Multibeam antenna, method and system of creating cells for a wireless communication network, whereby the multibeam antenna is situated on a high-altitude aeronautical vehicle

Abstract: A multi-beam antenna (220) for a wireless communication network, the antenna being held aloft by an aeronautical vehicle (210), projects: (1) a first antenna beam to create a first cell (241) upon a generally circular first terrestrial area below the multi-beam antenna and (2) a second antenna beam to create a second cell (242) upon a generally circular second terrestrial area below the multi-beam antenna, the first cell having a smaller radius than, and substantially concentric with, the second cell.

Description: This invention relates to multi-beam antennas for a wireless communication network, to methods of creating cells for a wireless communication network, and to wireless infrastructures for communicating with a plurality of mobile stations. The use of cellular mobile telecommunications has undergone substantial growth over the past few years and is projected to continue expanding as service is improved and new products and features are offered. To retain existing customers and entice others to adopt cellular telecommunications, however, services must be provided at a reasonable price. Therefore, the cost of providing cellular telecommunication services must be reduced. Conventional terrestrial-based cellular systems provide service to geographical areas divided into hexagonal cells 110 as shown in FIGURE 1. The number and size of these cells are selected by the service provider such that geographical coverage is optimized, cost is reduced, and capacity within the service area is maximized. Each cell 110 is equipped with transmitters, receivers, and control apparatus located at a cell site 120, which is typically located near the geographical center of the cell. Each cell site 120 within a particular service area is connected to a central office 130 that serves as a mobile telephone switching office (MTSO) and which controls mobile operation within the cells. The cell-sites 120 connect to the MTSO over data links 125. The MTSO switches calls to other mobile units and to the local telephone system. As a practical matter, cell boundaries are not precise. The conventional hexagonal cell shape was chosen because it provides a practical way of covering an area without the gaps and overlaps in coverage that would occur if circular cells were used. Although circular cells could be serviced by omni-directional antennas, directional antennas must be used to approximate the hexagonal shape. Because of the above, and other, limitations of conventional terrestrial-based cellular systems, researchers have begun to design wireless communications systems that use high-altitude aeronautical platforms (HAAP) to carry radio-relay transponders. A HAAP can take, for example, the form of an airship or a piloted, or pilotless, airplane circling over a geographical service area. One advantage of an airborne antenna platform is that it can service a much larger geographical area than conventional terrestrial-based cellular antenna systems.. Attempts to realize an operational HAAP have heretofore relied on geographical service areas divided into conventional adjacent hexagonal cells. The use of conventional cells, however, requires that the HAAP on-board antenna be capable of dynamically changing its radiation pattern as the aeronautical vehicle flies in a circle above the service area. This is because the relative position between each hexagonal cell and the HAAP is not constant and, thus, the antenna beam must be mechanically and/or electronically steerable, which adds cost and complexity to a cellular system employing HAAP-mounted antennas. Thus, from the wireless point of view, the most challenging technical issue in realizing such systems is the sophisticated, steerable multi-beam antennas required onboard the HAAP. Accordingly, what is needed in the art is a way of clustering cells that does not require steerable-beam antennas. US-A-5408237 discloses Earth-fixed cell beam management methods which may be employed to allocate beams generated by a constellation of low Earth orbit satellites flying in orbits below geosynchronous altitudes are disclosed. These beams are electronically steered so that they illuminate "Earth-fixed cells" as opposed to "satellite-fixed cells." An "Earth-fixed cell" is a stationary region mapped onto the surface of the Earth that has permanent fixed boundaries. Although the rapidly moving satellites still shine their beams over the ground in rapidly moving footprints, the locations of the footprints at any given time do not determine the location of the unchanging Earth-fixed cells. The Earth-fixed cell methods allocate 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. EP-A-0762254 discloses a satellite communication system including a satellite with an antenna that generates a moving beam pattern on the surface of the earth, the beam pattern comprising a plurality of sub-beams. An attitude correction signal for the satellite is determined by providing a reference transmitter at a known location on the earth and transmitting a signal from the reference transmitter into a sub-beam and transponding the signal to a ground station. The ground station determines a gain of the transponded signal and compares it to expected values to derive a correction signal indicative of an attitude error of the satellite. EP-A-0531090 discloses a re-use partition of cells in a mobile communication system including an outer cell and an inner cell in the outer cell. A base station includes a first beam tilt antenna for the outer cell and a second beam tilt antenna for the inner cell. Patent abstracts of Japan, vol. 007, no. 264 (E-212), 24.11.83, JP(A) 58146148 discloses using a wide antenna beam for the portion of a desired service area having less traffic, and a narrow antenna beam for the portion of the desired service area having more traffic. High-speed transmission is performed in the narrow beam, whereas low-speed transmission is performed in the wide beam. Patent abstracts of Japan, vol. 005, no. 137 (E-072), 16.6.1981, JP(A) 56072547 discloses a service area divided into concentric circles, wherein a different frequency of a communication signal from a base station antenna is assigned to each concentric circle. According to one aspect of this invention there is provided a multi-beam antenna as claimed in claim 1. According to another aspect of this invention there is provided a method as claimed in claim 5. According to a further aspect of this invention there is provided a wireless infrastructure as claimed in claim 8. The present invention provides a multi-beam antenna for a wireless communication network, a method of creating cells for a wireless communication network with a multi-beam antenna held aloft by an aeronautical vehicle, and a wireless infrastructure. The multi-beam antenna projects: (1) a first beam to define a first cell upon a generally circular first terrestrial area below the multi-beam antenna and (2) a second beam to define a second cell upon a generally circular second terrestrial area below the multi-beam antenna, the first cell having a smaller radius than, and substantially concentric with, the second cell. Any number of cells may be defined by projecting additional beams from the multi-beam antenna. The present invention therefore introduces a cell-clustering scheme wherein cells are concentrically arranged, one inside another. This is in contrast with the conventional cell-clustering scheme, wherein cells never completely surround one another. One of the advantages of the cell-clustering scheme of the present invention is that, should the multi-beam antenna begin to orbit horizontally above a centerpoint of the first cell at a generally-uniform radius (such as could occur if the aeronautical vehicle were an airplane), the location and size of the first and second cells remain independent of the orbital position of the multi-beam antenna. This eliminates the need to steer the beams and substantially diminishes the complexity of the multi-beam antenna as a whole. In one embodiment of the present invention, the multi-beam antenna is held aloft substantially directly above a centerpoint of the first cell. In an alternate embodiment, the multi-beam antenna orbits above a centerpoint of the first cell at a substantially constant orbital radius therefrom. A helicopter or stationary airship can hold the multi-beam antenna aloft in a single location, assuming that atmospheric conditions do not prevent the vehicle from maintaining a relatively stable position. Although an airplane must stay in motion to stay aloft, as long as the airplane assumes a generally horizontal, circular orbit above the centerpoint of the cell cluster, the beams emanating from the multi-beam antenna do not require steering. In the present invention, the multi-beam antenna projects oblique conical beams to define concentric cells, respectively, an eccentricity of the oblique conical beams being a function of an orbital radius of the multi-beam antenna from a centerpoint of the concentric cells and a relative altitude of the multi-beam antenna. If the multi-beam antenna is directly above the centerpoint, the conical beams are right cones. As the multi-beam antenna moves from the centerpoint in its orbit, the conical beams preferably become more oblique, allowing the projection of the beams on the ground below to remain generally circular in shape. In one embodiment of the present invention, a radius of a second cell (r 2 ) is related to a radius of a first cell (r 1 ) by the equation: r 2 = r 1 2 . In this configuration, the area uniquely covered by the second cell (that portion of the second terrestrial area that does not intersect the first terrestrial area) is made equal to the area covered by the first cell (the entirety of the first terrestrial area). This produces cells of substantially equal area. Assuming that mobile stations are more or less evenly distributed, wireless traffic is therefore more or less evenly divided between the first and second cells. In one embodiment of the present invention, in addition to the multi-beam antenna, there is an antenna that provides feeder-band communication with a ground station of the wireless communication network, the ground station located proximate a centerpoint of the concentric cells. Locating the ground station at the centerpoint substantially eliminates Doppler effects that may occur if the multi-beam antenna is orbiting the centerpoint. The broad scope of the present invention does not limit the ground station positionally. Conventionally, the "feeder-band" is defined as including the Ku-band (12 to 18 GHz). Other frequency bands are certainly within the broad scope of the present invention. In one embodiment of the present invention, the first and second beams are user-band beams. Conventionally, the "user-band" is defined as the L-band (2 to 4 GHz) and the less than 1 GHZ band (frequencies conventionally employed in cellular telephones or personal communication systems ("PCS")). Other frequency bands are certainly within the broad scope of the present invention. In one embodiment of the present invention, the aeronautical vehicle is selected from the group consisting of: (1) a dirigible, (2) an airplane, (3) an airship and (4) a helicopter. The multi-beam antenna may also be held aloft by a satellite. As new technologies emerge for holding multi-beam antennas aloft, those of skill in the art will perceive the applicability of those technologies to the broad scope of the present invention. The foregoing has outlined, rather broadly, preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the scope of the invention as claimed in its broadest form. Brief Description of the Drawings For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: FIGURE 1 illustrates a terrestrial-based cellular communications network employing conventional hexagonal-shaped cells; FIGURE 2 illustrates a cell-clustering arrangement and corresponding antenna patterns for a wireless communication network that employs a multi-beam antenna held aloft by an aeronautical vehicle; and FIGURE 3 illustrates a system diagram of a wireless infrastructure employing a plurality of high-altitude aeronautical antenna platforms. Detailed Description Referring initially to FIGURE 1, illustrated is a terrestrial-based cellular communications network 100 employing conventional hexagonal-shaped cells 110. Each cell 110 is equipped with an antenna array located at a cell site 120, which is typically located near the geographical center of the cell. Each cell site 120 within a particular service area is connected to a central office 130 that serves as a mobile telephone switching office (MTSO) and which controls the operation of mobile units 140 within the cells 110. The cell-sites 120 connect to the MTSO over data links 125. The MTSO switches calls to other mobile units 140 and to the local telephone system (not shown). Turning now to FIGURE 2, illustrated is a cell-clustering arrangement and corresponding antenna patterns for a wireless communication network that employs a multi-beam antenna held aloft by an aeronautical vehicle. The present invention overcomes the difficulty of using conventional hexagonal cell shapes with non-terrestrial cellular communications systems. The use of conventional cells with an antenna held aloft by an aeronautical vehicle requires that the antenna be capable of dynamically changing its radiation pattern as the vehicle flies above the service area. This is because the relative position between each cell and the vehicle is not constant and, thus, the antenna beam must be mechanically and/or electronically steerable, which adds cost and complexity to a cellular system. Thus, from the wireless point of view, the most challenging technical issue in realizing such non-terrestrial systems is the sophisticated and steerable multi-beam antennas required. The present invention discloses a multi-beam antenna 220 mounted to a high-altitude aeronautical platform (HAAP) 210. The multi-beam antenna 220 projects: (1) a first antenna beam 231 to create a first cell 241 upon a generally circular first terrestrial area below the multi-beam antenna and (2) a second antenna beam 232 to create a second cell 242 upon a generally circular second terrestrial area below the multi-beam antenna. The first cell 241 has a smaller radius than, and is substantially concentric with, the second cell 242. Additionally, the first (innermost) cell 241, although illustrated as having a circular shape, may be considered as a ring having an inner radius equal to zero. Those of skill in the art will recognize that, to avoid gaps in coverage, the outer radius of each cell should be substantially coextensive with the inner radius of the adjacent outer cell. The multi-beam antenna 220 may further project a third antenna beam 233 to create a third cell 243 upon a generally circular third terrestrial area below the multi-beam antenna. Although only three cells 241, 242, 243 are illustrated in FIGURE 1, those of skill in the art will recognize that the principles of the present invention may be extended to any number of concentric cells. Those of skill in the art will recognize that if the outer radius of the second cell (r 2 ) is related to the outer radius of the first cell (r 1 ) by the equation: r 2 = r 1 2 , the area uniquely covered by the second cell (that portion of the second terrestrial area that does not intersect the first terrestrial area) will be equal to the area covered by the first cell (the entirety of the first terrestrial area). This relationship may be extended to any number of cells by satisfying the relationship r n = r 1 √n (where r 1 is equal to the radius of the innermost (circular) cell) for each n th (ring-shaped) cell, whereby all cells will have the same area. Assuming that mobile stations are geographically evenly distributed, wireless traffic will be more or less evenly divided between the first and second cells. In one embodiment of the present invention, the multi-beam antenna is held aloft substantially directly above the centerpoint 260 of the first cell 241. It should be recognized that centerpoint 260 of the first cell 241 is also the centerpoint for all other circular cells concentric with the first cell 241. In an alternate embodiment, the multi-beam antenna orbits above centerpoint 260 at a substantially constant orbital radius therefrom. A dirigible, helicopter or stationary airship can hold the multi-beam antenna 220 aloft in a single location, assuming that atmospheric conditions do not prevent the vehicle from maintaining a relatively stable position. Although an airplane must stay in motion to stay aloft, as long as the airplane assumes a generally horizontal, circular orbit about the centerpoint 260 of the cell cluster, the beams 231, 232, 233 emanating from the multi-beam antenna 220 do not require steering, Those of skill in the art will recognize that if the HAAP 210 is held stationary above the centerpoint 260 of the cell cluster, the antenna beams 231, 232, 233 form right cones. If the HAAP 210 is orbiting about the centerpoint 260, however, the antenna beams 231, 232, 233 of the multi-beam antenna 220 must form oblique conical beams in order to define substantially circular cells where the antenna beams 231, 232, 233 intersect the earth's surface. The required eccentricity of the oblique conical beams will be a function of the orbital radius of the multi-beam antenna 220 from the centerpoint 260 of the cell cluster and the relative altitude of the multi-beam antenna. As the multi-beam antenna 220 moves away from the centerpoint 260 in its orbit, the conical beams preferably become more oblique, allowing the projection of the beams on the ground below to remain generally circular in shape. The multi-beam antenna 220 may also include an antenna that provides feeder-band communication with a ground station 250 of the wireless communications network. The "feeder-band" conventionally used in wireless communications systems is defined as including the Ku-band (12 to 18 GHz). Other frequency bands are certainly within the broad scope of the present invention. Those of skill in the art will recognize that the ground station 250 is preferably located proximate the centerpoint 260 of the cell cluster. Whereas a HAAP 210 orbiting about a ground station 250 located at the centerpoint 260 maintains a relatively fixed distance from the ground station 250, Doppler effects that would occur if the multi-beam antenna 220 were continuously moving toward or away from the ground station 250 are substantially eliminated. Doppler compensation is required, however, if the ground station 250 is not located at substantially the centerpoint 260. One ground station 250, however, may support more than one HAAP 210, in which case Doppler compensation will be required for at least one HAAP 210. The ground station 250 provides an interface other mobile users, as well as an interface to the public switched telephone network (not shown). The first and second antenna beams 231, 232 are preferably user-band beams that provide communications to mobile units (not shown). Conventionally, the "user-band" is defined as the L-band (2 to 4 GHz) and the less than 1 GHZ band (frequencies conventionally employed in cellular telephones or personal communication systems ("PCS")). Those of skill in the art will recognize that other frequency bands are certainly within the broad scope of the present invention. Turning now to FIGURE 3, illustrated is a system diagram of a wireless infrastructure employing a plurality of high-altitude aeronautical antenna platforms. The system includes one or more HAAP/multi-beam antennas 320 that provide wireless communications with mobile units 310 as described supra . Each HAAP/multi-beam antenna 320 also receives and sends wireless communications from and to a ground station 350. The ground stations 350 are connected to the public switched telephone network (PSTN), thus providing for communications between mobile units 310 and traditional wired communications devices (not shown). As noted previously, one ground station 350 may support more than one HAAP/multi-beam antenna 320; although if orbiting vehicles are used, Doppler correction may be required. Those of skill in the art will also recognize that each HAAP/multi-beam antenna 320 may communicate with more than one ground station 350. The ability of a HAAP/multi-beam antenna 320 to communicate with more than one ground station 350 would allow mobile-to-mobile communications, between different HAAP service areas, without the need to use the public switched telephone network. Although the present invention has been described in detail, those skilled in the art should understand that they can make various changes, substitutions and alterations herein without departing from the scope of the invention as claimed in its broadest form.

Claims: A multi-beam antenna (220) for a wireless communication network, said multi-beam antenna (220) being configured to be held aloft by an aeronautical vehicle, and being adapted to simultaneously project: a first antenna beam (231) that creates a first cell (241) upon a generally circular first terrestrial area below said multi-beam antenna (220); and a second antenna beam (232) that creates a second cell (242) upon a generally circular second terrestrial area below said multi-beam antenna (220), said first cell (241) having a smaller radius than, and being substantially concentric with, said second cell (242), said first and second antenna beams (231, 232) substantially occupying said generally circular first and second terrestrial areas, respectively; wherein said first and second antenna beams (231, 232) form oblique conical beams to project said first and second cells (241, 242), respectively, an eccentricity of said oblique conical beams being a function of an orbital radius of said multi-beam antenna (220) from a centerpoint of said first cell (241) and a relative altitude of said multi-beam antenna (220), whereby the orbital radius is the horizontal distance between the multi-beam antenna and the centerpoint of said first cell and the relative altitude is the vertical distance between the multi-beam antenna and the surface of the earth. An antenna as claimed in claim 1 wherein a radius (r 2 ) of said second cell (242) is related to a radius (r 1 ) of said first cell (241) by the equation: r 2 = r 1 2 . An antenna as claimed in claim 1 comprising an antenna that provides Ku-band communication with a ground station (250) of said wireless communication network, said ground station (250) being located proximate a centerpoint of said first cell (241). An antenna as claimed in claim 1 wherein said first and second antenna beams (231, 232) operate at frequencies ranging between about 2 GHz and about 4 GHz. A method of creating cells for a wireless communication network with a multi-beam antenna (220) configured to be held aloft by an aeronautical vehicle, said method comprising the steps of: holding said multi-beam antenna (220) aloft; projecting a first oblique conical beam (231) to create a first cell (241) upon a generally circular first terrestrial area below said multi-beam antenna (220); and projecting a second oblique conical beam (232) simultaneously with said first oblique conical beam (231) to create a second cell (242) upon a generally circular second terrestrial area below said multi-beam antenna (220), said first cell (241) having a smaller radius than, and being substantially concentric with, said second cell (242), said first and second antenna beams (231, 232) substantially occupying said generally circular first and second terrestrial areas, respectively; an eccentricity of said oblique conical beams (231, 232) being a function of an orbital radius of said multi-beam antenna (220) from a centerpoint of said first cell (241) and a relative altitude of said multi-beam antenna (220), whereby the orbital radius is the horizontal distance between the multi-beam antenna and the centerpoint of said first cell and the relative altitude is the vertical distance between the multi-beam antenna and the surface of the earth. A method as claimed in claim 5 wherein said step of holding comprises the step of orbiting said multi-beam antenna (220) above a centerpoint of said first cell (241) at a substantially constant orbital radius therefrom. A method as claimed in claim 5 wherein a radius (r 2 ) of said second cell (242) is related to a radius (r 1 ) of said first cell (241) by the equation: r 2 = r 1 2 . A wireless infrastructure for communicating with a plurality of mobile stations (310), comprising: a plurality of ground stations (350) coupled together for communication therebetween; and a plurality of high-altitude aeronautical platforms (HAAPs) (320), each of said plurality of HAAPs (320) comprising: an aeronautical vehicle; a feeder-band antenna for providing communication with at least one of said plurality of ground stations (350); and a multi-beam user-band antenna (320), adapted to simultaneously project: a first antenna beam (231) to create a first cell (241) upon a generally circular first terrestrial area below said multi-beam antenna (320) and to communicate with ones of said plurality of mobile stations (310), and a second antenna beam (232) to create a second cell (242) upon a generally circular second terrestrial area below said multi-beam antenna (320) and to communicate with others of said plurality of mobile stations (310), said first cell (241) having a smaller radius than, and being substantially concentric with, said second cell (242), said first and second antenna beams (231, 232) substantially occupying said generally circular first and second terrestrial areas, respectively; wherein said first and second antenna beams (231, 232) form oblique conical beams to project said first and second cells (241, 242), respectively, an eccentricity of said oblique conical beams (231, 232) being a function of an orbital radius of said multi-beam antenna (320) from a centerpoint of said first cell (241) and a relative altitude of said multi-beam antenna (320), whereby the orbital radius is the horizontal distance between the multi-beam antenna and the centerpoint of said first cell and the relative altitude is the vertical distance between the multi-beam antenna and the surface of the earth. An infrastructure as claimed in claim 8 wherein said multi-beam antenna (320) is held aloft substantially directly above a centerpoint of said first cell (241). An infrastructure as claimed in claim 8 wherein said multi-beam antenna (320) orbits above a centerpoint of said first cell (241) at a substantially constant orbital radius therefrom.

Inventors: DJUKNIC GORAN M, HOU DIANA YUH-LIN, OKUNEV YURIY B, DJUKNIC, GORAN M., HOU, DIANA YUH-LIN, OKUNEV, YURIY, B.
Applicants: LUCENT TECHNOLOGIES INC, LUCENT TECHNOLOGIES INC.
Application year: 1997
Main classification: H04B7
IPC codes: H04B7, H01Q25, H04Q7