Overview

Yeo-Sun Yoon, Lance M. Kaplan, and James H. McClellan

For many applications, wideband signals are exploited for localization. A wideband signal is any signal whose energy is distributed over a bandwidth that is large in comparison to the signal s center frequency. For example, ultrawideband (UWB) noise radars use wideband offering low probability of detection (LPD), while achieving good target detection and high resolution [1]. In the acoustic vehicle tracking scenario, the target emits a set of narrowband harmonics [2].

Direct exploitation of an array of raw wideband signals for localization using traditional narrowband techniques will fail miserably. The shortcoming is that the narrowband methods exploit the fact that time delays directly translate to a phase shift in the frequency domain [3].

For narrowband signals, where the bandwidth is small relative to the center frequency f _c, the phase-shift is approximately constant over the bandwidth. The delayed signal in the time domain is

The phase shift is now independent of time, where the time delay ? is a function of the location of the source relative to the array elements. When the signal is mixed with a pure tone at the center frequency (i.e., baseband conversion), the outputs along a linear array due to P far-field sources are viewed as an approximately constant signal. A well-accepted model for the linear array outputs is given by a weighted sum of steering vectors embedded in noise

where a( ? _i) is the M 1 steering...