Coverage, Rate, and Last Hop Selection in Multi-Hop Communications in Highway Scenarios

The recent 3GPP initiative to extend IAB technology to mobile nodes in recently stated Release 18 opens up new opportunities for services operators in highway scenarios, where the extreme density of base stations (BS) is required to deliver uninterrupted coverage. The latter problem is specifically important for millimeter wave (mmWave) and future sub-terahertz (sub-THz) deployments. However, in such systems, there are inherent trade-offs between the rate provided over the multi-hop chain, the so-called "bridge ", and the inter-site distance. One of the critical factors involved in this trade-off is the choice of the last hop. In this paper, we utilize realistic channel measurements at 300 GHz to develop a framework characterizing the above-mentioned trade-off. Then, we proceed proposing a simple technique to maximize the latter by addressing the "last-hop problem " and compare its performance to the set of alternative solutions. Our numerical results illustrate that bumper location is better in terms of relaying communication distance. Furthermore, the proposed last hop selection strategies allow for extreme performance gains in terms of data rate as compared to the traditional approaches reaching 100% for large ISD and 400-500% for small ISDs. In absolute numbers, the proposed relying with the last hop selection strategy allows for reducing the required BS density along the highways by 15-30% depending on the vehicle density and required level of connectivity.