Design of LDPC Encoder and Decoder for 40 Gb/s Optical Communication Systems

This paper presents a design approach for low-density parity-check (LDPC) encoder and decoder for applications in optical communication systems at 40 Gb/s. In order to get the best performance, the system is further optimized for the powers of the EDFA (Erbium Doped Fiber Amplifier) amplifiers used with the SMF (Single Mode Fiber) and DCF (Dispersion Compensating Fiber) fibers to achieve the highest Q factor. The designed LDPC coded system (using LDPC codes of r=0.8 for coding and sum-product algorithm (SPA) for decoding) is compared with the uncoded system at bit rate of 40 Gb/s and seen to provide significant performance improvement in terms of the BER. LDPC codes also provide near-capacity performance and significant system enhancement with respect to the state-of-the-art FEC (Forward Error Correction) schemes. High coding gains and their inherent low complexity of both the encoder and decoder have made them an attractive and viable choice for high-speed optical communication.