Patent ID: 6694010
Filing Date: 2004-02-17
Classification: H04B

Abstract:
A method for recognizing a tone in a signal using at least a second order non-biased auto-regressive model defined by a first auto-regressive coefficient and a second auto-regressive coefficient, said method comprising:(a) sampling the signal at a constant sampling rate and, for each sample thereof, recursively determining a finite number of current correlation coefficients using an exponentially weighted, future sliding equivalent of the signal, said signal being time reversed such that prior to each determination of the current correlation coefficients as aforesaid, a current received sample and consecutively received previous samples of the signal are time reversed such that the said current received sample is defined as an oldest sample, an oldest of the said consecutively received previous samples is defined as a current sample and, where more than two consecutively received previous samples of the signal are used in the said determination, all said consecutively received previous samples other than the said oldest thereof are also defined to be time reversed as to their received sampling order, and wherein the current correlation coefficients are determined using pre-existing values of correlation coefficients determined in a previous determination, the current sample and at least two consecutively received previous samples of the signal; (b) periodically determining at least a second auto-regressive coefficient for modelling the signal using the current correlation coefficients; and (c) recognizing the presence of the tone based on the second auto-regressive coefficient.