Study on Turbo Decoding Using Hard Decision Decoder -Principle of Hard-in Soft-out Decoding-
Kazuhiko Yamaguchi, Shinya Maehara, Brian M. Kurkoski, Kingo Kobayashi · 2006
We propose a new construction and decoding method for concatenated codes. One of the target coding schemes is a serially-concatenated coding scheme with a turbo code as the inner code and a Reed-Solomon (or other block) code as the outer code. The proposed decoding strategies include following two points. (1) New repetitive diagram of whole serial concatenated code is investigated. (2) To reduce complexity, hard- input soft-output decoding for the outer code is ap- plied. Using a double error-correcting Reed-Solomon code as outer code, the results are evaluated and dis- cussed. We do not know the decoding results is correct or not, but we know how many errors are changed in the estimated codeword. Therefore, the conditional error rate can be calculated, given the number of the cor- rected errors. Of course, the hard decision decoder may fail to decode correctly, or may detect an uncorrectable error. In such cases, symbol and bit error rate for the received word is evaluated in similar way. These con- ditional bit error rates are used to transform the hard decisions into a soft-output value. These values may be determined either analytically or experimentally. In this method, we assume all symbols and bits in an estimated codeword have same soft value. There- fore the code length of the corresponding component decoder must determined carefully. In Chapter 2, we introduce concept of hard-input soft-output decoding. We show a method for deriving soft-output values from hard decision decoding, and discuss a suitable coding scheme for turbo decoding using hard-input soft-output decoder. In Chapter 3, a new decoding algorithm based on hard-input soft- output decoding is discussed. In Chapter 4, an example code is evaluated by computer simulation.