• Packet Telemetry: A Possible Standard Protocol for Spacecraft Data Handling

      Greenberg, Edward; Hooke, Adrian J.; NASA Jet Propulsion Laboratory (International Foundation for Telemetering, 1978-11)
      Packetized telemetry-handling offers an opportunity to standardize major portions of the spacecraft-to-ground interface for future NASA missions. An end-to-end packet transport protocol is proposed which enables delivery of telemetry data from a remote space sensor to a ground-based user with virtually no project-unique intermediate processing. This paper reviews the possibility of creating a single telemetry format standard for both deep-space and near-earth missions. The proposed standard addresses the greatest NASA problem of the coming decade - cost - by allowing telemetry streams from many inflight spacecraft to be handled on the ground by common, simple, multimission processing elements.
    • Performance Evaluation for Shuttle/TDRSS Links Using Analytical Simulation

      Lindsey, William C.; Braun, Walter R.; LinCom Corporation (International Foundation for Telemetering, 1978-11)
      An analytical simulation package has been developed by LinCom Corporation for analytical verification of bit error rate and tracking services performance for both S- and K-band Shuttle user service through the Tracking and Data Relay Satellite System (TDRSS). The purpose of this effort was to provide a tool to assess overall system performance as well as the sensitivity to key subsystem parameters and to ensure compatibility of TDRSS and Shuttle transponder performance specifications. The evaluation is based on analytical simulation, i.e., a combination of simulation techniques and analytical performance evaluation. This allows the use of a more realistic signal format than is possible with a purely analytical approach and maintains the advantage of short computation time. The Shuttle forward and return link models and the main features of the simulation are described. Sample results of the computer runs are provided for current power budgets and system design parameters.
    • Performance Evaluation of Communication Channels by Computer Simulation

      Poza, H. B.; TRW Defense and Space Systems Group (International Foundation for Telemetering, 1978-11)
      A computer simulation model capable of aiding in the design and predicting the performance of complex end-to-end communication systems is described in this paper. The model is used to choose the optimal modulation scheme under certain communication channel constraints, define the signal distortion characteristics introduced by realizable channel components and select the demodulator/bit synchronizer designs for minimization of bit error rate. A parameter sensitivity analysis is conducted to demonstrate the usefulness of the model in evaluating the effect of different signal distortion phenomena on overall link performance.
    • Performance Evaluation of Step Stare Sensor for Space-Based Air Vehicle Detection

      Ho, C. Q.; Rockwell International (International Foundation for Telemetering, 1978-11)
      Detection of aircraft by a space-based infrared sensor is a demanding task using near-term technology. To achieve sufficient sensitivity, background noise suppression is required because of the relatively weak target signal. Background noise suppression techniques, first order, second order, and higher order temporal differencing, spatial and temporal differencing, are analyzed and compared. Background noise due to both background drift and system vibration effects are calculated. Pixel-to-Pixel offset-induced background noise leakage is also evaluated.
    • Performance of Bandlimited and Hardlimited PSK Signals

      Rey, R. D.; TRW Defense and Space Systems Group (International Foundation for Telemetering, 1978-11)
      Transmission of a signal through a channel, such as a satellite communication channel, results in distortion of the signal due to bandlimiting in the individual channels and hardlimiting. The purpose of this paper is to study the effects that channel distortion due to filtering and hardlimiting have on the performance of BPSK and QPSK. The results will be used to determine the maximum bit rate which can be transmitted through a channel having a particular bandwidth with a specified limit in degradation of performance.
    • Performances of Regenerative and Nonregenerative Satellite Repeaters with MPSK Signalling

      Woo, K. T.; California Institute of Technology (International Foundation for Telemetering, 1978-11)
      Linear (translation), hard-limited, and demod/remod types of satellite repeaters are considered in this paper. Both uncoded and coded multiple phase shift keyed (MPSK) signals are assumed to be transmitted through these repeaters. Relative performances of these repeaters in the presence of uplink and downlink noises are then compared quantitively. Probabilities of bit errors and the computational cutoff rates are computed for 2, 4, and 8 phases PSK signals, with uplink and downlink SNR's as parameters.
    • Phase Referencing for MA Demultiplexing in the TDRSS

      Gagliardi, R. M.; University of Southern California (International Foundation for Telemetering, 1978-11)
      The TDRSS performance is based, to a large extent, on the ability to maintain phase coherency between user, satellite, and ground segment. This is especially true for the MA return subsystem, which uses coherent referencing for multiplexing and demultiplexing between the TDRS and ground processor. Phase noise appearing on these referencing waveforms destroy the phase coherency, and will degrade the overall MA return operation. In this paper the manner in which this phase referencing is achieved is described. In addition, the results of a preliminary study to distinguish the key MA return phase noise sources, and the manner in which each will ultimately influence performance, is presented. The results show that the return phase noise effects can be separated into "coherent" and "noncoherent" contributions, and each must be separately evaluated. The effect of the various tracking loop bandwidths throughout the link is shown, and the manner in which the specific phase noise spectra are eventually filtered is developed.
    • The Power of Desarguesian Sets

      Wu, W. W.; Communications Satellite Corporation (International Foundation for Telemetering, 1978-11)
      A Desarguesian set is a planar Euclidean geometry difference set which can be used to derive new cyclic block codes, convolutional self-orthogonal codes, and random multiple access codes. This paper discusses the usefulness of these codes and presents the step-by-step procedure for the purpose of constructing such sets. Comparisons are also made with planar projective geometry sets in which two types of existing codes were obtained.
    • Processing Satellites

      Omura, Kim; University of California, Los Angeles (International Foundation for Telemetering, 1978-11)
      With few exceptions, satellite communications systems today employ conventional nonprocessing satellites that are often referred to as "bent pipes in the sky." These satellites merely act as nonlinear (TWT) amplifiers that transmit on the downlink the same signals plus noise (frequency shifted) that it receives on the uplink. It is now clear that the "micro-processor revolution" will impact on satellite technology and result in a new generation of communication satellites with various on-board digital processing. The orbiting experimental military satellites Les-8/9 are the first-of the new generation of processing satellites. Many more such satellites are now being considered with increasingly complex digital processing on the satellites. For military applications these on-board processing capabilities are listed below in increasing order of complexity.
    • Pulse to Pulse Encoding in Optical Communications

      Prati, G.; Gagliardi, R.; University of Pisa; University of Southern California (International Foundation for Telemetering, 1978-11)
      Optical pulsing of a laser beam provides a convenient manner for transmitting digital information, and such procedures have led to well-accepted classes of pulse amplitude and pulse position modulation formats. However the excessive pulse dispersion and background light bursts that characterize several optical channels severely limit performance and achievable data rates. One procedure for combating these effects is to encode data over a multiple of pulse frames, and decode sequences of pulses rather than each pulse individually. In the paper pulse to pulse encoding and decoding of an optical beam is examined, considering both photodector gain effects and receiver thermal noise. Theoretical performance results are presented, and the relation between this type of decoding and "tree searching" is developed.
    • 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.