An ADSL front end is implemented with an adaptive AM interference canceller to
cancel out either a carrier signal of an interfering AM radio signal, or a carrier
signal and its sidebands of an interfering AM radio signal, from a received ADSL
signal. By canceling an interfering AM radio signal rather than simply filtering
out the relevant interfered with frequency band, the interfered with frequency
band remains useable for ADSL transmission. In one embodiment, a reference AM radio
receiver is either fixedly or adaptively tuned to the carrier frequency of an interfering
AM radio station, and the received signal in the frequency band surrounding that
carrier frequency is digitized and provided to an adaptive interference canceller.
The adaptive interference canceller adaptively adjusts a time delay and phase of
the generated AM interference signal to optimize cancellation at a hybrid of the
same AM radio signal received as interference over a subscriber line. The AM interference
canceller may include a Hilbert bandpass filter, tuned to an appropriate carrier
frequency by, e.g., an FFT analyzer. An LMS module adaptively adjusts the parameters
of the I and Q channels of the Hilbert filter. In another embodiment, instead of
including a reference AM radio receiver, only the carrier signal is removed from
the received ADSL signal, leaving the presumably less significant sidebands intact.
Preferably, a ratio of differential mode coupling to common mode coupling of the
interfering AM radio station is determined to result in a better cancellation of
the coupled AM interference signal.