Delta Modulation Quantizing Noise Analytical and Computer Simulation Results for Gaussian and Television Input Signals

Delta modulation (AM) is one way in which an analog signal may be converted into pulses suitable for transmission over binary channels. Since the modulation process may be simpler and cheaper for AM than for standard pulse code modulation (PCM), there is considerable interest in determining how the performance of AM relates to that of * Picturephone is a service mark of the Bell System. 117 118 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1966 standard PCM. Digital transmission of an analog signal is one way to effectively trade bandwidth for noise immunity in the transmission medium. Indigenous to this trade, however, is the introduction of quantizing noise in the encoding and decoding processes. Bennett 1 has studied this problem for standard PCM. De Jager 2 and Van de Weg3 have studied quantizing noise for AM, but their results are somewhat restricted due to the difficulties encountered in analyzing a nonlinear feedback system such as AM. Zetterberg 4 discusses AM through the discipline of information theory. This study was initiated primarily to determine what kind of performance could be expected if AM were used for narrow-band television signals such as Picturephone signals, but more general results are also presented. The metric used as a figure of merit is the ordinary signalto-quantiz.ing-noise ratio S / N . Recently, the concept of delta modulation has been subject to a rash of embellishments and modifications, some of which may improve its ability to transmit television signals and all of which add equipment complexity.