Now showing items 21-40 of 73

    • MFSK Frequency Acquisition and Synchronization for the Jupiter Probe-to-Relay Communication Link

      Fluchel, R. B.; Lee, G. M.; Paddon, E. A.; McDonnell Douglas Astronautics Co. (International Foundation for Telemetering, 1976-09)
      This paper discusses the coarse frequency acquisition problem and the fine frequency tracking problem for a communication link between a spacecraft and a probe entering the atmosphere of Jupiter. A coded noncoherent MFSK modulation format is assumed along with a severely fading link. Fine frequency tracking is shown to be a more serious problem than coarse acquisition.
    • 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.
    • A Low Level Amplifier for Precision Multiplexing

      Temkin, Bruce M.; General Dynamics (International Foundation for Telemetering, 1976-09)
      An amplifier has been designed for high or low level multiplexing for aerospace PCM data acquisition systems. It was designed to provide "instrumentation amplifier" quality under conditions of high common mode, high or low rate random access operation and broad operating temperatures. It has shown versatility in operation, provides common mode rejection in excess of 125 db (RTI) and can be tailored for a drift temperature coefficient of less than 0.2 μV/°C (RTI)
    • Comparison of PCM Codes for Direct Recording

      King, D. A.; Pacific Missile Test Center (International Foundation for Telemetering, 1976-09)
      The bit packing performance of randomized-non-return-to-zero (randomized- NRZ,) odd parity-NRZ, delay modulation, and bi-phase (Bi-Ø) in direct recording was experimentally compared at a bit error probability (BEP) of 10⁻⁶. The effect of bit patterns, record and reproduce levels, bias level, tape speed, tape recorder bandwidth, bit synchronizers, and crossplay between tape recorders on bit packing density was investigated. At high bit packing densities, significant variations in data quality were found for changes in these parameters. This imposes limitations on practical bit packing densities. Some bit synchronizers were found to seriously reduce bit packing densities. Results show randomized-NR.Z to be superior to the other codes in bit packing density.
    • The Application of High Density Tape Recording to Image Processing

      Heffner, Paul; NASA Goddard Space Flight Center (International Foundation for Telemetering, 1976-09)
      The Image Processing Facility at Goddard Space Flight Center has the requirement to move volumes of digital data (10¹¹ data bits per day) that exceed the capacity of conventional computer tape. This paper presents the requirements for a high density digital tape recorder compatible with conventional computer systems. The steps leading to the formulation of these requirements are described. The use and interaction of the recorder with the various elements in the facility are treated. The formulation of the requirements resulted in the selection of a Honeywell Model 96 Wideband II tape transport modified by Martin Marietta Corporation for digital serial-in, serial-out operation. This selection followed a competitive procurement action.
    • Candidate Receivers for Unbalanced QPSK

      Weber, Charles L.; University of Southern California (International Foundation for Telemetering, 1976-09)
      Candidate receivers for unbalanced QPSK signal foremats have been studied. The fourth power receiver is shown to be an unsatisfactory choice unless the power division is close to 50-50 or 100-0. The Costas loop receiver which tracks on the high data rate signal of the unbalanced QPSK waveform is shown to perform satisfactorily. Approximate error rate computations, show that the Costas loop considered performs within a few tenths of a dB of the ideal receiver.
    • 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.
    • 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.
    • Degradation of FSK Detection Performance Due to Tone Phase Jitter

      Holmes, Jack K.; Hedin, George L.; TRW Defense; Space Systems (International Foundation for Telemetering, 1976-09)
      The paper develops some new results for the degradation in SNR, due to unwanted phase jitter, for a FSK receiver system. The unwanted phase modulation is assumed to be present equally on either FSK tone and is modeled as a sample function of a Gaussian random process. Results are derived based on a standard type FSK system employing bandpass filters, square law envelope detectors, a subtractor, and a post detection lowpass data filter. The degradation was found to depend on the mark-space filter bandwidths, the doppler frequency of the received tones, the nominal SNR and the post detection filter bandwidths. The degradation is minimal for small doppler shifts; however, once the tones, in the predetection filters were displaced to within the post detection filter bandwidth of the predetection filter band edge, the degradation increased dramatically. This was due to the fact that the filtering of the phase noise caused the envelope detectors to produce self noise. In fact, at high SNR's the degradation is primarily due to self noise or envelope distortion due to filtering of the phase jitter spectrum. It is important to point out that the degradation found here is due only to phase noise effects and not sin χ/χ losses. The results derived here are accurate for phase jitter variances ≲0.1. In addition, it is assumed that the lowpass equivalent filter impulse response of the bandpass filter be real, that is, the lowpass equivalent transfer function must be hermetian symetric.
    • Method for Determination of System Parameters in Telemetry Baseband Modulation Systems

      Rosen, Charles; Microcom Corporation (International Foundation for Telemetering, 1976-09)
      The purpose of this article is to complete the work for specifying the system parameters for all types of modulation used in telemetry systems. The original work is contained in the ITC Proceeding Volume 10 1974, and deals only with FM/FM systems. The combined works of the two articles will consider single type modulation formats, or a combination of the different types of modulations used in present day system.
    • 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.
    • 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.
    • 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.
    • Telemetry Packetization for Improved Mission Operations

      Greene, Edward P.; NASA (International Foundation for Telemetering, 1976-09)
      The requirements for mission operations data management will accelerate sharply when the Space Transportation System (i.e., Space Shuttle) becomes the primary vehicle for research from space. These demands can be satisfied most effectively by providing a higher level source encoding function within the spaceborne vehicle. An Instrument Telemetry Packet (ITP) concept is described which represents an alternative to the conventional multiplexed telemetry frame approach for acquiring spaceborne instrument data. By providing excellent data integrity protection at the source and a variable instrument bandwidth capability, this ITP concept represents a significant improvement over our present data acquisition procedures. Realignments in the ground telemetry processing functions are described to take advantage of the ITP concept and to make the data management system more responsive to the scientific investigators.
    • 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.
    • Analysis and Decomposition of Complex Real-Time Processes with a Real-Time Schemata Model

      Adrion, W. R.; Frick, P. A.; Szulewski, P. A.; Oregon State University (International Foundation for Telemetering, 1976-09)
      In this paper a formal model for real-time processes is expanded to analyze structured, complex algorithms. Structured forms have inherent modularity and the authors discuss advantages of mapping such processes on distributed micro or mini processor networks. Processes under consideration are subject to random interrupts by independent I/O demands. Degradation of total system performance due to these demands is discussed. Extentions and ongoing research are mentioned.
    • Optimal Link Capacity Assignments in Teleprocessing and Centralized Computer Networks

      Rubin, Izhak; UCLA (International Foundation for Telemetering, 1976-09)
      We consider a centralized network model representing a teleprocessing or a centralized computer communication network. The network is topologically described by a tree structure. A single central node represents a data-processing center, while the other nodes correspond to remote terminals. A maximal average message delay value is prescribed. A cost function is assumed to incorporate a term representing link costs, dependent only on the link flows, and a term involving weighted (distance related) sum of the powers of the link-capacity values. We then solve for the optimal link capacity assignment, yielding the minimal value of the cost function under the prescribed maximal message delay value.
    • Digital Data Transmission in a PAM Communication System

      King, D. A.; Pacific Missile Test Center (International Foundation for Telemetering, 1976-09)
      This paper presents the results of an experimental evaluation of the effectiveness of digital data transmission in a pulse-amplitude modulation (PAM) communication system. A PAM communication system was simulated and equipment was developed to obtain experimental results indicative of PAM's effectiveness in transmission of digital data. The results consist of word, channel, and bit error probability curves for different numbers of digital bits per PAM channel. The digital bits were converted to analog voltage levels which amplitude-modulated selected PAM channels. After decommutation the digital bits were recovered from the analog voltage levels by an analog to digital conversion. The data indicates that the number of bits per channel should be 4 or less depending upon the digital data quality requirements. The error probability curves can be used to determine whether or not a PAM communication system can telemeter digital data within given constraints. In addition, the results provide guidelines for the implementation of digital data in a PAM system.
    • Broadcast Channels: Some Recent Developments and Open Problems

      Leighton, William J.; Tan, Harry H.; Princeton University (International Foundation for Telemetering, 1976-09)
      In this paper we consider some recent developments and open problems on broadcast channels. In particular we consider general discrete memoryless broadcast channel with two information sources. For the case where the two sources are independent we define a rate region R and show that arbitrarily reliable transmission of information over a general broadcast channel may be achieved with suitable coding at all rates in R. For the special case of degraded broadcast channels, R reduces to a previously known expression for the capacity region. R is calculated for a nondegradable broadcast channel which shows that previously known achievable rate regions can be substantially improved upon. We also define an achievable rate region for the case of dependent information sources. Finally, some open problems are discussed.
    • MIDISS: A Unique Multi-Processor Telemetry Ground Station

      Feinberg, Donald L.; Spacetac, Inc. (International Foundation for Telemetering, 1976-09)
      An optimum architecture for real-time telemetry data acquisition and display has been developed. It provides a high degree of flexibility and throughput while using a minimum of hardware: as applied to the MIDISS system, this approach enables users to specify data processing for each sensor on several satellites independently of downlink formats. Each user can specify and modify CRT displays without interrupting the data processing performance. Processing may include algebraic manipulation, logical branching, logic products, time averaging, etc. This flexibility is provided by SPACETALK, a FORTRAN-like language that enables the user to deal with each sensor by name. Users can also format and transmit uplink commands. Hardware minimization is evidenced by MIDISS's compactness. It consists of a 16-bit minicomputer and a SPACEPIPE (microcomputer-based, front-end processor) that decommutates multiple downlinks, provides rate-buffering, and performs data compression and alarm-checking. The minicomputer is thus free to perform extensive data processing for those downlink channels that are changing at significant rates,