0498369-A2 is referenced by 48 patents.
When the transmitter and receiver of a duplex multicarrier modem are connected to a two-wire line, echoes of the transmitted signal are reflected back into the receiver by mismatches between the output impedance of the modem and the input impedance of the line. These echoes are cancelled by an echo emulator which operates on samples of the transmitted signal. The parameters of the emulator are adapted by correlating, in the frequency domain, the transmitted data with the received signal. A specialiyed phase-locked loop, which uses a unique phase detector, tracks both frequency offset and phase of the far echo seperately from the adaptation of the emulator parameters. Initial training of the canceller is performed with a simple cyclic training signal that allows the use of efficient fast transforms.