Coverage Recovery Analysis of UAV Base Station Networks

Unmanned Aerial Vehicles (UAV) deployed in the air can be used as base stations (BSs) to provide uplink and downlink transmissions for ground cellular users in a target area. This paper considers the coverage recovery problem in a cellular network with UAVs as base stations when one or more UAVs go offline due to energy replenishment or extreme environment. A coverage analysis of the target area is first presented in order to obtain the condition on the coverage radius of a UAV BS (UBS) for producing a full coverage of the target area. In the case of UAV offline, the coverage radius of a UBS needs to be adjusted to recover the full coverage of the target area, which can be implemented by adjusting either the altitude or the transmission power of the UBS. Based on the obtained full coverage condition on the UBS coverage radius, a coverage recovery analysis is further presented for determining the adjustment range of the altitude or transmission power of a UBS. For this purpose, the relationship between the coverage radius and the altitude and that between the coverage radius and the transmission power are analyzed. Through numerical results, it is demonstrated that the full coverage of a target area can effectively be recovered by adjusting either the altitude or transmission power of a UBS in the case of UBS offline.