Localization in the Presence of Coherent Interference

This paper obtains analytical expressions for the Cramer-Rao bounds on the bearing and range of a Gaussian signal source observed by a two-dimensional array in the presence of strong Gaussian interference. It shows that: 1) all relevant features of array geometry are summarized by a function closely related to the conventional beam pattern; 2) the minimum signal-interference separation at which bearing estimation can be accomplished without serious loss of performance varies inversely with the first power of the signal-to-noise ratio; 3) in contrast to the localization problem in spatially incoherent noise, there is significant coupling between the estimation errors of bearing and signal power. Lack of prior knowledge of signal power can seriously degrade the quality of the bearing estimate; 4) the coupling of bearing and power estimates depends on the slope of the conventional beam pattern, not its magnitude. Control on sidelobe levels is therefore not sufficient to insure satisfactory localization performance; and 5) at ranges large compared with the array dimensions there is no coupling between the estimation of range and signal power.