This paper presents the results of a study in data compression of adaptive delta modulated video signals. The Song mode ADM is first investigated at a sampling rate of 16 Mbits/s and shown not to produce enough redundancy to warrant entropy encoding. We then present a modified adaptive delta modulator algorithm that operates at a sampling rate of 16 Mbits/s and does produce sufficient redundancy to yield a 40-50 percent data compression by using a simple code on 4 bit data blocks. Other techniques such as field interpolation and direct substitution are shown to increase the possible data compression further without noticeable degradation in the two input images used in this investigation. The effects of channel errors in the transmission of packet video over a computer network are considered. A leaky integrator is used to reduce the effects of channel errors in the data bits. We show that the effects of channel errors can be reduced by field interpolating those packets that can be shown to contain errors.

The purpose of this paper is to show that signals which are adaptive delta modulation (ADM) encoded can be arithmetically processed directly, without first decoding or converting to pulse code modulation (PCM) format. By operating on the serial DM bit streams, the sum, difference and product can be obtained in PCM and ADM format. Employing a four-term, non-recursive, averaging filter after the processors, we show that, for constant inputs, the signal-to-noise ratio (SNR) of the DM devices is exactly the same as that of their PCM counterparts. Although we have used the Song audio mode ADM [1] in the realization of our arithmetic processors, the designs are general enough to be applied to a large class of digital ADMs. To keep all systems practically realizable, we only employ operations which can be constructed with standard digital hardware, that is, adder, delays, hard-wired scalars and common logic circuits. Consequently, all our ADM devices can be manufactured with large scale integration where the distinct advantage is low cost and high reliability.

Two algorithms for voice encoding are described. One, the modified Abate, is a simplified version that is the type designed for the Space Shuttle. Waveforms of the response of the delta modulators to channel errors are given and performance data that shows the relationship between channel errors and word intelligibility are included. An analytic derivation yielding a comparison between PCM and adaptive delta modulation with respect to channel errors is also given.

This paper describes several adaptive delta modulators designed to meet NASA's potential need to digitally encode video signals. The adaptive delta modulators described are: (1) One-dimensional ADM to encode black-and-white pictures and also transmit digitally encoded voice with no increase in bandwidth (2) An ADM to encode field-sequential color; (3) An ADM to encode color video signals. The units described operate at bit rates that can be adjusted from 6 Mbits/s to 24 Mbits/s. The effects of the bit rate and channel errors on the response of the picture are discussed.

An all digital phase-locked loop (DPLL) is designed, analyzed, and tested. Three specific configurations are considered, generating first, second, and third order DPLL's; and it is found, using a computer simulation of a noise spike, and verified experimentally, that of these configurations the second-order system is optimum from the standpoint of threshold extension. This substantiates results obtained for analog PLL's.

The theory of operation and the design of an all-digital FM discriminator is presented in this paper. It is shown that the digital discriminator is equivalent to the Foster-Seely demodulator, i.e., a discriminator that converts the FM signal into an AM signal and then recovers the AM by using envelope detection. The output signal-to-noise ratio is found analytically above and below threshold and the results are verified experimentally. The theoretical analysis includes the effect of quantization noise, frequency jitter in the internal oscillator, and thermal noise. The system can be integrated and with the use of readily available emitter-coupled logic (ECL) can operate at intermediate frequencies suitable for many space, industrial, and commercial applications.