Free‐space optical link with dual‐branch transmit laser selection diversity over double generalised gamma turbulence channel

Very recently, double generalised gamma (GG) distribution has been proposed for describing irradiance fluctuation in free‐space optical (FSO) communication systems. As a generic model, double GG contains commonly used turbulence models such as gamma–gamma distribution as its special cases. In this study, first we derive an exact closed‐form expression in terms of Meijer's G ‐function for the average bit error rate (BER) of FSO communication system with differential phase shift keying modulation over double GG turbulence channel. This study shows that in the special case, the derived BER expression coincides with the existing BER results presented in the literature for gamma–gamma turbulence channel. Then, to improve the BER performance of the system, dual‐branch transmit laser selection diversity scheme is used and derive exact closed‐form expression for the BER in terms of bivariate Fox's H ‐function. Numerical and simulation results are demonstrated to confirm the accuracy and applicability of the derived analytical expressions.