STPM Based Performance Analysis of Finite-Sized Differential Serial FSO Network

This paper analyzes the performance of serial decode-and-forward (DF) relay assisted free-space-optical (FSO) network with pointing errors and finite-sized receivers employing differential M-ary phase shift keying (DMPSK) data. The atmospheric fading optical links are modeled by unified Gamma-Gamma (ΓΓ) distribution subject to both heterodyne and intensity modulation/direct detection (IM/DD) techniques. In particular, we derive the average symbol error rate (SER) by utilizing symbol transition probability matrix (STPM) whose entries are the average symbol transition probabilities (ASTPs) of a relay. The ASTPs of single link STPM are then utilized to calculate the SER of serial DF relaying network. Further, the unified outage probability of considered network is obtained. The results indicate that the point receiver performance is more affected with pointing error as compared to the finite-sized receiver. Further, it is showcased through results that when the number of serial relays increases, the improvement in error performance is more in case of heterodyne as compared to that of IM/DD.