KR20100091585A - A communication method of cooperation transition with base stations using codebook designed for multi-cell in a wireless communication network and a system thereof - Google Patents

Abstract

PURPOSE: A cooperation transmission method using a code book designed by multi cells in a wireless communication network and the wireless communication system therefor are provided to generate a multi cell code book in a plurality of base stations to perform cooperation communication through the multi cell code book in the base stations, thereby increasing performance of a multi cell MIMO(Multi Input Multi Output) system. CONSTITUTION: A serving base station receives a PMI(Precoding Matrix Indication or Precoding Matrix Index) and average receiving power from a terminal(S301). The serving base station transmits the received PMI and the average receiving power to a cooperation base station(S303). The serving base station and the cooperation base station generate a multi cell code book using a shared single cell code book(S305). The serving base station and the cooperation base station are cooperated with a terminal by applying a precoding matrix that the received PMI indicates(S307).

Description

A communication method of cooperation transition with base stations using codebook designed for multi-cell in a wireless communication network and a system approximately}

The present invention relates to a cooperative transmission method and a wireless communication system for the same, and more particularly, to a method for generating a codebook for multiple cells in a multi-input multi-output system environment, a cooperative transmission method using the same and a wireless communication system for the same. .

Multiple Input Multiple Output (MIMO) wireless channels formed using antenna arrays at the transmit and receive ends ensure high capacity and high quality wireless communication links. To achieve the gain provided by such a MIMO channel, a space-time modulation and reception algorithm with high sensitivity performance and complex tradeoffs is required.

Spatial Diversity refers to a method of demultiplexing one bit stream into multiple sub-streams to be transmitted through different antennas. This type of spatial multiplexing method is a space-time modulation technique, which can select "optimal", "near-optimal", and "suboptimal" receivers. However, this spatial multiplexing technique is, unfortunately, sensitive to poor channel conditions.

The above-described precoding (spatial multiplexing or preprocessing) for spatial multiplexing is to multiplex a transmission data stream using a precoding matrix selected by channel information. This precoding (line multiplexing or preprocessing) is one way to protect the rank deficiencies in the wireless channel and improve the error rate performance.

Basically, precoding utilizes channel state between transmitter and receiver, which is known at the transmitter according to the feedback information of the receiver, which processes the transmitted signal into a specific channel matrix structure.

The precoding technique is proposed on the assumption that the channel state at the transmitter is completely known. In other words, perfect channel state information is needed to obtain the maximum gain from precoding. This is because precoding processes a channel measured by a receiver into a specific structure of a channel matrix.

The transmitter can obtain complete channel state information in a time division duplex system with a suitable ping-pong time from the receiver. In a frequency division duplex system, however, the transmitter must receive complete channel state information over the feedback channel.

Feedback of such perfect channel information is difficult to realize in reality. This is because the channel information must be quantized by the number of channel coefficients and provided to the transmitter through the limited band of the control channel (control channel).

Codebooks for current feedback limited MIMO systems are primarily designed for single cell systems.

For the design of systems with limited feedback, the main task is to design the optimal codebook for a given codebook size. Selecting the best codeword from the codebook is very simple.

In the multi-cell MIMO scheme, that is, a cooperative base station transmission method is a technique in which two or more base stations transmit a signal to one terminal, and a neighbor base station cooperates to transmit a signal to the same user to remove inter-cell interference. It is an effective way to do this.

However, if one base station directly applies a single cell MIMO scheme for transmitting a signal to one terminal to a multi-cell MIMO, the performance of the base station is degraded. This is because the signal received by different terminals from different base stations is reduced by its large scale fadings, so that the received power averages of the terminals are different, so that the accuracy of the channel structure for precoding is inferior.

In addition, if at least two base stations simultaneously transmit the downlink signal to the same user using a precoding matrix designed for a single base station, waste of performance is caused. This is because the receiver of the terminal corresponds to only one channel link.

Accordingly, an object of the present invention in view of the above-described conventional problem is to provide a method for constructing a multi-cell codebook, in which two or more base stations are used to transmit a downlink signal to one terminal.

In addition, to provide a cooperative transmission method using a codebook designed for a multi-cell in a wireless communication network in which at least two base stations downlink transmission to one terminal using a multi-cell codebook according to a cooperative transmission method and a wireless communication system for the same have.

In accordance with an aspect of the present invention, there is provided a cooperative transmission method of base stations including a serving base station and at least one cooperative base station, each terminal including the serving base station and at least one cooperative base station. Measuring a channel state with the base stations, generating a multi-cell codebook using the average received power calculated from the measured channel state and a pre-stored single cell codebook, and precoding having the highest received SINR in the multi-cell codebook. Selecting a matrix, and transmitting a precoding matrix indicator indicating the selected precoding matrix and the calculated average received power to the serving base station so that the base stations perform cooperative transmission using the selected precoding matrix. It includes.

Receiving, by the serving base station, the precoding matrix indicator and the average received power, and transmitting the received signal to the at least one cooperating base station; and the serving base station and the at least one cooperating base station, the average received power and the prestored single cell codebook. Generating a multi-cell codebook by using a precoding vector and using a precoding vector indicated by the precoding matrix indicator in the multi-cell codebook generated by the serving base station and the at least one cooperative base station according to the cooperative transmission scheme. The method may further include transmitting a downlink signal to the terminal.

A wireless communication system for cooperative transmission using a codebook designed for multiple cells in a wireless communication network according to a preferred embodiment of the present invention for achieving the above object, includes the serving base station and at least one cooperative base station A multi-cell codebook is generated using an average received power from each base station and a pre-stored single cell codebook, and a precoding matrix having the highest received SINR is selected from the generated multi-cell codebook to indicate a selected precoding matrix. A terminal for transmitting a coding matrix indicator and an average received power to the serving base station; And transmitting and sharing the precoding matrix indicator and the average received power to the at least one cooperating base station, and generating a multi-cell codebook using the average received power and the pre-stored single cell codebook. And a serving base station for transmitting a downlink signal to the terminal according to a cooperative transmission scheme using a precoding vector indicated by a precoding matrix indicator.

The multi-cell codebook is generated using the average received power and the pre-stored single cell codebook, and the downlink from the serving base station according to the cooperative transmission scheme using the precoding vector indicated by the precoding matrix indicator in the generated multicell codebook. The at least one cooperative base station for transmitting a link signal to the terminal; characterized in that it further comprises.

According to the present invention, as described above, a multi-cell codebook reflecting a channel environment of a multi-cell MIMO system in which a plurality of base stations cooperatively transmits a downlink signal to one terminal is generated, and a plurality of base stations cooperate by using the same. By performing the communication, the performance of the multi-cell MIMO system is improved.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be noted that in the following description, only parts necessary for understanding the operation according to the present invention will be described, and descriptions of other parts will be omitted so as not to distract from the gist of the present invention.

First, a wireless communication system according to an exemplary embodiment of the present invention will be described. 1 is a view for explaining the structure of a wireless communication system for performing a cooperative base station communication method according to an embodiment of the present invention.

Referring to FIG. 1, in a wireless communication system according to an exemplary embodiment of the present disclosure, at least one cooperative base station located adjacent to the terminal 100, the serving base station 200 of the terminal 100, and the serving base station 200. 300.

The cooperative base station 300 transmits a downlink signal to the terminal 100 together with the serving base station 200 to perform communication according to the base station cooperative communication technique. In particular, the cooperative base station 300 may be a plurality. In addition, since the method of selecting at least one cooperative base station 300 performing the cooperative communication technique together with the serving base station 200 is not the gist of the present invention, detailed description thereof will be omitted.

Basically, the terminal 100, the serving base station 200, and the cooperative base station 300 according to the embodiment of the present invention share a codebook. The shared codebook is a codebook for one cell (base station) to transmit to one terminal in a MIMO system, and this codebook will be referred to as a "single cell codebook" in an embodiment of the present invention. Meanwhile, a codebook according to an embodiment of the present invention, which corresponds to a single cell codebook, is a codebook used when at least two base stations transmit the same data to one terminal, and the codebook is referred to as a "multi-cell codebook." It will be called.

The serving base station 200 and the at least one cooperative base station 300 are different transmit power constraints, different power allocation schemes for each base station, and a terminal from each of the base stations 200 and 300. There are up to 100 different wide scale fading channels (large scale fading or large scale fading channels). Accordingly, the multi-cell codebook according to an embodiment of the present invention is generated based on the single cell codebook described above, and further considers transmission power limitation and power allocation structure for each base station in addition to the channel environment (wide fading).

This multi-cell codebook generation method according to the embodiment of the present invention will be described. 2 is a diagram illustrating a method of generating a multi-cell codebook according to an embodiment of the present invention.

In FIG. 2, it is assumed that the terminal 100, the serving base station 200 of the terminal, and the cooperative base station 300 of the serving base station share a single cell codebook. This single cell codebook is described. Table 1 below is for explaining a codebook according to an embodiment of the present invention.

Table 1 shows an example of a single cell based codebook. Here, it is assumed that the number of transmitting antennas of the base stations is "M ₁ , .. M _n ".

Then, the precoding matrices given in the single cell codebook may be expressed as Equation 1 below.

The g th precoding matrices corresponding to the r th transmission rank in each precoding matrix given in the codebook of Equation 1 may be expressed as Equation 2 below.

는

Is

Considering each factor of the precoding matrix, Equation 3 below shows the i th precoding vectors in the precoding matrix.

According to an embodiment of the present invention, a multi-cell codebook is configured by using a factor of a channel and a power of a received signal received from the base stations 200 and 300 to the terminal 100 in the aforementioned precoding vector.

Referring to FIG. 2, the average reception power received from different base stations 200 and 300 in the terminal 100 at the cell edge is different. Accordingly, the terminal 100 measures the channel state of the base stations 200 and 300 based on the downlink reference signal (RS) in step S201. This channel state assumes large scale fading. The wide fading channel measured by the terminal 100 may be represented by Equation 4 below.

는 x 번째 기지국으로부터 단말기까지의 광범위 페이딩 채널을 의미한다. In Equation 4,

Denotes a wide fading channel from the x th base station to the terminal.

In the subchannel of the downlink channel transmitted by the base stations 200 and 300 to the terminal, each base station allocates different power. The terminal 100 derives a power vector from the channel measured in step S203. This power vector may be a product of a power allocation factor and a transmit power constraint.

The power vector of the signal transmitted in the subchannels of the respective base stations may be represented by Equation 5 below.

는 i 번째 기지국의 전력 할당 팩터(power allocation factor)이며,

은 i 번째 기지국의 전송 전력 제한(transmit power constraint) 값이다. In Equation 5,

Is the power allocation factor of the i th base station,

Is the transmit power constraint of the i-th base station.

Then, the terminal 100 calculates the average received power from the channel environment and the calculated power vector in step S205.

Considering the wide fading channel of Equation 4 and the power vector of Equation 5, the average received power of the signal received by the terminal 100 is represented by Equation 6 below. Can be.

) 및 단일 셀 코드북을 이용하여 다중 셀 코드북을 생성한다. Next, the terminal 100 at step S207 average received power (

And a single cell codebook.

)을 곱하여 다음의 <수학식 7>과 같은 다중 셀 코드북을 얻을 수 있다. In order to configure a multi-cell codebook, the terminal 100 may include an average received power in a single-cell codebook as described in Table 1.

By multiplying), a multi-cell codebook as shown in Equation 7 can be obtained.

As described above, according to an exemplary embodiment of the present invention, an average reception power is calculated using a channel environment for each base station and a power vector of each base station. Then, a multi-cell codebook is generated using the calculated average received power and the shared single cell codebook.

The terminal 100 generating the multi-cell codebook selects one precoding matrix from the multi-cell codebook generated in step S209. It is preferable that the precoding matrix selects the highest received signal to interference noise ratio (SINR).

)을 서빙 기지국(200)으로 전송한다. Then, the terminal 100 indicates a PMI (Precoding Matrix Indication or Precoding Matrix Index) and an average received power indicating the precoding matrix selected in step S211.

) Is transmitted to the serving base station 200.

The average received power is for the serving base station 200 and the cooperative base station 300 to generate a multi-cell codebook from a single cell codebook. In addition, the PMI is for the serving base station 200 and the cooperative base station 300 to select a precoding matrix having a high reception SINR of the terminal.

Next, a method of transmitting data by the base stations 200 and 300 to the terminal 100 according to the cooperative transmission scheme using the multi-cell codebook as described above will be described.

3 is a diagram illustrating a cooperative transmission method using a multi-cell codebook according to an embodiment of the present invention.

)을 수신한다. As described above, the serving base station 200 is a PMI and the average received power from the terminal 100 in step S301 (

).

)을 협력 기지국(300)에 전송한다. Then, the serving base station 200 receives the PMI and the average reception power (

) Is transmitted to the cooperative base station 300.

) 및 단말기(100), 서빙 기지국(200) 및 협력 기지국(300)을 포함하는 3자간에 공유하고 있는 단일 셀 코드북을 이용하여 다중 셀 코드북을 생성한다. 이로써, 3자(100, 200, 300)간에 다중 셀 코드북을 공유하게 된다. Subsequently, the serving base station 200 and the cooperative base station 300 perform the average received power (S305).

And a multi-cell codebook using a single cell codebook shared between the three parties including the terminal 100, the serving base station 200, and the cooperative base station 300. As a result, the multi-cell codebook is shared among the three characters 100, 200, and 300.

Accordingly, the serving base station 200 and the cooperative base station 300 transmit data in cooperation with the terminal 100 by applying the precoding matrix indicated by the PMI received in step S307. At this time, in the data transmission method, as is known, each base station (200, 300) may transmit the data divided, or may transmit the same data at the same time.

A cooperative transmission method using a series of multi-cell codebooks as described above will be described. 4 is a flowchart illustrating a cooperative communication method using a multi-cell codebook according to an embodiment of the present invention.

In step S401, the terminal 100 measures a channel by using a reference signal such as a preamble or a midamble of a signal received from the base stations 200 and 300 to obtain channel information. . This channel measurement assumes a channel undergoing large scale fading from each of the base stations 200, 300 to the terminal 100.

Referring to Equations 4 to 6, such channel information includes a large scale fading channel (L), a power allocation factor, and a transmit power constraint. , Mean average received power.

Subsequently, the terminal 100 configures a multi-cell codebook as described above using the channel information in step S403.

Then, the terminal 100 derives an optimal precoding matrix from the configured multi-cell codebook, and selects a PMI indicating the selected precoding matrix. For example, the optimal precoding matrix may select a precoding matrix for which the received SINR may have a maximum value.

)을 서빙 기지국(200)에 피드백(feedback)한다. 여기서, 서빙 기지국(200)과 1개의 협력 기지국(300)이 협력 전송 기법에 따라 통신을 수행하는 환경을 가정하면, 단말기(100)는 기지국들(200, 300)의 평균 수신 전력의 비율을 양자화(quantization)하여 서빙 기지국(200)에 피드백 할 수 있다. Then, the terminal 100 in step S405 PMI and the average received power indicating the optimal precoding matrix (

) Is fed back to the serving base station 200. Here, assuming that the serving base station 200 and one cooperative base station 300 performs communication according to a cooperative transmission scheme, the terminal 100 quantizes the ratio of average received power of the base stations 200 and 300. It may be quantized and fed back to the serving base station 200.

)을 포함하는 피드백 정보를 전송한다. Next, the serving base station 200 receives the PMI and the average received power received from the terminal 100 at the cooperative base station 300 in step S407.

Transmits feedback information including a).

)을 이용하여, 다중 셀 코드북을 생성하고, 생성한 다중 셀 코드북으로부터 단말기(100)가 전송한 PMI가 지시하는 프리코딩 매트릭스를 선택한다. Subsequently, the serving base station 200 and the cooperative base station 300 receive the average received power (S409).

), A multi-cell codebook is generated, and a precoding matrix indicated by the PMI transmitted by the terminal 100 is selected from the generated multi-cell codebook.

)을 적용한 다중 셀 코드북을 생성한다. 이에 따라, 단말기(100), 서빙 기지국(200) 및 협력 기지국(300)은 동일한 다중 셀 코드북을 공유하게 된다. 그런 다음, 서빙 기지국(200) 및 협력 기지국(300)은 S411 단계에서 생성한 다중 셀 코드북에서 수신한 PMI가 지시하는 프리코딩 매트릭스를 선택할 수 있다. That is, the serving base station 200 and the cooperative base station 300 is the average received power received from the codebook as shown in <Table 1> (

Create a multi-cell codebook with). Accordingly, the terminal 100, the serving base station 200 and the cooperative base station 300 will share the same multi-cell codebook. Then, the serving base station 200 and the cooperative base station 300 may select a precoding matrix indicated by the PMI received from the multi-cell codebook generated in step S411.

Subsequently, the serving base station 200 and the cooperative base station 300 transmit the downlink signal to which the precoding matrix selected previously is applied to the corresponding terminal 100 in step S413.

)을 서빙 기지국에 피드백하면 된다. Basically, since the codebook based MIMO transmission structure is mainly applied to the less mobile terminals, the power allocation factor, transmission power limitation, and large scale fading assigned to the subchannel are more stable and do not change quickly. Therefore, a multi-cell codebook constructed according to an embodiment of the present invention does not change frequently. In addition, after the multi-cell codebook is configured, the terminal merely checks the PMI index and the average received power of each base station.

Is fed back to the serving base station.

According to this embodiment of the present invention, power allocation factor, transmit power limitation, and large scale fading are used in a multi-cell codebook design. This shows better performance compared to optimizing a conventional single cell in a wide fading environment.

That is, information about the transmission power limitation, the power allocation factor, and the large scale fading of each cooperative base station is collected by the cell edge terminal receiving the wireless communication service by the cooperative base station. The terminal feeds back to the serving base station a quantized value of a power allocation factor allocated to a subchannel of the nth base station, a ratio of a product of transmit power limitation and large scale fading, and an optimal PMI index. The base station constructs a multi-cell codebook based on the feedback value of the terminal and information shared with other cooperative base stations and an optimal PMI index, thereby establishing an environment suitable for terminals receiving signals from multiple base stations in a multi-cell MIMO environment. can do.

While the present invention has been described with reference to several preferred embodiments, these embodiments are illustrative and not restrictive. As such, those of ordinary skill in the art will appreciate that various changes and modifications can be made according to equivalents without departing from the spirit of the present invention and the scope of rights set forth in the appended claims.

1 is a view for explaining the structure of a wireless communication system for performing a cooperative base station communication method according to an embodiment of the present invention.

2 is a view for explaining a multi-cell codebook generation method according to an embodiment of the present invention.

3 is a diagram illustrating a cooperative transmission method using a multi-cell codebook according to an embodiment of the present invention.

4 is a flowchart illustrating a cooperative communication method using a multi-cell codebook according to an embodiment of the present invention.

Claims (4)

In the cooperative transmission method of base stations comprising a serving base station and at least one cooperative base station, The terminal measures the channel state with each base station including the serving base station and at least one cooperative base station, and generates a multi-cell codebook using the average received power calculated from the measured channel state and a pre-stored single cell codebook. Process, Selecting a precoding matrix having the highest received SINR in the multi-cell codebook; Transmitting a precoding matrix indicator indicating the selected precoding matrix and a calculated average received power to the serving base station so that the base stations perform cooperative transmission using the selected precoding matrix. Cooperative transmission method using codebook designed for multiple cells. The method of claim 1, Receiving, by the serving base station, the precoding matrix indicator and the average received power, and transmitting the received base station to the at least one cooperating base station; Generating, by the serving base station and the at least one cooperating base station, a multi-cell codebook using the average received power and a pre-stored single cell codebook; Transmitting, by the serving base station and the at least one cooperative base station, a downlink signal to the terminal according to a cooperative transmission scheme using a precoding vector indicated by the precoding matrix indicator in the generated multi-cell codebook; A cooperative transmission method using a codebook designed for multiple cells, characterized in that. A wireless communication system for cooperative transmission using codebooks designed for multiple cells in a wireless communication network, A multi-cell codebook is generated using an average received power from each base station including the serving base station and at least one cooperative base station and a pre-stored single cell codebook, and the precoding matrix having the highest received SINR is generated from the generated multi-cell codebook. A terminal for transmitting a precoding matrix indicator and an average received power indicating the selected precoding matrix to the serving base station; And The precoding matrix indicator and the average received power are transmitted to the at least one cooperating base station and shared, and a multi-cell codebook is generated using the average received power and the pre-stored single cell codebook, and the pre-coded multi-cell codebook is generated. The serving base station for transmitting a downlink signal to the terminal according to a cooperative transmission scheme using a precoding vector indicated by a coding matrix indicator; wireless for cooperative transmission using a codebook designed for multiple cells Communication system. The method of claim 3, A multi-cell codebook is generated using the average received power and a pre-stored single cell codebook, and the downlink from the serving base station according to the cooperative transmission scheme using a precoding vector indicated by the precoding matrix indicator in the generated multicell codebook. The at least one cooperative base station for transmitting a link signal to the terminal; wireless communication system for cooperative transmission using a codebook designed for multiple cells characterized in that it further comprises.

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