Asymmetric digital subscriber loop transceiver and method

Abstract

A discrete multi-tone, asymmetrical transceiver and method wherein a modem at a central office transmits information to a modem at a remote terminal on a down-stream signal and the modem at the remote terminal transmits information to the modem at the central office on an up-stream signal. The up-stream signal comprising data carried by a lower portion of a predetermined band of frequencies and the down-stream signal comprising data carried by an upper portion of the predetermined band of frequencies. The system includes an interpolator, at the remote terminal, for adding interpolated data into a stream of data distributed by the remote terminal modem among the lower portion of the predetermined band of frequencies for transmission in the up-stream signal. An ADC is provided at the modem of the central office, for converting the down-stream signal into digital samples at a sampling rate greater than the frequency of the highest frequency in the down-stream signal. A decimator is fed samples from the ADC at the ADC sampling rate and produces output samples at a lower sampling rate. A demodulator is fed the samples produced by the decimator at the lower sampling rate and converts such samples into the lower portion of the predetermined band of frequencies. The interpolator increases the rate of samples produced on the up-stream signal and thereby increases the frequency of images in such up-stream signal for more effective removal by the band pass filter of the remote terminal. Images in the up-stream signal which may couple into the receiver at the central office are increased in frequency and then are effective filtering by the decimator.