Centillium Communications, Inc.

Yaron Bar-Ness

Guozhu Long

Chin Ngek Hung

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.

Method and apparatus for timing recovery in ADSL transceivers under a TCM-ISDN crosstalk environment

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).

Transceiver training for DSL modems under TCM-ISDN interference

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.

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. Due to the introduction of the cyclic prefix and the time-domain equalizer, the inter-symbol interference is basically eliminated. Therefore, the FEXT symbols adjacent to NEXT symbols are not affected by the TCM-ISDN noise that exists in NEXT symbols only. As a result, the received signal on those symbols can also be used to train FEQ. In a show-time phase, the FEQ is updated on FEXT and NEXT symbols for bins where the number of bits per symbol is non-zero.

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San Jose, CA, United States of America

Yaron Bar-Ness