BROADBAND SATELLITE COMMUNICATION SYSTEM USING OPTICAL FEEDER LINKS

• US 20190123813A1
• Filed: 06/29/2018
• Published: 04/25/2019
• Est. Priority Date: 12/31/2015
• Status: Active Grant

• Current Assignee: ViaSat Incorporated
• Original Assignee: ViaSat Incorporated
• Inventors: MENDELSOHN, AARON J
• Granted Patent: US 10,454,570 B2
• Time in Patent Office: Days
• CPC Class Codes: H01Q 1/288 Satellite antennas
• 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 10/118 specially adapted for satellite communication
• 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

Abstract

Broadband satellite communications systems using optical feeder links are disclosed. Various optical modulation schemes are disclosed that can provide improved capacity for fixed spot beam, on board beamforming, and ground-based beamforming broadband satellite systems.

Claims

1. (canceled)

2. A satellite communication system comprising:

a beamformer comprising;

a plurality of beamformer inputs, each configured to receive signals to be directed to a user spot beam;

a plurality of beamformer outputs, each configured to output a beam element signal;

a pilot output configured to output a timing pilot signal; and

a SAN comprising;

a plurality of optical modulators each having an electrical input and an optical output, at least one electrical input coupled to a corresponding output from the beamformer and at least one electrical input configured to receive the timing pilot signal;

an optical combiner coupled to the optical outputs of the plurality of optical modulators; and

an optical lens coupled to the output of the optical combiner and configured to transmit an optical signal;

a satellite comprising;

a satellite optical receiver having a steerable lens pointed at the SAN and configured to receive the optical signal, the satellite optical receiver having a plurality of radio frequency (RF) outputs;

a plurality of power amplifiers (PA), each having an input and an output, the inputs coupled to the RF outputs; and

an antenna array having a plurality of antenna elements, each antenna element having an input coupled to a corresponding one of the PA outputs.

3. The system of claim 2, wherein the steerable lens can be positioned by rotation about at least two axis in response to ground commands.

4. The system of claim 2, wherein the steerable lens can be positioned by rotation about at least two axis in response to on-board processing.

5. The system of claim 2, further comprising a second SAN comprising:

a plurality of second optical modulators each having an electrical input and an optical output, at least one electrical input coupled to a corresponding output from the beamformer and at least one electrical input configured to receive the timing pilot signal;

a second optical combiner coupled to the optical outputs of the plurality of second optical modulators; and

a second optical lens coupled to the output of the second optical combiner and configured to transmit a second optical signal;

wherein the satellite further comprises;

a second satellite optical receiver having a steerable lens pointed at the second SAN and configured to receive the second optical signal, the satellite optical receiver having a plurality of second radio frequency (RF) outputs;

a plurality of second power amplifiers (PA), each having an input and an output, the inputs coupled to the second RF outputs; and

wherein the antenna array has a plurality of second antenna elements, each second antenna element having an input coupled to a corresponding one of the second PA outputs.

6. The system of claim 5, wherein the SANs each have a SAN optical receiver configured to receive an optical signal from a satellite and to demultiplex and demodulate a timing correction signal from the optical signal.

7. The system of claim 6, wherein the beamformer further comprises a timing module having a timing control input, and wherein each SAN further comprises a timing pilot modem coupled to the SAN optical receiver, the timing pilot modem having an output coupled to the beamformer timing control input, wherein the timing module within the beamformer generates a delay in the transmission of beam elements signals in response to signals presented to the timing control input.

8. The system of claim 6, where the SANs each further comprise a timing module coupled between the beamformer and each optical modulator, the timing module having a timing control input coupled to receive the timing correction signal from the SAN optical receiver, wherein the timing module within the SAN generates a delay in the transmission of beam elements signals in response to signals presented to the timing control input.

9. The system of claim 2, wherein the antenna patterns of at least some of the antenna elements overlap such that signals transmitted therefrom will be superposed upon one another and thus coherently combine to form a user spot beam.

10. The system of claim 2, wherein the satellite optical receiver comprises an optical demultiplexer having an input and a plurality of outputs, each output associated with a corresponding optical wavelength, wherein the wavelengths associated with the outputs of the optical demultiplexer are grouped in optical bands and wherein wavelengths in the same optical band define unique optical channels.

11. The system of claim 2, wherein the satellite optical receiver comprises a plurality of satellite receiver optical detectors each having an RF output coupled to a corresponding RF output of the satellite optical receiver.

12. The system of claim 11, wherein the RF signal output from the satellite receiver detector has an amplitude that tracks the intensity of the optical signal applied to the satellite receiver optical detector input.

13. The system of claim 12, wherein the satellite receiver optical detector is a photo diode.

14. The system of claim 2, further comprising at least one frequency converter coupled between a corresponding one of the optical receiver RF outputs and a corresponding one of the antenna element inputs.

15. The system of claim 2, wherein each of the plurality of optical modulators comprise at least one light source operating at an optical wavelength within one of four optical bands, wherein the four optical bands are centered at approximately 1100 nm, 1300 nm, 1550 nm and 2100 nm, wherein the wavelength of each light source within the same optical band is spaced apart by approximately 100 GHz, and wherein the electrical input to the plurality of optical modulators is further configured to receive a signal having a bandwidth of approximately 3.5 GHz.

16. The system of claim 2, the SAN further comprising a plurality of baseband to IF converters, each having:

an input coupled a corresponding one of the plurality of beamformer outputs, and

an output coupled to the electrical input of a corresponding one of the plurality of optical modulators.

17. The system of claim 2, the SAN further comprising a SAN optical receiver configured to receive an optical signal and to output a plurality of beam element signals.

18. The system of claim 17, wherein the SAN optical receiver is further configured to output at least one timing correction signal.

19. A method of transmitting information through a satellite of a satellite communications system, comprising:

receiving a plurality of binary data streams within a beamformer, the binary data streams for transmission to a plurality of user beam coverage areas;

generating a plurality of beam element signals, each beam element signal generated such that when transmitted from an antenna array in the satellite the beam element signals superpose with one another to form at least one user spot beam; and

transmitting the beam element signals from the beamformer to a SAN;

receiving beam element signals with the SAN;

modulating the received beam element signals onto an optical carrier;

transmitting the modulated optical carrier from the at least one SAN to the satellite;

receiving the modulated optical carrier within a satellite;

demultiplexing the modulated optical carrier and outputting a plurality of optical signals, each of the plurality of demultiplexed optical signals having a wavelength in a unique optical channel;

generating a plurality of analog electrical signals, each having an amplitude determined in response to the optical intensity of one of the demultiplexed optical signals;

applying the plurality of analog electrical signals to elements of an antenna array such that when the beam element signals are superposed with one another, they form at least one user spot beam.

20. The method of claim 19, further including generating the plurality of beam element signals based on the quality of the optical links between the satellite and the SAN.

21. The method of claim 19, further including:

generating at least one timing pilot signal within the beamformer;

transmitting the timing pilot signal together with the beam element signals to a first SAN and a second SAN;

receiving timing pilot signals within the first SAN and the second SAN;

modulating the received timing pilot signals onto a first and second optical carriers in the first and second SAN respectively;

transmitting the first and second optical carrier from the corresponding SANs;

receiving in the satellite the first and second optical carriers from the first and second SAN;

demodulating the first and second optical carrier to obtain a corresponding first and second timing pilot signal in the satellite;

determining a time difference between the first timing pilot signal and the second timing pilot signal, and generating a timing correction signals based on the time difference; and

transmitting the timing correction signal to the first and second SAN.

22. The method of claim 21, further including delaying the transmission of the beam element signals from one or both of the SANs to reduce the time difference.

23. The method of claim 21 wherein each of the first and the second SAN receives a subset of the plurality of beam element signals.

24. The method of claim 21, further comprising positioning lenses within the satellite to receive optical signals from a subset of the SANs, wherein SANs are included in the subset based on the attenuation of optical signals transmitted over the optical link between each of the SANs and the satellite.

25. The method of claim 24, wherein positioning the lenses further comprises redirecting a lens away from the first SAN and pointing the lens at the second SAN if the satellite is not currently receiving an optical signal from the second SAN and the optical link between the satellite and the second SAN has less attenuation than the optical link between the satellite and the first SAN.