  We propose occupying guard-bands in closely-spaced WDM systems with redundant
signal spectral components, to increase tolerance to frequency misalignment and
channel shaping from multiplexing elements. By cyclically repeating the
spectrum of a modulated signal, we show improved tolerance to impairments due
to add/drop multiplexing with a commercial wavelength selective switch, in
systems using 5-20% guard bands on a 50-GHz DWDM grid.
