D2D Multi-hop Multi-path Communications in B5G Networks: A Survey on Models, Techniques, and Applications

In 5G networks, device-to-device (D2D) communications have played an important role in enlarging the coverage, relaxing the workload of backhaul links of both macro base stations (MBSs) and small-cell basestations (SBSs), and serving the mobile users (MUs) local applications and services at high capacity. However, beyond 5G (B5G or 6G) networks will require disruptive solutions that can assist D2D communications to meet numerous advanced applications and services requested by dense MUs. One of the most efficient solutions for D2D communications is multi-hop multi-path (MHMP). In this paper, we present a detailed survey of the so called D2D MHMP communications in terms of models, techniques, and applications for B5Gnetworks. We discuss and propose the future research directions of D2D MHMP communications. All themodels, techniques, and applications as well as future research directions of D2D MHMP communications provide the useful insights into B5G networks design and optimisation.