Transmission performance of 4D 128SP-QAM with forward error correction coding

The performance of the 4-D 128SP-QAM format is experimentally investigated in a Nyquist-wavelength division multiplexing system for two different forward error correction (FEC) scenarios. Two soft-decisions FEC schemes are experimentally evaluated for 128SP-QAM, namely, a turbo product code (TPC) and a low-density parity-check (LDPC) code. The results show that after full convergence the LDPC code outperforms the TPC with respect to coding gain at a bit error ratio of 10(-8). However, it requires more decoding iterations to achieve convergence toward an optimum performance state.