Optimum PAM filters are always band limited (Corresp.)
Thorild Ericson · IEEE Transactions on Information Theory · 1973
Joint optimization of transmitting and receiving filters in pulse-amplitude-modulated stationary Gaussian channels has been considered by a large number of authors under a variety of different circumstances. In most cases it has been found that the optimum filters are strictly band limited. In the present correspondence we give a direct argument why this must be so for a broad class of joint optimization problems.