Micro cell architecture for mobile user tracking communication system

• US 20020126042A1
• Filed: 09/05/2001
• Published: 09/12/2002
• Est. Priority Date: 06/06/2000
• Status: Active Grant

• Current Assignee: DIRECTV, LLC (AT&T, Inc.)
• Original Assignee: Hughes Electronics Corporation (Rtx Corporation)
• Inventors: Wang, Weizheng, Cha, Alan, Chang, Ming, Chang, Donald C.D., Feria, Ying, Yung, Kar W., Hagen, Frank A.
• Granted Patent: US 6,914,557 B2
• Time in Patent Office: Days
• US Class Current: 342/354
• CPC Class Codes: H04B 7/0617 for beam forming
• CPC Class Codes: H04B 7/086 using weights depending on external parameters, e.g. direction of arrival [DOA], predetermined weights or beamforming
• CPC Class Codes: H04B 7/18504 Aircraft used as relay or high altitude atmospheric platform

Abstract

A system and method for tracking a user. The system is adapted for use in a wireless communication system and creates a plurality of beams within a coverage area. A first beam is directed at a user in a first microcell and a number of additional beams illuminate microcells immediately adjacent the first microcell. The system is equipped with a mechanism for detecting movement of the user from the first microcell to one of the immediately adjacent microcells. On the detection of movement of the user, the system redirects the first beam from the first microcell to a second microcell, the second microcell being one of the adjacent microcells. In the illustrative embodiment, the system is implemented in a stratospheric platform based communication system including a hub adapted to communicate with a stratospheric platform. A transceiver and a phased array antenna are disposed on the platform to communicate with the hub and with the user. A second antenna is provided on the platform to communicate with the hub. Beamforming and direction are implemented on the hub and communicated to the platform. The user'"'"'s position is detected with a global positioning system receiver, by measuring the strength of a signal received from the user, or by other suitable means. On detection of user movement from the first microcell, the beamforming system redirects the beam to follow the user into a second microcell. Additional beams around the user'"'"'s microcell are illuminated to facilitate detection of the users movement.

Claims

1. A user tracking system for a wireless communication system, comprising:

a hub having a digital beam forming network for forming a plurality beams with different shapes and sizes within a coverage area, said plurality of beams including at least one beam that is wider than the other beams of said plurality of beams to provide links supporting lower data rates, and at least one narrow beam that is narrower than the other beams of said plurality of beams for providing coverage at a center of coverage, said coverage area being subdivided into a plurality of microcells including a first microcell and a plurality of adjacent microcells; and

an above-ground platform having a transceiver and a phased array antenna for using the beams formed by said digital beam forming network and directing at least a first narrow beam of said at least one narrow beam to a first microcell at which a first user is located.

2. The system of claim 1, wherein said first narrow beam tracks the first user as the first user travels from the first microcell to one of a plurality of adjacent microcells.

3. The system of claim 2 wherein said first narrow beam tracks the first user such that the user is kept within less than about 1 dB antenna directivity roll-off from peak.

4. The system of claim 2, wherein the first microcell and the plurality of adjacent microcells form a nonuniform pattern.

5. The system of claim 2, wherein the digital beam forming network generates phasings, weighting and codes for each of the plurality of beams.

6. The system of claim 5, wherein the beam weightings for the first narrow beam are changed for the first user as the user travels from the first microcell to one of a plurality of adjacent microcells.

7. The system of claim 1, wherein the at least one beam that is wider is used to pick up new users.

8. The system of claim 1, wherein said first microcell and at least one of the plurality of adjacent microcells partially overlap.

9. The system of claim 1 further including means for reusing frequencies.

10. The system of claim 9, wherein the means for reusing frequencies comprises means for assigning a code to each one of the plurality of beams.

11. A method for tracking users in a wireless communication system, comprising the steps of:

forming a plurality beams with different shapes and sizes within a coverage area using a digital beam forming network, said plurality of beams including at least one beam that is wider than the other beams of said plurality of beams to provide links supporting lower data rates, and including at least one narrow beam that is narrower than the other beams of said plurality of beams for providing coverage at a center of coverage, said coverage area being subdivided into a plurality of microcells including a first microcell and a plurality of adjacent microcells; and

directing at least a first narrow beam of said at least one narrow beam to a first microcell at which a first user is located via an above-ground platform having a transceiver and a phased array antenna for using the plurality of beams.

12. The method of claim 11, further comprising the step of tracking the first user as the first user travels from the first microcell to one of a plurality of adjacent microcells using the first narrow beam.

13. The method of claim 12, wherein the first narrow beam tracks the first user such that the user is kept within less than about 1 dB antenna directivity roll-off from peak.

14. The method of claim 12, wherein the first microcell and the one of a plurality of adjacent microcells at least partially overlap.

15. The method of claim 14 wherein the first user is assigned to the one of a plurality of adjacent microcells when the user leaves the area of the first microcell area completely.

16. The method of claim 11, wherein the first microcell and the plurality of adjacent microcells form a nonuniform pattern.

17. The method of claim 11, further comprising generating phasings, weighting and codes for each of the plurality of beams.

18. The method of claim 17 further comprising the step of changing the beam weightings for the first narrow beam as the user travels from the first microcell to one of a plurality of adjacent microcells.

19. The method of claim 11, further comprising the step of reusing frequencies.

20. The method of claim 19, wherein the step of reusing frequencies comprises assigning codes to each one of the plurality of beams.

21. The method of claim 19, wherein the step of reusing frequencies comprises providing a group of a plurality of codes.

22. The method of claim 21, wherein the group of a plurality of codes is further divided into a plurality of subgroups, each subgroup having at least two of the plurality of codes.

23. The method of claim 22, wherein each new user is assigned one of the plurality of subgroups based on a selected criterion such that no user is located within a contour of another user using the same code.

25. The method of claim 24, further comprising the step of:

scanning a beam for acquiring new users.

26. The method of claim 24, further comprising the step of forming a wide beam for acquiring new users in the coverage area.

24. A method of mobile user tracking using a microcell architecture, comprising the steps of:

dividing a coverage area into a plurality of microcells with associated beam weights;

forming a plurality of narrow beams around an user in a first microcell;

tracking the user when the user leaves the first microcell by shifting the plurality of narrow beams.