• Quantization for Signal Detection and Representation

      Kassam, Saleem A.; University of Pennsylvania (International Foundation for Telemetering, 1978-11)
      For digital representation of analog data the minimum mean-squared-error criterion is commonly used as a criterion for the basis of optimum quantizer design. In this paper we show that in some situations measures other than the minimum mean-squared-error may be more appropriate. For the signal representation problem, it is shown that the mean-absolute-error criterion has theoretical justification, as again for some signal detection problems it is shown that the mean-squared-error criterion is not the most appropriate criterion.
    • Quasi-Optimal Decoding of Linear Block Codes Using Soft Decision Detection

      Greene, Edward P.; NASA/Goddard Space Flight Center (International Foundation for Telemetering, 1978-11)
      A simple but effective decoding procedure, applicable to any (n,k) linear block code with symbols from GF(q), is described. The technique involves a transformation of the parity check equations which focuses the code's correction power on the soft symbol set while still retaining the capability to correct one symbol error from outside this set. The soft symbol set is defined to be the n-k least reliably detected code symbol positions whose parity check rowspaces are linearly independent. The process generates a number of error vector screening candidates, each a solution to the parity check equations, and the maximum-likelihood candidate is accepted. If P(opt) and P(qopt) are the decoder error rates for the optimal and quasi-optimal decoders respectively, then P(opt) < P(qopt) < P(opt) + P(se) where P(se) is the probability that the actual error vector is not included in the screening candidate set. Since P(se) can be shown to approach zero for a wide range of codes and operating conditions, the performance of this decoder can be quasi-optimal in these cases.
    • A Rate Distortion Surface for Images

      Jones, Richard A.; University of Arkansas (International Foundation for Telemetering, 1978-11)
      In this paper the concept of a rate distortion surface is introduced. A signal class is considered such that the source can be viewed as a composite source that consists of a finite number of subsources. Also, it is demonstrated that the overall transmission requirement can be treated as different but connected transmission requirements. The connection arises through an intermediate fidelity criterion. It is shown that the rate distortion bound for a composite source is a convex surface with a unique minimum for any specified signal to noise ratio. It is further demonstrated that the locus of these minima, projected onto a composite source information rate-composite source average distortion plane, is the rate distortion curve for the composite source.
    • The Role of Microprocessor-Based Terminals in Computer Interpretation of ECG's: Engineering Considerations

      Ewing, Richard; Comp-U-Med, Inc. (International Foundation for Telemetering, 1978-11)
      This paper presents a case history of the selection and application of a microprocessor for a low cost phone-coupled computer electrocardiograph terminal. All phases of the project will be covered, from the ingredients which went into the decision to employ a microprocessor, through processor selection, design, program and manufacture.
    • The Role of Microprocessor-based Terminals in Computer Interpretation of ECG's: The View of Management

      Stuckelman, Robert; Comp-U-Med, Inc. (International Foundation for Telemetering, 1978-11)
      This paper discusses management considerations in the utilization of microcomputers in a new product design. Topics to be discussed include cost considerations in applying a new technology; dealing with development costs; and cost effectiveness of microprocessor utilization.
    • Ruggedized Cable and Connector for Fiber Optic Systems

      Wichansky, Howard; US Army Communications Research and Development Command (International Foundation for Telemetering, 1978-11)
      Achieving a ruggedized optical fiber cable and connector is the key to implementing Army fiber optic communication systems. The paper describes the results of a series of programs to develop the required cable and connector. Efforts to incorporate low loss optical fibers into a practical cable construction as well as optical transmission and mechanical properties, environmental resistance, and cost are discussed. Resistance of the cable to moisture and temperature exposure, tensile stress, impact, bend, and twist are summarized. The paper also includes concurrent development of a fiber optic connector consistent with the military environment. The alignment factors contributing to coupling loss are presented along with various concepts being employed to achieve fiber alignment. The details of a three-sphere connector design pursued under Army contract are included.
    • Satellite Communication Simulation and Its Applications

      Wang, Lily L.; Yeh, Paul P.; The Aerospace Corporation (International Foundation for Telemetering, 1978-11)
      The computer simulation activities which have been carried out at The Aerospace Corporation for satellite link performance studies and system analysis are reported. A brief description of the modelings of a filter, nonlinear device, modulator, detector and receiver is also given. Some results from the simulation studies, such as the basic link performance in the presence of filters and nonlinear device (hard limiter or TWT), the comparisons of various modulation techniques (OK-QPSK, MSK and PFQPSK), the study of cross talk in a FDMA system, the interference or jamming at the presence of a nearby source, and finally, the intermodulation problem of a multiple channel MFSK system using the frequency hopping, are addressed.
    • Satellite, Surface, and Subsurface Optical Communications

      Mooradian, G. C.; Naval Ocean Systems Center (International Foundation for Telemetering, 1978-11)
      Optical communication in the atmosphere, space, the marine boundary layer, and underwater are being investigated for a variety of applications. Three classes of optical communications systems will be addressed: OCULT (Optical Communications Using Laser Transceivers), ELOS (Extended Line-of-Sight) optical communications and satellite to subsurface optical communications. OCULT is a 10.6μ high rate reciprocal tracking heterodyne laser communications system designed for nearly all-weather duplex video bandwidth communications to horizon limited ranges. Of special interest are effects of coherent propagation through fogs and turbulence. The ELOS system is a 1.06μ optical aerosol scatter communications system for ranges of 30 to 300 miles. Scattering measurement at 40 to 80 miles through the marine boundary layer will be presented. The satellite to subsurface communication efforts deal with blue/green transmission from a satellite, through the atmosphere (including clouds) to a submerged receiver, exploiting the blue/green "window" in ocean water. The multiple forward scattered and diffusion transport of serm-plane waves through clouds and ocean waters will be discussed.
    • A SEASAT Synthetic Aperture Radar Preprocessor (SARP)

      Waltz, Edward L.; Bendix Aerospace Systems Division (International Foundation for Telemetering, 1978-11)
      A Synthetic Aperture Radar Preprocessor (SARP) for the SEASAT radar is described. The SARP system permits playback of Synthetic Aperture Radar (SAR) data for digital processing into ocean imagery. The system includes a High Data Rate Recorder, SAR Digital Preprocessing (SDP), array processor, mass storage disc, and host computer. Data tapes are played back at reduced rates and the SDP performs the functions of frame synchronization, decommutation of time and status data, presummation of adjacent azimuth returns and correction of gain as a function of range. The data are formatted into presummed range returns and are transferred to the array processor for buffering and subsequent storage on the mass disc. This preprocessing operation loads a 100 x 100 km swath of data on the disc for subsequent range and azimuth correlation to convert the SAR data to imagery. The SAR Data Preprocessor equipment is described and the implementation of the 35 Mbps frame synchronizer and presum arithmetic logic are detailed. A SAR Test Pattern Generator for simulation of SAR and other image data formats is also described. The test generator permits simulation of a wide range of digital data formats (including NASA and IRIG standards) and includes a programmable data pattern capability.
    • SEASAT-A: An Experiment in End-to-End Information System Design

      MacMedan, Mervyn L.; NASA Jet Propulsion Laboratory (International Foundation for Telemetering, 1978-11)
      The SEASAT-A ocean dynamics monitoring satellite was designed with a keen awareness of the problems of handling huge volumes of data from an Earth-orbiting applications mission. An "End-to-End" approach to the entire information system was adopted very early in the life of the Project. Some innovations introduced include the provision of a "Packet Telemetry" system which is very similar to the NEEDS program objectives, and the incorporation of an adjustable satellite clock which directly time-tags the sensor data in GMT. This paper will review the mission and information system performance, and will summarize lessons learned from the experiment in system design.
    • Serial High Density Digital Recording Using an Analog Magnetic Tape Recorder/Reproducer

      Law, Eugene L.; Pacific Missile Test Center (International Foundation for Telemetering, 1978-11)
      A great deal of interest is being generated in the area of high density digital recording (HDDR) because of the need to record high rate digital signals. This paper presents the results of a study where digital data was recorded on ordinary analog magnetic tape recorder/reproducers using several of the currently popular codes. It is shown that bit packing densities of 25 kilobits per inch (or higher) are achievable with analog wideband 2.0 MHz recorder/reproducers.
    • Shallow Bulk Acoustic Wave Devices - A New Type of Acoustic Wave Device for Communication Systems

      Lau, K. F.; Yen, K. H.; Kagiwada, R. S.; TRW Defense and Space Systems Group (International Foundation for Telemetering, 1978-11)
      This paper reviews the present status of a new type of acoustic wave device which has many potential applications. These devices are called Shallow Bulk Acoustic Wave (SBAW) devices because the signal propagates just below the surface of the piezoelectric substrate. These waves can be efficiently generated and detected by interdigital transducer and fabricated by techniques similar to those of surface acoustic wave (SAW) devices. These planar devices have been configured into bandpass filters, delay lines, oscillators and resonators. Because they utilize bulk waves rather than surface waves, SBAW devices possess many advantages over SAW devices. They have a higher frequency of operation, lower loss, better temperature stability, and, most likely, better aging characteristics. With these advantages, SBAW devices promise to replace both bulk crystals and SAW devices in many future communication systems.
    • Signal Processing with Saw Devices

      Milstein, L. B.; Arsenault, D. R.; Das, P. K.; UCSD; Rensselaer Polytechnic Institute (International Foundation for Telemetering, 1978-11)
      The use of surface acoustic wave devices to perform real time Fourier transformation for time-limited signals is well known. In this paper a detailed analysis justifying the implementation most typically employed will be presented, as well as the description of a scheme which extends the above technique by allowing the transformation of a long sequence of contiguous random data. This latter situation, of course, is that normally encountered in a digital communication system.
    • Simulation of Two Bandwidth Efficient Modulation Efforts in Satellite Communications

      White, Brian E.; The MITRE Corporation (International Foundation for Telemetering, 1978-11)
      A bandpass limited satellite channel with uplink and downlink noise was simulated for several constant envelope modulation schemes. Minimum shift keying (MSK) significantly outperformed quadriphase shift keying (QPSK) in achieving bit error rates of 0.005 with less than 1 dB degradation for a channel bandwidth to data rate ratio B/R = 0.78, for example. Frequency division multiple access (FDMA) scenarios with unsynchronized satellite signals were also simulated. A processing satellite performed the functions of Doppler and symbol timing correction and demodulation of each uplink. Additional filtering mitigated intersymbol interference (ISI) deliberately introduced for spectral shaping by prolate spheroidal data windows. Even when the received power in each satellite signal was 10 dB above the desired signal, 16 kbps rate-1/2 coded QPSK satellite signals on odd 12.5 kHz centers could coexist with line of sight (LOS) signals on 25 kHz centers. These results are applicable to the ever growing problems deriving from increased spectral occupancy.
    • A Simulator for the SEASAT-A Synthetic Aperture Radar Ground Support Network

      Jones, S. C.; Colson, J. D.; Grunberger, P. J.; John Hopkins University (International Foundation for Telemetering, 1978-11)
      The characteristics and capabilities of link measurement and simulation equipment for the NASA ground stations supporting the SEASAT-A synthetic aperture radar (SAR) are described. The Spaceflight Tracking and Data Network (STDN) SEASAT-A SAR Simulator generates SAR radar and data link signals, including chirp, radar return, pilot, PRN radar timing, and noise components. After injection into and passage through the STDN SAR equipment, the simulated SAR signals are processed in real time to determine ground support equipment readiness and performance. The equipment has been used to verify the performance of SAR unique support equipment prior to site delivery and during integration testing at NASA, European Space Agency (ESA), and Canada Centre for Remote Sensing (CCRS) ground support stations. It has also been used to test SAR flight equipment. It is currently being used for site prepass readiness testing.
    • Soft Decision Decoding of Block Codes

      Baumert, L. D.; McEliece, R. J.; California Institute of Technology (International Foundation for Telemetering, 1978-11)
      Using a general decoding technique of Solomon we evaluate the performance of certain block codes on a gaussian channel. Quadratic residue codes of lengths 48 and 80 as well as BCH codes of length 128 and rates 1/2 and 1/3 are considered. All four of these codes perform quite favorably with respect to the constraint-length 7 rate 1/2 convolutional code presently used on NASA's Mariner-class spacecraft.
    • A Solid State Data Recorder for Spacecraft Telemetry Applications

      Stermer, Robert L, Jr.; NASA Langley Research Center (International Foundation for Telemetering, 1978-11)
      A Solid State Data Recorder (SSDR) has been developed which offers a high reliability alternative to tape recorders in many spacecraft telemetry applications. The storage medium used in this recorder was ferrimagnetic garnet films supporting nonvolatile magnetic "bubble" domains. This technology is very flexible and permits a recorder design which can simplify much of the interface with the telemetry system. The recorder was designed using modular construction consisting of a Digital Control Unit (DCU), Power Supply, and two Memory Modules. The Digital Control Unit (DCU) is made up of four independent microprocessor controlled data channels, configuration control, and a telemetry and test interface. The configuration can be programed so that the SSDR can operate as a 1, 2, or 4 serial channel recorder, or a single 8-bit parallel channel configuration. Each channel has a complete command set and can operate independently of the other channels. Details of the system organization and operational characteristics are presented. The Memory Module was designed with 32 magnetic assemblies, or cells, each containing 16 serial 102.4K bit magnetic "bubble" memory chips. Sense and operator electronics, and field coil drive electronics are also located in the memory module. A prototype SSDR has been fabricated. This prototype is designed for 10⁸ bits of storage but was populated with 128 chips for a 1.3 x 10⁷ bit capacity. Preliminary tests indicate satisfactory operation. Results of these tests are presented and variations with designed characteristics discussed.
    • Solid State Microwave Power Amplifiers - An Overview

      Lewinter, S. W.; The Aerospace Corporation (International Foundation for Telemetering, 1978-11)
      This paper summarizes results that have been achieved with various types of microwave solid state power amplifying devices and presents some projections of advances that can be expected within approximately a five year period. The frequency band surveyed extends from 1 to 100 GHz. The emphasis is on CW or high duty cycle pulse applications, where long life is of great importance, such as in a satellite communication system. The types of devices considered include the gallium arsenide field-effect transistor (GaAs FET), IMPATT diodes, bipolar transistors, Gunn diodes, TRAPATT diodes and electron bombarded semiconductor (EBS) devices. An overview of the technology of microwave power combiners is also included.
    • Some Modeling Aspects in the Simulation of Digital Links

      Jeruchim, Michel C.; General Electric Company (International Foundation for Telemetering, 1978-11)
      Computer simulation of satellite digital links has become a useful tool for the accurate estimation of system bit error rate (BER) performance. This paper describes a simulation facility developed for such a purpose, and in particular discusses two aspects of modeling that bear on the accuracy of the system representation, namely the inclusion of uplink noise and the treatment of carrier phase tracking.
    • Source Coding and Speech Compression

      Gray, R. M.; Buzo, A.; Matsuyoma, Y.; Gray, A. H., Jr.; Markel, J. D.; Stanford University; Signal Technology, Inc. (International Foundation for Telemetering, 1978-11)
      An overview of recent applications of source coding theory and techniques to Linear Predictive Coded Coded speech compression systems is presented. Several distortion measures proposed for use in speech compression systems are described and compared. These distortion measures are then combined with an algorithm for computing "optimum" (minimum distortion) vector quantizers to obtain optimum quantizers for reflection coefficient vectors in Linear Predictive Coded speech systems. The quality of the system is evaluated via the speech distortion measures and listening to demonstration tapes. Some implications for speech compression theory and practice are discussed.