Earticle

본 논문에서는 가우시안 이진 대칭 채널에서 쇄상부호를 사용할 때의 최적 내·외 부호율에 관하여 연구한다. 쇄상부호의 전체 부호 율이 고정되어 있을 때, 내 부호율이 감소할수록 내 부호의 오류 검출 능력은 향상되지만, 반대로 외 부호의 오류 정정 능력은 감소하 게 된다. 이러한 trade-off 관계를 이용하여 본 논문에서는 쇄상부호의 최대 성능 이득을 얻기 위한 내 부호와 외 부호에의 최적의 중복(redundancy) 분포에 관하여 연구한다. 분석한 결과, 가우시안 이진 대칭 채널에서는 외 부호화율을 최소화하고 내 부호화율을 최대화함으로써 전체 쇄상부호 시스템의 성능을 극대화 시킬 수 있음을 알 수 있었다.

In this paper, we address a problem of finding the optimum inner and outer code rates for a concatenated code in Gaussian binary symmetric channels. Clearly, as the inner code rate decreases, the error detection capability of the inner code increases. However, decreasing the inner code rate implies a decrease in error-correction capability of the outer code when overall code rate is fixed. With this notion in mind, we examine the optimum distribution of redundancy on the outer and inner codes to achieve a maximum performance gain in the concatenated coding scheme. Our analysis shows that the maximum coding gain can be obtained when the inner code rate is maximized and the outer code rate is minimized under the constraint of total code rate is fixed.

본 논문에서는 내 부호의 복호화 방식에 따른 쇄상부호 시스템의 성능 변화를 분석한다. 내 부호의 복화화 방식으로는 오류 검출 방식과 오류 검출 및 정정 방식의 두 가지를 고려한다. 주파수 도약 대역확산 다중접속 통신시스템에 쇄상부호가 적용되었을 때 두 복호화 방식에 따른 성능을 비교하는데, 외 부호의 블록 길이가 유한한 경우와 무한한 경우에 그 성능을 분석하고 비교한다. 분석 된 결과를 바탕으로 무한의 블록 길이의 경우에는 두 방식의 성능이 다중 접속자 수에 따라서 trade-off가 있음을 알 수 있고, 유한한 블록 길이의 경우에는 오류 검출 및 정정 방식의 성능이 더 우수함을 관찰하였다.

In this paper, we analyze the performance of a concatenated code with two different inner decoding schemes. One is the error-detecting inner decoding, and the other is the error-detecting-and-correcting inner decoding scheme. We compare the performances of the two decoding schemes for finite and infinite block length cases when the concatenated code is applied to slow frequency-hopping spread-spectrum multiple access (FH-SSMA) communication systems.

Hierarchical modulation has been considered for achieving higher data rates in Terrestrial-DMB(T-DMB) systems. And for achieving a higher data rates transmission, the low-priority (LP) data, which is used to carry additional data, such as video data, audio data and textual data, should be perfectly decoded in a certain value of $E_b/N_o$. Unfortunately, the man-made noise badly affects the high-priority (HP) symbol, which is used to carry the conventional data in the existed T-DMB system; and since the advanced T-DMB system is proposed to fit for the legacy T-DMB receivers, the low-priority symbols in the hierarchical modulation are much worse affected by the neighbors, who are both in the same quadrant. Because of the feature that mentioned previously, the turbo code has been considered to deal with the LP data. And due to the degradation which caused by the shortened symbol distance, the error performance of LP data is not sufficient by only using the turbo code. In this paper, we propose a Reed-Solomon code used outside of turbo code, and with the turbo code, it becomes a concatenated code. In this paper, there are some simulation results, within the comparison of those performances, we can see how a Reed-Solomon code is utilized for degradation of error performance which is caused by the hierarchical constellation, and how to design a Reed-Solomon code which is suitable for improving the degradation of error performance.

Hierarchical modulation has been considered for achieving higher data rates in Terrestrial-DMB(T-DMB) systems. And for achieving a higher data rates transmission, the low-priority (LP) data, which is used to carry additional data, such as video data, audio data and textual data, should be perfectly decoded in a certain value of $E_b/N_o$. Unfortunately, the man-made noise badly affects the high-priority (HP) symbol, which is used to carry the conventional data in the existed T-DMB system; and since the advanced T-DMB system is proposed to fit for the legacy T-DMB receivers, the low-priority symbols in the hierarchical modulation are much worse affected by the neighbors, who are both in the same quadrant. Because of the feature that mentioned previously, the turbo code has been considered to deal with the LP data. And due to the degradation which caused by the shortened symbol distance, the error performance of LP data is not sufficient by only using the turbo code. In this paper, we propose a Reed-Solomon code used outside of turbo code, and with the turbo code, it becomes a concatenated code. In this paper, there are some simulation results, within the comparison of those performances, we can see how a Reed-Solomon code is utilized for degradation of error performance which is caused by the hierarchical constellation, and how to design a Reed-Solomon code which is suitable for improving the degradation of error performance.

The use of serial concatenated codes is an effective technique for alleviating the error floor phenomenon of low-density parity-check (LDPC) codes. An enhanced sum-product algorithm (SPA) for LDPC codes, which is suitable for serial concatenated codes, is proposed in this paper. The proposed algorithm minimizes the number of errors by using the failed check nodes (FCNs) in LDPC decoding. Hence, the error-correcting capability of the serial concatenated code can be improved. The number of FCNs is simply obtained by the syndrome test, which is performed during the SPA. Hence, the decoding procedure of the proposed algorithm is similar to that of the conventional algorithm. The error performance of the proposed algorithm is analyzed and compared with that of the conventional algorithm. As a result, a gain of 1.4 dB can be obtained by the proposed algorithm at a bit error rate of $10^{-8}$. In addition, the error performance of the proposed algorithm with just 30 iterations is shown to be superior to that of the conventional algorithm with 100 iterations.

The effect of block interleaving in a low density parity check (LDPC)-turbo concatenated code is investigated in this letter. Soft decoding can be used in an LDPC code unlike the conventional Reed-Solomon (RS) code. Thus, an LDPC-turbo concatenated code can show better performance than the conventional RS-turbo concatenated code. Furthermore, the performance of an LDPC-turbo code can be improved by using a block interleaver between the LDPC and turbo code. The average number of iterations in LDPC decoding can also be reduced by a block interleaver.

In this paper, a concatenated RS and Turbo code is proposed for OFDM system over burst error channel. The concatenated code used in this study is a RS(255,2D2) code and a rate 1/2 turbo code. The turbo code uses 2 recursive systematic convolutional (RSC) code as the constituent codes and the parity bit are punctured to get the desired code rate. It is shown by simulation that the conventional OFDM system fails when there exists burst noise. The concatenated RS and turbo code obtains at least 5dB gain over the turbo code at the bit error probability of $10^{-3}$.

An optical fiber code-division multiple-access (CDMA) network is proposed in which encoding is based on the use of concatenated sequences of relatively large weight. The first short component sequence in the concatenated sequence permits realistic electronic encoding of each data bit. The chips of this sequence are then all-optically encoded at substantially higher rate. In spite of the relatively large weight of the sequence the all-optical encoder is practical by virtue of the shortness of the component sequences. The use of Gold and Lempel sequences as component sequences for generating the concatenated sequences is studied and the bit-error rate (BER) performance of the proposed system is presented as a function of the received optical power with the number of simultaneous users as parameter.

본 논문에서는 무선 데이터 전송에서 데이터 전송의 신뢰성을 얻기 위해 STBC와 컨볼루션 코드를 연계하며 높은 시스템 이득을 취하기 위해 수정된 비터비 알고리즘을 사용한 시스템을 제안한다. 제안한 시스템은 STBC의 다이버시티 이득과 컨볼루션 코드의 부호화 이득을 동시에 얻을 수 있다. 수정된 비터비 알고리즘은 기존의 비터비 알고리즘과 달리 브랜치 매트릭스를 구하기 위해 해밍디스턴스를 사용하지 않고 수신 심볼과 레퍼런스 심볼 사이의 유클리디안 디스턴스를 사용한다. 제안한 시스템을 분석하기 위해 STBC의 송수신 안테나의 개수와 컨볼루션 코드의 구속장을 변경하며 시뮬레이션하였다.

In this paper, the proposed scheme is STBC system combined with convolutional code to ensure the reliability of data transmission for a high rate wireless communication. In addition, this scheme uses a modified viterbi algorithm in order to get a high system gain when data is transmitted. Because we combine STBC and comvolutional code, the proposed scheme can get a diversity gain of STBC and coding gain of convolutional code at the same time. Unlike existing viterbi docoding algorithm using Hamming distance in order to calculate branch matrix, the modified viterbi algorithm uses Euclidean distance value between received symbol and reference symbol. To analyze the system proposed, it was simulated by changing the constraint length of the convolutional code and the number of transmit and receive antennas of STBC.

In this paper, a serially concatenated space-time code (SCSTC) with bandwidth efficiency and high data rate is studied. The suggested SCSTC is composed of space-time code, the convolutional code and Interleaver. The SCSTC has a very high BER performance than the conventional space-time code. The BER performance of the suggested SCSTC can be proven by using computer simulation through the iterative decoding method. The first decoder uses Symbol-MAP algorithm and the second decoder uses Bit-MAP algorithm for decoding tile information bits. The simulation results show the performance of the suggested SCSTC is better than the conventional Space-Time Code.