KR101997822B1 - Methods for cooperative transmission in multi-cell cooperation systems - Google Patents

Methods for cooperative transmission in multi-cell cooperation systems Download PDF

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KR101997822B1
KR101997822B1 KR1020120065086A KR20120065086A KR101997822B1 KR 101997822 B1 KR101997822 B1 KR 101997822B1 KR 1020120065086 A KR1020120065086 A KR 1020120065086A KR 20120065086 A KR20120065086 A KR 20120065086A KR 101997822 B1 KR101997822 B1 KR 101997822B1
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state information
channel
base station
channel state
information
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KR1020120065086A
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KR20130141941A (en
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이효진
박정수
이용환
변용석
김윤선
이주호
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삼성전자주식회사
서울대학교산학협력단
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
    • H04L25/03891—Spatial equalizers
    • H04L25/03898—Spatial equalizers codebook-based design
    • H04L25/03904—Spatial equalizers codebook-based design cooperative design, e.g. exchanging of codebook information between base stations
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/022—Site diversity; Macro-diversity
    • H04B7/024—Co-operative use of antennas of several sites, e.g. in co-ordinated multipoint or co-operative multiple-input multiple-output [MIMO] systems

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  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Power Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Mathematical Physics (AREA)
  • Mobile Radio Communication Systems (AREA)
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Abstract

The present invention relates to a method for transmitting a signal by selecting a cell to be cooperatively served by a base station and a user in a cooperative communication (CoMP) environment in which multiple cells cooperate to service a user. In accordance with the present invention, by selecting a cell to be actually served in a service candidate cell according to a channel state of a user in consideration of a channel quantization error, not only the frequency efficiency is improved at the time of multi-cell cooperative transmission but also channel information feedback Thereby reducing multi-user scheduling complexity.

Figure R1020120065086

Description

[0001] METHODS FOR COOPERATIVE TRANSMISSION IN MULTI-CELL COOPERATION SYSTEMS [0002]

In a wireless communication system in which a plurality of cells cooperate to transmit signals to a user, a user selects cells having small quantization errors of channel direction information in a process of determining cells to be actually served among signal transmission candidate cells, And a cooperative transmission technique between a base station and a user, which can improve channel efficiency and channel feedback overhead by feeding back channel information for the corresponding cells.

Multi-antenna technology has attracted much attention as a technique for improving transmission efficiency of a wireless communication system. Particularly, when using beamforming using multiple antennas, a signal-to-interference noise ratio (SINR) of a wireless communication transmission link can be improved due to constructive interference between multiple channels. In addition, cooperative operation technology (CoMP) between multiple cells based on multiple antennas is a technique for eliminating interference received from adjacent sectors or neighboring cells, and achieving cell boundary user performance improvement by transmitting signals cooperatively by multiple cells. .

In order to efficiently apply the multi-cell cooperative operation technique, it is necessary to feedback the channel information estimated by the user at the receiver to the transmitter base station. For example, in the case of explicit channel quantization, the channel direction information (CDI) estimated by the UE is considered as a method of feedbacking a codebook index with a smallest error. In particular, in a multi-cell collaborative operating environment, feedback of channel direction information for a plurality of cells is serviced, thereby causing a problem of a large feedback overhead.

In addition, when multiple beams are generated using multiple antennas and multiple users are simultaneously served on the same resource, incorrect channel direction information due to quantization error causes interference between multiple beams. With respect to the SINR, due to the characteristics of the radio channel capacity increasing on a log scale, the inter-multi-beam interference is a main cause of user performance degradation due to the characteristics of the spatial multiplexing beamforming used when the strength of the serving signal is large.

In order to reduce the feedback overhead and mitigate the performance degradation due to the quantization error at the time of multi-cell cooperative transmission, the intelligently moving UE adaptively selects the cells with small quantization error among the cooperative candidate cells, Information can be fed back together to improve the channel capacity of the wireless communication.

According to an aspect of the present invention, there is provided a communication method for a terminal in a communication system using at least one antenna, the method comprising: receiving a pilot signal from at least one base station; Estimating channel state information based on the received pilot signal; And quantizing the channel state information based on the estimated channel state information and determining an error between the quantized channel state information and the estimated channel state information.

Further, in a communication system using one or more antennas according to another aspect of the present invention, a communication method of a base station includes: transmitting a pilot signal; And receiving the selected base station information and quantized channel state information.

In multi-cell cooperative operation, the multi-user beamforming using multiple antennas can dramatically increase the radio channel capacity. However, incorrect channel direction information feedback causes interference problems between multiple beams, Occurs. The present invention can improve the performance of the multi-base station cooperative operation in case of using the conventional scheme by allowing only the base stations having a small quantization error among the base stations participating in cooperation to select and transmitting the channel direction information together with the selected base station index .

1 is a diagram showing a configuration of a communication system according to an embodiment.
2 is a flowchart illustrating a procedure for feedback of channel information in a UE according to an embodiment.
3 is a block diagram showing a configuration of a terminal according to an embodiment.
4 is a flowchart illustrating a communication procedure in a base station according to an embodiment.
5 is a block diagram showing a configuration of a base station according to an embodiment.
6 is a diagram illustrating a signal transmission procedure between a Node B and a UE according to an embodiment of the present invention.

The operation principle of the preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. In the following description, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear. And the definitions of the following terms should be based on the contents throughout this specification.

In the following description, a terminal communicating with a base station can be displayed as a user.

1 is a diagram showing an overall system configuration according to an embodiment.

1, a communication system according to an embodiment includes at least one base station 1 participating in a cooperative transmission. , N (101), and the users u 1 , ..., u (k) serving by the one or more base stations through cooperative beamforming , u M (103).

One or more base stations 101 participating in the cooperation may service the users 103 with one or more receive antennas using N T transmit antennas each. According to the embodiment, it is possible to easily expand to a case where a user uses a plurality of reception antennas.

In an embodiment, it is assumed that the users 103 have different channel environments for the one or more base stations 101. Also, the user can feedback the channel direction information estimated through the pilot signal to one or more serving base stations for cooperative operation.

The beam generator 105 of the at least one base station 101 that has received the channel direction information transmits a signal generated by the signal generator 107 using the beam weight vector generated in consideration of the fed channel direction information, (103).

Here, the base stations participating in cooperation may be connected to a wired backhaul link 109 to share a data signal to be transmitted to the user and channel direction information fed back by the user. According to an embodiment, the base stations can determine a user to be served based on the channel direction information fed back by the user received via the wired backhaul link 109.

A channel vector representing the channel characteristics between the base station i and the user u k

Figure 112012048299818-pat00001
, The user u k Can be expressed by Equation (1) below. ≪ EMI ID = 1.0 >

Figure 112012048299818-pat00002

here

Figure 112012048299818-pat00003
The base station i and the user u k Gt; path loss < RTI ID = 0.0 >
Figure 112012048299818-pat00004
The average is 0 and the variance is
Figure 112012048299818-pat00005
(Complex Gaussian noise) < RTI ID = 0.0 >
Figure 112012048299818-pat00006
The base station i and the user u k And a small-scale fading component between the first and second sub-
Figure 112012048299818-pat00007
Lt; RTI ID = 0.0 > uj < / RTI >
Figure 112012048299818-pat00008
Beam weight,
Figure 112012048299818-pat00009
Represents data to be transmitted to the user u j .

The user u k quantizes the channel direction information with respect to the channel h i , uk between itself and the base station i, and feeds back the channel direction information to the base station i. In this case, in a system using explicit channel quantization, quantized channel direction information

Figure 112012048299818-pat00010
Is a set of codebook vectors consisting of unit vectors
Figure 112012048299818-pat00011
And satisfy the following conditions (2) and (3). &Quot; (3) "

Figure 112012048299818-pat00012

Figure 112012048299818-pat00013

In this case, B represents the number of channel quantization feedback bits,

Figure 112012048299818-pat00014
Denotes an Euclidean norm operator,
Figure 112012048299818-pat00015
The matrix
Figure 112012048299818-pat00016
(Hermitian matrix) < / RTI >

On the other hand, the base station i transmits the user < RTI ID = 0.0 >

Figure 112012048299818-pat00017
Orthogonal to
Figure 112012048299818-pat00018
&Lt; / RTI > forms a beam that can attain the greatest SINR gain. This satisfies Equation (4)
Figure 112012048299818-pat00019
Can be expressed by Equation (5).

Figure 112012048299818-pat00020

Figure 112012048299818-pat00021

In such a system,

Figure 112012048299818-pat00022
Is expressed as Equation (6) below. &Quot; (6) &quot;

Figure 112012048299818-pat00023

Therefore,

Figure 112012048299818-pat00024
If the channel information is fed back due to the quantization error, the signal transmitted to the adjacent user is interfered and the performance is deteriorated.

In order to prevent such an interference problem, the user selects a base station having a small quantization error among all the candidate base stations for cooperation and provides a method of feedbacking channel direction information.

First user

Figure 112012048299818-pat00025
Can calculate a quantization error occurring when quantizing channel direction information estimated for all candidate cooperative candidate base stations. For example, the quantization error for the base station i is calculated by Equation (7) below.

Figure 112012048299818-pat00026

user

Figure 112012048299818-pat00027
Is the quantization error calculated above
Figure 112012048299818-pat00028
Based on the quantization error,
Figure 112012048299818-pat00029
Of base stations can be selected. Also, channel information can be fed back to the serving BS together with the index information on the selected base stations. remind
Figure 112012048299818-pat00030
May be a predetermined value.

2 is a flowchart illustrating a procedure for feedback of channel information in a UE according to an embodiment.

Referring to FIG. 2, in step 201, a user receives a pilot signal, estimates a channel between each base station and itself using the received pilot signal, and calculates channel direction information.

In operation 203, the user quantizes the channel direction information calculated in operation 201. The channel direction information is quantized through a codebook, and channel information can be quantized using channel quantization according to an embodiment.

In step 205, the user can calculate a quantization error value between the quantized channel direction information and the actual channel direction information obtained in step 203. [

In step 207, based on the quantization error calculated by the user in step 205, the quantization error of all N base stations is minimized

Figure 112012048299818-pat00031
&Lt; / RTI &gt;

In step 209, quantized channel information for the corresponding base stations may be fed back along with the index of the base station selected in step 207.

3 is a block diagram showing a configuration of a terminal according to an embodiment.

Referring to FIG. 3, the terminal K 300 according to the embodiment may include a transmission / reception unit 310 capable of transmitting and receiving signals. The transceiver 310 may include one or more antennas.

Also, the terminal K 300 determines channel information based on the signal received through the transceiver 310, quantizes the channel information, and calculates a quantization error value between the quantized channel direction information and the actual channel direction information And a control unit 320 that can control the operation of the apparatus. The control unit 320 calculates a quantization error value based on the calculated quantization error value,

Figure 112012048299818-pat00032
You can choose dogs. Meanwhile, the selected base station information and the quantized channel information may be fed back to the base station through the transceiver 310.

4 is a flowchart illustrating a communication procedure in a base station according to an embodiment.

Referring to FIG. 4, in step 410, a base station can broadcast a pilot signal to neighboring terminals. The pilot signal to be broadcast may be a predetermined signal, and the terminal receiving the pilot signal can grasp the channel information.

In step 420, the base station may receive the selected base station index and channel direction information feedback from the terminal. The base station indices selected by the UE may be calculated by calculating a quantization error as described with reference to FIG. 2, and a predetermined number of base stations among the base stations having small calculated quantization errors may be selected.

In step 430, the base station can select a user to be served based on the received selected base station index. Also, beam weight corresponding to the user to be served can be generated based on the received channel direction information feedback.

In step 440, the base station may transmit the data by applying the beam weight to the user to be served

5 is a block diagram showing a configuration of a base station according to an embodiment.

Referring to FIG. 5, The control unit 500 may include a data receiving unit 501, a signal generating unit 503, a feedback information receiving unit 505, a signal transmission determining unit 507, and a signal transmitting unit 509. The data receiving unit 301, the feedback information receiving unit 305, and the signal transmitting unit 309 can be referred to as a transmitting and receiving unit. The signal generation unit 303 and the signal transmission determination unit 307 may be referred to as a control unit.

The data receiving unit 501 can receive data on the service candidate users from the upper network and transmit the data to the signal generating unit 503. [ In addition, the feedback information receiving unit 505 can transmit the base station index and channel direction information fed back from the users to the signal transmission determination unit 507.

The signal transmission determination unit 507 determines which user is to be served according to the base station index fed back by the users and transmits the signal to the signal generation unit 503 together with the channel direction information for the users.

The signal generating unit 503 selects only the data to be transmitted to the users to be served from the signal transmission deciding unit 507 from the user data received from the data receiving unit 501, Generates a beam weight to be transmitted, generates a signal to be actually transmitted, and transmits it to the signal transmitting unit 509.

6 is a diagram illustrating a procedure for signal transmission performed between a base station and a user according to an embodiment of the present invention.

Referring to FIG. 6, N cooperative transmission candidate base stations 601 may broadcast (605) a pilot signal to neighboring users 603.

The users 603 receiving the pilot signal can estimate a channel corresponding to each base station 401 and calculate 607 a quantization error.

In addition, the terminal 603 selects a base station to which channel information is fed back in consideration of a quantization error (609), and can feed back (611) channel direction information for the base station along with the selected base station index.

Based on the feedback information, the base stations can determine the users to be served and generate (613) beam weights for serving the determined users. Based on the set beam weights, base stations can transmit data to be provided to users.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, And is not intended to limit the scope of the invention. It is to be understood by those skilled in the art that other modifications based on the technical idea of the present invention are possible in addition to the embodiments disclosed herein.

101: base station
103: Terminal
105: Beamformer
107: Signal generator
109: Wired backhaul link

Claims (18)

A communication method of a terminal of a communication system including one or more antennas,
Receiving a pilot signal from a plurality of base stations;
Estimating channel state information based on the received pilot signal;
Quantizing the estimated channel state information into a codebook vector set consisting of unit vectors into any one of the following elements (1) and (2);
Determining an error between the quantized channel state information and the estimated channel state information generated in the quantization step based on Equation (3);
Selecting N base stations to transmit the quantized channel state information among the plurality of base stations that transmitted the pilot signal, in ascending order of the determined error; And
And transmitting only the selected base station information and the quantized channel state information for the selected base station only to the selected base station,
And the N is a preset value.
Equation (1)
Figure 112018130014282-pat00039

Equation (2)
Figure 112018130014282-pat00040

Equation (3)
Figure 112018130014282-pat00041

here
Figure 112018130014282-pat00042
Is a channel vector indicating the channel characteristics between the base station i and the user u k ,
Figure 112018130014282-pat00043
Is the quantized channel direction information,
Figure 112018130014282-pat00044
Is an error generated in the quantization process of the channel direction information between the base station i and the user u k ,
Figure 112018130014282-pat00045
B is the number of channel quantization feedback bits,
Figure 112018130014282-pat00046
Is an Euclidean norm operator,
Figure 112018130014282-pat00047
The matrix
Figure 112018130014282-pat00048
Is a Hermitian matrix. The method according to claim 1,
Wherein the channel state information includes channel direction information. The method according to claim 1,
Wherein estimating the channel state information comprises estimating an instantaneous short-term fading channel for the one or more base stations. The method according to claim 1,
Wherein quantizing the channel state information comprises determining channel state information of the codebook that is most similar to the estimated channel state information based on a predetermined codebook. A communication method of a base station in a communication system including one or more antennas,
Transmitting a pilot signal to a terminal; And
(4) and (5) among a codebook vector set consisting of N base station information and unit vectors selected from a plurality of base stations transmitting the pilot signal, Comprising: receiving quantized channel state information with one element;
The BS information includes information on N base stations selected in descending order of the error between the channel state information estimated based on the pilot signal and the channel state information quantized by the UE, Information is included,
And the N is a preset value.
Equation (4)
Figure 112018130014282-pat00049

Equation (5)
Figure 112018130014282-pat00050

Equation (6)
Figure 112018130014282-pat00051

here
Figure 112018130014282-pat00052
Is a channel vector indicating the channel characteristics between the base station i and the user u k ,
Figure 112018130014282-pat00053
Is the quantized channel direction information,
Figure 112018130014282-pat00054
Is an error generated in the quantization process of the channel direction information between the base station i and the user u k ,
Figure 112018130014282-pat00055
B is the number of channel quantization feedback bits,
Figure 112018130014282-pat00056
Is an Euclidean norm operator,
Figure 112018130014282-pat00057
The matrix
Figure 112018130014282-pat00058
Is a Hermitian matrix. 6. The method of claim 5,
And generating a transmission signal based on the received selected base station information and quantized channel state information. The method according to claim 6,
Wherein the step of generating the transmission signal generates a transmission signal when the base station is included in the received selected base station information. The method according to claim 6,
Wherein generating the transmit signal comprises determining a beamforming weight corresponding to the one or more antennas based on the received quantized channel state information. A transmitting and receiving unit including at least one antenna unit and receiving a pilot signal from a plurality of base stations; And
Estimates channel state information on the basis of the received pilot signal, and outputs the estimated channel state information as a codebook vector set of unit vectors as shown in Equations (7) and (8) ), And determines an error between the quantized channel state information and the estimated channel state information generated at the quantization on the basis of the following equation (9) Selects the N base stations to transmit the quantized channel state information among the plurality of base stations that have transmitted the signals in the ascending order of the error and transmits the selected base station information and the quantized channel state information only to the selected base station And a control unit,
And N is a preset value.
Equation (7)
Figure 112018130014282-pat00059

Equation (8)
Figure 112018130014282-pat00060

Equation (9)
Figure 112018130014282-pat00061

here
Figure 112018130014282-pat00062
Is a channel vector indicating the channel characteristics between the base station i and the user u k ,
Figure 112018130014282-pat00063
Is the quantized channel direction information,
Figure 112018130014282-pat00064
Is an error generated in the quantization process of the channel direction information between the base station i and the user u k ,
Figure 112018130014282-pat00065
B is the number of channel quantization feedback bits,
Figure 112018130014282-pat00066
Is an Euclidean norm operator,
Figure 112018130014282-pat00067
The matrix
Figure 112018130014282-pat00068
Is a Hermitian matrix. 10. The method of claim 9,
Wherein the channel state information includes channel direction information. 10. The method of claim 9,
Wherein the controller estimates the channel state information by estimating an instantaneous short-term fading channel for the at least one base station. 10. The method of claim 9,
Wherein the controller determines channel state information of the codebook that is most similar to the estimated channel state information based on a predetermined codebook. A transmitting and receiving unit including one or more antenna units and transmitting and receiving data; And
And a control unit configured to control the transmitting and receiving unit to transmit the pilot signal to the mobile station and to transmit the pilot signal to the mobile station using a codebook vector set of N base station information and unit vectors selected from a plurality of base stations, And a controller for receiving channel state information quantized by any one element satisfying the equations (10) and (11)
The base station information includes information on N base stations selected in descending order of the error between the channel state information estimated based on the pilot signal and the channel state information quantized by the terminal, Information is included,
And the N is a preset value.
Equation (10)
Figure 112018130014282-pat00069

Equation (11)
Figure 112018130014282-pat00070

Equation (12)
Figure 112018130014282-pat00071

here
Figure 112018130014282-pat00072
Is a channel vector indicating the channel characteristics between the base station i and the user u k ,
Figure 112018130014282-pat00073
Is the quantized channel direction information,
Figure 112018130014282-pat00074
Is an error generated in the quantization process of the channel direction information between the base station i and the user u k ,
Figure 112018130014282-pat00075
B is the number of channel quantization feedback bits,
Figure 112018130014282-pat00076
Is an Euclidean norm operator,
Figure 112018130014282-pat00077
The matrix
Figure 112018130014282-pat00078
Is a Hermitian matrix. 14. The method of claim 13,
Wherein the controller is further configured to generate a transmission signal based on the received selected base station information and the quantized channel state information. 14. The method of claim 13,
Wherein the controller is further configured to generate a transmission signal based on the received selected base station information and quantized channel state information. 15. The method of claim 14,
Wherein the controller is further configured to determine beamforming weights corresponding to the one or more antenna units based on the received quantized channel state information. delete delete
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