Effective Capacity of Coherent POLMUX OWC Impaired by Atmospheric Turbulence and Pointing Errors

Effective capacity is defined as the maximum constant traffic arrival rate that a communication channel can support in order to guarantee a certain statistical delay constraint. We investigate the effective capacity performance of the optical wireless communications employing the coherent detection and polarization multiplexing over the Gamma–Gamma turbulence fading channels with pointing errors. We consider two different power adaptation techniques, namely, independent power adaptation and joint power adaptation. Closed-form effective capacity expressions are developed for both power adaptation schemes. Asymptotic analyses provide the increments of the effective capacities in the high signal-to-noise ratio regimes, in both nonstringent and stringent statistical delay constraints, for every 1 dB increase of the average transmit optical power. Our analysis reveals the superiority of the joint power-adaptation technique in order to support the stringent statistical delay constraint services over the optical wireless communication channels impaired by the strong turbulence fading and/or large pointing errors. However, the numerical results demonstrate that the performance gap between the joint and independent power adaptations becomes significantly reduced as the statistical delay constraints become loose and/or the channel impairments (i.e., turbulence fading and/or pointing error) become weak.