Satellite communications system employing frequency reuse

• US 4,879,711 A
• Filed: 10/14/1987
• Issued: 11/07/1989
• Est. Priority Date: 08/14/1986
• Status: Expired due to Term

• Current Assignee: Hughes Electronics Corporation (Rtx Corporation)
• Original Assignee: Hughes Aircraft Company (Rtx Corporation)
• Inventors: Rosen, Harold A.
• Primary Examiner(s): NOT, DEFINED
• Assistant Examiner(s): Marcelo, Melvin
• Application Number:
  US07/108,831
• Time in Patent Office: 755 Days
• Field of Search: 370/75, 370/104, 370/50, 455/12, 455/13, 455/33
• US Class Current: 370/325
• CPC Class Codes: H01Q 25/00 Antennas or antenna systems providing at least two radiating patterns arrangements for changing or varying the orientation or the shape of the directional pattern H01Q3/00
• CPC Class Codes: H04B 7/18515 Transmission equipment in satellites or space-based relays
• CPC Class Codes: H04B 7/2041 Spot beam multiple access
• CPC Class Codes: H04B 7/2045 SS-FDMA, FDMA satellite switching
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

A satellite communications system employs separate subsystems for broadcast and point-to-point two-way communications using the same assigned frequency band and employs an antenna system which uses a common reflector (12). The point-to-point subsystem achieves increased communication capacity through the reuse of the assigned frequency band over multiple, contiguous zones (32, 34, 36, 38) covering the area of the earth to be serviced. Small aperture terminals in the zones are serviced by a plurality of high-gain downlink fan beams (29) steered in the east-west direction by frequency address. A special beam-forming network (98) provides in conjunction with an array antenna (20) the multiple zone frequency address function. The satellite (10) employs a filter interconnection matrix (90) for connecting earth terminals in different zones to permit multiple reuse of the entire band of assigned frequencies. A single pool of solid-state transmitters allows rain-disadvantaged users to be assigned higher than normal power at minimum cost and geographically disperses the transmitter intermodulation products. In an alternate embodiment, the satellite (200) employs direct radiating array antennas (202, 204) for reception and transmission. The system (200 ) utilizes hybrid-coupled dual amplifiers (251) to reduce amplifier production costs. In another embodiment, both point-to-point and broadcast services are available on a single polarization by allocating one-half of the frequency spectrum to each service and by using separate direct radiating arrays from horizontal and vertical polarization for both reception (235, 236) and transmission (237, 238). The frequency spectrum is reused in each of the contiguous receive zones (220, 222, 224, 226) and the transmit zones (228, 230, 232, 234) because sufficient spatial isolation is achieved by subdividing the receive zones in two halves (220a, 220b, 222a, 222b, 224a, 224b, 226a, 226b), and by using one-half of the frequency spectrum in each subdivided zone.

Claims

1. A method of communicatively interconnecting any of a plurality of terminals within an area on the earth using an earth-orbiting communications satellite, comprising the steps of:

(A) forming a first plurality of groups of radio frequency beams respectively between each of a plurality of essentially contiguous zones covering said area on the earth and said satellite, the beams in said groups thereof carrying communications signals over the same first preselected range of frequencies, such that said first preselected range of frequencies is reused by the beams for all of said zones;

(B) separating each group of said radio frequency beams into first and second sets thereof respectively carrying communications signals over first and second sets of frequencies within said first preselected range of frequencies, and spatially distributing said first preselected range of frequencies over each of the zones as a function of frequency such that the frequencies of one set of said beams in one zone is spatially separated from the frequencies of one set of said beams in a zone substantially contiguous to said one zone;

(C) alternately transmitting the first and second sets of said beams between said zones and said satellite by simultaneously transmitting the beams in the first set thereof for all the zones and then simultaneously transmitting the beams in the second set thereof for all the zones.

2. The method of claim 1, wherein step (C) is performed by transmitting the first and second sets of beams from each of said zones to said satellite.

3. The method of claim 2, including the steps of:

(D) receiving said first and second sets of beams at said satellite; and

(E) transmitting a second plurality of groups of radio frequency beams respectively from said satellite to said zones, the beams in each group of said second plurality thereof carrying communications signals over the same second preselected range of frequencies, whereby said second preselected range of frequencies is reused by all of the groups of beams in said second plurality thereof.

4. The method of claim 3, wherein step (E) is performed by spatially distributing the beam in each of said second plurality of groups thereof across the corresponding zone as a function of said second preselected range of frequencies.

5. A method of communicatively interconnecting a plurality of terminals within an area on the earth using an earth orbiting communications satellite, comprising the steps of:

(A) dividing said area into a plurality of essentially contiguous zones;

(B) dividing each zone into at least first and second contiguous sections;

(C) alternately transmitting at least first and second radio frequency beams respectively between said first and second sections for each of said zones and said satellite, said first and second beams respectively carrying communications signals over first and second different sets of frequencies defining a first preselected range of frequencies, wherein said first preselected range of frequencies is reused by the first and second beams for all of said zones, and

(D) spatially distributing the frequencies in the beams respectively transmitted to the first and second sections of each of the zones as a function of frequency.

6. The method of claim 5, including the step of forming said first and second beams for each of said zones such that said first and second beam for each of said zones collectively define a rectangularly shaped area of communications service on the earth which corresponds to the associated zone.

7. The method of claim 5, wherein the sets of frequencies of said contiguous two sections are different from each other, whereby to avoid communications interference between said contiguous two sections.

8. The method of claim 5, including the steps of:

(D) receiving said first and second beams at said satellite; and

(E) transmitting to each of said zones a plurality of downlink radio beams, each plurality of said downlink beams carrying communications signals over the same, second preselected range of frequencies, whereby said second preselected range of frequencies is reused by the downlink beams for all of said zones.

9. The method of claim 8, wherein step (E) includes the step of spatially disbursing the downlink beams in each plurality thereof as a function of frequency.

10. A satellite communications system for communicatively interconnecting a plurality of earth terminals covering an area on the earth, comprising:

a satellite disposed in orbit above the earth;

first means for forming a plurality of uplink radio frequency beams between said satellite and each of a plurality of respectively associated contiguous zones covering said area, said zones being divided into at least two essentially contiguous sections, each plurality of said uplink beams carrying communications signals destined to be received by downlink terminal sites in said zones, the uplink beams for each zone being arranged in first and second sets of said beams respectively originating from said two sections in the zone and carrying communication signals over first and second sets of frequencies, said first and second set of frequencies defining a first range of frequencies and being respectively spatially distributed over said two sections as a function of frequency, the uplink beams for all of said zones using said first range of frequencies;

second means at said satellite for alternately receiving in time said first and second sets of beams to prevent interference between signals originating from adjacent ones of said sections; and

third means at said satellite coupled with said second means for forming a plurality of groups of downlink radio frequency beams between said satellite and said zones, each of said groups of downlink beams carrying communication signals destined to be received at downlink terminal sites in one of said zones.

11. The system of claim 10, wherein each of said groups of downlink beams covers one of said zones with each group carrying a plurality of signals over a second range of frequencies such that the same range of frequencies are used by all the groups of downlink beams.

12. The system of claim 10, wherein said second means includes a receiving antenna array, a receiver and a two position switch for successively switching said receiver to alternately receive said first and second sets of frequencies respectively.

13. The system of claim 12, wherein said third means includes a transmitting antenna array for transmitting said downlink beams, said receiving antenna array and said transmitting antenna array each being defined by a two dimensional array of direct radiating elements.