KR101335898B1

KR101335898B1 - Method of feedback for interference alignment in multi user mimo interference channel

Info

Publication number: KR101335898B1
Application number: KR1020120145383A
Authority: KR
Inventors: 김동구; 차현수; 조영민
Original assignee: 연세대학교 산학협력단
Priority date: 2012-12-13
Filing date: 2012-12-13
Publication date: 2013-12-02

Abstract

A feedback method for interference alignment in a multi-user MIMO interference channel is disclosed. The disclosed method is characterized in that in a system with three transmitters and three receivers, each receiver determines its own receive filter matrix using a precoder matrix of a particular transmitter and a channel matrix with that transmitter, The precoder matrix of the predetermined other transmitter is determined and transmitted using channel information with the other transmitter. According to the disclosed method, since the precoder matrix having a smaller data amount than the channel information is fed back, the feedback overhead can be reduced.

Description

Feedback Method for Interference Alignment in Multi-User MIMO Interference Channels

Embodiments of the present invention relate to a feedback method, and more particularly, to a feedback method for interference alignment in a multi-user MIMO interference channel.

Interference alignment is a technique of maximizing the number of data free from interference known as degrees of freedom (DoF), and it is a technique for aligning unwanted signals into available subspaces at each receiver.

1 is a diagram illustrating an interference channel model for three users among existing multi-user interference channel models.

Referring to FIG. 1, three transmitters 100, 102, 104 and three receivers

110, 112, and 114 are shown, and each transmitter and receiver has a plurality of antennas, and assumes that they have four antennas.

In the model of FIG. 1, the first transmitter 109 is set to communicate with the first receiver 110, the second transmitter 102 is set to communicate with the second receiver 112, and the third transmitter ( 104 is configured to communicate with third receiver 114.

From the point of view of the first receiver 110, the signals transmitted from the second transmitter 102 and the third transmitter 104 in addition to the first transmitter 100 are interference, and in the wood receivers, other than the preset transmitter, Signals from two transmitters act as interference.

The arrow shown in FIG. 1 illustrates the interference transmitted to each receiver, and illustrates that the signals provided from the second transmitter 102 and the third transmitter 104 act as interference.

Interference alignment relates to a method of aligning interference signals provided from a plurality of transmitters into specific subspaces. If a transceiver of FIG. 1 has four antennas and each transmitter transmits two independent signals, one receiver is used. 4 receives four interference signals in addition to the two desired signals, so that four antennas cannot handle all interference.

Therefore, in the system as shown in FIG. 1, interference alignment with respect to interference signals of transmitters transmitting an interference signal is required to process both a desired signal and an interference signal with four antennas.

In the system as shown in FIG. 1, four interference signals are received from the second transmitter 102 and the third transmitter 104 from the perspective of the first receiver 110, and the interference signals of the second transmitter 102 The interference signals of the three transmitters 104 are arranged in the same subspace so that they can be processed by two antennas.

For interference alignment, each transmitter needs channel information with a receiver other than the communication target, and the channel matrix fed back becomes a 4x4 matrix when there are four antennas, and the feedback of the channel information causes considerable feedback overhead. do.

The present invention proposes a feedback method that can reduce the feedback overhead that occurs during interference alignment.

According to a preferred embodiment of the present invention to achieve the above object, a feedback method for interference alignment in a MIMO communication system comprising three receivers and three transmitters, the first receiver in the first receiver Determining (a) the filter matrix R1 and the precoder matrix F2 of the second transmitter and providing them to the second transmitter; In the third receiver, the reception filter matrix of the third receiver is determined using the precoder matrix F2 of the second transmitter and the channel matrix of the second transmitter and the third receiver, and the reception filter of the third receiver is determined. (B) determining a precoder matrix of the first transmitter using the matrix of the first transmitter and providing it to the first transmitter; In a second receiver, a reception filter matrix of the second receiver is determined by using a precoder matrix F1 of the first transmitter and a channel matrix of the first transmitter and the second receiver and a reception filter matrix of the second receiver. (C) determining a precoder matrix of the third transmitter and providing the third transmitter to the third transmitter; (D) determining, at a first receiver, a receive filter matrix (R1 ') of the first receiver using a precoder matrix (F3) of the third transmitter and a channel matrix of the first and third transmitters; And repeating steps (a) to (d) when the difference between the reception filter matrix R1 of step (a) and the reception filter matrix R1 'of step (d) is greater than or equal to a preset threshold. There is provided a feedback method for interference alignment in a MIMO interference channel comprising < RTI ID = 0.0 >

The third receiver receives a precoder matrix F2 of the second transmitter from the second transmitter, the second receiver receives a precoder matrix F1 of the first transmitter from the first transmitter, The first receiver receives a precoder matrix F3 of a third transmitter from the third transmitter.

The first receiver, the second receiver, and the third receiver transmit a precoder matrix of transmitters determined by each receiver through broadcasting, and each receiver receives a precoder matrix of each transmitter from another receiver.

The first receiver, the second receiver and the third receiver receive a precodo matrix of transmitters transmitted by the respective receivers through a repeater.

Each receiver determines a null space value of a product of a channel information matrix with a specific transmitter and its received filter matrix as the precoder matrix of the corresponding transmitter.

Each of the receivers determines its reception filter matrix using the hummit matrix of the precoder matrix of the specific transmitter and the channel matrix of the channel matrix with the transmitter.

In step (a), the first receiver arbitrarily determines a reception filter matrix of the first receiver from a predetermined codebook.

In step (a), the first receiver calculates a null space value of the product of the channel matrix with the second transmitter and the determined filter matrix of the first receiver as the precoder matrix of the second transmitter, The candidate precode matrix closest to the calculated precoder matrix of the second transmitter among the plurality of candidate precode matrices included in the battery codebook is determined as the precoder matrix of the second transmitter.

According to another aspect of the present invention, a feedback method for interference alignment in a MIMO communication system including three receivers and three transmitters, the reception filter matrix R1 and the second transmitter of the first receiver in a first receiver Determining (a) the precoder matrix F2 and providing it to a second transmitter; In the third receiver, the reception filter matrix R3 of the third receiver is determined using the precoder matrix F2 of the second transmitter, and the first transmitter is received using the reception filter matrix R3 of the second receiver. (B) determining a precoder matrix (F1) of and providing it to the first transmitter; In the second receiver, the reception filter matrix R2 of the second receiver is determined using the precoder matrix F1 of the first transmitter, and the third transmitter is received using the reception filter matrix R2 of the second receiver. Determining (c) the precoder matrix F3 and providing it to the third transmitter; (D) determining the reception filter matrix R1 'of the first receiver using the precoder matrix F3 of the third transmitter in the first receiver and the reception filter matrix R1 of step (a). ) And repeating steps (a) to (d) when the difference between the reception filter matrix R1 'of step (d) is greater than or equal to a preset threshold. A feedback method is provided.

According to the present invention, there is an advantage that can reduce the feedback overhead generated during interference alignment.

1 is a diagram illustrating an interference channel model for three users of a conventional multi-user interference channel model.
2 illustrates a multi-user MIMO channel interference model in accordance with an embodiment of the present invention.
3 is a flowchart illustrating a flow of a feedback method for interference alignment in a multi-user MIMO interference channel according to an embodiment of the present invention.
4 is a graph showing the number of iterations when the feedback according to the present invention is applied.
5 is a diagram illustrating a structure for delivering a precoder matrix of a transmitter in a feedback method according to another embodiment of the present invention.
6 is a diagram illustrating a structure for delivering a precoder matrix of a transmitter in a feedback method according to another embodiment of the present invention.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the invention is not intended to be limited to the particular embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention. Like reference numerals are used for like elements in describing each drawing.

2 is a diagram illustrating a multi-user MIMO channel interference model according to an embodiment of the present invention.

The present invention proposes a feedback method for interference alignment in a three-user model in which there are three transmitters 200, 202, 204 and three receivers 210, 212, 214.

2, a first transmitter 200 is set up to communicate with a first receiver 210, a second transmitter 202 is set up to communicate with a second receiver 212, and a third transmitter 204 is configured. Is set to communicate with the third receiver 214.

The plurality of transmitters 200, 202, and 204 and the receivers 210, 212, and 214 have a plurality of antennas, and the present embodiment will be described with four antennas. When this case is assumed, each transmitter 200, 202, 204 transmits two independent signals.

Each receiver 210, 212, 214 receives signals from all transmitters 200, 202, 204 and from the perspective of the first receiver 210 the second transmitter 202 and the third transmitter 204. The signal transmitted from is an interference signal.

In addition, the second receiver 212 receives an interference signal from the first transmitter 200 and the third transmitter 204, the third receiver 214 from the first transmitter 200 and the second transmitter 202 Receive an interference signal.

The signal received by each receiver may be expressed by Equation 1 below.

In Equation 1, y is a received signal, Hij is a channel matrix, F is a transmitter precoder matrix, s is a transmission signal, and n is noise. As can be seen from Equation 1, the received signal is composed of the sum of the signal transmitted from the desired transmitter and the interference signal and noise transmitted from the unwanted transmitter.

3 is a flowchart illustrating a flow of a feedback method for interference alignment in a multi-user MIMO interference channel according to an embodiment of the present invention.

Referring to Figures 2 and 3 will be described in detail the feedback method according to an embodiment of the present invention.

First, the first receiver 210 of the three receivers 210, 212, 214 sets the receive filter matrix R1 (step 200). Here, the reception filter matrix R1 may be arbitrarily set and, for example, may be arbitrarily set from one of the unitary codebooks.

The first receiver 210 determines the precoder matrix F2 of the second transmitter using the reception filter matrix R1 and transmits the precoder matrix F2 to the second transmitter (step 202). According to an embodiment of the present invention, the precoder matrix F2 of the second transmitter is set to a null space value of a value obtained by multiplying a reception filter matrix of the first receiver by a channel vector between the second transmitter and the first receiver.

Upon receiving the precoder matrix F2 from the first receiver 210, the second transmitter transmits the precoder matrix F2 to the third receiver (step 204).

The third receiver receiving the precoder matrix F2 of the second transmitter uses the Hermitian matrix of the precoder matrix of the second transmitter and the channel matrix between the second transmitter and the third receiver. The receive filter matrix R3 of the third receiver is determined (step 206).

Specifically, the reception filter matrix of the third receiver is determined by using a null space value of a product of the hermition matrix of the precoder matrix of the second transmitter multiplied by the hermition matrix of the channel matrix between the second transmitter and the third receiver.

The operation of determining and transmitting the precoder matrix F1 of the second transmitter in the first receiver and determining the reception filter matrix of the third receiver in the third receiver is expressed by Equation 2 below.

The third receiver determines the precoder matrix of the first transmitter using the receive filter matrix of the third receiver and the channel matrix between the third receiver and the first transmitter and transmits to the first transmitter (step 208). A null space value of a product of the reception filter matrix of the third receiver and the channel matrix between the first transmitter and the third receiver may be determined as the precoder matrix F1 of the first transmitter.

The first transmitter transmits the received precoder matrix F1 of the first transmitter to the second receiver (step 210).

The second receiver that has received the precoder matrix F1 of the first transmitter uses the second receiver using the hermition matrix of the precoder matrix of the first transmitter and the channel matrix between the second receiver and the first transmitter. Receive filter matrix R2 is determined (step 212).

Specifically, the second receiver receives a reception filter of the second receiver by using a null space value of a product of the hermition matrix of the precoder matrix of the first transmitter multiplied by the hermition matrix of the channel matrix between the second receiver and the first transmitter. Determine the matrix R2.

The process of transmitting the precoder matrix F1 of the first transmitter from the third receiver to the first transmitter and determining the reception filter matrix of the second receiver is represented by Equation 3 below.

The second receiver determines the precoder matrix F3 of the third transmitter using the receive filter matrix of the second receiver and transmits the determined precoder matrix F3 to the third transmitter (step 214). The precoder matrix F3 of the third transmitter is set to a null space value of the product of the reception filter matrix of the second transmitter times the channel matrix between the second receiver and the third transmitter.

The third transmitter transmits the received precoder matrix F3 to the first receiver (step 216).

The first receiver determines (218) the reception filter matrix R1 'of the first receiver using the received precoder matrix F3 of the third transmitter. The receive filter matrix of the first receiver is determined using the hummit matrix of the precoder matrix of the third transmitter and the hummit matrix of the channel matrix between the third transmitter and the first receiver.

Specifically, the reception filter matrix of the first receiver is determined by using a null space value of a product of the hermition matrix of the precoder matrix of the third transmitter and the channel of the channel matrixes of the third transmitter and the first receiver.

Equation 4 below is a method for determining and transmitting the precoder matrix of the third transmitter from the second receiver to the third transmitter and determining the reception filter matrix of the first receiver at the first receiver.

It is determined whether the difference between the reception filter matrix R1 ′ of the first receiver determined in step 218 and the reception filter matrix R1 of the first receiver arbitrarily set in step 200 is equal to or less than a preset threshold (step 220).

If it is less than or equal to the preset threshold, the feedback process ends (step 222), and if it is greater than or equal to the preset threshold, the feedback operation from step 202 is repeated using the receive filter matrix of the first receive filter of step 218.

According to the above-described feedback process, the channel matrix is not fed back to the transmitter, but the precoder matrix is fed back to each transmitter. Since the channel matrix has the size of MxM while the precoder matrix has the size of Mx (M / 2), the amount of information fed back can be reduced, thereby reducing the feedback overhead.

4 is a graph showing the number of iterations when the feedback according to the present invention is applied.

In the present invention, iteration is performed when the difference between the reception filter matrix of the first reception filter set arbitrarily initially and the reception filter matrix of the first reception filter determined in the feedback procedure is greater than or equal to a threshold value. It can be seen that it is not performed more than twice.

2 and 3 illustrate a case in which the precoder matrix of a specific transmitter determined by each receiver is transmitted from the corresponding transmitter to the receiver. However, the present invention is not limited to receiving a precoder matrix of a specific transmitter from the transmitter, and the precoder matrix of the specific transmitter may be transmitted to a desired receiver in various ways.

5 is a diagram illustrating a structure for transmitting a precoder matrix of a transmitter in a feedback method according to another embodiment of the present invention.

Referring to FIG. 5, when the precoder matrix F2 of the second transmitter is determined in the first receiver by the same method as in FIG. 3, the first receiver transmits the determined precoder matrix to the second transmitter and the third receiver together. (Broadcasting) By this process, the process of transmitting the precoder matrix from the second transmitter to the third receiver may be omitted.

Further, when the precoder matrix F1 of the first transmitter is determined at the third receiver, the third receiver transmits the precoder matrix of the first transmitter to the first transmitter and the second receiver together.

By this process, the process of transmitting the precoder matrix from the first transmitter to the second receiver may be omitted.

In addition, when the precoder matrix F3 of the third transmitter is determined in the second receiver, the second receiver transmits the precoder matrix F3 of the third transmitter together to the third transmitter and the first receiver. By this process, the process of transmitting the precoder matrix from the third transmitter to the first receiver may be omitted.

The feedback method as shown in FIG. 5 may be applied when the receivers are at a distance capable of communicating with each other.

6 is a diagram illustrating a structure for delivering a precoder matrix of a transmitter in a feedback method according to another embodiment of the present invention.

Referring to FIG. 6, the process of transmitting the precoder matrix of the specific transmitter determined by each receiver to the corresponding transmitter is performed as it is, but the precoder matrix of the specific transmitter determined by each receiver is provided to the desired receiver through the repeater RS. .

That is, according to the method shown in FIG. 6, each transmitter may transmit a precoder matrix by a repeater without performing a process of transmitting its own precoder matrix to a corresponding receiver. Can be alleviated.

Meanwhile, when the digital transmission scheme of the limited feedback system is applied to the present invention in which each receiver provides a precoder matrix of the transmitter, the precoder matrix determined at the receiver may be selected from a preset unitary codebook.

In this case, one of the candidate precoders having a value closest to the precoder matrix determined by the operation is selected as the precoder matrix selected from the codebook.

For example, when the codebook is expressed as Equation 5 below, the precoder matrix of the second transmitter may be selected from candidate precoders that satisfy Equation 6 below. In Equation 5 below, B means the number of available feedback bits.

As described above, the present invention has been described by specific embodiments such as specific components and the like. For those skilled in the art, various modifications and variations are possible from these descriptions. Accordingly, the spirit of the present invention should not be construed as being limited to the embodiments described, and all of the equivalents or equivalents of the claims, as well as the following claims, belong to the scope of the present invention .

Claims

A feedback method for interference alignment in a MIMO communication system including three receivers and three transmitters,
(A) determining, at a first receiver, a receive filter matrix (R1) of the first receiver and a precoder matrix (F2) of a second transmitter and providing it to a second transmitter;
In the third receiver, the reception filter matrix of the third receiver is determined using the precoder matrix F2 of the second transmitter and the channel matrix of the second transmitter and the third receiver, and the reception filter of the third receiver is determined. (B) determining a precoder matrix of the first transmitter using the matrix of the first transmitter and providing it to the first transmitter;
In a second receiver, a reception filter matrix of the second receiver is determined by using a precoder matrix F1 of the first transmitter and a channel matrix of the first transmitter and the second receiver and a reception filter matrix of the second receiver. (C) determining a precoder matrix of the third transmitter and providing the third transmitter to the third transmitter;
(D) determining, at a first receiver, a receive filter matrix (R1 ') of the first receiver using a precoder matrix (F3) of the third transmitter and a channel matrix of the first and third transmitters; And
(E) repeating steps (a) to (d) when the difference between the reception filter matrix R1 of step (a) and the reception filter matrix R1 'of step (d) is greater than or equal to a preset threshold; Feedback method for interference alignment in a MIMO interference channel comprising a.

The method of claim 1,
The third receiver receives a precoder matrix F2 of the second transmitter from the second transmitter, the second receiver receives a precoder matrix F1 of the first transmitter from the first transmitter, And the first receiver receives a precoder matrix (F3) of a third transmitter from the third transmitter.

The method of claim 1,
The first receiver, the second receiver and the third receiver transmits a precoder matrix of transmitters determined by each receiver through broadcasting, and each receiver receives a precoder matrix of each transmitter from another receiver. Feedback method for interference alignment in a MIMO interference channel.

The method of claim 1,
And the first receiver, the second receiver and the third receiver receive a precodo matrix of transmitters transmitted by the respective receivers through a repeater.

5. The method according to any one of claims 2 to 4,
Wherein each receiver determines a null space value of a product of a channel information matrix with a specific transmitter and its received filter matrix as a precoder matrix of the corresponding transmitter.

5. The receiver of claim 2, wherein each of the receivers determines its received filter matrix using a hermition matrix of a precoder matrix of a specific transmitter and a channel matrix of a channel matrix with the corresponding transmitter. Feedback method for interference alignment in a MIMO interference channel, characterized in that.

The method of claim 1,
And in step (a), the first receiver arbitrarily determines a reception filter matrix of the first receiver from a predetermined codebook.

The method of claim 1,
In step (a), the first receiver calculates a null space value of the product of the channel matrix with the second transmitter and the determined filter matrix of the first receiver as the precoder matrix of the second transmitter, The candidate precode matrix closest to the calculated precoder matrix of the second transmitter among the plurality of candidate precode matrices included in the battery codebook is determined as the precoder matrix of the second transmitter. Feedback method for sorting.

A feedback method for interference alignment in a MIMO communication system including three receivers and three transmitters,
(A) determining, at a first receiver, a receive filter matrix (R1) of the first receiver and a precoder matrix (F2) of a second transmitter and providing it to a second transmitter;
In the third receiver, the reception filter matrix R3 of the third receiver is determined using the precoder matrix F2 of the second transmitter, and the first transmitter is received using the reception filter matrix R3 of the second receiver. (B) determining a precoder matrix (F1) of and providing it to the first transmitter;
In the second receiver, the reception filter matrix R2 of the second receiver is determined using the precoder matrix F1 of the first transmitter, and the third transmitter is received using the reception filter matrix R2 of the second receiver. Determining (c) the precoder matrix F3 and providing it to the third transmitter;
(D) determining, at the first receiver, a reception filter matrix R1 'of the first receiver using the precoder matrix F3 of the third transmitter; and
(E) repeating steps (a) to (d) when the difference between the reception filter matrix R1 of step (a) and the reception filter matrix R1 'of step (d) is greater than or equal to a preset threshold; Feedback method for interference alignment in a MIMO interference channel comprising a.

10. The method of claim 9,
The third receiver receives a precoder matrix F2 of the second transmitter from the second transmitter, the second receiver receives a precoder matrix F1 of the first transmitter from the first transmitter, And the first receiver receives a precoder matrix (F3) of a third transmitter from the third transmitter.

10. The method of claim 9,
The first receiver, the second receiver and the third receiver transmits a precoder matrix of transmitters determined by each receiver through broadcasting, and each receiver receives a precoder matrix of each transmitter from another receiver. Feedback method for interference alignment in a MIMO interference channel.

10. The method of claim 9,
And the first receiver, the second receiver and the third receiver receive a precodo matrix of transmitters transmitted by the respective receivers through a repeater.