Hybrid PPM-BPSK subcarrier intensity modulation for free space optical communications

In this paper, a new hybrid pulse position modulation — binary phase shift keying subcarrier intensity modulation (PPM-BPSK-SIM) modulation scheme for free space optical (FSO) communications is presented. The theoretical analysis error probability of the PPM-BPSK-SIM in turbulence atmospheric channel is carried out and verified using computer simulation. The performance of PPM-BPSK-SIM is compared with PPM and BPSK-SIM in a lognormal atmospheric channel for a range of turbulence variance σ2 l = {0, 0.1, 0.3, 0.5 and 1.2}. The results show that the performance of PPM-BPSK-SIM is superior to BPSK-SIM for all turbulence levels, while its performance becomes better than 2-PPM for σ2 l > 0.3.