Near and far echo canceller for data communications
AssigneeMassachusetts Institute of Technology
InventorsThomas F. Quatieri, Jr., Gerald C. O'Leary
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Abstract
A method for eliminating echos in modems used for full-duplex data communication is disclosed. The technique improves the cancellation of the echos by synthesizing an estimate of the desired signal and subtracting this estimate from the received waveform to improve the estimate of the residual echo. An adaptive filter is used to match the transmitted bit pattern to make an estimate of the frequency offset in the far echo, so that it can be cancelled more accurately.
Claims16
An arrangement for receiving a far end-generated signal carried on an incoming signal which is affected by a frequency-offset far echo of a near end-generated signal, the arrangement comprising
- echo cancelling means for generating an echo-compensated incoming signal estimate as a function of the difference between a far echo estimate and the incoming signal, the far echo estimate being formed by modifying the near end signal to replicate the frequency-offset far echo,
- a far end signal receiver connected to the echo cancelling means for generating a far end signal estimate from the echo-compensated incoming signal estimate, and
- an echo receiver connected to the echo cancelling means and the far end signal receiver for refining the far echo estimate as a function of the difference between delayed samples of the incoming signal and the far end signal estimate and further including means for estimating the frequency offset of the far echo to refine the far echo estimate.
Dependencies are inferred from the claim text.