RFI CANCELLER USING NARROWBAND AND WIDEBAND NOISE ESTIMATORS

摘要

In order to overcome problems when using an adaptive filter for cancellation of common-mode noise in digital subscriber loops, caused by a portion of the differential signal being converted to common mode, which degrades the performance of the filter, a noise cancellation technique is proposed which compensates for this cross- coupled signal energy. In particular, 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 estimation unit derives from the remainder of the common mode signal a second noise estimation signal. Both the first and second noise estimation signals are subtracted from the differential signal. The wideband noise estimation unit comprises a bandstop filter for removing the frequencies detected by the narrowband noise estimator, an analog-to-digital converter for converting the bandstopped signal to digital form, 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.