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

An apparatus that determines a phase error to use to synchronize a receiver clock frequency with that of a transmitter, the apparatus comprising:

• a transmitter that transmits at least one pilot tone symbol and a training mode indicator to the receiver;
• a sample clock that generates a sample clock signal;
• a symbol identifier coupled to receive the sample clock signal and that indicates a symbol index associated with the most recent symbol, the symbol index indicative of the cross talk environment of the symbol;
• a phase error measurer device that measures the phase error between two pilot tone symbols and outputs the phase error;
• and
• a phase error determination device (“PEDD”) coupled to receive the phase error from the phase error measurer device, the symbol index from the symbol identifier and the training mode indicator from the transmitter, wherein the PEDD determines whether to set the phase error to zero based on the cross talk environment of the most recent symbol and the training mode indicator, wherein the PEDD adjusts the sample clock signal frequency using the phase error.

A computer system adapted for determining a phase error that is used to adjust a clock frequency, the system comprising:

• a module for recognizing at least one pilot tone symbol;
• a module for recognizing a training mode indicator;
• a module for indicating a symbol index associated with the most recent symbol, the symbol index indicative of the cross talk environment of the symbol;
• a module for measuring phase error between two pilot tone symbols and for outputting the phase error;
• a module for determining whether to set the phase error to zero based on the cross talk environment of the most recent symbol and the training mode indicator;
• and
• a module for using the phase error to adjust the clock frequency.

A computer implemented method for adjusting a clock frequency, the method comprising:

• receiving training mode indicator signals;
• receiving pilot tone symbols;
• determining a phase error between time separated pilot tone symbols;
• selectively setting the phase error to zero when the cross talk environment of the current symbol and the training mode indicator signal indicate a noisy environment;
• and
• adjusting the frequency of the clock based on the phase error.

A computer-readable medium that adjusts a clock frequency, the computer-readable medium comprising:

• a code segment for recognizing training mode indicator signals;
• a code segment for recognizing pilot tone symbols;
• a code segment for determining a phase error between time separated pilot tone symbols;
• a code segment for selectively setting the phase error to zero when the cross talk environment of the current symbol and the training mode indicator signal indicate a noisy environment;
• and
• a code segment for adjusting the clock frequency based on the phase error.