Parameter estimation of MIMO FSO systems using saddlepoint approximation

In this paper, the challenges of parameter estimation for multiple-input multiple-out (MIMO) free-space optical (FSO) communication systems employing equal gain combining diversity techniques over the Gamma-Gamma turbulence channels with pointing errors are addressed. According to the goodness-of-fit statistical tests results previously reported by Kolmogorov-Smirnov, the approximate probability density function obtained by a saddlepoint approximation (SAP) method provide a highly efficient approximation of the actual channel models over a wide range of channel conditions. To reveal the importance of the SAP approximation method, we propose a maximum likelihood estimation algorithm to estimate its parameters. The accuracy of the proposed estimator is investigated by using the mean square error (MSE) and normalized mean square error (NMSE); they exhibit satisfactory performance in both noiseless and noisy environments. The bit error rate (BER) performance for MIMO FSO systems with an SAP estimator is also discussed.