Communication system having frequency reuse in non-blocking manner

The present application is related to U.S. Patent Application Ser. No. 09/584,374 entitled “Communication System Supporting Multiple Service Providers” filed simultaneously herewith and incorporated by reference hereby.

The present invention relates generally to communications systems, and more particularly, to a system allowing frequency reuse with existing systems in a non-blocking manner.

In this communication age, content providers are increasingly investigating ways in which to provide more content to users as well as interfacing with users.

Communication satellites have become commonplace for use in many types of communication services, e.g., data transfer, voice communications, television spot beam coverage, and other data transfer applications. As such, satellites transmit and receive large amounts of signals used in either a “bent pipe” or “spot array” configuration to transmit signals to desired geographic locations on the earth.

Because the frequency of resources are scarce for over-the-air transmission, various encoding schemes are used to provide a greater number of communication signals within an allocated communication band spectrum. Such encoding schemes include code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), or combination of these schemes. Further, to prevent interference the schemes may operate at various frequencies.

There is a continual need to provide new systems. However, if no spectrum is available typically potential system operators must forgo a pursuing a system. Typically, the same spectrum can not be assigned to different systems because of the potential for interference of the communications signals.

It would therefore be desirable to provide a system that allows reuse of frequency spectrums allocated to other systems in a non-blocking manner.

It is therefore one object of the invention to provide an improved communications system that allows frequency reuse in a manner which prevents interference with existing systems.

In one aspect of the invention, a method for operating a communication system comprises the steps of:

defining a service area having a blocking area therein, said blocking area having a separation angle between a first position of the satellite and a second position of the stratospheric platform less than a predetermined angle;

generating a first beam using a first frequency directed at the service area with the satellite; and

generating a second beam using the first frequency directed at the service area outside the blocking area from the stratospheric platform.

In a further aspect of the invention, a communications system includes a high altitude communication device that communicates with a plurality of user terminals and a gateway station. The gateway station couples the users to terrestrial networks and other users. The high altitude communication device has a controller that generates a second beam having the first frequency to a service area. The stratospheric platform does not generate the second beam within a blocking area. User terminals within the service area and outside the blocking area are configured to receive the first beam and the second beam.

One advantage of the invention is that the user terminals for existing systems may be reused. Another advantage of the system is that several users platforms reusing the as frequency spectrum may be employed within the system.

Other objects and features of the present invention will become apparent when viewed in light of the detailed description of the preferred embodiment when taken in conjunction with the attached drawings and appended claims.

FIG. 1 is a high level system diagram relative of a preferred embodiment in the invention to the Earth of a preferred embodiment in the invention.

FIG. 2 is a plot illustrating various angles of the satellite systems according to FIG. 1 .

FIG. 3 is a system diagram of a preferred embodiment in the invention.

FIGS. 4 and 4A are plots illustrating two elevation angles between a first terminal and a second terminal

FIG. 5 is a rectangular map of the Los Angeles area illustrating a service area and a plurality of blocking areas forming a band.

FIG. 6 is a plot of the Los Angeles area having blocking areas corresponding to known geostationary satellites.

FIG. 7 is a plot of the Los Angeles area illustrating blocking areas of several geostationary satellites.

FIG. 8 is a plot of the New York area illustrating blocking areas with known geostationary satellites.

In the following figures the same reference numerals are used to identify the same components in the various views.

The present invention is applicable to many communications systems including various mobile, fixed, point-to-point broadcast and other types of communications.

Referring now to FIG. 1, the present invention is a communications system 10 that employs a stratospheric platform 12 positioned above Earth 14 . Stratospheric platform 12 communicates with a user 16 positioned on Earth 14 . A geosynchronous satellite 18 having a geosynchronous orbit 20 is also illustrated. The geosynchronous orbit 20 allows the geosynchronous satellite 18 to maintain a relatively fixed position above a particular point on the Earth. Although only one stratospheric platform 12 and one geosynchronous orbit satellite 18 are illustrated, the present invention may include several of each.

As illustrated, the line of sight 22 of stratospheric platform 12 has a significantly different elevation angle than line-of-sight 24 . As will be illustrated below, the line-of-sight corresponds to different elevation angles relative to user 16 . The difference in line-of-sights 22 , 24 allows frequency reuse between geosynchronous satellite 18 and stratospheric platform 12 .

Stratospheric platform 12 may comprise one of many types of proposed stratosphere based devices such as unmanned plane, balloons, dirigibles or the like. Stratospheric platform 12 preferably may also comprise a stratosphere-based platform such as those under development by AeroVironment. Helios is one such project being developed by AeroVironment. The Helios stratospheric platform is an unmanned vehicle that can fly for several months at an altitude of about 60,000 feet above the Earth. Helios is a solar powered electric plane that is modular in design and may be configured to carry a variety of payloads. Stratospheric platforms also deploy relatively rapidly compared to satellites and thus, if the need increases, the system capability may be increased or modified.

Referring now to FIG. 2, stratospheric platform 12 is illustrated having an elevation angle E 1 with respect to the user 16 . Also, the azimuth angle A 1 of stratospheric platform 12 is also illustrated. Azimuth angle A 1 is the angle from north. Although different, the azimuth angle and elevation angle for a satellite 18 is equally applicable. Of course, the elevation angle and azimuth angle for stratospheric platform 12 will vary depending on its location that may vary depending on the stratospheric platform 12 . Of course, the height of the stratospheric platform must also be taken in consideration.

Referring now to FIG. 3, communications system 10 having a plurality of platforms 12 A, 12 B and 12 C is used to cover a predetermined service area 26 on the Earth's surface. Although three are used for illustrative purposes, only one is required. A plurality of user terminals 28 are used to illustrate mobile users and fixed users respectively. Mobile user terminals 28 M may comprise but are not limited to automotive applications, personal digital assistant applications, and cellular phone applications. Fixed user terminals 28 F may, for example, comprise business-based or home-based communications systems. Each user terminal 28 F, 28 M may receive a signal with a predetermined signal strength or receive an antenna radiation spot in a spot beam pattern that is available from and provided by stratospheric platform 12 .

Communications system 10 further includes a gateway station 30 that is coupled to terrestrial networks 32 and a device operations center 34 . Both gateway station 30 and device operations center 34 are in communication with platforms 12 . Gateway station 30 provides a link between user terminals 28 F, 28 M and terrestrial networks 32 through stratospheric platform 12 .

Device operations center 34 provides command and control functions to platforms 12 A- 12 C. Although illustrated as two separate units, gateway station 30 and device operations center 34 may be combined into the same physical location.

The platforms 12 A- 12 C are used as a communications node for gateway station 30 and user terminals 28 M and 28 F, each of which have antennas that are pointed in the direction of the platform. The gateway antenna 30 A of gateway station 30 and user terminal antennas 28 A has a beam width wide enough to maintain communication links with platform 12 throughout the flight path. The antennas 28 A, 30 A allow for large data throughput.

Platforms 12 A-C each have a controller 36 that is used to control communications with the user terminals 28 F, 28 M. In the present invention, the controller 36 is used to generate a plurality of beams as is discussed below. The frequency of the beams may be within the spectrum of a geostationary satellite. Various numbers of users may communicate within a beam.

Controller 36 may be a secondary payload for the platforms. That is, to reduce system expense, the controllers 36 may be secondary to a primary controller 38 for another type of system already carried on the platform. The selective size and weight of controller 36 relative to controller 38 may be kept small to reduce the burden on platform 12 .

Referring now to FIG. 4A, an elevation plot illustrates user terminal 28 having an elevation angle EL 1 with respect to a stratospheric platform at a position P 1 .

Referring now to FIG. 4, the elevation angle EL 2 between a satellite 18 having a position P 2 is illustrated. If FIGS. 4 and 4A are superimposed, a separation angle between points P 1 and P 2 with the user at the vertex will be formed. The separation angle is preferably above 4 degrees and preferably greater than 7 degrees. By providing the separation angle of at least a predetermined separation angle, the frequencies between the platform 12 and satellite 18 may be reused. By providing the separation angle greater than a predetermined angle, no interference will be formed between the transmitting and receiving beams of the respective satellite and stratospheric platform.

Of course, the azimuth angle AZ 1 and the azimuth angle AZ 2 also should be factored into the separation angle. That is, the separation angle is a function of both the azimuth angles AZ 1 , AZ 2 and the elevation angles EL 1 and EL 2 .

Referring now to FIG. 5, a blocking area 50 is defined over service area 26 . Blocking area 50 corresponds to an area where the separation angle between the satellite and the stratospheric platform is below a predetermined value. In this case, the blocking area forms a continuous band. In this case, the area between the satellite and the stratospheric platform is greater than 7 degrees in the service area. Within the blocking area the separation angle is less than 7 degrees. Thus, the stratospheric platform does not transmit beams into the service area.

Referring now to FIG. 6, a plot of a service area 26 over the Los Angeles area is illustrated having four blocking areas 50 A, 50 B, 50 C, and 50 D. Blocking areas 50 A, 50 B, 50 C, and 50 D correspond to areas in which the separation angle between beams from a stratospheric platform 12 and beams from satellites located at geostationary locations West 91, West 100, West 109, and West 118, respectively.

Referring FIG. 7, a plot of the Los Angeles area illustrating the position of stratospheric platform 12 with respect to service area 26 is illustrated. A plurality of block areas 50 E- 50 L are illustrated. Blocking areas 50 E- 50 L correspond to direct broadcasting satellites in geostationary orbit. The blocking areas correspond to satellites located at 61.5 West, 101 West, 110 West, 119 West, 148 West, 157 West, 166 West, and 175 West, respectively.

Referring now to FIG. 8, blocking areas 50 M, 50 N, 50 P, and 50 Q, are positioned over a service area 26 of the New York area. The blocking areas 50 M, 50 N, 50 P, 50 Q correspond respectively to satellites located in geostationary orbit located at 61.5 West, 101 West, 110 West, and 119 West.

In operation, a user located within the service area 26 but outside the blocking area 50 M will receive signals from both satellite 18 and stratospheric platform 12 . For user terminals located within blocking area 50 , the user terminals therein will receive signals only from one of either the satellite 18 or stratospheric platform 12 . In actuality, it is more likely that the satellite 18 will have priority over stratospheric platform 12 . Thus, users within the blocking area 50 will receive signals only from satellite 18 . The separation angle that is used to define the blocking area may vary. However, it is preferred that the separation angle between the position of the stratospheric platform and the satellite be at least 4 degrees due to limitations in communications circuitry.

While particular embodiments of the invention have been shown and described, numerous variations alternate embodiments will occur to those skilled in the art. Accordingly, it is intended that the invention be limited only in terms of the appended claims.