MEANS FOR SYNCHRONIZING CLOCKS IN A TIME ORDERED COMMUNICATIONS SYSTEM

• US 3,798,650 A
• Filed: 10/02/1972
• Issued: 03/19/1974
• Est. Priority Date: 10/02/1972
• Status: Expired due to Term

• Current Assignee: Aaron Mall, Arthur D. Mccomas, Charles H. Doeller III, James A. Kessler, James R. Ransom
• Original Assignee: Aaron Mall, Arthur D. Mccomas, Charles H. Doeller III, James A. Kessler, James R. Ransom
• Inventors: McComas, Arthur D., Ransom, James R., Kessler, James A., Doeller, Charles H. III, Mall, Aaron
• Primary Examiner(s): Caldwell, John W.
• Assistant Examiner(s): Curtis, Marshall M.
• Application Number:
  US05/294,055
• Time in Patent Office: 533 Days
• Field of Search: 343/225 340/147SY
• US Class Current: 375/356
• CPC Class Codes: G01S 11/08 using synchronised clocks
• CPC Class Codes: G04G 7/00 Synchronisation radio-controlled time-pieces G04R
• CPC Class Codes: H04J 3/0682 by delay compensation, e.g. by compensation of propagation delay or variations thereof, by ranging

Abstract

A time ordered communications system wherein a master station equipped with a master clock which includes a reference oscillator disseminates correct time to remote stations equipped with local clocks which include local oscillators by transmitting a synchronization signal whose time of arrival at the remote station with respect to an internal reference pulse generated by the remote station is a measure of remote station clock error. The time interval between receipt of the synchronization signal and generation of the internal reference pulse is digitally determined to produce an error signal which is used to add or delete local oscillator pulses so as to immediately phase correct the local clock. In addition, the first and second time derivatives of the error signal are obtained and used to compensate the local clock for oscillator drift and other errors.

Claims

1. In a time ordered communications system including a master station having a master clock and at least one remote station which includes a local clock comprised of a binary divider for generating local timing signals used in operating said remote station in said communications system, and wherein said local clock is driven by a local frequency, and wherein said master station disseminates absolute time by broadcasting a synchronization signal via a radio link to said remote station in response to which said remote station generates an external reference pulse (ERP) a predetermined time after receiving said synchronization signal and additionally generates an internal reference pulse (IRP) at a predetermined local clock time, the system being so structured that the time deviation of said ERP with respect to said IRP being a measure of the absolute error of the local clock time with respect to master clock time and said master station transmits a synchronization signal for only a small percentage of IRP'"'"''"'"'s, means for maintaining the local clock synchronized with said master clock comprising:

a source of a first train of pulses;

means responsive to correction signals comprised of correction pulses and a sign signal for adding or deleting a pulse in said first train for each of said correction pulses, the resultant pulses comprising said local signal;

a source of clock pulses;

means for generating a time window about said IRP;

counter means for accumulating a first number proportional to the number of said clock pulses occurring between said ERP and IRP when said ERP occurs in said time window;

means for generating said sign signal in response to one of said ERP anD IRP occurring first;

means for accumulating a second number correlated to the number of consecutive time windows generated since the last ERP occured in one of the time windows;

means for dividing said first number by at least said second number to generate a further pulse train, the number of pulses in said further pulse train being proportional to the average time error of said local clock with respect to said master clock;

means responsive to said first number for generating a first of said correction signals; and

, means responsive to said further pulse train for generating a second of said correction signals.

2. The means for maintaining a local clock synchronized with a master clock as recited in claim 1 with additionally:

a first pulse divider for dividing said further pulse train by at least a constant, said means for generating a second of said correction signals being additionally responsive to the divided further pulse train.

3. The means of claim 2 wherein said means for generating a second of said correction signals comprises:

an offset register for accumulating pulses from said further pulse train and the divided further pulse train in a direction determined by said sign signal;

a second pulse divider having a variable divisor set in accordance with the number of pulses instantaneously contained in said offset register, said second pulse divider dividing said first train of pulses to generate said second of said correction signals.