Performance analysis of BPPM and M-ary PPM in free-space optical communication systems under gamma-gamma distribution using APD and PIN

Free-space optical (FSO) communication offers highly directional, high bandwidth communication channels, which is why it is often used in digital communication systems. However, atmospheric turbulence has a voluminous degradation in the performance of FSO communication system. Therefore, different modulation techniques are introduced to improve the performance of the FSO communication systems. In this paper, the modulation schemes considered for the proposed FSO system, are binary pulse position modulation (BPPM) and M-ary pulse position modulation (M-ary PPM). The channel fading is characterized using gamma-gamma distribution. APD and PIN photodiode are used as photodetectors. Performance of the FSO systems has been compared in terms of their bit error rates (BERs). The results obtained in the paper show the suitability of BPPM over M-ary PPM for both photodetectors and also indicate the suitability of APD over PIN photodiode for the considered modulation techniques.