Soft Decoding in Optical Systems

Abstract—We consider the application of concatenated codes with interleaver and iterative decoding to optical communication systems. We show how to obtain the optimum log-likelihood ratio to be provided to the soft decoder in the optical channel environment, and compare the performance of a decoder using it with the one employing a Gaussian approximation of the optical channel. Sim-ulation results refer to practical turbo-product codes, and encom-pass the effect of quantization on the log-likelihood ratio. The re-sults show that the Gaussian assumption in computing the log-like-lihood ratio for the optical channel leads to significant losses. Index Terms—Modeling, optical communication, product codes, soft-decision decoding. I