Dual-pulse pulse position modulation (DPPM) for deep-space optical communications: Performance and practicality analysis

Due to its simplicity and robustness against wave-front distortion, pulse position modulation (PPM) with photon counting detector has been seriously considered for long-haul optical wireless systems. This paper evaluates the dual-pulse case and compares it with the conventional single-pulse case. Analytical expressions for symbol error rate and bit error rate are first derived and numerically evaluated, for the strong, negative-exponential turbulent atmosphere. The capacity of the turbulent FSO channel modeled as a Z-channel is evaluated, and throughput, bandwidth efficiency and energy efficiency of Dual-pulse and single-pulse PPM are subsequently assessed. It is shown that, under a set of practical constraints including pulse width and pulse repetition frequency (PRF), dual-pulse PPM enables a better channel utilization and hence a higher throughput than its single-pulse counterpart. This result is new and different from the previous idealistic studies that showed multi-pulse PPM provided no essential information-theoretic gains over single-pulse PPM.