Howling rejection

Hello

My aim is to set up a howling detector (and canceller)
I tried an adaptive IIR notch filter (using LMS), but I have still problems with
this system (due to harmonics frequencies, and fixed-point implementation)

I read : "howling rejection, typically done by shifting the frequency of
the signal as it goes through the canceller." (.. through an AEC)
But i didnt find any documents about the way to do that

Can someone tell me about howling rejection, or give me some links ?

Thank you for your help