Differential pulse-position modulation for power-efficient optical communication

In this paper, we examine the use of differential pulse-position modulation (DPPM) for optical communication systems using intensity modulation with d irect detection in the presence of additive white Gaussian noise, We presen t expressions for the error probability and power spectral density of DPPM. We show that for a given bandwidth, DPPM requires significantly less avera ge power than pulse-position modulation (PPM). We also examine the performa nce of DPPM in the presence of multipath intersymbol interference (ISI), We find that the ISI penalties incurred by PPM and DPPM exhibit very similar dependencies upon the channel rms delay spread. We discuss the use of chip- rate and multichip-rate equalization to combat ISI, Finally, we describe po tential problems caused by the nonuniform bit-rate characteristic of DPPM, and we propose several solutions.