KR101608708B1 - Multiple-input multiple-output communication system using differential codebook including unitary matrices - Google Patents

Abstract

A multi-input / output communication system using a differential codebook comprising unitary matrices is provided. A receiver is a target corresponding to a relationship between a previous preferred codeword of a receiver from a differential codebook comprising a plurality of unitary matrices and explicit feedback information related to an explicit channel matrix between the receiver and the transmitter Searches for a unitary matrix, and feeds back information on the target unitary matrix. The transmitter can determine the preferred codeword of the receiver based on the target unitary matrix.

Differential codebook, MIMO, preferred code word, explicit feedback, unitary matrix

Description

[0001] MULTIPLE-INPUT MULTIPLE-OUTPUT COMMUNICATION SYSTEM USING DIFFERENTIAL CODEBOOK INCLUDING UNITARY MATRICES [0002]

The following embodiments relate to a multi-input / output communication system, and more particularly to a technique for adaptively generating a new codebook.

2. Description of the Related Art In recent years, various studies have been conducted to provide various multimedia services including voice service and support high-quality and high-speed data transmission in a wireless communication environment. In particular, a technology for a multi-input multi-output (MIMO) communication system using a plurality of channels in a spatial domain is rapidly developing.

In a MIMO communication system, a base station and terminals use a codebook to appropriately cope with a channel environment. The specific space can be quantized into a plurality of codewords, and a plurality of codewords generated by quantizing the space according to a certain criterion can be stored in the base station and the terminals.

For example, in the downlink, each of the terminals can select a preferred code word among the codewords included in the codebook according to a channel formed between the base station and each of the terminals, and the base station also selects a preferred code word By receiving information on the codeword, the channel can be grasped. The selected preferred codeword may then be used by the base station to perform precoding or transmit via multiple antennas.

When the MIMO communication system uses a fixed codebook, the fixed codebook quantizes the entire space, so that a relatively large quantization error may occur. Such a quantization error may deteriorate the performance of the MIMO communication system, and a technique for reducing such a quantization error is needed.

A method of operating a receiver using a differential codebook according to an embodiment of the present invention includes: accessing a memory in which a differential codebook including a plurality of unitary matrices is stored; A target unitary matrix corresponding to the relationship between the previous preferred codeword of the receiver among the plurality of unitary matrices and the explicit feedback information between the receiver and the transmitter and the explicit channel matrix between the receiver and the transmitter ; And feedbacking information on the target unitary matrix to the transmitter.

The step of searching for the target unitary matrix may include searching the target unitary matrix among the plurality of unitary matrices by considering how close the previous preferred code word is to the explicit feedback information .

The method may further comprise generating a new codebook using the differential codebook and the previous preferred code word.

The step of generating the new codebook may be a step of generating the new codebook with the previous codebook until a predetermined reset period is reached.

The explicit feedback information may comprise a covariance of the explicit channel matrix or the explicit channel matrix.

The previous preferred codeword may be any one of the codewords of the fixed base codebook.

A method of operating a transmitter using a differential codebook according to an embodiment of the present invention includes generating a new codebook based on a differential codebook including a plurality of unitary matrices and a previous preferred code word of a receiver; Receiving information on a target unitary matrix, which is one of the plurality of unitary matrices, from the receiver; And accessing the memory to extract the target unitary matrix from the differential codebook.

The method may further comprise detecting a preferred codeword of the receiver among a plurality of codewords in the new codebook based on the target unitary matrix.

The method may further include performing precoding in consideration of the preferred codeword.

A receiver using a differential codebook according to an embodiment of the present invention includes a memory storing a differential codebook including a plurality of unitary matrices; A target unitary matrix corresponding to the relationship between the previous preferred codeword of the receiver among the plurality of unitary matrices and the explicit feedback information between the receiver and the transmitter and the explicit channel matrix between the receiver and the transmitter ; And a feedback unit for feeding back information on the target unitary matrix to the transmitter.

The receiver may further include a codebook generator for generating a new codebook using the differential codebook and the previous preferred code word.

The retrieval unit retrieves the target unitary matrix among the plurality of unitary matrices considering how close the previous preferred code word is to the explicit feedback information.

A transmitter using a differential codebook according to an embodiment of the present invention includes a codebook generator for generating a new codebook based on a differential codebook including a plurality of unitary matrices and a previous favorite code word of a receiver; A receiver for receiving information on a target unitary matrix, which is one of the plurality of unitary matrices, from the receiver; A detector for detecting a preferred code word of the receiver among the plurality of code words in the new codebook based on the target unitary matrix; And a precoder for performing precoding considering the preferred codeword.

Embodiments of the present invention may use a differential codebook comprising unitary matrices to generate an optimal new codebook that matches the state of the channel.

Embodiments of the present invention can generate an optimal new codebook with less computational effort and less feedback overhead by using a differential codebook comprising unitary matrices.

Hereinafter, embodiments according to the present invention will be described in detail with reference to the accompanying drawings.

1 is a diagram showing an example of a multi-input / output communication system.

1 is a diagram illustrating a closed loop MIMO communication system according to an embodiment of the present invention.

Referring to FIG. 1, a closed loop MIMO communication system includes a base station 110 and users 120, 130, and 140. 1 is an example of a multi-user MIMO communication system, and embodiments of the present invention can be applied to a single-user MIMO communication system. In addition, 'closed loop' means that the users 120, 130 and 140 on the downlink provide feedback information to the base station 110, and the base station 110 performs precoding based on the feedback information, .

A plurality of antennas are installed in the base station 110, and one or a plurality of antennas may be installed in each of the users 120, 130, and 140. Channels are formed between the base station 110 and the users 120, 130, and 140, and signals are transmitted / received through the channels.

Base station 110 may transmit pilot signals to users 120, 130, and 140 via downlink channels. Here, the pilot signal is a well-known signal to the base station 110 and the users 120, 130 and 140.

Each of the users 120, 130 and 140 estimates a channel formed between the base station 110 and the users 120, 130 and 140 using the pilot signal. Each of the users 120, 130, and 140 selects one of the codewords included in the codebook stored in advance based on the estimated channel, as a preferred codeword. Here, the preferred codeword may also be referred to as a preference vector or preference matrix.

The base station 110 may transmit one or more data streams to the users 120, 130, At this time, the base station 110 may use a spatial division multiplexing access (SPD) scheme or a space division multiplexing (SDM) scheme, and the base station 110 may use codewords included in the codebook ), And generate a transmission signal using the generated precoding matrix.

In order for the base station 110 to generate the transmission signal, each of the users 120, 130, and 140 must provide information on the corresponding channel to the base station 110 as 'feedback information'. At this time, the feedback information provided from each of the users 120, 130, and 140 to the base station 110 depends on two types of 'implicit feedback' and 'explicit feedback'.

Each of the users 120, 130, and 140, after applying a predetermined receive filter (e.g., a receive filter or an MMSE receive filter corresponding to a zero forcing beamforming technique) to the received signal, , The preferred code word is determined. For example, if each of users 120, 130, and 140 use a zero forcing beamforming receiver, each of users 120, 130, and 140 may receive a receive filter corresponding to a zero forcing beamforming technique Estimates the corresponding channel under the premise that it passes, and determines a preferred code word based on the corresponding channel. According to this 'intrinsic feedback', each of the users 120, 130 and 140 determines the preferred transmission rank as well as information about the index information (direction information) of the preferred codeword and the quality of the channel concerned .

In a multi-input / output communication system using 'implicit feedback', the base station 110 has relatively many limitations. For example, since each of the users 120, 130, and 140 determines a preferred transmission rank, the base station 110 may not be able to freely determine the transmission rank, MIMO transmission mode, SU-MIMO transmission mode, transmission diversity mode, and the like can be freely determined (for example, only the channel after the reception filter of each of users 120, 130, and 140 is applied) I can not.

The limitations of the base station 110 due to this 'implicit feedback' can be solved through 'explicit feedback'. For example, in a multi-input / output communication system using 'explicit feedback', the base station 110 can know the channels themselves and therefore can freely determine the transmission rank and transmission mode.

In addition, the channels between the base station 110 and the users 120, 130, and 140 may vary over time. If base station 110 and users 120, 130, 140 use a fixed codebook, it may be difficult to adaptively adapt to the state of the varying channels. However, as will be described in detail below, the base station 110 and the users 120, 130, and 140 according to an embodiment of the present invention adaptively generate new codebooks and use the new codebooks to reduce quantization errors . When the base station 110 and the users 120, 130, 140 adaptively generate a new codebook, the new codebook quantizes relatively less space than the previous codebook, and thus has a relatively low quantization error. Hereinafter, a mode for adaptively generating a new codebook according to embodiments of the present invention will be referred to as a 'differential mode'.

As a result, embodiments of the present invention provide techniques that can efficiently perform a differential mode in an explicit feedback environment. The techniques are described in detail below.

2 is a conceptual diagram showing an example of a fixed codebook and a new codebook according to embodiments of the present invention, which is an example of a fixed codebook.

Referring to FIG. 2, a basic codebook 210 having a size of 3 bits includes 8 codewords (arrows). Here, the basic codebook 210 may be either a fixed codebook, a DFT codebook comprising several DFT (Discrete Fourier Transform) matrices or vectors, a codebook defined in several standards, or any codebook.

In general, codewords included in the basic codebook 210 quantize the entire space, so that the distance between the codewords is distant. Therefore, the basic codebook 210 has a relatively large quantization error, and in order to reduce the quantization error, the size of the basic codebook 210 must increase. However, increasing the size of the basic codebook 210 increases the feedback overhead, so that the quantization error and the feedback overhead have a trade-off relationship.

Since the state of the channel does not vary greatly statistically, the channel at the next time does not deviate greatly from the channel at the previous time, and the preferred codeword at the next time does not deviate greatly from the previous preferred codeword. Thus, if we construct a new codebook that includes the code words around the previous preferred code word, we can reduce the quantization error without increasing the feedback overhead.

The code words included in the 3-bit new codebook 220 shown in FIG. 2 are distributed intensively in the A region and not in the B region. That is, if the previous preferred codeword is located adjacent to the A region or the A region, the quantization error can be reduced by creating a new codebook 220 that includes codewords that are distributed intensely in the A region.

3 is a conceptual illustration of an example of a new codebook containing several codewords around the previous preferred codeword.

Referring to FIG. 3, embodiments of the present invention may construct a new codebook that includes codewords that exist around a previous preferred codeword. In particular, embodiments of the present invention may generate codewords that exist around a previous preferred codeword using a predefined set of unitary matrices.

이고, 기본 코드북은 C라고 가정한다. 여기서, 유니터리 매트릭스들의 집합의 사이즈는 B 비트이다. A set of predefined unitary matrices (differential codebook)

, And the basic codebook is assumed to be C. Here, the size of the set of unitary matrices is B bits.

또는

로 선택하고, 그 선호 코드워드에 관한 정보(예를 들어, 인덱스 정보)는 송신기로 피드백된다. Assuming that the explicit channel matrix at time t = 0 is H ₀ , the receiver sets the explicit feedback information to H ₀ Or it can be generated by ^H ₀ H H _0. At this time, the receiver extracts explicit feedback information H ₀ of the code words included in the base codebook C ₀ Or a codeword that corresponds to (or best matches) H ₀ ^H H ₀ with a preferred codeword at time t = 0

or

And the information (for example, index information) about the preferred code word is fed back to the transmitter.

또는

및

를 기초로 새로운 코드북을 구성한다. 즉, 수신기 및 송신기는

을 이용하여 새로운 코드북에 포함된 코드워드들이 시간 t=0에서의 선호 코드워드

또는

의 주변에 존재하도록 새로운 코드북을 구성할 수 있다.Also, the receiver and the transmitter may transmit the preferred code word < RTI ID = 0.0 >

or

And

A new codebook is constructed. That is, the receiver and transmitter

The code words included in the new codebook are used as the preferred code words at time t = 0

or

A new codebook can be constructed so as to exist in the vicinity of the codebook.

인 경우, 시간 t=1에서의 새로운 코드북은For example, if the preferred codeword at time t = 0 is

, The new codebook at time t = 1 is < RTI ID = 0.0 >

or

로 나타낼 수 있다.

.

에 포함되는 여러 유니터리 매트릭스들 중에 다음의 수식을 가장 잘 만족하는 대상 유니터리 매트릭스를 선택한다. 여기서, 대상 유니터리 매트릭스는 상기 새로운 코드북에서의 선호 코드워드

를 지시한다.In addition, the receiver calculates the explicit channel matrix H ₁ at time t = 1, and generates the explicit feedback information H ₁ or H ₁ ^H H _1. Then, the receiver

Among the plurality of unitary matrices included in the target unitary matrix, the target unitary matrix that best satisfies the following equation is selected. Here, the target unitary matrix is a code word of the new codebook

.

또는

or

, 를 기초로 시 간 t=1에서 새로운 코드북에서의 선호 코드워드

를 파악한다.Then, the receiver feeds back the index of the target unitary matrix to the transmitter, and the transmitter transmits the target unitary matrix and the previous preferred code word,

, We obtain the preference code word in the new codebook at time t = 1

.

인 경우, 시간 t=2에서의 새로운 코드북은 Also, at time t = 1, the preferred code word

, The new codebook at time t = 2 is < RTI ID = 0.0 >

or

.

에 포함되는 여러 유니터리 매트릭스들 중에 다음의 수식을 가장 잘 만족하는 대상 유니터리 매트릭스를 선택한다. 여기서, 대상 유니터리 매트릭스는 상기 새로운 코드북에서의 선호 코드워드

를 지시한다.Further, the receiver calculates the explicit channel matrix H ₂ at time t = 2, and outputs the explicit feedback information H ₂ H ₂ ^H ₂ . Then, the receiver

Among the plurality of unitary matrices included in the target unitary matrix, the target unitary matrix that best satisfies the following equation is selected. Here, the target unitary matrix is a code word of the new codebook

.

또는

or

, 를 기초로 시간 t=2에서 새로운 코드북에서의 선호 코드워드

를 파악한다.Then, the receiver feeds back the index of the target unitary matrix to the transmitter, and the transmitter transmits the target unitary matrix and the previous preferred code word,

, A new code word in the new codebook at time t = 2,

.

The above-described process (the process of adaptively generating a new codebook based on the set of the previous preferred code word and the unitary matrix) is repeated until a reset period is reached. Then, when the reset period is reached, all the preceding processes are reset and the state returns to the time t = 0.

4 is a diagram illustrating an operation method of a transmitter and a receiver using a differential codebook according to an embodiment of the present invention.

Referring to FIG. 4, the receiver determines (410) any of the codewords in the base codebook (base codebook) as a preferred codeword based on the estimated explicit channel matrix. Then, the receiver feeds back the index information of the preferred codeword to the transmitter as information on the preferred codeword (420), and the transmitter performs precoding based on the preferred codeword (430).

In addition, the transmitter and receiver generate a new codebook using the differential codebook comprised of the preferred code word and the unitary matrices of step 410 (440).

The receiver also recalculates 450 the explicit feedback information based on the explicit channel matrix and retrieves from the differential codebook an object unitary matrix corresponding to the relationship between the preferred code word and the explicit feedback information in step 410 (460). Then, the receiver feeds index information of the target unitary matrix to the transmitter as information on the target unitary matrix (470), and the transmitter recognizes a new preferred code word from the new codebook based on the index information of the target unitary matrix (480). The transmitter also performs precoding using the new preferred codeword (490).

In addition, after the transmitter and receiver generate a new codebook again (491), the above procedure is repeated until the reset cycle is reached. When the reset period is reached, the transmitter and receiver are reset (492) the previously processed processes.

The methods according to the present invention may be implemented in the form of program instructions that can be executed through various computer means and recorded in a computer-readable medium. The computer-readable medium may include program instructions, data files, data structures, and the like, alone or in combination. The program instructions recorded on the medium may be those specially designed and constructed for the present invention or may be available to those skilled in the art of computer software. Examples of computer-readable media include magnetic media such as hard disks, floppy disks and magnetic tape; optical media such as CD-ROMs and DVDs; magnetic media such as floppy disks; Magneto-optical media, and hardware devices specifically configured to store and execute program instructions such as ROM, RAM, flash memory, and the like. Examples of program instructions include machine language code such as those produced by a compiler, as well as high-level language code that can be executed by a computer using an interpreter or the like. The hardware devices described above may be configured to operate as one or more software modules to perform the operations of the present invention, and vice versa.

5 is a block diagram illustrating a transmitter and a receiver using a differential codebook according to an embodiment of the present invention.

5, the transmitter 510 includes a memory 511, a receiver 512, a detector 513, a precoder 514 and a codebook generator 515. The receiver 520 includes a memory 521 A search unit 522, a feedback unit 523, and a codebook generation unit 524. [

The memory 511 stores a differential codebook including a plurality of unitary matrices and a previous codebook of the receiver 520, a codebook currently in use, a basic codebook, and a new codebook generated by the codebook generator 515.

In addition, the receiver 512 receives information on a target unitary matrix, which is one of a plurality of unitary matrices included in the differential codebook, from the receiver.

Further, the detecting unit 513 detects, from the memory 511, the preferred code word of the receiver among the plurality of codewords in the target unitary matrix and the new codebook.

In addition, the codebook generator 515 generates a new codebook based on the previous preferred code word and the differential codebook.

In addition, the transmitter 510 may further include a precoder 515 that performs precoding based on the preferred codeword of the receiver.

The memory 521 stores a differential codebook including a plurality of unitary matrices and a previous codebook of the receiver 520, a codebook currently in use, a basic codebook, and a new codebook generated by the codebook generator 524.

In addition, the search unit 522 searches for a target unitary matrix corresponding to a relation between the previous preference code word of the receiver 520 and the explicit feedback information among the plurality of unitary matrices of the differential codebook.

Also, the feedback unit 523 feeds back information on the target unitary matrix to the transmitter.

In addition, the codebook generator 524 generates a new codebook based on the previous preferred code word and the differential codebook.

While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. This is possible.

Therefore, the scope of the present invention should not be construed as being limited to the described embodiments, but should be determined by the scope of the appended claims, as well as the appended claims.

1 is a diagram showing an example of a multi-input / output communication system.

2 is a conceptual diagram showing an example of a fixed codebook and a new codebook according to embodiments of the present invention, which is an example of a fixed codebook.

3 is a conceptual illustration of an example of a new codebook containing several codewords around the previous preferred codeword.

4 is a diagram illustrating an operation method of a transmitter and a receiver using a differential codebook according to an embodiment of the present invention.

5 is a block diagram illustrating a transmitter and a receiver using a differential codebook according to an embodiment of the present invention.

Claims (14)

Accessing a memory in which a differential codebook comprising a plurality of unitary matrices is stored; Generating a new codebook using the differential codebook and the receiver's previous preferred code word; Calculating explicit feedback information based on an explicit channel matrix between the receiver and the transmitter; Retrieving from the differential codebook an object unitary matrix corresponding to a relationship between the preferred code word and the explicit feedback information; And Feedback information on the target unitary matrix to the transmitter ≪ / RTI > wherein the differential codebook comprises a differential codebook. The method according to claim 1, The step of retrieving the target unitary matrix And retrieving the target unitary matrix among the plurality of unitary matrices considering how close the previous preferred code word can be rotated to the explicit feedback information. delete The method according to claim 1, The step of generating the new codebook And generating the new codebook using the previous preferred code word until a preset reset period is reached. The method according to claim 1, The explicit feedback information And using a differential codebook comprising the covariance of the explicit channel matrix or the explicit channel matrix. The method according to claim 1, The previous preferred code word A method of operating a receiver using a differential codebook that is one of codewords in a fixed base codebook. Generating a new codebook based on a differential codebook comprising a plurality of unitary matrices and a previous preferred code word of a receiver; Receiving information on a target unitary matrix, which is one of the plurality of unitary matrices, from the receiver; And Accessing a memory to extract the target unitary matrix from the differential codebook Wherein the differential codebook comprises a differential codebook. 8. The method of claim 7, Detecting a preferred codeword of the receiver from among a plurality of codewords in the new codebook based on the target unitary matrix ≪ / RTI > 9. The method of claim 8, Performing pre-coding considering the preferred codeword ≪ / RTI > A computer-readable recording medium having recorded thereon a program for carrying out the method according to any one of claims 1, 2, 4 to 9. A memory in which a differential codebook containing a plurality of unitary matrices is stored; Generate a new codebook using the differential codebook and the receiver's previous preferred codeword, calculate explicit feedback information based on an explicit channel matrix between the receiver and the transmitter, A search unit for searching, from the differential codebook, an object unitary matrix corresponding to a relation between the input unit matrix and the object unitary matrix; And A feedback unit that feeds back information on the target unitary matrix to the transmitter; Gt; codebook < / RTI > delete 12. The method of claim 11, The search unit Using a differential codebook that retrieves the target unitary matrix among the plurality of unitary matrices in consideration of how close the previous preferred code word can be rotated to the explicit feedback information. A codebook generator for generating a new codebook based on a differential codebook including a plurality of unitary matrices and a previous favorite code word of a receiver; A receiver for receiving information on a target unitary matrix, which is one of the plurality of unitary matrices, from the receiver; A detector for detecting a preferred code word of the receiver among the plurality of code words in the new codebook based on the target unitary matrix; And A pre-coder for performing precoding in consideration of the preferred codeword Gt; codebook < / RTI >

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