Efficient coding/decoding scheme for phase-shift keying optical systems with differential encoding

Phase-shift keying (PSK) has been demonstrated as an efficient modulation format for long-haul high-bit-rate optical transmission systems. Differential encoding between successive PSK symbols is required for practical implementations in both coherent and direct detection. However, this kind of encoding increases the input bit error rate of the forward error correction (FEC) and thus affects its performance. In order to reduce the penalties induced by differential encoding, the authors, in this study, propose a structured symbol interleaving of the FEC codewords and the corresponding decoding algorithm. The authors' scheme allows obtaining a decoding complexity reduction of 50% compared to the usual decoding method and a redundancy reduction about 25% without any loss of performance.