Study On Three Generation FECs In Fiber Communication System And Application Of NB-LDPC Codes On WDM-PON

With the development of Internet and information technology, optical fiber communication systems need to meet information demands of large capacity and high data rate through technology of high order phase modulation and channel multiplex, which leads to bad bit-error-rate performance. Forward Error Correction (FEC) codes are being used to improve system’s reliability and divided into three generations in optical fiber communication systems. The first generation’s FEC is mainly hard-decision code, like RS code; the second generation’s FEC is concatenated code, like interleaved concatenated code; the third generation’s FEC is soft-decision code, like Low Density Parity Check (LDPC) code, while performance of Nonbinary LDPC (NB-LDPC) code is better than that of binary LDPC code.Three generations’ FECs are simulated in this paper. Using encoding principle of cyclic code and decoding algorithm based on Berlekamp’s iteration, we investigate RS code, like RS(255,239).Performance of interleaved concatenated code is analyzed and found to be better than that of separate code. Through structured construction of parity check matrix, fast encoding algorithm and sum-product decoding algorithm, LDPC code is simulated and verified its performance. With structured construction of parity check matrix of NB-QC-LDPC code, encoding in nonbinary domain and decoding by combination of sum-product algorithm and FFT fast algorithm, NB-LDPC code is simulated and verified its performance which is obtained by extension binary domain to nonbinary domain.For wavelength-division-multiplexing passive optical network (WDM-PON) in access network, the needs of the users are not only confined to the point-to-point data transmission but also to new services like broadcast and multicast. With investigation of different kinds of new service overlaid WDM-PON, we find that new service overlaid WDM-PON modulated by amplitude keying/differential phase shift keying (ASK/DPSK) has the advantages of low system complexity and controllable cost. A novel NB-LDPC coding scheme of WDM-PON system with ASK/DPSK modulation is proposed in this paper, and is verified through system simulation with better performance.