Interleavers and BCH Codes for Coherent DQPSK Systems With Laser Phase Noise

Abstract

Abstract-The relatively high phase noise of coherent optical systems poses unique challenges for forward error correction (FEC). In this letter, we propose a novel semi-analytical method for selecting combinations of interleaver lengths and binary Bose-Chaudhuri-Hocquenghem (BCH) codes that meet a target post-FEC bit error rate (BER). Our method requires only short pre-FEC simulations, based on which we design interleavers and codes analytically. It is applicable to pre-FEC BER around 10 −3 , and any post-FEC BER. Additionally, we show that there is a trade-off between code overhead and interleaver delay. Finally, for a target of 10 −5 , numerical simulations show that interleavercode combinations selected using our method have post-FEC BER around 2× target. The target BER is achieved with 0.1 dB extra signal-to-noise ratio.

Low-complexity BCH codes with optimized interleavers for DQPSK systems with laser phase noise

“…1, which is similar to that in [13] but with a different interleaver/deinterleaver. The DQPSK signal is Gray coded.…”

“…3. Unlike [13], where random interleaver permutations in combination with specific error realizations may result in a worse distribution of errors after deinterleaving than before, our deterministic mapping always improves the distribution of errors for coding purposes. We identify suitable codes for this system in three steps.…”

“…However, due to the correlation, the selected codes have high overhead, which reduces system throughput. In [13], we use interleaving to decorrelate errors, thereby reducing code overhead. The analysis in [13] is for theoretical uniform interleavers, so the results there are general.…”

“…In [13], we use interleaving to decorrelate errors, thereby reducing code overhead. The analysis in [13] is for theoretical uniform interleavers, so the results there are general. However, those interleavers are too complex for practical implementation.…”

“…As in [13], interleaving enables us to use codes with lower overheads. However, compared to [13], the interleavers and codes in this paper have much simpler implementations. First, we propose an optimized interleaver and method for selecting binary BCH codes for use with this interleaver.…”