TONE DETECTION USING DISCRETE FOURIER TRANSFORM TECHNIQUES

摘要

Supervisory audio tone (SAT) in a receive signal in a wireless communicationssystem is detected using a discrete Fourier transform (DFT) supplied withsamples of afiltered and decimated signal derived from the receive signal. The DFT cancomprise M2-input butterfly computation stages for computing an N-point DFT where N =2M. Eachof the stages m from 1 to M-1 determines and stores, for each current sampleat the input,at most 2m intermediate results forming only a subset of intermediate resultsrequired forcomputation by the next stage. Each of up to 2m other intermediate resultsrequired forcomputation by the next stage is produced by shifting of a respective storedintermediateresult of the respective subset determined in respect of an input samplepreceding thecurrent sample by 2M-m-1 samples. For example there are M = 5 stages for a 32-pointDFT having 18 outputs, 6 outputs for each of three SAT frequencies.