Soft handoff method and apparatus for mobile vehicles using directional antennas
First Claim
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 the first lobe based on a predetermined threshold.
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Accused Products
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.
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Citations
26 Claims
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1. A method of providing a communication link for a mobile platform, the method comprising:
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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 the first lobe based on a predetermined threshold. - View Dependent Claims (2, 3)
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4. A system for providing a cellular communications link between a mobile platform traversing a region served by a plurality of base transceiver stations (BTSs), the system comprising:
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an antenna controller;
a radio transceiver for communicating cellular signals between cellular users traveling on the mobile and at least one of the BTSs;
an antenna system carried on the mobile platform in communication with said radio transceiver, said antenna system being operable to;
form a single antenna beam having a first lobe and a second lobe coverage pattern, and for aiming the first lobe of the beam at a first said BTS to maintain a first communications link;
use the second lobe to simultaneously establish a second communications link with a second BTS different from the first BTS; and
to gradually reduce a gain of the first lobe to gradually fade out the first communications link, while simultaneously increasing a gain of said second lobe to gradually increase a quality of said second communications link, to effect a communications handoff from said first BTS to said second BTS. - View Dependent Claims (5, 6, 7, 8, 9)
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10. A system for providing air-to-ground (ATG) cellular communications between an airborne mobile platform traversing a region served by a plurality of base transceiver stations (BTSs), the system comprising:
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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 cellular signals between cellular users traveling on the mobile and at least one of the BTSs;
an antenna system carried on the mobile platform responsive to the radio transceiver, the antenna system being operable to;
form a single antenna beam having either a single lobe or a dual lobed coverage pattern, and for aiming the single lobe of the beam at a first said BTS when no handoff is needed; and
for aiming the first lobe of the single beam at the first said BTS and a second lobe of the single beam at a second said BTS when a handoff from the first said BTS to the second said BTS is needed. - View Dependent Claims (11, 12, 13, 14, 15, 16)
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17. A system for providing air-to-ground (ATG) cellular communications between an airborne mobile platform traversing a region served by a plurality of base transceiver stations (BTSs), where each said BTS serves a subregion representing a coverage cell, the system comprising:
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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 cellular signals to at least one of the BTSs;
an antenna system carried on the mobile platform;
a beam forming network responsive to the antenna controller and operable to generate a single beam having a single lobe coverage pattern or a dual lobe coverage pattern, the beam forming network operating to;
form the single beam with a single lobe coverage pattern, and to aim the single lobe coverage pattern at a first said BTS;
cause the single beam to be modified to provide the dual lobed coverage pattern when a handoff is to be made from the first said BTS to a second said BTS, in which the first lobe of the dual lobed coverage pattern is aimed at the first said BTS and a second lobe of the dual lobed coverage pattern is aimed at the second said BTS; and
to fade out said first lobe coverage pattern while fading in the second lobe coverage pattern so that communication with said radio transceiver is smoothly transferred from the first said BTS to the second said BTS. - View Dependent Claims (18, 19, 20, 21, 22, 23)
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24. 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:
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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. - View Dependent Claims (25, 26)
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Specification