Abstract: 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.

Abstract: 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 digital noise detector is used to detect one or more noisy frequency bands of the common mode signal and pass only the digitized common mode signal in those detected frequency bands through the adaptive filter to produce a digital common mode noise estimate signal. A control unit adjusts coefficients of the adaptive filter to reduce correlation between the differential signal and common mode signal. It is also proposed to compensate for the effects of stray capacitive coupling across the usual hybrid device by including an equivalent capacitive component in a common mode noise estimation circuit.

Abstract: A noise suppression circuit for a communications channel (10) comprises a hybrid device (11) coupled to the channel for providing a differential output signal corresponding to a received signal. A delay unit (12) delays the differential signal by a suitable amount to allow for the generation and subtraction of a noise estimate. A summing device (13) extracts a digital common mode signal from the channel, and a noise estimation unit (16) provides a common mode noise estimate signal in dependence upon a history of the common mode signal over a predetermined period of time and over a plurality of frequency bands. The common mode noise estimate signal is combined subtractively (19) with the delayed differential signal to cancel common mode noise elements of the delayed differential signal.

Abstract: An high speed analog-to-digital converter, for converting an analog input signal (u(t)) with a maximum frequency (Fmax) to a digital output signal (x(n)) with an output sampling rate (Fs) at least double the maximum frequency (Fmax), comprises a plurality of analog narrowband filters (Fo-FM−1) for filtering the analog input signal (u(t)) to produce a corresponding plurality of narrowband signals (X0-XM−1). Each narrowband filter has a passband. The sum of the gains of the narrowband filters at any frequency within an operating frequency band of the plurality of narrowband filters is substantially unity. Each of a corresponding plurality of analog-to-digital converter units (AD0-ADM−1) comprises a sample-and-hold device (SH) and a quantizer (Q).

Abstract: A high speed analog-to-digital converter, for converting an analog input signal (u(t)) with a maximum frequency (Fmax) to a digital output signal (x(n)) with an output sampling rate (Fs) at least double the maximum frequency (Fmax), comprises a plurality of analog narrowband filters (F0-FM−1) for filtering the analog input signal (u(t)) to produce a corresponding plurality of narrowband signals (X0-XM−1), which is supplied to a corresponding plurality of analog-to-digital converter units (AD0-ADM−1). The converter also comprises sampling and summing circuitry for sampling the outputs of the analog-to-digital converter units sequentially at the predetermined sampling rate (Fs) and summing the resulting sampled signals to produce the digital output signal (x(n)).

Abstract: A method and apparatus for processing an input signal for transmission and/or storage, uses an analysis filter bank (21;51) to decompose the signal into sub-band signals which are used to modulate a plurality of carriers. The carriers are combined into a single encoded signal for transmission/storage. The encoder/decoder is especially applicable to telecommunications systems and recording systems. The analysis filter bank may comprise a multiresolution filter, such as an octave band filter bank (40A/B/C/D . . . 43A/B/C/D) implementing Discrete Wavelet Transform. The modulation may comprise double-sideband, single sideband, quadrature amplitude modulation, and so on. Where the input signal is analog, the carriers may be modulated directly by the sub-band signals. Where the input signal is digital, however, the sub-band signals are interpolated, all to the same rate, and then used to modulate the carriers.

Abstract: A noise suppression circuit for a communications channel (12) comprises a noise reference extraction device (14), for example a hybrid transformer or circuit, for extracting from an input signal (S) a reference signal (NCM) corresponding to a noise component in the input signal and supplying the noise reference signal to a noise estimation unit (16) which derives therefrom a noise estimate (Yj) which is subtracted from the input signal to produce a noise-suppressed output signal (DOUT). The noise suppression circuit comprises a first analog-to-digital converter (24) for digitizing the input signal at a first sampling rate (Fs) and a second analog-to-digital converter for sampling the noise reference signal (NCM) at a second, lower sampling rate (FS/M), the ratio (M) between the two sampling rates being an integer. A decimator (40) decimates the input signal to produce a decimated signal (Dj+Nj).

Abstract: In order to provide DSL service to more subscribers, at least part of the DSLAM is provided at a location, e.g. an outside plant interface unit (16), that is intermediate the subscriber premises (101, . . . 10N) and the central office (13) housing the remainder of the DSLAM. An optical fiber conveys signals between the two parts of the DSLAM, thus reducing the length of the twisted-wire portion of the subscriber loop. To reduce complexity and equipment costs, access apparatus for connecting a plurality of DSL lines to a data network (28) comprises a plurality of interface units connected to a plurality of DSL lines, respectively, for converting high frequency analog signals to digital signals, or vice versa; at least one digital signal processor (DSP) modem (30) for processing the digital signals and routing the processed signals to the data network, and for processing signals from the data network and supplying the resulting digital signals to the interface units, respectively.

Abstract: 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.

Abstract: A noise suppression circuit for a two-wire communications channel comprises a hybrid device, for example a hybrid transformer or circuit, for providing a differential mode signal corresponding to a differential signal received from the two-wire channel. A summing device extracts from the two-wires of the channel a common mode signal and supplies it to a noise estimation unit which derives from the common mode signal an estimate of a noise level in at least one frequency band having a bandwidth considerably narrower than an operating bandwidth for the channel. The noise estimation unit adjusts the amplitude of the noise estimate to correspond to the residual noise in the differential mode signal and subtracts it from the differential mode signal to produce a noise-suppressed output signal. A noise detection and control unit scans the operating band, identifies a frequency band having an instant highest noise level, and sets the noise estimation unit to the detected noisy band.