Pseudobinary Viterbi detector

Among the detection processes that have recently been described for use in a 9600 bit/s modem are `pseudobinary¿¿ processes that are developments of the pseudobinary Viterbi detector. Although no information has been published on the latter, it is of considerable interest both in its own right and in its performance relative to that of other detectors. The aim of the paper is to correct this omission. The pseudobinary Viterbi detector effectively recodes the received multilevel data signal into a binary signal having the same element (symbol) rate as the original signal and implements the conventional Viterbi-algorithm detection process for the corresponding binary signal, thus verygrcatly reducting the complexity of the detector. The paper considers this detector and also a basically different technique, that is a development of a conventional nonlinear qualiser. The two systems may be used with multilevel signals in many different applications and are studied here in an application of digital data transmission at 9600 bit/s over the pulic switched telephone network, where the transmitted signal is a 16-level QAM signal. The particular development of the nonlinear equaliser studied here has not previously been tested under these conditions, and it has furthermore been found to have an interesting relationship with the pseudobinary Viterbi detector. After describing the two detection processes, the paper presents the results of computer-simulation tests over models of two different telephone circuits, comparing the tolerances to additive white Gaussian noise of various arrangements of each process.