Many algorithms for soft and near-soft decision decoding of block codes start by implementing hard decision decoding. In several instances it has been noted that simple tests of the hard decision result may allow the algorithm to terminate at this point. This paper explores this notion in detail.
The problem of decoding binary linear block codes has received much attention; the two extremes are optimal, high-complexity soft-decision (or maximum-likelihood) decoding and lower performance, much lower complexity hard-decision (or algebraic) decoding. This article considers a class of decoders which first implements hard-decision decoding; second, tests to see if that is enough, that its result matches the result of soft-decision decoding; and third, continues to search if a match is not found. The advantage of such a testing procedure is that if the hard-decision decoding result is found to be enough (called a success for the test), then the computational effort expended by the decoder is low. The performance, as measured by the probability of a success, of a variety of simple tests of the hard-decision codeword are analyzed.
In many modern communication systems, the full benefits of error-correction coding are only realised if the decoder is able to utilise soft decision decoding. In this chapter, we give both approximate and exact bounds on the performance of soft decision decoding compared to hard decision decoding. The effects of soft decision quantisation are explored as a function of the number of quantisation levels. Examples are given of the different performance achieved using soft and quantised soft decision decoding for (100,50) and (200,100) binary codes. A modified version of the near maximum likelihood decoder, the Dorsch decoder described in Chap. 15 , is presented for hard decision decoding. The performance improvements achieved by the decoder, compared to bounded distance decoding, are evaluated for some BCH codes. These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.
In this paper,the ChaseⅡ algorithm,which is well known as a reliability-based decoding algorithm,is used for the soft decoding of the(23,12,7)Golay code.This soft-decision decoding algorithm improves greatly the error-correcting capacity compared with algebraic hard-decision decoding algorithms,but also results in more computational complexity.To overcome this,a optimality condition is introduced to quickly terminate the ChaseⅡ decoding process.Computer simulation results got by VC6.0 show that soft decoding obtains 1.7 dB coding gain compared with hard decoding case at BER of 10-5,and the modified chase-II algorithm based on the optimality condition reduces the total simulation time by 87.64%,and thus improves greatly the decoding efficiency.