Showing papers on "Clock synchronization published in 1973"

Dissemination of System Time

Abstract: This paper considers the problem of estimating the offset in timing of like events at geographically separated locations as a basis for establishing common knowledge of time and, hence, system synchronism. Configurations discussed involve interrogation and reply between a user and a single donor, and one-way propagation between a user and the multiple sites of a reference system. The latter category includes navigation systems, which are shown to be appropriate means for disseminating time. Further ramifications of time dissemination are discussed, including the characteristics of clocks suitable for airborne application. Variables and their relationship and solution are defined for stationary and moving users, and for users of atomic and crystal clocks. For the case in which frequency is offset between clocks, as is likely when crystal oscillators are used, methods are described that permit the estimate of offset in frequency as well as in time. Recursive minimum-variance methods are examined in some detail, and a parametric analysis of performance relative to random and systematic sources of error is given.

Variable block length synchronization system

Abstract: Framing or block synchronization of digital information signals grouped in blocks of variable length is provided by preceding each block with a synchronization code word. Each synchronization code word is error correction encoded in accordance with a BCH code to indicate the number of information bits in the following block and, hence, the location of the next succeeding synchronization code word. Since only the synchronization code words are error correction encoded, they can be distinguished from the information bits to obtain synchronization. A synchronization receiver acquires synchronization upon the occurrence of an error-free synchronization code word in the incoming signal. Synchronization is maintained thereafter by utilizing the inherent error correction capability offered by the BCH code to correct up to two errors in each received synchronization code word before decoding it to locate the next synchronization word. If, however, three errors are detected in a received synchronization word, synchronization is assumed to be lost and synchronization is thereafter recovered with the occurrence of a succeeding error-free synchronization code word in the incoming digital signal. Two receiver embodiments are disclosed which perform the above-described operation. The first embodiment is adapted to perform a general type of framing synchronization, while the other embodiment is specifically adapted to provide video synchronization.

Time-of-day clock synchronization among multiple processing units

Abstract: Circuits and method for synchronizing and checking a plurality of time-of-day (TOD) clocks in a multiprocessing system. Unique hardware synchronizes the low order part of the TOD clocks and a unique method synchronizes the high order part in the same clocks by using carry pulses derived from an intermediate bit position in each TOD clock. The carry pulses from all TOD clocks are combined in an OR circuit with each clock to provide common carry pulses for synchronizing each TOD clock in the system.

Time-division multiplex communication system

Abstract: A time-division multiplex system including multiple transmitters and receivers; a master clock cyclically generating once per clock frame a series of different clock numbers in the form of differing sequences of binary signals, each clock number constituting a different time slot; a clock highway interconnecting the transmitters and receivers and to which the clock number signals are applied; a comparison network at each transmitter and receiver which sequentially compares the clock number signals on the clock highway with a number at the transmitter and receiver for the purpose of selecting the time slot during which each transmitter and receiver operates to transmit and receive audio information, respectively, over an audio information highway which also interconnects the transmitters and receivers.

Control and synchronisation of clocks

Abstract: A plurality of slave clocks are controlled and synchronised from a central station which transmits to each slave clock frequent coded signals each of which conveys in coded form complete information as to the time, and possibly also the date, to be displayed by each slave clock.

Clock Synchronization Experiments Performed via the ATS-1 and ATS-3 Satellites

Abstract: Clock synchronization experiments were carried out May 10 to June 10, 1971, by the NASA/Goddard Space Flight Center and the Smithsonian Astrophysical Observatory 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 rise time and of 10-?s 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 ns. A very long baseline interferometer (VLBI) 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.

Circuit arrangement for mutual synchronization of the clock oscillators provided in the central offices of a pcm time-division multiplex telecommunication network

Abstract: For the mutual synchronization of the central office clock oscillators of a time-division multiplex telecommunication network in accordance with the phase-averaging principle, the phase comparators are directly energized with the line timing pulses and exchange timing pulses. The same synchronization results are qualitatively achieved as with combined usage of the frequency-division and the double-ended principle.

Demonstration of intercontinental DSN clock synchronization by VLBI

Abstract: The prototype system for Deep Space Network clock synchronization by VLBI has been demonstrated to operate successfully over intercontinental baselines in a series of experiments between Deep Space Stations at Madrid, Spain, and Goldstone, California. As predicted by analysis and short baseline demonstration, the system achieves reliable synchronization between 26m and 64m antenna stations with 17 and 37K nominal system temperatures using under one million bits of data from each station. Semi-real-time operation is feasible since this small amount of data can be transmitted to JPL and processed within minutes. The system resolution is 50 to 400ns, depending on the amount of data processed and the source intensity. The accuracy is believed to be comparable to the resolution, although it could be independently confirmed to only about 5 microseconds using LORAN C.