Browsing International Telemetering Conference Proceedings, Volume 12 (1976) by Submit Date
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120 Mb/s and 240 Mb/s Bit SynchronizerSignal Conditioners for NASA High Data Rate ApplicationsTwo bit synchronizersignal conditioners (BSSC) developed for NASA high data rate applications such as earth resources monitoring are described. One BSSC is centered at 120 Mb/s and the other at 240 Mb/s. These subsystems are featured out of the total hardware developed* because the BSSC is such a key subsystem in determining overall system statistical performance. These units represent an evolution of high data rate technology toward the versatile any data rate BSSC's available at low data rates. Numerous inputs/outputs, control functions, indicators, plus the ability to minimize the effects of various signal perturbations are provided. Examples of allowed perturbations are input level variations, bit rate variance static and dynamic, baseline, transition density, bandlimiting, etc., as well as noise. Emphasis in the past has been primarily concerned only with noise.

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.

Automatic Control System for Routing of Telemetry Data SignalsThe primary role of the Space and Missile Test Center (SAMTEC) is to provide support for the relatively large number of various types of missiles launched from Vandenberg Air Force Base (VAFB). Associated with this function is the requirement to provide telemetry decommutation/data processing systems capable of processing the telemetry transmitted by the missiles. At present, the telemetry data is routed to and from the analog tape recorders and bit synchronizers through patch boards, which totals over 200 inputs. This represents a myriad of patching combinations when considering the number of different missile formats and outputs that have to be manually patched and unpatched. SAMTEC contracted with Electrospace Systems, Inc., (ESI) for a dry reed relay switching system. The switching system, Analog Data Equipment Switching System (ADESS), consists of seven matrices under the control of a Digital Equipment Corporation (DEC) Model PDP11/05 minicomputer. The ADESS matrices 1 and 2 are three stage switching systems with the respective input/output  100 x 90 and 60 x 70. Matrices 3 through 7 range from a 40 x 40 down to a 10 x 20 rectangular matrix configuration. Matrix 1 has a frequency response range of DC12MHz, matrices 2 through 6 have a range from DC 3MHz, and matrix 7 ranges from DC15MHz. The PDP11/05 peripherals include a CRT/Keyboard and dual floppy disk which controls the latching and status of the matrix switches and stores the mission set up files which can be rapidly called up by the operator. The ADESS will decrease turn around by up to ten times as compared to present operations.

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.

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.

CostEffective Coding Implementations for Computer Communication SystemsDue 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 interrelationships. 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.

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.

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.

Universal Source Coding of Finite Alphabet SourcesThe application of Shannon's rate distortion theory to real data compression practice has been limited by a lack of effective distortion measures for most real users and incomplete statistical knowledge of real sources. Universal source coding techniques attempt to overcome the latter limitation by developing codes that are effective (in the sense of approaching the theoretical rate distortion limit) for a large class of sources. Here we examine one such technique for sources with finite alphabets where source sequences are divided into composition classes and a universal code is formed from codes designed for each composition class.

An FSK/FDM Multiplexed Fiber Optics System for Multichannel Asynchronous Digital Data TransmissionIn this paper the use of frequency division multiplexing to reduce the cost of fiberoptic 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 allparallel 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 nearterm future, at least, multiplexing offers substantial cost savings over allparallel transmission.

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.

On Zero Memory Nonlinear Transformations of Gaussian ProcessesThis 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.

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.

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.

A Mass Memory Unit for the Space Shuttle OrbiterA highcapacity, 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 online 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 wearrelated 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 slowaccess tape drives of highstorage capacity and disks or drums with fast access time and relatively lowstorage capacity. In contrast with disk or drum memories, the MMU consumes operating power only when active, which yields a very low average mission power.

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.

Convolutional Coding At 50 Mbps for the Shuttle Kuband Return LinkError 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.

A Code Structure for Certain Coma EnvironmentsCertain 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.

Telemedicine: Patient Monitoring in Unusual EnvironmentsOf the several advantages telemetry systems have to offer the burgeoning field of patient monitoring, we have previously stressed recording from freely moving patients unencumbered by lengthy cables and unattached to conventional bulky machines. Paramount in the applications of systems designed and fabricated in our laboratory of Environmental Neurobiology have been the monitoring of patients afflicted with temporal lobe epilepsy in which the capture of unilateral or bilateral EEG seizure activity dictates the possibility or futility of neurosurgical intervention (1). Together with sophisticated computer analyses of neurophysiological data, telemetry has also made it possible to identify EEG correlates of bizarre schizophrenic ritualistic behavior virtually impossible to capture by conventional hardwire techniques (2). This presentation emphasizes another aspect of the utility of telemetry: the opportunity to record from patients in meaningful circumstances outside the sterile environs of the Neurophysiology Laboratory which sometimes involves freedom of movement and sometimes quiescence. The critical element in these situations is the unacceptability of bulky machinery and its attendant problems. Two such environments are the operating room and the sleep research and treatment laboratory or bedroom. Our current fairly extensive telemetry studies involve both of these surrounds. These activities will now be discussed.

Elements of a Broadband Biomedical Communications NetworkThis 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 CanadianAmerican Communications Technology Satellite (CTS) to evaluate the costeffective use of interactive broadband communications systems.