Unmanned aerial vehicles (UAVs) have found numerous applications and are expected to
bring fertile business opportunities in the next decade. Among various enabling
technologies for UAVs, wireless communication is essential and has drawn significantly
growing attention in recent years. Compared to the conventional terrestrial communications,
UAVs' communications face new challenges due to their high altitude above the ground and
great flexibility of movement in the 3-D space. Several critical issues arise, including the line …