Analysis of LDPC Codes in FSO Communication System Under Fast Fading Channel Conditions

The free-space optical (FSO) communication represents a promising futuristic technology due to several benefits, which has attracted significant attention recently for various applications. FSO communication is susceptible to fading due to atmospheric turbulence. FSO channel, being a slow fading channel, inherently does not allow the efficient use of error-correcting codes (ECCs). ECCs have shown to have good performance in a fast fading channel. A way to convert the slow fading channel into a fast fading channel is by using techniques like diversity. Diversity makes the bits pass through many channels simultaneously, and thus the fast fading channel effect is observed at the receiver. In this paper, we first derive the capacity and bit error rate performance of the low-density parity-check (LDPC) codes in a fast fading channel. We then study the performance of LDPC codes in receiver diversity systems. Finally, we see the impact of using LDPC coded multiple-input multiple-output (MIMO) systems in the FSO channel. We use regular (3,6) LDPC code and irregular LDPC codes of rate 0.5, where the desired degree distribution is optimized for the channel condition.