• A Digital Data Interleaver

      Goodwin, John E.; Martin Marietta (International Foundation for Telemetering, 1976-09)
      Many future space programs such as Space Shuttle contain a number of payloads, each generating its own digital data stream. It is frequently desirable to combine these data streams in a composite serial stream for the telemetry down link. The circuitry for combining these data streams should be as transparent as possible to the design and operation of individual data source subsystems. A concept is described for interleaving the data of several sources without any subsystem synchronization, few limitations on data rates, a no restrictions on formats. All data are accepted without loss and the composite stream is formatted in accordance with IRIG standards. The interleaver requires the use of artificial fill data to assure the possibility of accepting and formatting asynchronous data symmetrically; therefore, methods of error detection and correction of fill words are discussed to ensure nonambiguity of data and fill work.
    • Cascaded Coherent Tracking Systems with Time-Varying Channels

      Weber, William J., III; Yuen, Joseph H.; California Institute of Technology (International Foundation for Telemetering, 1976-09)
      An approach is given to the analysis of two-way coherent tracking systems in which the transmitted signals have passed through linear time-varying channels. The specific channel considered is the lognormal fading channel, although the results and techniques can be extended to other channels such as the Rice and Rayleigh channels. The performance of the system is characterized by the steady state probability density function of the reduced phase error process in the second tracking loop. Particular numerical examples and system performance curves are given to illustrate the theory for channel models and two-way systems of practical interest.
    • An LSI Controller for Satellite Switched TDMA

      Dobson, D. P.; Ring, A. E.; Hawker Siddeley Dynamics Limited (International Foundation for Telemetering, 1976-09)
      Satellite-switched time division multiple access (SSTDMA) is a high efficiency technique likely to be exploited soon in communications satellites. Besides needing special equipment at the earth stations, two major units are required in the satellite to complete the system, namely, a microwave switching matrix (MSM) and a distribution control unit (DCU). The MSM connects any one uplink to any one downlink in a "telephone exchange" arrangement and the DCU, which can be programmed from the ground, controls the switching of the MSM connection patterns in real time. The DCU also provides the master clock for the complete SSTDMA system. This paper describes an implementation of a DCU using custom large scale integration (LSI), which employs only four chips (two each of two types) for the entire logic to control an 8 x 8 MSM. This offers considerable advantages in terms of mass, power consumption and reliability. Some of the benefits and problems of the LSI implementation are also discussed.
    • On Zero Memory Nonlinear Transformations of Gaussian Processes

      Wise, Gary; Thomas, John B.; University of Texas; Princeton University (International Foundation for Telemetering, 1976-09)
      This paper treats the second moment properties of a zero memory nonlinearity, given that the input is a stationary Gaussian process. The output autocorrelation function is shown to be expressed conveniently in terms of the input autocorrelation function and a set of coefficients describing the ZNL. Two theorems are proved concerning the output process bandwidth. The first shows that the output bandwidth is generally greater than the input bandwidth. The second gives necessary and sufficient conditions for the output process to be strictly bandlimited.
    • A Code Structure for Certain Coma Environments

      Milstein, Laurence B.; Ragonetti, Ronald R.; R.P.I. (International Foundation for Telemetering, 1976-09)
      Certain communication systems which employ code division multiple access as a means of supporting multiple users need very long codes to guard against the threat of intentional jamming, but cannot tolerate the lengthy acquisition time which long codes usually require. As a possible solution to this problem, the use of combination sequences has been suggested, and this paper presents some new results, both analytical and numerical, on this technique.
    • On Access Control Disciplines for a TDMA System with Multiple-Rate Real-Time Sources

      Louie, Ming; Rubin, Izhak; University of California (International Foundation for Telemetering, 1976-09)
      We consider a communication medium, such as a satellite communication channel, which is shared by a number of sources on a time-division multiple-access (TDMA) basis. Sources require real-time transmission over the channel. A central controller stores the requests for transmission by the sources and assigns the freed slots within the time-frame to the appropriate sources, following a dynamic demand-assignment access control discipline. Sources are further assumed to require real-time transmission at different information rates, and thus require different number of slots per frame. Two access-control disciplines are studied, structurally optimized, and compared. A fixed-assignment discipline divides the frame slots among the various source classes on a predetermined basis. A priority-assignment discipline dynamically modifies the latter division by allowing one class of requests to utilize the freed slots of the other. The analysis demonstrates the extent to which the second scheme is preferrable, incorporating a message maximal waiting-time objective function and adaptability considerations.
    • High Capacity Optical Data Storage and Retrieval Systems

      Nelson, Richard H.; Otten, Thomas H.; HARRIS Corporation (International Foundation for Telemetering, 1976-09)
      Recording of digital data on photographic film is the practical solution to a broad spectrum of computer memory and data storage and retrieval requirements. Mass memory systems with bulk storage capacities between 1011 and 1013 bits with multi-second access times are currently being built. Development effort is also continuing in the specialized area of ultra-high speed transfer of data into and out of large intermediate bulk stores. Systems currently being produced by Harris Electronic Systems Division take advantage of holographic principals: (1) a natural distributive encoding by recording the information over the entire hologram rather than at discrete points, thereby reducing susceptibility to dust, scratches and recording media imperfections, (2) reconstruction of the data into parallel non-skewed channels, and (3) insensitivity of the recording medium placement relative to the detector array, greatly reducing mechanical tolerances necessary for rapid access and ultra-high speed data transfers. The purpose of this paper is to present a synopsis of the current status of each of two storage and retrieval systems under development for the U. S. Air Force. The first system we describe (HRMR Microfilm Mass Memory System) uses photographic film in the form of microfiche to provide a mass storage capability with automatic, computer-controlled, random access to stored records. The second system we consider (Wideband Holographic Recorder) uses multichannel recording on roll film for storage and retrieval of large unit records at hundreds of megabits per second.
    • Earth Terminal Design Considerations for Biomedical Communications via CTS

      Thoma, George R.; National Library of Medicine (International Foundation for Telemetering, 1976-09)
      This paper describes the earth terminals in the Biomedical Communications Experiment via the Communications Technology Satellite (CTS). Important analyses performed in the selection of the earth terminal parameters are summarized. In particular, analyses of the link, inter-modulation products, and rain attenuation are presented as rationales for selecting ground transmitter power, receiver G/T, frequency spacing, that are optimum for TASO Grade 1 video quality, full-duplex color video/audio and an audio order-wire capability.
    • Processing Commands for Geostationary Satellites

      Bates, N. F.; Harris, P.; Aeronutronic Ford (International Foundation for Telemetering, 1976-09)
      This paper discusses command techniques that are employed for weather and communication satellites. The introduction describes the essential requirements for a command system. Detection of the baseband signal is analyzed with error budgets assigned to the command receiver. Subsequent discussions consider the command processor, low power, decrypters, critical commands, bus supply, remote command distribution, and redundancy. Finally, the command function in an operational spacecraft is presented.
    • Predicting Performance of Convolutional Coded Communication Systems

      Huth, G. K.; Axiomatix (International Foundation for Telemetering, 1976-09)
      The probability of error for a convolutional coded communication system can be predicted using three approaches. The first approach is using Gallager's [1] exponential bound for random codes. The second technique is the use of transfer function union bounds developed by Viterbi [2]. Finally, an approximation to the transfer function developed by Huth and Weber [3] can be used. This paper compares the three approaches for predicting performance and presents results for Viterbi decoding bit error probability, burst error probability, and decoder memory length.
    • Automated Meteorological Data Acquisition System

      Ohmae, Yoshitsugu; Nippon Telegraph and Telephone Public Corp. (International Foundation for Telemetering, 1976-09)
      This paper describes the Automated Meteorological Data Acquisition System (AMeDAS) developed co-operatively by the Japan Meteorological Agency (JMA) and the Nippon Telegraph and Telephone Public Corporation (NTT). The object of this system is to collect exact meteorological data in Japan automatically, and to process it expeditiously by computer. The automatic meteorological observation equipments which observe the amount of precipitation, wind speed/direction, sunshine duration and air temperature, are located at about 1,300 points throughout Japan. The data obtained are collected at the computer center through NTT's telecommunication network by automatic telemetering. After rearrangement, data are sent to about 60 forecasting centers through leased lines. Using these data, the forecasting centers can make accurate weather forecasts to enable taking appropriate measures against disasters.
    • 120 Mb/s and 240 Mb/s Bit Synchronizer-Signal Conditioners for NASA High Data Rate Applications

      Gray, J. S.; Harris Electronic Systems Division (International Foundation for Telemetering, 1976-09)
      Two bit synchronizer-signal conditioners (BSSC) developed for NASA high data rate applications such as earth resources monitoring are described. One BSSC is centered at 120 Mb/s and the other at 240 Mb/s. These subsystems are featured out of the total hardware developed* because the BSSC is such a key subsystem in determining overall system statistical performance. These units represent an evolution of high data rate technology toward the versatile any data rate BSSC's available at low data rates. Numerous inputs/outputs, control functions, indicators, plus the ability to minimize the effects of various signal perturbations are provided. Examples of allowed perturbations are input level variations, bit rate variance static and dynamic, baseline, transition density, bandlimiting, etc., as well as noise. Emphasis in the past has been primarily concerned only with noise.
    • Selection of an Optimal Frame Synchronization Strategy

      Straehley, E. H.; Straehley Associates (International Foundation for Telemetering, 1976-09)
      The operation of preprogrammed and adaptive frame synchronization strategies is simulated, based upon previous mathematical derivations. The simulation, coded in APL, describes operation over a range of Signal to Noise ratios of -4db to +14 db. Both the "Go-to-Lock" and the "Return-to-Search" modes of operation are studied. A specific optimal strategy is determined for the conventional synchronizer for each 2db interval over the range. This synchronizer is compared with an adaptive synchronizer, using the SPRT technique, and optimized for a -2db SNR. The SPRT synchronizer reaches Lock significantly faster for SNR<8db, and reverts to Search faster for SNR<2db. It adapts less readily to improving SNR in the "Return-to- Search" operation, but will still produce optimum results in this mode with fewer controls than a conventional design.
    • Performance of Convolutionally Encoded Noncoherent MFSK Modem in Fading Channels

      Modestino, J. W.; Mui, S. Y.; R.P.I. (International Foundation for Telemetering, 1976-09)
      The performance of a convolutionally encoded noncoherent multiple frequency shift-keyed (MFSK) modem utilizing Viterbi maximum likelihood decoding and operating on a fading channel is described. Both the lognormal and classical Rician fading channels are considered for both slow and time-varying channel conditions. Primary interest is in the resulting bit error rate as a function of E(b)/N(0) parameterized by both the fading channel and code parameters. Fairly general upper bounds on bit error probability are provided and compared with simulation results in the two extremes of zero and infinite channel memory. The efficacy of simple block interleaving in combatting channel memory effects are thoroughly explored. Both quantized and unquantized receiver outputs are considered.
    • The Implementation of an On-Board Data Handling System by a Programmable Modular Concept

      Frölich, Horst; Dornier System GMBH (International Foundation for Telemetering, 1976-09)
      The implementation of On-Board Data Handling Systems by individually tailored electronics leads to high development costs and risk. In order to overcome these shortcomings for future applications of on-board tasks, a complete modular concept has been developed for control, data acquisition, data reduction and telemetry encoding in onboard aerospace vehicles. This highly flexible concept consisting of a large spectrum of real time peripherals and different central processing units has meanwhile proven its high flexibility in a wide spectrum of applications. The system is freely programmable and supported by extensive software for program development and testing. The application software can be developed on host computers of different types. The paper gives a description of the system. By the example of an application in an aerospace telemetry and control system the advantage of using this modular approach is demonstrated.
    • Simulation of the Effects of Hard Limiting on Image Quality of Synthetic Aperature Radar

      Lipes, Richard G.; Butman, Stanley A.; Caltech’s Jet Propulsion Laboratory (International Foundation for Telemetering, 1976-09)
      Starting with a magnetic tape of a scene viewed by the ERTS (Landsat) satellite, we simulated the radar return of reflectors whose average intensity matched that of the picture elements in the scene. The returns were processed in three ways: normally or with no quantization, with a procedure simulating IF (intermediate frequency) hard limiting, and with a procedure simulating video (baseband) hard limiting. For each type of processing we developed an image for a one, two, and four-look system. We found that IF limiting is slightly better than video limiting, while both can be reasonable trade-offs of image quality for reduced data rates when the number of looks is four or less. These conclusions are supported by photographs representing the different processing techniques.
    • Trends in the Control and Monitoring of Future European Satellites

      Fiorica, F.; European Space Agency (International Foundation for Telemetering, 1976-09)
      Current and future programmes of the European Space Agency (ESA) consist of relatively few missions but widely diversified in nature. The control and monitoring operations can be performed using either a specialized common band or the different payload frequency bands as assigned to each mission. The trade-off is discussed in the paper and considerations for the choice of the most suitable band presented. Some features of the preferred approach both for the ground and the space segments are illustrated as well.
    • A Sampling Window Test Method for Evaluation of Phase Encoded Recorder Systems

      Lerma, J. P.; Lindquist, C. A.; Odetics, Inc. (International Foundation for Telemetering, 1976-09)
      Self-clocking, digital phase encoded data formats have gained popular acceptance in the field of high density digital magnetic recording. At high transition densities, random noise processes can play a prominent role in determining system performance and reliability. The eye pattern technique of assessing the relative merit of a signal with respect to noise is severely limited at high transition densities. The stringent requirements associated with high density recording and the limitations of eye pattern analysis have stimulated the development of a digitally implemented sampling window analyzer which permits the direct evaluation of the statistical properties of a digital phase encoded reproduce waveform. The analyzer observes data transitions through two time sampling windows for the purpose of estimating pattern independent conditional probability. The statistical parameters of the conditional probability obtained can be used to detect latent sources of noise and to define optimum record zone parameters.
    • Microprocessors for Satellite Telemetry - A Universal Approach

      Campoli, Peter H.; Brede, S. K.; Spacetac, Inc.; Analytyx Electronic Systems, Inc. (International Foundation for Telemetering, 1976-09)
      A system has been developed which can be flexibly tailored to meet most telemetry requirements. The concept results in higher reliability, greater modularity, and lower cost than classical approaches. It also offers more system capability. The development was realized by adaptation of the telemetry requirements to a computer system architecture. Such an adaptation is made possible by the use of a microprocessor as a device controller. The concept has been successfully applied to a specific telemetry requirement for use on a satellite. The results have far-reaching implications on the future of spacecraft electronics. Reductions in overall system hardware are possible while increasing the functional capability.
    • ATS-6 European L-Band Aeronautical Experiments

      Brown, D. L.; Guérin, Y.; Melchior, G.; Absolonne, F.; European Space Tecnhology Centre (International Foundation for Telemetering, 1976-09)
      This paper describes the European experiments and test results obtained in L-band (1550-1650 MHz),using the NASA ATS-6 satellite, to conduct communication and navigation tests over the North Atlantic thus assisting in the definition of modulation techniques to be used with an Aeronautical Satellite System, AEROSAT. The experiments conducted by ESA and some of its member states covered voice, data transmission and ranging measurements. The tests were performed on board a Comet IV aircraft equipped with a slot dipole array antenna, especially designed to operate within the coverage required in the AEROSAT MOU (Memorandum of Understanding for the AEROSAT programme signed by Europe (ESA), the USA (FAA) and Canada (DoT) in August 1974. The voice tests compared DELTA-PSK with adaptive NBFM using test tapes consisting of logatoms, SCIM sequences, and PB word lists. An investigation of multipath noise effects on the PSK data transmission system was carried out and led to the general conclusion that this problem is a serious one for coherent demodulators. The DECPSK system tested exhibited a strong tendency towards a Rayleigh channel BER situation at low antenna signal to multipath interference ratios. The ranging results show the feasibility of achieving standard deviations of range of around 500-600 m for the PLACE tone system with its rather short integration time of 120 ms, and 100 m for the DIOSCURES pseudo random coded system operated on a CW basis.