• A VERY HIGH SPEED HARD DECISION SEQUENTIAL DECODER

      Gilhousen, K. S.; Lumb, D. R.; LINKABIT Corporation; NASA (International Foundation for Telemetering, 1972-10)
      There are numerous applications for high data rate coding systems for earth orbiting space-missions with power limited links. Studies indicated that a 40 Mbps hard decision sequential decoder would best meet the requirements. A prototype decoder has been designed and fabricated using the fastest commercially available digital integrated circuits, MECL III. Thus far, an internal computational rate of 70 Million computations per second has been achieved. Computational efficiency of the decoding algorithm was greatly improved by incorporating two modifications to the Fano algorithm; “double quick threshold loosening” and “diagonal steps.” Preliminary results indicate that an output error rate of 10^-5 can be achieved with E(b)/N(o) less than 5.4 dB at data rates up to 40 Mbps. At lower data rates, even less signal energy is required. This decoder is believed to be at least 5 times faster than any previous sequential decoder.
    • SATELLITE NETWORKS FOR EDUCATION

      Singh, J. P.; Morgan, R. P.; Rosenbaum, F. J.; Center for Development Technology (International Foundation for Telemetering, 1972-10)
      This paper is concerned with satellite-based educational networking. It is based on work performed in a continuing study of the potential uses of communications satellites to help meet educational needs in the United States. The paper is divided into four main sections. The first is concerned with the characteristics and structure of networks. The second section contains a discussion of pressures within the educational establishment that are providing motivation for various types of networks. This latter section also identifies studies in which networking needs for educational sectors and services are defined. Section three examines the current status of educational networking for educational radio and television, Instructional Television Fixed Services, inter- and intrastate educational communication networks, computer networks, cabletelevision for education, and continuing and proposed educational experiments using NASA’s Applications Technology Satellites. The fourth section describes possible satellite-based educational telecommunication services and three alternatives for implementing educational satellite systems. The paper concludes with some remarks concerning public policy aspects of future educational satellite system development.
    • PHYSIOLOGICAL CONSIDERATIONS IN IMPLANTABLE UNDERWATER TELEMETRY

      Adey, W. R.; Zweizig, J. R. (International Foundation for Telemetering, 1972-10)
      Monitoring the internal environment of marine organisms as well as that of man in the oceanic milieu presents unique problems to the physiologist as signals used for data telemetry may have clear behavioral effects. The question of a tolerable level using different transmission modes is found to be species specific, but general guidelines are drawn on the basis of filtering and detection theory, the properties of the transmission media and the excitability characteristics of biological tissue. Transmission through water is surveyed and attenuation characteristics are presented. Experimental findings indicate that waves propagated through water and tissues are time dispersive and thus at sufficiently high frequencies the received signal process must be carefully evaluated with regard to optimal demodulation. Frequencies up to 1 MHz appear to be within the immediately usable range for distances of 1 meter or less. This bandwidth may be used for frequency-division multiplexed subcarriers or appropriately coded PCM transmission. Successful underwater transmission of physiological signals has been accomplished using frequency modulation of carriers transmitted by return-current-density methods, as part of an external biotelemetry system. Experimental evidence shows that implanted devices operating at high frequencies and at levels far below stimulation threshold can be used for transmission to the external transponder where adequate power is available for transmission to an underwater habitat or through data buoys to remote recording centers.
    • FEEDBACK DECODERS FOR NAVAL APPLICATIONS

      Heller, J. A.; Peterson, R. D.; LINKABIT Corporation; Naval Electronics Laboratory Center (International Foundation for Telemetering, 1972-10)
      Feedback decoding is a simple technique for obtaining a significant improvement in performance on a wide range of binary channels. Code interleaving for burst error correction is particularly simple to implement with feedback decoding. A flexible feedback decoder built by LINKABIT Corporation was tested on a simulated shipboard satellite communication channel. The channel was characterized as being additive Gaussian with a superimposed 5% duty factor periodic burst during which the channel error rate is close to .5. The precise radar induced error burst locations are assumed unknown to the decoder. The simple feedback decoder, operated with the error bursts,provided performance equivalent to t at of an uncoded system operating against additive Gaussian noise alone.
    • AIRBORNE VISIBLE LASER OPTICAL COMMUNICATION EXPERIMENT

      Randall, J. L.; Marshall Space Flight Center (International Foundation for Telemetering, 1972-10)
      A series of optical communication experiments between a high altitude aircraft at 18.3 km (60,000 ft) and a ground station are planned by NASA in the summer of 1972. The basic concept is that an optical tracker and transmitter will be located in each terminal. The aircraft transceiver consists of a 5-mW HeNe laser transmitter with a 30-megabit (Mbit) modulator. The ground station beacon is an argon laser operating at 488 mn. A separate pulsed laser radar is used for initial acquisition. The objective of the experiment is to obtain engineering data on the precision tracking and communication system performance at both terminals. Atmospheric effects on the system performance are of prime importance.
    • U.S. AIR FORCE TELEMETRY IN THE 1970’S

      Hargrove, W. W.; Norton Air Force Base (International Foundation for Telemetering, 1972-10)
      The telemetry systems used by the U.S. Air Force in the ‘70’s must be highly reliable, flexible, possess growth potential and meet the requirements of operational realism, An attempt must he made to provision the basic weapon system design for the required telemetry hardware in order to prevent the tested version from incurring a penalty due to its subsequent incorporation. The components associated with future U.S. Air Force telemetry systems will be lighter, smaller, consume less power, withstand more severe environments, and cost much less than those of the past.
    • IMPLANTABLE TELEMETRY IN THE CHIMPANZEE

      Stone, H. L.; Sandler, Harold; Fryer, Tom; Marine Biomedical Institute; NASA Ames Research Center (International Foundation for Telemetering, 1972-10)
      The chimpanzee has been proposed as a possible human analogue for a myriad of human disease states. The lack of knowledge about the cardiovascular system in this animal or the cardiovascular response to stress is understandable because of the cost and handling problems with the chimpanzee. Part of this difficulty, namely handling, can be overcome with the proper selection of cardiovascular instrumentation. Implantable telemetry systems have the advantage that the animal does not have to be handled for any reason. Several animals have been successfully used with implantable telemetry units in the chest. A vigorous antibiotic therapy program must be used for the first few days after surgery, but there have not been any complications after this period of time. The life of the implanted unit has been prolonged by the use of a power switch which also allows remote collection of data. At the present time there is one such unit still functioning 14 months after implantation. The ease with which these units can be used makes them ideally suited for use in the chimpanzee. Examples of the various types of data collected are given and described briefly.
    • BIT SYNCHRONIZATION

      McRae, D. D.; Smith, E. F.; Radiation Incorporated (International Foundation for Telemetering, 1972-10)
      In this paper the trade off between acquisition and noise performance for several bit synchronizer techniques are examined. Results are presented for random NRZ input data with an initial frequency offset between the incoming bit rate and the a priori estimate of this rate.
    • MANAGEMENT OF A MAGNETIC TAPE DUBBING AND EVALUATION STATION

      McKelvey, George R.; Schoeck, Kenneth O.; ITT-Federal Electric Corporation; Vandenberg Air Force Base (International Foundation for Telemetering, 1972-10)
      An instrumentation magnetic tape dubbing and evaluation station is being established at SAMTEC in an effort to improve the quality of data provided to the range users. An analysis of the problems associated with the dubbing process along with the development, configuration and operation of the station are presented.
    • COMPUTER NETWORK DESIGN PRINCIPLES DERIVED FROM EXPERIENCE AND MEASUREMENTS ON THE ARPA NETWORK

      Kleinrock, Leonard; University of California (International Foundation for Telemetering, 1972-10)
      The design of the ARPA experimental computer network was a distributed effort which benefited from the talents of many people working both in concert and independently. In this paper we discuss some of the principles of design which have evolved from that effort. The measures, models and analytical results from design are further compared to simulation and measurement of the network itself; this permits us to evaluate the design tools themselves. We find that these principles are applicable to message-switching networks in general, and therefore the scope of this paper goes beyond that of the ARPA network.
    • USE OF IMPLANTED TELEMETRY IN VASCULAR RESEARCH

      Rader, R. D.; Stevens, C. M.; Henry, J. P.; Meehan, J. P.; University of Southern California (International Foundation for Telemetering, 1972-10)
      This paper outlines a program to study the development and progression of essential hypertension in dogs through the use of totally implanted telemetry. In light of the role that social interaction may play in the development of hypertension in man, emphasis is placed on inducing and monitoring the effects of social strain in the dog: and because of the role the kidney may play in the development of hypertension, a model for renal flow has been developed. The effect that pharmacological concentrations of vasodilator and vasoconstrictor agents have on renal hemodynamics are evaluated. Preliminary data from investigations on the renal hemodynamics of unrestrained dogs in various stages of psychophysiological stress are presented.
    • IMPLANTABLE ULTRASONIC BLOOD FLOWMETERS

      Meindl, J. D.; Stanford University (International Foundation for Telemetering, 1972-10)
      Accurate measurement of pulsatile blood flow can be achieved on a chronic basis in research animals through the use of totally implantable ultrasonic flowmeters. The continuous wave Doppler flowmeter provides an attractive technique for measurement of flow velocity at a particular location such as the center of the lumen; the pulsed Doppler flowmeter is attractive for measurement of flow velocity distribution or profile across the vessel and lumen diameter, and hence volume flow. Both instruments can be electronically precalibrated and exhibit no baseline or scale factor changes during chronic experiments. Custom designed silicon monolithic integrated circuits offer significant advantages in reduced size and power drain as well as improved reliability in these instruments.
    • A 10.6 MICROMETER LASER COMMUNICATION SYSTEM FOR TERRESTRIAL USE

      Goodwin, F. E.; Hughes Research Laboratories (International Foundation for Telemetering, 1972-10)
      This paper reports the development of an experimental type 10.6 μm laser communication system consisting of a transmitting terminal and a receiving terminal designed to operate one way over a nominal five mile terrestrial path. The system will provide a 5 Mbit/sec digital data channel utilizing intra-cavity optical frequency modulation, or frequency shift keying modulation format. It uses optical heterodyne detection with a mercury cadmium telluride detector operating at a temperature of 77°K and an i.f. frequency of 30 MHz. Since the system operates from fixed (non-mobile) terminals, acquisition and alignment procedures are simplified. Predicted performance in rain and fog is discussed and compared with a limited amount of actual data.
    • DATA NETWORKS AND POLICY: AN INTRODUCTION

      Enslow, Philip H. Jr; U.S. Army Signal Corps (International Foundation for Telemetering, 1972-10)
      The data and computer communications services, including data networks, to be made available in the future will depend not only upon the needs and desires of the users; but also upon the economic, social, and regulatory factors that must be considered. The Office of Telecommunications Policy in the Executive Office of the President has the responsibility for recommending to the President national policies and goals in this area as well as telecommunications in general.
    • CHANNELIZATION AND CHANNEL MONITORING IN FDMA COMMUNICATIONS

      Gagliardi, R. M.; University of Southern California (International Foundation for Telemetering, 1972-10)
      In this paper the concept of spacecraft self-regulation of downlink power output is investigated for a hypothetical frequency division multiple access (FDMA) communication net. In this operation channels are filtered off (channelization) and monitored to determine those channels that are inactive; i.e., not transmitting. The results of the activity survey are then used to control channel gain in the spacecraft and regulate the drive power into the output amplifier. In this way, available repeater power normally not used during periods of low activity can be redistributed over the active channels to improve their performance. For maximum improvement, this requires not only adjustment of the individual channel gains, but removal of the inactive channels from the limiter. Equations are developed which are useful for system design and aid in the evaluation of resulting system performance and assessment of feasibility of implementation.
    • BIOTELEMETRY IN THE 1970’S

      Rader, D. R.; University of Southern California (International Foundation for Telemetering, 1972-10)
      A date cannot be pinpointed for the concept of using telemetry for acquiring biological data; however, it is known that the birth of biotelemetry in the form of hardware occurred about 1921--with the report of a heart sound transmitter. Biotelemetry matured only slightly from the twenties to the early fifties. During the fifties and sixties large amounts of money were administered through the money pipeline of the federal government. As a consequence, the growth during this period was bath rapid and grotesque, with tentacles reaching into scores of industrial and educational institutions. Duplication of efforts was quite common during this period and hundreds of miniature biotelemetry systems were built, but results deriving from practical application were quite limited. During the last few years, much of the chaff was shucked from this new growth, a root system developed, and biotelemetry found limited use as a tool in clinical medicine and in medical research. In the past biotelemetry has not lived up to the expectations. What about the future--will it really occupy an important place in clinical medicine and medical research? What is the economic outlook--how many jobs will it support? Which areas will require new talent? And, finally, what are the most common problems and haw can they be solved?
    • POLICY ISSUES IN CABLE COMMUNICATIONS

      Hinchman, Walter R.; Office of Telecommunications Policy (International Foundation for Telemetering, 1972-10)
      Cable communications constitutes a complex and dynamic new medium for both selective and mass distribution of entertainment and information programming, as well as new information exchange services. The complexity of technical, operational, social, political, and economic issues relating to cable probably exceeds that of any electronic communications development to date. Fortunately, there are relevant experiences from many other communications operations -- common carriers, broadcasters, the publishing industry, etc. -- which provide insights into the probable evolution of cable communications and into the many policy issues which exist or will arise. By carefully selecting from among several options for industry structure and integration, it should be possible to achieve -with minimal detailed regulation -- a cable communications industry which encourages diversity of information and entertainment services, guarantees access by all responsible interests, avoids excesses of monopoly powers, and is truly responsive to public needs and interests. That, at least, is the objective of the Administration’s current Cabinet-level policy review.
    • SPECIAL SERVICES TO NEIGHBORHOOD AND HOME: A COMMUNITY TELECOMMUNICATION DEMONSTRATION CONCEPT

      Hiibner, Calvin W.; Siegel, Alan R.; Department of Housing and Urban Development (International Foundation for Telemetering, 1972-10)
      This paper discusses the potential impact of cable television or broadband communications on the urban environment. It suggests that the availability of improved two-way communications between individuals and public institutions presents new opportunities for delivering social services in a cost effective manner. Also, that this mode of delivery may be superior in other ways to our present system of delivery. Unanswered questions do remain on the use of technology for this purpose, however, and to answer these questions an experimental demonstration in one or more “real” cities is suggested so that future urban telecommunications systems can be designed with social service delivery in mind.
    • 10-MICROMETER BAND COMMUNICATION TERMINALS IN SPACE

      McAVOY, N.; Goddard Space Flight Center (International Foundation for Telemetering, 1972-10)
      10-micrometer band communication systems using CO2 lasers for space to space links are discussed. Particular emphasis is on low earth orbiting earth observation satellites to geosynchronous satellites at high data rate. Four key technology areas are discussed: Wideband mixers for Doppler tracking; tunable laser local oscillators; high data rate modulators; laser transmitters.
    • DIGITALLY IMPLEMENTED CLOCK ACQUISITION LOOPS FOR LOW SNR DATA SIGNALS

      Schoolcraft, R. W.; Magnavox Research Laboratories (International Foundation for Telemetering, 1972-10)
      The development of powerful error correction codes for binary data channels has generated a requirement for high performance clock acquisition loops. These loops must provide clean estimates of the data clock at very low data SNR in order to prevent dissipation of the coding gain through noise in the data recovery timing. The key element in high performance clock loops is the method of extracting clock information from the received data stream. Three loops are described which illustrate several extraction concepts and which can be used as design guides. The first loop extracts clock information by use of the function D(t)•D(t+ T/2). The extractor is implemented almost entirely with digital logic elements and is very compact. The third loop is extremely efficient due to the use of a time window which is open for only a short time around the transitions of the data. Its implementation is heavily analog. The second loop is a hybrid of the first and the third falls between them in both performance and complexity. Performance curves are presented for the three loops in terms of data SNR degradation as a function of data SNR and loop bandwidth. Experimental data is presented for the first loop.