Method and apparatus for detecting signaling tones in wide-band digitized cellular-telephone signals
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United States of America Patent
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Jul 27, 1999
Grant Date -
N/A
app pub date -
Feb 1, 1996
filing date -
Feb 1, 1996
priority date (Note) -
Expired
status (Latency Note)
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Abstract
A cellular-telephone-system base station (10) employs a digital band-exclusion filter (30) to detect a supervisory tone, but the filter's record length is shorter than that dictated by the necessary resolution and produces output values at a frequency much lower than the frequency of the supervisory tone. A second filter (32) receives the output, operating on a record whose time duration is long enough to achieve the necessary frequency resolution. The second filter's coefficients are chosen to match the frequency of the signal to which the previous filter's subsampling translates the frequency of the supervisory tone. In this way, the supervisory tone can be detected with the necessary resolution but at storage computational costs less than the input sample rate and required frequency resolution would seem to require.
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