Linear Time Encoding of Low-Density Parity Check Codes and its Performance in Weak Atmospheric Turbulent Channels

A major drawback of low-density parity -check (LDPC) Codes is their apparently high encoding complexity and consequent encoding delay. A linear time encoding method proposed by Richardson and Urbanke can effectively reduce the encoding complexity to only linear encoding complexity. In this paper, LDPC codes based on the linear time encoding method is adopted for improving the bit-error rate (BER) performance of an on-off keying (OOK) modulated optical signal through a weak atmosphere turbulence channel. The optical atmosphere channel is modeled as a stationary ergodic channel with lognormal intensity fading. We simulate and analyze the BER performance of the channel using the linear time encoding method. Simulation results show that the presented encoding method can be greatly reduce the BER Moreover, as the code length increases or code rate decreases, the coding gain of LDPC codes over the uncoded system becomes large. Therefore, the presented encoding method with both large code length and low code rate obtain high encode gain for the optical atmosphere turbulence channel.