Engineering topics

Schilling, D. L.

Publications and source records attributed to Schilling, D. L..

At least 19 records

NASA NTRS1983

Investigation of digital encoding techniques for television transmission

Composite color television signals are sampled at four times the color subcarrier and transformed using intraframe two dimensional Walsh functions. It is shown that by properly sampling a composite color signal and employing a Walsh transform the YIQ time signals which sum to produce the composite color signal can be represented, in the transform domain, by three component signals in space. By suitably zonal quantizing the transform coefficients, the YIQ signals can be processed independently to achieve data compression and obtain the same results as component coding. Computer simulations of three bandwidth compressors operating at 1.09, 1.53 and 1.8 bits/ sample are presented. The above results can also be applied to the PAL color system.

Schilling, D. L.↗

NASA NTRS1983

Computer simulator for a mobile telephone system

A software simulator was developed to help in the design of the LMSS. The simulator is used to study the characteristics and implementation requirements of the LMSS' configuration.

Schilling, D. L.↗

NASA NTRS1983

VLSI technology and applications

Metal oxide semiconductor and GaAs devices are discussed. Digital and analog circuits are described. Applications to communications circuits are presented.

Schilling, D. L.↗

NASA NTRS1983

Computer simulator for a mobile telephone system

A software simulator to help NASA in the design of the LMSS was developed. The simulator will be used to study the characteristics of implementation requirements of the LMSS's configuration with specifications as outlined by NASA.

Schilling, D. L.↗

NASA NTRS1982

Modulation techniques

Bandwidth efficient digital modulation techniques, proposed for use on and/or applied to satellite channels, are reviewed. In a survey of recent works on digital modulation techniques, the performance of several schemes operating in various environments are compared. Topics covered include: (1) quadrature phase shift keying; (2) offset - QPSK and MSK; (3) combined modulation and coding; and (4) spectrally efficient modulation techniques.

Schilling, D. L.↗

NASA NTRS1981

A modified adaptive delta modulator

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. A modified adaptive delta modulator algorithm is presented 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. It is shown that the effects of channel errors can be reduced by field interpolating those packets that can be shown to contain errors.

Barba, J.↗

NASA NTRS1981

Computer simulator for a mobile telephone system

A software simulator was developed to assist NASA in the design of the land mobile satellite service. Structured programming techniques were used by developing the algorithm using an ALCOL-like pseudo language and then encoding the algorithm into FORTRAN 4. The basic input data to the system is a sine wave signal although future plans call for actual sampled voice as the input signal. The simulator is capable of studying all the possible combinations of types and modes of calls through the use of five communication scenarios: single hop systems; double hop, signal gateway system; double hop, double gateway system; mobile to wireline system; and wireline to mobile system. The transmitter, fading channel, and interference source simulation are also discussed.

Schilling, D. L.↗

NASA NTRS1981

Entropy encoding applied to a video DM bit stream

This paper investigates bandwidth compression of delta modulated video signals using a variety of novel techniques. The video signal is encoded at 16 MHz with an adaptive delta modulator (ADM) using the Song video mode algorithm. One method of achieving bandwidth compression is through the detection and reduction of steady state patterns in the DM bit stream. Further reduction is obtained by deleting the horizontal and vertical drive information. Finally, a modified ADM algorithm is introduced to increase the frequency of steady state patterns. When the modified ADM is combined with entropy coding a 30-50% data compression can be realized.

Barba, J.↗

NASA NTRS1980

The correlation of the output of a binary convolutional encoder

In this paper we discuss the correlation properties of the output of a binary convolutional encoder. We consider both random statistically independent inputs and first-order Markov inputs. It is shown that for random inputs, the ensemble average of the product of the outputs of a convolutional encoder taken two at a time is always either 0 or 1, and that for almost all good codes the ensemble average is always 0.

Braff, M.↗

NASA NTRS1980

Bandwidth compression of color video signals

The different encoder/decoder strategies to digitally encode video using an adaptive delta modulation are described. The techniques employed are: (1) separately encoding the R, G, and B components; (2) separately encoding the I, Y, and Q components; and (3) encoding the picture in a line sequential manner.

Schilling, D. L.↗

NASA NTRS1980

Digital encoding of NTSC color video signals using adaptive delta modulation

This paper presents the initial results of our study of the use of adaptive delta modulation to encode color signals. The techniques considered include direct encoding of the color video signal, encoding of each of the three color components, i.e., R, G and B, and encoding of the chrominance and luminance signals I, Y and Q. It is shown that at any transmitted bit rate between 8 Mb/s and 24 Mb/s the best quality picture reproduction occurs when the I, Y and Q signals are encoded and the poorest quality picture reproduction occurs when the composite video signal is encoded. Furthermore, the differences in quality are significant.

Davidovici, S.↗

NASA NTRS1980

Universal delta modulation receivers using the bit slice approach

The architecture of programmable processors is described, with particular reference to the design of a programmable delta-modulation decoder capable of receiving DM encoders employing different schemes. A switching receiver implementation, allowing communication between different DM algorithms, is designed and shown.

Apelewicz, T.↗

NASA NTRS1979

The effect of interference on delta modulation encoded video signals

The results of a study on the use of the delta modulator as a digital encoder of television signals are presented. The computer simulation was studied of different delta modulators in order to find a satisfactory delta modulator. After finding a suitable delta modulator algorithm via computer simulation, the results are analyzed and then implemented in hardware to study the ability to encode real time motion pictures from an NTSC format television camera. The effects were investigated of channel errors on the delta modulated video signal and several error correction algorithms were tested via computer simulation. A very high speed delta modulator was built (out of ECL logic), incorporating the most promising of the correction schemes, so that it could be tested on real time motion pictures. The final area of investigation concerned itself with finding delta modulators which could achieve significant bandwidth reduction without regard to complexity or speed. The first such scheme to be investigated was a real time frame to frame encoding scheme which required the assembly of fourteen, 131,000 bit long shift registers as well as a high speed delta modulator. The other schemes involved two dimensional delta modulator algorithms.

Schilling, D. L.↗

NASA NTRS1979

The effect of interference on delta modulation encoded video signals

An adaptive delta modulator which encodes composite color video signals was shown to provide a good response when operating at 16 Mb/s and near-commercial quality at 23Mb/s. The ADM was relatively immune to channel errors. The system design is discussed and circuit diagrams are included.

Schilling, D. L.↗

NASA NTRS1978

Voice encoding for the Space Shuttle using adaptive delta modulation

The paper describes the SONG and modified ABATE adaptive delta modulation algorithms for voice encoding. Waveforms of the response of the delta modulators to channel errors are given, and performance data which show the relationship between channel errors and word intelligibility are provided. An analytic derivation yielding a comparison between PCM and adaptive delta modulation with respect to channel errors is given. The Space Shuttle is employing the modified-ABATE device because it can tolerate a high error rate and operates at a relatively low sampling rate.

Schilling, D. L.↗

NASA NTRS1978

Video encoding using adaptive delta modulation

Research work is described that was carried out to develop adaptive delta modulators (ADM) capable of encoding black-and-white and color video signals in the presence of high bit error rates. These were a one-dimensional ADM capable of encoding black-and-white pictures and transmitting digitally encoded voice without increase in bandwidth; an ADM capable of encoding color video signals; and an ADM capable of encoding field-sequential color. For each of these three units, the bit rate could be adjusted within the range from 6 to 24 Mbits/sec. The effects of the bit rate and channel errors on the response of the picture are examined.

Schilling, D. L.↗

NASA NTRS1978

Communication system analysis for manned space flight

The development of adaptive delta modulators capable of digitizing a video signal is summarized. The delta modulator encoder accepts a 4 MHz black and white composite video signal or a color video signal and encodes it into a stream of binary digits at a rate which can be adjusted from 8 Mb/s to 24 Mb/s. The output bit rate is determined by the user and alters the quality of the video picture. The digital signal is decoded using the adaptive delta modulator decoder to reconstruct the picture.

Schilling, D. L.↗

NASA NTRS1978

Delay decomposition at a single server queue with constant service time and multiple inputs

Two network consisting of single server queues, each with a constant service time, are considered. The external inputs to each network are assumed to follow some general probability distribution. Several interesting equivalencies that exist between the two networks considered are derived. This leads to the introduction of an important concept in delay decomposition. It is shown that the waiting time experienced by a customer can be decomposed into two basic components called self-delay and interference delay.

Ziegler, C.↗