Showing papers on "Clock synchronization published in 1979"

A Majority consensus approach to concurrency control for multiple copy databases

Abstract: A “majority consensus” algorithm which represents a new solution to the update synchronization problem for multiple copy databases is presented. The algorithm embodies distributed control and can function effectively in the presence of communication and database site outages. The correctness of the algorithm is demonstrated and the cost of using it is analyzed. Several examples that illustrate aspects of the algorithm operation are included in the Appendix.

Practical implications of relativity for a global coordinate time scale

Abstract: Frontiers of technology now need synchronization between remote clocks to an accuracy of about a nanosecond. Rate changes arising from the velocity and gravitational potential of a transported clock used for synchronization of a network must be accounted for. In addition, one cannot assume that the earth is an inertial frame, i.e., not spinning. If classical Einstein synchronization is used, where from the midpoint between clocks at A and at B, one simultaneously sends light pulses to A and B to synchronize them, two problems arise. First, the synchronization process will not be transitive; i.e., if A is synchronized with B and B with C, then A will not necessarily be synchronized with C. Second, starting at a point on the equator and transporting a portable clock eastward (westward), while establishing a synchronized time grid on the way, will result in a discontinuity upon returning to the original point of about −200 ns (+200 ns); minus (−) means that the portable clock will be late. This paper will discuss the construction of a coordinate clock network on the earth's surface which does not have these problems; i.e., synchronization is transitive, and there is no discontinuity. This may be done by adjusting clocks to read coordinate time on an underlying nonrotating local inertial frame. The theoretical and practical implications of setting up such a coordinate clock network using either electromagnetic signals (e.g., laser, Loran-C) or portable clocks will be discussed. It will be shown how this network may be applied in making UTC or any other global scale more useful for state-of-the-art navigation and communication systems.

Phase locked loop clock synchronizing circuit with programmable controller

Abstract: A clock synchronization unit for controlling frequency and phase of a local clock and synchronism with an external clock signal, employs a programmable controller as a part of a phase-locked loop. The controller provides highly accurate control of the clock, including verification of the accuracy of the clock control signal before applying it to the clock oscillator as well as control of the magnitude to the clock oscillator to avoid rapid changes in frequency. In one particular embodiment, the programmable controller comprises duplicated microprocessors which perform operations in step. In a master/slave oscillator arrangement, the controller controls the slave clock oscillator as well as the master to assure tracking of the slave to the master.

Borehole acoustic telemetry clock synchronization system

Abstract: In a borehole telemetry system for acoustically transmitting data over a pipe suspended in a borehole, the level of noise in the data stream is inherently high, making the use of discrete frequencies advantageous to provide useful data. Any drift in electrical circuits which might affect or be affected by the use of precise frequencies is undesirable. A clock synchronization or bit rate clock circuit in a data signal processing system is operated by a local crystal oscillator which is operated at substantially the same precise frequency as a crystal oscillator that is used to generate and transmit the data signal. The synchronization of the bit rate clock is arranged to make only small corrections in order to keep the frequencies fully synchronized at all times thus false signals will not shift the clocks out of synchronization. The bit rate clock has an early late detector that determines if received data is expected early or late with respect to the data clock that is transmitting the data and shifts a window in the circuit accordingly. Another feature includes a fast search mode that causes the clock systems of the transmitted data signal and the clock system in the data signal processing circuit to move rapidly into synchronization when the signals are far out of synchronization, bypassing arrangements in the circuit that make only small corrections. The output of the bit rate clock operates a transmitter section to transmit the data signal at any desired frequency but at the same bit rate.

Redundant clock system utilizing nonsynchronous oscillators

Abstract: A clock system is disclosed having two identical clocks not synchronized with each other. Each of the clocks includes a circuit for selecting the output of one of the clocks as the present system output. Further, each clock includes logic for detecting errors in the operation of itself, and of the other. When an error is detected in the operation of the clock selected to be the present system output, a switchover sequence control switches the output signal of the nonselected clock to become the new system output. The switchover sequence control includes a feature which ensures that the interval between pulses in the system output is greater than a predetermined period in order to minimize detrimental effects on circuitry utilizing the clock system output.

Clock check circuits using delayed signals

Abstract: In a data processing or transmission system which includes at least two synchronized clocks, for example--T-rings A and B which generate timing pulses Tai and Tbi for microinstruction execution, synchronism is checked by logic circuitry which receives pulses from the clocks. At least one of the pulses is delayed by one or more pulse period durations ti. The logic circuit output signal is used as an input to an indicator latch which is periodically set by an independent check oscillator or clock. In a preferred embodiment, the delays are introduced by master-slave flip-flops, which receive predetermined combinations of the T-signals and set by the independent check clock. Several delay latches and associated AND gates may be used for different logical combinations of delayed and undelayed T-signals. This scheme can easily be expanded to accommodate more than two synchronously operating clocks. These circuits check not only the instantaneous synchronism of the clocks, but also the correct sequencing of clock pulses. The check is also feasible if the T-ring counters are operated with a variable number of clock pulses per microinstruction execution.

Method of synchronizing a quadphase receiver and a clock synchronization device for carrying out the method

Abstract: 15.5.79 1 PHN.9387 ABSTRACT "Method of synchronizing a quadphase receiver and clock synchronization device for carrying out the method" The invention relates to a method for the clock synchronization of a receiver for demodulating a quadphase coded data signal and to a clock synchroniza-tion device for carrying out the method. Four elementary signal forms can be distinguished in a quadphase coded data signal. Each ele-mentary signal form represents two-bit information, these two bits being transmitted in a first and a second half bit interval and these two bits being transmitted in the inverted form in a third and a fourth half bit interval. The information in the second interval is consequently highly correlated with the information in the first bit interval. The four quadphase code words have been chosen from the sixteen code words which can be formed with four bits and that in such a manner that only two-bit information is transmitted with these four bits. This is achieved by making the first and the second bit of the quadphase code word equal to the two-bit information of the signal to be coded and by making the third and the fourth bit equal to the inverse value of the two-bit information. In the method according to the invention the first bit is compared (correlated) with the third bit and the second bit with the fourth bit: a high degree of correlation indicates 15.5.79 2 PHN.9387 that synchronization has been obtained and a low degree indicates absence of synchronization. The invention is used in the field of optical and magnetic recording and in the field of data transmission over physical pairs of wires.

Clock invariant synchronization for random binary sequences

Abstract: The present invention relates to method and apparatus for performing miss identification (MID) and decoding messages communicated to an identified missile without the use of a synchronous internal clock.

A review of satellite time transfer technology: Accomplishments and future applications

Abstract: A brief review of the research accomplishments by NASA in meeting the needs of the space program for precise time in satellite tracking is presented. As a major user of precise time signals for clock synchronization of NASA's worldwide satellite tracking networks, the agency provided much of the necessary impetus for the development of stable frequency sources and time synchronization technology. The precision in time required for both satellite tracking and space science experiments has increased at a rate of about 1 order of magnitude per decade from 1 ms in the 1950's to 100 microsec during the Apollo era in the 1960's to 10 microsec in the 1970's. In the 1980's, when the Tracking and Data Relay Satellite System (TDRSS) comes into operation, satellite timing requirements will be extended to 1 microsec and below. These requirements are needed for spacecraft autonomy and data packeting which are now in active planning stages.

Synchronization for Telecommunications in a Switched Digital Network

Abstract: In a telecommunications network, the use of time division switches which directly operate on Pulse Code Modulated bit streams requires the use of some means for synchronizing the clock rates of such switches. Various methods for achieving synchronization are discussed. Master-slave synchronization has been selected as the most appropriate approach for the Bell System's switched digital network. Some aspects of this approach are considered.

Clock synchronization for data communication receiver

Abstract: With respect to a synchronous communications receiver, this specification discloses a decoder for generating a clock signal to synchronize the receiver with the information data rate of the received signal. The implementation of a decoder apparatus as a periodic finite state machine allows a clock signal to be extracted from the energy or transitions of the encoded signal. Such a decoder can define clock information over a large range of data rates. A bandpass filter tuned to the characteristic frequency being received can be coupled to the input of the decoder to limit the synchronization range to that desired by the receiver.

Direct Digitally Controlled Network Synchronization

Abstract: This paper describes a computer based, time discrete frequency regulator for network synchronization of digital telephone exchanges. All the known concepts for synchronization may be achieved after suitable manipulation of a few constants in the Control program. Some results of experiments are also reported upon.

Submicrosecond comparison of intercontinental clock synchronization by VLBI and the NTS satellite

Abstract: The intercontinental clock synchronization capabilities of Very Long Baseline Interferometry (VLBI) and the Navigation Technology Satellite (NTS) were compared using both methods to synchronize the Cesium clocks at the NASA Deep Space Net complexes at Madrid, Spain and Goldstone, California. Verification of the accuracy of both systems was examined. The VLBI experiments used the Wideband VLBI Data Acquisition System developed at the NASA Jet Propulsion Laboratory. The NTS Satellites were designed and built by the Naval Research Laboratory used with NTS Timing Receivers developed by the Goddard Space Flight Center. The two methods agreed at about the one-half microsecond level.

Relativistic effects on time scales and signal transmission

Abstract: The current view of space-time chronometry is reviewed in its different elements, clock transport and the ‘twin paradox,’ the effect of a gravitational field, and the Doppler effect. In this view a class of privileged, local inertial frames is assumed, and all good clocks measure proper time, the only observable one needs. Relativistic effects on clock synchronization and frequency comparison are described, and the essential role of the geoid is stressed. The available experimental precision makes these effects an essential ingredient of current and future work in this field. The role of distant matter in determining inertia and local dynamics (‘Mach's principle’) is not adequately described in this view. The cosmic background radiation provides a precise definition and a measurement of the local standard of rest with respect to the universe, which might have a privileged character among all the inertial frames. Different kinds of violations of the conventional view based upon this conjecture are discussed in terms of free dimensionless parameters. Finally, we review the upper bounds to the discrepancies from the relativistic values as deduced from several experiments.

Clock synchronization experiment in India using Symphonie satellite

Abstract: A recent clock synchronization experiment between the National Physical Laboratory (NPL), New Delhi and Space Applications Centre (SAC), Ahmedabad via geostationary satellite symphonie-II, stationed at 49°E longitude, is reported in this paper. As only one satellite transponder was available for this experiment, the two-way transmission of the clock pulses was carried out by switching the transmit—receive roles at the two stations at 5 minute intervals to achieve a nearly simultaneous two-way transmission. Taking into account all the additional delays, the results demonstrated a clock—synchronisation accuracy of better than 0.5 μs. A crystal-based portable clock flown aboard an aircraft confirmed this clock-synchronization to within a microsecond.

Clock synchronization circuit between central processors

Abstract: PURPOSE:To enable to access the same memory, by waiting the readout cycle of one processor until the readout cycle of other processor is finished and by reading out it after the end of waiting.

Submicrosecond comparison of intercontinental clock synchronization by VLBI and the NTS satellite

Abstract: The intercontinental clock synchronization capabilities of Very Long Baseline Interferometry (VLBI) and the Navigation Technology Satellite (NTS) were compared in May 1978 by using both methods to synchronize the cesium clocks at the NASA Deep Space Net complexes at Madrid, Spain, and Goldstone, California. The VLBI experiments used the Wideband VLBI Data Acquisition System. The Navigation Technology Satellites were used with NTS Timing Receivers developed by the Goddard Space Flight Center. The two methods agreed at about the one-half microsecond level. The VLBI system also obtained long-term stability information on the HP5061A004 cesium standards by measuring delta T/T over four 3- to 4-day intervals, obtaining stability estimates of (1 + or - 1)x10 to the -13th power for the combined timing systems.

External Clock Synchronization Plans for the GTD 3 EAX Digital Toll/Tandem

Abstract: The GTD 3 EAX local clock was designed with external synchronization in mind. The initial control algorithms and control circuits required a minimum of change to incorporate the ability to maintain clock synchronization with an external timing reference. The synchronization technique used is a frequency lock method and the considerations necessary for synchronization are described in this paper.

Source structure errors in the synchronization of clocks by radio interferometry

Abstract: Radio interferometry has the potential of synchronizing clocks across intercontinental distances with accuracies better than one nanosecond. One of the potential error sources in such determinations is the spatial structure of the natural radio sources that provide the reference signals. Due to their extent, the effective position of these sources can vary as a function of the length and orientation of the baseline vector joining the two antennas. If they are not corrected, such variations can lead to errors in clock synchronization. The theory of structure corrections is presented and specific examples are given to illustrate the nature and size of the effect.

Clock synchronization in a rotating frame

Abstract: Special- and general-relativistic synchronization are compared and experimental tests are discussed.

Some implications of reciprocity for two-way clock synchronization

Abstract: The difficulties related to propagation perturbances in one-way and two-way methods for the synchronization of remote clocks are defined, and a possible means of circumventing these problems in the two-way method is suggested. In the two-way method, if signals are launched from two sources, A and B, then the two signals arriving at A and B will be displaced in arrival time by an amount that is equal to the difference in launch times of the two signals. Thus, the only condition to comparing clocks is that the medium be isotropic. The practice implementation of this is explored theoretically, in some detail, with respect to the Loran-C navigation system.

Comparison of different time synchronization techniques

Abstract: The plans to set up an international TV synchronization network between four locations are discussed A feasibility study was conducted between two of the locations and significant results are reported

Ramp time synchronization

Abstract: A new method of intercontinental clock synchronization has been developed and proposed for possible use by NASA' s Deep Space Network (DSN), using a two-way/three-way radio link with a spacecraft. Analysis of preliminary data indicates that the real-time method has an uncertainty of 0.6 μs, and it is very likely that further work will decrease the uncertainty. Also, the method is compatible with a variety of non-real-time analysis techniques, which may reduce the uncertainty down to the tens of nanosecond range.