Capacity and BER analysis of BCH and LDPC coded FSO communication system for different channel conditions

Abstract

Free space optical (FSO) communication is of paramount importance for the design of next-generation 5G+ wireless networks. These are, however, susceptible to degrading effects of atmospheric turbulence. The use of error correcting codes (ECCs) can mitigate the effects of fading caused by atmospheric turbulence. We evaluate the performance of uncoded and coded FSO communication system, where we use Bose Chaudhuri Hocquenghem (BCH) and low-density parity-check codes for the coded system. Both the systems under consideration are based on intensity-modulation and direct detection. We investigate the performance of a coded communication system under various channel conditions, viz., slow fading and fast fading gamma-gamma channels for different turbulence regimes and subsequently, obtain the coding gain. We derive the expressions of channel capacity for a fast fading channel and outage capacity for a slow fading channel. We conclude that ECCs deteriorate the bit error rate performance in a slow fading channel. However, for this kind of channel, the combination of ECCs with an interleaver reduces the burst errors and improves the performance which leads to positive coding gain. In a fast fading channel, coding gain is not much and it remains almost same in different turbulence conditions. The analytical results are supported by simulation study.