On the Reduction of Background Radiation for Differential Signaling FSO Systems

Abstract

In this paper, we propose a weighted differential signaling scheme for a 2 ⨯ 1 free-space optical (FSO)communication system to suppress the correlated background radiations, while minimizing the bit error rate (BER)of the system. In contrast to conventional differential signaling which is based on equal gain combining (EGC)of the two wavelengths, here, the two wavelengths are combined at the receiver using non-equal channel-dependent weighting factors. By formulating the BER of the system and the background suppression criterion, the optimal weights are derived by minimizing the BER under background suppression constraints. Since the aforementioned optimization problem is non-convex, we optimize the upper bound of BER and show that the optimal scheme outperforms the conventional EGC scheme. Numerical results confirm the superiority of the proposed scheme in terms of achievable BER upper-bound compared to classical EGC method.