Differential Two-Pulses Position Modulation for Synchronized Wireless Optical Communications

In Wireless Optical Systems (WOS), Multi-pulse Pulse Position Modulation and Differential Pulse Position Modulation are two famous modulation schemes compatible with free space optical communication system. In this paper we present a modified form of the existing DPPM based on MPPM coding, called Differential Two-Pulses Position Modulation (D2PPM). In this new form, every symbol ends with a pulse, thus it doesn't require any synchronization, and moreover it shows an improvement in terms of spectral efficiency and data rate. We present the expressions of spectral efficiency, power requirements, and the data rate improvement normalized to PPM, and we present also comparison results to MPPM modulation scheme.