H - Electricity – 04 – L
Patent
H - Electricity
04
L
H04L 27/30 (2006.01) H04M 1/738 (2006.01) H04M 1/82 (2006.01) H04Q 1/45 (2006.01)
Patent
CA 2279264
To determine whether a received signal represents a dual tone multi frequency (DTMF) code, a characteristic of the received signal is repeatedly measured over a period of time, thereby obtaining a plurality of parameter measurements. This may include separating the received signal into low band and high band signals and for each of the low band and high band signals, determining a plurality of squared magnitude measurements over the period of time. A deviation value is then determined for each of the plurality of parameter measurements, and an average deviation value is determined from the plurality of deviation values. The average deviation value is compared to a threshold value, thereby obtaining a comparison result. The received signal as alternatively designated as representing or not representing a DTMF code on the basis of the comparison result. The step of determining a deviation value for each of the plurality of parameter measurements may include, for each of the plurality of squared magnitude measurements, determining a deviation from a predefined (e.g., unit) circle only if the squared magnitude measurement is less than the radius of the predefined circle, and setting the deviation equal to zero for all other cases. The step of determining the average deviation value from the plurality of deviation values may include determining which of the plurality of deviation values is a maximum deviation value, and determining an average deviation value from the plurality of deviation values not including the maximum deviation value.
Nicolaescu Sawyer
Telefonaktiebolaget Lm Ericsson
LandOfFree
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