Research On Adaptive Coding In Remote High-speed Optical Fiber Communication System

In the long haul ultra-high speed optical fiber communication systems, performance is degraded significantly due to several transmission impairments including fiber loss, chromatic dispersion and interchannel nonlinearities. Forward error correction code is one of the key technologies to deal with those impairments. Conventional FEC codes used in optical is with fixed rate. Channel knowledge is not exploited. System throughout capacity is limited by the worst case channel states. The best rate of network is not guaranteed. Fountain codes are rateless FEC codes with high robustness, code rate can be adjusted flexible. In this paper, Fountain code is proposed to be applied to optical fiber communication system.Traditionally, the forward error correction (FEC) code cannot adjust the code rate automatically according to the channel condition in the optical fiber communication system. This paper designs a rate-adaptive fiber communication model system based on the Luby Transform (LT) code. As LT code is the first available rate-less codes, the system can adjust code rate flexibly according to the channel state. In addition，for the accuracy problem of model commonly used in optical fiber channel, we designed a fiber communication model system of asymmetric2noise distribution, because the amplified spontaneous emission (ASE) noise in optical fiber communication systems has non-gaussian statistics. On this basis, for the decoding problem of degree1chasm and generator matrix short loop, a new coding of robust exponential distribution with avoiding4-loop was proposed.The LT codes based on robust exponential distribution with avoiding4-loop are simulated in optical fiber channels. For contrasting established model, this paper set three kinds of channel model, which contain the Chi-square channel, the asymmetric Gaussian channel and the AWGN channel. Simulation results show that, the LT codes based on new method can get better decoding performance in optical fiber channel. The LT code in2channel model outperforms other channel coding and decoding.Lastly, a scheme that Fountain code is combined with OFDM or equalization is designed to compensate the dispersion and nonlinearity. Through this research, optical fiber system can adjust transmission rate flexible according to channel states. The system not only has high code gain but also have flexible cost. The results show that, LT code in the permissible error range can effectively increase the transmission distance of optical fibers with the same SNR or the transmitting power.