# US 5,353,344 A · Method of determining levels at given frequencies of a VF signal > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,353,344 A - Document ID: US5353344A - Status: Granted - Kind: A - Application number: 07/947,069 - Filed: 1992-09-18 - Granted: 1994-10-04 - Earliest claimed: 1991-09-24 - Assignees: Alcatel STR AG - Inventors: Martin A. Knitsch - Web page: https://patentgrep.com/patent/US5353344A ## CPC - H04L 27/30: wherein each code element is represented by a combination of frequencies - H04Q 1/444: with voice-band signalling frequencies - H04Q 1/457: with conversion of multifrequency signals into digital signals - H04Q 1/46: comprising means for distinguishing between a signalling current of predetermined frequency and a complex current containing that frequency, e.g. speech current - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) - H04Q: SELECTING (switches, relays, selectors H01H; wireless communication networks H04W) ## Abstract A dialing receiver (1) for determining multifrequency dialing signals on an incoming signal in a telecommunication switching system, including a sampling circuit (4) for taking N values of the incoming signal at a given sampling rate, where N is a positive integer; a zero value generator circuit (6) for supplementing at the given sampling rate the N samples with M successive zero values so as to yield N+M values, where M is a positive integer; a discrete Fourier transformation circuit (7) for performing a discrete Fourier transform (DFT) of said N+M values in accordance with the Goertzel algorithm; and a result evaluating circuit (8) for directly evaluating the results of the DFT processing of the N+M values without interpolation so as to determine the identity of the multifrequency dialing signals. ## Claims ### Claim 1 Method for identifying at least one given frequency in a multifrequency signal in a processing unit, comprising, in combination, the steps of: sampling in a sampling circuit the multifrequency signal at a sampling frequency and generating N samples; generating in a zero value generator M samples having a value of zero; receiving the N samples and the M samples in a transformation circuit in form of a sequence having a length of N+M samples, transforming the sequence with a discrete Fourier transform in accordance with a Goertzel algorithm, and generating a series of discrete Fourier coefficients; evaluating in an evaluating circuit the series of the discrete Fourier coefficients at different frequencies to identify said at least one given frequency in the multifrequency signal without using interpolation between the coefficients and providing said at least one given frequency as an output signal of the processing circuit. ### Claim 2 (depends on 1) A method according to claim 1, wherein the method includes the step of arranging in the transformation circuit the N samples and the M samples in such a manner that the M samples have an effect of samples having arrived chronologically prior to the N samples. ### Claim 3 (depends on 2) A method according to claim 2, wherein the method further includes the step of choosing a value of M+N to equal the sampling frequency in Hertz so that said at least one given frequency can be identified from a 1 Hz-grid. ### Claim 4 (depends on 1) A method according to claim 1, wherein the method further includes the step of choosing a value of M+N to equal the sampling frequency in Hertz so that said at least one given frequency can be identified from a 1 Hz-grid. ### Claim 5 (depends on 1) A method according to claim 1, wherein the method includes the step of choosing N equal to 205, choosing M equal 7,795 and the sampling frequency equals 8k HZ. ### Claim 6 A dialing receiver for determining multifrequency dialing signals on an incoming signal in a telecommunication switching system, comprising; A) a sampling circuit for taking N values of the incoming signal N times at a given sampling rate, where N is a positive integer; B) a zero value generator circuit for supplementing at the given sampling rate the N values with M successive zero values so as to yield N+M values, where M is a positive integer; C) a discrete Fourier transformation circuit for performing a discrete Fourier transform (DFT) of said N+M values in accordance with a Goertzel algorithm and providing a result in form of a series of Fourier coefficients; and D) a result evaluating circuit for directly evaluating the results of the discrete Fourier transform (DFT) processing of the N+M values without interpolation so as to determine an identity of the multifrequency dialing signals. ### Claim 7 (depends on 6) A dialing receiver as defined in claim 6, wherein the transformation circuit includes means for arranging the M values having successive zero values so the M zero values have a effect of samples having arrived chronologically prior to the N values. ### Claim 8 (depends on 7) A dialing receiver as defined in claim 7, wherein an at least one given frequency has integer values in Hertz and the value of M+N is chosen to equal the sampling frequency in Hertz. ### Claim 9 (depends on 8) A dialling receiver as defined in claim 8, wherein the multifrequency dialling signals each comprise two different simultaneously present frequencies, and wherein each frequency is one of a set of eight predetermined frequencies. ### Claim 10 (depends on 7) A dialling receiver as defined in claim 7, wherein the multifrequency dialling signals each comprise two different simultaneously present frequencies, and wherein each frequency is one of a set of eight predetermined frequencies. ### Claim 11 (depends on 6) A dialing receiver according to claim 6, wherein the value of N equals 205, the value of M equals 7,795 and the sampling range equals 8k HZ. ### Claim 12 Method for identifying at least one given frequency in a multifrequency signal in a dialing receiver, comprising, in combination, the steps of: sampling the multifrequency signal in a sampling circuit at a sampling frequency and generating N samples; generating in a zero value generator M samples having a value of zero; receiving the N samples and the M samples in form of a finite duration sequence of length N+M in a discrete Fourier transformation computation circuit, transforming successively said sequence with a discrete Fourier transform using a Goertzel algorithm, and generating a series of discrete Fourier coefficients; evaluating in a results evaluation circuit the presence of said at least one frequency of the multifrequency signal based on an absolute value of said coefficients at a given frequency without using interpolation between coefficients being evaluated and generating an output signal indicating presence of absence of said at least one frequency. ### Claim 13 (depends on 12) A method according to claim 12, wherein the method further includes the step of providing to the transformation circuit the N samples and the M zero values in such a manner that the M zero-value samples have an effect of samples having arrived chronologically prior to the N samples. ### Claim 14 (depends on 13) A method according to claim 13, wherein the method further includes the step of choosing a value of M+N to equal the sampling frequency in Hertz so that said at least one given frequency can be identified from a 1 Hz-grid. ### Claim 15 (depends on 12) A method according to claim 12, wherein the method further includes the step of choosing a value of M+N to equal the sampling frequency in Hertz so that said at least one given frequency can be identified from a 1 Hz-grid. ### Claim 16 (depends on 12) A method according to claim 12, wherein the method includes the step of choosing N equal to 205, choosing M to equal 7,795 and the sampling frequency equals 8k HZ.