  To improve capacity and overcome some of the limitations of cellular wireless
networks, drones with aerial base stations can be deployed to assist the
terrestrial cellular wireless networks. The mobility of drones allows flexible
network reconfiguration to adapt to dynamic traffic and channel conditions.
However, this is achieved at the expense of more handovers since even a static
user may experience a handover when the drones are mobile. In this letter, we
provide an exact analysis of the handover rate and sojourn time (time between
two subsequent handovers) for a network of drone base stations. We also show
that among different speed distributions with the same mean, the handover rate
is minimum when all drone base stations move with same speed.
