An adaptive equalizer for amplitude-modulation (AM) signal received by over-the-air
radio transmission comprises feed-forward finite-impulse-response (FIR) filtering
and further comprises infinite-impulse-response (IIR) filtering for feeding back
decisions. The echo content of baseband signal demodulated from the AM signal is
measured for initially determining the reception channel impulse response (CIR)
in the time-domain. Thereafter, the CIR is updated by decision feedback. Periodically,
the CIR is normalized with respect to the strength of a cursor component thereof.
The strengths of longer-delay post-echoes in the normalized CIR are used to determine
the weighting coefficients of the IIR filtering, which suppresses the longer-delay
post-echoes. The pre-echo and short-delay post-echo portion of the normalized CIR
is convolved with the normalized CIR to generate a synthetic normalized CIR. The
strengths of pre-echoes and short-delay post-echoes in the synthetic normalized
CIR are used to determine the weighting coefficients of the feed-forward FIR filtering,
which suppresses the pre-echoes and short-delay post-echoes.