Earth-fixed cell beam management for satellite communication system using dielectic lens-focused scanning beam antennas

• US 5,736,959 A
• Filed: 04/17/1995
• Issued: 04/07/1998
• Est. Priority Date: 10/28/1991
• Status: Expired due to Term

• Current Assignee: Wengen Wireless LLC (Intellectual Ventures LLC)
• Original Assignee: Teledesic, LLC (Michael J. Larson, MBA)
• Inventors: Sturza, Mark Alan, Patterson, David Palmer
• Primary Examiner(s): Issing, Gregory C.
• Application Number:
  US08/423,677
• Time in Patent Office: 1,086 Days
• Field of Search: 342/354, 342/372, 455/12.1, 455/13.1, 455/13.3, 379/60
• US Class Current: 342/354
• CPC Class Codes: H01Q 1/242 specially adapted for hand-held use
• CPC Class Codes: H01Q 1/244 extendable from a housing along a given path
• CPC Class Codes: H01Q 1/288 Satellite antennas
• CPC Class Codes: H01Q 15/02 Refracting or diffracting devices, e.g. lens, prism
• CPC Class Codes: H01Q 21/065 Patch antenna array
• CPC Class Codes: H01Q 25/008 lens fed multibeam arrays
• CPC Class Codes: H01Q 3/24 varying the orientation by switching energy from one active radiating element to another, e.g. for beam switching
• CPC Class Codes: H01Q 3/242 Circumferential scanning
• CPC Class Codes: H01Q 3/2605 Array of radiating elements provided with a feedback control over the element weights, e.g. adaptive arrays
• CPC Class Codes: H04B 7/18521 Systems of inter linked satellites, i.e. inter satellite service for optical links between satellites H04B10/118
• CPC Class Codes: H04B 7/18532 Arrangements for managing transmission, i.e. for transporting data or a signalling message
• CPC Class Codes: H04B 7/18541 for handover of resources
• CPC Class Codes: H04B 7/18552 using a telephonic control signal and a second ranging satellite determining absolute distances from a plurality of spaced points of known location G01S5/14
• CPC Class Codes: H04B 7/18584 Arrangements for data networking, i.e. for data packet routing, for congestion control data switching networks H04L12/00
• CPC Class Codes: H04B 7/18589 Arrangements for controlling an end to end session, i.e. for initialising, synchronising or terminating an end to end link
• CPC Class Codes: H04B 7/195 Non-synchronous stations
• CPC Class Codes: H04B 7/2041 Spot beam multiple access

Abstract

Earth-fixed cell beam management methods which may be employed to allocate beams generated by a constellation of low Earth orbit satellites (12) flying in orbits below geosynchronous altitudes are disclosed. These beams (19) are electronically steered so that they illuminate "Earth-fixed cells" (26) as opposed to "satellite-fixed cells." Beam steering apparatus using a spherical dielectric lens (106) is disclosed. In a system that employs satellite-fixed cells, the "footprint" of the beams propagated by a spacecraft defines the zone on the ground called a "cell" which is illuminated by the spacecraft. This satellite-fixed cell moves constantly as the spacecraft moves around the globe. In sharp contrast, an "Earth-fixed cell" (26) is a stationary region mapped onto the surface of the Earth (E) that has permanent fixed boundaries, just like a city or a state. Although the rapidly moving satellites (12) still shine their beams over the ground in rapidly moving footprints (16), the locations of the footprints at any given time do not determine the location of the unchanging Earth-fixed cells (26). The great advantage provided by using cells having boundaries that are fixed to an Earth-fixed grid (20) is realized when a subscriber being served by one satellite must switch to another beam in the same satellite or to a second satellite because the first is moving out of range below the local horizon. With satellite-fixed cells, this "hand-off" involves the assignment to the terminal of a new communication channel within the new beam or new satellite. This assignment process takes time and consumes processing capacity at both the terminal and the satellite. It is also subject to blocking, call interruption, and call dropping if there is not an idle communication channel in the next serving beam or satellite. The Earth-fixed cell method avoids these problems by allocating communication channels (frequency, code, and/or time slot) on an Earth-fixed cell basis rather than on a satellite-fixed cell basis. Regardless of which satellite/beam is currently serving a particular cell, the terminal maintains the same channel assignment, thus ameliorating the "hand-off" problem.

Claims

1. A method for allocating a plurality of beams (19) transmitted from and received at positions in Earth orbit for communicating with a plurality of portable (P), mobile (M) and fixed (F) terminals and gateways (G) comprising the steps of:

forming a plurality of footprints (16) using a plurality of electronically steered antenna elements (13a, 13b, 13c &

     140) which generate said plurality of beams (19);

said plurality of antenna elements (13a, 13b, 13c &

     140) being carried onboard a plurality of satellites (12) flying in orbits (11) below geosynchronous altitude;

one of said plurality of satellites (12) including a first serving satellite (12a) and a second satellite (12b) positioned next to said first serving satellite (12a);

said plurality of footprints (16) illuminating portions of an Earth-fixed grid (20) with said plurality of beams (19);

said plurality of beams (19) being capable of conveying a plurality of packets (Pk);

said Earth-fixed grid (20) defining a plurality of Earth-fixed supercells (24);

said plurality of Earth-fixed supercells (24) including a plurality of Earth-fixed cells (26);

said plurality of Earth-fixed cells (26) including a target Earth-fixed cell (26t);

scanning electronically, by using a sequence of individual antenna elements (13a, 13b, 13c &

     140), each beam (19) of said plurality of beams (19) to the centroid of an Earth-fixed cell (26), which said Earth-fixed cell (26) is nearest to a nominal non-scanned position of said beam (19);

addressing each said Earth-fixed cell (26) of said plurality of Earth-fixed cells (26) by shaping and focusing said beam (19) to illuminate said Earth-fixed cell (26), said illuminated Earth-fixed cell (26) being said target Earth-fixed cell (26t);

tracking a target Earth-fixed cell (26t) by using said sequence of individual antenna elements (13a, 13b, 13c &

     140) aboard said first serving satellite (12a) so that said plurality of beams (19) are maintained over said target Earth-fixed cell (26t) as long as one of said plurality of individual antenna elements (13a, 13b, 13c &

     140) aboard said first serving satellite (12a) is capable of serving said target Earth-fixed cell (26t);

measuring the distance from said first serving satellite (12a) which is currently serving said target Earth-fixed cell (26t) to the centroid of said target Earth-fixed cell (26t);

measuring the distance from said second satellite (12b) which is the next closest satellite to said target Earth-fixed cell (26t) compared to said first serving satellite (1 2a) to the centroid of said target Earth-fixed cell (26t); and

switching responsibility for providing said plurality of beams (19) to said target Earth-fixed cell (26t) from said first serving satellite (12a) to said second next satellite (12b) when the distance from said second next satellite (12b) to the centroid of said target Earth-fixed cell (26t) is less than the distance from said first serving satellite (12a) to the centroid of said target Earth-fixed cell (26t).

3. The method as claimed in claim 1 further including the step of:

communicating with said terminals (P, M, F) and gateways (G) in each of said plurality of target Earth-fixed cells (26t) with said packets (Pk) carried as signals on said plurality of beams (19);

each of said plurality of beams (19) operating at one of nine frequencies (F₁ -F₉), said nine frequencies (F₁ -F₉) being reused one-hundred percent for communications in each one of said plurality of Earth-fixed supercells (24).

4. The method as claimed in claim 1 in which the step of tracking a target Earth-fixed cell (26t) by using a sequence of individual antenna elements (13, 140) further includes the steps of:

providing a plurality of antenna elements (13,

     140) having a plurality of dielectric lenses(160), and having a plurality of feed elements (163,

     182) which are disposed at a surface of each of said dielectric lenses (160) at nominal beam center positions;

simultaneously receiving said plurality of beams (19) with at least one of said plurality of antenna elements (13,

     140);

simultaneously transmitting a plurality of said beams (19) with at least one of said plurality of said antenna elements (13,

     140);

simultaneously receiving and transmitting a plurality of beams (19) with at least one of said plurality of antenna elements (13,

     140);

each of said plurality of beams (19) having a footprint (142) on the surface of the Earth (E);

forming said plurality of beams (19) with each of said plurality of antenna elements (13,

     140) and continuously illuminating each said target Earth-fixed cell (26t) by focusing each of said plurality of beams (19) on each said target Earth-fixed cell (26t) with said dielectric lenses (160), as each of said plurality of beams (19) emerges from each of said plurality of feed elements (163,

     182); and

electronically shaping and steering each of said plurality of beams (19) to keep each of said plurality of target Earth-fixed cells (26t) within said footprint (142) of a corresponding one of said plurality of beams (19) as said satellite (12) progresses along its said orbit (11), by amplitude weighting a beam (19) emerging from an antenna feed element (163,

     182) disposed at said surface of said dielectric lens (160) at a nominal beam center position, and amplitude weighting each of a plurality of beams (19) emerging from antenna feed elements (163,

     182) at adjacent positions.

5. The method as claimed in claim 4 in which the step, of providing a plurality of antenna elements (13, 140) having a plurality of dielectric lenses (160), includes the step of

providing a plurality of antenna elements (13, 140) having a plurality of spherical Luneberg lenses.

6. The method as claimed in claim 4 in which the step, of providing a plurality of antenna elements (13, 140) having a plurality of dielectric lenses (160), includes the step of

providing a plurality of antenna elements (13, 140) having a plurality of spherical constant-k lenses.

7. The method as claimed in claim 4 in which the step, of providing a plurality of antenna elements (13, 140) having a plurality of dielectric lenses (160), includes the step of

providing a plurality of antenna elements (13, 140) having a plurality of hemispherical constant-k lenses with Schmidt correction at a radiating aperture.

2. An apparatus for communicating among a plurality of portable (P), mobile (M), and fixed (F) terminals and gateways (G) comprising:

a plurality of satellites (12) operating in low Earth orbit;

each of said plurality of satellites (12) having a plurality of electronically steered antennas (13,

     140);

said plurality of electronically steered antennas (13, 140a, b) being capable of generating a plurality of beams (19);

said plurality of satellites (12) flying in orbits (11) below geosynchronous altitude;

said plurality of electronically steered antennas (13) being capable of forming a plurality of footprints (16);

an Earth-fixed grid (20) mapped over the surface of the Earth (E);

said plurality of footprints (16) illuminating portions of said Earth-fixed grid (20) with said plurality of beams (19);

said plurality of beams (19) being capable of conveying a plurality of packets (Pk);

said Earth-fixed grid (20) defining a plurality of Earth-fixed supercells (24);

said plurality of Earth-fixed supercells (24) including a plurality of Earth-fixed cells (26);

said plurality of Earth-fixed cells (26) including a target Earth-fixed cell (26t);

each of said plurality of antennas (13, 140a, b) having a plurality of individual antenna elements (13a, 13b, 13c &

140a, b) for scanning electronically, in a sequence, each beam (19) of said plurality of beams (19) to the centroid of an Earth-fixed cell (26) which said Earth-fixed cell (26) is nearest to a nominal non-scanned position of said beam (19); and

said Earth-fixed grid (20), said Earth-fixed supercells (24) and said Earth-fixed cells (26) being used to allocate said plurality of beams (19) to provide communications service to said plurality of portable (P), mobile (M) and fixed (F) terminals and gateways (G).

8. The apparatus as claimed in claim 2 in which said plurality of electronically steered antennas (13, 140) includes a plurality of scanning beam antennas (140);

at least one of said scanning beam antennas (140) capable of simultaneously receiving a plurality of said beams (19);

at least one of said plurality of scanning beam antennas (140) capable of simultaneously transmitting a plurality of said beams (19);

at least one of said plurality of scanning beam antennas (140) capable of simultaneously receiving and transmitting a plurality of said beams (19);

each one of said scanning beam antennas (140) including a dielectric lens (160) and having a plurality of individual antenna feed elements (163,

     182) disposed at a surface of said dielectric lens (160) at nominal beam center positions;

each one of said plurality of beams (19) having a footprint (142) on the surface of the Earth (E) which is capable of overlaying one of a plurality of target Earth-fixed cells (26t), said plurality of target Earth-fixed cells (26t) being members of said plurality of Earth-fixed cells (26);

each of said plurality of scanning beam antennas (140) capable of forming said plurality of beams (19) and continuously illuminating each said target Earth-fixed cell (26t) by focusing each of said plurality of beams (19) on one said target Earth-fixed cell (26t) with said dielectric lens (160); and

each of said plurality of scanning beam antennas (140) capable of electronically shaping and steering each of said plurality of beams (19) by amplitude weighting each of said beams (19) emerging from each of said individual antenna feed elements (163,

     182) disposed on said dielectric lens (140) at a nominal beam center position and amplitude weighting each of said beams (19) emerging from each of said individual antenna feed elements (163,

     182) at adjacent positions, to keep each of said target Earth-fixed cells (26t) within said footprint (142) of each of a corresponding one of said beams (19) as said satellite (12) progresses along its said orbit (11).

9. The apparatus as claimed in claim 8 in which said dielectric lens 160 is a spherical Luneberg lens.

10. The apparatus as claimed in claim 8 in which said dielectric lens 160 is a spherical constant-k lens.

11. The apparatus as claimed in claim 8 in which said dielectric lens 160 is a hemispherical constant-k lens with a Schmidt correction at a radiating aperture.