Design of Large-scale UAV-assisted Multi-tier Heterogeneous Networks and Performance Research

In view of the hotspot scenarios in B5G/6G, in order to meet the needs of its ultra-large network capacity, a multi-Unmanned Aerial Vehicle (UAV) assisted millimeter wave heterogeneous network model is constructed. In this network model, the distribution of Ground Base Station (G-BS) is modeled as Poisson point process, the distribution of UAV is modeled as Poisson cluster process, and the projection of the UAV on ground and the Ground User Equipment (GUE) are distributed around the G-BS. For the sake of exploring the contribution of inter-cluster association and the impact of inter-cluster interference, the 2-tier network model is extended to 4-tier network model composed of inter-cluster and intra-cluster Base Station (BS). And the 4-tier association scheme in which the GUE is associated with intra-cluster BS and inter-cluster BS at the same time is proposed. Initially, the path loss of each tier's association distance is analyzed through the propagation model. Furthermore, using stochastic geometry method, combined with the interference of GUE in the downlink, the Signal-to-Interference plus Noise Ratio (SINR) coverage probability expression of GUE is derived. Finally, the simulation results show that the height of UAV and the average number of cluster members have non-monotonic effect on SINR coverage probability. When UAV height is low, compared with the 2-tier association scheme that GUE is only associated with the intra-cluster BS, the 4-tier association scheme proposed in this paper can improve the SINR coverage probability significantly.