Coarse and fine search methods to identify and measure noisy sinusoidal signals in a spectrum-monitoring system

Crowded broadcasting bands require the use of high-resolution monitoring equipment to measure common-channel signals individually. A measuring system for this purpose based on the FFT (fast Fourier transform) evaluation of the intermediate-frequency signal in a receiver is described. In the system, broadcasting carriers are identified by a coarse search of the spectrum while their parameters are measured to high accuracy by a fine search. Approximating expressions and simulation results are given to determine the false-alarm rate and peak-find probability of the coarse-search method for different weighting functions. For calculation of the variance of the fine-search estimate, a linearized model is derived and the computed variances are compared against simulations. A sample variance is defined which estimates the expected value of the variance of the frequency estimate in the fine search