Disambiguation of interferometric DOA estimates in vehicular passive radar

Abstract

Passive sensing involves the exploitation of ambient radio-frequency transmissions to infer the presence and properties of reflectors in the vicinity. With multiple receivers the directions of arrival (DOA) may be estimated. Interferometry is a simple means of DOA estimation, requiring minimal computational cost and as few as two receivers. However, interferometry suffers from ambiguity: signals incident from several distinct DOAs are indistinguishable because they yield the same measurement. This study considers interferometrical DOA estimation applied to the vehicular communications environment, assuming a vehicle equipped with two receivers. An algorithm for the disambiguation of DOA estimates using measurements from a second baseline is presented and a probabilistic analysis of this method is undertaken. The construction of extra baselines by consideration of the vehicle motion between signal frames is considered. The use of second-order measurement ratios generates baselines of acceptable length, given typical vehicle speeds. The effect of bias induced by second-order methods is explored.