Soft Decision FEC for 200G Optical

ViaSat 66200 SDFEC (Soft Decision Forward Error Correction) is a family of turbo product code (TPC) designed for use in 200 Gbps communications applications. The multi rate SDFEC handles BPSK, QPSK, and 16-QAM modulation formats. With either 7% or 20% overhead, TPCs are the optimum FEC for high data rate, high coding gain applications where low latency and high net equivalent coding gain (NECG) are desired.

TPC’s have large minimum distances leading to a very low error floor, which is desired for 200 Gbps optical network applications. Further, TPCs have low complexity while achieving high performance. The 66200 series of cores are based on a soft decision TPC code that ViaSat has used extensively for a variety of applications; hence the architecture is well tested in both simulations and hardware.

The NECG of 20% overhead TPC code is 11.3 dB for coherent QPSK modulation in an AWGN channel at 1x10-15 BER. The 7% overhead TPC code has an NECG of 10.2 dB. Asymptotic analysis reveals that the error floor is more than five orders of magnitude below the 1x10-15 BER performance target.