• 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.
    • 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.
    • Generalized Criterion for Nonlinear Modulation

      Papantoni-Kazakos, P.; Rice University (International Foundation for Telemetering, 1976-09)
      In this paper a high order error measure is used for the evaluation and design of nonlinear modulation schemes. This high order measure works as a deterrent against thresholds effects. Through the use of the above measure, a simple two-dimensional nonlinear modulation scheme is fully analyzed and efficiently designed.
    • 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,
    • An Operational Video Tape Recording System Utilizing Irig Standard 129-73 [1] Segmented Helical Scan Recording Format

      Damron, S. S.; Schoettmer, G. L.; Strahm, A. E.; Echo Science Corp. (International Foundation for Telemetering, 1976-09)
      Part I. An Operational Video Tape Recording System. An Operational Video Tape Recording (OVTR) system has been developed which fulfills the requirements of the USAF prime specification ASD/ENACC-73-4. The system is comprised, in part, by a highly versatile MIL-E-5400 Airborne Video Recorder and Remote Control Unit which are designed to produce high band [2], [3] video recordings in the environments encountered on deployment in jet fighter aircraft. The companion ground system consists of a video recorder/reproducer for playback of mission tapes and a video Discassette® recorder/reproducer with slow motion/stop action capability for complete analysis of the recorded data. The system design incorporates multi-line rate flexibility to provide record capability of video signals from a multitude of electro-optical sensors including FLIR, LLTV and scan converted radar. The high band performance of the OVTR system makes it suitable for utilization with numerous weapon systems such as PAVE TACK, TISEO, MAVERICK, WALLEYE, HOBO and PAVE SPIKE and various airborne ASW applications. Part II. Expanded Capability for a Wide Range of Instrumentation Applications. The OVTR system is easily expanded in capability to enable the recording of any type of instrumentation data that fits within a 6.5 MHz bandwidth, such as an 8 mB/s serial digital stream, radar, spread spectrum or other down converted communications data. The system features continuous data reproduction capability with no switching transients resulting from sequentially recombining the segmented scan data. The very precise timebase stability and high linearity are key performance factors in enabling the handling of these signals with extremely high fidelity. Further extensions in bandwidth, SNR and time-base stability are under development. Predictions are made on expected performance improvements. Other developments to extend the versatility of the transport systems will be discussed.
    • 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.
    • Frequency Response of Tape Transport Servo Systems

      Law, E. L.; Pacific Missile Test Center (International Foundation for Telemetering, 1976-09)
      A method of measuring the frequency response of the tape servo system of analog magnetic tape recorder/reproducers is presented. The servo responses of three tape machines were measured using this method. The results of these measurements are shown to be in good agreement with the difference (in decibels, (dB)) between the flutter spectra in tachometer and tape servo modes. It is also shown that all three servo systems amplified some flutter components. Therefore if the flutter spectrum of the record machine is known, the total flutter can be reduced by carefully choosing the reproduce machine.
    • Remote Controlled Telemetry Receiver Considerations

      Knowles, Robert C.; Microdyne Corporation (International Foundation for Telemetering, 1976-09)
      As the complexity of telemetry systems increases, the desirability of using remote controlled receivers in these systems to reduce human error, setup time, and premission calibration time increases. The specification of such receivers needs to be done carefully to stay within economic and space limitations. A general discussion of possible system objectives is given in which basic decision questions are raised on the degree of remote control required. A tabulation of receiver functions and controls is given followed by detailed discussion of these various parameters in terms of feasibility, problem areas, space requirements and cost where it represents a major impact. The computer-receiver interface is discussed in terms of how this choice will affect cost and system compatibility with other types of equipment. These discussions should provide some insight in the tradeoffs required in specifying a remotely controlled telemetry receiver.
    • 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.
    • 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.
    • A Mass Memory Unit for the Space Shuttle Orbiter

      Brobst, R. E.; Odetics, Inc. (International Foundation for Telemetering, 1976-09)
      A high-capacity, medium access time data storage system has been developed to interface with the five General Purpose Computers (GPC) in the Space Shuttle System. Termed a Mass Memory Unit (MMU), this system uses magnetic tape as the storage medium. There are two basic functions for the MMU in the Space Shuttle System. First, the MMU will be used to provide display format storage. These displays will be used for vehicle operational procedures and on-line status. The second function is as an auxiliary memory to be used to store and load/reload all phases of flight/ground software. The stored data is catalogued by using eight longitudinal channels (tracks) and eight transverse channels (files). Each file is divided into eight subfiles, and each subfile is divided into 32 blocks. Any one or more blocks or any subfile can be addressed by the GPC. The MMU is capable of storing 1.31 X 10⁸ bits and has a nominal access time (to the nearest block of data) of 600 milliseconds. The data transfer rate is 1 X 10⁶ bits per second and recording is at a packing density of 5 X 10³ bits per inch. The MMU is a hermetically sealed unit which occupies approximately 1,000 cubic inches and weighs approximately 25 pounds. The wear-related items have been designed to ensure over 20,000 tape passes without maintenance. As an advanced form of data storage, the MMU fills a void between slow-access tape drives of high-storage capacity and disks or drums with fast access time and relatively low-storage capacity. In contrast with disk or drum memories, the MMU consumes operating power only when active, which yields a very low average mission power.
    • 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.
    • 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.
    • 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.
    • Convolutional Coding At 50 Mbps for the Shuttle Kuband Return Link

      Batson, Bartus H.; Huth, G. K.; Lyndon B. Johnson Space Center; Axiomatix (International Foundation for Telemetering, 1976-09)
      Error correcting coding is required for 50 Mbps data link from the Shuttle Orbiter through the Tracking and Data Relay Satellite System (TDRSS) to the ground because of severe power limitations. Convolutional coding has been chosen because the decoding algorithms (sequential and Viterbi) provide significant coding gains at the required bit error probability of 10⁻⁶ and can be implemented at 50 Mbps with moderate hardware. While a 50 Mbps sequential decoder has been built, the highest data rate achieved for a Viterbi decoder is 10 Mbps. Thus, five multiplexed 10 Mbps Viterbi decoders must be used to provide a 50 Mbps data rate. This paper discusses the tradeoffs which were considered when selecting the multiplexed Viterbi decoder approach for this application.
    • 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.
    • Cost-Effective Coding Implementations for Computer Communication Systems

      Chien, R. T.; Coordinated Science Laboratory (International Foundation for Telemetering, 1976-09)
      Due to the recent developments in computer hardware and cost reduction, many powerful coding techniques can now be implemented to achieve high reliability at low cost. In this paper we examine the necessary ingredients for successful applications and delineate the systems variables and their inter-relationships. A number of sample applications will be presented to illustrate a systematic procedure to evaluate, select design and implement high performance and low cost systems for error correction and error detection. Implementation approach is considered including hardware, software, microprogramming ROMs, RAMs and LSI.
    • 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.
    • 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.