1974-08-12
1976-01-20
Claffy, Kathleen H.
328138, H04M 150
Patent
active
039340970
ABSTRACT:
A method and apparatus for detecting multifrequency tones in a received signal by summing aperiodic samples and without using bandpass filters. In a receiver capable of detecting m different tones each comprised of n different frequencies, the apparatus performs m parallel summations each of 2.sup.n samples of the received signal. Each summation corresponds to a different detectable tone. In each summation, an initial sample is followed by samples delayed from it by respective half-periods of the frequencies comprising the corresponding tone and by samples delayed from the initial sample by combinations of different ones of such half-periods. The detection of a particular tone is indicated when the corresponding sum is zero and all other sums have finite values.
REFERENCES:
patent: 3441682 (1969-04-01), Pasternack
patent: 3514697 (1970-05-01), Oswald
patent: 3573613 (1971-04-01), Oswald
patent: 3578919 (1971-05-01), O'Neill
International Switching Symposium, MIT, Cambridge, Mass., S. G. Pitroda, "Digital Multifrequency Tone Receiver", June 1972, pp. 431-441.
Bell Telephone Laboratories Incorporated
Claffy Kathleen H.
Phelan C. S.
Popek Joseph
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