Combined echo canceller and time domain equalizer
First Claim
Patent Images
1. A combined echo canceller and equalizer for use in a transceiver that is matched to a distant end transceiver, wherein the echo canceller removes a local echo signal from a received signal and the equalizer removes channel distortion from the received signal, said combined echo canceller and equalizer comprising:
- a digital data source;
a local training sequence source;
a hybrid circuit having a full duplex port for connection to a two-wire transmission line over which data signals are sent and received, a transmit port connected to said digital data source, and a receive port;
a front-end pole canceling filter connected to said receive port;
an echo canceller filter connected to said digital data source;
a first summer connected to said echo canceller filter and said front-end pole canceling filter;
a channel pole canceling filter connected to said first summer;
a channel zero canceling filter connected to said local training sequence source;
a second summer connected to said channel pole canceling filter and said channel zero canceling filter, and having an output for providing a partially equalized and substantially echo free signal.
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Abstract
A method and structure that reduces the computational requirements of both echo cancellation and time domain equalization in symmetrical transceivers. The structure exploits pole-zero modeling of both the echo and transmission path response in order to realize an improved level of system performance with shorter filters than would be required with direct FIR modeling.
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Citations
15 Claims
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1. A combined echo canceller and equalizer for use in a transceiver that is matched to a distant end transceiver, wherein the echo canceller removes a local echo signal from a received signal and the equalizer removes channel distortion from the received signal, said combined echo canceller and equalizer comprising:
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a digital data source;
a local training sequence source;
a hybrid circuit having a full duplex port for connection to a two-wire transmission line over which data signals are sent and received, a transmit port connected to said digital data source, and a receive port;
a front-end pole canceling filter connected to said receive port;
an echo canceller filter connected to said digital data source;
a first summer connected to said echo canceller filter and said front-end pole canceling filter;
a channel pole canceling filter connected to said first summer;
a channel zero canceling filter connected to said local training sequence source;
a second summer connected to said channel pole canceling filter and said channel zero canceling filter, and having an output for providing a partially equalized and substantially echo free signal. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A method of training a combined echo canceller and equalizer comprising the steps of:
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receiving a training signal from a distant end transceiver;
transmitting a training signal to the distant end receiver and receiving a corresponding local echo signal;
training a front-end pole canceling filter that removes distortion from the received training signal and the local echo signal, the distortion of the received training signal being associated with the dominant poles of a distant end transmit filter and a local receive filter, and the distortion of the local echo signal being associated with the dominant poles of a local transmit filter and local receive filter;
training an echo canceller filter to generate a replica of the local echo signal;
training a channel pole canceling filter and channel zero canceling filter. - View Dependent Claims (9, 10, 11, 12, 13, 14)
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15. A combined equalizer and echo canceller for removing a local echo signal and reducing channel distortion in a system having two transceivers that communicate over a channel having dominant channel poles and zeros, each transceiver having transmit and receive filters having dominant front-end poles and zeros, said combined equalizer and echo canceller comprising:
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a first filter that cancels signal distortion associated with the dominant front-end poles of the transmit and receive filters;
a second filter that generates a replica of a local echo signal;
a third filter that cancels signal distortion associated with the dominant poles of the channel; and
,a fourth filter that generates a replica of the received training sequence;
whereby signal distortion from the channel and local echoes is reduced.
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Specification