Abstract
We analyse the performance of cross quadrature amplitude modulation (X-QAM) scheme in subcarrier intensity modulation (SIM) based free space optical (FSO) communication system under the influence of atmospheric turbulence and generalized pointing error. The QAM signalling is the preferred modulation scheme for multimedia transmission over wireless channels due to its high bandwidth efficiency. The FSO links are vulnerable to atmospheric fading and misalignment errors. Most of the previous works model the random radial displacement component of pointing error by Rayleigh distributed random variable. However, for a non-ideally fasttracked laser beam, the radial displacement component may not obey the Rayleigh distribution, since the displacements in vertical and horizontal directions may not always follow a zeromean Gaussian distribution. In this work, we derive the closed form expression of the probability density function (PDF) for the aggregated channel with atmospheric turbulence modeled by gamma-gamma distribution and the pointing error modeled by Rician distributed radial displacement component. Further, we derive the closed form expressions of the exact average symbol error rate (ASER) for general order cross QAM.
Published Version
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