Downstream Broad Beam Diversity

• US 20080144734A1
• Filed: 08/22/2007
• Published: 06/19/2008
• Est. Priority Date: 08/22/2006
• Status: Active Grant

• Current Assignee: ViaSat Incorporated
• Original Assignee: ViaSat Incorporated
• Inventors: Pateros, Charles N., Dankberg, Mark D.
• Granted Patent: US 7,944,993 B2
• Time in Patent Office: Days
• US Class Current: 375/267
• CPC Class Codes: H04B 7/10 Polarisation diversity; Directional diversity
• CPC Class Codes: H04B 7/18513 Transmission in a satellite or space-based system
• CPC Class Codes: H04B 7/18515 Transmission equipment in satellites or space-based relays
• CPC Class Codes: H04B 7/18517 Transmission equipment in earth stations
• CPC Class Codes: H04B 7/2041 Spot beam multiple access
• CPC Class Codes: H04L 27/2647 Arrangements specific to the receiver only equalisation H04L27/01
• CPC Class Codes: H04L 5/0016 Time-frequency-code
• CPC Class Codes: H04L 5/0026 Division using four or more dimensions
• CPC Class Codes: H04L 5/12 the signals being represented by different phase modulations of a single carrier

Abstract

A satellite communication system is provided according to one embodiment of the invention. The satellite communication system includes a plurality of satellites, a gateway and a plurality of subscriber terminals in communication with the gateway through the satellites. The gateway includes a plurality of antennas pointed toward a specific satellite. Each antenna may transmit the same signal to the satellites. The signal may be an OFDM signal. The subscriber terminals may include an antenna pointed toward at least one of the satellites and configured to receive OFDM signals. The OFDM signal time is proportional to the longest transmission time difference of all subscriber terminals within the geographic area serviced by the satellites. The transmission time difference is a measure of the difference between the transmission time of a signal over the longest transmission path and the transmission time of a signal over the shortest transmission path at a subscriber terminal.

Claims

1. A satellite communication system comprising:

a plurality of satellites;

a gateway with a plurality of antennas, wherein one or more of the plurality of antennas is pointed toward more than one of the plurality of satellites, and the gateway is configured to transmit a data stream using orthogonal frequency-division multiplexing (OFDM); and

a plurality of subscriber terminals, wherein each of the plurality of subscriber terminals include an antenna pointed toward at least two of the plurality of satellites and are configured to receive an OFDM signal from the gateway through the plurality of satellites,

wherein the OFDM signal time is proportional to the largest transmission time difference at a subscriber terminals within a geographic area serviced by the satellites; and

wherein the transmission time difference is the difference between the transmission time of a signal over the longest transmission path and the transmission time of a signal over the shortest transmission path at a subscriber terminal.

2. The satellite communication system according to claim 1, wherein the number of orthogonal sub-carriers within the OFDM signal is proportional to the OFDM symbol time.

3. The satellite communication system according to claim 1, wherein the gateway is configured to modulate the signal using quadrature amplitude modulation.

4. The satellite communication system according to claim 1, wherein the gateway is configured to modulate the signal using phase-shift keying.

5. The satellite communication system according to claim 1, wherein the plurality of satellites comprise three satellites.

6. The satellite communication system according to claim 1, wherein the plurality of antennas comprise three antennas.

7. The satellite communication system according to claim 1, wherein the plurality of satellites are in adjacent orbital slots.

8. The satellite communication system according to claim 1, wherein the subscriber terminals are mobile.

9. The satellite communication system according to claim 1, wherein the subscriber terminal antenna is a broad beam antenna.

10. A method for communicating with a plurality of subscriber terminals through a plurality of satellites using orthogonal frequency-division multiplexing (OFDM), wherein the plurality of subscriber terminals are located within a geographic area, the method comprising:

converting a data stream into an OFDM signal, wherein the OFDM signal time is proportional to the largest transmission time difference at a subscriber terminal within a geographic area serviced by the satellites, and the transmission time difference is the difference between the transmission time of a signal over the longest transmission path and the transmission time of a signal over the shortest transmission path at a subscriber terminal; and

transmitting the OFDM data string to the plurality of subscriber terminals through the plurality of satellites.

11. The method according to claim 10, wherein the number of orthogonal sub- carriers within the OFDM signal is proportional to the OFDM symbol time.

12. The method according to claim 10, further comprising modulating the data stream with quadrature amplitude modulation.

13. The method according to claim 10, further comprising modulating the data stream with phase-shift keying.

14. The method according to claim 10, wherein the plurality of satellites comprises three satellites.

15. A satellite communication system comprising:

a plurality of satellites;

a gateway with a plurality of antennas, wherein one or more of the plurality of antennas are pointed toward more than one of the plurality of satellites; and

a reference terminal with one or more antennas pointed toward the plurality of satellites and configured to receive signals from the gateway through the plurality of satellites.

16. The satellite communication system according to claim 15, wherein the gateway is configured to provide timing precorrection to one or more of the signals transmitted from the gateway to a plurality of mobile subscriber terminals through the satellites, wherein the timing precorrection is based on the time delay between signals received at the reference terminal.

17. The satellite communication system according to claim 15, wherein timing delays are transmitted from the reference terminal to the gateway through the satellites.

18. The satellite communication system according to claim 17, wherein the timing delays are transmitted over the Internet.

19. The satellite communication system according to claim 15, wherein the reference terminal is configured to transmit signals to one or more subscriber terminals.

20. The satellite communication system according to claim 15, wherein the signals received from the gateway are OFDM signals.

21. The satellite communication system according to claim 15, wherein the plurality of satellites comprises three satellites.