The Application of Information Feedback to an Amplitude-Modulated Laser Communications System

The application of information feedback to amplitudemodulated (AM) laser communication systems used to transmit the value, of a continuous parameter is considered. The laser system is assumed to be quantum-noise limited. The particular information feedback technique used is here termed feedback averaging. It is found that the use of this technique improves the accuracy of the estimate of the parameter at the receiver over a corresponding one-way system. The effect of a multiplicative error (slow fading for example), background shot noise, and the fluctuation in the photon arrivals at the receiver due to the laser itself are considered. Both experimental and simulation results bear out the analysis. A Chebyshev bound for the probability of error is derived for the special case of an -ary AM system, both with and without feedback.