Use of the Null Zone in Voice Communications

This paper presents a discussion of four QPPM (quantized pulse position modulation) voice communication systems that make use of the ideas of Wald\´s sequential decision theory. The "double-threshold, speech statistics" system and the "doublethreshold, largest of S" system are applicable to the situation of interference consisting of narrow-band Gaussian noise. The "fourthreshold, speech statistics" system and the "four-threshold, nearest to reference" system are for interference by narrow-band Gaussian noise and an impulse-like noise. The systems receive their titles from the way information in the null zone is used. They are not represented as being optimum in any sense. The interest in them lies in the fact that they represent a novel application of the ideas of sequential decision theory.