Hachiro Fujita

Forward error correction based on block turbo code with 3-bit soft decision for 10-Gb/s optical communication systems

The first experimental demonstration of a forward error correction (FEC) for 10-Gb/s optical communication systems based on a block turbo code (BTC) is reported. Key algorithms, e.g., extrinsic information, log-likelihood ratio, and soft decision reliability, are optimized to improve the correction capability. The optimum thresholds for a 3-bit soft decider are investigated analytically. A theoretical prediction is verified by experiment using a novel 3-bit soft decision large scale integrated circuit (LSI) and a BTC encoder/decoder evaluation circuit incorporating a 10-Gb/s return-to-zero on-off keying optical transceiver. A net coding gain of 10.1 dB was achieved with only 24.6% redundancy for an input bit error rate of 1.98/spl times/10/sup -2/. This is only 0.9 dB away from the Shannon limit for a code rate of 0.8 for a binary symmetric channel. Superior tolerance to error bursts given by the adoption of 64-depth interleaving is demonstrated. The ability of the proposed FEC system to achieve a receiver sensitivity of seven photons per information bit when combined with return-to-zero differential phase-shift keying modulation is demonstrated.

Next generation FEC for optical transmission systems

Technical challenges of forward error correction (FEC) are reviewed. Block turbo code having a net coding gain of higher than 10 dB will mature with the development of 3-bit soft decision LSI.

Third generation FEC employing turbo product code for long-haul DWDM transmission systems

In this paper, we describe the design concept of the third generation forward error correction (FEC) employing turbo product code (TPC) based on BCH product code using soft input soft output iterative decoding. The proposed TPC is composed of two constituent BCH codes, BCH(128,113,6) and BCH(256,239,6), so that the TPC has minimum distance 36 and code rate 0.82 (21.3% of redundancy). Simulation results demonstrate a coding gain of 10.1 dB, which can be applied to the next generation submarine cable systems.