Sampling principle for continuous signals with time-varying bands

The sampling principle for continuous signals specified by time-varying spectra with time-varying bands is studied theoretically. In the first place, the expansion corresponding to the usual sampling theorem is introduced for the representation of such a signal, and then the essential properties are briefly shown. Also, the reproduction problems of the original signals from the nonuniformly sampled pulse trains are discussed, from the standpoints of both the exact and approximate theories