Abstract: A grounding key detecting device and method for interference-proof detection of the operation of grounding keys in telephones. A circuit that detects the operation of a grounding key includes a current detection device configured to detect a current flowing when the grounding key is in operation, a comparator configured to compare the detected current with at least one threshold value, and a monitoring circuit configured to detect a first period when the current exceeds the threshold value, detect a second period when the current drops below the threshold value, and output a grounding key detection signal when the first period is greater than the second period.

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: 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: 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: The present invention includes a method and system for compensating for cross-talk interference in communication systems. The method includes estimation of the interfering signals. Further, the method includes performing a compensation operation on at least one interfering signal.

Abstract: A circuit arrangement prevents clipping of pulse metering (teletax) signals in a telephone line card channel that results from the differential impedance between a subscriber line interface circuit (SLIC) and the line at the frequency band of teletax signals. The circuit arrangement is configured to sense pulse metering signals through a delay circuit, which is coupled to a reflected signal cancellation circuit. The reflected signal cancellation circuit contains a transconductance amplifier circuit that generates a pair of complementary polarity output currents representative of the sensed teletax signal. One of these output currents is fed back to a programmed impedance element in the transmission channel path of the SLIC so as to effectively cancel the reflected teletax signal.

Abstract: In at least one embodiment, a current mode differential active hybrid circuit having an H-bridge output driver with a first output resistor coupled across a transmission medium output. Drive circuitry is coupled to the output H-bridge and constructed to supply data modulated signals to the output H-bridge. A second H-bridge is coupled to the drive circuitry in parallel with the output H-bridge to allow a second output across a second output resistor.

Abstract: In accordance with a first aspect of the present invention there is provided a telephone apparatus including a transmitter portion and a receiver portion, an input transducer for converting input audio signals into electrical signals, a connectable input link between the input transducer and the transmitter portion to deliver when connected an input electrical signal to the transmitter portion to be transmitted by the transmitter portion, an output transducer for converting an output electrical signal into an audio signal and a connectable output link between the receiver portion and the output transducer for delivering when connected an output signal to the output transducer, optionally an echo cancellation circuitry portion adapted to sample the output signal and produce an echo replica signal, optionally a mixer included in the input link for mixing an echo replica signal produced by the echo cancellation circuit with an input signal produced by the input transducer, and an echo suppression circuitry porti

Abstract: An apparatus for reducing electromagnetic interference on signals being communicated through one or more communications conductors is disclosed. The apparatus of the present invention is preferably situated in a communications circuit having a first area for receiving one or more communications conductors and an intermediate ground, and a second area having a reference ground. The apparatus includes one or more first capacitors, where each first capacitor is coupled between a communications conductor and the intermediate ground, and a second capacitor coupled between the intermediate ground and the reference ground. In preferred embodiments, the first area is a telephone network voltage (TNV) area, the second area is a secondary extra low voltage (SELV) area, the first capacitors are regular high voltage capacitors, and the second capacitor is a Y capacitor.

Abstract: An apparatus and method to implement a highly efficient low power line driver. In a first embodiment, the invention provides a method to increase the power efficiency of a line driver. The method includes supplying a digital signal processor output to a first subtractor; supplying the first subtractor output as an input to a modulator of a line driver; subtracting the line driver output from the digital signal processor output at the first subtractor; filtering the line driver output with a low pass filter; routing the line driver output to an impedance match filter; providing a first analog-to-digital converter and a second subtractor to subtract the line impedance match filter output from the low pass filter output; providing a digital filter and a second analog-to-digital converter; and subtracting the digital filter output from the first analog-to-digital converter output at a third subtractor to output a feedback signal to the digital signal processor.

Abstract: In an electronic system having logic agents that communicate with each other through one or more signal lines, a method for testing high speed digital signaling on the signal lines is disclosed. The method involves sensing a first crosstalk signal induced by a first digital signal. The first digital signal is driven by a first logic agent into a signal line to communicate with a second agent. The second agent is coupled to receive the first digital signal from the signal line. A logic waveform that represents the digital signal is recorded and/or displayed, based upon the crosstalk signal. The technique may also be used for testing simultaneous bidirectional signaling on the same signal line.

Abstract: For measuring the influence of noise on the talking quality of a telephone link in a telecommunications network, a talker speech signal (s(t)) and a degraded speech signal (s′(t)) are fed to an objective measurement device (22) for obtaining an output signal (q) representing an estimated value of the talking quality. The degraded signal includes a returned signal (r(t)) originating from the network during transmission of the talker speech signal over the telephone link. The objective measurement carried out by the device is a modified PSQM-like measurement, which is modified as to include a modelling (32b) of masking effects in consequence of noise present in the returned signal. Preferably the modelling includes a noise suppression (42) carried out to a difference signal (D(t, f)) in the loudness density domain using a noise estimation (41).

Abstract: A communication circuitry for providing effective detection of tones in a communication network. The communication circuitry comprises filtration circuitry, summation circuitry, detection circuitry, and interface circuitry. The filtration circuitry is coupled to the summation circuitry and is configured to receive a communication, process the communication to estimate an echo return in the communication, and provide the estimated echo return to the summation circuitry. The summation circuitry is coupled to the detection circuitry and configured to receive the estimated echo return from the filtration circuitry, receive a tone transmission and echo return from the interface circuitry, subtract the estimated echo return from the tone transmission to generate a substantially pure tone, and provide the substantially pure tone to the detection circuitry. The detection circuitry is configured to receive the substantially pure tone and process the substantially pure tone to perform a programmed operation.

Abstract: A low-pass filter arrangement associated a clamping circuit for limiting unwanted transient signals to be transmitted through the filter. Mainly the variations (dI/dt) of the current flowing through the filter are eliminated. The filter may form part of a splitter used in an ADSL system to separate low frequency POTS signals from high frequency ADSL signals simultaneously transmitted over a same copper twisted-pair transmission line. The filter comprises the series connection of a coil and the main path of a transistor of which the gate terminal is connected to the opposite end of the coil. In an ADSL system, a classical 7th order low-pass filter may advantageously be replaced by a 3rd order filter arrangement.

Abstract: In a splitterless xDSL communications services set-up providing data and voice services to co-connected equipment, data signals may cause audible interference in POTs handsets. The degree of the interference varies widely due to a wide variation of customer tolerance and of susceptibility of the handsets. Reducing data channel transmission power during an off-hook event may reduce interference. A method and system are provided for user adjusted cutback. While making a POTs call, data channel power may be adjusted until acceptable performance is obtained. The customer selected power cutback influences both ATU-R and ATU-C transmit levels.

Abstract: A device and method of eliminating the interference to a voice command from the sound from the speaker, thereby improving the success rate of speech recognition even in the presence of the direct and echoed sound.

Abstract: A balanced spectrum limiter for limiting the frequency spectrum of signals transmitted through a telephone or communication system includes one or more filters and an energy surge protection circuit. Each filter includes a pair of inductors wound around a single core and a capacitor connected between the two inductors. The energy surge protection circuit can be any type of energy surge protection circuit known in the art. The range of frequencies which can be transmitted is determined by the filter. The filter is removably connected to the energy surge protection circuit so that filters of varying parameters may be easily interchanged.

Abstract: The present invention provides a method and apparatus for eliminating or reducing local area and broad area interference in a twisted pair transmission system. The apparatus of the present invention includes a detection device, such as an antenna, for example, for detecting electromagnetic interference coupled into a twisted pair line, a sampling/scaling device which samples and scales the detected signal, and a combiner device which combines a signal correction component with the signal received over the twisted pair by a differential receiver. The sampling/scaling device preferably includes an analog-to-digital converter (ADC) which converts the detected analog signal into a digital signal and a digital signal processor, which receives the digital signal from the ADC and processes the signal to generate a correction signal. The correction signal is then subtracted from the signal received by the differential receiver. The sampling/scaling device may be fixed or adaptive.

Abstract: A communication apparatus includes circuitry operable to facilitate communication over a digital subscriber line. The apparatus also includes a filter operable to be coupled between the circuitry and the digital subscriber line. The filter has a corner frequency and is operable to attenuate transients associated with the circuitry when the apparatus is in use. The filter is tuned to an impedance of the circuitry.

Abstract: In a system including a plurality of telephones coupled to an asymmetric digital subscriber line, a circuit operable to facilitate communication using the asymmetric digital subscriber line includes a filter having a corner frequency and being operable to be coupled between one of the plurality of telephones and the asymmetric digital subscriber line. The filter is also operable to attenuate transients associated with the telephone operating in an off-hook state. The circuit also includes a switch coupled to the filter. The switch is operable to effect a change in the corner frequency of the associated filter depending on whether the telephone coupled to the filter is operating in an on-hook or an off-hook state, the change in the corner frequency operating to attenuate parasitic interference associated with telephones in an on-hook state.

Abstract: A receiver for high-speed data communications, which receives a differential signal through a pair of signal lines. The receiver includes a common-mode choke, which has first and second signal windings, which are respectively coupled in series to the pair of signal lines so as to attenuate common-mode interference in the differential signal. The choke also has a sampling winding, which is inductively coupled to the signal windings so as to generate a sampled signal responsive to current flowing in the signal windings. Signal processing circuitry is coupled to receive the sampled signal from the sampling winding and to receive the differential signal from the signal windings and to process the differential signal responsive to the sampled signal.

Abstract: A method and apparatus are provided for reducing the amplitude of signals that often are inadvertently coupled to a telephone line from an isolation barrier system, or that cause undesirable interference within the circuitry of the isolation barrier system. Such signals have undesirable peaks in the frequency domain (spectral peaks) due to the existence of periodicities in the data signal that is transmitted across the isolation barrier. Such spectral peaks are reduced by this invention, which comprises randomizing or scrambling the data signal before it crosses the isolation barrier, and descrambling the data after it has crossed the isolation barrier. In one embodiment, the data signal is scrambled by combining it with a random bit stream (or a pseudo random bit stream), which effectively “whitens” the resulting scrambled signal, thus removing spectral peaks that exist in the original data signal.

Abstract: A method of and apparatus for noise reduction for a transceiver transmitting frames over a transmission medium in a frame-based communications network. A transceiver transmit path and a transceiver receive path is provided. A blocking switch is located in the transceiver transmit path, the blocking switch allowing transmit signal propagation when enabled, while preventing both transmit signal propagation and circuit device noise coupling from the transceiver transmit path to the transceiver receive path when the blocking switch is disabled. The blocking switch is disabled when the transceiver transmit path is not transmitting frames over the frame-based communications network.

Abstract: A system for processing audio signals in two channels, wherein each channel includes a plurality of band pass filters for dividing the signal in each channel into a plurality of bands and a plurality of variable gain amplifiers coupled one each to a band pass filter. Control logic coupled to the variable gain amplifiers prevents the signals in adjacent bands within a channel from being attenuated simultaneously. The control logic attenuates the signals in one channel in accordance with the signal in the corresponding bands in the other channel. In some circumstances, the signal in the band in the one channel is attenuated.

Abstract: A process for noise reduction during the transmission of acoustic useful signals includes the following steps:

Abstract: A system and method for determining transmission characteristics for a communications channel and for transmitting data on the communications channel. In one embodiment, the method starts by determining the channel's transfer function and determining interference characteristics for the channel. The interference characteristics preferably include transfer functions describing the channel's susceptibility to cross talk from neighboring channels. The channel transfer function and the interference characteristics are then examined and a transmit spectrum (or power spectral density function) is constructed for the channel. The transmit spectrum preferably uses orthogonal separation of upstream and downstream communications to increase channel capacity.

Abstract: A system for determining FEXT and ELFEXT of generic cabling systems provides accurate measurements of these parameters by determining and removing the effect of the connectors at the respective ends of the link, thereby giving measurement values that correspond to the defined link, rather than including the crosstalk contributions of the connectors, which can be substantial.

Abstract: A transmission system comprises a plurality of transmission apparatuses which use a single channel commonly. Each transmission apparatus comprises switches for connecting and disconnecting transmission paths with adjacent transmission apparatuses, a line signaling-signal monitoring and detecting portion, and a network dividing logic portion which opens and closes the switches based on an output of the line signaling-signal monitoring and detecting portion. The network dividing logic portion closes switches of transmission paths between transmission apparatuses which perform a telephone conversation and opens the other switches.

Abstract: The present invention provides a method and apparatus for eliminating or reducing local area and broad area interference in a twisted pair transmission system. The apparatus of the present invention comprises a detection device, such as an antenna, for example, for detecting electromagnetic interference coupled into a twisted pair line, a sampling/scaling device which samples and scales the detected signal, and a combiner device which combines a signal correction component with the signal received over the twisted pair by a differential receiver. The sampling/scaling device preferably comprises an analog-to-digital converter (ADC) which converts the detected analog signal into a digital signal and a digital signal processor which receives the digital signal from the ADC and processes the signal to generate a correction signal. The correction signal is then subtracted from the signal received by the differential receiver. The sampling/scaling device may be fixed or adaptive.

Abstract: A transmission line impedance matching apparatus is disclosed that limits longitudinal signals and matches the longitudinal characteristic impedance between two conductors and comprises a common mode choke and an impedance matching device. The common mode choke, comprising two windings wound in the same direction, acts as a high impedance to longitudinal high frequency signals. As a result of this, standing waves are caused by the metallic signals reflecting off the choke. The impedance matching device, comprising two windings wound in the same direction, provides a good match to the longitudinal characteristic impedance and thus reduces standing longitudinal waves and reflections. The apparatus may include a terminal corrector or a mid-line corrector, or a combination thereof. This invention may allow greater bandwidth to be dedicated to services and allow transmission over longer subscriber loops before the minimum S/N ratio is achieved.

Abstract: A Radio Frequency Interference Filter (10, 12) is connectable in series in the tip (T) and ring (R) branches of a telephone circuit. A first suppression stage (20) has a first inductor (L1) connectable to the tip (T) branch of the circuit and a second inductor (L2) connectable to the ring (R) branch of the circuit. The second suppression stage (22) of one embodiment of the filter (10) has a transformer (T1) with one winding (W1) connected in series with the first inductor (L1) for the tip (T) branch of circuitry and the second winding (W2) connected in series with the second inductor (L2) for the ring (R) branch of circuitry. In a second, alternative embodiment of the filter 12, the second suppression stage (22) has one ferrite-core inductor (L3) connected in series with the first inductor (L1) for the tip (T) branch of circuitry and a second ferrite-core inductor (L4) connected in series with the second inductor (L2) for the ring (R) branch of circuitry.

Abstract: Modems using a telephone line for high speed communications between them are arranged to monitor crosstalk from other existing communications systems with which they may mutually interfere, and adjust the power spectral densities (PSDs) of their transmitted signals to reduce overlap between the PSDs of the different systems, thereby reducing near end crosstalk. Communications can thereby be optimized for whatever crosstalk conditions may exist. The modems can have a master-slave relationship for communicating buffered frames in a half-duplex manner using a collision avoidance protocol for computer network access. Analysis of monitored crosstalk PSD information can be performed by each modem, by the master modem, or by a separate computer on the network. A digital signal processor used in each modem for receiving signals can be configured to be used at other times for the monitoring of crosstalk.

Abstract: This invention relates to telecommunications systems. In a subscriber loop carrying high speed data signals, noise cancellation is achieved by a data signal demodulator having first and second inputs 81,82, arranged to receive differential data signal and local field RFI input signals respectively. A feedback signal of the demodulator is sampled, processed, vector modulated and then combined with the local field RFI input signal of the demodulator. The combined signal is summed with the differential input signal to thereby reduce interference coupled with the first input.

Abstract: An isolation regulator including a regulator circuit couples a source of power to an electrically noisy dc load connected in parallel with a load capacitor. Peak noise across the load is used to control the regulator circuit to set the current level to the load and determine the operating set point of the regulator circuit which includes a FET operated close to saturation to minimize the voltage drop across the FET. The illustrated electrically noisy dc load is a dc motor and the peak noise is the peak ripple across the motor which is monitored and compared to the saturation voltage of the FET. Positive peaks of the ripple, which could cause the FET to saturate, control the regulator circuit to reduce current flow and prevent saturation. Current provided by the regulator circuit increases gradually over time and is reduced as necessary by positive peak ripple signals to provide stable current flow to the dc motor. As illustrated, the dc motor drives a fan which cools associated electrical equipment.

Abstract: A two-wire line and a four-wire line telephone system interface with each other through a hybrid (12). After a connection between the two and four-wire line systems is made, an echo canceler (10) provides training signals to the hybrid on the transmit path an generates echo cancellation signals on the receive path. An adaptive filter (16) is employed to provide the proper echo cancellation signals, while a controller (22) provides filter coefficients based on an error signal. The training signals include the convolution of an impulse function with a sin(x)/x function. Once the filter coefficients are determined for the particular call, the transmit path of the four-wire line system is switched in and voice data between the two systems my commence.

Abstract: A speech processor uses a plurality of speech processing features to enhance the quality of speech signals received by a user during a telephone call. The activation of a second speech processing feature is delayed for a time duration measured after the initiation of a particular call or measured after the activation of a first speech processing feature. This delay eliminates any interference between the second speech processing feature and the first speech processing feature that is active when the call is initiated. The delay also increases the time it takes for the speech processing features to become fully effective, thus making the enhancement in the quality of the speech signals more noticeable to the user. Further, an optionally generated audio indicator is provided when the second speech processing feature is applied so that the additional feature is even more noticeable to the user.

Abstract: A termination is provided for a differential transmission line such as unshielded twisted pair (UTP) to isolate a connected device from electromagnetic interference present on the UTP in the form of differential mode and common mode noise. An example of an electromagnetic interference isolator comprises a common mode and a differential mode termination, a common mode choke which exhibits substantially constant impedance over a wide bandwidth and a centre tapped isolation transformer.

Abstract: A noise reduction filter (28) is provided. The noise reduction filter (28) comprises a signal analysis block (30). The signal analysis block (30) is operable to receive an input audio signal and to determine a short term signal level. A noise floor block (32) is coupled to the signal analysis block (30). The noise floor block (32) is operable to receive the short term signal level from the signal analysis block (30) and to determine a noise floor level based upon the value of the short term signal level. A noise factor block (34) is coupled to the signal analysis block (30) and to the noise floor block (32). The noise factor block (34) is operable to receive the short term signal level and the noise floor level and operable to calculate a noise factor. A multiplier node (36) is coupled to the noise factor block (34) and receives the input audio signal.

Abstract: An EMC filter for a balanced multi-wired telecommunication line has an oblong closed magnetic path core 50 having at least one first core arm 50a with a first length and second core arms 50b with a second length which is equal to or shorter than the first length, and a plurality of coils 51 constituted by at least one pair of wires. The at least one first core arm 50a and the second core arms 50b constitute a closed magnetic path. The wires of each pair are closely positioned each other and wound around the at least one first core arm 50a so as to produce magnetic fluxes in the first core arm 50a flowing toward the same direction when a common-mode current flows through the wires. Each of the coils 51 has a signal input end and a signal output end, and the wires run in a one-way direction from the signal input ends to the signal output ends, respectively.

Abstract: A circuit for, and method of, reducing cross-coupled interference between first and second telephone lines of a multi-line telephone instrument and a telephone instrument containing the same. The circuit includes: (1) a first differential input amplifier having first tip and ring inputs coupled to conductors of the first telephone line and first tip and ring shunt resistors coupling the first tip and ring inputs to a signal reference of the telephone instrument and (2) a second differential input amplifier having second tip and ring inputs coupled to conductors of the second telephone line and second tip and ring shunt resistors coupling the second tip and ring inputs to the signal reference, the first and second tip and ring shunt resistors decreasing a common mode input resistance of the first and second differential input amplifiers, thereby attenuating cross-coupled interference common to both of the first and second telephone lines.

Abstract: A printed circuit board for connectors in symmetrical communications and data systems engineering distribution systems, which includes a pair of substantially parallel circuit board tracks on a front face thereof arranged substantially congruently with a pair of substantially parallel circuit board tracks of a back face of the printed circuit board, and wherein one of the pair of tracks on the back face crosses over the other track of the pair by means of two through-hole platings, which are electrically interconnected on the front face through an interconnecting circuit board track.

Abstract: A termination is provided for a differential transmission line such as unshielded twisted pair (UTP) to isolate a connected device from electromagnetic interference present on the UTP in the form of differential mode and common mode noise. An example of an electromagnetic interference isolator comprises a common mode and a differential mode termination, a common mode choke which exhibits substantially constant impedance over a wide bandwidth and a centre tapped isolation transformer.

Abstract: An electromagnetic interference by-pass filtering mechanism suppresses RF noise currents conducted over the tip and ring leads of a telephone line-powered telephone instrument. Such RF noise currents may result from amplitude modulated radio broadcast signals emanating in the vicinity of the telephone instrument. The filtering mechanism comprises a conductive material coated on the interior surface of the housing of the telephone instrument, so as to surround the printed circuit board containing the telephone circuitry of the instrument. The conductive material is coupled to earth. First and second capacitors are coupled between the tip and ring leads and the conductive material, and first and second inductors are coupled in series with the tip and ring conductors and connections of the tip and ring conductors to the printed circuit board containing the telephone circuitry.

Abstract: A facility is provided in a telecommunications network which causes Digital Speech Interpolation (DSI) apparatus to transmit noise signals toward a destination if the level of the noise signals at least equals a predetermined threshold value, in which the predetermined threshold value is selected, in accord with an aspect of the invention, as a function of a type of telephone service subscribed to by the telephone station set involved in the associated telephone call.

Abstract: A high speed signal transport system (10) provides data transmission across a balanced channel (14). The balanced channel (14) carries differential signals from the output of a differential transmitter (12). An equalizer (18) compensates for distortion in the balanced channel in order to reduce timing jitter of the signal. The signal is applied to the input of a differential receiver (20) which exploits the precise quantization threshold inherent in differential data to accurately convert the signal to digital data. The differential receiver (20) also employs a known frequency reference along with digital transition detection to rephase the digital data to the local clock. No duty-cycle limitation is placed on the signal carried by the balanced channel (14) and therefore the differential transmitter (12) and differential receiver (20) are not required to encode the signal.

Abstract: The device comprises a first input (E1) and a first output (S1) which are capable respectively of receiving and delivering a plurality of analog signals and corresponding digital signals having different predetermined types of transmission specifications and associated with substantially homothetic predetermined elementary frequency attenuation templates. A second input (E2) and a second output (S2) are also provided, capable respectively of receiving and delivering a plurality of digital signals and corresponding analog signals having different predetermined types of transmission specifications, associated with different, substantially homothetic predetermined elementary frequency attenuation templates, as well as first and second signal conversion means arranged respectively between the first input and output and between the second input and output and including a single digital filter (6) in common, having a single frequency attenuation template which is compatible with all the elementary templates.

Abstract: An apparatus that automatically adjusts the adaptation block size for a least-mean square (LMS) adaptive filter depending on the input signal-to-noise ratio (SNR) is disclosed. The apparatus monitors the instantaneous SNR and continually adjusts the block size to provide high noise immunity, thereby increasing the convergence speed of the filter and decreasing the asymptotic mean-square error. An exemplary embodiment of the present invention is presented in the context of acoustic echo cancellation, though it is noted that the adaptive filter of the present invention is useful in any environment in which the noise characteristics are subject to change.

Abstract: In a quaded cable, coupling between circuits (side circuit 1, side circuit 2, and phantom circuit) is compensated for at the receiving end of a transmission system. By transmitting known signals from the transmission end separately on each circuit, coupling between circuits is initially estimated by measuring the signals received at the opposite end on each of the circuits. Following startup, during data transmission the received data signals are modified in accordance with this initially determined coupling between circuits to produce estimated transmitted data signals. During data transmission the coupling between circuits is reestimated by storing (303) N data signals received on each circuit and the corresponding N estimated transmitted data signals on each circuit. The coupling between circuits is determined as a function of the covariance of these N received signals on each circuit and the covariance of these N estimated transmitted data signals on each circuit.

Abstract: A circuit for synthesizing an impedance associated with a telephone subscriber's circuit connected to a two-wire telephone line is described. The circuit of the invention is adapted to synthesize a complex impedance which can function both as a termination impedance and a balance impedance. The termination impedance utilizes a positive feedback loop structure having a loop gain which is at all times less than unity. The circuit that implements both the termination and balance impedances with sidetone suppression is also described. Each of the embodiments is realizable with a single external component consisting of a resistor.

Abstract: Adaptive analog equalizer permitting 16 Mbit/s token ring (TR) transmission over unshielded twisted-pair (UTP) cables. The equalizer (29) is located at the wiring concentrator (25), and consists of a variable and a fixed filter section. The existing TR receiver (49) and transmitter (53) remain unchanged. To compensate for distortion introduced by the cable section (19b) preceding the equalizer, the level of the signal (B) at the equalizer output (35) is used as a control criterion. The additional distortion contributed by the cable section (21a) following the equalizer is accounted for by measuring the level of the signal (D) received from the transmitter (53) of the next TR station. By these two measurements, the equalizer is adjusted such that the cable-length dependent distortion is eliminated at the next receiver (49).