• 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.
    • The Space Shuttle Orbiter Communication and Tracking System

      Carrier, Louis M.; Pope, Warren S.; Rockwell International (International Foundation for Telemetering, 1978-11)
      During space flight, the communications and tracking system of the Space Shuttle orbiter uses S- and Ku-band links to provide tracking; reception of digitized voice, commands, and printed or diagramatic data at a maximum rate of 216 kilobits a second; and transmission of digitized voice, telemetry, television, and data at a maximum rate of 50 megabits a second. S-band links may be established directly with a ground station and both S- and Ku-band links may be routed through NASA's Tracking and Data Relay Satellite System A simultaneous capability to communicate with other satellites or spacecraft, using a variety of formats and modulation techniques on more than 850 S-band channels, is provided. UHF is used for communication with extravehicular astronauts. Audio and television subsystems serve on-board needs as well as interfacing with the RF equipment. During aerodynamic flight following entry, a UHF link provides two-way simplex voice communication with Air Traffic Control facilities. Air navigation aids include TACAN, a microwave scan-beam landing system and radar altimeters.
    • Space Shuttle Orbiter PN Code Synchronization

      Houston, Sam W.; TRW Defense and Space Systems Group (International Foundation for Telemetering, 1978-11)
      The S-band Communications link to the Space Shuttle Orbiter from ground stations via TDRSS are transmitted spread spectrum to reduce the incident power flux density on the Earth's surface. This paper describes the requisite spread spectrum processing onboard Shuttle.
    • Space Shuttle Orbiter Processing, Monitoring, and Telemetry Systems

      Carrier, Louis M.; Robitaille, Richard A.; Rockwell International (International Foundation for Telemetering, 1978-11)
      The transportation vehicle for launching personnel and payloads into earth orbit during the 1980's and subsequent years will be NASA's space shuttle. The space shuttle flight system consists of an orbiter, an external tank, and two solid rocket boosters. The orbiter, a key element of the Space Shuttle, is launched into space like a conventional launch vehicle, performs on-orbit payload missions, enters the atmosphere, and lands much like a conventional commercial jet aircraft. This paper provides an overview of the Space Shuttle avionics with prime emphasis on how the orbiter's on-board processing, monitoring, and telemetry systems function during the on-orbit mission phase. Included is a description of the S-band and Ku-band RF transmission link and its relationship to the ground systems, payload interfaces, and support equipment. Also discussed are the flexibility of its instrumentation system (including capability to provide formats), features of the on-board monitoring systems (dedicated displays, cathode-ray tubes, and caution and warning systems), and methods for storing and processing data (recorders, mass memory, and on-board computers). The orbiter's avionic services to the payloads and the future growth of the Space Transportation System and the orbiter are also discussed briefly.
    • Space Shuttle Payload Communication Links

      Springett, James C.; Udalov, Sergei (International Foundation for Telemetering, 1978-11)
      One mission of the Shuttle is to place payloads into Earth orbit or on escape trajectories and to recover payloads from Earth orbit. In order to properly deploy and retrieve such payloads, operational and diagnostic communications must take place between the payloads and the Shuttle. The results of such communications, in the form of tracking, commands, and telemetry, will be interpreted both aboard the Shuttle and on the ground. To accommodate a diverse set of payloads for both NASA and DOD programs, multimode avionic equipment dedicated to payload communications is being installed aboard the Shuttle. This equipment, operating at RF and baseband and providing capability for digital and analog signal forms, will furnish all required capabilities to communicate with both attached and detached payloads.
    • Spectral Shaping Without Subcarriers

      Welch, Lloyd R.; University of Southern California (International Foundation for Telemetering, 1978-11)
      For proper operation of the phase lock loop which tracks a carrier it is important to minimize the spectral energy at frequencies near the carrier. A traditional method is to modulate the data onto a subcarrier in such a way that there is little energy near D.C. The resulting signal then is used to modulate the carrier. The problem with such a scheme is that the total bandwidth is much larger than necessary to transmit the data. This paper proposes and analyzes a simpler scheme which increases the data bandwidth by a very small fraction, yet reduces the energy near D.C. to nearly zero.
    • Spread Spectrum and Coding Techniques in Communication Systems

      Gerardi, F. R.; Otsuki, W. T.; The Aerospace Corporation (International Foundation for Telemetering, 1978-11)
      With the increase in complexity of military communications networks, a combination of spectrum spreading and error correction coding is typically required to provide adequate antijam protection. The specific system architecture utilizing these techniques is established in this presentation by performance requirements, system constraints, interface problems, and assumed jammer models. This presentation will describe various processing techniques with emphasis on their interactions and limitations. Two spread spectrum techniques for permitting operations in a jamming environment are considered: direct sequence (PN) and frequency hopping. The advantages and limitations of each technology will be discussed. The antijam capability of these spread spectrum systems can be improved by using various error correction coding schemes. These can (make more efficient use of the bandwidth allocation) as well as provide enhanced protection against pulse and tone jammers. The advantages, limitations, and constraints imposed on a communication system using various combinations of these techniques are discussed with particular emphasis on the system performance.