Communication receiver for receiving satellite broadcasts

• US 5,797,082 A
• Filed: 01/09/1997
• Issued: 08/18/1998
• Est. Priority Date: 06/17/1994
• Status: Expired due to Term

• Current Assignee: Datasec Corporation
• Original Assignee: Terrastar, Inc.
• Inventors: Lusignan, Bruce B.
• Primary Examiner(s): Powell, Mark R.
• Assistant Examiner(s): Miller, John W.
• Application Number:
  US08/781,161
• Time in Patent Office: 586 Days
• Field of Search: 455/3.2, 455/269, 455/272, 455/110, 455/130, 455/131, 343/781 R, 343/781 P, 343/782, 343/840, 343/DIG. 2, 343/913, 343/914, 375/268, 375/269, 375/271, 375/272, 375/274, 375/322, 375/334, 375/336
• US Class Current: 725/70
• CPC Class Codes: H01Q 13/02 Waveguide horns
• CPC Class Codes: H01Q 19/12 wherein the surfaces are concave H01Q19/18 takes precedence
• CPC Class Codes: H01Q 19/13 the primary radiating source being a single radiating element, e.g. a dipole, a slot, a waveguide termination H01Q19/15 takes precedence
• CPC Class Codes: H01Q 19/132 Horn reflector antennas; Off-set feeding
• CPC Class Codes: H01Q 19/17 the primary radiating source comprising two or more radiating elements H01Q19/15, H01Q25/00 take precedence
• CPC Class Codes: H01Q 21/24 Combinations of antenna units polarised in different directions for transmitting or receiving circularly and elliptically polarised waves or waves linearly polarised in any direction circularly polarised patch antennas H01Q9/0428; circularly polarised horns H01Q13/0241; cross-polarised horns H01Q13/0258; polarisation converters H01Q15/242; cross-polarised rear feeds H01Q19/136; crossed polarisation dual antenna H01Q25/001
• CPC Class Codes: H01Q 21/28 Combinations of substantially independent non-interacting antenna units or systems multiple beam H01Q25/00
• 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: H01Q 3/26 varying the relative phase or relative amplitude of energisation between two or more active radiating elements; varying the distribution of energy across a radiating aperture H01Q3/12, H01Q3/22, H01Q3/24 take precedence
• CPC Class Codes: H04B 7/18517 Transmission equipment in earth stations
• CPC Class Codes: H04B 7/1858 Arrangements for data transmission on the physical system, i.e. for data bit transmission between network components
• CPC Class Codes: H04B 7/18597 Arrangements for system physical machines management, i.e. for construction, operations control, administration, maintenance
• CPC Class Codes: H04H 40/90 specially adapted for satellite broadcast receiving
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

A C-Band or Ku-Band satellite communication system uses a relatively small receiving antenna while operating within current FCC designated bandwidth and using existing satellite configurations. Aperture synthesis techniques create nulls in orbit locations from which potential interference is expected. Bandwidth inefficient modulation techniques reduce transmission power flux density. Video compression reduces the power necessary to transmit video information. These three features make possible a receiving antenna with a receiving area equivalent to that of a three foot diameter dish, at C-Band frequencies. Comparable reductions are possible for Ku-, Ka-, S- and L-Band systems. Compressing the data reduces the required transmitted power by a factor of ten. Spreading the bandwidth reduces the power density below the FCC limitation. However, reducing the antenna diameter increases the beam width of the antenna, hence, the smaller antenna can no longer discriminate between adjacent C-Band satellites in their current orbital configuration. By designing the receiving antenna with nulls in orbital locations where potentially interfering satellites would be located, the small antenna avoids this interference. The same general technique is possible for a Ku-Band Antenna system. The FCC power limits are higher at Ku-Band than C-Band, however, losses due to rain absorption and thermal noise are higher at Ku-Band frequencies. Nevertheless, equivalent size savings on Ku-Band antennas are possible with the combination of the above techniques, when tailored for the Ku-Band environment.

Claims

1. A receiver for receiving a video signal being broadcast via a satellite to a terrestrial antenna as a wideband power efficient signal, comprising:

a) a means for demodulating a received shaped frequency shift keyed signal being output from the terrestrial antenna into a received compressed digital signal, said demodulating means being coupled to the terrestrial antenna;

b) a means for decompressing the received compressed digital signal into a received digital signal, said decompressor means being coupled to the shaped frequency shift keyed demodulator; and

c) a means for converting the received digital signal into a signal resembling the video signal being broadcast from the satellite, said digital to analog converting means being coupled to the data decompressor.

2. The receiver according to claim 1, wherein the received shaped frequency shift keyed signal contains 3 to 8 dB of coding gain.

3. A receiver for receiving a video signal being broadcast via a satellite to a terrestrial antenna as a wideband power efficient signal, comprising:

a) a shaped frequency shift keyed demodulator being coupled to the terrestrial antenna and demodulating a received shaped frequency shift keyed signal being output from the terrestrial antenna into a received compressed digital signal;

b) a data decompressor being coupled to the shaped frequency shift keyed demodulator and decompressing the received compressed digital signal into a received digital signal; and

c) a digital to analog converter being coupled to the data decompressor and converting the received digital signal into a signal resembling the video signal being broadcast from the satellite.

4. The receiver according to claim 3, wherein the received shaped frequency shift keyed signal contains 3 to 8 dB of coding gain.

5. A ground station for receiving a television signal being broadcast as a wideband power efficient RF signal via a main satellite within a constellation of satellites, which includes at least two pairs of adjacent satellites adjacent to the main satellite and spaced at regular angular intervals from the main satellite relative to the ground station, said ground station comprising:

a) a terrestrial antenna receiving the television signal being broadcast from the constellation of satellites, outputting a received signal, and having a diameter such that a beamwidth of the terrestrial antenna encompasses the main satellite and the at least the two pairs of adjacent satellites;

b) a shaped frequency shift keyed demodulator being coupled to the terrestrial antenna and demodulating the received signal into a received compressed digital signal, wherein the received signal contains 3 to 8 dB of coding gain;

c) a data decompressor being coupled to the shaped frequency shift keyed demodulator and converting the received compressed digital signal into a received digital signal; and

d) a digital to analog converter being coupled to the data decompressor and converting the received digital signal into a received television signal available to the user.

6. The ground station according to claim 5, wherein the terrestrial antenna has an antenna aperture forming a main beam including two nulls matched to said at least two pairs of adjacent satellites in the constellation, the two nulls prevent signals being broadcast from said at least two adjacent satellites from interfering with a signal being broadcast from the main satellite.

7. The ground station according to claim 6, wherein the aperture with a shape that is a function of the regular angular intervals of the constellation of satellites.

8. The ground station according to claim 6, wherein the aperture has at least three primary areas separated by effective gaps, each gap having a width that is a function of the regular angular intervals of the constellation of satellites.

9. The ground station according to claim 8, wherein the three primary areas include a central area and two side areas, an east-west dimension of the central area relative to an east-west dimension of the side areas is such that energy of the signals being transmitted from the at least two pairs of adjacent satellites impinging upon the central area cancels with energy of the signals being transmitted from the at least two pairs of adjacent satellites impinging upon the side areas.

10. The ground station according to claim 5, wherein the terrestrial antenna further includes a feedhorn having a controlled gain such that energy of the signals being transmitted from the at least two pairs of adjacent satellites impinging upon the central area cancels with energy of the signals being transmitted from the at least two pairs of adjacent satellites impinging upon the side areas.

11. The ground station according to claim 5, wherein the terrestrial antenna further comprises:

(i) a central reflector;

(ii) a first side reflector;

(iii) a second side reflector;

(iv) a first gap between the central reflect or and the first side reflector; and

(v) a second gap between the central reflector and the second side reflector, wherein said first and second gaps create at least two nulls in received energy, which two nulls inhibit signals being broadcast from said at least two pairs of adjacent satellites.

12. The ground station according to claim 11, wherein the central reflector has a first parabolic reflecting surface, and the first and second side reflectors have a second parabolic reflecting surface.

13. The ground station according to claim 12, wherein the central reflector of the terrestrial antenna is separated from the first side reflector and from the second side reflector by a fresnel step.

14. The ground station according to claim 12, wherein a first parabola defining the first parabolic reflecting surface has a first focal length that is shorter than a second focal length of a second parabola defining the second parabolic reflecting surface.

15. The ground station according to claim 12, wherein a first parabola defining the first parabolic reflecting surface has a first focal length that is different than a second focal length of a second parabola defining the second parabolic reflecting surface.

16. The ground station according to claim 12, wherein a first parabola defining the first parabolic reflecting surface has a first focal length that is longer than a second focal length of a second parabola defining the second parabolic reflecting surface.

17. The ground station according to claim 11, wherein the terrestrial antenna further includes a feed horn, wherein the first and second gaps lie in an area obstructed from receiving signals from the central satellite by the feed horn.

18. The ground station according to claim 11, wherein the terrestrial antenna further includes a feed horn having a controlled gain such that energy of the signals being transmitted from the at least two pairs of adjacent satellites impinging upon the central area cancels with energy of the signals being transmitted from the at least two pairs of adjacent satellites impinging upon the side areas.

19. The ground station according to claim 11, wherein a width of the central reflector is smaller in a north-south or vertical dimension than the first and second edge reflectors.

20. The ground station according to claim 11, wherein the first and second side sections are physically separate from the main section.