Adaptive signal receiving method and apparatus
First Claim
1. A method of adapting the amplitude sensitivity of a telephone system tone signal receiver to successive tone signals received from telephone stations on a per call basis, in which the receiver has an initial amplitude range for valid tone signals, said method BEING CHARACTERIZED BY the steps ofascertaining the amplitude of a first valid tone signal received during a call, andnarrowing the initial amplitude range according to a prescribed algorithm based on the amplitude of the first valid tone signal for validating succeeding tone signals received during the call.
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Accused Products
Abstract
A tone receiver suitable for use in a telephone system and which adaptively narrows its amplitude sensitivity range defining valid tone signals on a per call basis in accordance with the amplitude of a first tone signal received on a call. The signal range adaptability improves signal echo rejection and spurious noise talkoff. A preferred embodiment is implemented by a programmed digital signal processor which increases the lower amplitude signal threshold in accordance with the amplitude of the first signal. An alternative embodiment adaptively attenuates the level of incoming signals before signal validation. A further improvement of both embodiments allows further amplitude range narrowing in response to any subsequent signal on a call which has an amplitude greater than that of any preceding signal in the call.
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Citations
16 Claims
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1. A method of adapting the amplitude sensitivity of a telephone system tone signal receiver to successive tone signals received from telephone stations on a per call basis, in which the receiver has an initial amplitude range for valid tone signals, said method BEING CHARACTERIZED BY the steps of
ascertaining the amplitude of a first valid tone signal received during a call, and narrowing the initial amplitude range according to a prescribed algorithm based on the amplitude of the first valid tone signal for validating succeeding tone signals received during the call.
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10. A telephone system signal receiver comprising
means for detecting tone signals of prescribed frequencies and having amplitudes falling within a prescribed initial amplitude range, and means responsive to the detection of a said tone signal during a telephone call for adaptively narrowing the amplitude range for the detection of succeeding said tone signals during the call according to a predetermined algorithm based on the value of the amplitude of the detected tone signal.
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15. A telephone system tone receiver adaptable on a per telephone call basis for detecting tone signals transmitted over the telephone network, comprising
means operative on each call for establishing an initial signal amplitude threshold below which incoming tone signals are rejected, means for measuring the amplitude of a first tone signal arriving during a call in which the amplitude is greater than the initial threshold, and means for establishing a new threshold for validating subsequently arriving tone signals during said call equal to the difference between the amplitude of the first tone signal and a predefined amount selected to be approximately the maximum amplitude variation of tone signals received on any given call.
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16. A telephone system tone receiver adaptable on a per telephone call basis for detecting tone signals transmitted over the telephone network, comprising
detection circuitry operative to reject tone signals having amplitudes below a prescribed threshold, variable amplitude attenuator means located ahead of the detection circuitry in the incoming tone signal path, means for measuring the amplitude of tone signals at the input to the attenuator means, and means for controlling the attenuator means to establish a first level of attenuation at the beginning of a call, including means connected to the amplitude measuring means and responsive to the detection of a first tone signal by the detection circuitry for controlling the attenuator means to increase the level of attenuation for subsequent tone signals on the call by an amount sufficient to reduce the amplitude of the first tone signal to a level above the threshold equal approximately to the statistical maximum variation in amplitude of all tone signals on any given call.
Specification