Performance of optimum and suboptimum synchronizers.
Optimum and suboptimum synchronizers for extracting bit synchronization from binary data, showing performance dependence on pertinent system parameters
Luecke, E. J.↗
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Time synchronization system utilizing moon reflected coded signals Patent
Time synchronization system for synchronizing clocks at remote locations with master clock using moon reflected coded signals
Easterling, M. F.↗
Supply and resupply of stations in synchronous orbit
Logistics system for synchronous orbit space stations supply, discussing parking to synchronous orbit transfer of reusable and disposable logistics vehicles
Dugan, D. W.↗
ATS-5 solar cell experiment results after one year in synchronous orbit
The results of the ATS-5 solar cell experiment after one year in synchronous orbit are reported. A partial failure in the experimental electronics package has caused a loss of data from half the 80 experimental solar cells. Procedures for extracting data due to a partial spacecraft failure are described and discussed. Data from the remaining 40 solar cells, including 15 mounted on a thin flexible structure are analyzed. Data are corrected to a solar intensity of 140 mW/sq cm and a temperature of 25 C. It was found that after one year in synchronous orbit: (1) cells with 1.52-mm-thick coverslides did not show a clear-cut advantage over those with 0.15-mm coverslides, (2) cells with solderless grid lines are degrading at the same rate as are cells with solder-dipped grid lines, (3) cells not quite completely covered with coverslides suffered a large power loss in comparison to cells fully covered, (4) no clear-cut advantage of 10-cm cells over 2-cm cells has yet been observed, (5) cells mounted on the flexible panel with relatively little backshielding did not degrade any faster than those with substantial backshielding, and (6) the flight data in large part confirms the adequacy of the ground-based techniques used in our preflight radiation test program.
Anspaugh, B. E.↗
Handbook of operation and maintenance instructions for Model 5208A bit synchronizer unit
Electrical/mechanical characteristics, operation, theory of operation, parts list, and electrical diagrams for the model 5208A bit synchronizer unit are provided. The unit is capable of performing the functions of bit synchronization and signal conditioning on demodulated wave trains containing amplitude, frequency, and phase distortions, as well as additive noise. Operating frequencies in the 1 to 27 MHz bit rate range are accommodated through the use of discrete frequency plug-in subunits. The unit provides 0 and 180 degree clocks and either a single signal hard decision, or a three bit quantized soft decision data output.
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A simple branch synchronizer for convolutional decoders.
A simple branch synchronizer for rate 1/3, constraint length five, nonsystematic convolutional code is described. The scheme derives the sync information from the received channel bits, thus avoiding the extra formatting of the sync data at the transmitter and receiver, and increasing the data rate. The synchronizer detects the proper sync bits for both the in-phase and phase ambiguous cases. The design is adaptable to nonsystematic codes of different constraint lengths.
Taqvi, S. Z. H.↗
Dual transponder time synchronization at C band using ATS-3.
The use of artificial satellites for time synchronization of geographically distant clocks is hindered by problems due to satellite motion or equipment delay measurements. The ATS-3 satellite with its two C-band transponder channels helps solve these problems through techniques for synchronization to accuracies of tenths of microseconds. Portable cesium clocks were used to verify the accuracy of the described system.
Mazur, W. E., Jr.↗
Phase shift keyed, pulse code modulated signal synchronizer
Signal is demodulated and synchronized by three loop circuits: ''Q'' loop uses quadrature signal to stabilize frequency; ''B'' loop acts on baseboard signal to stabilize phase; and decoding ''I'' loop acts on in-phase signal. Synchronizer may be used to eliminate false-lock.
Kobayashi, H. S.↗
Synchronization using pulsed edge tracking in optical PPM communication system
A pulse position modulated (PPM) optical communication system using narrow pulses of light for data transmission requires accurate time synchronization between transmitter and receiver. The presence of signal energy in the form of optical pulses suggests the use of a pulse edge tracking method of maintaining the necessary timing. The edge tracking operation in a binary PPM system is examined, taking into account the quantum nature of the optical transmissions. Consideration is given first to pure synchronization using a periodic pulsed intensity, then extended to the case where position modulation is present and auxiliary bit decisioning is needed to aid the tracking operation. Performance analysis is made in terms of timing error and its associated statistics. Timing error variances are shown as a function of system signal to noise ratio.
Gagliardi, R.↗
Pseudonoise (PN) synchronization of data system with derivation of clock frequency from received signal for clocking receiver PN generator
A digital communicating system for automatically synchronizing signals for data detection is described. The systems consists of biphase modulating a subcarrier frequency by the binary data and transmitting a carrier phase modulated by this signal to a receiver, where coherent phase detection is employed to recover the subcarrier. Data detection is achieved by providing, in the receiver, a demodulated reference which is in synchronism with the unmodulated subcarrier in transmitting system. The output of the detector is passed through a matched filter where the signal is integrated over a bit period. As a result, random noise components are averaged out, so that the probability of detecting the correct data transmitted is maximized.
Couvillon, L. A., Jr.↗
ATS-5 solar cell experiment after 699 days in synchronous orbit.
The data from the ATS-5 solar cell experiment for the first 699 days in synchronous orbit is presented. Comparison of the performance of several different types of solar cell/coverslide configurations is made. This behavior is in turn compared with the calculated performance for such cell/coverslide configurations in synchronous orbit and with the results of accelerator irradiations designed to simulate the omnidirectional electron environment. It is generally found that the cells on the flight experiment perform like the cells irradiated with the accelerator, but they degraded more than predicted by the calculation. Solar cells mounted on a thin kapton panel are degrading about the same as are their counterparts mounted on a rigid panel.
Anspaugh, B. E.↗
An amplitude-steered, electronically despun antenna for the synchronous meteorological satellite.
Description of the design and performance of a dual-band electronically despun, high-gain, earth-coverage satellite antenna for use on the Synchronous Meteorological Satellite. The SMS satellite is designed to take high-resolution cloud cover pictures from synchronous altitude. Several unique design features are described, including a scheme for steering energy around the array in a continuous fashion to avoid 'phase jumps' caused by sudden energy switches.
Dietrich, F. J.↗
An adaptive bit synchronization algorithm under time-varying environment.
This paper presents an adaptive estimation algorithm for bit synchronization, assuming that the parameters of the incoming data process are time-varying. Experiment results have proved that this synchronizer is workable either judged by the amount of data required or the speed of convergence.
Chow, L. R.↗
Clock synchronization experiments performed via the ATS-1 and ATS-3 satellites.
Clock synchronization experiments were carried out May 10 to June 10, 1971, via the ATS-1 and ATS-3 geostationary satellites between the NASA tracking stations at Rosman, N.C., and Mojave, Calif., in order to determine the offset and the relative drift rate between the two station clocks. Pulses at C band with very sharp risetime and of 10 microsec duration were exchanged by the two stations through the dual transponders of the satellites. At each station, a time-interval counter was started by the transmitted pulse and stopped by the pulse received via satellite from the other station. The probable error of the clock offset as measured by the counter is 10 msec. A very long baseline interferometer experiment was also performed between the two stations at the same time and provided independent clock-offset data to check the accuracy of the time-synchronization experiment.
Ramasastry, J.↗
Delta-102 Synchronous Meteorological Satellite (SMS-A): Operations summary
The Synchronous Meteorological Satellite (SMS) program is a joint effort of the National Aeronautics and Space Administration and the Department of Commerce. This program is intended to provide systematic worldwide weather coverage on an operational basis. The pilot SMS program is expected to launch three spacecraft: two prototype spacecraft designated SMS-A and SMS-B and one operational spacecraft designated SMS-C. The SMS program will use spacecraft in synchronous orbit to obtain day and night information on the earth's weather by means of earth imaging instruments, retransmission of image data, data collection, data relay, and space environmental monitoring.
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Synthesis of a correcting filter with phase stabilization of the angular velocity of a synchronous motor by the feedback system method
The operating characteristics of a synchronous electric motor are discussed. A system of phase stabilization of the instantaneous angular velocity of rotation of a synchronous-reaction motor is diagrammed. A mathematical model is developed to show the parameters which affect the operation of the motor. The selection of a correcting filter to use with the motor in order to reduce the reaction of the system to interference is explained.
Kazlauskas, K. A.↗
An analysis and demonstration of clock synchronization by VLBI
A prototype of a semi-real time system for synchronizing the Deep Space Net station clocks by radio interferometry was successfully demonstrated on August 30, 1972. The system utilized an approximate maximum likelihood estimation procedure for processing the data, thereby achieving essentially optimum time sync estimates for a given amount of data, or equivalently, minimizing the amount of data required for reliable estimation. Synchronization accuracies as good as 100 ns rms were achieved between Deep Space Stations 11 and 12, both at Goldstone, Calif. The accuracy can be improved by increasing the system bandwidth until the fundamental limitations due to baseline and source position uncertainties and atmospheric effects are reached. These limitations are under 10 ns for transcontinental baselines.
Hurd, W. J.↗
Optimum frame synchronization for biorthogonally coded data
Many recent American unmanned planetary probes have used biorthogonally coded spacecraft-to-earth telemetry links. An examination of the frame-synchronization (sync) techniques employed on these missions revealed that they were not specifically designed for coded data. This led to a consideration of the optimum frame-sync problem for biorthogonally coded data received over the additive white Gaussian noise (AWGN) channel and decoded prior to sync acquisition. A frame-sync algorithm for biorthogonally coded data based on a super-symbol distance rule is proposed, along with a corresponding selection criterion for the sync sequence. It is argued heuristically that this approach is optimum with regard to minimizing the probability of false synchronization.
Levitt, B. K.↗