Synchronizing of clocks

Details Synchronizing of clocks Synchronizing of clocks

1982-05-12

1985-09-24

Griffin, Robert L.

Pulse or digital communications

Repeaters

Testing

368 47, 375115, G04G 900, G04G 700

Patent

active

045436576

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention relates to the standardization of clocks as is required for example in modern communications systems.
In the field of communications, particularly where net-working systems are used, there is frequently a need to acquire and then maintain over long periods of time an accurate time-signal reference to operate electronics communications equipment.
Modern atomic frequency standards are readily available having drift rates of 1 in 10.sup.12 which can maintain an accurate reference over a long period of time without the need for frequent checking or correcting. The difficulty experienced in standardizing distant clocks is to obtain a sufficiently accurate synchronizing time-signal. Generally, current net-working systems require an accuracy of only better than 1 second as they run at relatively low band rates and/or they have been specifically designed to operate from such timing sources. However recent developments in HF/VHF communication systems indicate that timing accuracies within the range of 100 microseconds to 10 milliseconds will be necessary.
The requirement for a time signal source can be met at present using a reasonably stable clock and a standard time signal transmission such as MSF, WWV or GBR etc. The high speed time codes used by these services are transmitted in short bursts one per minute on the minute. The transmitted sequence contains a simple framing preamble followed by a 100 band data code giving GMT and the date. Although in principle a simple serial to parallel conversion is all that is required to decode the information contained in these transmitted codes in practice sophisticated error checking would be essential to discriminate against unwanted signals and to avoid erroneous decoding.
Errors in time code acquisition can occur because of poor propagation or high interference levels which frequently pervade the HF radio spectrum. The accuracy with which the time code signal can be received will depend on the signal to noise ratio of the transmitted time signal, the band width of the receiver and the coding format.


SUMMARY OF THE INVENTION

The object of the present invention is to provide a time code modem which adopts a special modulating technique to provide a timing accuracy which is better than has been previously possible for a given bandwidth.
In one form the invention provides a transmission clock modem for transmitting time-coded signals which comprises: pseudo-random numbers; transmission PNG such that the output numbers from the transmission PNG are equi-spaced in time; such that the transmission PNG is reset to a predetermined condition, hereinafter referred to as zero, after a preselected time interval: and
PNG's are well known circuits which produce an apparently random series of encoded numbers up to a maximum number which then repeats cyclically. Thus by making an appropriate choice of transmission PNG, clocking pulse rate and preselected time interval the total of pseudo-random numbers within the train of numbers can be kept within the maximum possible number for the PNG and therefore each number in the train will uniquely define the time within the preselected time interval.
Preferably the resetting means comprises a transmission reference clock which produces an output resetting pulse at the end of each of the preselected time intervals.
Advantageously the time interval is 24 hours. Thus after the PNG output is a number representative of 2400 hours the PNG is reset and the random number train starts again from zero.
In order to synchronize the transmission PNG and the transmission reference clock there is provided a pulse generator which can be actuated to add to the transmission PNG a number of clocking pulses equal to the number of pseudo-random numbers which can be generated by the transmission PNG within the preselected time interval and to simultaneously advance the transmission reference clock by the preselected time interval. By thus advancing both the PNG and the transmission reference clock through one complete cy

REFERENCES:
patent: 3244808 (1966-04-01), Roberts
patent: 3648173 (1972-03-01), Elliott
patent: 3756012 (1973-09-01), Kiss
patent: 3823377 (1974-07-01), Keane et al.
patent: 3852534 (1974-12-01), Tilk
patent: 3861134 (1975-01-01), Chacon et al.
patent: 4014166 (1977-03-01), Cateora et al.
patent: 4112368 (1978-09-01), Ewanus et al.
patent: 4117661 (1978-10-01), Bryant, Jr.
patent: 4122393 (1978-10-01), Gordy et al.
patent: 4158193 (1979-06-01), D'Antonio
Sharma, "Application of Redundant Codes to a Digital Communication System", Proc. Nat. Electronic Conf., No. 16 (1960) p. 243.
Townsend & Watt, "Effectiveness of Error Control in Data Communication Over the Switched Telephone Network", by The Bell System Technical Journal, Nov. 1964, pp. 2632-2633.

Affiliated with

Also associated with

Rating

Synchronizing of clocks does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Synchronizing of clocks, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Synchronizing of clocks will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-1617630