Link delay calculation and compensation system

• US 6,049,720 A
• Filed: 04/11/1997
• Issued: 04/11/2000
• Est. Priority Date: 04/12/1996
• Status: Expired due to Term

• Current Assignee: E F Johnson Company (JVC Kenwood Corporation)
• Original Assignee: TRANSCRYPT INTERNATIONAL / E.F. JOHNSON COMPANY
• Inventors: Rude, Michael J.
• Primary Examiner(s): LE, THANH C
• Application Number:
  US08/838,853
• Time in Patent Office: 1,096 Days
• Field of Search: 455/502, 455/503, 455/12.1, 455/11.1, 455/13.2, 455/13.1, 455/67.1, 455/67.3, 455/67.6, 375/355, 375/356
• US Class Current: 455/503
• CPC Class Codes: H04H 20/67 Common-wave systems, i.e. using separate transmitters operating on substantially the same frequency
• CPC Class Codes: H04L 1/24 Testing correct operation

Abstract

The present link delay calculation system using a common reference signal and a pulsed or gated tone signal to determine the link delay. The system using a discrete-time Fourier transform to measure phase information and obtain the link delay time. One such system employing a global positioning satellite signal to synchronize signal generation at a control site and demodulation at a remote site.

Claims

1. A method for measuring delay, comprising the steps of:

receiving a signal at a remote site;

processing the signal using Fourier transforms to determine a time delay using an external timing reference;

transmitting a gated signal from a central site, the gated signal having a first periodic component which is substantially less than a link time delay between repeaters of the repeater system and a second periodic component which is substantially greater than the link time delay, wherein the first periodic component and the second periodic component are aligned in phase to a reference timing signal;

receiving the gated signal at a remote site;

analog to digital converting the gated signal to create a sequence of digitized samples, wherein the analog to digital converting is performed in phase with the reference timing signal;

locating transition pairs in the sequence of digitized samples;

predicting zero crossings associated with each of the transition pairs;

averaging the zero crossings and using the averaged value to predict a starting point of the gated signal; and

introducing a delay to compensate for a link delay calculated from the starting point of the gated signal.

2. The method of claim 1, where the signal is a tone, the remote site is a remote repeater site, the external timing reference is a global positioning satellite system, and the time delay is a link delay between a central repeater site and the remote repeater site.

3. The method of claim 2, further comprising the step of:

introducing the delay at the central repeater site to compensate for the link delay.

4. The method of claim 3, wherein compensation is performed at the central repeater site.

5. The method of claim 3, wherein compensation is performed at the remote site.

6. The method of claim 1, wherein the step of processing comprises the steps of:

analog to digital converting the signal to create a sequence of digitized samples, wherein the analog to digital converting is performed in phase with the external timing reference;

detecting a crossing of a threshold amplitude of the gated signal by inspecting amplitudes of the digitized samples;

performing a discrete-time Fourier transform N periods of the first periodic component after the crossing to get phase information from the digitized samples;

generating a partial time delay from the phase information; and

adding N periods to the partial time delay to calculate the time delay.

7. The method of claim 1, wherein the external timing reference is a global positioning satellite system.

8. A method for alignment of a repeater system, comprising the steps of:

transmitting a gated signal from a central site, the gated signal having a first periodic component which is substantially less than a link time delay between repeaters of the repeater system and a second periodic component which is substantially greater than the link time delay, wherein the first periodic component and the second periodic component are aligned in phase to a reference timing signal;

receiving the gated signal at a remote site;

analog to digital converting the gated signal to create a sequence of digitized samples, wherein the analog to digital converting is performed in phase with the reference timing signal;

detecting a crossing of a threshold amplitude of the gated signal by inspecting amplitudes of the digitized samples;

performing a discrete-time Fourier transform N periods of the first periodic component after the crossing to get phase information from the digitized samples;

generating time delay from the phase information;

adding N periods to the time delay to calculate the link delay;

introducing a delay to compensate for the link delay;

measuring a plurality of time delays; and

deleting time delays which exceed a predefined maximum time delay.

9. The method of claim 8, wherein N=2.

10. The method of claim 8, wherein the reference timing signal is a signal from a global positioning satellite system.

11. The method of claim 8, wherein the compensation is performed at the central site.

12. The method of claim 8, wherein the compensation is performed at the remote site.

13. A method for alignment of a repeater system, comprising the steps of:

transmitting a gated signal from a central site, the gated signal having a first periodic component which is substantially less than a link time delay between repeaters of the repeater system and a second periodic component which is substantially greater than the link time delay, wherein the first periodic component and the second periodic component are aligned in phase to a reference timing signal;

receiving the gated signal at a remote site;

analog to digital converting the gated signal to create a sequence of digitized samples, wherein the analog to digital converting is performed in phase with the reference timing signal;

detecting a crossing of a threshold amplitude of the gated signal by inspecting amplitudes of the digitized samples;

performing a discrete-time Fourier transform N periods of the first periodic component after the crossing to get phase information from the digitized samples;

generating time delay from the phase information;

adding N periods to the time delay to calculate the link delay;

introducing a delay to compensate for the link delay;

measuring a plurality of time delays;

calculating a standard deviation of the plurality of time delays; and

deleting time delays which exceed the standard deviation.