System and method for the application of an LMS method to updating an echo canceller in an ADSL modem

Abstract

An echo cancellation device relies on the known characteristics of the sync frame to monitor, update in an off-line fashion and determine the accuracy of an echo canceller in, for example, a modem, such as an ADSL modem. Specifically, time domain samples are read from the transmit (Tx) and receive (Rx) paths of the modem. These samples are stored in memory. When the sync frame has received a predetermined number of the same Tx samples and Rx samples, the samples are stored. Running averages, over the sync frames, of the TX and RX samples are maintained. These averages are subtracted from a sync frame of samples, to allow LMS updating of the echo canceller taps, free of extraneous signals. Updating, i.e., tracking of changes in the echo channel, is done for the echo canceller in an off-line fashion. The coefficients for the in-line version are updated, while the off-line version is updated over several sync frames. Periodically, the performance of the off-line version is compared with the in-line version. The coefficients of the in-line version are replaced by those of the off-line version only if it is determined the off-line version, which is tracking echo channel changes, has better performance. After replacement of the in-line coefficients, the off-line tracking is continued in the off-line version.

1 - 21 . (canceled)  
   
   
       22 . A method of updating an echo canceller in multicarrier communication system comprising: 
 receiving a plurality of known, periodically transmitted, sync frame signals;    determining an average sync frame signal by averaging the plurality of received, known sync frame signals; and    determining an echo for a received sync frame signal by subtracting the determined average sync frame signal from the received sync frame signal.    
   
   
       23 . Means for updating an echo canceller in multicarrier communication system comprising: 
 means for receiving a plurality of known, periodically transmitted, sync frame signals;    means for determining an average sync frame signal by averaging the plurality of received, known sync frame signals; and    means for determining an echo for a received sync frame signal by subtracting the determined average sync frame signal from the received sync frame signal.    
   
   
       24 . An echo canceller in a multicarrier communications environment comprising: 
 a sync frame detection device designed to receive a plurality of known, periodically transmitted, sync frame signals;    a controller designed to determine: 
 an average sync frame signal by averaging the plurality of received, known sync frame signals, and  
 an echo for a received sync frame signal by subtracting the determined average sync frame signal from the received sync frame signal.  
   
   
   
       25 . An information storage media having stored thereon information that when executed updates an echo canceller in multicarrier communication system comprising: 
 information that receives a plurality of known, periodically transmitted, sync frame signals;    information that determines an average sync frame signal by averaging the plurality of received, known sync frame signals; and    information that determines an echo for a received sync frame signal by subtracting the determined average sync frame signal from the received sync frame signal.