Optimisation of subcarrier intensity modulation binary phase‐shift keying free space optical link with avalanche photodiode receiver influenced by gamma–gamma atmospheric turbulence and pointing errors

Abstract

This study presents the average bit error rate (BER) performance analysis of free space optical (FSO) systems employing subcarrier intensity modulation with binary phase-shift keying and avalanche photodiode (APD) receiver. Intensity fluctuations of received optical signal are assumed to originate from both the gamma–gamma atmospheric turbulence and pointing errors. Besides theoretical derivation of the average BER expression, numerical integration is performed assuming specified relative calculation errors. Numerical results are presented and validated by Monte Carlo simulations. Furthermore, closed-form expressions are derived for thermal noise and shot noise limited conditions, which represent special cases of the system under investigation. On the basis of the presented results, effects of the FSO link and receiver parameters on BER performance are investigated and discussed. It is shown that optimal values of laser beam waist and average APD gain exist for minimising the average BER. The optimal values of laser beam waist depend strongly on the normalised jitter standard deviation, while the optimal values of APD gain are mostly dependent on receiver noise temperature, bit rate and atmospheric conditions.