Multipath Mitigation on an Operational Telemetry Link

Abstract

Transmitter mobility and multipath propagation make the telemetry channel both time and frequency selective, which results in telemetry link errors, sometimes in crucial flight phases. Only part of these impairments are compensated by various diversity techniques, but a fast converging adaptive channel equalization is probably the best suited and most cost effective solution. This paper first presents an analysis of mobile multipath propagation in telemetry based on recorded operational signals, both at the transmitter and at the receiver sides. Then it provides performance evaluation of a novel blind equalizer, assessed by offline processing of the recorded signals. The paper focuses on typical environments at a flight test centre, which exhibit critical multipath channel characteristics, namely during parking, taxiway and flight. The channel analysis exploits the recorded signals as well as the time frequency response of the novel equalizer filter. Performance evaluation shows that the equalizer outperforms state of the art Constant Modulus Algorithm (CMA). In particular, it is shown to significantly increase the telemetry link availability even in severe conditions, sometimes from nearly 0% to almost 100%, whereas the CMA fails to improve the signal quality as soon as the channel varies in time.