ISDN crosstalk cancellation in a DSL system
View Patent ↗To reduce the ISDN crosstalk in an incoming DSL signal, a crosstalk canceller observes at least a portion of the crosstalk signal and reproduces an estimate of the crosstalk signal for at least a portion of that signal within the DSL band. The crosstalk canceller applies a canceling signal based on the estimated crosstalk signal to reduce the crosstalk in the received DSL signal.
1. A method for reducing Integrated Services Digital Network (ISDN) crosstalk in a DSL signal, and the method comprising:
high pass filtering the ISDN crosstalk to obtain at least one high frequency side lobe thereof over a frequency range of negligible DSL signal strength;
shifting the at least one high frequency side lobe of the ISDN crosstalk onto at least one lower frequency corresponding to at least one lower frequency side lobe of the LSDN crosstalk within a DSL band; and
applying a canceling signal, corresponding to the ISDN side lobe shifted in the shifting act, to the DSL signal to substantially cancel the ISDN crosstalk in the DSL signal.
2. The method of claim 1 , wherein the shifting act further comprises:
reshaping the shifted ISDN side lobe based on a strong correlation between side lobes of an ISDN signal.
3. A crosstalk canceller in a DSL system for canceling Integrated Services Digital Network (ISDN) crosstalk in a received DSL signal; and the crosstalk canceller comprising:
a high pass filter for isolating at least one high frequency side lobe of an ISDN reference signal over a frequency range of negligible DSL signal strength;
at least one modulator coupled to the high pass filter and configured to shift the isolated at least one high frequency side lobe of the ISDN reference signal onto a lower frequency at which crosstalk from other ISDN side lobes affects the DSL signal;
at least one reshaping filter coupled to the at least one modulator to reshape the at least one isolated side lobe to correspond to at least one of the other ISDN side lobes the crosstalk from which affects the DSL signal; thereby obtaining an estimated ISDN signal for canceling an ISDN signal component from the received DSL signal based on the strong correlation between side lobes of an ISDN signal.
4. The crosstalk canceller claim 3 , further comprising:
a subtractor for determining an error signal between the ISDN reference signal and the estimated ISDN signal; and
a control module coupled to the subtractor to receive the error signal, and to adjust the at least one reshaping filters to reduce a magnitude of the error signal.
5. The crosstalk canceller of claim 3 , further comprising:
an other reshaping filter coupled to the high pass filter for adjusting the at least one high frequency side lobe of the ISDN signal; and
an adder block coupled to the at least one reshaping filter to combine the reshaped ISDN side lobe there from to obtain an estimated ISDN signal, the estimated ISDN signal for canceling an ISDN signal component in the received DSL signal.
6. The crosstalk canceller of claim 3 , wherein the at least one modulator modulates the high pass filtered ISDN reference signal with cosine wave corresponding to:
cos 4 πf c k/f s
where f c an ISDN symbol rate and f s is a DMT sampling rate thereby shifting the isolated at least one high frequency side lobe of the ISDN reference signal onto a lower frequency at which crosstalk from other ISDN side lobes affects the DSL signal.