Measurement and Modeling of the Aeronautical Channel for Galileo

Abstract

Power, delay and bandwidth of reflections at aircraft structures are not modelled accurate enough for new GNSS signal structures. For that reason ESA commissioned a contract about a measurement campaign in 2002. Only reflections which arrive shorter than the chip duration mainly contribute to the positioning error of a navigation receiver. This nature of the system made it necessary to measure the channel with an extremely high bandwidth of 100MHz, which results in a time resolution of 20ns, enhanced down to 1ns by using a super-resolution algorithm. The most important scenario for this channel type is the final approach. In the experiment we used an aircraft (Pilatus Porter) as the transmitting platform. The receiver was mounted in the 25m span experimental jet VFW-614 approaching Thalerhof airport of Graz/Austria. In a second step a helicopter as transmitter circled the parked VFW-614, while reflections on the plane were measured. To allow extensions of the measurements to larger aircrafts, the ground measurements were repeated with an Airbus A340. Evaluating the measurement data we were able to disprove the existence of a significant wing reflection. Due to the large bandwidth of the measurement we have been able to detect and model a strong, short delayed reflection on the fuselage, whose narrow bandwidth makes it nearly impossible to suppress its influence by averaging. As second contribution to the multipath channel the ground reflection was detectable. It was modulated by the changing terrains reflectivity and was Doppler shifted according to the aircrafts movement. We were able to correlate the Doppler shift with the sink rate. This achievement was used to model the ground echo properly. To gain more precise results, physical optics simulation was used to verify the measurements and proof the existence of the fuselage echo. We will present channel models for both aircrafts.