Physical Layer Design for Free Space Optical Communication

Abstract

A small size Free Space Optical Communication System is introduced, including the hardware and the hardware specified physical layer protocol. In detail, the rapid synchronization method to reduce the handshake bandwidth requirement is demonstrated. The hardware of the system includes the laser driver system, the signal amplifying and shaping system, the data interface system. The hardware specified physical layer protocol is used to interface the outer data, serialize and deserialize the data stream, check transmission errors and schedule the data transmission. The overall system is a FIFO-like system and the user can use it as if he's operating a FIFO. The system is designed mainly for terrestrial FSO link whose signal channel is the atmosphere. Due to the complex composition and activity of the atmosphere, this signal channel brings in great influence on the transmitting laser in it, for example, the absorption and scattering of the atmosphere molecules and aerosols, the scintillation of received laser power caused by the turbulence of the atmosphere, all of which results in a much higher Bit Error Rate (BER) of the communication system than wired communication systems leading to frequent resynchronization. In our system, the sampling clock is generated locally using multi-phase sampling technique rather than PLLbased clock recovery, which helps to rapid synchronization.