Shuttle voice processing uses a Variable Slope Delta Modulation scheme which is a variant of the ABATE algorithm. This paper summarizes the ground terminal subsystem which processes the multiplexed voice and telemetry data digital sequence in the downlink processing and digitizes the voice signal in the uplink processing. The Delta Modulation System (DMS) performance characteristics are given in terms of an intelligibility test score and in terms of time and frequency responses measured on a production system developed for NASA Goddard Space Flight Center. Implementation details of the encoder and decoder algorithms are given in terms of the circuit logic used to implement them.

The classical approach of considering intersymbol interference as a modulation problem is replaced by less conventional information decoding considerations. We present the concept of viewing time-dispersive channels as natural convolutional encoders. Several channels are presented as examples and computer simulations exhibit some of the benefits.

The problem of Chernoff bounding is analyzed for symmetric channels with input alphabet of arbitrary finite size or erasure channels with no crossover errors whose memory may be described in terms of the noise sequences by an infinite ergodic irreducible aperiodic Markov chain. Necessary and sufficient conditions are described which guarantee the existence of an exponential upper bound to the probability of error for block coding. These conditions are given in terms of the transition matrix of the Markov chain. It will be observed that, although their application involves merely an inspection of the transition matrix, they are based on the topology of the Markov chain and the convergence of sequences of transition probabilities.