Project/Area Number  10650363 
Research Category 
GrantinAid for Scientific Research (C).

Section  一般 
Research Field 
情報通信工学

Research Institution  Hiroshima City University 
Principal Investigator 
KASAMI Tadao Hiroshima City University, Faculty of Information Sciences, Professor, 情報科学部, 教授 (50029378)

CoInvestigator(Kenkyūbuntansha) 
FUJIWARA Toru Osaka University, Graduate School of Engineering Science, Professor, 大学院・基礎工学研究科, 教授 (70190098)

Project Fiscal Year 
1998 – 1999

Project Status 
Completed(Fiscal Year 1999)

Budget Amount *help 
¥3,400,000 (Direct Cost : ¥3,400,000)
Fiscal Year 1999 : ¥2,600,000 (Direct Cost : ¥2,600,000)
Fiscal Year 1998 : ¥800,000 (Direct Cost : ¥800,000)

Keywords  binary linear code / suboptimum decoding / complexity of decoding / cosets / weight distribution / quantization level / 2元線形符合 / 準最適復号法 / 復号複雑度 / 剰余類 / 重み分布 / 量子化 / 2元線形符号 
Research Abstract 
1. A softdecision decoding algorithm is derived by approximating some computations in the recursive maximum likelihood decoding (RMLD) algorithm. In the RMLD algorithm, the most likely code vector is computed by constructing tables of most likely local vectors in a divideand conquer manner. In the proposed suboptimum algorithm, vectors in the tables are pruned according to a certain criteria. The relation among the criteria of pruning, error performance and the decoding complexity is analyzed. A simulation result for the third order ReedMuller code of length 64 shows that we can realize a suboptimum decoder which achieves almost the same error performance as an ML decoder and costs only onefourth decoding complexity compared to the RMLD algorithm [1,2]. 2. The original RMLD is not adaptive to signaltonoise (SN) ratios. In RMLD, every most likely local vectors are computed in bottomup way. We propose a new version of RMLD which is very adaptive to SNratios by introducing "lazy evaluation" in a topdown way. That is, most likely local vectors are computed when it is required for the first time. These computation can be efficiently carried out by using parity check matrices of certain local subcodes of the entire code [3,4]. For several ReedMuller codes and extended permuted BCH codes, simulation results show remarkable reduction of time and space complexity of decoding. 3. The weight distribution of coset leaders of cosets with respect to a local subcode provides primary information on how to prune an insignificant subtables for most likely local vectors. A new relatively efficient algorithm for computing the weight distribution of coset leaders of binary linear block codes is proposed [5]. 4. The quantization levels for received sequences and the accuracy of the metric computation have effect on the probability of decoding error and the complexity of decoding circuits. A detailed case study of RMLD decoder for a (64, 35) ReedMuller subcode has been done [6].
