Method of authenticating beacon

• US 6,510,401 B2
• Filed: 05/11/2001
• Issued: 01/21/2003
• Est. Priority Date: 05/11/2001
• Status: Expired due to Fees

• Current Assignee: United States Government, as represented by the National Security Agency
• Original Assignee: The United States of America As Represented By The Director National Security Agency
• Inventors: Summers, Kenneth E., Martin, Kenneth I.
• Primary Examiner(s): Hoff, Marc S.
• Assistant Examiner(s): West, Jeffrey R
• Application Number:
  US09/854,194
• Publication Number:
  US 20020173937A1
• Time in Patent Office: 620 Days
• Field of Search: 702/193, 702/94, 702/95, 702/150, 702/151, 702/152, 359/2, 359/159, 359/172, 342/37, 342/417-449, 380/258, 356/71, 356/614, 356/615, 356/622
• US Class Current: 702/150
• CPC Class Codes: G01S 1/024 of beacon transmitters
• CPC Class Codes: G01S 17/74 Systems using reradiation of electromagnetic waves other than radio waves, e.g. IFF, i.e. identification of friend or foe

Abstract

A beacon modulated by a pattern is authenticated by recording an array of light intensities for each point in a field of view; digitizing the array of light intensities; modifying a first array according to the digitized light-intensities and the modulation pattern; repeating these steps for additional frames at the current viewpoint; if the beacon is found then repeating these steps for additional frames; if the beacon is found and additional frames were processed then authenticating the beacon at the point in the current viewpoint corresponding to the value in the first array that exceeds a first threshold by the widest margin; if the beacon was not found, moving to a new point in the field of view and repeating the steps above; if the beacon is again not found, adjusting the modulation bit pattern x bits, and reprocessing the viewpoints in the field of view using the steps above.

Claims

1. A method of authenticating a beacon modulated by a user-definable bit pattern, comprising the steps of:

(a) establishing a first user-definable threshold and a second user-definable threshold;

(b) identifying a field of view in a search area as a current field of view, where the current field of view includes a number of elements;

(c) initializing each entry in a first array to a user-definable value;

(d) recording a signal intensity value for each element in the current field of view and storing the same in corresponding entries in a second array, where the second array is the same size as the first array;

(e) if a signal intensity value recorded in step (d) exceeds the second threshold then setting the corresponding value in the second array to a first value, otherwise setting the corresponding value in the second array to a second value;

(f) for a present bit in the user-definable bit pattern, mathematically altering the values of the first array in accordance with the values of the second array;

(g) if additional processing of the current field of view in the search area is desired, returning to step (d) for additional processing, otherwise proceeding to the next step;

(h) if at least one of the values in the first array exceeds the first threshold and additional processing is desired then returning to step (d) for additional processing;

(i) if at least one of the values in the first array exceeds the first threshold and no additional processing is desired then authenticating the beacon in the current field of view at which the first threshold is exceeded by a value in the first array by the greatest amount and stopping;

(j) if none of the values in the first array exceeds the first threshold then setting the current viewpoint to an unprocessed point in the search area and returning to step (c) for additional processing; and

(k) if each field of view in the search area is processed and no beacon is found and further processing is desired then adjusting the user-definable bit pattern x bits and using the adjusted pattern as the user-definable bit pattern for processing purposes, ignoring the results of previous steps, and returning to step (a) for further processing.

2. The method of claim 1, wherein the modulated beacon to be authenticated is modulated using a pattern of any length selected from the group of patterns consisting of a fixed pattern, a pseudo-random pattern, and a cryptographically generated pattern.

3. The method of claim 1, wherein said step of mathematically altering, for a bit in the user-definable bit pattern, the values of the first array in accordance with the values of the second array is comprised of the steps of:

(a) identifying the present bit in the user-definable bit pattern that will be used to mathematically alter the values in the first array;

(b) subtracting corresponding values in the second array from the first array if the present bit is of the second value;

(c) adding corresponding values from the second array to the first array if the present bit is of the first value; and

(d) setting the present bit to a different bit in the user-definable bit pattern.

4. The method of claim 1, further including the step of moving to a new field of view if no beacon is found after the previous fields of view were processed.

5. The method of claim 1, further including the step of subtracting a decay value from each entry in the first array.

6. The method of claim 1, wherein said step of recording a signal intensity value for each area in the current field of view and storing the same in corresponding entries in a second array is comprised of the step of recording a signal intensity value for each element in the current field of view at a rate greater than the rate of the user-definable modulation bit pattern.

7. The method of claim 1, wherein said step of setting the current viewpoint to an unprocessed point in the search area is comprised of the step of setting the current viewpoint to an unprocessed point in the search area using a spiral pattern.

8. The method of claim 2, wherein said step of mathematically altering, for a bit in the user-definable bit pattern, the values of the first array in accordance with the values of the second array is comprised of the steps of:

(a) identifying the present bit in the user-definable bit pattern that will be used to mathematically alter the values in the first array;

(b) subtracting corresponding values in the second array from the first array if the present bit is of the second value;

(c) adding corresponding values from the second array to the first array if the present bit is of the first value; and

(d) setting the present bit to a different bit in the user-definable bit pattern.

9. The method of claim 8, further including the step of moving to a new field of view if no beacon is found after the previous fields of view were processed.

10. The method of claim 9, further including the step of subtracting a decay value from each entry in the first array.

11. The method of claim 10, wherein said step of recording a signal intensity value for each area in the current field of view and storing the same in corresponding entries in a second array is comprised of the step of recording a signal intensity value for each element in the current field of view at a rate greater than the rate of the user definable modulation bit pattern.

12. The method of claim 11, wherein said step of setting the current viewpoint to an unprocessed point in the search area is comprised of the step of setting the current viewpoint to an unprocessed point in the search area using a spiral pattern.