Frequency Resolution Enhancement of a Compressive Receiver by Spectral Estimation

Abstract

Conventional electronic countermeasures (ECM) receivers cannot readily detect the transmission of spread spectrum signals. The ideal (Neyman-Pearson) detector is very difficult to implement since it would require the use of several hundred, and perhaps thousands of matched filters contiguously spaced in frequency. Thus, noncoherent radiometric detectors are generally used due to the simplicity of their implementation. The situation is further complicated by the very low operating signal to noise ratio requirements and the extremely wide bandwidth which must be searched. The detection of spread spectrum transmissions in a tactical situation may be the first step in signal interception or repeat back jamming schemes. It is therefore desirable to detect a signal as rapidly as possible. This detection time (or probability of intercept) is more a function of signal power spectral density for the direct sequence spread spectrum waveform, and the frequency hop rate for a frequency hopping spread spectrum signal. In either case, an optimal receiver is called for with a rapid signal/data processing capability. In this paper, we propose the use of the Chirp Z transform implemented by using a surface acoustic wave (SAW) spectrum analyzer as a detector of jamming signals and other spread spectrum signals. The SAW spectrum analyzer is modeled by a digital implementation of the Chirp Z algorithm. The resulting spectrum will be processed digitally to produce a high resolution (fast) spectral estimate. This estimate will be optimal in the sense that a norm of error is minimized.