| 摘要 |
<p>Supervisory audio tone (SAT) in a receive signal in a wireless communications system is detected using a discrete Fourier transform (DFT) supplied with samples of a filtered and decimated signal derived from the receive signal. The DFT can comprise M 2-input butterfly computation stages for computing an N-point DFT where N=2M. Each of the stages m from 1 to M-1 determines and stores, for each current sample at the input, at most 2m intermediate results forming only a subset of intermediate results required for computation by the next stage. Each of up to 2m other intermediate results required for computation by the next stage is produced by shifting of a respective stored intermediate result of the respective subset determined in respect of an input sample preceding the current sample by 2M-m-1 samples. For example there are M=5 stages for a 32-point DFT having 18 outputs, 6 outputs for each of three SAT frequencies.</p> |
