Abstract: Crosstalk between subscriber loops used to transmit different broadband services through the same bundled telephone cable is a significant limitation to providing digital subscriber line services. A method for estimating the crosstalk, identifying the sources of the crosstalk and predicting additional sources of crosstalk are disclosed. The crosstalk sources are identified in the frequency domain by maximizing the correlation with a “basis set” of received crosstalk PSDs which consist of the cascade of a finite set of known transmit PSDs types times a representative set of crosstalk couplings. Multiple crosstalk types are identified with a technique of successive spectral subtraction. Once a type is identified the crosstalk disturber is compared against all other members of the complete set for that type. Additionally, Mutliple Regression (MR) techniques and a Matching Pursuit (MP) algorithm are used to increase the ability of the system and method to identify various crosstalk disturbers.

Abstract: A digitized input signal is sampled, to obtain a reference input signal. The reference input signal is spuriously whitened, to obtain a pseudo whitened signal. An echo replica signal is generated on the basis of the pseudo whitened signal and an adaptive filter coefficient. A cancellation error signal is obtained on the basis of an echo signal and the echo replica signal. The adaptive filter coefficient is updated on the basis of the cancellation error signal, the adaptive filter coefficient, and the pseudo whitened signal.

Abstract: Real and imaginary components of the discrete Fourier transform (DFT) of the residual echo in an acoustic echo cancellation system are separately estimated using mapping functions derived without an assumption of statistical independence between separate components of a near-end microphone input signal. The residual echo estimator calculates the real and imaginary components using an approximation of the microphone input signal without the echo. A different approximation is used depending on whether the near-end talker and/or the far-end talker are talking.

Abstract: Cascade low-pass filters are useful in attenuating the xDSL band in a POTS splitter. The design of the low-pass filter is a sixth-order filter having two stages. A first stage includes a fourth-order filter, preferably with a stop-band frequency of approximately 48 kHz. A second stage includes a second-order filter in cascade with the fourth-order filter. For this filter, the stop-band frequency is preferably approximately 29 kHz. The inductance value of the second stage is relatively small in comparison to the inductance values of the first stage. In this manner, improvements in xDSL band attenuation are facilitated with little or no eroding of the voice band performance such as insertion loss, pass-band attenuation and return loss.

Abstract: A telephone receiver circuit with sidetone signal generation controlled by voice activity detection in accordance with the present invention uses the voice activity detector (VAD) to detect the presence of voice activity within the microphone signal and dynamically adjust the sidetone signal generation to compensate for noisy environments by eliminating or reducing the sidetone signal in the absence of voice activity. Hence, a sidetone signal is generated in the presence of voice activity, when feedback is required, while the sidetone signal is not generated in the absence of voice activity, since audio feedback for the user is not required then.

Abstract: A method and apparatus that performs specific automatic gain control in an echo canceller (16). The disclosed method and apparatus utilize a low complexity algorithm that performs automatic gain control to achieve greater speed of convergence of the echo canceller (16) and an increased ability to distinguish between near-end speech and echo through the use of specific automatic gain control. A double talk threshold of the echo canceller is adjusted by using, in part, computed gains of inbound and outbound signals internally within the echo canceller in order to adjust the echo canceller double talk threshold.

Abstract: A terminating device for interconnecting service provider wiring with subscriber wiring includes a base, a customer bridge, a removable cover and insulation displacement contacts for terminating the service provider wiring and the subscriber wiring. The insulation displacement contacts for the subscriber wiring are housed within the customer bridge and terminate the subscriber wiring by moving an actuating arm from a disconnected position to a connected position. The insulation displacement contacts for the service provider wiring terminate the service provider wiring by moving a stuffer from a disconnected position to a connected position. The cover includes a locking slide having a movable clasp for deterring unauthorized access to the customer bridge, while permitting authorized access. A plug on the cover and a jack on the base each have a resilient seal that telescope together to effectively seal test contacts located within the jack when the plug is inserted into the jack.

Abstract: System and methods for determining an optimized transmit spectra (spectral distributions of transmission power) for a set of communications channels that experience cross-talk among themselves and for transmitting data on the channels. The transmit spectra are preferably constructed so that largely contiguous frequency bands are allocated to each signaling direction (upstream/downstream) on each communications channel and/or to each channel in the set of channels. In one embodiment, each communications channel is restricted to a maximum time-averaged power. The method preferably includes steps of determining the channel transfer functions of the communications channel, determining interference characteristics of the channels, calculating substantially optimal transmit spectra for the communications channels, and redistributing the frequency bins so that they are contiguously grouped in each transmit spectra. The contiguous groupings allow wider frequency bands for signaling in the channel.

Abstract: A method and apparatus enables echo reduction in a full duplex transceiver system. A replica current is subtracted from a receiver via a first differential circuit path that adaptively matches a time constant associated with a second differential circuit path that connects the receiver with an external data line.

Abstract: A method and apparatus is capable of detecting the presence of a non-linear echo path as well as transitions from non-linear echo path to linear echo path and vice versa. Additionally, when non-linear echo path is detected, the echo canceller (12) is configured to follow a prescribed logic routine that combats possible echo leak-through as a result of compromised cancellation due to non-linearity. This prescribed logic routine affords the echo canceller (12) protection against non-linear echo path by preserving an already converged state of the echo canceller (12) from possible divergence due to the occurrence of non-linearity in the echo path and thereby prevents echo leak-through that would occur due to divergence of the echo canceller (12).

Abstract: A digital subscriber line and POTS voice interface between a telephone line and central office equipment is provided. For POTS band frequencies, a reactive impedance coupled across the two wire interface of the POTS line card, and serially coupled to the line side of the DSL coupling transformer, has an open state magnitude. The magnitude of the line side windings of the DSL coupling transformer is low at POTS band frequencies. POTS band signal power is therefore delivered to the POTS line card. For DSL band frequencies, the reactive impedance across the POTS line card has a closed state magnitude. The POTS line card is therefore essentially short-circuited at DSL band frequencies, and DSL band signal power is delivered to the DSL modem. The frequency band in which the reactive impedance transitions from an open state magnitude to a closed state magnitude corresponds to the frequency band between the POTS frequency band and the DSL frequency band.

Abstract: A base band echo cancellation method and apparatus utilizing Laguerre echo estimation. The method begins with a series of transmitted symbols that are stored in a buffer. The buffer is segmented into a head portion and a tail portion. The symbols in the tail portion are passed through a Laguerre or IIR filter and then reinserted into the tail portion of the buffer. An echo estimation signal is generated based on the symbols in the buffer. The apparatus includes a transmit symbol buffer that is coupled through a modulator to a Laguerre or IIR filter. A demodulator couples the filter back to the buffer. An echo estimator is also coupled to the buffer.

Abstract: A digital direct access arrangement (DAA) circuitry may be used to terminate the telephone connections at the user's end to provide a communication path for signals to and from the phone lines. Briefly described, a means for providing a proper hookswitch transition for a variety of international phone standards is provided. The invention may also be utilized with means for transmitting and receiving a signal across a capacitive isolation barrier. More particularly, a DAA circuitry may be utilized which satisfies many or all hookswitch transition standards without the use of additional discrete devices. The hookswitch transition standards may be satisfied by ramping down the current flowing through the hookswitch prior to transitioning the hookswitch state. In this manner the hookswitch current change as a function of time (di/dt) may be decreased. Thus, the current through the hookswitch may be actively controlled prior to switching the hookswitch from an off-hook condition to an on-hook condition.

Abstract: An echo canceler has its otherwise conventional tapped delay line basis functions augmented with at least one pair of basis functions realizing two quadrature responses of a complex pole. The frequency of this complex pole is selected as substantially equal to the frequency of the dominant pole of a highpass filter inserted into the echo path of the echo canceler, where the dominant pole is the pole closest to the unit circle. This echo canceler arrangement results in a substantial improvement in attainable echo-return-loss enhancement (ERLE).

Abstract: A telecommunications device including a chassis having a card housing for containing a plurality of splitter cards. The card housing includes front and back ends. The front end of the card housing defines an access opening for allowing the splitter cards to be inserted into or removed from the card housing. The device also includes a plurality of card edge connectors for providing electrical connections with the splitter cards. The card edge connectors are located within the card housing adjacent to the back end of the housing. Each card edge connector is arranged in a generally horizontal orientation. The device further includes forwardly facing LINE, POTS and DATA connectors that are electrically connected to the card edge connectors. At least the LINE and POTS connectors are positioned in a generally horizontal orientation.

Abstract: A method and system for improving performance of an echo canceller with low additional complexity. Specifically, the present invention discloses using information from internal variables of Code Excited Linear Prediction (CELP) based codecs in a digital communication network to significantly improve the rate of convergence of the echo canceller. In one embodiment of the present invention, an error signal associated with a voice signal is filtered by a transversal filter using Linear Predictive Coefficients (LPC) coefficients to provide filter transfer functions for a Filtered-X Least Mean Squares algorithm. Additionally, an adaptive filter applies the Filtered-X Least Mean Squares algorithm using the pre-filtered voice signal available in a CELP-based decoder to create a synthetic echo signal which is subtracted from the echo signal for attenuation.

Abstract: A telecommunications device including a plurality of splitter cards mounted in a chassis, a circuit board, and plurality of card edge connectors for providing electrical connections between the splitter cards and the circuit board, and POTS, LINE, and DATA connectors. The circuit board includes three layers, each layer having tracings that electrically connect at least one POTS, LINE, or DATA connector to at least one of the card edge connector. A center layer includes a grounding plane that is adapted to reduce cross-talk between tracings on a top layer and tracings on a bottom layer. The grounding plane is co-planar with tracings on the center layer such that the grounding plane adds additional thickness to the center layer.

Abstract: In a speakerphone system, the signal that is directed to a loudspeaker is filtered by a dynamically controllable highpass filter. The filter characteristics are adjusted on the basis of the power of the signal and the degree of recent microphone activity. The filtered signal is a far-talker signal, while the microphone activity is represented as a near-talker signal that includes an echo component as a consequence of loudspeaker-to-microphone coupling. The degree of microphone activity is determined by a subband analyzer. A noise floor estimator may be used to determine the degree to which the near-talker signal is comprised of background noise, so that the noise can be eliminated in the process of controlling the highpass filter.

Abstract: A general purpose network tone detection method and apparatus that allows the precise and accurate recognition of North American tones (MF, DTMF (Dual-Tone Multifrequency), and CPT (Call Progress Tones)) and international MF-R2 tones as well as taking into consideration other common tones such as Calling Card Service Prompt and Recall Dial. Through the use of the Discrete Fourier Transform (DFT) on small time windows and by providing phase continuity between these windows, the results of the successive DFTs may be combined and processed by a second DFT computation. This second DFT allows higher frequency resolution without requiring the re-computation of the DFT from the time samples. The resulting effect is a tone receiver with both high time and frequency resolution which consequently leads to robust and accurate tone recognition systems conforming even to the most stringent specification while maintaining low computational requirements.

Abstract: An echo canceling apparatus includes a long-response echo canceler that removes an echo of an incoming signal from an outgoing signal by operating on a most recent segment of the incoming signal, stored in a tapped delay unit. The apparatus has a control unit that calculates a cancellation characteristic for each tap of the tapped delay unit. The cancellation characteristics are used to select a subset of taps corresponding to a changing component of the echo, the subset being empty if there is no changing component. A short-response echo canceler, operating on the outputs of the selected taps, cancels the changing component of the echo left uncanceled by the long-response echo canceler. Alternatively, the step gain of the selected taps is increased. The short-response echo canceler is preferably disabled in the double-talk state.