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A method for the evaluation of performance of free space optical communications systems utilising modulating retro reflectors under weak turbulence is presented. The model considers the effects of system physical parameters, such as the modulating retro reflector effective size and receiver aperture diameter, on the bit-error rate (BER) and the capacity. Different spatial spectrums are used with the model and the effect of aperture averaging is evaluated directly from the normalised spatial covariance in each case. The log-normal distribution is adopted for the evaluation of BER in the weak fluctuation regime. Finally, for the first time the capacity of a system using modulated retro reflectors is calculated using a recently proposed closed-form expression. The model can be used as a performance metric in network routing algorithms.

Abstract-In this paper, the authors derive the moment generating function (MGF) of the decision variable for a practical optical differential quadrature phase shift keying (DQPSK) receiver affected by phase noise and the amplifier spontaneous emission noise. The effect of the different optical filters, Gaussian, Fabry-Pérot (FP), and optical integrator, on the phase noise is examined. Using the saddle point approximation, the authors obtain numerically the bit error rate (BER) for the above system, as a function of the optical-signal-to-noise ratio (OSNR) and the source linewidth. The model is found to agree with previous published simulation results and the Monte Carlo simulations presented in this paper. The authors also calculate the BER floors for DQPSK inflicted by the phase noise and compare its performance with differential phase shift keying (DPSK). Finally, the authors examine the effect of interferometric demodulation on the relative intensity noise (RIN) spectra and the impact on the DQPSK system performance. In particular, the authors examine the influence of system dispersion on the receiver sensitivity.Index Terms-Differential phase shift keying (DPSK), moments method, optical communication.

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