US4813073A
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Echo cancellation
Assignee: Motorola Solutions Inc
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Filing: 1987-07-02
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Granted: 1989-03-14
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Expires: 2007-07-02
Abstract
Abstract Echo cancellation to remove, from a locally received data communication signal, an echo signal component having a changing phase difference relative to the phase of a locally transmitted data communication signal, said locally transmitted communication signal are generated by modulating a carrier based on sequences of complex data signal points, is accomplished by correcting the phase of an input sequence of complex samples of the modulated carrier based on the changing phase difference to generate complex phase corrected samples, and generating a real-valued simulation of the echo signal based on the complex, phase corrected samples. Another aspect is estimating the phase difference between two signals based on samples of the real signal component of one of the signals, and the real component of the difference between the signals; successive estimates of the phase difference are generated based on successive applications of an approximate Hilbert transform to samples of each of the real signal component of one of the signals, and to the samples of the real component of the difference between the signals, each application of the Hilbert transform being limited to two of the samples. Another aspect is averaging a succession of sample values and scaling the result of the averaging in accordance with a variable scaling factor; the succession of sample values is accumulated as a cumulative sample value, and an output indicative of the result is provided by comparing the cumulative sample value with a threshold that is based on the variable scaling factor.
Inventors
- 👤 Fuyun Ling
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-23 12:04
CPC Classifications
H; H04; H04B; H04B3/00; H04B3/02; H04B3/20; H04B3/23; H04B3/232; H04B3/237; H04B3/238
Claims Analysis
Total Claims: 22
Claim 1
Independent Claim
105 words
Echo cancellation apparatus for removing, from a locally received data communication signal, an echo signal component having a changing phase difference relative to the phase of a locally transmitted data communication signal, said locally transmitted communication signal being generated by modulating a carrier based on sequences of complex data signal points, said apparatus comprising a phase corrector for correcting the phase of an input sequence of complex samples of said modulated carrier based on said changing phase difference to generate complex, phase corrected samples, and an echo canceller for generating a real valued simulation of said echo signal based on said complex, phase corrected samples.
Claim 2
Dependent Claim
105 words
Echo cancellation apparatus for removing, from a locally received data communication signal, an echo signal component having a changing phase difference relative to the phase of a locally transmitted data communication signal, said locally transmitted communication signal being generated by modulating a carrier based on sequences of complex data signal points, said apparatus comprising a phase corrector for correcting the phase of an input sequence of complex samples of said modulated carrier based on said changing phase difference to generate complex, phase corrected samples, and an echo canceller for generating a real valued simulation of said echo signal based on said complex, phase corrected samples.
Claim 3
Dependent Claim
26 words
The apparatus of claim 1 wherein said changing phase difference includes a phase roll at a particular frequency which is substantially lower than the signaling rate.
Claim 4
Dependent Claim
30 words
The apparatus of claim 1 wherein said communication signals are carried on a channel between a local terminal and a remote terminal and said echo signal comprises a far echo.
Claim 5
Dependent Claim
31 words
The apparatus of claim 1 wherein said phase corrector comprises a complex modulator for correcting said input sequence of signals in the complex domain in accordance with said changing phase difference.
Claim 6
Dependent Claim
15 words
The apparatus of claim 1 wherein said echo canceller comprises a linear adaptive transversal filter.
Claim 7
Independent Claim
15 words
The apparatus of claim wherein said transveral filter generates a simulated real-valued far echo signal.
Claim 8
Dependent Claim
61 words
Apparatus for filtering a succession of sample values and generating a filtered output inversely proportional to a variable scaling factor, comprising an integrating circuit for accumulating said succession of said sample values as a cumulative data value, and threshold circuitry for generating said output by comparing said cumulative data value with a threshold that is based on said variable scaling factor.
Claim 9
Dependent Claim
61 words
Apparatus for filtering a succession of sample values and generating a filtered output inversely proportional to a variable scaling factor, comprising an integrating circuit for accumulating said succession of said sample values as a cumulative data value, and threshold circuitry for generating said output by comparing said cumulative data value with a threshold that is based on said variable scaling factor.
Claim 10
Dependent Claim
26 words
The appartus of claim 7 wherein said sample values comprise estimates of the phase difference between a simulated echo signal and a corresponding actual echo signal.
Claim 11
Dependent Claim
20 words
The apparatus of claim 7 wherein said variable scaling factor comprises an estimate of the power of an echo signal.
Claim 12
Dependent Claim
20 words
The apparatus of claim 8 or 9 wherein said echo is a far echo in a full duplex communication system.
Claim 13
Dependent Claim
84 words
Apparatus for estimating the phase difference between two signals based on samples of the real signal component of one of the signals, and samples of the real component of the difference between said signals, comprising means for generating successive estimates of said phase difference based on successive applications of an approximate Hilbert transform to said samples of said real signal component and to said samples of said real component of said difference, each application of said Hilbert transform being limited to two said samples.
Claim 14
Dependent Claim
84 words
Apparatus for estimating the phase difference between two signals based on samples of the real signal component of one of the signals, and samples of the real component of the difference between said signals, comprising means for generating successive estimates of said phase difference based on successive applications of an approximate Hilbert transform to said samples of said real signal component and to said samples of said real component of said difference, each application of said Hilbert transform being limited to two said samples.
Claim 15
Dependent Claim
44 words
The apparatus of claim 11 wherein said logic implements an expression of the form e(k)*E.sub.f (k-1)-e(k-1)*E.sub.f (k) where e(k) denotes the kth sample of the difference between the two signal components, and E f (k) denotes the kth sample of said real signal component.
Claim 16
Dependent Claim
98 words
The apparatus of claim 11 wherein said means comprises a pair of delay elements for receiving said samples of said respective real signal components, a pair of multipliers, one said multiplier for multiplying the delayed sample of said real signal component by the current sample of the real component of the difference, the other said multiplier for multiplying the current sample of the real signal component by the delayed sample of the real component of the difference, and a summer for subtracting the respective products generated by said multipliers to generate each said estimate of said phase difference.
Claim 17
Dependent Claim
97 words
An echo cancellation method for removing, from a locally received data communication signal, an echo signal component having a changing phase difference relative to the phase of a locally transmitted data communication signal, said locally transmitted communication signal being generated by modulating a carrier based on sequences of data signal points, said method comprising correcting the phase of an input sequence of complex samples of said modulated carrier, based on said changing phase difference to generate complex phase corrected samples, and generating a real valued simulation of said echo signal based on said complex, phase corrected samples.
Claim 18
Dependent Claim
97 words
An echo cancellation method for removing, from a locally received data communication signal, an echo signal component having a changing phase difference relative to the phase of a locally transmitted data communication signal, said locally transmitted communication signal being generated by modulating a carrier based on sequences of data signal points, said method comprising correcting the phase of an input sequence of complex samples of said modulated carrier, based on said changing phase difference to generate complex phase corrected samples, and generating a real valued simulation of said echo signal based on said complex, phase corrected samples.
Claim 19
Independent Claim
54 words
A method for filtering a succession of sample values and generating a filtered output inversely proportional to a variable scaling factor, comprising accumulating said succession of sample values as a cumulative sample value, and generating said output by comparing said cumulative sample value with a threshold that is based on said variable scaling factor.
Claim 20
Independent Claim
54 words
A method for filtering a succession of sample values and generating a filtered output inversely proportional to a variable scaling factor, comprising accumulating said succession of sample values as a cumulative sample value, and generating said output by comparing said cumulative sample value with a threshold that is based on said variable scaling factor.
Claim 21
Independent Claim
83 words
A method for estimating the phase difference between two signals based on samples of the real signal component of one of the signals, and samples of the real component of said phase difference, comprising generating successive estimates of said phase difference based on successive applications of an approximate Hilbert transform to samples of said real signal component and to said samples of said real component of said difference of said signals, each application of said Hilbert transform being limited to two said samples.
Claim 22
Independent Claim
83 words
A method for estimating the phase difference between two signals based on samples of the real signal component of one of the signals, and samples of the real component of said phase difference, comprising generating successive estimates of said phase difference based on successive applications of an approximate Hilbert transform to samples of said real signal component and to said samples of said real component of said difference of said signals, each application of said Hilbert transform being limited to two said samples.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1992-03-13 | 1992-09-12 | 1993-03-14 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1996-03-13 | 1996-09-12 | 1997-03-14 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2000-03-13 | 2000-09-12 | 2001-03-14 | $7700.00 | Window Closed / Lapsed |