Asynchronous Transmission for Cooperative Free-Space Optical Communication System

Cooperative Free Space Optical (FSO) communication aims to combat atmospheric attenuation and turbulence by transmitting and receiving multiple copies of signal along different paths, and thus it relies on transmission redundancy. In this letter, we propose an asynchronous transmission scheme for cooperative FSO system. Different from the traditional cooperative FSO system with synchronous transmission, the source node in the proposed system can send different data to destination node. In order to recover the data of different links, a squared signal combination method is proposed and implemented at the receiver of destination. Therefore, compared to synchronous transmission, the asynchronous transmission not only brings diversity gain for cooperative FSO system, but also improves the channel utilization and thus the effective data rate. It is demonstrated that the Bit Error Rate (BER) of the asynchronous transmission is lower than that of the direct transmission and the synchronous transmission with equal data rate.