Senniger, Powers, Leavitt & Roedel
Multi-frequency receiver with arbitrary center frequencies
 A multi-frequency receiver for detecting the presence of one or more of a plurality of m frequency tones in an incoming signal. A digital signal processor executes a fast algorithm for accurately calculating the spectral energies in a plurality of m frequency bands. Each frequency band is centered on one of the frequencies to be detected. The center frequencies of those bands are independent of the data length used. The calculated spectral energies are compared to a set of predefined thresholds. As a result, the presence of particular tones within the incoming signal are detected. 
Talx Corporation
H
H04Q
inventional
Baohua
Zheng