Performance of BICM-Based QAM-SIM OWC Over Gamma-Gamma Turbulence Channels

We derive a series expression for the pair-wise error probability (PEP) of bit interleaved coded modulation (BICM)-based subcarrier intensity modulation (SIM) optical wireless communication (OWC) system employing
$M^{2}$
-ary quadrature amplitude modulation (
$M^{2} $
-QAM) over the Gamma-Gamma turbulence channels. Using this expression, we develop an upper bound (UB) to predict the bit-error rate performance of such system. Simulation results are presented to verify the analytical results. We also develop an asymptotic UB which reveals that the diversity order depends on the smaller channel parameter and the free distance of the convolutional code.