information Cn about a precoder deemed appropriate for communication with a base station, and reports information Pn about a precoder that is expected not to generate an MAI. The base station may use a method of performing MU-MIMO on a combination Un and Um of a terminal where Cn = Pm by comparing Cn and Pn reported by each terminal.

For example, referring to FIG. 15, the terminal U0 feeds back to the base station information about the precoder C ₀ and the precoder P ₀ that are not expected to generate MAI as channel information. Doing. In addition, the terminal U1 is fed back to the base station as channel information information on the precoder C ₁ and the precoder P ₁ which are not expected to generate MAI. Here, when C ₁ = P ₀ or C ₀ = P ₁ , the base station may perform MU-MIMO on the terminals U0 and U1.

However, this method is useful when there are a large number of terminals performing MU-MIMO and the reception channel characteristics of each terminal are very different, but otherwise, for example, MU-MIMO for a small number of terminals requiring high-speed information transmission. The disadvantage of doing this is that it is not easy to find a combination of Cn = Pm.

16 is an illustration of a second method of channel information feedback for MAI avoidance. Each terminal additionally reports information about the precoder In, which may cause a negligible interference when acting as an interference, other than the information Cn about the precoder determined to be suitable for receiving a signal from the base station. This method has a disadvantage in that more information should be reported to the base station than the first method. However, as the amount of reporting increases, more appropriate MAI control is possible.

For example, referring to FIG. 16, the terminal U0 reports a precoder C ₀ , which is determined to be suitable for receiving a signal from the base station, and a precoder I ₀ , which may cause an MAI of an unsizable size, to the base station. Of course, in addition to I ₀ , U0 may report two or more In corresponding to the conditional expression Th _low <| F ₀ H ₀ In | <Th _high to the base station.

Referring to FIG. 16, the terminal U1 reports to the base station a precoder C ₁ that is determined to be suitable for receiving a signal from the base station and a precoder I ₁ that can cause an MAI of a size that cannot be ignored. From here

Or

In the case of the base station, the base station may perform MU-MIMO on the terminals U0 and U1.

Meanwhile, in the above-described two methods, only the information about the precoder Cn determined by the UE to be suitable for signal reception from the base station is fed back to the base station and the MMU is avoided without feeding back other information (for example, Pn or In). Other methods of performing MIMO may be used. This is referred to as a third method of channel information feedback for avoiding MAI.

In the case of Rel-10 MIMO supporting MIMO by 8 transmitting antennas (8Tx), assuming that the correlation between the transmitting antennas is large, each terminal infers an Angle of Departure (AoD) that is suitable for signal transmission after channel measurement. CSI reporting is performed in the form of reporting information necessary for such AoD implementation. This method is referred to as the third method described above. In this case, the information required for AoD implementation becomes a value corresponding to Cn in the first and second methods.

Referring to FIG. 17, the terminal U0 reports a precoder C ₀ determined to be suitable for signal reception of the terminal corresponding to 0, 30, or -60, to the base station, and the terminal U1 corresponds to 90, 120 of the AoD. The precoder C ₁ determined to be suitable for signal reception of the terminal is reported to the base station, and the terminal U2 reports the precoder C ₂ determined to be suitable for signal reception of the terminal corresponding to AoD 45 and 30, to the base station. have.

C ₀ and C ₂ commonly have high precoding gains for AoD 30. If MU-MIMO is performed with both precoders, MAI is likely to occur. Accordingly, the base station may perform MU-MIMO by setting U0 and U1 having a large difference in AoD as MU-MIMO UE pairing.

This third method has an advantage that the feedback overhead is smaller than that of the first and second methods. Then, it is examined whether this third method can be applied to 3D MIMO.

In 3D MIMO, in the vertical domain, the difference of AoD according to the location of each terminal is not large compared to the horizontal domain, and each terminal is multipled by the scatter distribution difference. When the signal is received by the path, the AoD difference between each path constituting the main lobe (the portion forming the largest peak in the waveform) is also small. Due to this channel characteristic, the existing MU-MIMO technique (third method) that performs UE pairing with AoD difference is not suitable. In other words, it is difficult to find two UEs having a large AoD difference based on the same criteria as the horizontal domain because the difference of AoD is not large, and for this reason, it is difficult to find UE pairing for MU-MIMO only by the difference of AoD.

Referring to FIG. 18, the range of AoD is shown to 120 degrees in the horizontal domain, but the AoD is limited to a maximum of 33 degrees in the vertical domain.

Meanwhile, in order to perform spatial multiplexing using MU-MIMO in the vertical domain, the resolution of beamforming should be high. As described above, since the range of the AoD is narrow in the vertical domain, if the resolution of the beamforming is not high, interference occurs between UEs pairing with UEs, making it difficult to perform spatial multiplexing.

The first way to increase the resolution of beamforming in the vertical domain is to increase the number of vertical antennas. However, when more antennas are disposed for the vertical domain than the number of antennas in the horizontal domain for resolution, a very large number of antennas are required. For example, if 8 antennas are used in the horizontal domain, when 16 antennas are used as the vertical antennas, a total amount of 16 × 8 = 128 antennas is required.

The second way to increase the resolution of beamforming in the vertical domain is to increase the spacing between vertical antennas. In a scattered channel environment (rich scatter environment), this second method is difficult to apply, but the distance between antennas increases due to the limited scatter distribution in the vertical domain (carrier wavelength / 2 (

Correlation between antennas is maintained even in the case of (i.e.), and it is possible to increase the beamforming resolution using this second method.

However, as in this second method, the distance between antennas

If exceeded, the disadvantage is that side lobes (large peaks other than the main lobe in the waveform) are created that cause interference.

19 shows that the distance between antennas is twice the carrier wavelength (

An example of configuring an array using four antennas ().

Referring to FIG. 19, antennas constituting the array in the vertical direction correspond to twice the wavelength.

It is installed while maintaining the separation distance.

Referring to FIG. 20, the dotted line waveform has a separation distance between antennas.

And a waveform with four transmitting antennas, and the dashed-dotted waveform shows that the separation distance between antennas

And a waveform using eight transmitting antennas, and the solid line waveform has a separation distance between antennas as shown in the antenna array of FIG.

This is a waveform when four transmission antennas are used.

Referring to Figure 20, the separation between the antenna

Compared to the case of using four transmit antennas, the resolution is increased by decreasing the thickness of the waveform when the transmission antenna is increased (dashed dashed line waveform) and when the separation distance between the antennas is increased (solid waveform).

Among them, the separation between antennas

We can see that the case supports very narrow 3dB beam high resolution. However, it can also be seen that in this case a very serious side lobe occurs.

If the goal is to increase resolution, then increasing the distance between transmit antennas may be more effective than increasing the number of transmit antennas. In this case, however, high power side lobes may cause unexpected interference between terminals.

20 shows an example of interference caused by side lobes.

According to the existing AoD-based CSI reporting and MAI prediction scheme (the third method of channel information feedback for avoiding the MAI described above), in the case of FIG. 20 (a), the UE prefers AoD = 10 and AoD = -40, respectively. Report to the base station. However, as can be seen in FIG. 20 (b), side lobes near AoD = 10 occur during beam formation for AoD = −40. That is, the two terminals are not capable of spatial multiplexing, and when the base station applies MU-MIMO to the two terminals without recognizing this, serious MAI may occur. That is, the conventional CSI (PMI) reporting method (the third method described above) has a distance between antennas

It may be used only in the following limited cases, and may not be used in vertical domain precoding or beamforming in which large spacing between antennas is considered to increase resolution.

The present invention provides a method for generating and reporting channel information necessary for supporting precoding and MU-MIMO UE paring suitable for each terminal in a closed loop MIMO system performing multidimensional precoding. In order to support closed-loop MIMO operation for performing spatial multiplexing of rank 1 or more, the receiving terminal should collect channel information or channel characteristics that may be used for precoding and transmit the information to the base station. By using the pre-coding suitable for each terminal. Precoding is a signal processing operation, also referred to as channel virtualization, and the interference between terminals may be increased or decreased by this signal processing operation.

When the terminal reports accurate and precise information on the channel to the base station, the base station may select two or more terminals capable of spatial multiplexing without mutual interference by comparing channel characteristics of the plurality of terminals. However, this method of reporting channel information requires a very high feedback overhead, and thus, instead of reporting channel information, current communication systems imply that the indicator implies only some information determined to be effective for precoding after the channel characteristic measurement. Use the format reported to the base station. This channel information reporting method is called codebook based CSI feedback. The reporting method can report various channel characteristics according to the design method of the codebook, and in the case of the current LTE Rel-10 8Tx MIMO scheme, a high signal-to-signal when using a highly correlated linear antenna array is used. After identifying an AoD capable of guaranteeing a noise ratio, a format for reporting phase related information between transmission antenna ports to be applied for the AoD implementation is reported.

In addition to the advantage of transmitting the information required to increase the received SNR to the base station, such a report may be used for inferring a combination of terminals capable of spatial multiplexing without the MAI by a linear antenna array characteristic. Has However, the above report has the disadvantage that MAI can be avoided only when a highly correlated linear antenna array is used.

The present invention provides a CSI reporting technique for estimating MAI information in a horizontal domain and a vertical domain in a multidimensional array antenna including a horizontal domain and a vertical domain and reporting the same to the base station. According to the present invention, in the case of MAI for a horizontal domain in which the AoD separation between terminals is large, the information corresponding to the AoD may be delivered as in the conventional 8Tx MIMO scheme (the third method described above). In addition, in a vertical domain having a small AoD separation between terminals, in addition to an index of information related to precoding that guarantees a high SNR gain, a companion index that guarantees low interference in multiplexing may be reported together. have. The present invention provides a reference signal structure for companion index extraction and a companion index reporting method extracted through the reference signal.

The present invention may consider a case where the precoded CSI-RS described with reference to FIG. 8 in the vertical domain of the closed loop 3D MIMO system is used for CSI measurement and reporting of the vertical domain. When using Precoded CSI-RS, the base station transmits precoded CSI-RS for measuring AoD information for each terminal suitable for performing precoding in the vertical direction domain for each terminal.

The precoded CSI-RS is a reference signal precoded through a precoding vector (or matrix) to have different vertical AoD, that is, azimuth angle or vertical angle. As the distance between antennas constituting the transmit antenna array is shown in the example of FIG. 19,

If exceeded, by side lobe generation, each precoded CSI-RS is propagated with more than one direction.

21 is a distance between transmission antennas

In case of excess, it is an example of transmission of precoded CSI-RS.

Referring to FIG. 21, a precoded CSI-RS is propagated to have directivity in a vertical direction. At this time, the separation distance between the antennas is increased to increase the resolution in the vertical direction.

The antenna is installed in excess of and the precoded CSI-RS propagates with the side lobe in addition to the main lobe. With continued reference to FIG. 21, Precoded CSI-RS 0 propagates in the lowermost direction by the side lobe and also propagates in the center direction.

When the precoded CSI-RS is propagated as shown in FIG. 21, each UE measures received power for each precoded CSI-RS, and reports an index for the RS that guarantees the highest received power among the precoded CSI-RSs to the base station. Information about vertical domain precoding can be reported. According to this method, it is possible to support MIMO operation similar to the existing PMI report without searching the codebook related to PMI, and also overcomes the problem that interference prediction by side lobe generation is impossible.

For embodiments using the Precoded CSI-RS of the present invention, the separation distance between antennas is increased.

Although described as an example in which the antenna is installed in excess of, the embodiment of the present invention is not limited to such a distance between the antenna, the distance between the antenna is

The following may also be applied. In embodiments in which the number of antennas is increased to increase the resolution of the beam, the separation distance between these antennas

The following may correspond to an example.

FIG. 22 illustrates an example in which a UE feeds back channel information when a precoded CSI-RS as shown in FIG. 21 is transmitted.

Referring to FIG. 22, the U0 terminal is located in a region where Precoded CSI-RS 0 is received with the greatest power, and thus, the UE U0 feeds back an index R0 indicating Precoded CSI-RS 0 to the base station as channel information. do. In the same manner, the UE U1 feeds back an index R3 for Precoded CSI-RS 3 and the UE U2 feeds back an index R0 for Precoded CSI-RS 0.

In the case of using the channel information feedback method using the Precoded CSI-RS as a reference signal, as described with reference to FIG. 8, the terminal simply measures the maximum received power without a separate codebook search. Information can be fed back.

Previous studies show that, unlike the horizontal domain, vertical multi-rank transmission is performed for each terminal because the vertical domain is not easy to generate a scattering environment and the AoD range is narrow. ) Were not many cases that could be supported.

However, as described above, when using a high resolution precoding by increasing the number of antennas or increasing the separation distance between antennas, there may be a plurality of paths that can be distinguished by each terminal in the vertical domain.

23 illustrates the propagation path in the vertical domain.

Referring to FIG. 23, U0 receives radio waves through two paths, and U1 and U2 similarly receive radio waves through two paths.

When the existing channel information reporting method is used for the reception path, the terminal U0 reports a vertical direction RI (Rank Indicator) indicating a rank 2 to the base station. In addition, as described above with the channel information feedback method for the Precoded CSI-RS, RS0 and RS1, which are indices for the Precoded CSI-RS having a large reception power, may be fed back to the base station (the best in the channel information feedback for the Precoded CSI-RS). In addition to the large received power, the indexes for two or more precoded CSI-RSs that guarantee a smaller but sufficient received power may be fed back to the base station as channel information). The UE U1 may report the vertical domain RI indicating the rank 1 to the base station because the Precoded CSI-RS having a sufficiently large reception power is RS3, and report the index RS3 to the base station as channel information about precoding. In addition, U2 reports the vertical domain RI indicating rank 2 to the base station, and reports RS0 and RS2 as precoding related information to the base station.

As described above with reference to FIG. 23, when the UE reports an index for RI and a preferred Precoded CSI-RS to the BS, the BS MU-MIMO UEs U2 and U1 in which the indices of the preferred Precoded CSI-RS do not overlap. MU-MIMO can be performed by pairing. However, as can be seen from FIG. 23, since U1 is not sufficiently large and difficult to use as a channel, it is located in an area where Precoded CSI-RS 2 propagates when it is used as a channel for other terminals, which may act as interference. Therefore, the signal transmission for U2 can act as interference to U1.

In order to use the channel information feedback first method for avoiding MAI in order to avoid the above interference, the channel information reported by the UE is shown in FIG. 24.

FIG. 24 illustrates an example of channel information reported by a terminal when using the channel information feedback first method for MAI avoidance for a vertical direction domain.

Referring to FIGS. 23 and 24, the UE U1 reports information on precoding determined to be the most suitable as an index for RS3, and reports an index for RS0 and RS1 as a companion index BCI (Best Companion Index). .

According to the first method described above, when the precoding information Cn determined to be most suitable for one terminal and the companion index Pm of the other terminal match, the two terminals are performed as UE pairing to perform MU-MIMO. Referring to 24, since the precoding information of U0 and the companion index of U1 coincide, MU-MIMO can be performed by pairing the two UEs.

However, this method has a problem in that the CSI reporting overhead increases rapidly as the precoded CSI-RS increases.

Accordingly, when the precoded CSI-RS is used in the vertical domain of a closed loop 3D MIMO system, the present invention provides channel information for precoding, channel information for MAI avoidance, and rank information without a sharp increase in overhead. Provided is a method for transmitting and receiving between terminals.

PMI, RI and CQI have been reported as channel information. In particular, PMI has been reported classified into first PMI and second PMI. Where first PMI is a value for wideband and second PMI is a PMI value for a subband (narrow band). The present invention provides a method for replacing such a PMI and RI reporting method with an Exclusion Index (ECI) and a Reference Signal Index (RSI). Of course, ECI and RSI may be used only for the vertical domain, and PMI and RI reporting methods may be used for the horizontal domain. In other words, the ECI / RSI method provides channel information corresponding to the channel information provided by the PMI / RI method, and the ECI / RSI method exists exclusively with the PMI / RI method, so that only one method should be used. no.

Looking at the PMI / RI method corresponding to the ECI / RSI method in order to understand more, the types can be classified as follows according to the type of information reported to the base station in the PMI / RI method.

Type 1: UE selected subband CQI

Type 1a: subband CQI and second PMI

Type 2: wideband CQI and PMI for 2/4 Tx

Type 2a: wideband first PMI for 8Tx

Type 2b: wideband CQI and second PMI for 8Tx

Type 2c: wideband CQI and first / second PMI for 8Tx

Type 3: RI

Type 4: wideband CQI

Type 5: RI and wideband PMI

Type 6: RI and PTI

In addition, the reporting period in the PMI / RI method may follow the following rules.

(1) The RI may be reported with the longest period among the other information, and one RI report is performed after N PMI and CQI reports with a period less than or equal to the maximum reporting period defined by RRC (Radio Resource Control). Can be. The RI may be reported with the same period as the first PMI.

(2) First PMI is always selected as wideband PMI, and may be reported with a period longer than the second PMI, which may be selected as a subband PMI, or with the same period.

FIG. 25 illustrates a period in which PMI / RI and CQI are reported and the type of channel information reported in the period.

Referring to FIG. 25, an RI indicating a rank is reported in the longest period, and a second PMI is reported in the shortest period.

When report periods overlap, channel information with low priority may be omitted, which is called a dropping rule. The dropping rule in the PMI / RI method is as follows.

Among the channel information types in the above-described PMI / RI method, Type 3, Type 5, and Type 6 have a higher priority of reporting than other types, so that one of the Types has the same subframe on the same subframe as the CSI of the other Type. If scheduled to, the UE performs a CSI report of a type having a high priority and omits CSI reporting of other types.

Hereinafter, the ECI / RSI method in the present invention will be described.

The ECI / RSI method according to the embodiment of the present invention is performed by the following steps.

First, the UE estimates a precoded CSI-RS having a very low reception power (where MAI is not expected even when used for other UE precoding in MU-MIMO) and reports the information about the precoded CSI-RS as an index to the base station. The information reported here is ECI information. Through such ECI information, the base station can obtain indirect information (precoding information to be excluded) about the preferred precoding while acquiring information on precoding that can avoid MAI.

Next, the UE reports to the base station an index indicating a precoded CSI-RS that can express precoding information suitable for itself among the remaining precoded CSI-RSs except for the precoded CSI-RS reported through the ECI. The information reported here is RSI information. Through this RSI information, the base station can obtain the direct information of the precoding for the terminal. The RSI information includes RI information that is rank information and may also be considered to include PMI information in the above-described PMI / RI.

The RSI may be represented in a bitmap form or may be represented by an index of a codebook expressed as a combination of precoded CSI-RS indices.

26 is an illustration of a codebook for RSI.

Referring to FIG. 26, a maximum rank classified as a column indicates the number of precoded CSI-RSs excluded by ECI. For example, if there are eight total precoded CSI-RSs, the maximum rank is 1 in the codebook when information about seven precoded CSI-RSs with very low reception power is transmitted through the ECI. In this case, since the remaining one precoded CSI-RS is determined as the preferred precoded CSI-RS, information of the RSI may not be needed.

Referring to FIG. 26, when the maximum rank is 2, the RSI may be 10 or 01 (when one of the two is a preferred precoded CSI-RS) as a bitmap as shown in FIG. 26, and also a bitmap 11. (If both are preferred precoded CSI-RSs). For each of the three cases, the RSI may be reported as a bitmap, or as shown in FIG. 26, a codebook indicating each case as an index may be designed to report a

codebook index

0, 1, or 2.

If the maximum rank is 5, there are 31 possible combinations. However, including all of these possible combinations in the codebook requires too many bits and increases the overhead of channel information feedback.

To solve this problem, the number of precoded CSI-RSs reported through RSI can be limited. Since the number of precoded CSI-RSs reported through RSI means rank, this can be understood in the same way as limiting the number of ranks.

Referring to FIG. 26, the maximum rank is limited to 2 when the maximum rank is 5. In this case, a total of 15 combinations are possible, which can also be reduced by applying other rules. One of the rules is that when selecting a precoded CSI-RS, it restricts the selection of the precoded CSI-RS spaced more than a certain interval. For example, the separation between precoded CSI-RSs can be limited to two or more. In more detail, it is possible to set different separation distance limit values between precoded CSI-RSs according to the maximum rank. When the maximum rank is 4, the distance between the precoded CSI-RSs is limited to 2 or more, and when the maximum rank is 5, the precoded CSI -RS separation can be limited to 3 or more.

Referring to FIG. 26, when the maximum rank is 4, the maximum rank is limited to 2, and the distance between the precoded CSI-RSs is 2 or more. Accordingly, the case where the rank is 2 is limited to three cases of 1010, 0101, and 1001 in the bitmap. When the maximum rank is 5, the maximum rank is limited to 2, and the spaced interval between the precoded CSI-RSs is 3 or more. Accordingly, the case where the rank is 2 is limited to three cases of 10010, 01001, and 10001 in the bitmap, and the codebook can be configured in a total of eight combinations.

The ECI / RSI method may define different types of channel information by feeding back different information from the PMI / RI method. An example of the type of channel information defined differently is as follows.

Type 7: ECI (exclusion index)

Type 7a: ECI and RSI

Type 7b: ECI and RI

Type 7c: ECI and RSI and RI

Type 8: wideband RSI

Type 8a: wideband RSI and wideband PMI

Type 8b: wideband RSI and first PMI

The size of channel information may be different for each type as described above. FIG. 27 is an example of the size of channel information of types newly defined in relation to an ECI / RSI method.

In FIG. 27, Configuration 0, Configuration 1, and Configuration 2, which are information related to the number of transmit antennas and the antenna separation distance, are information transmitted from the base station to the terminal through RRC.

In the ECI / RSI method, the same reporting periods and dropping rules as the PMI / RI method can be applied.In the ECI / RSI method, ECI can be reported at a longer period than the RSI. When Type 7a / Type 7b / Type 7c are determined to have a high priority and overlap in the same subframe as other types of channel information, other types of channel information may be dropped.

Referring to FIG. 28, the method 3500 for receiving channel information by the base station may include transmitting a plurality of reference signals, each precoded in different matrices, to different radio resources and transmitting them to the terminal (S3510); A channel including first indicator information for one or more reference signals whose reception power strength is less than or equal to a reference value among a plurality of reference signals, and second indicator information for one or more reference signals among remaining reference signals except for the one or more reference signals. And receiving information from the terminal (S3520).

A wireless communication system to which an embodiment of the present invention can be applied may be composed of one or more base stations and one or more terminals, which may be a system using a multidimensional antenna array.

An example of a base station using a multidimensional antenna array has been described with reference to FIG. 3. Referring to FIG. 3 again, the base station may implement the MIMO system in a space including the vertical direction by arranging the antenna array in the vertical domain as well as the antenna array in the horizontal domain. Such a system may be referred to as a 3D MIMO system.

When the base station uses a multi-dimensional antenna array, different matrices in step S3510 may be a beamforming matrix such that the aforementioned plurality of reference signals are transmitted with different propagation directions in the vertical domain of the antenna array. Can be.

Multiplying a specific signal by the beamforming matrix shown in Equation 1 produces eight signals whose phases only change. When these signals are included and propagated in eight vertical antenna arrays, these signals have a specific direction. It will spread. Therefore, for each specific signal, multiply different precoding matrices of v1, v2, and v3 (precoding matrices with different propagation directions) and propagate them using vertical antenna arrays. It is possible to generate a plurality of reference signals to be transmitted with.

An example of propagation of the Precoded CSI-RS propagated with different propagation directions in the vertical direction is shown in FIG. 8. Referring to FIG. 8 again, the base station precodes reference signals to have different propagation directions and transmits them to the terminal. Since these reference signals have different propagation directions, as shown in FIG. 8, the Precoded CSI-RS The zero reference signal 810 propagates downward and the precoded CSI-RS 5 reference signal 815 propagates upward.

After transmitting the reference signal, the base station receives the channel information from the terminal generating the channel information through the reference signal. Receiving such channel information is step S3520.

The UE measures the received power strengths of the plurality of reference signals precoded with different precoding matrices.

Referring back to FIG. 8, since a plurality of reference signals precoded with different precoding matrices are propagated through different paths with different propagation directions, the strength of received power measured by the terminal may be different. For example, since the terminal 110 is located in a region where the Precoded CSI-RS 3 813 propagates, the strength of the received power for the Precoded CSI-RS 3 813 will be measured the largest. In contrast, since the precoded CSI-RS 0 810 or the precoded CSI-RS 5 815 propagates to a relatively remote area, the received power strength of the terminal 110 will be small.

In a method for receiving channel information according to an embodiment of the present invention, the UE measures received power strengths of a plurality of reference signals, and includes information on one or more reference signals whose received power strengths are equal to or less than a reference value in channel information. Send. In addition, except for a reference signal having a received power intensity lower than or equal to the reference value, information on one or more other reference signals among the remaining reference signals is also included in the channel information and transmitted to the base station.

The ECI / RSI method described above may be applied here.

Receiving power of the terminal is less than the reference value means that when the base station transmits data to the terminal using the precoding matrix used in the corresponding Precoded CSI-RS, it is difficult to correctly receive the data from the terminal. Therefore, it is ECI information not to use this precoding matrix in data transmission for the corresponding terminal.

At the same time, the reception power strength of the terminal is less than the reference value has no effect on the terminal even if the base station transmits data to another terminal using the precoding matrix used in the Precoded CSI-RS, that is, the possibility of avoiding the MAI It means high.

As a result, according to an embodiment of the present invention, the terminal measures the received power strengths of the plurality of reference signals, and among them, information about one or more reference signals having the received power intensity less than or equal to the reference value (described above, 'first indicator information') Transmitting to the base station means not using the precoding matrix used for such a reference signal to itself (terminal) and simultaneously using the precoding matrix for the other terminal when trying to MU-MIMO with another terminal. It means that you may. For example, the above-described ECI information may be used.

The terminal also transmits to the base station by including at least one reference signal of the remaining reference signals in the channel information, except for the reference signal having a received power strength of less than the reference value as the channel information, the information (described above 'second indicator information') Preferred information. Once the information about precoding that is to be excluded or used for MU-MIMO with other terminals is transmitted as the first indicator information, then the precoding matrix that is most suitable for itself (terminal) other than this precoding matrix is next transmitted. You need to give information about. This is the second indicator information.

As the second indicator information, the RSI information in the above-described ECI / RSI method may be used. RSI information is information used to select the most suitable Precoded CSI-RS for the terminal through the information measured through the reception of the Precoded CSI-RS, and transmit the indicator information to the base station. The UE may select a preferred Precoded CSI-RS according to various criteria, but in one embodiment, an indicator for selecting a predetermined number of Precoded CSI-RSs in higher order in order of increasing received power according to the received power strength The information can be utilized as RSI information.

As a method of representing the RSI information, there may be a method of using a bitmap form and a method of using a codebook as described with reference to FIG. 26. Of course, the ECI information may also be information in the form of a bitmap and may also be index information of a codebook.

Since the ECI information may take a long length of data while lengthening a transmission / reception period between the terminal and the base station, even when using a bitmap form or using a codebook, a combination of all possible reference signals as an ECI may be included in the codebook. .

However, in the case of RSI, since a preferred reference signal may change from time to time, it should be reported to the base station in a short period. Accordingly, in order to reduce overhead, the size of data can be reduced by limiting objects to be included in RSI according to some rules. .

This rule has been described with reference to FIG. 26. Once again, some of the codebooks for the RSI include N or less of the reference signals among all possible combinations of one or more reference signals, except for the reference signals included in the ECI. The difference may be composed of a combination of M or more.

For example, when the number of reference signals other than the reference signals included in the ECI is five, all 31 combinations may be made, of which the limit of the number of preferred reference signals to 2 or the preferred reference signals is limited. The number of combinations can be reduced by making the difference between the indexes equal to 3 or more. In this case, as described with reference to FIG. 26, all of them are limited to eight combinations and information can be transmitted using a 3-bit signal.

The method of transmitting and receiving channel information using the Precoded CSI-RS as a reference signal can be used not only in the vertical domain but also in the horizontal domain. However, the existing method may be used as it is for the horizontal domain in order to increase compatibility with previous versions of the terminal.

Therefore, the base station further transmits a cell-specific reference signal (CRS) or a channel state information reference signal (CSI-RS) to the terminal in step S3510, and receives the CRS or the CSI-RS in step S3520. Channel information further including at least one of a Rank Indicator (RI), a Precoder Matrix Indicator (PMI), and a Channel Quality Indicator (CQI) may be received from the terminal as horizontal domain channel estimation information.

Referring to FIG. 29, in a method 3600 of transmitting channel information of a terminal, receiving a plurality of reference signals mapped to different radio resources and precoded in different matrices, respectively (S3610), Measuring received power strength with respect to each of the reference signals in, and receiving first indicator information on one or more reference signals having a received power intensity less than or equal to the reference value, and second indicator information on one or more reference signals, except one or more reference signals. The method may include transmitting channel information including a to the base station (S3620).

When the base station uses a multi-dimensional antenna array, different matrices in step S3610 may be a beamforming matrix such that the aforementioned plurality of reference signals are transmitted with different propagation directions in the vertical domain of the antenna array. Can be.

Referring to FIG. 8, it has been described that Precoded CSI-RS can be used as a reference signal for channel estimation for the practice of the present invention. In operation S3620, the reference signals precoded in different matrices transmitted by the base station to the terminal mean Precoded CSI-RS.

The base station precodes a plurality of reference signals according to a preset reference and transmits the plurality of reference signals to the terminal. As described above, the base station may use a beamforming matrix having different propagation directions in the vertical direction as the precoding matrix.

Referring back to FIG. 8, since a plurality of reference signals precoded with different precoding matrices are propagated through different paths with different propagation directions, the strength of received power measured by the terminal may be different. For example, referring back to FIG. 8, since the terminal 110 is located in a region where the Precoded CSI-RS 3 813 propagates, the strength of the received power for the Precoded CSI-RS 3 813 is measured the largest. Will be. In contrast, since the precoded CSI-RS 0 810 or the precoded CSI-RS 5 815 propagates to a relatively remote area, the received power strength of the terminal 110 will be small.

In the method for transmitting channel information according to an embodiment of the present invention, the UE measures received power strengths of a plurality of reference signals, and includes information on one or more reference signals whose received power strengths are equal to or less than a reference value in the channel information. Send. In addition, except for a reference signal having a received power intensity lower than or equal to the reference value, information on one or more other reference signals among the remaining reference signals is also included in the channel information and transmitted to the base station.

The ECI / RSI method described above may be applied here.

The terminal also transmits to the base station by including at least one other reference signal among the remaining reference signals in the channel information, except for the reference signal having a received power intensity of less than the reference value as the channel information, the information (described above 'second indicator information') Is preference information. Once the information about precoding that is to be excluded or used for MU-MIMO with other terminals is transmitted as the first indicator information, then the precoding matrix that is most suitable for itself (terminal) other than this precoding matrix is next transmitted. You need to give information about. This is the second indicator information.

As a method of representing the RSI information, there may be a method of using a bitmap form and a method of using a codebook as described with reference to FIG. 21. Of course, the ECI information may also be information in the form of a bitmap and may also be index information of a codebook.

However, in the case of RSI, since a preferred reference signal may change from time to time, it should be reported to the base station in a short period. Accordingly, in order to reduce overhead, the size of data can be reduced by limiting the target to be included in the RSI according to some rules. have.

Accordingly, the terminal further receives a cell-specific reference signal (CRS) or a channel state information reference signal (CSI-RS) in a receiving step (S3610), and horizontally through the CRS or CSI-RS in a transmitting step (S3620). Channel information further including at least one of a Rank Indicator (RI), a Precoder Matrix Indicator (PMI), and a Channel Quality Indicator (CQI) may be transmitted to the base station as the horizontal domain channel estimation information.

Referring to FIG. 30, the base station 120 may include a transmitter 121, a receiver 122, a controller 123, and the like.

The transmitter 121 may perform a function of transmitting a channel estimation reference signal to a terminal according to an embodiment of the present invention, and the receiver 122 may perform a function of receiving channel information from a terminal according to an embodiment of the present invention. Can be done. In addition, the controller 123 controls a transmitter 121 and a receiver 122 according to an embodiment of the present invention, and performs a series of control operations for a method for receiving channel information for transmitting a reference signal to a terminal and receiving channel information. The transmitter 121 may transmit a plurality of reference signals, each of which is precoded in different matrices, to different radio resources and transmit them to the terminal.

The base station may be a system using a multi-dimensional antenna array, in which case different matrices allow the aforementioned plurality of reference signals to be transmitted with different propagation directions in the vertical domain of the antenna array. It may be a beamforming matrix. The transmitter 121 may transmit a plurality of reference signals precoded with the same power.

In one example, the receiver 122 may receive channel information that is information obtained by sorting received power strengths of each of the plurality of reference signals measured by the terminal in ascending or descending order. The information indicating one or more reference signals received by the receiver 122 may be indexes of reference signals or index information of radio resources to which reference signals are mapped.

In another example, the receiver 122 may include first indicator information about one or more reference signals having a received power intensity of a plurality of reference signals less than or equal to a reference value, and one or more reference signals except for the one or more reference signals. Channel information including second indicator information may be received from the terminal.

The first indicator information or the second indicator information may be bitmap information or index information of a codebook, and the second indicator information may be indicator information on one or more reference signals selected according to the received power strength among the remaining reference signals. have.

In addition, the second indicator information may be index information of a codebook configured by a combination of one or more reference signals selectable by the number of remaining reference signals, wherein the codebook is one or more reference signals selectable by the number of remaining reference signals. Of all the combinations, the number of reference signals may be equal to or less than N (N is a natural number of 1 or more), or the index of the index given to the reference signal may be a combination of M or more (M is a natural number of 1 or more).

The transmitter 121 further transmits a cell-specific reference signal (CRS) or a channel state information reference signal (CSI-RS) to the terminal, and the receiver 122 transmits a horizontal domain channel through the CRS or CSI-RS. As estimation information, channel information further including at least one of a Rank Indicator (RI), a Precoder Matrix Indicator (PMI), and a Channel Quality Indicator (CQI) may be received from the terminal.

Referring to FIG. 31, the terminal 110 may include a transmitter 111, a receiver 112, a controller 113, and the like.

The receiver 112 may perform a function of receiving a reference signal for channel estimation from a base station according to an embodiment of the present invention, and the transmitter 111 performs a function of transmitting channel information to a base station according to an embodiment of the present invention. Can be done. In addition, the controller 113 controls a transmitter 111 and a receiver 112 according to an embodiment of the present invention, and performs a series of control operations for a method of transmitting channel information for receiving a reference signal from a base station and transmitting channel information. Can be.

The receiving unit 112 may receive a plurality of reference signals mapped to different radio resources and precoded in different matrices, respectively, from the base station, and the control unit 113 may receive power for each of the plurality of reference signals. Intensity can be measured.

In one example, the transmitter 111 instructs the reference signal described above with the index information of the reference signal or the index information of the radio resource to which the reference signal is mapped with respect to the information indicating one or more reference signals in order of receiving power strength. The information can be transmitted to the base station 120.

In another example, the transmitter 111 may include first indicator information about one or more reference signals having a received power intensity lower than or equal to a reference value, and second indicator information about one or more reference signals among the reference signals except for the one or more reference signals. Channel information may be transmitted to the base station.

The base station may be a system using a multi-dimensional antenna array, in which case different matrices allow the aforementioned plurality of reference signals to be transmitted with different propagation directions in the vertical domain of the antenna array. It may be a beamforming matrix.

The receiver 112 further receives a cell-specific reference signal (CRS) or a channel state information reference signal (CSI-RS), and the transmitter 111 transmits horizontal domain channel estimation information through the CRS or CSI-RS. As an example, channel information further including at least one of a Rank Indicator (RI), a Precoder Matrix Indicator (PMI), and a Channel Quality Indicator (CQI) may be transmitted to the base station.

The above description is merely illustrative of the technical idea of the present invention, and those skilled in the art to which the present invention pertains may make various modifications and changes without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are not intended to limit the technical idea of the present invention but to describe 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.

CROSS-REFERENCE TO RELATED APPLICATION

This patent application is related to the patent application No. 10-2012-0125502 filed in Korea on November 7, 2012 and the patent application No. 10-2012-0150007 filed in Korea on December 20, 2012. Priority is claimed under section (a) (35 USC § 119 (a)), all of which is incorporated by reference in this patent application. In addition, if this patent application claims priority for the same reason for countries other than the United States, all its contents are incorporated into this patent application by reference.

Claims

In a method for receiving a channel information in a base station in a wireless communication system,

Mapping a plurality of reference signals, each of which is precoded in different matrices, onto different radio resources and transmitting them to the terminal; And

Receiving channel information from the terminal including first information indicating one or more reference signals selected according to the received power strength among reference signals having a received power intensity greater than a reference value among the plurality of reference signals; How to receive channel information.
The method of claim 1,

And receiving second information indicating at least one reference signal having a received power intensity at the terminal less than the reference value among the plurality of reference signals.
The method of claim 1,

The base station is a system using a multi-dimensional antenna array (antenna array),

Wherein the different matrices are beamforming matrices for transmitting the plurality of reference signals with different propagation directions in a vertical domain of the antenna array.
The method of claim 1,

Transmitting a cell-specific reference signal (CRS) or a channel state information reference signal (CSI-RS) to the terminal; And

The channel information including at least one of RI (Rank Indicator), PMI (Precoder Matrix Indicator) and CQI (Channel Quality Indicator) as the horizontal domain channel estimation information through the CRS or the CSI-RS. And receiving from the terminal.
The method of claim 1,

And the first information is bitmap information or index information of a codebook.
In a method of transmitting channel information by a terminal in a wireless communication system,

Receiving a plurality of reference signals mapped to different radio resources and precoded in different matrices, respectively, from a base station; And

Measuring received power intensity with respect to each of the plurality of reference signals, and including first information indicating one or more reference signals selected according to received power strength among reference signals having a received power intensity greater than a reference value among the plurality of reference signals; And transmitting channel information to the base station.
The method of claim 6,

And transmitting second information indicating one or more reference signals having a received power intensity less than or equal to the reference value among the plurality of reference signals.
The method of claim 6,

The base station is a system using a multi-dimensional antenna array (antenna array),

Wherein the different matrices are beamforming matrices such that the plurality of reference signals are transmitted with different propagation directions in the vertical domain of the antenna array.
The method of claim 6,

Receiving a cell-specific reference signal (CRS) or a channel state information reference signal (CSI-RS) from the base station; And

The channel information including at least one of RI (Rank Indicator), PMI (Precoder Matrix Indicator) and CQI (Channel Quality Indicator) as the horizontal domain channel estimation information through the CRS or the CSI-RS. And transmitting to the base station.
The method of claim 6,

And the first information is bitmap information or index information of a codebook.
A terminal for receiving a reference signal and transmitting channel information in a wireless communication system,

A receiving unit for receiving a plurality of reference signals mapped to different radio resources and precoded in different matrices, respectively, from a base station;

A control unit measuring a received power intensity of each of the plurality of reference signals; And

And a transmitter configured to transmit channel information including first information indicating one or more reference signals selected according to the received power strength among reference signals having a received power intensity greater than a reference value among the plurality of reference signals.
The method of claim 11,

And the transmitter further transmits second information indicating one or more reference signals having a received power intensity less than or equal to the reference value among the plurality of reference signals.
The method of claim 11,

The base station is a system using a multi-dimensional antenna array (antenna array),

Wherein the different matrices are beamforming matrices for transmitting the plurality of reference signals with different propagation directions in a vertical domain of the antenna array.
The method of claim 11,

The receiver further receives a cell-specific reference signal (CRS) or a channel state information reference signal (CSI-RS) from the base station,

The transmitter may include at least one of RI (Rank Indicator), PMI (Precoder Matrix Indicator) and CQI (Channel Quality Indicator) as horizontal domain channel estimation information through the CRS or the CSI-RS. And further transmitting channel information to the base station.
The method of claim 11,

And the first information is bitmap information or index information of a codebook.