Handover Probability Analysis in Multi-Tier Aerial Networks at Varying Altitudes

Existing works on user mobility in unmanned aerial vehicle (UAV)/drone-based aerial networks consider either fixed height drone base stations (DBSs), or are limited to two-tier networks only, and do not take into account tier association biasing, which is important for developing intelligent traffic offloading and load balancing schemes to support the diverse use cases enabled by emerging networks. This paper addresses these gaps by analyzing the impact of user mobility in a multi-tier UAV heterogeneous network at varying heights serving ground users and taking into account the biased average receive power association, where each tier has an independent cell range extension (CRE) factor. We evaluate the handover probability of a mobile user by first deriving the distance distributions to the serving DBS and the probability of user association with a DBS of a specific tier. The quantification and insights from our theoretical analysis, corroborated with numerical simulations reveal that the probability of handover (dependent on the CRE factor of the tiers, height of the DBSs and velocity) must be optimized in tandem with coverage probability for optimal network performance.