1. C E Shannon, A mathematical theory of communication,Bell Sys. Tech. J., Vol. 27, pp. 398–403, July 1948.
2. R M Fano,The transmission of information, Technical Report No. 65, Research Laboratory of Electronics, M.I.T., Cambridge, Mass., 1949.
3. L G Kraft,A device for quantizing, grouping, and coding amplitude-modulated pulses, Electrical Engineering Thesis, M.I.T., Cambridge, Mass., 1949.