Performance of Optically-Preamplified, Direct-Detection, M-ary PPM for Inter-Satellite Links

In this paper, we evaluate the end-to-end performance of optically-preamplified, direct-detection, 16-ary and 64-ary Pulse Position Modulation (PPM) receivers with optical Fabry-Perot and electrical filters for the use in inter-satellite links. Monte-Carlo simulations are used to evaluate the bit error ratio (BER) versus the optical signal-to-noise ratio per bit without the need to assume that the noise at the decision sample is Gaussian. Extensive simulations are carried out to optimize the bandwidths of the optical and electrical filters at the receiver for three different pulse shapes while considering the combined effects of the extinction ratio (ER) of the optical transmitter, the dual-polarized amplifier noise, intra-symbol, and inter-symbol interference (ISI). The performance penalties due to timing jitter and frequency drift at the receiver are also evaluated. The results indicate that for ER > 25 dB, 64-ary PPM systems outperform 16-ary PPM systems by up to 1.2 dB, however, under realistic system imperfections of ER > 20 dB, timing jitter, and frequency drift, the performance of both systems becomes comparable.