Soft handoff method and apparatus for mobile vehicles using directional antennas

• US 20060229104A1
• Filed: 12/21/2005
• Published: 10/12/2006
• Est. Priority Date: 04/08/2005
• Status: Active Grant

• Current Assignee: The Boeing Co.
• Original Assignee: The Boeing Co.
• Inventors: de La Chapelle, Michael, Monk, Anthony D.
• Granted Patent: US 9,306,657 B2
• Time in Patent Office: Days
• US Class Current: 455/562.100
• CPC Class Codes: H01Q 1/28 Adaptation for use in or on aircraft, missiles, satellites, or balloons
• CPC Class Codes: H01Q 1/283 Blade, stub antennas
• CPC Class Codes: H01Q 1/3208 characterised by the application wherein the antenna is used
• CPC Class Codes: H01Q 3/2611 Means for null steering; Adaptive interference nulling
• CPC Class Codes: H04B 7/18506 Communications with or from aircraft, i.e. aeronautical mobile service
• CPC Class Codes: H04W 36/08 Reselecting an access point
• CPC Class Codes: H04W 36/18 for allowing seamless reselection, e.g. soft reselection
• CPC Class Codes: H04W 84/06 Airborne or Satellite Networks space-based or airborne stations H04B7/185

Abstract

A system and method for implementing soft handoffs in a cellular communications system on a mobile platform. The system employs an antenna controller in communication with a beam forming network that generates two independently aimable lobes from a single beam. The single beam is radiated by a phased array antenna on the mobile platform. In an Air-to-Ground implementation involving an aircraft, a base transceiver station (BTS) look-up position table is utilized to provide the locations of a plurality of BTS sites within a given region that the aircraft is traversing. The antenna controller controls the beam forming network to generate dual lobes from the single beam that facilitate making a soft handoff from one BTS site to another. In a ground-based application, one lobe of the beam is used to maintain a communications link with one BTS site while a second lobe of the beam is continuously scanned about a predetermined arc to receive RF signals from other BTS sites and to determine when a new BTS site has become available that will provide a higher quality link than the link presently made with the one BTS site. A soft handoff is then implemented from the one BTS site to the new BTS site.

Claims

1. A method of providing a communication link for a mobile platform, the method comprising:

generating a single beam;

controlling the single beam to generate first and second communication lobes from the single beam, the first communication lobe communicating with a first base transceiver station (BTS);

using the second communication lobe to communicate with the second BTS; and

fading out the first lobe so that communication with said mobile platform is transferred to said second BTS.

2. The method of claim 1, further comprising fading the first lobe based on a signal to noise ratio consideration for signals being received by the first lobe, relative to a predetermined threshold.

3. The method of claim 1, further comprising fading the first lobe based on a distance separating each of the first BTS and a second BTS from a given reference point.

4. A system for providing a communications link between a mobile platform traversing a region served by a plurality of base transceiver stations (BTSs), the system comprising:

an antenna controller;

a radio transceiver for communicating signals between users traveling on the mobile platform and at least one of the BTSs;

an antenna system carried on the mobile platform in communication with said radio transceiver, said antenna system generating;

a single antenna beam having a first lobe coverage pattern and a second lobe coverage pattern, with the first lobe coverage pattern steerable toward a first said BTS to maintain a first communications link, and the second lobe coverage pattern steerable toward a second BTS to simultaneously establish a second communications link with the second BTS; and

the beam former further comprising gain control to enable gradual reduction of a gain of the first lobe to gradually fade out the first communications link, while simultaneously enabling increasing a gain of said second lobe to gradually increase a quality of said second communications link, to enable a communications handoff from said first BTS to said second BTS to be effected.

5. The system of claim 4, further comprising a BTS locating subsystem in communication with said antenna system for providing locations of each of said BTSs located in said region.

6. The system of claim 5, said BTS locating subsystem comprising a look-up table in communication with said antenna controller for providing latitude, longitude and altitude position information for each of said BTSs existing within said region;

and

said antenna controller able to access said look-up table to acquire location information for various BTSs.

7. The system of claim 4, said antenna system comprising:

an antenna controller;

a beam forming subsystem in communication with said antenna controller; and

a phased array antenna disposed on an exterior surface of said mobile platform, in communication with said beam forming subsystem.

8. The system of claim 4, said antenna system enabling scanning of said second lobe about a predetermined azimuth arc to sample signal strengths of remotely located BTSs with said coverage region to determine the existence of said second BTS and that a handoff from said first BTS to said second BTS needs to be initiated.

9. The system of claim 4, said antenna system being able to scan the second lobe of the single beam about a predetermined path to enable continuously searching for a second BTS that is expected to provide a higher quality communications link than said first communications link;

and

the antenna system enabling a handoff from said first BTS to said second BTS when a second BTS is found that is expected to provide a higher quality communications link than said first BTS.

10. A system for providing air-to-ground (ATG) communications between an airborne mobile platform traversing a region served by a plurality of base transceiver stations (BTSs), the system comprising:

an antenna controller;

a subsystem for providing the locations of the BTSs located within the coverage region to the antenna controller;

a radio transceiver for communicating signals between users traveling on the mobile platform and at least one of the BTSs;

an antenna system carried on the mobile platform responsive to the radio transceiver, the antenna system forming a single antenna beam having;

a single lobe coverage pattern steered to point in a vicinity of a first said BTS when no handoff is needed, and;

selectively having a dual lobe coverage pattern in which the first lobe of the single beam can be aimed at said first BTS and a second lobe of the single beam is aimed at a second said BTS when a handoff from said first BTS to said second BTS is needed.

11. The system of claim 10, said antenna system including components operable to control the lobes to fade out said first lobe of the single beam while fading in said second lobe of the single beam so that communication with said radio transceiver is smoothly transferred from the first said BTS to the second said BTS.

12. The system of claim 10, said antenna system comprising:

an antenna controller;

a beam forming network responsive to the antenna controller and to the radio transceiver, for forming the single antenna beam with either the single lobe or the dual lobe pattern; and

a phased array antenna for radiating the single antenna beam with the single lobe and dual lobed patterns.

13. The system of claim 11, further comprising an aircraft navigation system for providing real time information regarding the latitude, longitude and altitude of the mobile platform, the aircraft navigation subsystem being in communication with the antenna controller.

14. The system of claim 10, further comprising:

a server/router in communication with the radio transceiver and with a local area network (LAN) on the mobile platform.

15. The system of claim 10, the antenna system comprising a phased array antenna including a plurality of antenna elements supported from an undercarriage of the mobile platform.

16. The system of claim 10, the subsystem for providing the locations of the BTSs comprising a look-up table having the longitude, latitude and altitude of each said BTS in the region.

17. A system for providing continuous communications between a mobile platform having an antenna system traversing a region served by a plurality of base transceiver stations (BTSs), where each said BTS serves a subregion of said region and each BTS has unique location information, the system comprising:

a. a subsystem for providing the unique location of at least one of the BTSs located within the region to the antenna system;

b. a radio transceiver coupled to the antenna system for communicating cellular signals to at least one of the BTS located within the region by said subsystem;

c. a beam forming network coupled to the antenna system and operable to form a single beam for communication with at least one BTS;

(1) said single beam having a single lobe coverage pattern for communication with a first BTS, and selectively;

(2) having a dual lobed coverage pattern comprising a first lobe coverage pattern for communication with a first BTS and a second lobe coverage pattern for communication with a second BTS when a handoff is to be made from said first BTS to said second BTS.

18. The system of claim 17, said subsystem comprising a look-up table with the latitude and longitude of each said BTS within the coverage region.

19. The system of claim 17, further comprising a server/router in communication with the radio transceiver and with a local area network (LAN) on-board the mobile platform.

20. The system of claim 17, the antenna system comprising a phased array antenna system supported on an undercarriage of the mobile platform.

21. The system of claim 17, the mobile platform comprising an aircraft.

22. The system of claim 17, the antenna system comprising a phased array antenna including a plurality of adjacently positioned monopole antenna elements.

23. The system of claim 17, further comprising an aircraft navigation system for supplying latitude, longitude and altitude information to said antenna controller pertaining to a real time location of said mobile platform.

24. A system for providing communications between a first platform and a plurality of second platforms, comprising:

an antenna carried on the first platform;

a beam former for controlling electrical signals applied to the antenna to form a single beam pattern for the antenna, with the single beam pattern having a first lobe able to be steered toward a first one of said second platforms, and a second lobe able to be steered toward a second one of said second platforms.

25. The system of claim 24, the lobes each comprising a receive lobe for receiving electromagnetic wave signals.

26. The system of claim 24, the lobes each comprising transmit lobes for radiating electromagnetic wave energy.

27. A method for providing communications between a mobile platform and a terrestrial cellular network employing a plurality of base transceiver stations (BTSs) at spaced apart locations within a region being traversed by the mobile platform, the method comprising:

using a radio transceiver located on the mobile platform to provide a cellular communications link with at least one of the BTSs;

generating a single antenna beam having a first lobe for establishing a first communications link with a first BTS;

determining when a second BTS becomes available that is expected to provide a higher quality communications link with said terrestrial cellular network;

initiating a handoff of said first communications link from said first BTS to said second BTS by using a second, independently aimable lobe of said single antenna beam to establish a second communications link with said BTS while maintaining said first communications link with said first BTS; and

gradually fading out said first communications link with said first BTS while simultaneously fading in said second communications link to complete said handoff of said cellular communications link from said first BTS to said second BTS.

28. The method of claim 27, the operation of aiming the first and second lobes comprising using location information obtain from a look-up table as to the location of each of said first and second BTSs.

29. The method of claim 27, the operation of determining when a second BTS becomes available comprising:

continuously scanning said second lobe about a predetermined arc;

receiving radio frequency (RF) signals from one or more remotely located BTSs via the second lobe; and

determining from a signal strength of each said received RF signal from each said remotely located BTS whether one of said remotely located BTSs will provide a higher quality communications link than said first BTS.