Multidimensional signaling for intersymbol interference channels

The authors consider the use of multidimensional signaling and block demodulation for digital transmission over intersymbol interference (ISI) channels. As an example, the theory is developed for the unit-memory 1+αz^-1 channel. The authors first explain why multidimensional signals should be used over ISI channels by showing how the minimum Euclidean distance and the cutoff rate R₀ increase by increasing the dimensionality of the signals transmitted. Two ways of increasing the reliability of transmission over an ISI channel are discussed. The first way consists of increasing the energy associated with the symbols more affected by ISI. The second way uses a coding scheme which selectively protects those symbols. Generalized concatenated-codes are advocated for this purpose