• 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.
    • 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.
    • 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.
    • An FSK/FDM Multiplexed Fiber Optics System for Multichannel Asynchronous Digital Data Transmission

      McDevitt, F. R.; Patisaul, C. R.; Harris Corporation (International Foundation for Telemetering, 1976-09)
      In this paper the use of frequency division multiplexing to reduce the cost of fiber-optic digital data interconnects is investigated. An analysis is performed to determine the level of multiplexing achievable for a typical optical cable link and the cost of the multiplexed link is compared to that of all-parallel transmission for link distances of 0.5, 1.0 and 2.0 km and data rates of 100 kb/s and 1 Mb/s. The results of this work show that for the present and the near-term future, at least, multiplexing offers substantial cost savings over all-parallel transmission.
    • A Microprocessor-Based Computer Developmental System for Satellite Application

      Redman, Paul C.; COMSAT Laboratories (International Foundation for Telemetering, 1976-09)
      This paper describes the hardware and software requirements for a microprocessor-based onboard computer developmental system. In particular, it describes the use of standardized modules which may be assembled in flight form to permit the microprocessor to become a viable alternative to dedicated hard-wired logic implementation in satellite electronic control applications. In addition, it addresses the problem of using electronic control hardware which is common to a majority of applications, with the uniqueness contained in the software. The processor development system includes the basic characteristics of the onboard processor as well as those of the ground-based software development system. The use of these two components to realize a finished onboard processor system is described, and the efficiency advantages of the developmental system are indicated.
    • 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.
    • Elements of a Broadband Biomedical Communications Network

      Henderson, Earl; National Library of Medicine (International Foundation for Telemetering, 1976-09)
      This paper describes the experimental Broadband Biomedical Communications network being developed by the Public Health Service. This network will combine modern satellite communications technology with modified television broadcast techniques to support health experiments in decentralized education, research dissemination and teleconferencing. Small satellite earth terminals will be located in six cities to transmit and receive audiovisual programs. This network will incorporate the Canadian-American Communications Technology Satellite (CTS) to evaluate the cost-effective use of interactive broadband communications systems.
    • 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.
    • 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.
    • Command and Control of a Large, Unmanned, Undersea Vehicle

      Linders, Thomas E.; Lockheed Missiles & Space Co., Inc. (International Foundation for Telemetering, 1976-09)
      A system incorporating commercial modems and two twisted-pair shielded wires makes it possible to control/monitor a large unmanned undersea vehicle from a surface vessel. This paper summarizes the design, explains the rationale for it, and describes some of the problems encountered and their solution.
    • 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.
    • 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.
    • High-Density Digital Data Recording/ Reproducing System

      Leighou, Robert O.; Martin Marietta Corporation (International Foundation for Telemetering, 1976-09)
      Problems associated with reliably recording and reproducing digital data at densities of 10 to 30 kilobits per inch and the solutions to these problems are discussed. The three problems are skew, dc offset, and tape imperfections. The solutions are to use a 14-track, wideband II tape recorder; record NRZ-L; use a 24-bit sync word, 504-bit frame length, and odd parity in every 8-bit byte; and to employ circuit design techniques that minimize the effects of the remaining dc offset and tape imperfections.
    • 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.
    • 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.
    • 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.
    • 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.
    • 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.