Correlative level coding and maximum-likelihood decoding

Modems for digital communication often adopt the socalled correlative level coding or the partial-response signaling, which attains a desired spectral shaping by introducing controlled intersymbol interference terms. In this paper, a correlative level encoder is treated as a linear finite-state machine and an application of the maximumlikelihood decoding (MLD) algorithm, which was originally proposed by Viterbi in decoding convolutional codes, is discussed. Asymptotic expressions for the probability of decoding error are obtained for a class of correlative level coding systems, and the results are confirmed by computer simulations. It is shown that a substantial performance gain is attainable by this probabilistic decoding method. Manuscript received August 6, 1970. The author is with the IBM Thomas J. Watson Research Center, Yorktown Heights, N.Y. 10598.