Paradyne Corporation

Conexant Systems, Inc.

At+t Corp.

Rockwell International Corporation

At&t Bell Laboratories

Edward S Zuranski

William Lewis Betts

Kenneth David Ko

Jamal Haque

Shrenik P Patravali

Anthony A Tzouris

Keith A Souders

Manuel I Rodriguez

P Michael Henderson

John S Walley

Steven A Gronemeyer

Joel D Peshkin

Raphael Rahamim

Ganning Yang

Yongbing Wan

Kenneth Scott Walley

Frederic M Stubbe

David O Anderton

Ismail I Eldumiati

Don L Harmer

Gordon F Bremer

Luke J Smithwick

Robert Earl Scott

Kenneth Martinez

Robert E Scott

Chad Balka

David W Springer

A digital subscriber line (DSL) communication system that utilizes the high frequency band of a standard telephone line does not require the use of a plain old telephone service (POTS) splitter in the resident's home, which provided isolation between the POTS frequency band (0 to 4 kHz) and the DSL frequency band. A digital subscriber line modem utilizes either constant envelope modulation or quadrature amplitude modulation for outputting DSL signals upstream to a central office. When a telephone in the resident's home is detected as being off-hook, then the constant envelope modulation is used by the DSL modem in order to lessen the intermodulation product distortion that results in audible noise heard by a user of the telephone. When the telephone is on-hook, then another type of modulation, such as QAM, is used to maximize the upstream data rate capability in the DSL frequency band, since any noise generated by the QAM is not a problem due to the non-use of the POTS frequency band.

Modulation switching for DSL signal transmission

A digital subscriber line communication system does not require the use of a plain old telephone service (POTS) splitter in the resident's home. Digital signal processing techniques are utilized to adapt to varying subscriber line conditions due to POTS telephone equipment. The digital signal processing techniques eliminate the need for a splitter by reducing susceptibility to distortion due to varying subscriber line characteristics. The digital subscriber line modem characterizes the subscriber line under a variety of conditions when the modem is in a non-idle mode. The digital subscriber line modem includes a control circuit which performs rapid retrain operation utilizing line characterization information.

Method of and apparatus for performing line characterization in a non-idle mode in a subscriber line communication system

A digital subscriber line communication system does not require the use of a plain old telephone service (POTS) splitter in the resident's home. Digital signal processing techniques are utilized to adapt to varying subscriber line conditions due to POTS telephone equipment. The digital signal processing techniques eliminate the need for a splitter by reducing susceptibility to distortion due to varying subscriber line characteristics. The digital subscriber line modem characterizes the subscriber line under a variety of conditions. The digital subscriber line modem includes a control circuit which performs rapid retrain operation utilizing line characterization information.

Method of and apparatus for performing line characterization in a subscriber line communication system

A digital subscriber line communication system does not require the use of a plain old telephone service (POTS) splitter in the resident's home. Digital signal-processing techniques are utilized to accommodate varying subscriber line conditions coming from POTS telephone equipment. The digital signal-processing techniques eliminate the need for a splitter by reducing susceptibility to distortion resulting from varying subscriber line characteristics. The digital subscriber line modem can utilize quadrature amplitude modulated (QAM) signals and frequency division multiplexing. The digital subscriber line modem includes a control circuit that implements an echo canceler and an analyzer to reduce near-end cross-talk noise. The analyzer performs spectral analysis to preemphasize or to predistort the transmitted signals in accordance with the cross-talk noise.

Digital subscriber line modem utilizing echo cancellation to reduce near-end cross-talk noise

A digital subscriber line (DSL) communication system that utilizes the high frequency band of a standard telephone line does not require the use of a plain old telephone service (POTS) splitter in the resident's home, which provided isolation between the POTS frequency band (0 to 4 kHz) and the DSL frequency band. Digital signal processing techniques are utilized to adapt to varying subscriber line conditions due to POTS telephone equipment. The digital signal processing techniques eliminate the need for a splitter by reducing susceptibility to distortion due to varying subscriber line characteristics. The digital subscriber line modem utilizes constant envelope modulated signals and frequency division multiplexing, where the constant envelope modulations lessens the intermodulation distortion products due to DSL signals that are transmitted by the modem and which may result in audible noise at the POTS telephone equipment due to non-linearities of the POTS telephone equipment.

Constant envelope modulation for splitterless DSL transmission

A digital subscriber line communication system does not require the use of a plain old telephone service (POTS) splitter in the resident's home. Digital signal processing is utilized to adapt to varying subscriber line conditions coming from POTS telephone equipment. The digital subscriber line modem includes a control circuit that utilizes a Reed-Solomon decoder and a synchronization error generator. The Reed-Solomon decoder provides a frame error signal, and the synchronization error generator responds to the frame error signal to generate a synchronization error signal. The synchronization error generator is configured as a leaking integrator to provide the synchronization error signal in response to a relatively large number of frame error signals occurring in a period of time. A resynchronization operation is performed in the modem in response to the synchronization error signal.

Communication system utilizing Reed-Solomon code to achieve auto frame

A digital subscriber line communication system does not require the use of a plain old telephone service (POTS) splitter in the resident's home. Digital signal processing techniques are utilized to adapt to varying subscriber line conditions due to POTS telephone equipment. The digital signal processing techniques eliminate the need for a splitter by reducing susceptibility to distortion due to varying subscriber line characteristics. The digital subscriber line modem utilizes quadrature amplitude modulated (QAM) signals and frequency division multiplexing. The digital subscriber line modem includes a control circuit which includes a rapid retrain circuit. The rapid retrain circuit can retrain the digital subscriber line modem in less than 0.5 seconds.

Splitterless digital subscriber line communication system

A fast response gain tracker operates to adjust the magnitude of an echo cancellation signal. The latter signal is developed from an echo canceler. The fast response gain tracker provides an adjusted echo cancellation signal that is subtracted from an echo-corrupted received signal to provide an echo-canceled signal. In particular, the fast response gain tracker correlates the echo-canceled signal with the echo cancellation signal from the echo canceler. If the gain of the gain tracker is correct the echo is canceled and there is zero correlation between the echo-canceled signal and the echo cancellation signal. However, if the echo level changes then a residual echo component appears in the echo-canceled signal, which now becomes correlated with the echo cancellation signal. In response, the magnitude of the gain tracker automatically adjusts the gain of the echo cancellation signal to match the change in echo level and thereby subsequently eliminates the residual echo.

Echo canceler gain tracker for cellular modems

A system having an improved startup sequence for connecting two communicating modems, wherein the system includes a calling modem and an answer modem for communicating across an established communication link. Preferably, the system uses V.34 modulation protocol for information transfer after startup. In accordance with one aspect of the invention, an improved startup method includes the step of transmitting a unique calling signal from the calling modem, wherein the calling signal identifies the configuration of the calling modem. The modem 'configuration' includes information relating to the communication capabilities of the modem, as well as information relating to the physical interconnection (or communication link) of the modem. The method further includes the step of transmitting a unique answer signal from the answer modem to the calling modem, wherein the answer signal identifies the configuration of the answer modem. Thereafter, the system operates to analyze the configuration of the calling modem and answer modem to determine whether the established link passes through a hybrid converter circuit. If the established link does not pass through a hybrid circuit, then the system omits line probing and echo training sequences that are typically executed in connection with the V.34 modulation standard. If, however, the established link does pass through a hybrid circuit, then the system proceeds with the execution of the line probing and echo training in accordance with the V.34 protocol.

Rapid startup protocol for communication between a plurality of modems

To improve the signal to noise ratio of the receiver of a transmitting modem, the transmitting modem is equipped with the ability to cancel the far listener echo. Advantageously, doing so allows higher data rates or reduced error rates. Cancellation of the far listener echo is achieved by coupling the signal containing the in-phase, quadrature (also known as X and Y, or real and imaginary) components of the modem transmit signal to a far echo canceller that is included in the modem in addition to the far echo canceller conventionally found in modems. However, the bulk delay employed by the additional far echo canceller is arranged to be a delay of two round trips between the transmitting modem and the receiving modem rather than the conventional single round trip delay of the conventional far echo canceller.

Echo cancellation for modems

To improve the signal to noise ratio of the receiver of a receiving modem, the receiving modem is equipped with the ability to cancel the listener echo. Cancellation of the listener echo is achieved by coupling to the listener echo canceller of the receiving modem the phase corrected adaptive equalizer output signal, which is conventionally found in modems. The phase corrected adaptive equalizer output signal contains the in-phase, quadrature (also known as X and Y, or real and imaginary, components of the) received modem signal at the symbol rate. Advantageously, doing so results in an improved SNR for the receiver of the receiving modem, thus allowing higher data rates or reduced error rates without requiring extension of the length of the modem equalizer. When the telephone network does not introduce any frequency offset of the modem signal in the channel, the listener echo canceller may be simplified to reduce its cost.

Listener echo cancellation for modems

In a simultaneous voice and data communications system comprising two modems, an autorate feature is implemented in one illustrative method by adding a silence detector to the receiver circuitry of at least one of the modems in such a way that noise statistics for the communications channel are only accumulated during intervals of silence. If the resulting noise statistics exceed a predetermined threshold, i.e., the communications channel is too noisy, the receiving modem negotiates a lower data rate with the transmitting modem. In another illustrative method, the transmitting modem provides a signal, which represents an interval of silence, to the receiving modem. Upon receipt of the signal, the receiving modem accumulates error statistics in order to determine if the communications channel is too noisy.

Autorate method for simultaneous transmission of voice data

A communications system simultaneously transmits both a primary data signal and a secondary voice signal in such a way that the dynamic range of the secondary voice signal is increased even though deliberate errors are introduced into the transmitted data portion of the signal. In particular, the communications system includes an error correcting technique like channel encoding and the constellation signal space is divided into a number of regions, where at least one of the regions overlaps with another region. The primary signal is channel encoded to select a particular one of the number of regions, the region being represented by a reference signal point value. The voice signal is encoded to provide a signal point vector, which is added to the reference signal point in such a way that the resultant signal point is located in the overlapping region thereby deliberately introducing an error into the resulting transmitted signal point stream. Notwithstanding the deliberately introduced error, the channel encoding of the primary signal allows a receiver to recover the originally selected reference signal point value, which when subtracted from the received signal point value approximates the voice signal.

Method for increasing the dynamic range of a signal in a simultaneous

The present invention discloses an improvement over existing techniques for transmitting data over voice-band telephone channels by automatically adapting the amount of warping or compression that is applied to a sequence of signal points. A sequence of warped signal points, each of which is related to a respective signal point of a predetermined base constellation according to a warp function, is received in a decoder via a transmission channel having a non-linear component. After each of the received signal points is unwarped using substantially an inverse of the warp function, the average dispersions of the received inner and outer signal points about corresponding sequences of expected signal points are calculated. The difference between the average dispersion of the inner and outer points is then computed and used to update the amount of warping or compression in order to further minimize the effects of the channel non-linearity. The desired amount of warping is communicated to the transmitting encoder.

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Largo, FL, United States of America

Edward S Zuranski