Constrained coding techniques for soft iterative decoders

Soft iterative decoding of turbo codes and low-density parity check codes has been shown to offer significant improvements in performance. To apply soft iterative decoding to digital recorders, where binary modulation constraints are often used, modifications must be made to allow reliability information to be accessible by the decoder. A solution is proposed which uses a modified concatenation scheme, in which the positions of the modulation and error-correcting codes are reversed. In addition, a soft decoder based on the BCJR algorithm is introduced for the modulation constraint, and improved performance is obtained by iterating with this soft constraint decoder