Power Allocation and CAR Optimization of Dual-Hop Multiuser RF and Hybrid FSO/RF With Co-Channel Interference

This paper explores cumulative distribution function (CDF)-based user scheduling scheme for a dual-hop multi-user RF and hybrid FSO/RF decode and forward (DF) relaying system under independent and non-identically distributed (i.n.i.d) co-channel interference (CCI), ensuring precise temporal fairness among users. The RF links are modeled using Nakagami-<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</i> fading, whereas the FSO link is characterized by a Fisher-Snedecor <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F</i> distribution with boresight pointing errors. At the destination, selection combining is employed, and a closed-form expression for the outage probability (OP) is derived. To further analyze the system behavior, an asymptotic OP is evaluated, providing insights into the diversity order. To improve the system performance, expressions for power allocation and channel access ratio (CAR) optimization are obtained using the asymptotic expression. The analytical expressions are validated through Monte-Carlo simulations. The findings indicate that boresight pointing errors have only a marginal impact on the performance of the dual-hop RF–hybrid FSO/RF system. Moreover, both optimized power allocation and CAR yield substantial performance improvements compared to equal resource allocation strategies. Specifically, power allocation optimization provides SNR gains of around 2 dB for Nakagami-<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</i> and Rayleigh fading, while CAR optimization achieves SNR improvements which is nearly double for Nakagami-<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</i> fading in comparison to Rayleigh fading.