  Aerial vehicles (AVs) such as electric vertical take-off and landing (eVTOL)
make aerial passenger transportation a reality in urban environments. However,
their communication connectivity is still under research to realize their safe
and full-scale operation, which requires stringent end-to-end (E2E) reliability
and delay. In this paper, we evaluate reliability and delay for the downlink
communication of AVs, i.e., remote piloting, control/telemetry traffic of AVs.
We investigate direct air-to-ground (DA2G) and air-to-air (A2A) communication
technologies, along with high altitude platforms (HAPs) to explore the
conditions of how multi-connectivity (MC) options satisfy the demanding E2E
connectivity requirements under backhaul link bottleneck. Our considered use
case is ultra-reliable low-latency communication (URLLC) under the finite
blocklength (FBL) regime due to the nature of downlink control communication to
AVs. In our numerical study, we find that providing requirements by single
connectivity to AVs is very challenging due to the line-of-sight (LoS)
interference and reduced gains of downtilt ground base station (BS) antenna. We
also find that even with very efficient interference mitigation, existing
cellular networks designed for terrestrial users are not capable of meeting the
URLLC requirements calling for MC solutions.
