3com Corporation

2wire, Inc.

Other

The Grass Valley Group, Inc.

3 Com Corporation

U.S. Robotics Access Corp.

Carl H Alelyunas

Andrew L Norrell

Vladimir G Parizhsky

Scott A Lery

Larry S Thomson

Philip Desjardins

Cotter W Sayre

Brian L Hinman

James T Schley-May

Mark A Waldron

Michael Poimboeuf

Bert Buxton

Systems and methods are disclosed for improving DSL performance, including ADSL and VDSL performance, over a local loop between a telephone company central office and a customer premises. In particular, a DSL repeater is coupled to the local loop and amplifies downstream and upstream DSL signals to at least partially compensate for DSL signal attenuation that occurs as DSL signals pass over the local loop. Pursuant to one embodiment, the DSL repeater includes a POTS load coil to improve the POTS, or voice band, transmission over the local loop. According to this embodiment, the DSL repeater provides both improved POTS band signal transmission and DSL service. One embodiment of the load coil includes a coupled inductor having compensating capacitors coupled thereto for counter-balancing the inter-winding capacitance of the coupled inductor. In another embodiment, the load coil includes a high intra-winding capacitance for counter-balancing the inter-winding capacitance of a coupled inductor. Pursuant to yet another embodiment, the load coil comprises a pair of discrete, uncoupled inductors and a low intra-winding capacitance. Still another embodiment includes a pair of discrete, uncoupled inductors having a pair of compensating capacitors coupled thereto for counter-balancing the intra-winding capacitance of the uncoupled inductors. Reducing, eliminating, or counter-balancing the capacitance of the load coil improves the impedance of the load coil to DSL signals improved, thereby permitting sufficient gain to be developed across the load coil.

Load coil and DSL repeater including same

A robust packet arrival time detector using a power estimate to validate a packet arrival time measurement. A packet arrival time measurement is considered valid when the value of the power estimate signal indicates that a packet is being received. A power estimator comprises a bandpass filter, a Hilbert transform, two squaring devices, an adder, and a lowpass filter.

Robust packet arrival time detector using estimated signal power

Method and apparatus for shifting of a lowpass signal to a higher frequency and for precompensating distortion caused by a digital to analog converter (DAC). Higher frequency signals are generated by filtering the output of the DAC so that at least one of the replicas generated by the DAC is the signal of interest. In this manner, the higher frequency signals for wireless transmitters, or for other applications, may be generated more easily. Moreover, compensation for distortion caused by the DAC is performed by a precompensator which modifies for distortion, not at the baseband signal, but at a passband frequency.

Direct digital conversion of baseband signals to super-nyquist frequencies

An apparatus and method for transmitting envelope modulated data signals on a Radio Frequency (RF) carrier system, which produces high error performance through remodulation of the data signals onto an RF carrier are provided. The apparatus includes a transmit chain where, the data signal is input to a mixer to create upper and lower sidebands of the data signal. A low pass filter removes the upper sideband and passes the lower sideband to a frequency modulation (FM) modulator which modulates an RF carrier with the lower sideband. The apparatus also includes a receiver chain that has an FM receiver which receives the FM RF carrier signal transmitted by the transmit chain and recovers the lower sideband, which is then input to a multiplier to again generate upper and lower sideband signals. A bandpass filter removes the lower sideband and passes the upper sideband as a received envelope modulated data signal.

Apparatus and method for FM remodulation of envelope modulated data signals

An interpolating bandpass filter for packet-data receiver synchronization comprises a single delay line that delays the passband-sampled data from the analog-to-digital converter, and a convolving structure that uses the delay line to implement a L-times oversampling bandpass filter. A separate accumulator accumulates a fractional phase difference that represents the frequency offset between the remote transmitter's frequency and the receiver's sampling frequency. The integer portion of the accumulator is used to determine the number of samples to delay the input of the filter, while the fractional portion is used to choose two coefficient sets closest to the desired delay and to interpolate between these two filter sets.

Interpolating bandpass filter for packet-data receiver synchronization

An efficient demodulation and low pass filter structure comprises a shift-add-negate structure that effectively multiplies each received sample by a combined demodulation and filter coefficient, and an accumulator that accumulates the products. Low pass filter coefficients are selected such that the shift-add-negate structure implements multiplications by shifts, adds, and negations. In the preferred embodiment, the demodulation and low pass filter structure outputs three complex samples per symbol.

System and method for efficient demodulation and filtering of a received signal

A method and apparatus for estimating the frequency of a periodic signal and for canceling the interference in a modem signal. Power line noise may interfere with electronic signals. Since power lines may be either 50 Hz or 60 Hz, depending on the country, frequency estimation of the periodic power line noise is necessary. Modem signals are received and autocorrelated in order to identify the periodic characteristics of the signal over time. Once the frequency is identified, the power line noise is modeled based on creating a circular buffer. Initially, the circular buffer is composed of scaled samples of one cycle of the fundamental frequency of the power line noise. Thereafter, samples are received, scaled, and combined with previous buffer values in order to update the buffer. In this manner, the buffer models the power line noise, so that the power line noise may be removed from the system.

Low complexity frequency estimator and interference cancellation method and device

A signal for exception processing is provided. The signal includes a first sequence of PCM codewords. Each PCM codeword in the sequence has a magnitude corresponding to a maximum point within an active constellation. The signal further includes a timing mark following the first sequence. In addition, a client device is provided. The client device includes a receiver and a detector coupled to the receiver. The receiver is coupled to an analog subscriber loop and has a decision feedback equalizer. The receiver provides a decision corresponding to data sent by a digital data source. The detector monitors the decision of the receiver to determine when an exception has been requested by the digital data source. Further, a method of requesting a change in a mode of operation of a client device when the client device is operating in a data mode is provided. The data mode includes receiving signal points selected from an active constellation and deciding which points have been received to thereby recover data. The method includes the step of transmitting, to the client device, a predetermined sequence of points from the active constellation. Each of the points in the predetermined sequence has the same index relative to a maximum point within the active constellation. The method further includes the steps of receiving the transmitted sequence, and detecting the predetermined sequence.

In-Band signal and detector for PCM modem exception processing

Apparatus and methods of compensating for distortions introduced in communication signals received over a telephone network. An adaptive linear equalizer (LE) pre-filter is used for filtering incoming sampled communication signals received via the telephone network transmission medium. An adaptive decision feedback equalizer (DFE) is used in conjunction with the LE to provide error filtering as a hybrid equalizer system to determine which of a plurality of communication states of the sampled communication signals as an accurate estimate of the originally transmitted signals over the transmission medium, responsive to the filtered communication signals from the LE. An error signal is generated relative to the difference between the determined states of the decision mechanism of the DFE and the filtered communication signals from the LE. Further, an error filter provides a filtered output of the generated error signal, wherein the error filter has an error filter characteristic defined in accordance with the known telephone network transmission medium. The LE for the received sampled communication signals has a LE pre-filter characteristic defined in accordance with the filtered output of the error filter, using a recursive least-mean-square (LMS) technique.

Error filtering in a hybrid equalizer system

The present invention provides a method of generating a signal that may be used to determine the characteristic response of a communication channel that utilizes the public Digital Telephone Network (DTN). The channel includes the DTN, which may have Network Digital Attenuators (NDA) and/or Robbed Bit Signalling (RBS), and a Digital-to-Analog Converter (DAC), (also known as a codec), as well as the analog characteristics of the local loop, typically a twisted pair of copper wires. The present invention provides a method and apparatus to determine the optimal sampling instant of the received data stream. The present invention provides a probing signal that is well-suited for use in determining the channel's response to a known sequence of PCM codes used as data symbols. This is especially useful in so-called PCM modulation schemes that utilize the DTN, where knowledge of network and DAC distortion predicates the selection of available PCM codes used to represent data. This information is also useful when the data receiver, or PCM modem, makes determinations of which codes were actually sent.

Method and apparatus for generating a probing signal for a system having non-linear network and codec distortion

A method of detecting the presence of signal impairments that introduce distortion in one or more time slots of a communication link by comparing a received training sequence of signal points with hypothetical received signal points, where the hypothetical points are predistorted versions of the training sequence, and are based on the known, predetermined training sequence of signal points. A detection matrix is formed where one dimension of the matrix corresponds to a time slot within a frame, preferably six time slots to a frame, and the other dimension corresponds to a particular impairment, or combination of impairments. The individual signal impairments are generally one or more of the following: robbed bit signaling where the robbed bit is replaced with a logic `0`; robbed bit signaling where the robbed bit is replaced with a logic `1`; robbed bit signaling where the robbed bit is replaced with a logic `1/2`; 3 dB digital attenuator; 6 dB digital attenuator. The hypotheses are based on individual impairments and combinations/permutations of these impairments. The minimum value of each column (corresponding to a time slot within the frame) of the detection matrix indicates the type of impairment in that time slot.

Method of detecting network impairments for high speed data

Decision-based timing information extraction from a baud-rate sampled digital transmission system. Samples are interpolated from a data sample stream to obtain samples shifted forward and backward in time. A timing metric is applied to the forward and backward shifted sample stream to create forward and backward timing metric values. A timing recovery metric is applied to the forward and backward timing metric values, and is used as a phase feedback term to recover timing information. The method and system yield a very fast, data-driven convergence for baud-rate timing, and does not rely on any specific data sequence. The method and system are used in digital communication devices such as digital modems.

Method and system for timing recovery in a baud-rate sampled data stream

Abbreviated subsystem retraining in a local modem including an information processor having a plurality of subsystems configurable with the information processor for data communications over a first transmission medium, e.g., an analog local loop of a public telephone network. The local modem subsystems are configured with the information processor in accordance with at least one operating characteristic of the first transmission medium, such as the echo characteristics or the like. A remote modem for data communications over a second transmission medium, e.g., a digital telephone network (DTN) is coupled to the first transmission medium for providing an exchange of information between the local modem and the remote modem. The local modem is operable in a retraining mode, responsive to the at least one operating characteristic of the first transmission medium, e.g., echo divergence, observed by the information processor during the exchange of information between the local modem and said remote modem. The local modem then sends an informational signal to the remote modem for reconfiguring at least one of the plurality of subsystems such as the echo canceller with the information processor.

Echo canceller touch-up period in an echo-cancelling modem

A method and apparatus are provided that improve data transmissions in a wireless network, optimized for the transmissions of voice signals, by companding data signals electrically about a spectral shaping module in data handling devices, preferably modems, at both the transmitting and receiving ends of the wireless network. At the transmitting end, the companding is performed by a compressor, electrically preceding a data de-emphasis module, and an expander, electrically succeeding the data de-emphasis module. At the receiving end, the companding is performed by a compressor, electrically preceding a data pre-emphasis module, and an expander, electrically succeeding the data pre-emphasis module. At both ends of the wireless network, companding better serves to facilitate the transmission of data across the wireless network because complimentary functions are performed symmetrically at both ends and because data streams are more complimentarily coupled to, and from, wireless transceivers that similarly perform companding electrically about voice and data streams between the transmitting and receiving ends. Such wireless transceivers being spectrally optimized for voice signal transmissions wherein spectral advantages occurring for voice signals causes spectral disadvantages for data signals within the same transceiver.

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Nevada City, CA, United States of America

Carl H Alelyunas