  Aircraft cabin is one of the last venues without mobile broadband.
Considering future 5G applications and connectivity requirements, direct
air-to-ground communications (DA2GC) is the only technique which can provide
high capacity and low latency backhaul link for aircraft via a direct
communication link. To this end, we propose an analytical framework to
investigate the ground station deployment problem for DA2GC network employing
multi-user beamforming with dual-polarized hybrid DA2GC antenna arrays. In
addition, the proposed framework is utilized to analyze and optimize the total
cost of ownership (TCO) of the DA2GC network to provide coverage for European
airspace. We present the interplay between different network parameters: the
number of ground stations, array size, transmit power and bandwidth, and TCO
optimizing deployment parameters are calculated in order to satisfy capacity
requirements. At the end, we show that, depending on the cost of different
network resources, a terrestrial cellular network can be designed to cover the
whole European airspace with limited number of ground stations with a certain
array size, i.e., 900 and 361 antenna elements for ground station and air
station, respectively.
