Predictive quantizing systems (differential pulse code modulation) for the transmission of television signals

Differential pulse code modulation (DPCM) and predictive quantizing are two names for a technique used to encode analog signals into digital pulses suitable for transmission over binary channels. It is the purpose of this paper to determine what kind of performance can be expected from well-designed systems of this type when used to encode television signals. Systems using both previous sample and previous line feedback are considered. A procedure is presented for the design of nonadaptive, time invariant systems which are near optimum in the sense that the resulting signal to unweighted quantizing noise ratios (S/N) are nearly maximum. Simple formulas are derived for these S/N ratios which apply to DPCM as well as standard PCM. Standard PCM is shown to be a special case of DPCM. These formulas are verified by digital computer simulation. Any advantage of DPCM stems from removing the redundancy from the signal to be transmitted. Redundancy in a signal, however, affords a certain protection against noise introduced in the transmission medium. The penalty for removing this redundancy, through DPCM or other means, is that the transmitted signal becomes more fragile and requires a higher-quality transmission medium than would otherwise be required. This penalty is discussed in quantitative terms.