Test tone detector apparatus and method modem using same

Claim 1

An electrical signal detector for detecting the presence of a predetermined electrical signal having a predetermined and predictable wave-shape, said detector comprising: digitizing means for repetitively sampling an input electrical signal U for providing a series of digital actual sample signals U n , U n+1 , U n+2 . . . each representing the actual value of said input electrical signal U n at respectively corresponding sampling times t n , t n+1 , t n+2 . . . ; prediction means for producing a series of digitized predicted sample signals UP m , UP m+1 , UP m+2 . . . each representing the predicted value UP q of said predetermined electrical signal at a respectively corresponding sampling time t q using as input the digitized actual sample signals U q-1 associated with a prior occurring sampling time t q-1 ; comparison means for comparing the predicted sample signals UP m with the actual sample signals U m for respectivly corresponding times t m and for producing error signals E m related to the differences therebetween; error accumulation means for producing an average error signal E av using as input said error signals E m ; detection means for comparing said average error signal E av to predetermined threshold signal T and for producing a detected signal output in response thereto; said predetermined electrical signal being a single frequency F sinusoid and wherein said digitized means and said prediction means jointly operate to generate predictions at times t m which recur at intervals substantially greater than the digitizing sampling interval t n corresponding to the higher sampling frequency f; and said digitizing means including a phase-splitter means for producing a pair of digitized sample signals U n1 , U n2 for each U n , said pair of signals representing the quadrature-phase components of a complex valued vector U n such that U n =U n1 +jU n2 and wherein said prediction means includes means for computing the next excepted U.sub.(n+1)1 and U.sub.(n+1)2 values in accordance with the following relationships: U.sub.(n+1)1 =U.sub.n1 cos (2πF/f)-U.sub.n2 sin (2πF/f) U.sub.(n+1)2 =U.sub.n1 sin (2πF/f)+U.sub.n2 cos (2πF/f).

Claim 7

A method for detecting the presence of a predetermined electrical signal having a predetermined and predictable wave-shape, said method comprising the steps of: repetitively sampling an input electrical signal U and generating a series of digital actual sample signals U n , U n+1 , U n+2 . . . each representing the actual value of said input electrical signal U n at respectively corresponding sampling times t n , t n+1 , t n+2 . . . ; generating a series of digitized predicted sample signals UP m , UP m+1 , UP m+2 . . . each representing the predicted value UP q of said predetermined electrical signal at a respectively corresponding sampling time t q using as input the digitized actual sample signals U q-1 associated with a prior occurring sampling time t q-1 ; comparing the predicted sample signals UP m with the actual sample signals U m for respectively corresponding times t m and generating error signals E m related to the differences therebetween; generating an average error signal E av using as input said error signals E m ; comparing said averaged error signal E av to a predetermined thresh hold signal T and generating a detected signal output in response thereto; said predetermined electrical signal being a single frequence F sinusoid and wherein said repetitive sampling and said generating steps are jointly performed to generate predictions at times t m which recur at intervals substantially greater than the sampling interval t n corresponding to the higher sampling frequency f; and repetitive sampling step including generating a pair of digitalized sample signals U n1 , U n2 for each U n , said pair of signals representing the quadrature-phase components of a complex valued vector U n such that U n =U n1 +jU n2 and wherein said generating step includes generating the next expected U.sub.(n+1)1 and U.sub.(n+1)2 values in accordance with the following relationships: U.sub.(n+1)1 =U.sub.n1 cos (2πF/f)-U.sub.n2 sin (2πF/f) U.sub.(n+1)2 =U.sub.n1 sin (2πF/f)+U.sub.n2 cos (2πF/f).

Claim 8

A method for detecting the presence of a predetermined electrical signal having a predetermined and predictable wave-shape, said method comprising the steps of: repetitively sampling an input electrical signal U and generating a series of digital actual sample signals U n , U n+1 , U n+2 . . . each representing the actual value of said input electrical signal U n at respectively corresponding sampling times t n , t n+1 , t n+2 . . . ; generating a series of digitized predicted sample signals UP m , UP m+1 , UP m+2 . . . each representing the predicted value UP q of said predetermined electrical signal at a respectively corresponding sampling time t q using as input the digitized actual sample signals U q-1 associated with a prior occurring sampling time t q-1 ; comparing the predicted sample signals UP m with the actual sample signals U m for respectively corresponding times t m and generating error signals E m related to the differences therebetween; generating an average error signal E av using as input said error signals E m ; comparing said averaged error signal E av to a predetermined thresh hold signal T and generating a detected signal output in response thereto; said predetermined electrical signal being a single frequence F sinusoid and wherein said repetitive sampling and said generating steps are jointly performed to generate predictions at times t m which recur at intervals substantially greater than the sampling interval t n corresponding to the higher sampling frequency f; and repetitive sampling step including generating a pair of digitalized sample signals U n1 , U n2 for each U n , said pair of signals representing the quadrature-phase components of a complex valued vector U n such that U n =U n1 +jU n2 and wherein said generating step includes generating the next expected U.sub.(n+1)1 and U.sub.(n+1)2 values in accordance with the following relationships: U.sub.(n+1)1 =U.sub.n1 cos (2πF/f)-U.sub.n2 sin (2πF/f) U.sub.(n+1)2 =U.sub.n1 sin (2πF/f)+U.sub.n2 cos (2πF/f).

Claim 10

A method of detecting a pure tone signal, said method comprising: generating pairs of successive output electrical signals U n1 , U n2 which represent the phase quadrature components of an incoming signal at successive sampling time intervals t n ; generating predicted digital signals based on said sample signals U n1 , U n2 and having values which are expected to occur at future sample times if the incoming signal is a single frequency sinusoid; and comparing the respectively corresponding actual and predicted digital signals to generate a tone detection output based on the difference between said actual and predicted signals.

Claim 11

A method of detecting a pure tone signal, said method comprising: generating pairs of successive output electrical signals U n1 , U n2 which represent the phase quadrature components of an incoming signal at successive sampling time intervals t n ; generating predicted digital signals based on said sample signals U n1 , U n2 and having values which are expected to occur at future sample times if the incoming signal is a single frequency sinusoid; and comparing the respectively corresponding actual and predicted digital signals to generate a tone detection output based on the difference between said actual and predicted signals.