Soft handoff method and apparatus for mobile vehicles using directional antennas

• US 20060229077A1
• 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: Monk, Anthony D.
• Granted Patent: US 8,280,309 B2
• Time in Patent Office: Days
• US Class Current: 455/442
• CPC Class Codes: H01Q 1/283 Blade, stub antennas
• CPC Class Codes: H01Q 3/26 varying the relative phase or relative amplitude of energisation between two or more active radiating elements; varying the distribution of energy across a radiating aperture H01Q3/12, H01Q3/22, H01Q3/24 take precedence
• CPC Class Codes: H04B 7/18506 Communications with or from aircraft, i.e. aeronautical mobile service
• CPC Class Codes: H04W 16/28 using beam steering
• 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 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. An antenna system of a mobile platform comprising:

an antenna aperture;

a beam former for controlling the antenna aperture to generate a single beam having at least two lobes; and

an antenna controller for controlling the beam former to enable steering at least one of the two lobes in a desired direction by adjusting a phase array distribution of signals being communicated via said antenna aperture aperture.

2. The antenna system of claim 1, the antenna controller further controlling the two lobes by adjusting both the phase array distribution and the array amplitude distribution of said signals.

3. The antenna system of claim 1, further comprising a full duplex transmit/receive subsystem.

4. The antenna system of claim 1, further comprising a transmit subsystem for generating a transmit signal.

5. The antenna system of claim 3, the antenna aperture comprising a phased array antenna aperture including a plurality of antenna elements;

and

the beam former comprising elements to control the lobes by adjusting the phase array distribution and array amplitude distribution of said signals communicated via said antenna aperture.

6. A method for generating a single beam having at least a pair of lobes for use with an antenna, the method comprising:

generating a single beam having a pair of independent lobes each forming an independent communications link with a remotely located communications terminal; and

controlling a phase array distribution and an array amplitude distribution of signals applied to said antenna that are used to form at least one of the lobes, to thus steer said one lobe in a desired direction independently of the other said lobe.

7. An antenna system for use in communicating with a terrestrial network, where a communications handoff is required to be made by the antenna system from communication with a first base transceiver station (BTS) to communication with a second BTS, the system comprising:

an antenna controller having information as to the location of the first and second BTSs;

an antenna component adapted to be carried by a mobile platform;

a beam forming network responsive to the antenna controller for controlling signals communicated via said antenna component to radiate a single antenna beam having a first lobe having a first gain, and a second lobe having a second gain, with the first and second lobes being independently steerable in desired directions, and with the first and second gains being controllable; and

the lobes being steerable to enable simultaneously establishing two independent communication links with said BTSs, the BTSs being located at spaced apart locations within two overlapping coverage regions, so that a handoff from the first BTS to the second BTS can be made.

8. The antenna system of claim 7, the antenna component comprising a phased array antenna having a plurality of antenna elements.

9. The antenna system of claim 8, said antenna system including a plurality of diplexers, one said diplexer for each said antenna element, for interfacing said beam forming network to said antenna elements.

10. The antenna system of claim 8, said phased array antenna comprising a plurality of monopole blade antenna elements adapted to be mounted closely adjacent one another on an exterior surface of said mobile platform.

11. The antenna system of claim 8, said beam forming network including a transmit beam forming subsystem and a receive beam forming subsystem.

12. The antenna system of claim 11, said receive beam forming subsystem including a plurality of phase shifters and signal attenuators responsive to signals from the antenna controller for controlling an array distribution pattern in both phase and amplitude across said antenna elements.

15. The antenna system of claim 11, said transmit beam forming subsystem including a plurality of phase shifters, one each of said phase shifters being associated with each said antenna element, for controlling a phase of signals applied to said antenna elements.

13. The antenna system of claim 13, the receive beam forming subsystem includes a plurality of low noise amplifiers, with one each of said low noise amplifiers being associated with each of said antenna elements.

14. The antenna system of claim 13, further comprising a receiver-combiner that interfaces said receive beam forming subsystem to an external transceiver.

16. A method for generating at least two independently steerable beam lobes from a single antenna beam of a phased array antenna, comprising:

a) determining complex voltage distributions needed to steer a single beam in each one of a plurality of predetermined directions;

b) calculating a complex voltage distribution needed to generate the plurality of lobes from the single antenna beam by;

b₁) multiplying each said complex voltage distribution obtained at operation a) by (1−

α

), where α

is a predetermined blending factor having a value between 0 and 1, and such that the sum of the blending factors used is no greater than 1; and

b₂) adding together the products of b₁.

17. The method of claim 16, further comprising using the complex voltage distribution obtained at operation b) to generate a plurality of complex weight settings to be applied to each said element of the antenna array, wherein each said weight setting comprises both an amplitude value and a phase value.

18. The method of claim 17, further comprising normalizing a distribution of the amplitude values to be applied to each said element of said phased array antenna by determining a maximum amplitude value present from all of said amplitude values, and subtracting the maximum amplitude value from each of said amplitude values to produce a plurality of normalized amplitude values.

19. The method of claim 18, further comprising applying the normalized amplitude values and the phase values of each said signal to the elements of the phased array antenna.

20. The method of claim 16, operation a) comprising determining phase distribution values for signals to be applied to said elements of said phased array antenna, needed to steer a single beam in each of the plurality of predetermined directions.

21. The method of claim 16, operation a) comprising determining amplitude distribution values for signals to be applied to said elements of said phased array antenna.

22. A method for generating two independently steerable lobes from a single beam of a phased array antenna, in which the phased array antenna has a plurality of independent antenna elements, comprising:

a) defining a fixed amplitude distribution;

b) determining a phase distribution needed to steer a single beam in a first direction;

c) using the amplitude distribution from operation a) and the phase distribution from operation b), determining a complex voltage distribution needed to steer a single beam in the first direction;

d) determining a phase distribution needed to steer a single beam in a second direction;

e) using the amplitude distribution from operation a) and the phase distribution from operation d), determining a complex voltage distribution needed to steer a single beam in the second direction;

f) calculating the complex voltage distribution needed to form dual lobes from the single beam by multiplying the complex voltage distribution determined from operation c) by a blending factor (1−

α

), and adding a quantity;

(1−

α

)×

(the voltage distribution at operation e); and

g) using the information obtained from operation f), generating an amplitude value and a phase value to be applied to each element of the phased array antenna to generate two lobes aimed in desired directions, from the single beam of the phased array antenna.

23. The method of claim 22, further comprising altering the blending factor α

between values of zero and one to control the gain of each of the two lobes of the single antenna beam.

24. The method of claim 22, operation g) further comprising normalizing the amplitude distribution of the amplitude values applied to all of the elements of the phased array antenna.

25. The method of claim 24, the normalizing operation comprising determining a maximum amplitude value, in decibels, obtained at operation g), subtracting the determined maximum amplitude value from the amplitude values obtained at operation g) to produce a plurality of normalized amplitude values, and applying the normalized amplitude values to the elements of the phased array antenna.

26. A method for generating two independently steerable lobes from a single beam of an antenna, comprising:

a) calculating a phase distribution needed to steer a single beam from a plurality of elements of said antenna in a first direction;

b) using a baseline, fixed amplitude distribution for said antenna, together with said calculated phase distribution of operation a), calculating a complex voltage distribution needed to steer a single beam in said first direction;

c) calculating a phase distribution needed to steer a single beam from said phased array antenna in a second direction different than said first direction;

d) using the fixed amplitude distribution from operation b), and the phase distribution calculated at operation c), calculating a complex voltage distribution needed to steer the single beam in the second direction;

e) calculating a complex voltage distribution needed to form a blended dual beam by multiplying the complex voltage distribution obtained from operation b) by a value (1−

α

), and adding (1−

α

) times the complex voltage distribution from operation d);

f) applying the calculation of operation e) to each said element of the antenna;

g) using the complex blended dual beam distribution from operations e) and f), converting the complex voltage value at each said antenna element to an amplitude value and a phase value;

h) determining a maximum amplitude value across the elements of the antenna;

i) subtracting the maximum amplitude value obtained at operation h) from the amplitude value at each of the elements of the antenna obtained at operation g) to thus normalize the amplitude distribution across the elements; and

j) applying amplitude values from operation i) and phase values from operation g) to said electronically adjustable attenuators and phase shifters associated with each said element of the antenna to generate the lobes of the single antenna beam.

27. An aircraft comprising:

an antenna system for use in communicating with a terrestrial network, where a communications handoff is required to be made by the antenna system from communication with a first base transceiver station (BTS) to communication with a second BTS, the system comprising;

an antenna controller having information as to the location of the first and second BTSs;

an antenna component adapted to be carried by said aircraft;

a beam forming network responsive to the antenna controller for modifying signals applied to said antenna component to cause said antenna component to radiate a single beam having;

a first lobe, and

selectively a second lobe, with the first and second lobes being independently steerable and controllable to simultaneously establish two communication links with said BTSs, and to effect a handoff of communications with the first BTS to the second BTS.

28. The aircraft of claim 27, the beam former further comprising gain control to control a gain of each of said lobes.