Browsing International Telemetering Conference Proceedings, Volume 12 (1976) by Issue Date
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Reduction of Base Television Bandwidth by Special Sampling TechniquesThere are many possible ways to reduce the bandwidth of a wideband television system. One of these methods is called Spiraldot which samples the pixels in such a way to keep the data rate resolution high in the center of the TV display but permits reduced resolution and data rate at the extreme edges of the TV image. Bandwidth reductions of 8/1 are possible. A random access memory is required at each end of the data link.

Analysis and Decomposition of Complex RealTime Processes with a RealTime Schemata ModelIn this paper a formal model for realtime 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.

Telemetry Packetization for Improved Mission OperationsThe 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.

Method for Determination of System Parameters in Telemetry Baseband Modulation SystemsThe 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.

MIDISS: A Unique MultiProcessor Telemetry Ground StationAn optimum architecture for realtime 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 FORTRANlike 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 16bit minicomputer and a SPACEPIPE (microcomputerbased, frontend processor) that decommutates multiple downlinks, provides ratebuffering, and performs data compression and alarmchecking. The minicomputer is thus free to perform extensive data processing for those downlink channels that are changing at significant rates,

Broadcast Channels: Some Recent Developments and Open ProblemsIn 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.

An Operational Video Tape Recording System Utilizing Irig Standard 12973 [1] Segmented Helical Scan Recording FormatPart 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/ENACC734. The system is comprised, in part, by a highly versatile MILE5400 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 multiline rate flexibility to provide record capability of video signals from a multitude of electrooptical 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 timebase stability are under development. Predictions are made on expected performance improvements. Other developments to extend the versatility of the transport systems will be discussed.

Optimal Link Capacity Assignments in Teleprocessing and Centralized Computer NetworksWe 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 dataprocessing 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 linkcapacity 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.

Degradation of FSK Detection Performance Due to Tone Phase JitterThe 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 markspace 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.

Digital Data Transmission in a PAM Communication SystemThis paper presents the results of an experimental evaluation of the effectiveness of digital data transmission in a pulseamplitude 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 amplitudemodulated 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.

Performance Bounds on Spread Spectrum Multiple Access Communication SystemsSeveral approaches for the evaluation of upper and lower bounds on error probability of spread spectrum multiple access communication systems are presented. These bounds are obtained by utilizing an isomorphism theorem in the theory of moment spaces. From this theorem, we generate closed, compact, and convex bodies, where one of the coordinates represents error probability, while the other coordinate represents a generalized moment of the multiple access interference random variable. Derivations for the second moment, fourth moment, single exponential moment, and multiple exponential moment are given in terms of the partial cross correlations of the codes used in the system.

Optimum Detection of Quantized PAM Data SignalsThe degree of complexity of a digital signal processor is closely related to the precision with which samples of an incoming analog waveform are represented. There is considerable interest in determining how coarse this representation can be without seriously degrading performance from that of an ideal processor of unquantized samples. This question is examined for a receiver of noisy, linearlydistorted PAM signals. An optimum (maximum likelihood) detectors analogous to the Viterbi detector for unquantized samples, is derived for the case of a quantized sample sequence. Performance is evaluated under the assumption of high signaltonoise ratio, and the resultant error probability is a good approximation for coarse quantization, and an upper bound for any degree of quantization. For a specified error probability, the degree of quantization suggested by this approach is conservative. Since receiver complexity is closely associated with the length of the digital representation of an input sample, an upper bound on receiver complexity is also suggested. Numerical evaluation of the error probability is quite tedious for an arbitrary Channel; however, system performance may be readily evaluated for partialresponse signaling. For the partialresponse channels(1,1) and (1,2,1), it is shown that five and six bit quantizers provide, respectively, a degradation of less than 1 dB in SNR from the infinitely quantized (Viterbi) receiver.

Production Counting Using a Computer NetworkThe advent of microprocessors has made possible the development of low cost intelligent terminals for industrial applications. Several of these "smart" terminals can be connected to a communications network which is controlled by a it "master" computer. Such a computer network has been developed at Whirlpool Research for use in production counting for inventory control purposes. This paper discusses the design, development, installation and debugging of the production counting system. The advantages and limitations of this type of computer network are discussed in the context of the industrial environment.

A Bound on Viterbi Decoder Error Burst LengthA maximum likelihood (Viterbi) decoder used with a convolutional code on a Gaussian channel produces decoding errors which tend to occur in clusters or bursts. A method is described for deriving an upper bound on the probability of occurrence of error bursts of a given length. The method applies to the optimum convolutional codes found by Odenwalder, for which the codeword weight distribution is partially known. Laboratory measurements of error burst length at signaltonoise ratios greater than 4 dB indicate that the upper bound is useful for approximating the length of highprobability bursts, but is not precise enough to predict the probability of very long, lowprobability bursts.

Maximum Likelihood Decoding Scheme for Convolutional CodesIn recent years the application of coding techniques to enhance digital data transmission has become widely accepted. In general, one would assume that a maximum likelihood decoding of convolutional codes would be impractical for long constraint length codes because the general approach of sequential decoding algorithms utilize very few properties of the code and hence require a considerable effort to decode the received data sequence. In this paper, several structure and distance properties of the convolutional codes for different constraint lengths are derived and utilized in developing an efficient maximum likelihood decoding scheme. Under the proposed decoding threshold conditions, which are functions of the distance properties of the utilized codes, the required number of decoding operations can be reduced markedly. The analysis has been supported by computer simulations and by the development and testing of a prototype decoder. Key results are presented and discussed.

DualK Convolutional Codes for Noncoherently Demodulated ChannelsWhile the advantages of convolutional coding for coherently demodulated channels have become widely accepted, less work has been done on coding techniques for noncoherently demodulated channels used in channels experiencing fading or intentional interference. Here we describe a simple class of convolutional codes called dualk [1] codes for use on 2ᵏary orthogonal signal modulated channels and show how they can be used with softdecision Viterbi decoding on noncoherently demodulated channels. The main result of this paper is a derivation of a closed form expression for the transfer function [2], T(D,N,L), for optimum (in the sense of best Hamming distance) dualk convolutional codes. Examples of the technique of obtaining upper bounds on the bit error probability using this transfer function are also given for a noncoherently demodulated Rayleigh fading channel.

A Digital Instrumentation System for Automotive Impact TestsAutomotive impact tests require the transmission of large amount of measurement data through drag cables. The traditional practice of using FM technique is tedious and expensive. An onboard PCM system which accepts 112 analog inputs and 91 bilevel inputs has been used successfully at the Daisy Impact Sled Test Track located at the Holloman AFB. This system utilizes a twoconductor pair drag cable. It can also be telemetered by pulse modulating a radio frequency carrier.

Considerations for Distributed Industrial Control SystemsFor a variety of reasons, industrial plant control systems have been increasingly complex and expensive. Economic and reliability considerations have initiated a trend toward distributing control system functions among communicating components, utilizing the new microprocessor and communication technologies. Any new technology brings new capabilities, but also new engineering design considerations and tradeoffs. This paper attempts to outline some of the important system design issues.

Relationship of Noise Power Ratio to FM/FM Data QualityThe IRIG (InterRange Instrumentation Group) 118 series "Test Methods for Telemetry Systems and Subsystems" has standardized the notchnoise loading test for frequency division systems. This paper presents a practical method for predicting subcarrier output SNR (signaltonoise ratio) from NPR (noise power ratio) measurements at the video output of a telemetry receiver. A laboratory test is described in which NPR test data and FM (frequency modulation) subcarrier output SNR data were measured using the same FM radio link and modulation level. The test data show satisfactory agreement between predicted and measured subcarrier output signaltonoise ratios. In addition, the data show that a flat NPR test spectrum is adequate for predicting performance of frequency division systems using the normal 6 dB/octave and 9 dB/octave tapers.

Frequency Response of Tape Transport Servo SystemsA 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.