KR101371179B1 - Apparatus and method for interference cancellation in multilple antenna system - Google Patents

Abstract

The present invention relates to a receiving apparatus and method for interference cancellation in a multi-antenna system, and a receiving apparatus for interference cancellation in a multi-antenna system, comprising: a receiving unit for receiving modulated symbols from a plurality of transmitting antennas; A log-likelihood ratio of decoded bits and encoded bits, respectively, for a MIMO detector for outputting soft decision symbols for symbols and for modulated symbols from the plurality of transmit antennas using the soft decision symbols A decoder that generates a Log Likehood Ratio (LLR), and an interference that is repeatedly performed according to the reliability of a bit by using each of the decoded bits and the LLR value of the encoded bit from the plurality of transmission antennas. Including multiple cancellations, iteratively accesses soft information in multiple antenna systems that do not use channel interleaving. And there is an advantage in that, by decoding the data to perform, reliable in decoding.

Multiple Antennas, Interference Cancellation, Coding Bits, Maximum Ratio Combining (MRC), Log-Likelihood Ratio (LLR).

Description

Receiving device and method for interference cancellation in multi-antenna system {APPARATUS AND METHOD FOR INTERFERENCE CANCELLATION IN MULTILPLE ANTENNA SYSTEM}

1 is a block diagram of a transmitter in a multi-antenna system according to the present invention;

2 is a receiver block diagram in a multi-antenna system according to an embodiment of the present invention;

3 is an interference cancellation apparatus in a receiver of a multi-antenna system according to an embodiment of the present invention;

4 is a flowchart illustrating a reception operation in a multi-antenna system according to an exemplary embodiment of the present invention.

The present invention relates to an apparatus and method for interference cancellation in a multi-antenna system, and more particularly, to an apparatus and method for removing interference by performing repeated detection and decoding in a multi-antenna system.

Multiple Input Multiple Output (hereinafter referred to as "MIMO") in wireless communication is a technology that transmits signals using multiple antennas at both ends of transmission and reception, and has high reliability and increases channel capacity within limited frequency resources. To provide high data rates. In the MIMO technology, a spatial multiplexing technique for transmitting an independent signal to increase the amount of information, and a space-time encoding for generating diversity effects and code gains by generating and transmitting different symbols from one piece of information, respectively, time coding). A representative method of the spatial multiplexing method is the BLAST (Bell Labs layered space-time) method, which is a layered MIMO transmission scheme proposed by Lucent Technologies in the United States.

There is an iterative detection and decoding scheme known as Turbo MIMO to perform decoding at the receiving end. The turbo MIMO has a channel interleaver after the channel encoder in the transmission system. Currently, the Institute of Electrical and Electronics Engineers (IEEE) proposes several types of single encoding and modulation schemes (eg, IEEE 802.16d and IEEE 802.16e) based on a system without a channel interleaver. However, in a system without a channel interleaver at the transmitter, the performance of the schemes cannot be improved and the receiver is more complicated.

Accordingly, there is a need for an apparatus and method for detecting and decoding a signal that is encoded and modulated based on a single encoding and modulation scheme and a system without channel interleaving.

Accordingly, an object of the present invention is to provide an apparatus and method for interference cancellation in a multi-antenna system.

Another object of the present invention is to provide a receiving apparatus and method for performing a single encoding and modulation without a channel interleaving function in a multi-antenna system.

It is still another object of the present invention to provide an apparatus and method for improving performance by repeatedly passing soft information between a soft input soft output decoder and a SISO interference cancellation in a multi-antenna system.

According to a first aspect of the present invention for achieving the above object, in a receiver for interference cancellation in a multi-antenna system, a receiver for receiving modulated symbols from a plurality of transmit antennas, and the modulated symbols A log likehood of the decoded bits and the encoded bits for the modulated symbols from the plurality of transmit antennas using the MIMO detector for outputting soft decision symbols for each of the plurality of transmit antennas. A decoder for generating a ratio (LLR), and an interference cancellation unit for performing interference cancellation repeatedly according to the reliability of bits using the decoding bits from the plurality of transmission antennas and LLR values of the encoding bits. Characterized in that.

According to a second aspect of the present invention for achieving the above object, in a receiving method for interference cancellation in a multi-antenna system, receiving the modulated symbols from a plurality of transmit antennas, Outputting soft decision symbols for each of the symbols; and log likehood ratios of decoded bits and encoded bits for modulated symbols from the plurality of transmission antennas using the soft decision symbols, respectively. Generating an LLR, and repeatedly performing interference cancellation based on reliability of bits using the decoding bits and the LLR values of the encoding bits from the plurality of transmission antennas. It features.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description of the present invention, 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. The following terms are defined in consideration of the functions of the present invention, and may be changed according to the intentions or customs of the user, the operator, and the like. Therefore, the definition should be based on the contents throughout this specification.

Hereinafter, an apparatus and method for improving reliability by repeatedly performing detection and decoding for performing interference cancellation and maximum ratio combining in a multi-antenna system will be described.

1 illustrates a transmitter block diagram in a multiple antenna system according to the present invention.

Referring to FIG. 1, N _T A single code scheme is used for all transmission antennas, and N _F of all transmission antennas A single modulation scheme is used for all four frequency subchannels. The transmitter includes an encoder 100, a modulator 102, a demultiplex (Demux) 104, a subcarrier mapper (106 to 106_n), an IFFT unit (108 to 108_n), and an RF processor (110 to 110_n). It is composed.

The encoder 100 receives and encodes traffic data (ie, information bits) according to a coding scheme selected to provide encoded bits. The encoding can increase the reliability of data transmission. The selected code scheme may include any combination of Cyclic Redundancy Check (CRC), Convolution Code, Turbo Code, Block Code, and the like.

The modulator 102 modulates the code bits from the encoder 100 in a predetermined modulation scheme to generate modulation symbols and outputs the modulation symbols to the demultiplexer 104. Here, the modulation scheme includes BPSK (Binary Phase Shift Keying) for mapping one bit to one signal point (modulation symbol), QPSK (Quadrature Phase Shift Keying) for mapping two bits to one modulation symbol, 10-ary Phase Shift Keying (8PSK) mapping bits to one modulation symbol, and 16QAM mapping four bits to one modulation symbol.

The demultiplexer 104 demultiplexes the modulation symbols from the modulator 102 to N _T. The number of transmission antennas is output. Depending on the implementation, the number that is demultiplexed and output may vary. Then, the demultiplexed N _T Modulation symbols are provided to the subcarrier mappers 106 to 106_n, respectively.

The subcarrier mappers 106 to 106_n map corresponding demultiplexed modulation symbols output from the demultiplexer 104 to respective subcarriers according to subcarrier mapping information.

The IFFT units 108 to 108_n convert the modulation symbols from the subcarrier mappers 106 to 106_n into Inverse Fast Fourier Transforms (IFFTs), thereby converting them into signals in a time domain (referred to as OFDM symbols). do. In this case, the IFFT units 108 to 108_n may perform cyclic prefix (CP) insertion.

The RF processor 110 to 100_n converts the baseband OFMD symbols from the IFFT units 108 to 108_n into signals of a radio frequency (RF) band and transmits them to a wireless channel through a transmission antenna.

2 shows a receiver block diagram in a multiple antenna system according to the present invention. Here, the receiver performs decoding by repeatedly passing soft information between the soft-input soft-output decoder 208 and the soft-input soft-output interference canceller 210.

Referring to FIG. 2, the receiver includes a plurality of RF processors 200 to 200_m, a plurality of FFTs 202 to 202_m, a plurality of subcarrier demappers 204 to 204_m, a MIMO detector 206, a decoder. 208, the interference canceling unit 210, and the maximum ratio coupling unit 212.

Each of the plurality of RF processors 200 to 200_m includes a filter, a frequency converter, and the like, and converts an RF band signal received through a corresponding antenna into a baseband signal and outputs the digital signal.

Each of the plurality of FFT operators 202-1 ˜ 202-m performs fast Fourier transform of data from the corresponding RF processors 200 ˜ 200_m to output data in a frequency domain.

Each of the plurality of subcarrier demappers 204-1 to 204-m sorts the data of the frequency domain from the corresponding FFT operators 202-1 to 202-m according to the used subcarrier structure. Output to the MIMO detector 206.

The MIMO detector 206 receives data (modulation symbols generated in the transmitter) from the subcarrier demappers 204-1 to 204-m and performs symbol demodulation on the modulation symbol to perform demodulation. Then, soft decision symbols of the transmitted encoded bits are provided to the decoder 208. Here, the MIMO detector 206 may be implemented by a ML (Maximum Likelihood) or Minimum Mean Square Error (hereinafter referred to as "MMSE") detection scheme, and N _F frequency subcarriers of all N _T transmit antennas. Derive a soft decision symbol from the Each soft decision symbol is obtained from an estimate of the coded bits sent by the transmitter. In addition, the soft decision symbols are represented by a log likelihood ratio (hereinafter referred to as "LLR").

The decoder 208 receives the soft decision symbols from the MIMO detector 206 and decodes based on the coding scheme used in the transmitter. In this case, the decoder 208 provides the interference canceller 210 with the LLR value of the coded bit and hard decision bits. Here, the decoder 208 may be implemented by a turbo code, a convolutional code, or the like.

)를 빼서 상기 최대비 결합부(212)로 출력한다. 상기 간섭제거기(210)의 상세한 기능은 하기 도 3에서 설명하기로 한다.The interference canceller 210 recodes the decoded bits from the decoder 208 and has an LLR value of the recoded bits and the encoded bits from the decoder 208, wherein the interference canceller 210 has one. It is decided whether or not to remove interference to restore the transmission signal of the receiver. And, when performing interference cancellation, the interference signal (in the input signal r of the MIMO detector)

) Is subtracted and output to the maximum ratio combining unit 212. Detailed functions of the interference canceller 210 will be described with reference to FIG. 3.

The maximum ratio combining unit 212 recovers the signal by performing the maximum ratio combining on the signal from which the interference is removed from the interference canceller 210.

Here, for coded bits that are not updated by the interference canceller 210, the decoder 208 uses soft information of previous iteration in order to perform decoding. Thus, the detection and decoding which perform interference cancellation and maximum ratio combining are repeated many times so that during the repeated detection and decoding process, the reliability of the bit decision is improved with each iteration.

3 illustrates an interference cancellation apparatus in a receiver according to an exemplary embodiment of the present invention.

Referring to FIG. 3, the interference canceling unit 210 includes an encoder 300, a hard decision unit 302, a comparator 304, a modulator 306, a channel simulator 308, and the signal synthesizer 310. It is configured to include.

The encoder 300 may provide recoding bits from another transmit antenna. The decoded bits from the decoder 206 of FIG. 2 are re-encoded using the code method used in the transmitter.

The hard decision unit 302 compares the LLR values of the coded bits from the decoder 208 of FIG. 2 with a preset threshold value, so that the LLR of the coded bit is hardened only when the absolute values of the LLRs are larger than the threshold value. Convert to a decision binary bit. Here, if the LLR value of the encoded bits is larger than the threshold value, it means that the bit having the LLR value is reliable.

The comparison unit 304 compares the recoding bits from the encoder 300 with the hard decision binary bits from the hard decision unit 302. Here, the two related bits having the same value mean that the corresponding bit is reliable.

Thus, during the same frequency subcarrier, if the recoding bits for a particular transmit antenna and the corresponding binary bits determined by hard decision from the LLR of the encoding bit coincide, then the modulator 306 may select the recoding bit. Remodulate with modulation symbols (QPSK, 16QAM, 64 QAM). The modulated symbol is then provided to the channel simulator 308.

If not, if the LLR of the encoded bits is less than the hard decision or the recoded bits are different from the hard decision binary bits from the LLR of the encoded bit, the recoded bits will not be used to generate interference of the corresponding transmit antenna. . The interference cancellation for one transmit antenna will only be performed if the interference cancellation for one transmit antenna is appropriate only if all re-coded bits for the other N _T -1 transmit antennas are suitable to be used to generate interference. .

과 채널행렬

를 곱한다. 즉, 원하는 송신 안테나의 데이터를 제외한 다른 송신 안테나들로부터의 변조 심벌들에 대해 간섭 신호(

)를 생성한다.In order to perform interference cancellation, during each frequency subcarrier, the channel simulator 308 re-modulated the symbols.

And channel matrix

Lt; / RTI > That is, for the modulation symbols from other transmit antennas except for the data of the desired transmit antenna,

).

은 L-번째 주파수 부캐리어 동안에 다른 N_T-1 송신 안테나(원하는 송신 안테나 제외)와 N_R 수신 안테나 사이의 채널추정 값이다. 상기

은 L 번째 주파수 부캐리어를 제외한 송신 안테나들과 대응하는 N_T-1 재변조 심벌들이다. 상기

는 하기 <수학식 1>로 표현된다.Here,

Is the channel estimate between the other N _T -1 transmit antennas (except the desired transmit antenna) and the N _R receive antennas during the L-th frequency subcarrier. remind

Are N _T -1 remodulation symbols corresponding to transmit antennas except the L th frequency subcarrier. remind

Is expressed by Equation 1 below.

Where n is the index of the transmit antenna from which data is recovered and L is the index of the frequency subcarrier.

으로 표현되며. 상기 신호 합성부(310)로 제공된다.Thus, the estimated interference component

Represented by. The signal synthesizer 310 is provided.

)를 빼서 n번째 송신 안테나로부터 전송된 심벌을 추정한다. 상기 추정된 전송 심벌(

)은 하기 <수학식 2>로 표현된다. The signal synthesizing unit 310 generates an interference signal from the channel simulator 308 at the input signal r of the MIMO detector 206 of FIG. 2.

) To estimate the symbol transmitted from the nth transmit antenna. The estimated transmission symbol (

) Is expressed by Equation 2 below.

는 n 번째 송신 안테나로부터의 변조 심벌을 제외한 그 이외의 다른 송신 안테나들로부터의 변조 심벌들로써 n 번째 송신 안테나 입장에서 간섭신호가 된다.Here, r is an input signal of the MIMO detector 206 of FIG. 2 and includes all modulation symbols from the multiplexing antenna.

Is the modulation symbols from other transmit antennas except the modulation symbol from the nth transmit antenna, and becomes an interference signal from the nth transmit antenna.

로 표현되면, 상 기 MRC는 전송된 심벌들을 하기 <수학식 3>을 이용하여 복구한다. 상기 MRC는 상기 도 2의 최대 결합부(212)에서 수행된다.After interference cancellation from the channel simulator 308, the MIMO channel is decomposed into an N _T Single Input Multiple Output (SIMO) channel. After interference cancellation, the N _R × 1 recovered vector symbols then perform Maximum Ratio Combining (hereinafter referred to as “MRC”). If the estimate of the corresponding SIMO channel response is

If expressed as, the MRC recovers the transmitted symbols using Equation 3 below. The MRC is performed at the maximum coupling portion 212 of FIG.

는 최대비 결합으로 복구된 전송된 심벌이고, 상기

는 SIMO 채널추정 값이고, 상기

는 추정된 전송 심벌이고, 상기

는 2 놈(norm) 연산기호이다.Here,

Is the transmitted symbol recovered with the maximum ratio combining, and

Is the SIMO channel estimate value, and

Is an estimated transmission symbol, and

Is a two norm operator.

)은 이때 복조되고, 복조된 부호화 비트의 LLRs은 계산되어 복호기(206)로 통과한다. 간섭제거는 수행되지 않는 경우에, 이전 반복의 해당 비트의 소프트 정보가 복호기(206)에서 사용된다.Recovered transmit symbols (

) Is then demodulated, and the LLRs of the demodulated coded bits are calculated and passed to the decoder 206. If no interference cancellation is performed, the soft information of the corresponding bit of the previous iteration is used in the decoder 206.

Decoding and interference cancellation are repeated many times. In general, the number of repetitions is fixed or fluid. In the latter case (fluid case), when the packet error rate (PER) converges or reaches a certain magnitude, when the worst or average LLR reaches a particular magnitude, or meets a slightly different criterion, triggered by criterion for the number of iteration.

4 is a flowchart illustrating an operation of a receiver in a multi-antenna system according to an exemplary embodiment of the present invention.

Referring to FIG. 4, the receiver receives modulation symbols from a transmitter in step 400. The transmitter is N _T A single code scheme is used for all transmission antennas, and N _F of all transmission antennas A single modulation scheme is used for all four frequency subchannels.

Thereafter, the receiver outputs soft decision symbols for the modulation symbols received from the transmitter in step 402. The soft decision symbol is output based on ML detection or MMSE detection.

In step 404, the receiver outputs LLR values of the decoded bits and the encoded bits using the soft decision symbol.

Thereafter, the receiver checks whether the decoding bit or the LLR value of the encoding bit is determined in step 406, and if the decoding bit is the decoded bit, re-encodes the decoding bit in step 408. In step 412, if the LLR value is larger than the threshold value compared to the preset threshold, hard decision is performed to output a binary bit for the LLR value. If the LLR value of the coded bit is smaller than the threshold, the mode proceeds. In the corresponding mode, since the reliability of the corresponding bit is not reliable, decoding is performed using soft information of the corresponding bit of the previous repetition without performing interference cancellation.

Then, in step 414, the receiver re-modulates the bits if the re-encoding bit and the binary bit value for the LLR value are the same. If the re-encoding bit and the binary bit value for the LLR value are different, the operation proceeds to the corresponding mode.

In step 418, the receiver multiplies the remodulated symbol by a channel estimate to perform interference estimation. In this case, the remodulated symbol is a remodulated symbol for transmission bits from other transmission antennas except for the corresponding transmission antenna, and the channel estimation is estimated as a channel response between the other transmission antennas and the reception antennas.

In step 420, the receiver removes the interference estimation signal from the received signal to perform interference cancellation.

Thereafter, the receiver recovers the signal by performing the maximum ratio combining on the interference canceled signal in step 422.

Thereafter, the algorithm of the present invention terminates.

While the present invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments, but is capable of various modifications within the scope of the 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.

As described above, in a multi-antenna system that does not use channel interleaving, data is repeatedly decoded using soft information, thereby providing an advantage that reliable decoding can be performed.

Claims (24)

In the receiver for interference cancellation in a multi-antenna system, A receiver for receiving modulated symbols from a plurality of transmission antennas; A MIMO detector for outputting soft decision symbols for the modulated symbols; A decoder for generating a log likehood ratio (LLR) of decoded bits and encoded bits, respectively, for the modulated symbols from the plurality of transmission antennas using the soft decision symbols; And an interference canceller for repeatedly performing interference cancellation according to the reliability of a bit by using each of the decoded bits from the plurality of transmit antennas and the LLR value of the encoded bit. The method according to claim 1, The receiving unit An RF processor for converting a radio frequency (RF) band signal received from a plurality of receiving antennas into a baseband signal; An FFT unit for fast Fourier transforming the converted data; And a subcarrier demapper that aligns data in the frequency domain from the fast Fourier transform operation. The method according to claim 1, And the soft decision symbols are obtained from an estimate of the coded bits sent by the transmitter. The method according to claim 1, And the LLR value of the coded bit is converted to a binary bit by hard decision. The method according to claim 1, The interference canceller An encoder for re-encoding the decrypted bits, A hard decision unit for performing a hard decision and outputting a binary bit for the LLR value when the LLR value of the encoded bit is larger than a threshold value by comparing with a preset threshold value; A modulator for remodulating the bits if the recoding bit and the binary bit value for the LLR value are the same; A channel simulator for performing an interference estimation signal by multiplying the remodulated symbol by a channel estimate; And a signal synthesizing unit for performing interference cancellation by subtracting the interference estimation signal from the received signals from the plurality of transmission antennas. 6. The method of claim 5, The interference-rejected estimated transmission symbol signal is represented by Equation 4 below.

Here, r is all modulation symbol signals received from a plurality of transmit antennas,

Is a modulation symbol signal from other transmit antennas except the modulation symbol from the nth transmit antenna. 6. The method of claim 5, If the LLR value of the coded bit is less than the threshold value, there is no reliability of the corresponding bit, so that the decoding is performed using the soft information of the corresponding bit of the previous repetition without performing interference cancellation. 6. The method of claim 5, If the re-encoding bit and the binary bit value for the LLR value are different, there is no reliability of the corresponding bit, so that decoding is performed using soft information of the corresponding bit of the previous repetition without performing interference cancellation. 6. The method of claim 5, Wherein the channel estimation is estimated by a channel response between a desired transmit antenna and other transmit antennas and receive antennas of the plurality of transmit antennas. 6. The method of claim 5, And performing maximum ratio combining on the estimated transmission symbols after the interference cancellation. The method of claim 10, And a transmission symbol signal recovered by the maximum ratio combining with respect to the transmission symbol estimated after the interference cancellation is represented by Equation 5 below.

Here,

Is the transmitted symbol recovered with the maximum ratio combining, and

Is the SIMO channel estimate value, and

Is an estimated transmission symbol, and

Is a 2 norm operator. 12. The method of claim 11, And the recovered transmission symbol is decrypted. In the reception method for interference cancellation in a multi-antenna system, Receiving modulated symbols from a plurality of transmit antennas; Outputting soft decision symbols for the modulated symbols; Generating a log likehood ratio (LLR) of decoded bits and encoded bits, respectively, for the modulated symbols from the plurality of transmission antennas using the soft decision symbols; And repeatedly performing interference cancellation according to the reliability of a bit by using each of the decoded bits and the LLR value of the encoded bit from the plurality of transmission antennas. 14. The method of claim 13, Receiving modulated symbols from a plurality of transmit antennas Converting a signal of a radio frequency (RF) band received from a plurality of receiving antennas into a baseband signal, Fast Fourier transforming the converted data; Sorting data in the frequency domain from the fast Fourier transform operation. 14. The method of claim 13, And the soft decision symbols are obtained from an estimate of the coded bits sent by the transmitter. 14. The method of claim 13, And the LLR value of the encoded bit is converted to a binary bit by hard decision. 14. The method of claim 13, The process of iteratively eliminating interference according to the reliability of a bit by using each of the decoded bits from the plurality of transmission antennas and the LLR value of the encoded bit may be performed. Recoding the decoded bits; Comparing the LLR value of the encoding bit with a predetermined threshold value and outputting a binary bit for the LLR value by performing hard decision; Remodulating the bits if the recoding bit and the binary bit value for the LLR value are the same; Performing an interference estimation signal by multiplying the remodulated symbol by a channel estimate; And subtracting the interference estimation signal from the received signals from the plurality of transmission antennas to perform interference cancellation. 18. The method of claim 17, The interference canceled estimated transmission symbol signal is represented by Equation 6 below.

Here, r is all modulation symbol signals received from a plurality of transmit antennas,

Is a modulation symbol signal from other transmit antennas except the modulation symbol from the nth transmit antenna. 18. The method of claim 17, If the LLR value of the coded bit is less than a threshold value, the reliability of the bit is not reliable, and thus the decoding is performed using soft information of the corresponding bit of the previous repetition without performing interference cancellation. 18. The method of claim 17, If the re-encoding bit and the binary bit value for the LLR value are different, there is no reliability of the corresponding bit and thus decoding using the soft information of the corresponding bit of the previous repetition without performing interference cancellation. 18. The method of claim 17, Wherein the channel estimation is estimated by a channel response between a desired transmit antenna and other transmit antennas and receive antennas of the plurality of transmit antennas. 18. The method of claim 17, And performing maximum ratio combining on the estimated transmission symbols after the interference cancellation. 23. The method of claim 22, The transmission symbol signal recovered by the maximum ratio combining with respect to the transmission symbol estimated after the interference cancellation is represented by Equation (7).

Here,

Is the transmitted symbol recovered with the maximum ratio combining, and

Is the SIMO channel estimate value, and

Is an estimated transmission symbol, and

Is a 2 norm operator. 24. The method of claim 23, And wherein the recovered transmission symbol is decrypted.

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