KR20150094365A - Modified Block Turbo Decoding Apparatus Using Channel State Information and Algorithm thereof - Google Patents

Abstract

The present invention relates to a block turbo decoding algorithm whereby error correction performance can be significantly enhanced by using channel state information during a process of repeatedly decoding a block turbo code. According to an embodiment of the present invention, a modified block turbo decoding apparatus using channel state information includes: a channel measurement unit which measures CSI of a wireless channel; a reception unit which receives transmitted data; and a block turbo decoder which receives the transmitted data from the reception unit and decodes the input data. The transmitted data includes distortion generated by frequency-selective fading of the wireless channel. The block turbo decoder repeatedly performs decoding in the predetermined number of times. Error correction performance of the block turbo decoder can be increased by removing at least a portion of the distortion as the measured CSI is applied to the data input in the block turbo decoder.

Description

Field of the Invention [0001] The present invention relates to a modified block turbo decoding apparatus and a method thereof,

The present invention relates to a modified block turbo decoding algorithm using channel conditions, and more particularly, to a block turbo decoding algorithm capable of significantly improving error correction performance by using channel state information in an iterative decoding process of a block turbo code .

The Orthogonal Frequency Division Multiplexing (OFDM) scheme, which is widely regarded as a technology for high-speed multimedia communication, is a frequency selective fading ), A method of dividing a data stream to be transmitted into a plurality of parallel bit streams having a lower bit rate, and then transmitting the data stream on a corresponding sub-carrier.

This is because the transmission period of the signal is longer than the maximum delay spread in terms of the time domain and the frequency domain characteristic of the radio channel is frequency non-selective fading, Interference is not generated in the performance analysis of the block turbo encoded OFDM system using the information.

Due to the characteristics of the OFDM scheme, a standard modulation scheme has been adopted in digital broadcasting (DAB, DVB), WLAN (IEEE 802.11a, HIPERLAN), WMAN (IEEE 802.16)

However, since there is still interference between adjacent subcarriers, channel coding and decoding processes of the transmitting and receiving end must be performed in order to reduce errors caused by such interference.

Various methods have been studied as channel encoding and decoding techniques for error correction codes for transmitting and receiving signals. Various methods have been studied and can be easily configured using two linear block codes with excellent error correction capability Block turbo codes are applied to various systems.

According to the conventional technique, in the block turbo decoding process, a weak point of the received codeword is found. If the signal is compensated by the equalizer, the weak point is not selected as a weak point but decreased by AWGN. The selected signal is selected as a weak point.

As a result, since a weak point is not selected as a result of actually distorting the signal due to the channel, the additional information on the signal also becomes unreliable, thereby degrading the error correction capability.

According to such conventional techniques, it is difficult to precisely detect the uncertainty of the radio channel, thereby reducing the reliability and narrowing the utilization. In order to improve the reliability, increasing the number of iterations of the block turbo decoding increases the complexity of the system. There is a problem that the weight can be increased.

Korean Patent No. 10-1314222

R. Pyndish, A. Glavieux, A. Picart and S. Jacq, "Near optimal decoding of product codes", in Proc. IEEE Globecom Conference

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a block turbo decoding algorithm capable of greatly improving error correction performance by using channel state information in an iterative decoding process of a block turbo code It has its purpose.

Also, since the number of iterative decoding of a block turbo code can be reduced by applying the CSI of a radio channel, it is possible to reduce complexity due to iterative decoding, reduce the time required for decoding, and to provide the user with a block turbo decoding algorithm capable of obtaining a soft output value.

It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are not intended to limit the invention to the precise form disclosed. It can be understood.

An apparatus for decoding a block turbo code in a wireless communication system in which data is transmitted through a wireless channel, the apparatus comprising: a modified block turbo decoder that uses channel states associated with an example of the present invention for realizing the above- The decoding apparatus includes a channel measurement unit for measuring CSI (Channel State Information) of the radio channel, a receiving unit for receiving the transmitted data, and a receiving unit for receiving the transmitted data from the receiving unit and performing the decoding on the input data Wherein the transmitted data includes a distortion caused by frequency selective fading of the radio channel, and the block turbo decoder repeatedly repeats a predetermined number of times, Decodes the data to be input to the block turbo decoder, By applying a CSI by removing at least a portion of the distortion can improve the error correcting performance of the turbo decoder block.

을 따라 이루어질 수 있다. 여기서,

는 상기 블록터보 복호기의 soft-input이고,

은 상기 블록터보 복호기에 입력된 데이터

를 원소로 갖는 벡터이며,

는 코드워드 집합

중 상기

를 구성하는 각각의 코드워드

와의 유클리드 거리인

가 가장 짧은 코드워드이고,

는 상기 코드워드 집합

에서

를 만족하는 코드워드 중 유클리드 거리인

가가 가장 짧은 코드워드를 나타낸다.Further, the application of the measured CSI can be expressed by the following equation

Lt; / RTI > here,

Is the soft-input of the block turbo decoder,

Is input to the block turbo decoder

As an element,

Is a set of codewords

Among them,

Each of the code words

Euclid Street with

Is the shortest codeword,

Lt; RTI ID = 0.0 >

in

Euclidean distance < RTI ID = 0.0 >

A represents the shortest codeword.

The receiver may further include an equalizer for removing at least a part of the distortion included in the transmitted data using the measured CSI and a demodulator for receiving the data from the equalizer and demodulating the demodulated signal in a predetermined manner, And a demodulator for inputting the data to the block turbo decoder.

In addition, the number of times the block turbo decoder repeats the decoding in response to the reflection of the CSI can be reduced.

Also, the wireless communication system uses an OFDM (Orthogonal Frequency Division Multiplexing) scheme, and uses a first subcarrier including the data, a second subcarrier for compensating for phase noise, and a third subcarrier for preventing interference between channels And symbols according to the OFDM can be transmitted.

In addition, the block turbo decoder may select a weak point based on a chase algorithm and remove a part of the distortion using the selected weak point.

A method for decoding a block turbo code in a wireless communication system in which data is transmitted through a wireless channel, includes the steps of: The method of block turbo decoding includes the steps of generating distortion by frequency selective fading of the radio channel in the transmitted data, measuring CSI (Channel State Information) of the radio channel, The method comprising the steps of: removing at least a portion of the distortion contained in the transmitted data using the measured CSI; demodulating the demodulator by receiving data from the equalizer and pre-demodulating the demodulated data; A step of inputting the data to the block turbo decoder; Wherein the error correction performance of the block turbo decoder is improved by removing the part of the distortion by applying the measured CSI to the data input to the block turbo decoder .

The present invention can provide a user with a block turbo decoding algorithm capable of greatly improving error correction performance by using channel state information in the iterative decoding of a block turbo code.

Further, since the number of iterative decoding of a block turbo code can be reduced by applying CSI of a radio channel, it is possible to reduce complexity due to iterative decoding, reduce time required for decoding, it is possible to provide a user with a block turbo decoding algorithm capable of obtaining a soft output value.

It should be understood, however, that the effects obtained by the present invention are not limited to the above-mentioned effects, and other effects not mentioned may be clearly understood by those skilled in the art to which the present invention belongs It will be possible.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate a preferred embodiment of the invention and, together with the description, serve to provide a further understanding of the technical idea of the invention, It should not be construed as limited.
FIG. 1 schematically shows a coding process of a block turbo code related to the present invention.
FIG. 2 schematically shows a decoding process of a block turbo code related to the present invention.
3 shows a transmitter structure of an OFDM system to which a block turbo code related to an example of the present invention can be applied.
4 shows a receiver structure of an OFDM system to which a block turbo code related to an example of the present invention can be applied.
5A to 5C show BER performance curves obtained by iterative decoding of a block turbo code of the present invention and BER performance curves by a general decoding system.

Hereinafter, a preferred embodiment of the present invention will be described with reference to the drawings. In addition, the embodiment described below does not unduly limit the contents of the present invention described in the claims, and the entire configuration described in this embodiment is not necessarily essential as the solution means of the present invention.

< Block of turbo code  Encoding and Decoding>

The turbo code is a coding method which shows excellent performance reaching the limit of Shannon, and the block turbo code, which is a type of turbo code, is one of powerful error correction codes proposed by Pyndiah. This block turbo code is a coding method for improving the error correction capability by increasing the minimum hamming distance using a linear block code, and coding is performed using two linear block codes.

이 파라미터

을 가지고,

가 파라미터

를 가진다고 한하면, 도 1에 나타난 것과 같이 블록터보코드

는 다음의 과정을 통하여 얻을 수 있다.FIG. 1 schematically shows a coding process of a block turbo code related to the present invention. Systematic linear block code

This parameter

To have,

A parameter

1, a block turbo code

Can be obtained through the following procedure.

크기의 행과

크기의 열로 데이터 비트를 배열하고,

크기의 행을

의 코드로 부호화하며,

크기의 열을

의 코드로 부호화한다.

A row of size

Arrange the data bits into columns of size,

A row of size

Lt; / RTI &gt; code,

Size column

As shown in FIG.

는 코드워드의 길이를 나타내고,

는 정보비트의 길이를 나타내며,

는 최소 해밍거리를 나타낸다.here,

Represents the length of the codeword,

Represents the length of the information bits,

Represents the minimum Hamming distance.

크기의 데이터 비트열은 도 1과 같은 형태의 블록터보코드가 된다. 새롭게 생성된 블록터보코드

는

,

,

의 파라미터를 각각 가지게 되고,

가 각 코드

의 부호율이라고 할 때, 블록터보코드의 부호율은

가 된다. Through the above process

The data bit string of the size becomes a block turbo code of the form as shown in FIG. The newly generated block turbo code

The

,

,

Respectively,

Each code

, The coding rate of the block turbo code is

.

Thus, a block turbo code combines a simple linear block code with a small Hamming distance to produce a robust code with a large hamming distance.

의 마지막

열은

의 코드워드이고, 마지막

열은

의 코드워드가 되며, 행렬

의 모든 행은

의 코드워드이고 모든 열은

의 코드워드이다. As can be seen in Figure 1, the resulting block turbo code

The end of

Heat

And the last

Heat

, And the matrix &lt; RTI ID = 0.0 &gt;

All rows in

And all columns are

Lt; / RTI &gt;

행렬을 생성하며, 보다 강력한 블록터보코드가 된다. Also, an extended block turbo code can be used to increase the hamming distance of the generated block turbo code. This inserts an even parity bit at the next end of the generated row and column

Matrix, resulting in a more powerful block turbo code.

의 첫 행의 첫 열부터 순차적으로 이루어진다.The transmission of the generated block turbo code generates the generated matrix

In order from the first column of the first row.

에 대한 soft-input 복호기의 출력

을 복호 반복 횟수만큼 신뢰도를 높이는 방법으로서, 출력

는 하기의 수학식 1과 같이 표현된다.A typical decoding algorithm for block turbo codes is an iterative decoding algorithm based on soft decoding / soft decision. In this soft decoding / soft decision method, a hard decision received signal

Output of the soft-input decoder to

As a method for increasing the reliability by the number of repetition times of decoding,

Is expressed by the following equation (1).

은 수신된 값이고, 체이스(chase) 알고리즘에 의하여 구하여진 코드워드 집합

가

개의 코드워드를 가지고 있다고 할 때

는 각각의 코드워드

와 수신된 신호와의 유클리드 거리

가 가장 짧은 코드워드이며,

는 코드워드 집합

에서

를 만족하는 코드워드 중 유클리드 거리

가가 가장 짧은 코드워드를 나타낸다. 여기서, 체이스 알고리즘에 대한 구체적인 내용은 "A class of algorithms for decoding block codes with channel measurement information"에 자세하게 개시되어 있다.here,

Is a received value, and is a codeword set obtained by a chase algorithm

end

Assume that you have two codewords

Each code word

And the Euclidean distance of the received signal

Is the shortest codeword,

Is a set of codewords

in

Euclidean distance &lt; RTI ID = 0.0 &gt;

A represents the shortest codeword. The details of the chase algorithm are described in detail in "A class of algorithms for decoding block codes with channel measurement information &quot;.

가 존재하지 않는다면 하기의 수학식 2를 이용하여 출력을 구할 수 있다.if,

The output can be obtained by using the following equation (2).

는

와 같은 값을 갖는다.Generally,

The

Lt; / RTI &gt;

에 대응하는 수신된 코드워드

과 체이스 알고리즘을 이용하여 첫 번째 복호화기는 행렬

의 행(혹은 열)의 soft output을 구하고, 복호화기에 입력된 soft input에서 soft output을 빼면 행(혹은 열)의 부가정보(extrinsic information)

를 얻을 수 있다. 여기서, 괄호 안의 숫자는 N번째 복호화를 말한다. 두 번째 복호화를 위한 행렬

의 열(혹은 행)의 soft input 값은 하기의 수학식 3과 같이 주어진다.FIG. 2 schematically shows a decoding process of a block turbo code related to the present invention. As shown in FIG. 2, an iterative decoding algorithm for a block turbo code is based on a transmitted codeword?

Lt; RTI ID = 0.0 &gt;

And Chase algorithm, the first decoder uses a matrix

(Or columns) of the row (or column) and subtracting the soft output from the soft input input to the decoder, extrinsic information of the row (or column)

Can be obtained. Here, the numbers in parentheses refer to the Nth decoding. The matrix for the second decoding

The soft input value of the column (or row) of the input data is given by Equation 3 below.

는

와 같은 값을 갖는 가중치이다. 이와 같은 방법으로 수신된 행렬

의 행과 열을 반복 복호하면 높은 신뢰성을 가지는 soft output 값을 구할 수 있다.
here,

The

Lt; / RTI &gt; In this way,

It is possible to obtain a soft output value with high reliability.

&Lt; &lt; Block turbo code >

The transmitter of the OFDM system to which the block turbo code is applied is shown in FIG. 3 shows a transmitter structure of an OFDM system to which a block turbo code related to an example of the present invention can be applied.

The information bit stream is coded using block turbo codes using two linear block codes and then divided into a group of bits carried in one subcarrier and subjected to modulation processes such as BPSK, QPSK, 16QAM, and 64QAM according to a modulation scheme, respectively do. In order to prevent interference between four subcarriers and channels to compensate for frequency offset and phase noise, twelve virtual carriers including a DC value are added to the 48 modulated signal sequences to perform a 64-point IFFT operation. A guard interval for preventing inter-symbol interference is inserted to form one OFDM transmission symbol.

4 shows a receiver structure of an OFDM system to which a block turbo code related to an example of the present invention can be applied.

Generally, the received signal is subjected to OFDM symbol demodulation through an FFT operation. After the OFDM symbol demodulation, the guard interval is removed to prevent intersymbol interference, and in order to compensate for the distorted signal due to multipath fading, Equalization is performed on the received signal using the channel state information (CSI).

The equalized signal sequence applies the CSI value to the signal sequence after the demodulation process, and the demodulated signal sequence to which the CSI value is applied is restored to the original data bitstream through the decoding process of the block turbo code.

Signals received through the wireless channel are severely distorted by frequency selective fading. The distorted signal is compensated for the distorted signal through the equalizer.

의 weak point(I)를 찾게 되는데, 만일 왜곡된 부분이 등화기에 의해 신호의 보상이 이루어졌다면 weak point(I)로 선택되지 않고 AWGN에 의해 감소된 신호가 weak point(I)로 선택되게 된다. 이렇게 되면 결과적으로 실제로 채널에 의해 신호가 왜곡된 부분에서 weak point(I)로 선택되지 않았기 때문에 그만큼 그 신호에 대한 부가정보도 신뢰도가 떨어지게 되어 에러정정 능력이 저하되게 된다. The chase algorithm for decoding the block turbo code is based on the received codeword

If the distorted part is compensated by the equalizer, the weak point (I) is not selected as the weak point (I) and the signal reduced by the AWGN is selected as the weak point (I). As a result, since the weak point (I) is not selected as a result of actually distorting the signal due to the channel, the additional information on the signal becomes less reliable and the error correction capability is lowered.

To solve these problems, we propose a new algorithm using channel state information (CSI). If the CSI value is applied after demodulating the signal, the soft-input value can be expressed by Equation (4) below.

The soft-input value input to the block turbo decoder in the case of applying the channel state information in order to appropriately select the weak point distorted by the channel is expressed by Equation (4) and the soft-input The value is the same as in Equation (1).

Equation 1, which is an existing soft-input value, can not determine a correct weak point distorted by a channel in the turbo block decoder because the soft-input value for each bit is determined after equalization is performed on the received signal. Assuming that no equalizer is used, this is also a problem because soft-input values can not be determined properly. By using the equalizer, the decoder can more appropriately determine the distorted weak point by the channel. By adding the influence of the channel to the soft-input value determined by the existing method, Therefore, it is possible to obtain the additional information of high size by the iterative decoding algorithm, so that the reliable soft-output value is obtained.

Therefore, when the CSI value is applied, additional information and soft-output values with high reliability can be obtained even if the number of iterative decoding times is reduced, and the error correction capability can be greatly increased.

<Performance Analysis>

5A to 5C show BER performance curves obtained by iterative decoding of a block turbo code of the present invention and BER performance curves by a general decoding system.

Each performance curve represents the performance in an ideal channel environment. In a multipath fading channel environment, the channel impulse response characteristics are represented by hn = [6.3548169e-001, 2.6436658e-001, 9.9426628e-002,7.0541056e-004, 1.6816199e- 005, 2.8749857e-006, 0], and assumes that frequency and time synchronization are perfectly achieved at the receiving end. And weak point (I) by Chase algorithm is applied to four, and one transmission packet consists of 1000 [byte]. Block turbo codes were generated using (168, 78) × (168, 78) as the configuration codes, and 64QAM-OFDM, 16QAM-OFDM, and QPSK-OFDM modulation schemes were used as modulation methods.

5A shows a performance curve of a block coded 64QAM-OFDM modulation scheme. Referring to FIG. 5A, in the case of iterative decoding (CSI in FIG. 5A) applying the CSI value proposed in the present invention, the number of times of repetition It is shown that the BER value improves from 10 ^-3 to 9 [dB]. In addition, it can be seen that the performance is improved by about 5 [dB] when the iterative decoding is performed by applying the CSI value to the case of the conventional iterative decoding.

FIG. 5B shows a performance curve of a block coded 16QAM-OFDM modulation scheme. Referring to FIG. 5B, in the case of the iterative decoding using the CSI value proposed in the present invention, the BER value is improved by about 10 ^-3 to 7 [dB] at the same repetition times as in the conventional decoding method Can be seen. Also, it can be seen that the performance is improved by about 4.5 [dB] when the iterative decoding is performed by applying the CSI value to the conventional iterative decoding.

FIG. 5C shows a performance curve of a block coded QPSK-OFDM modulation scheme. Referring to FIG. 5C, in the case of the iterative decoding using the CSI value proposed in the present invention, the BER value is improved from 10 ^-3 to 5 [dB] at a repetition frequency of 1 time . Also, it can be seen that the performance is improved by about 3 [dB] when the iterative decoding is performed by applying the CSI value to the case of the conventional iterative decoding.

According to the modified block turbo decoding algorithm using the channel state according to the present invention, the BER performance is improved from 5.0 [dB] to 9.0 [dB] according to the modulation method of the signal when the same number of times is repeated see. Also, it can be seen that the performance of the system which applied the CSI value and iteratively decoded once is 5 [dB] ~ 3 [dB] better than the case of 4 times iterative decoding of the existing decoding system not applying the CSI value.

The present invention can also be embodied as computer-readable codes on a computer-readable recording medium. A computer-readable recording medium includes all kinds of recording apparatuses in which data that can be read by a computer system is stored. Examples of the computer-readable recording medium include a ROM, a RAM, a CD-ROM, a magnetic tape, a floppy disk, an optical data storage device, and the like, and may be implemented in the form of a carrier wave (for example, transmission via the Internet) . The computer readable recording medium may also be distributed over a networked computer system so that computer readable code can be stored and executed in a distributed manner. In addition, functional programs, codes, and code segments for implementing the present invention can be easily inferred by programmers of the technical field to which the present invention belongs.

It should be understood that the above-described apparatus and method are not limited to the configuration and method of the embodiments described above, but the embodiments may be modified so that all or some of the embodiments are selectively combined .

Claims (7)

An apparatus for decoding data using a block turbo code in a wireless communication system in which data is transmitted through a wireless channel,
A channel measurement unit for measuring CSI (Channel State Information) of the wireless channel;
A receiving unit for receiving the transmitted data; And
And a block turbo decoder for receiving the transmitted data from the receiver and performing the decoding on the input data,
Wherein the transmitted data comprises a distortion caused by frequency selective fading of the wireless channel,
Wherein the block turbo decoder repeatedly performs the decoding by a predetermined number of times and applies the measured CSI to the data input to the block turbo decoder to remove at least a part of the distortion to thereby improve the error correction performance of the block turbo decoder Wherein the channel state is improved by using the channel state. The method according to claim 1,
Wherein the measured CSI is applied according to the following equation: &lt; EMI ID = 1.0 &gt;
Equation

here,

Is the soft-input of the block turbo decoder,

Is input to the block turbo decoder

As an element,

Is a set of codewords

Among them,

Each of the code words

Euclid Street with

Is the shortest codeword,

Lt; RTI ID = 0.0 &gt;

in

Euclidean distance &lt; RTI ID = 0.0 &gt;

A represents the shortest codeword. The method according to claim 1,
The receiver may further comprise:
An equalizer for removing at least a portion of the distortion included in the transmitted data using the measured CSI; And
And a demodulator for receiving the data from the equalizer, demodulating the demodulated data in a predetermined manner, and inputting the demodulated data to the block turbo decoder. The method according to claim 1,
And the number of times the block turbo decoder repeats the decoding in response to the reflection of the CSI is reduced. The method according to claim 1,
The wireless communication system uses an OFDM (Orthogonal Frequency Division Multiplexing) scheme and uses a first subcarrier including the data, a second subcarrier to compensate for phase noise, and a third subcarrier to prevent interference between channels, And a symbol according to OFDM is transmitted. The method according to claim 1,
Wherein the block turbo decoder selects a weak point based on a chase algorithm and removes a part of the distortion using the selected weak point. Device. A method for decoding a data block using a block turbo code in a wireless communication system in which data is transmitted through a wireless channel,
Generating distortion in the transmitted data by frequency selective fading of the wireless channel;
Measuring CSI (Channel State Information) of the wireless channel;
The equalizer removing at least a portion of the distortion included in the transmitted data using the measured CSI;
Receiving a data from the equalizer and demodulating the data in a predetermined manner;
The demodulator inputting the demodulated data to a block turbo decoder; And
Wherein the block turbo decoder repeatedly performs the decoding by a predetermined number of times with respect to the input data,
Wherein the error correction performance of the block turbo decoder is improved by removing the distortion by applying the measured CSI to data input to the block turbo decoder.

Images