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US 6,959,056 B2Granted
RFI canceller using narrowband and wideband noise estimators
AssigneeBell Canada
InventorsTet Hin Yeap, David Kenneth Fenton
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AssigneeBell Canada
InventorsTet Hin Yeap, David Kenneth Fenton
Estimating the term…
In an adaptive filter for cancelling common-mode noise in digital subscriber loops, a narrowband noise estimator is used to detect one or more noisy frequency bands of the common mode signal and derive therefrom a first noise estimation signal. A wideband noise estimator derives from the remainder of the common mode signal a second noise estimation signal. The first and second noise estimation signals are subtracted from the differential signal, The wideband noise estimator comprises a bandstop filter for removing the frequencies detected by the narrowband noise estimator, an analog-to-digital converter for digitizing the bandstopped signal, and an adaptive filter for deriving the second noise estimation signal from the digitized bandstopped signal and, in the process, compensating for phase and gain differences, especially attributable to the interference being injected at different points along the length of the channel.
Apparatus for cancelling radio frequency noise occurring in a communications channel, comprising input means (10, 12, 16, 26) for connection to the communications channel (14) and for extracting therefrom a differential signal (S) and a common mode signal (CM), narrowband noise estimation means (28) responsive to the common mode signal (CM) for producing a first noise estimate signal (EA) derived from relatively high amplitude narrowband radio frequency interference in one or more narrow frequency bands and wideband noise estimation means (30) responsive to the common mode signal for producing a second noise estimate signal (ED) derived from relatively low amplitude wideband radio frequency interference in frequency bands other than said one or more narrow frequency bands, control means (60) for controlling gain and/or phase of the noise estimate signals in relation to the differential signal (S), means (48) for subtracting the first and second noise estimate signals from the differential signal, and means for compensating for phase differences between the common mode component in the differential signal and each of the first and second interference estimate signals before the signals are summed or added.
A method of cancelling radio frequency noise occurring in a communications channel using a noise cancellation circuit having input means (10, 12, 16, 26) for connection to the communications channel (14), further comprising the steps extracting from the channel via the input means a differential signal (S) and a common mode signal (CM), deriving a first noise estimation signal from relatively high amplitude narrowband radio frequency interference in one or more narrow frequency bands of the common mode signal (CM), deriving from the common mode signal a second noise estimate signal (ED) from relatively low amplitude wideband radio frequency interference in frequency bands of other than said one or more narrow frequency bands, controlling gain and/or phase of the noise estimation signals in relation to the differential signal (S), subtracting the first and second noise estimation signals from the differential signal, and compensating for phase differences between the common mode component in the differential signal and each of the first and second noise estimation signals.
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