Listener echo cancellation for modems
First Claim
1. A modem receiver comprising:
- means for receiving a signal originated from a transmitting modem which contains a listener echo, said means for receiving a signal including means for processing the signal to produce a processed signal;
a listener echo cancellation circuit preceding a decoder circuit, and electrically coupled to said means for receiving a signal, said echo cancellation circuit including a delay means and a filter means, wherein said delay means receives at least a portion of said processed signal and delays said portion by a predetermined amount to obtain a delayed version of said processed signal, wherein said delay means provides the delayed version to said filter means, and wherein said filter means produces a signal which is a filtered version of said delayed version and combines said filtered version with said processed signal to substantially cancel the listener echo of said received signal such that a corrected signal is produced; and
a precoder noise whitening filter electrically coupled to said echo cancellation circuit for receiving said corrected signal and for filtering noise out of said corrected signal.
3 Assignments
0 Petitions
Accused Products
Abstract
To improve the signal to noise ratio of the receiver of a receiving modem, the receiving modem is equipped with the ability to cancel the listener echo. Cancellation of the listener echo is achieved by coupling to the listener echo canceller of the receiving modem the phase corrected adaptive equalizer output signal, which is conventionally found in modems. The phase corrected adaptive equalizer output signal contains the in-phase, quadrature (also known as X and Y, or real and imaginary, components of the) received modem signal at the symbol rate. Advantageously, doing so results in an improved SNR for the receiver of the receiving modem, thus allowing higher data rates or reduced error rates without requiring extension of the length of the modem equalizer. When the telephone network does not introduce any frequency offset of the modem signal in the channel, the listener echo canceller may be simplified to reduce its cost.
-
Citations
8 Claims
-
1. A modem receiver comprising:
-
means for receiving a signal originated from a transmitting modem which contains a listener echo, said means for receiving a signal including means for processing the signal to produce a processed signal; a listener echo cancellation circuit preceding a decoder circuit, and electrically coupled to said means for receiving a signal, said echo cancellation circuit including a delay means and a filter means, wherein said delay means receives at least a portion of said processed signal and delays said portion by a predetermined amount to obtain a delayed version of said processed signal, wherein said delay means provides the delayed version to said filter means, and wherein said filter means produces a signal which is a filtered version of said delayed version and combines said filtered version with said processed signal to substantially cancel the listener echo of said received signal such that a corrected signal is produced; and a precoder noise whitening filter electrically coupled to said echo cancellation circuit for receiving said corrected signal and for filtering noise out of said corrected signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
-
Specification