The average bit error rate(BER) performance of a free-space optical(FOS) system based on the multi-hop parallel decode-and-forward cooperative communication method with an M-ary phase shift keying subcarrier intensity modulation is studied systematically. With the max–min criterion as the best path selection scheme,the probability density function and the cumulative distribution function of the gamma–gamma distribution random variable signal-to-noise ratio are derived. The analytical BER expression is then obtained in terms of the Gauss–Laguerre quadrature rule. Monte Carlo simulation is also provided to confirm the validity of the presented average BER model.
