Disambiguation of interferometric DOA estimates in vehicular passive radar

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.