Single laser free-space duplex communication system with adaptive threshold technique and BER analysis in weak turbulent atmosphere.

A free space duplex communication system with a single laser and a modulated retro-reflector is presented. A method to minimize the echo wave bit error rate (BER) of this system is proposed by setting the optimum threshold automatically based on the measured mean power and irradiance variances with log-normal distribution and the Bayes minimum classification error criterion. Experiments were taken at a distance of 1.55 km in a weak turbulence and the measured BER was 0.0213. The BER performance of this system is studied and the result shows the experimental BER is in good accordance with the theoretical value.