Average BER Analysis of Differential Modulation in DF Cooperative Communication System over Gamma-Gamma Fading FSO Links

In this letter, we study differential modulation for decode-and-forward (DF) based free space optical (FSO) cooperative communication system over Gamma-Gamma fading channels. We derive exact bit error rate (BER) of the differential DF FSO system in terms of power series. The diversity order and coding gain of the differentially modulated DF FSO system are analytically obtained. It is demonstrated by analysis and simulation that the differential DF FSO system is able to achieve significant performance gain over a non-cooperative direct transmission based differential FSO system.