KR20080090032A - Apparatus and method for precoding mylti carrier quantization in multi input multi output system - Google Patents

Abstract

A system and a method for pre-processing multi-carrier quantization in a multi-input and multi-output system are provided to allocate sub-carrier power suitably for the system by checking environment of the system without additive feedbacks from the terminal. A base station(110) performs channel coding and adaptive modulation on a signal to be transmitted. The base station outputs pattern information from a specific sub-carrier group by using received feedback information. Herein, the pattern information is transmitted from a terminal to select a preprocessor or a terminal(150). The base station allocates power with respect to the adaptively modulated signal according to sub-carriers within the group by using the pattern information, and then preprocesses, modulates, and transmits the signal. A terminal performs channel estimation on the signal received from the base station. The terminal determines the preprocessor and preprocessing rates to transmit a feedback to the base station. The terminal performs modulation and demodulation on the channel-estimated signal and a received signal.

Description

Apparatus and method for multicarrier quantization preprocessing in a multi-antenna system {APPARATUS AND METHOD FOR PRECODING MYLTI CARRIER QUANTIZATION IN MULTI INPUT MULTI OUTPUT SYSTEM}

1 is a diagram illustrating a capacity curve in a general group of user terminals;

2 is a diagram illustrating a general multi-antenna system;

3 is a block diagram illustrating a user terminal and a network device according to an exemplary embodiment of the present invention.

4 is a view illustrating an operation process of a user terminal and a network device according to an embodiment of the present invention;

FIG. 5 is a diagram illustrating a result of calculating a cumulative distribution function showing a ratio between a highest data rate and a lowest data rate that can be achieved by a preprocessor selected from a subcarrier group according to an embodiment of the present invention; FIG.

FIG. 6 is a diagram illustrating a result of averaging the cases where each subcarrier has the largest capacity when a preprocessor is selected for each subcarrier group according to an embodiment of the present invention; FIG.

7 illustrates capacity equalization using statistical characteristics according to an embodiment of the present invention;

8 is a graph comparing the performance of the method in the correlation 0.4 and the conventional capacity performance according to an embodiment of the present invention, and

9 is a graph comparing bit error rates in a scheme of correlation 0.8 and a conventional scheme according to an embodiment of the present invention.

The present invention relates to a multiple input multiple output, i.e., a multiple antenna (MIMO) system, and more particularly, to an apparatus for allocating subcarrier power for improving performance of a multicarrier quantization preprocessor. It is about a method.

1 illustrates a typical multiple antenna system.

Referring to FIG. 1, a matrix type quantization preprocessing system in an existing multi-user terminal environment is illustrated. Each user terminal 110 feeds back the most preferred preprocessor and data rate for each group, and the base station 250 based on the feedback information received from the user terminal 210, the user terminal and its corresponding in a group unit Allocate data to service.

The closed loop MIMO system in a multi-user environment uses signal to noise plus interference ratio (hereinafter referred to as SNIR) for each pre-coding matrix for each user terminal. Diversity gain can be obtained in a multi-user terminal.

In the multi-carrier system, since the feedback information for each subcarrier is a heavy load, several subcarriers are grouped into a group and a single channel quality information (CQI) and a preprocessing index are transmitted.

2 is a diagram illustrating a capacity curve in a general group of user terminals.

Referring to FIG. 2, in general, a feedback scheme for selecting a preprocessing vector having the highest capacity for the lowest performing subcarrier uses a simple scheme of allocation and adaptive modulation scheme for a user terminal at a base station. It is widely used for application.

However, in order to prevent outage, subcarriers with higher capacity by feeding back the lowest capacity within the group of selected preprocessors suffer losses in terms of capacity. In this case, reducing the difference between the average capacity and the lowest capacity in the group is a way to reduce capacity loss.

To this end, it is possible to equalize the capacity in the group by allocating a small power to a subcarrier having a good channel environment and a large power to a subcarrier having a poor channel environment.

However, in this case, there is a problem in that power levels must be fed back for each group at every symbol time, and the base station must be allocated to them every symbol time.

An object of the present invention is to provide an apparatus and method for multicarrier quantization preprocessing in a multi-antenna system.

Another object of the present invention is to provide an apparatus and method for reducing capacity loss in a multi-antenna system.

It is still another object of the present invention to provide an apparatus and method for allocating power of an internal carrier in a group so as to minimize a loss of capacity of a system at a base station without additional feedback.

According to a first aspect of the present invention for achieving the above object, in a method of a base station for multicarrier quantization preprocessing in a multi-antenna system, a first process of receiving feedback information from a terminal and a specific subcarrier using the feedback information A second process of selecting a preprocessor and a terminal from a group, a third process of performing channel coding and adaptive modulation on a signal to be transmitted to the terminal, a statistical power pattern determination process or a long period feedback or a given system for each subcarrier in the group A fourth process of allocating power in consideration of information; and a fifth process of repeating the processes from the third process to the fourth process by a smaller value of the number of terminals and receiving antennas of the terminal in the specific subcarrier group. After the process and the fifth process, unitary fresco for the particular group And a sixth process of performing unitary precoding and band mapping processes, and a seventh process of repeating the processes from the first process to the sixth process for other groups within the entire group. It is characterized by.

According to a second aspect of the present invention for achieving the above object, in a base station for multicarrier quantization preprocessing in a multi-antenna system, channel coding and adaptation for a system parameter unit for receiving and outputting feedback information transmitted from a terminal and a signal to be transmitted An adaptive modulator that performs modulation and a power allocation pattern determiner that receives the feedback information and outputs pattern information for selecting a preprocessor and a terminal transmitted from the terminal in a specific subcarrier group and the adaptation using the pattern information And a band power allocator for allocating power for each subcarrier in the group and a unitary precoder for preprocessing the signals output by the band power allocator.

According to a third aspect of the present invention for achieving the above object, in the method of a terminal for multicarrier quantization preprocessing in a multi-antenna system, a process of performing channel estimation on information received from a base station and performing channel estimation And determining a preprocessor and a rate for the information, and feeding back the determination information to the base station.

According to a fourth aspect of the present invention for achieving the above object, in a terminal for multicarrier quantization preprocessing in a multi-antenna system, a channel estimator for channel estimation of a signal received from a network device and a signal output by the channel estimator And a precoder and a rate determiner for determining a preprocessor and rate and feeding back to the network device.

According to a fifth aspect of the present invention for achieving the above object, in a system for multicarrier quantization preprocessing in a multi-antenna system, channel coding and adaptive modulation are performed on a signal to be transmitted and specific subcarriers are received using the received feedback information. Outputs pattern information for selecting a preprocessor and a terminal transmitted from the terminal in a group, allocates power to each subcarrier in the group, performs preprocessing, and modulates the adaptively modulated signal using the pattern information And a terminal for channel estimation of a transmitting base station and a signal received from the base station, determining a preprocessor and a rate, feeding back the base station, and performing demodulation and decoding on the channel estimation signal and the received signal. Shall be.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In describing the present invention, when it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted.

Hereinafter, the present invention will be described an apparatus and method for multicarrier quantization preprocessing in a multi-antenna system. The present invention uses the statistical characteristics of the system to allocate the power of subcarriers to minimize the loss of capacity of the system without further feedback and increased complexity.

In general, in the multi-carrier system, since the feedback information for each subcarrier is a heavy load, several subcarriers are grouped into one group and one channel quality information (CQI) and a preprocessing index are represented. send.

A multi-user multi-subcarrier downlink MIMO system is described as follows.

)을 구비하고 있다고 설정한다.The base station has N _t transmit antennas and each user terminal has N _r receive antennas, where K represents the total number of user terminals present in the system, and M represents the number of subcarriers. In addition, the base station and all user terminals are assigned a common unitary matrix code set (

Is set.

According to the channel information transmitted from the user terminal, the base station selects one matrix code for each subcarrier and performs preprocessing. Subcarrier matrix code selection and stream user terminal selection are performed jointly.

)가 m 번째 부 반송파의 전 처리 매트릭스로 선택되고 각 스트림에 N_t 개의 사용자 단말기 그룹

이 선택되었다면, i 번째 스트림에 할당이 되는 사용자 단말기 k_i 의 전처리 벡터는 P _m 의 i 번째 행인

이 된다. 기지국에서 전송된 신호는 하기 <수학식 1>과 같이 표현된다.If matrix code (

) Is selected as the preprocessing matrix of the m th subcarrier and each group of N _t user terminals

If is selected, the preprocessing vector of user terminal k _i assigned to the i th stream is the i th row of P _m .

Becomes The signal transmitted from the base station is represented by Equation 1 below.

는 선택된 사용자 단말기의 정보로 이루어진 크기 N_t x 1 의 벡터이다. here

Is a vector of size N _t x 1 consisting of information of the selected user terminal.

If the user terminal k is allocated to the i th stream of the m th subcarrier, the SNIR at the receiver of the user terminal k is obtained as shown in Equation 2 below using the MMSE technique.

In this case, the attainable data rate is expressed by Equation 3 below.

It is assumed that the channel information transmitted from each user terminal to the base station has no errors and delays in the feedback channel, and each user terminal fully knows the channel information of all subcarriers. In this case, only limited channel information can be fed back to the base station.

Therefore, rather than feeding back each channel information for all subcarriers, a system is considered in which a certain number of subcarriers are grouped into one group to feed back channel information in group units.

가 된다. If the total subcarriers can be divided into G groups, in general, the total number of subcarriers (M) is a multiple of G and the number of subcarriers in one group is

Becomes

)를 구한다. 상기 대표 데이터 레이트는 하기 <수학식 4와> 같다.When one subcarrier group to be considered is g, the user terminal k has a representative data rate that can be achieved in group g for each matrix code P and all preprocessing vectors P (i) included therein.

) The representative data rate is shown in Equation 4 below.

은 그룹 g에 포함되어 있는 부 반송파를 나타낸다. here,

Represents a subcarrier included in the group g.

Here, the number of representative values obtained for each subcarrier is a number obtained by multiplying the number of matrix codes by N _t . Each representative value is taken as the subcarrier with the lowest data rate achievable in group g.

Then, the user terminal selects a representative value to feed back to the base station, the process is as shown in Equation 5 below.

If the user terminal k is allocated to a stream at the base station, all subcarriers in the group g satisfy all of the feedback data rates, so that the selection of the preprocessing matrix at the base station and the allocation of the user terminal for each stream are not subcarriers but subcarriers. It is done in groups.

The present invention operates in a manner in which the base station determines the power allocation pattern of the subcarrier according to the characteristics of the channel. That is, the base station is configured and operates in the part of determining the power allocation pattern from the channel information obtained through the upper layer and the part of allocating power in each subcarrier unit.

In addition, in the present invention, the base station determines the power of the subcarrier according to a predetermined pattern using statistical capacity characteristics in the group of the multicarrier quantization preprocessing system.

In the multi-carrier quantization preprocessing system, each group of each user terminal selects a preferred preprocessor using a "maxmin" technique. The process of selecting is shown in Equation 6 below.

Where Pg denotes the matrix code of the preprocessor for group g, H denotes the channel matrix and I denotes the unit matrix.

)이다. Here, the information fed back to the base station is the index of the selected matrix code and stream and the corresponding channel information (

)to be.

When each user terminal selects the most preferred preprocessor for each subcarrier group, the statistical characteristics between the lowest capacity and the highest capacity fed back within the corresponding subcarrier group can be obtained by creating multiple channels. have.

라고 할 때, 고려하는 부 반송파 그룹 g에서 선택한 전 처리기가 달성 가능한 가장 높은 데이터 레이트와 가장 낮은 데이터 레이트 간의 비율, (

)의 누적분포함수(CDF:Cummulative Density Function)는 도 5에 도시되어 있다.

Is the ratio between the highest and lowest data rates achievable by the preprocessor selected in subcarrier group g,

Cumulative Density Function (CDF) is shown in FIG. 5.

When choosing a preprocessor, if the difference between the maximum and minimum values is too large, the probability of being selected is small because the minimum value is likely to be small. When the preprocessors are selected for each subcarrier group, the results obtained by averaging the cases where each subcarrier has the largest capacity are shown in FIG. 6.

Looking at the case where the subcarriers at the outermost subcarrier group have the highest capacity, it can be seen that the relative capacity value does not decrease any more when the distance between the relative subcarriers drops to some extent.

Therefore, if the average capacity of the group is taken for all the selected preprocessors while changing the channel environment, a concave-shaped curve as shown in FIG. 6 can be obtained.

Then, as shown in FIG. 7, if the subcarrier power allocation pattern is determined to have the opposite shape of the statistical capacity curve in the base station and the subcarrier power allocation is performed accordingly, it is possible to equalize the capacity in the statistical group.

The subcarrier power allocation pattern may be determined according to the coherence bandwidth and the signal-to-noise ratio of the system. The smaller the coherence bandwidth and the higher the signal-to-noise ratio, the larger the slope of the subcarrier power allocation pattern.

In this case, since the transmitter uses statistical characteristics of the system when determining the power pattern, it is not necessary for each user terminal to additionally configure feedback information to the base station.

3 is a block diagram illustrating a network device and a terminal according to an exemplary embodiment of the present invention.

In the transmitting end, subcarrier power is allocated and serviced in one group unit according to a predetermined power allocation pattern. The system information required here is taken into account the statistical characteristics. The average signal-to-noise ratio and coherence bandwidth can be fed back in a long term. If there is a power pattern that exists and is considered according to the number of paths considered, there is no additional feedback information necessary for using the technique of the present invention.

이다. Referring to FIG. 3, the network device (base station) is described. The system parameterizer 312 receives feedback information transmitted from the terminal from the upper layer and provides the power allocation pattern determiner 313. The feedback information is an index of a matrix code and a stream of a preprocessor and corresponding channel information.

to be.

The power allocation pattern determiner 313 selects a preprocessor and a user transmitted from a terminal in a specific subcarrier group using the provided feedback information. In the selection process, the "maxmin" technique described above is used. The "maxmin" technique is described in Equation 6 above.

The selected pattern information is provided to a band power allocator 314, and the band power allocator 314 allocates power for each subcarrier in the group to a signal to be transmitted to a terminal.

The signal allocated power for each subcarrier is provided to the unitary precoder 318 and is preprocessed. After that, although not shown in the present invention, the signal is radiated through the antenna after the modulation process. The functions of the other blocks are the same as before.

)이다. 이외의 블록의 기능은 기존과 동일하다. 3, the precoder / rate determiner 352 determines the preprocessor and rate and feeds it back to the network device. The information fed back by the terminal to the network device includes the matrix code of the preprocessor and the index of the stream and corresponding channel information (

)to be. The functions of the other blocks are the same as before.

Although the terminal and the base station are not shown in the present invention, a memory which is a communication module and a storage device that provides a communication interface for communication to the outside is used.

4 is a flowchart illustrating an operation process of a user terminal and a network device according to an exemplary embodiment of the present invention.

Referring to FIG. 4, the network device (base station) is selected, and a preprocessor and a user (Nt name) transmitted from a terminal are selected in a g-th subcarrier group (step 405). In the selection process, the "maxmin" technique described above is used. The "maxmin" technique is described in Equation 6 above.

In step 410, channel coding and adaptive modulation are performed on the transmitted signal.

Thereafter, power is allocated for each subcarrier in the group with respect to the signal that has undergone the channel coding and adaptive modulation (step 415). During the above procedure or before the above procedure, the base station receives feedback information from the terminal.

In the power allocation step, although not shown in the drawing, the statistical power pattern determination process of the present invention and the power pattern determination process in consideration of a long period feedback or given system information are preceded.

Subsequently, the above steps (steps 410 to 415) are repeated by a smaller value of the number of user Nt in the g-th subcarrier group and the number of reception antennas Nr of the user terminal (steps 420 and 425), and the g-th Unitary precoding and band mapping are performed on the group (step 430).

Thereafter, the above steps (steps 405 to 430) are repeated for the other groups within the entire group G (step 440), and when the end of the repetition process is completed, the output signal is modulated and transmitted (step 445). Terminate the algorithm accordingly.

Referring to FIG. 4, the user terminal receives information transmitted by the network device through a communication module that provides a wireless communication interface, although not shown in the present invention (step 450). In step 465, channel estimation is performed.

)이다. Thereafter, the preprocessor and rate according to the present invention described above are determined and fed back to the network device (step 460). The information fed back by the user terminal to the network device includes the matrix code of the preprocessor and the index of the stream and corresponding channel information (

)to be.

Then, the general reception process such as demodulation and channel decoding is performed on the estimated data and the algorithm according to the present invention is terminated.

The lookup table for the statistical power pattern in the present invention can be obtained as shown in <Table 2> when considering <Table 1> as a system parameter corresponding to the embodiment.

Antenna configuration Tx: 4, Rx: 2 Number of sub-carriers 63 SNR 0, 5, 10 dB Number of sub-carriers in one band 9 Number of multipath 6 Codebook matrix 3bits 802.16E code book

Table 1 shows simulation parameters.

0/8 1/7 2/6 3/5 4 SNR 0dB 0.8168 0.8391 0.9183 1.0507 1.2835 SNR 5dB 0.7810 0.8103 0.9022 1.0699 1.3271 SNR 10dB 0.7520 0.7868 0.8951 1.0831 1.3590 SNR 15 dB 0.7389 0.7764 0.8950 1.0896 1.3694

Table 2 shows sub-carrier power distribution for each signal-to-noise ratio (SNR). Here, the average power is 1 and the number of multipaths is 6.

The capacity performance and bit error rate of the prior art and the present invention are compared according to the number of user terminals and the signal-to-noise ratio.

8 is a graph comparing the performance of the method in the correlation 0.4 and the conventional capacity performance according to an embodiment of the present invention.

Referring to FIG. 8 above, the capacity performance difference between the existing scheme and the scheme of the present invention is shown. Regardless of the number of user terminals and the signal-to-noise ratio, it can be seen that there is a gain of about 5% over the conventional method.

9 is a graph comparing bit error rates in the scheme of the correlation 0.8 and the conventional scheme according to an embodiment of the present invention.

9, the bit error rate of the conventional scheme and the scheme of the present invention in a multi-user terminal environment is shown.

The higher the signal-to-noise ratio, the larger the performance difference from the conventional method, because the larger the signal-to-noise ratio, the greater the slope of the power allocation pattern and thus the greater the room for performance improvement. In addition, it can be seen that in a multi-user terminal environment, performance gains such as 10 user terminals are obtained compared to the conventional methods.

Overall, there is an improvement in performance compared to the conventional scheme, there is no additional feedback required in the conventional scheme, and the complexity required for determining the power allocation pattern at the base station is also not great.

Meanwhile, in the detailed description of the present invention, specific embodiments have been described, but various modifications are possible without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined not only by the scope of the following claims, but also by the equivalents of the claims.

The present invention can minimize the capacity loss in the group when viewed on average by identifying the statistical capacity characteristics of the multi-carrier quantization preprocessing system and equalizing the capacity in the statistical group. That is, the subcarrier power allocation may be performed so that the environment of the system may be grasped without additional feedback from the user terminal to be suitable for the multicarrier quantization preprocessing system.

Claims (17)

A method of a base station for multicarrier quantization preprocessing in a multi-antenna system, A first process of receiving feedback information from a terminal, A second process of selecting a preprocessor and a terminal from a specific subcarrier group by using the feedback information; A third process of performing channel coding and adaptive modulation on a signal to be transmitted to the terminal; A fourth process of allocating power in consideration of a statistical power pattern determination process or a long period feedback or given system information for each subcarrier in the group; Thereafter, a fifth process of repeating the processes from the third process to the fourth process by a smaller value of the number of terminals and receiving antennas of the terminal in the specific subcarrier group; A sixth process of performing unitary precoding and band mapping on the specific group after the fifth process; And a seventh process of repeating the processes from the first process to the sixth process for another group within the entire group. The method of claim 1, And an eighth process of performing modulation on the output signal of the seventh process and transmitting through the antenna. The method of claim 1, The second process is characterized by using the following equation (7).

Where Pg denotes the matrix code of the preprocessor for group g, H denotes the channel matrix and I denotes the unit matrix. The method of claim 1, The feedback information is a representative data rate, which is an index of a matrix code and a stream of a preprocessor and corresponding channel information.

). A base station for multicarrier quantization preprocessing in a multi-antenna system A system parameter unit for receiving and outputting feedback information transmitted by the terminal; An adaptive modulator for performing channel coding and adaptive modulation on a signal to be transmitted; A power allocation pattern determination unit receiving the feedback information and outputting pattern information for selecting a preprocessor and a terminal transmitted from the terminal in a specific subcarrier group; A band power allocator for allocating power for each subcarrier in the group to the signal output by the adaptive modulator using the pattern information; And a unitary precoder for performing preprocessing on the signal output by the band power allocator. The method of claim 5, The base station further comprises a communication unit for modulating the signal output by the unitary precoder output through the antenna The method of claim 5, The feedback information is the index of the matrix code and stream of the preprocessor and the representative data rate that can be achieved in the corresponding channel information group g.

The base station characterized in that). The method of claim 5, The base station, characterized in that the power allocation pattern determination unit selects the preprocessor and the terminal by using Equation (8).

Where Pg represents the matrix code of the preprocessor for group g, H is the channel matrix, and I is the identity matrix. A method of a terminal for multicarrier quantization preprocessing in a multi-antenna system, Performing channel estimation on the information received from the base station; Determining a preprocessor and a rate for the information on which the channel estimation is performed; And feeding back the decision information to the base station. The method of claim 9,  And demodulating and channel decoding the information on which the channel estimation has been performed. The method of claim 9, The information fed back to the network device is the index of the matrix code and stream of the preprocessor and the representative data rate that can be achieved in the corresponding channel information group g (

). A terminal for multicarrier quantization preprocessing in a multi-antenna system, A channel estimator for channel estimating a signal received from the network device; And a precoder and a rate determiner for determining a preprocessor and a rate for the signal output by the channel estimator and feeding back the network apparatus. The method of claim 12, And a demodulation and decoding unit configured to receive a signal outputted from the channel estimator and a received signal to perform demodulation and decoding. The method of claim 12, The feedback information is the index of the matrix code and stream of the preprocessor and the representative data rate that can be achieved in the corresponding channel information group g.

Terminal). A system for multicarrier quantization preprocessing in a multi-antenna system, Perform channel coding and adaptive modulation on a signal to be transmitted, and output pattern information for selecting a preprocessor and a terminal transmitted from the terminal in a specific subcarrier group by using the received feedback information, and use the pattern information to output the pattern information. A base station for allocating power for each subcarrier in the group, performing preprocessing, modulating and transmitting the adaptively modulated signal; And a terminal for channel estimation of the signal received from the base station, determining a preprocessor and a rate, feeding back to the base station, and performing demodulation and decoding on the channel estimation signal and the received signal. The method of claim 15, The feedback information is the index of the matrix code and stream of the preprocessor and the representative data rate that can be achieved in the corresponding channel information group g.

System). The method of claim 15, The base station selects a preprocessor and a terminal by using Equation (9).

Where Pg denotes the matrix code of the preprocessor for group g, H denotes the channel matrix and I denotes the unit matrix.

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