Free-space communications over exponentiated Weibull turbulence channels with nonzero boresight pointing errors.

In this paper, we present analytical expressions for the performance of urban free-space optical (FSO) communication systems under the combined influence of atmospheric turbulence- and misalignment-induced fading (pointing errors). The atmospheric turbulence channel is modeled by the exponentiated Weibull (EW) distribution that can accurately describe the probability density function (PDF) of the irradiance fluctuations associated with a transmitted Gaussian-beam wave and a finite-sized receiving aperture. The nonzero boresight pointing error PDF model, which is recently proposed for considering the effects of both boresight and jitter, is adopted in analysis. We derive a novel expression for the composite PDF in terms of a convergent double series involving a Meijer's G-function. Based on the statistical results mentioned above, exact expressions for the average bit error rate of on-off keying modulation scheme and the outage probability are developed. To provide more insight, we also perform an asymptotic error rate analysis at high average signal-to-noise ratio. Our analytical results indicate that the diversity gain for the zero boresight case is determined only by the ratio between the equivalent beamwidth at the receiver and the jitter standard deviation, while for the nonzero boresight case, the diversity gain is related to the ratio of the equivalent beamwidth to the jitter variance as well as the parameter of the EW distribution.