Locating Noncooperative Radio Receivers Using Wideband Stimulated Emissions

Accurately determining the position of radio receivers can aid in the rapid discovery of radio-controlled explosives. Prior research has demonstrated that superheterodyne receivers unintentionally emit low-power radio signals during normal operation. By using a weak stimulation signal, it is possible to inject a known signal into these unintended emissions. This process is known as stimulated emissions. In this paper, a method is developed using radarlike techniques to determine the range to the radio receiver. Unlike conventional radar, it depends on the modification of the unintended emissions from the device and not on a passive reflection. High-bandwidth stimulated emissions measured from a typical superheterodyne receiver-which was not designed to be located-are used to make high-resolution time-of-arrival measurements. A continuous-wave radarlike system was designed, and its hardware realization is discussed. The accuracy of the radar is tested in a noisy multipath-rich indoor environment. Results indicate that the proposed radar can locate superheterodyne radio receivers that are 50 m away or more. The root-mean-square position error is less than 5 m when the signal-to-noise ratio is 15 dB or above. The proposed system offers a viable alternative to existing techniques for locating radio-controlled explosives.