Stabilizing fractionally-spaced equalizers

The authors analyze the instability of fractionally-spaced equalizers (FSEs) and show that this is caused by two different factors. The first is the vanishing of the signal power spectral density in some frequency intervals. The second, which does not seem to have been previously recognized, is the folding of the error signal spectrum at the equalizer output. The tap-leakage algorithm eliminates the FSE instability at the expense of increasing the output mean-square error. Previously proposed stabilizing algorithms eliminate only one of the two causes of instability. The performance of these algorithms is analyzed, and a new stabilizing algorithm is described which performs better than the tap-leakage algorithm