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 . An echo canceling system comprising: 
 a tracking echo canceller;    a current echo canceller; and    an echo cancellation accuracy determination device that compares the accuracy of the tracking echo canceller and the current echo canceller.    
   
   
       2 . The system of  claim 1 , further comprising an echo canceller updating device that updates the current echo canceller based on the comparison.  
   
   
       3 . The system of  claim 1 , wherein the accuracy is determined based on a sync frame.  
   
   
       4 . The system of  claim 1 , wherein the tracking echo canceller monitors the echo in a signal.  
   
   
       5 . The system of  claim 4 , wherein the signal is information within a digital communications environment.  
   
   
       6 . The system of  claim 1 , wherein one or more coefficients for the current echo canceller are updated, while the tracking echo canceller is updated one or more times.  
   
   
       7 . A method for updating an echo canceller comprising: 
 determining the accuracy of a tracking echo canceller;    determining the accuracy of a current echo canceller;    comparing the accuracy of the echo cancellers; and    updating the current echo canceller with the tracking echo canceller if the tracking echo canceller is more accurate.    
   
   
       8 . The method of  claim 7 , further comprising sampling an input signal.  
   
   
       9 . The method of  claim 7 , further comprising reading input samples into a memory device.  
   
   
       10 . The method of  claim 7 , further comprising updating the tracking echo canceller.  
   
   
       11 . The method of  claim 7 , further comprising sampling a portion of a sync frame.  
   
   
       12 . The method of  claim 11 , wherein the sync frame is a portion of a communication in a digital communication environment.  
   
   
       13 . The method of  claim 7 , wherein one or more coefficients for the current echo canceller are updated, while the tracking echo canceller is updated one or more times.  
   
   
       14 . An information storage media comprising information that updates an echo canceller comprising: 
 information that determines the accuracy of a tracking echo canceller;    information that determines the accuracy of a current echo canceller;    information that compares the accuracy of the echo cancellers; and    information that updates the current echo canceller with the tracking echo canceller if the tracking echo canceller is more accurate.    
   
   
       15 . The information storage media of  claim 14 , further comprising information that samples an input signal.  
   
   
       16 . The information storage media of  claim 14 , further comprising information that reads input samples into a memory device.  
   
   
       17 . The information storage media of  claim 14 , further comprising information that updates the tracking echo canceller.  
   
   
       18 . The information storage media of  claim 14 , further comprising information that samples a portion of a sync frame.  
   
   
       19 . The information storage media of  claim 18 , wherein the sync frame is a portion of a communication in a digital communication environment.  
   
   
       20 . The information storage media of  claim 14 , further comprising information that subtracts an estimate of the echo from a received sampled signal.  
   
   
       21 . The information storage media of  claim 14 , wherein one or more coefficients for the current echo canceller are updated, while the tracking echo canceller is updated one or more times.