A new selection mechanism for hybrid FSO/mmWave systems

Hybrid Free-Space Optical (FSO)/millimeter wave (mmWave) communication systems have garnered significant attention due to their ability to deliver high data rates while maintaining reliable connectivity across diverse atmospheric conditions. However, traditional switching mechanisms, such as signal-to-noise ratio (SNR) threshold-based, rely only on the link’s instantaneous SNR, ignoring the link’s bandwidth, which degrades the overall system’s reliability and efficiency. In order to mitigate this challenge, a channel capacity-based switching scheme for a hybrid FSO/mmWave system is proposed in this paper. Unlike existing schemes, the proposed mechanism dynamically switches between FSO and mmWave links based on the estimated channel capacity of the two links, rather than relying only on instantaneous channel conditions. This ensures that the system always selects the link with the highest achievable capacity, thereby improving the system’s throughput. The analysis incorporates both intensity modulation/direct detection (IM/DD) and heterodyne detection (HD) techniques under various weather conditions, including clear, hazy, and rainy scenarios. The FSO channel is modeled using the Gamma–Gamma (GG) distribution, while the mmWave link follows the Nakagami-m fading model. Closed-form expressions for key performance metrics, including link utilization and channel capacity for FSO, RF, and the proposed hybrid scheme, are derived and validated through simulation. Additionally, a comparative analysis conducted against existing switching mechanisms demonstrates that the proposed approach significantly enhances the performance of the hybrid FSO/mmWave system.