  In this paper, we propose and evaluate rate-maximizing pilot configurations
for Unmanned Aerial Vehicle (UAV) communications employing OFDM waveforms. OFDM
relies on pilot symbols for effective communications. We formulate a
rate-maximization problem in which the pilot spacing (in the time-frequency
resource grid) and power is varied as a function of the time-varying channel
statistics. The receiver solves this rate-maximization problem, and the optimal
pilot spacing and power are explicitly fed back to the transmitter to adapt to
the time-varying channel statistics in an air-to-ground (A2G) environment. We
show the enhanced throughput performance of this scheme for UAV communications
in sub-6 GHz bands. These performance gains are achieved at the cost of very
low computational complexity and feedback requirements, making it attractive
for A2G UAV communications in 5G.
