Predictive Quantizing Systems (Differential Pulse Code Modulation) for the Transmission of Television Signals

In this paper, the terms predictive quantizing and differential pulse code modulation (DPCM) will be used interchangeably. They describe a special kind of predictive communications system. A predictive communications system is one in which the difference between the actual 689 712 THE BELL SYSTEM TECHNICAL JOURNAL, MAY-JUNE 196fi signal and an estimate of the signal, based on its past, is transmitted. Both the transmitter and the receiver make an estimate or prediction of the signal's value based on the previously transmitted signal. The transmitter subtracts this prediction from the true value of the signal and transmits this difference. The receiver adds this prediction to the received difference signal yielding the true signal. Highly redundant signals, such as television, are well suited for predictive transmission systems because of the accuracy possible in the prediction. If the signal is sampled, and if the difference signal is quantized and encoded into PCM, then the system is a predictive quantizing or D P C M system. A block diagram of systems of this type is shown in Fig. 1. Although delta modulation which uses the feedback principle was introduced somewhat earlier, 1 D P C M systems are based primarily on an invention by Cutler. 2 In his original patent in 1952, Cutler used one or more integrators to perform the prediction function. His invention is based on transmitting the quantized difference between successive sample values rather than the sample values themselves.