Performance evaluation of decode-and-forward mixed RF-(FSO/RF) link with maximum ratio combining

We present the performance analysis and simulation of a dual-hop decode-and-forward RF-Hybrid (FSO/RF) communication link. The source-to-relay link is a Single Input Multiple Output (SIMO) RF link modeled using the Nakagami-m distribution. The relay-to-destination link consists of a hybrid parallel FSO/RF configuration. Both the source-to-relay and relay-to-destination RF links are SIMO links utilizing a maximum ratio combining (MRC) technique. The FSO link, on the contrary, is modeled using the Málaga distribution, which fits all kinds of atmospheric turbulence conditions. Misalignment errors and detection techniques, including intensity modulation with direct detection (IM/DD) and heterodyne detection, are also incorporated into the analysis. Moreover, at the destination, the RF and FSO links are combined using MRC techniques. The closed-form expressions for outage probability, bit error rate, and ergodic channel capacity are derived and validated using the Monte-Carlo simulation. The results reveal that the performance improvements achieved through diversity techniques are significantly influenced by atmospheric turbulence, pointing errors, and RF link fading. To address these challenges, optimization is performed to determine the optimal number of receiver antennas required at the relay and destination nodes to meet a target outage probability for a given signal-to-noise ratio and link parameters.