Hybrid FSO/Sub-THz-Based Vertical Networks for Internet of Vehicles

Vertical networks, including low Earth orbit (LEO) satellites and high-altitude platforms (HAP), are promising network paradigms to support diverse vehicular services in Internet of Vehicles (IoV). In addition, free-space optical (FSO) and subterahertz (sub-THz) communications are expected to play a vital role in 6G wireless networks due to the vast available bandwidth. This article addresses the performance of vertical networks, where the hybrid FSO/sub-THz link is deployed for the last-mile access of IoV. Specifically, both soft-switching and hard-switching schemes of hybrid FSO/sub-THz links are considered. The hybrid FSO/sub-THz channel is characterized by Doppler effect, atmospheric attenuation, fading, pointing misalignment, and weather conditions. A comprehensive analytical framework based on the cross-layer approach is then developed. This allows for assessing not only the physical-layer performance but also the upper-layer performance of transmission control protocol (TCP) under the impact of transmission errors at the last-mile access of hybrid FSO/sub-THz link. Numerical results quantitatively confirm the effectiveness of our proposal and illustrate the performance of hybrid FSO/sub-THz-based vertical networks in terms of outage probability, average transmission rate, average bit error rate, TCP throughput, and joint throughput-energy over various channel conditions. Monte Carlo simulations are also performed to validate the accuracy of theoretical derivations.