Multipath propagation for helicopter-to-ground MIMO links

Air-to-ground communication for aeronautical telemetry is often impaired by multipath propagation, particularly when the aircraft is near the flight-line. This paper experimentally studies such a channel using measurements from multiple antennas on a helicopter to multiple receiving antennas on the ground as the helicopter maneuvers on a taxiway near hangars and other buildings at Cairns Army Airfield, Ft. Rucker, AL. Analysis of the results reveals delay spreads of the multipath channels between 15 ns and 150 ns, with the longer delay spreads resulting when using a receive antenna with a wider beamwidth such that it that observes richer multipath propagation. The data also shows that on average, diversity signaling from three aircraft-mounted antennas can lead to gains in signal-to-noise ratio of approximately 13 dB, with the gain dependent on the multipath characteristics observed by the ground antenna.