BER Analysis of BCH Codes in Slow Fading Channel with L-PPM and DPPM Scheme

In this research paper, we have analyzed free space optical (FSO) link performance for intensity modulated/direct detection (IMDD) system utilizing L-ary pulse position modulation (L-PPM) and differential pulse position modulation (DPPM) schemes. Generally, FSO link performance is impaired by atmospheric turbulence. Error correcting codes (ECCs) is one of the mitigation techniques to reduce the impact of atmospheric turbulence. For this work, we have employed Bose-Chaudhuri-Hocquenghem (BCH) code under a slow fading channel condition with and without an interleaver. We have made the performance comparison in terms of bit error rate under different turbulence regimes viz., low, moderate and high regime for L-PPM (L=4,8 and 32) and differential PPM (DPPM) schemes. We conclude that BCH code with an interleaver for 32-PPM scheme provides a maximum coding gain of 25 dB in a high turbulence regime whereas BCH code without an interleaver degrades the BER performance in a slow fading channel. Also, with the DPPM scheme, neither coding nor interleaving can improve its performance. Therefore, the DPPM scheme will not be useful from this perspective.