3com Corporation

Martin Staszak

Tim Murphy

Richard G Williams

Timothy F Murphy

Lloyd Sarsoza

A method for determining symbol boundaries in an ADSL modem, comprising receiving multi-frequency modulated signals in the time domain, wherein the multi-frequency modulated signals include a pilot signal at a pilot frequency. Performing a time-to-frequency transform on the multi-frequency modulated signals to recover the pilot signal. Iteratively computing a phase error for the pilot signal over a number of transform regions. Selecting the transform region with the lowest phase error.

Method for achieving symbol alignment to a pre-existing ADSL data exchange

A digital subscriber line network allows a plurality of remote modems to communicate without interfering with the communication to the central office. Each symbol of a superframe is converted to a tone vector, and the tone vectors are integrated over a plurality of superframes. The tone vectors of the data symbols are random, and tend to cancel each other out. The tone vector of the synchronization symbol remains constant among the plurality of superframes, and the sum of these tone vectors over a plurality of superframes becomes large. By identifying the largest integrated tone vectors, the network may identify the position of the synchronization symbol. The modems may then align using the position of the synchronization symbol.

Superframe alignment to a pre-existing ADSL data exchange

A method for reducing noise from a non-linear device, such as a telephone, that shares a customer loop with a splitterless Asymmetric Digital Subscriber Line modem. The non-linearity of the device can cause some of the upstream signal to bleed into the downstream signal band. The modem examines the downstream band when it is transmitting fast retrain signals. By comparing the power in the band to a previous value when the modem transmitted upstream at a higher power level, the modem may determine whether to cut back its transmitted power to lessen the noise in the downstream band. In this manner, the method may allow optimal downstream data transfer regardless of what non-linear device shares the customer loop with the ADSL modem.

Method for reducing noise from a non-linear device that shares a customer loop with an asymmetric digital subscriber line modem

A method for optimizing downstream data transfer in a telephone from a splitterless asymmetric digital subscriber line modem. The modem examines the power spectrum of fast retrain signals both when the telephone is on-hook and off-hook. By comparing the power in the spectra, the modem may determine whether to cut back its transmitted power to lessen the noise in the downstream channel. In this manner, a customer may simultaneously use the telephone and the modem on the same telephone loop.

Method for optimizing downstream data transfer in an asymmetric digital subscriber line modem

A method for reducing audible noise in a telephone from a splitterless asymmetric digital subscriber line modem. The modem examines the shape of the power spectrum of fast retrain signals both when the telephone is on-hook and off-hook. By comparing the spectra, in particular the slopes of the spectra, the modem may determine the quality of the telephone that shares the telephone loop with the modem. The modem cuts back its transmitted power depending on the quality of the telephone by an amount that suppresses the audible noise in the telephone. In this manner, a customer may simultaneously use the telephone and the modem on the same telephone loop.

Method for reducing noise from an asymmetric digital subscriber line modem

A method for recovering from an excessive power cutback in a splitterless asymmetric digital subscriber line modem. The modem may apply a power cutback to enable simultaneous use of the modem and a telephone. The modem determines if the modem's power after the cutback is sufficient to support data communication with the central office. If the power is insufficient, the modem gradually reduces the power cutback, checks the sufficiency of the power again, and repeats this cycle. The modem repeats the cycle until the modem attains an acceptable transmit power where the power requirements for data transfer and noise reduction are balanced.

Method for asymmetric digital subscriber line modem recovery from insufficient transmit power

A method for rapid noise reduction from a splitterless ADSL modem. The modem stores a value for the power level of its transmitter in a table along with transmission characteristics of the telephone loop. The stored value for its power level is the power level that was previously successful with the transmission characteristics in achieving the Showtime data transfer mode. When the modem measures similar transmission characteristics of the telephone loop, such as a slope of the frequency response of the loop, a power level that would suppress downstream noise, or the dc voltage of the loop, the modem searches the table for matching transmission characteristics. If the table contains a table entry that matches these measured transmission to characteristics, the modem restores the stored transmitter power of the modem. In this manner, the modem may rapidly achieve Showtime because it is restoring a transmitter power level that was previously successful under the same condition of the telephone loop.

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Poway, CA, United States of America

Martin Staszak