Method and apparatus for transmission line equalization

1. A modem for receiving a multitone signal having a plurality of symbols with a cyclic extension of length M samples transmitted through a channel, comprising:

a signal input for receiving the multitone signal; and

a transversal equalizer coupled to the signal input and including a finite impulse response filter having coefficients such that a combined impulse response of the channel and the transversal equalizer targets a target impulse response having N taps, where N and M are integers and N<(M+1);

wherein the target impulse response is represented by a data set having M+1 data elements, wherein at least a first or a last of the M+1 data elements is set to zero.

2. The modem according to claim 1 , wherein the modem further comprises a bit adjustment means for lengthening or shortening a symbol for use in frequency domain interpolation.

3. The modem according to claim 1 , wherein N=M.

4. The modem according to claim 1 , including a means for calculating the coefficients of the finite impulse response filter to minimize an error function of a difference between a convolution of the channel with the transversal equalizer and a target impulse response having N taps.

5. The modem according to claim 1 , wherein a difference between the combined impulse response of the channel and the transversal equalizer and the target impulse response is minimized.

6. A method for equalizing a multitone signal formed of a stream of multitone symbols having an extension of length M samples passing through a channel with a finite impulse response filter having filter coefficients, including:

receiving the multitone signal from the channel;

passing the multitone signal through the finite impulse response filter;

delaying the multitone signal;

adjusting the filter coefficients so that a combined effect of the channel and the finite impulse response filter on the multitone signal targets a target impulse response having N samples of the delayed multitone signal, wherein N and M are integers and N<(M+1);

wherein the target impulse response is represented by a data set having M+1 data elements; and

setting at least a first or a last of the M+1 data elements to zero.

7. The method according to claim 6 , further including adding or deleting bits to keep a phase rotation within predetermined limits.

8. The method according to claim 6 , wherein N=M.

9. The method according to claim 6 , further including calculating the coefficients of the finite impulse response filter to minimize an error function of a difference between a convolution of the channel with a transversal equalizer and a target impulse response having N taps.

10. The method according to claim 6 , further including minimizing a difference between

the combined impulse response of the channel and a transversal equalizer; and

the target impulse response.

11. A computer program recorded on a data carrier for cooperating with a computer system having a processor and a memory including code to cause the processor to carry out the steps of:

receiving a multitone signal having an extension of length M samples from a channel;

passing the multitone signal through a finite impulse response filter having filter coefficients;

delaying the multitone signal;

adjusting the filter coefficients so that the combined effect of the channel and the finite impulse response filter on the multitone signal targets a target impulse response having N samples of the delayed multitone signal, wherein N and M are integers and N<(M+1 );

wherein the target impulse response is represented by a data set having M+1 data elements; and

setting at least a first or a last of the M+1 data elements to zero.

12. The computer program according to claim 11 , further including code for frequency modulating the multitone signal.

13. The computer program according to claim 11 , wherein N=M.

14. A system, comprising:

a first modem including

a cyclic extension addition module for adding M extension samples to a discrete multitone (DMT) symbol; and

a digital-to-analog converter for transmitting the DMT symbol and the M extension samples into a channel; and

a second modem including

a signal input connected to the channel; and

a transversal equalizer coupled to the signal input, the transversal equalizer including a finite impulse response filter having coefficients such that a combined impulse response of the channel and the transversal equalizer targets a target impulse response having N taps, where N and M are integers and N<(M+1);

wherein the target impulse response is represented by a data set having M+1 data elements, wherein at least a first or a last of the M+1 data elements is set to zero.

15. The system according to claim 14 , wherein the first modem includes a frequency phase rotation means and a means for at least one of bit addition and deletion to adjust a phase of the DMT symbol and the M extension samples.

16. The system according to claim 14 , wherein

the second modem further includes a second cyclic extension addition module and a second digital-to-analog converter; and

the first modem further includes a second signal input and a second transversal equalizer.

17. A method of modem communication, including:

transmitting a multitone signal having a phase from a first modem to a second modem through a channel, the multitone signal formed of plurality of symbols and having an extension of length M samples;

rotating the phase of multitone signal to align the plurality of symbols;

receiving the multitone signal from the channel;

passing the multitone signal through a finite impulse response filter having filter coefficients;

delaying the multitone signal;

adjusting the filter coefficients so that the combined effect of the channel and the finite impulse response filter on the multitone signal targets a target impulse response having N samples of the delayed multitone signal, wherein N and M are integers and N<(M+1);

wherein the target impulse response is represented by a data set having M+1 data elements; and

setting at least a first or a last of the M+1 data elements to zero.

18. The method of claim 17 , further including adding a bit to the multitone signal to align the plurality of symbols of the multitone signal.

19. The method of claim 17 , further including deleting a bit from the multitone signal to align the plurality of symbols of the multitone signal.