COLLISION AVOIDANCE SYSTEM GROUND STATION SYNCHRONIZATION

• US 3,781,803 A
• Filed: 04/10/1972
• Issued: 12/25/1973
• Est. Priority Date: 04/10/1972
• Status: Expired due to Term

• Current Assignee: Benton J. Mcclure, Brendan J. Spratt, Wayne G. Shear
• Original Assignee: Benton J. Mcclure, Brendan J. Spratt, Wayne G. Shear
• Inventors: Shear, Wayne G., Spratt, Brendan J., McClure, Benton J.
• Primary Examiner(s): Caldwell, John W.
• Assistant Examiner(s): Curtis, Marshall M.
• Application Number:
  US05/242,631
• Time in Patent Office: 624 Days
• Field of Search: 343/225 340/147SY 58/24-26 325/58 178/69.5
• US Class Current: 375/356
• CPC Class Codes: G01S 11/08 using synchronised clocks

Abstract

A collision avoidance system ground station has its clock phase synchronized with a master clock through the use of a line-ofsight radio link. Multiple two-way synchronization rangings are exchanged between the ground station and the master clock. A digital counter at the ground station obtains the average deviation of the ground station clock with respect to the master clock and applies this average deviation to calibrate or synchronize the ground station clock with the master clock. Subsequently, further multiple two-way synchronization rangings are exchanged between the ground station clock and the master clock. A digital counter at the master clock now obtains the average deviation of the master clock with respect to the ground station clock as a check of the validity of the ground station clock calibration.

Claims

1. A multiple unit system wherein each unit includes clock means intended to be operated in synchronism with a system-wide sequence of repeating cycles of time slots, said units additionally including means for synchronizing said clock means with one another by a two-way ranging technique wherein a unit requesting synchronization receives a synchronization signal the time of arrival of which at said unit requesting synchronization is a measure of the individual synchronization error existing between the unit requesting synchronization and a unit transmitting said synchronization signal as observed at said unit requesting synchronization and wherein one said unit includes a mobile master unit and another unit includes local clock means responsive to a local accurate frequency source for establishing said system-wide sequence of repeating cycles of time slots, said another unit additionally comprising:

means for obtaining from said master unit a synchronization signal during each of a plurality of said time slots;

means responsive to each of said synchronization signals as received at said unit requesting synchronization for generating a number of clock pulses related to said individual synchronization error;

first counter means for cumulating said clock pulses;

second counter means for keeping a count of the number of said synchronization signals received by said unit requesting synchronization and for generating an output signal when it attains a predetermined count;

means responsive to said output signal for extracting the average of the instantaneous count contained in said first counter means; and

, means responsive to said average for calibrating said local clock means.

2. The system of claim 1 wherein said another unit additionally includes:

means responsive to the calibration of said local clock means for transmitting a second signal from said another unit to siad master unit, said second signal containing uniquely coded information indicating calibration of said local clock means is complete.

3. The system of claim 2 wherein said master unit additionally includes:

means responsive to said second signal for obtaining a plurality of synchronization signals from said another unit; and

, means responsive to said plurality of synchronization signals for calculating the error of said local clock.

4. The system of claim 1 wherein said means for obtaining comprises:

means for memorizing which time slots are unoccupied;

means cooperating with said means for memorizing for transmitting synchronization requests in a plurality of unoccupied time slots, said master unit responding to each said synchronization request with a synchronization signal.