Abstract: To reduce the ISDN crosstalk in an incoming DSL signal, a crosstalk canceller observes at least a portion of the crosstalk signal and reproduces an estimate of the crosstalk signal for at least a portion of that signal within the DSL band. The crosstalk canceller applies a canceling signal based on the estimated crosstalk signal to reduce the crosstalk in the received DSL signal.

Abstract: Transceiver training is optimized for xDSL modems operating in TCM-ISDN environments under NEXT and FEXT interference. Current ITU-T draft recommendations provide for dual bitmaps that are switched synchronized with the burst cycle of TCM-ISDN to provide a data stream having dual bit rates. These recommendations also provide for a single bitmap mode where the NEXT bit map is off. Prior to transceiver training, a modem does not know which mode has been selected. Transceiver training is optimized if the mode selection is known prior to transceiver training and the training signals are designed properly for the selected mode. To accomplish this, the mode selection is exchanged early in the modem initialization process, for example, during initial handshaking. By exchanging the mode selection earlier in the modem initialization process, the modem is able to improve transceiver training and configure properly for the type of data communication (e.g., full-duplex, half-duplex).

Abstract: A system used to synchronize the clock frequency of a receiver with that of a transmitter, where both the receiver and transmitter communicate using the ADSL Annex C standard. The transmitter continuously transmits pilot tones to the receiver. The receiver determines the phase error between sequential pilot tone symbols to determine a phase error. The receiver uses the phase error to adjust the receiver clock frequency. However, if the most recently received symbol is subject to near end crosstalk or is subject to far end crosstalk and is a boundary symbol, the receiver ignores the phase error and does not adjust the receiver clock frequency.

Abstract: Techniques are disclosed for obtaining and maintaining synchronization of the TTR clock during a Channel Discovery Phase of DSL transceiver initialization for a DSL service operating in a TCM-ISDN crosstalk environment. The customer premises DSL transceiver achieves synchronization of its TTR clock throughout the Channel Discovery Phase of the DSL initialization procedure using a TTR indication signal transmitted by the central office transceiver. In addition to enabling basic communications, keeping TTR synchronization improves the accuracy of quiet noise measurement and the reliability of message exchanges, even on very long and noisy loops.

Abstract: The present invention provides techniques for performing loop diagnostics in DSL communication systems.

Abstract: A system used to synchronize the clock frequency of a receiver with that of a transmitter, where both the receiver and transmitter communicate using the ADSL Annex C standard. The transmitter continuously transmits pilot tones to the receiver. The receiver determines the phase error between sequential pilot tone symbols to determine a phase error. The receiver uses the phase error to adjust the receiver clock frequency. However, if the most recently received symbol is subject to near end cross talk or is subject to far end cross talk and is a boundary symbol, the receiver ignores the phase error and does not adjust the receiver clock frequency.

Abstract: Techniques for establishing TTR indication in ADSL Annex C based communication systems are disclosed. The techniques enable, for example, hyperframe alignment and synchronized initialization procedures (e.g., G.hs).

Abstract: A technique for training an equalizer of an ADSL Annex C transceiver is provided. The technique defines the points in the transmission sequence at which equalizer training should take place, and what symbols comprising the transmission should be used for training. The technique avoids the effect of strong TCM-ISDN cross-talk noise. The equalizer is trained so as to achieve optimal communication channel performance. During the TEQ training phase, the cyclic prefix is not introduced. The TEQ is trained only on FEXT symbols except the FEXT symbols adjacent to NEXT symbols. In the early phase of FEQ training, the cyclic prefix is not introduced. The FEQ is trained on FEXT symbols only except the FEXT symbols adjacent to NEXT symbols. During a late training phase after the cyclic prefix is introduced, the training of the FEQ is continued by using signals received on all FEXT symbols only.

Abstract: A Single Ended Line Probing (SELP) technique using combined Frequency Domain Reflectometry (FDR) and Time Domain Reflectometry (TDR) for characterizing a transmission medium (e.g., DSL) is disclosed. FDR is used to detect one or more reflectors (e.g., short, load coil, bridge tap) in the transmission medium. TDR is then used to determine the location of the reflectors in the transmission medium. In one embodiment, a wide band periodic probing signal is used to probe the transmission medium for reflectors. In another embodiment, gauge information can be used to increase the valid range of the combined FDR/TDR SELP technique.

Abstract: The taps of an equalizer are used as inputs to a discrete Fourier transform (DFT). Certain spectral components are extracted from the DFT and used to estimate the frequency difference. The frequency difference estimate is filtered using a phase locked loop and used to adjust one clock to synchronize the transmit and receive clocks.

Abstract: A metering tone is applied to a transmission line by a DSL modem on behalf of a voice circuit, rather than being applied directly by the voice circuit. Various techniques for applying the metering tone to the data path are described. Because the metering tone is passed to the network in the data path rather than in the voice path, the tone is subject to the high-pass filtering associated with the data path rather than the low-pass filtering associated with the voice path. Accordingly, the metering tone is not attenuated by the splitter or by analogous features in a splitterless system.

Abstract: Robust techniques for signaling the likes of exit/entry into low power idle mode, bit swapping, rate adaptation, rate repartitioning and other multicarrier communication system events and control functions are disclosed.

Abstract: Techniques described herein can be used at least by transceiver systems based on G.992.1 and G.992.2 to allocate management/control information for transmission using DMT symbols. In one embodiment of the present invention, a separate management/control information channel is allocated independent of interleaved and fast paths. Advantageously, if management and overhead information need to be transmitted quickly or often, valuable data payload bandwidth of the fast path is not used and the slow transmission of the interleaved path is avoided. In another embodiment of the present invention, a management/control information channel may be allocated independent of interleaved and fast paths, but distinct path specific sync bytes may be allocated to one or both of the interleaved and fast paths to carry path specific information.

Abstract: Framing techniques for ADSL systems that allow programmable fixed overhead efficient framing and seamless rate changes.

Abstract: A Digital-Subscriber Line (DSL) modem reduces signal peaks by digital processing. The peak-to-average ratio (PAR) is effectively reduced by the PAR reduction when the signal peaks are reduced before transmission. The DSL transmitter uses discrete multi-tone (DMT) signaling in which multiple carrier waves in different frequency bins simultaneously carry multiple data bits. After symbol encoding, the data in the multiple frequency bins are converted from the frequency domain to the time domain by an inverse fast-Fourier transform (IFFT). The IFFT is accomplished by two IFFT stages. The first stage produces an intermediate array that is input to the second stage, which produces the final time-domain output. The time-domain output is searched for peaks that exceed a clipping threshold of the transmitter's digital-to-analog converter. When an over-threshold peak is found, the intermediate-array inputs that contributed to the peak are examined.

Abstract: A Digital Subscriber Line (DSL) modem determines the proper transnit power level in a splitterless environment by transmitting a probe signal at different power levels to a telephone set and measuring the distortion signal reflected from the telephone set for each power level. The proper transmit power level is determined by detecting the “comer point” of the reflected distortion signal.

Abstract: A V.34 compliant modem uses a noise whitening filter to compensate for noise enhancement in an equalizer. The noise whitening filter uses a 3 tap FIR the response of which is determined by 3 coefficients. The coefficients are derived using a newly developed extension of the Levinson-Durbin algorithm to complex numbers. The coefficients thus derived are used to control the precoder as well as the noise whitening filter. The coefficients are also used to control precoding reconstruction after the decoder.

Abstract: Pulp-insulated telephone cables common in Japan and other countries have higher cross-talk interference than plastic-insulated cables common in the United States. Deployment of newer xDSL systems in Japan has been limited by the high cross-talk interference in those pulp cables, especially the near-end cross-talk (NEXT) from ISDN services using time-compression multiplexing (TCM). A TCM-DSL that can share pulp-cable bundles with TCM ISDN lines eliminates the NEXT interference by synchronizing transmission and reception with the TCM ISDN equipment for the same cable bundle. The TCM-DSL line uses TCM that is synchronized with the ISDN transmit and receive windows so that the TCM-DSL is transmitting but not receiving when the ISDN modems at the same side are transmitting. When ISDN at the same side are receiving and not transmitting, NEXT interference does not exist. Thus higher-speed TCM-DSL data can be received during the ISDN receive windows with reduced interference.

Abstract: Modem technology is implemented in a system including a personal computer (PC) to enable communication over a PSTN using communication software which includes a DC and near-DC signal suppresser.

Abstract: Modem technology is implemented in a system including a personal computer (PC) to enable communication over a PSTN using communication software which includes a mapping algorithm for mapping data into u-law signal points, which are divided into segments with different distances.