Research On Recognition Algorithms Of Channel Codes Under Error Conditions

Channel codes are used to correct errors caused by noise or interference in a communication system.In a cognitive communication system,the encoder is unknown,needs to be recognised.First,the algorithms are divided into two kinds of methods——“correcting errors” and “finding words”,while this paper conducts a research on them.The “correcting errors” method seems to be better,but with NP-Hard complexity,while the “finding words” method is low complexity,so we choose the “finding words” method.Then,a algorithm on punctured convolutional code is proposed based on the algorithm on 1/2 code.When the generator matrix is solved,the mother code and puncturing pattern can be got.So the generator matrix can be obtained from any canonical matrix by matrix transformation or solving linear equations system.The algorithm solves the problem that there are only “searching methods”.BCH codes are among the most used error correcting codes.The existing recognition methods most come from the generic methods of linear block codes,which can't be applied when the code length is long or the BER is high.An algorithm is proposed based on the sub-space of hamming codes,which make the amout of computation is reduced and the algorithm can tolerant much more errors.At last,for Turbo codes,the research focuses on the interleaver.Three algorithms are porposed for terminated Turbo code,unterminated Turbo code and 1/2 punctured Turbo code respectively.The existing algorithms are only suited for terminated Turbo code with few errors.For terminated Turbo code,using the characteristic of the parity-check vector,each position of the interleaver can be separated,solved independently.Thus,the algorithm solves the problem when the BER is high and the code length is long.For unterminated Turbo code,it's found that for some rational functions,their series are periodic.So a recognition algorithm comes: two interleaver positions are recovered first;other positions would be recovered step by step.The algorithm is sliced into several lists,and the number is just the period.For 1/2 punctured Turbo code,by making use of the parity-check vector of the 2/3 convolutional code,the algorithm here can always recover two former positions step by step.At last,only several positions can't be recovered.By some improvement,the algorithm can be applied for the codes with errors.Through the above research,we have achieved the recognition of the three main channel codes.