Performance of PPM on terrestrial FSO links with turbulence and pointing errors

In recent work, the error performance of on-off keying has been investigated for free-space optical (FSO) links impaired by both turbulence and pointing loss. In the current letter, the analytical framework is extended to M-ary pulse-position modulation (PPM), providing exact results for M = 2. Since the approach is not directly applicable to PPM signals with M > 2, a closed-form approximation of the average symbol error probability is derived for this case, which is shown via simulation to be tight over a wide SNR range of interest.