Effective Capacity Performance of Coherent POLMUX OWC with Power Adaptation

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 for two different power adaptation techniques, namely, independent power adaptation and joint power adaptation. In a polarization multiplexing system, independent power adaptation allocates transmit power to a particular channel considering only the signal-to-noise ratio statistics of that particular channel whereas the joint power adaptation allocates transmit power to a particular channel considering the joint signal-to-noise ratio statistics of both channels. Our analysis reveals the superiority of the joint power adaptation technique in order to support the stringent statistical delay constraint services over the strong turbulence fading channels compared to an independent power adaptation technique. However, the numerical results demonstrate that the performance gap between the joint and independent power adaptations gets significantly reduced as the statistical delay constraints become loose and/or the turbulence fading gets weaker.