Analysis and Modeling of Phase Noise for Verification and Optimization of Soft- Decision FEC

Abstract:
Soft-Decision forward error correction (Soft-FEC) is widely considered to be applied in enhanced high-speed transponders for long-haul transmission due to the large net coding gain of according decoders. Typically, an additive white Gaussian noise (AWGN) channel is applied in simulations to test different FEC methods. With an analysis of the softdecision signal statistics we demonstrate that all elements prior to the Soft-FEC decoder contribute to the signal statistics including optical linear and nonlinear channel impairments, component imperfections and the digital signal processing algorithms. In particular for highly nonlinear channels with 10G on/off-keying neighbors strong nonlinear phase noise can be observed, which can be interpreted as colored phase noise. Furthermore, realistic implementation constrained carrier recovery may induce non-Gaussian and non-white phase noise. For reliable test and verification of subsequent Soft-FEC performance we derive an according noise model. This noise model replaces the typical AWGN channel and can be applied in simulative or real-time FPGA verification.