1. A J Viterbi, Principal of coherent communication (McGraw Hill, New York, 1966)
2. D A Linden, Proc. IRE 47, 1219 (1959)
3. W R Bennett, Introduction to signal transmission (McGraw Hill, New York, 1970)
4. B Smith, Bell Syst. Tech. J. 36, 709 (1957)
5. Bell Telephone Laboratories, Transmission System for Communication, 4th ed (Murray Hill, NJ, 1970)