Irreducible components of canonical diagrams for spectral nulls

Irreducible components of canonical diagrams for spectral null constraints at f=f_sk/n are studied, where k and n are integers and f_s is the symbol frequency. To identify systematically all irreducible components of the canonical diagrams for first-order spectral nulls at f, we give a set of channel symbol sequences specifying all of them. If n is a prime number, then each sequence in the set corresponds to exactly one label-preserving graph isomorphism class of irreducible components. We also give a set of channel symbol sequences specifying all irreducible components of canonical diagrams for second-order spectral nulls at DC (i.e., f=0)