Feedforward-based free-space optical communication

We propose to use 1-bit feedforward information at the free-space optical (FSO) receiver to improve its error performance. We concentrate upon M-ary pulse amplitude modulation (PAM) signaling and design an error-optimal PAM constellation for providing efficient 1-bit feedforward information to the receiver. A maximum likelihood detector is derived, and the symbol error rate of the considered FSO system is analytically obtained in closed form by using a union-bound approach. It is shown by using the analysis and simulation that 1-bit feedforward can significantly improve the performance of PAM in FSO systems.