LAUSR

Free space optical system design and performance analysis are highly related to channel statistics obtained by the channel parameter estimation. The accurate estimation of the channel parameters and scintillation index needs to consider the photoelectric detection noise at the receiving end. We propose a maximum likelihood (ML) method for estimating the parameters of a gamma-gamma fading channel affected by photoelectric detection noise. The Newton-Raphson method and expectation maximization (EM) algorithm are developed to compute the ML estimates of atmospheric turbulence fading parameters and variance of the detection noise. We also derive the Cramer-Rao bound for the unknown parameters. By way of the mean square estimation errors, our estimation technique performance is compared with existing methods of the estimation which ignore detection noise. Based on the measured channel and detection noise data under three weather conditions, it is verified that the proposed EM algorithm, considering the influence of detection noise, can significantly improve the estimation accuracy of atmospheric turbulence fading parameters.