Detection of low cost radio frequency receivers based on their unintended electromagnetic emissions and an active stimulation

Detection of super-regenerative receivers using their unintended electromagnetic emissions at a significant distance is challenging due to high levels of ambient noise. The evolution of an approach used to solve this problem is chronicled within the three papers that combine to form this dissertation. First, a passive detection method was created for detecting devices based on the characterization of their unintended emissions and utilized a cascading correlation method to confirm detection. Using a simple sine-wave stimulation to modify these unintended emissions produced better results over passive detection techniques by improving the signal quality and the consistency of the unintended emissions, but was still rather limited in extending the reliable detection distance. Additionally, extensive characterization measurements of the target device were required. If the response of the receiver to a stimulation is known, however, a more complex stimulation can be used to embed additional information into the unintended emissions which does not require the previously essential characterization data. For regenerative receivers, an amplitude modulated stimulation generates a corresponding modulation in the unintended emissions of the target device. The receiver may thus be detected from these modulated emissions by calculating the received signal energy and then correlating it with the amplitude of the stimulation. A high correlation indicates the presence of the device. The receiver may be detected even when its emissions are well below the noise floor. Results show that five super-regenerative receivers from three different manufacturers can be detected in a noisy environment to distances of over 100 meters with an area under the receiver operating characteristic (ROC) curve of 94% --Abstract, page iv