Browsing International Telemetering Conference Proceedings, Volume 06 (1970) by Issue Date
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Video Bandwidth, if Bandwidth and Peak Deviation in Notch Noise TestingThis paper presents guidelines for conducting notch noise testing of telemetry transmitterreceiver systems. An understanding of the type of FMFM modulation format which random white noise accurately simulates leads to certain convenient relations between spectral power density, video bandwidth, peak deviation and IF bandwidth. Notch noise measurements were made on video noise in a video limiter to determine the dynamic range required of a system which transmits random white noise faithfully. These measurements were of significant importance because they show that a great deal of excess IF bandwidth is required to transmit random noise spectra. Specifically, it was found that to achieve a 50 db notch noise measurement the system dynamic range may be as much as 10 times greater than the RMS value of the composite signals.

Noiseless Linear Feedback and Analog Data TranmissionIt is well known that noiseless linear feedback achieves channel capacity for the additive Gaussian channel. It has also been shown that it can be used to achieve the ratedistortion bound on the mean squared error for an arbitrary Gaussian source sent over the infinite bandwidth white Gaussian channel. However, it is shown here that noiseless linear feedback by itself does not suffice when the channel is bandlimited. It is shown that, out of the more than countable variety of Gaussian sources that ordinarily exist, only a countable subset can be transmitted via the bandlimited noiseless feedback link at the theoretical efficiency predicted by Shannon's ratedistortion bound. Thus, some nonlinear operations are necessary in almost all cases even with feedback.

Optical Processing InterfacesA brief introduction to coherent optical data, processing is given. Several problems are discussed concerning the implementation of coherent optical data processing for general use. The major problems discussed are concerned with the imaging qualities of coherent systems and the material requirements for recording these images. The solution to several problems is presented and the stateoftheart in other areas is indicated.

The Upper Bounds of the Confidence Intervals of Bit Error Probabilities Based on a Markov Chain Bit Error ModelConfidence intervals for the bit error probability of an actual PCM telemetry data can be determined based on the analysis of received redundant bits. The procedure usually requires the assumption of independence of bit errors. However, bit errors may occur in clusters under various conditions of multipath, injection of nonthermal noise of long duration, and bit jitters. As a representation of bit errors in clusters, a Markov chain model is introduced. Some results on the confidence interval of bit error probability are obtained as functions of a Markovian parameter, which designates the degree of departure from the binomial model. The computations are quite laborious compared to the case of the binomial model. This paper gives stepbystep instructions for computing the probabilities that r error bits occur among mn received bits which can then be used for the derivation of the confidence interval.

Computer Augmented Telecommunications Performance AnalysisThe increased range, greater accuracy, and complex trajectory of modern ICBM's create a telemetry data acquisition problem which cannot be adequately analyzed by classical manual techniques. To ensure that flight test data requirements are satisfied, systems personnel must order and quantify (model) the elements of a very complex system, i.e., communications system, acquisition stations, flight trajectory, data processor, etc. To satisfy this need, MINUTEMAN Instrumentation Systems personnel developed ISMAP (Instrumentation System Margin Analysis Program); a computer augmented technique for accurately evaluating the performance of ICBM data acquisition systems.

Micro Miniature Intraoral Telemetry SystemIntraoral telemetry is oftenthe only method of evaluating dental problems involving environmentally dependent relationships between occlusion, jaw movements, and the neuromuscular system, and between pH, Eh and bacterial ecology. To study these dental problems a small transmitter (the size of a molar tooth crown) with low power requirements and capable of monitoring eight physiologic parameters has been developed. Such transmitters are now being used to evaluate the design of dental bridges and related neuromuscular dysfunction.

The Implmentation and Utilization of DSB/FM Telemetry SystemsTwo different double sideband suppressed subcarrier telemetry systems have evolved in the past few years: the harmonic subcarrier method (HSM) and the independent subcarrier method (ISM). This paper provides information pertinent to the implementation and utilization of both systems. The important features of the two systems are discussed by comparing the circuits used in their implementation. Test data is used to illustrate some of the important points about the performance of a DSB/FM telemetry system.

Effects of Multipath on Telemetry Data TransmissionSpurious amplitude and phase modulation effects occur in the received telemetry signal when both the direct waves and the indirect waves enter the receiving antenna. In this paper, a simple multipath model is used which has a single direct wave and a single indirect wave. The indirect wave differs from the direct wave by a time delay and a constant amplitude. With such a simple model, the effects of multipath on telemetry data transmission can be fully examined because of the mathematical simplicity. First an FM system operating above the threshold is considered. The intermodulation distortion and the degradation in the data signaltonoise ratio due to multipath are both examined. Next we consider two digital systems, namely the noncoherent FSK and the PCM/FM with the discriminator detection. Both systems utilize a splitphase baseband signal. And the error rates depend on the multipath time delay. Comparison is made between the splitphase and the NRZ (nonreturnto zero) baseband signals. Available performance improvement from using the predetection diversity combining and the synchronization problem are then discussed. Finally several methods to improve the telemetry data are suggested.

PreEmphasis for Constant Bandwidth FM Subcarrier Oscillators for FM and PM TransmittersThis paper shows that the proper preemphasis for the inputs of constant bandwidth subcarrier oscillators into an FM transmitter is a straight line through the origin, and into a PM transmitter is one of equal amplitude for all subcarrier oscillators. The proper method for calculation of the preemphasis for a mixture of channel bandwidths is to use the square root of the bandwidth ratio of the subcarrier channels for both FM and PM transmitters. Examples are given.

On Linear InformationFeedback Schemes for White Gaussian ChannelsFor the transmission of a Gaussian information source over an additive white Gaussiannoise (AWGN) channel, several noiseless, linearfeedback schemes are shown to be the same in the sense that they not only achieve the ratedistortion bound on the minimum attainable meansquare error (MSE), but also possess identical system parameters. These equivalent schemes can be easily applied to solving the problem of optimally matching a colored Gaussian source with an AWGN channel. These equivalent schemes can further be employed to send messages from digital information sources over AWGN channels. It can be shown that any of these equivalent schemes as a decisionerror probability which is the smallest among the class of all linear schemes. The condition of noiseless feedback can be relaxed to cover the more general noisy informationfeedback case. A suboptimal scheme is proposed for transmitting data from a Gaussian source, whose output process has a power spectral density function which is uniform in some frequency range and zero elsewhere, over some AWGN channels to some destination. This suboptimal noisy feedback scheme can also be used to send data from a digital information source over an AWGN channel with better performance than can be achieved without noisy feedback.

The Effects of Using a Finite Number of Bits and Approximate Division in a Data CompressorIn the design of a data compressor one of the basic problems is error due to the use of a finite number of bits in calculating various parameters. This is error due to truncation (or round off) after a set number of bits to the right of the binary point. Another error that could be introduced to the system is that error caused by the use of an approximate divide instead of a full divide. It is the purpose of this study to find the effect of these two errors so that (1) a judgment may be made as to how many bits to the right of the binary point are necessary, and (2) find if a double shift approximate divide may be used instead of the slower full divide. The study is divided into three basic parts (1) the effect of truncation (or round off), (2) the effect of the double shift approximate divide, an (3) the combined effect of truncation (or round off) and the double shift approximate divide. Each one of these errorcausing phenomenon has two variations; i.e., an error caused while compressing data and an additional error caused while reconstructing. The error during compression distorts the tolerance limits, and the error in reconstruction causes distortion of the reconstructed line segment. Each of the errors leads to an overall error in data magnitude over and above the normal allowable error of one tolerance level. For all of the analysis the maximum run length of the compressed data is assumed to be 128. A summary of the study is found in Table 6.

Performance Evaluation Medthos for PCM Bit Synchronizer/Signal ConditionersPCM Bit Synchronizer/Signal Conditioners (BSSC) possess 3 basic performance characteristics which directly affect the processing of PCM telemetry data. These characteristics are: bit error rate (BER), bit slippage rate (BSR), and bit sync acquisition (BSA). This paper describes proven methods to meaningfully, and accurately measure these characteristics with particular emphasis on BSR and BSA. These methods require relatively simple and inexpensive procedures and instrumentation, and could be used by manufacturers and users to evaluate and acceptance test BSSC. The basic principle employed in these methods is "fixed threshold frame synchronization" with a unique strategy. Thus, there is no requirement for bit delay between the reference and BSSC output data, and synchronization of the reference data in the comparator with the BSSC output data takes place automatically. Moreover, this approach to testing BSSC represents the actual situation in which the BSSC would be operating as part of the telemetry data system, and hence would provide a direct measure of system performance. In actual application, these methods proved to be very effective and accurate for input SNR of E(b) /N(0) > O dB, and slightly less accurate for E(b) /N(0) < O dB (data having more than 10% errors). In general, BSA and BSR measurement accuracies of 2030 bits can be achieved. A detailed discussion of accuracy is presented in the paper. In addition, the BSR and BER measurement methods are applicable to assessing the performance of tape recorders (TR) as it affects the actual system performance, rather than just the peculiar TR characteristics of TBE (time base error), bit dropout, and wow and flutter.

Data Tranmission Over Channels with Noisy FeedbackA lowcost error control technique is proposed for bulk data transmission with noisy feedback link. The scheme is ideally suited for tapetotape bulk data transmission as well as the storeandforward type of data transmission system. By partition data into superblocks, the technique can be used for any feedback retransmission system. We also show that the scheme can be modified to correct synchronization errors and that noise in the feedback link can be made extremely unlikely to contribute to decoding errors.

Apollo Lunar CommunicationsThe Apollo unified Sband system was developed to handle ranging, telemetry, and voice data using one carrier. Television is transmitted in another mode with the same system. Frequent references are made to the unified Sband system in this report because other systems must work in conjunction with it; however, no description is provided because the Sband system is discussed thoroughly in numerous other reports. The astronauts must coordinate their activities on the lunar surface, and communications are required between them as well as between them and Mission Control Center. A VHF system that has performed excellently in providing voice and telemetry information for lunarsurface use is described in this report. Interest in television has progressed from casual to intense as the Apollo Program has matured; technology has evolved to provide color presentations using the same RF system that was once limited to blackandwhite transmissions. The cameras that were developed for both blackandwhite and color transmissions are described. Future lunarsurface operations will require traverses too long to be accomplished easily on foot. A system that permits longrange communications from a motorized vehicle on the lunar surface is described. Finally, brief descriptions of several communicationsrelated lunarenvironment experiments that have been proposed for the Apollo Program are discussed.

Signal Designs for Apollo Scientific Data SystemsThe Apollo lunarexploration missions are being planned for the purpose of obtaining comprehensive scientific data. The system descriptions and key signaldesign considerations for two data transmission systems  the Phase II Scientific Data System and the Particles and Fields Subsatellite  are discussed. In both cases, the designs are constrained by the requirements to (1) use the existing spacecraft systems where possible, (2) use the existing ground stations, and (3) maintain the existing Apollo communications capabilities.

The Lunar Communications Relay Unit System DesignLunar Surface Exploration by Early Apollo Astronauts was limited by the range capabilities and configuration of the surface communications. To permit greater scientific yield from manned lunar exploration, it was necessary to provide improvements in crew mobility plus communications compatible with extended extravehicular activity. Expansion of EVA and video communications capability was constrained by the requirement of interfacing with existing earth and lunar surface facilities, vehicle payload requirements, and crew operational considerations. Various tradeoff s were conducted to permit rapid development of a feasible communication's system which are described herein. The revision of the EVA mission profile necessitated establishment of new signal design parameters compatible with mobile and fixed site relay configurations. The design approach selected required strict discipline to enable integration of the electrical, mechanical, thermal and human factor fields. The resultant design of the Lunar Communications Relay Unit is a portable communications package to provide relaytoearth of voice, data and color television from lunar surface locations far beyond the LM landing site and relay of ground voice to the EVA crew.

Notch Noise Loading Data on Baseband Tape RecordingNotch power ratio tests were performed on a magnetic tape recorder/ reproducer, using direct recording in the baseband. For the equipment tested, it is concluded that the IRIG method of setting the record power level as that which produces 1% third harmonic on a single tone, does not necessarily result in an optimum record/reproduce cycle. It is concluded that the input and output levels should be set with reference to notch noise test data to optimize baseband tape recording performance for baseband recording of frequency division multiplexed systems. In order to interpret the notch noise data, it was necessary to assume two nonlinear processes, one acting in conjunction with the record process and one in conjunction with the playback process.

VHF/UHF Antenna Calibration Using Radio StarsThis paper describes a stellar calibration technique, using radio stars, that determines receiving system noise temperature, or antenna gain, at frequencies below 500 MHz. The overall system noise temperature is referenced to radio star flux densities known within several tenths of a decibel. An independent determination of antenna gain must be made before computing system noise temperature and several methods are suggested. The preferred method uses celestial and receiving system parameters to compute gain; whereas a less desirable method requires an accurately known output level from a standard signal generator. Field test data, obtained at 136 MHz and 400 MHz in the NASA space tracking and data acquisition network (STADAN), demonstrates that antenna gain and system noise temperature can be determined with an accuracy of 1 db. The radio stars Cassiopeia A and Cygnus A were used to calibrate 40ft. diameter paraboloidal antennas, at 136 MHz and 400 MHz, and phase array antennas at 136 MHz. The radio star calibration technique, described herein, makes possible accurate stationtostation performance comparisons since a common farfield signal source is observed. This technique is also suitable for calibrating telemetry antennas operating in the IRIG 216260 MHz frequency band.

A BurstTrapping Code for Feedback Communication SystemsMany data communication channels are perturbed by "bursts" of noise separated by long intervals of comparatively low noise level. The block code described in this paper, a modification of the forwardacting scheme of S. Y. Tong, retransmits information which has been damaged by a noise burst in place of the paritycheck digits of future blocks. The responsibility for error detection and correction is divided between the receiver and (via the feedback channel) the transmitter in such a way as to maximize the defense against both noise bursts and the occasional random errors between bursts. There is a fixed delay for decoding, in contrast to the variable buffering delay of ordinary retransmissionrequest systems. As a result, storage requirements are minimized and there is a constant throughput rate. The feedback channel can incorporate as much delay and be as noisy as the forward channel without significantly impairing performance. Simulation results are provided to illustrate the performance.

Feedback in Data TransmissionA survey of the possible gains to be realized by the use of various feedback techniques is given. Noiseless information feedback is considered in detail, and a transmission system for this latter case is given and analyzed. This system is shown to achieve a transmission rate very close to the largest rate possible.