Abstract: A telephone subscriber line device for providing an interface between a legacy telephone circuit based on circuit-switched technology and a packet network has a legacy interface for connection to telephone circuit; a packet interface for connection to a packet network, processing circuitry for converting between legacy telephone signals and packet signals, and a cascadable expansion bus permitting multiple said devices to be connected to a common port on a packet network. Such a device is highly scalable.

Abstract: A telephone subscriber line device for providing an interface between a legacy telephone circuit based on circuit-switched technology and a packet network has a legacy interface for connection to telephone circuit; a packet interface for connection to a packet network, processing circuitry for converting between legacy telephone signals and packet signals, and a cascadable expansion bus permitting multiple said devices to be connected to a common port on a packet network. Such a device is highly scalable.

Abstract: A decision feedback equalizer is provided which is capable of canceling precursor Inter-Symbol Interference (ISI) even when knowledge of future data is unavailable. A novel DFE algorithm is utilized whereby the detection signal-to-noise ratio (SNR) is increased in two aspects: the precursor contribution is eliminated and the sampling location (relative to the channel response) is positioned at the maximum SNR location. As a result, the loop length for data transmission in a cable can be extended.

Abstract: A zero-delay structure to be used in sub-band echo cancellation systems. In telecommunications, a delay is usually introduced in sub-band decomposition and/or sub-band reconstruction. This invention will help remove this. This structure not only removes the delay but does not sacrifice the performance of the echo canceller. It is to be used in combination with any sub-band-based echo canceller or wavelet echo canceller.

Abstract: A method of canceling echo signals in a telephone network operating in a double talk mode has been developed. A system for implementing the method is also presented. In the invention the conventional normalized least mean square (NLMS) algorithm for echo cancellers is modified such that echo path changes continue to be tracked even after a double talk condition has been detected. The modified algorithm, known herein as a double-talk normalized least mean square (DNLMS) algorithm adaptively adjusts the convergence rate based on the power difference between the echo signal or the residual signal and the far end signal.

Abstract: A nonlinear processor (NLP) for selectively removing or reducing residual echo signals from an acoustic echo canceller associated with a telephony terminal is provided. Low level background noise and near end speech signals pass through the NLP structure substantially unaltered. Distortion, background noise above a preset threshold and echo signals including long duration echoes are replaced with a linear combination of previous noise data.

Abstract: A symbol synchronization and timing recovery method for stabilizing jitter in a data receiver is provided. A one tap LMS algorithm is used for a pre-cursor estimate. A dead zone is set around the desired timing location and the local clock in the receiver is updated only if the timing signal is outside of the dead zone.

Abstract: Algorithms for quickly and efficiently detecting a periodic signal such as a DTMF signal in a telephone system are described. The algorithms, implemented in a tone detector, detect the periodicity of the input data and do not require an estimation of the tone frequency.

Abstract: A circuit for applying a predetermined algorithm to an input signal, has an input for receiving the input signal, a signal processing device for processing the input signal in accordance with the predetermined algorithm, and a device for outputting the processed signal. The signal processing device incorporates distributed bit-serial logic circuits to implement the predetermined algorithm.

Abstract: An echo canceller comprising a first wavelet decomposition block for decomposing a reference signal into a plurality of reference wavelet packets; a second wavelet decomposition block for decomposing an echo signal into a plurality of echo signal packets; an adaptive filter bank for receiving and filtering the reference wavelet packets and in response generating a plurality of filtered output packets replicating the echo signal packets; a plurality of subtracters for receiving and subtracting respective ones of the filtered output packets from the echo signal packets and in response generating and applying a plurality of error signals to the adaptive filter bank for modifying the transfer function of the adaptive filter bank; and a wavelet reconstruction block for receiving and reconstructing the error signals to form a residual signal from which the echo signal has been cancelled. Optimum wavelet filters for the best echo cancellation are provided, as are two wavelet echo cancellation structures.

Abstract: A handsfree telephone circuit has separate transmit and receive audio paths for connection to a microphone and speaker respectively. The circuit comprises a controllable attenuator in each of said transmit and receive paths, an attenuator control responsive to control signals to set the attenuation level of said attenuators, and a separate monitoring circuit connected to each of said transmit and receive paths for sensing audio signals therein. Each monitoring circuit comprises a filter for band limiting the audio signals, a peak level detector receiving said band limited signals, and a speech detector for distinguishing speech from background noise. A switching comparator compares the outputs of the peak level detectors in the two monitoring circuits and produces directional control signals for said attenuator control means to determine which audio path has control. The circuit eliminates "hollow" effect in the speech due to bandlimiting filtering in the audio paths.

Abstract: A digital loudspeaking telephone for connection to a telephone line, including a microphone, speaker, codec and digital signal processor. Incoming and outgoing signals are received by the digital signal processor from remote and local subscribers via the telephone line and microphone respectively. The processor generates and compares incoming and outgoing envelope and noise floor signal levels derived from the received incoming and outgoing signals and in response suppresses a particular compared, and one of the incoming or outgoing signals. Automatic gain control of outgoing signals is implemented in order to allow smooth switching of the outgoing signals and to suppress background noise from being transmitted by the microphone. Room echo and reverberation are also detected, and the processor eliminates spurious channel switching due to the detected echo signals.

Abstract: A digital progess tone detector, for connection to a telephone line and a PABX, comprising circuitry for generating one or more reference tones having user definable frequencies and performing single frequency discrete Fourier transforms on one or more signals received from the telephone line at the defined frequencies, and providing an output signal to the PABX in response thereto. The output signal provides an indication of whether or not a predetermined one or more progress tone frequencies have been detected in the received signals. Because the generated reference tone frequencies are user definable, the present invention can be easily adapted for use in various foreign countries having different progress tone frequency requirements. A preferred embodiment of the invention is implemented on a single microcomputer chip in conjunction with peripherals (such as codecs, crosspoint switches, etc.).

Abstract: A digital progress tone detector, for connection to a telephone line and a PABX, comprising circuitry for generating one or more reference tones having user definable frequencies and performing single frequency discrete Fourier transforms on one or more signals received from the telephone line at the defined frequencies, and providing an output signal to the PABX in response thereto. The output signal provides an indication of whether or not a predetermined one or more progress tone frequencies have been detected in the received signals. Because the generated reference tone frequencies are user definable, the present invention can be easily adapted for use in various foreign countries having different progress tone frequency requirements. A preferred embodiment of the invention is implemented on a single microcomputer chip in conjunction with peripherals (such as codecs, crosspoint switches, etc.).