Scintillation mitigation in geographically distributed satellite access nodes

Patent metadata

Field	Value
Publication number	US-11245467-B2
Application number	US-201816634516-A
Country	US
Kind code	B2
Filing date	Jan 25, 2018
Priority date	Aug 1, 2017
Publication date	Feb 8, 2022
Grant date	Feb 8, 2022

Abstract

Systems and methods are described for scintillation mitigation in satellite communications systems with geographically distributed access nodes. Some embodiments operate in context of a bent-pipe satellite that illuminates user and gateway coverage areas with fixed spot beams. Beamforming can be used, along with coordinated, phase-synchronized communication by the distributed access nodes, to generate signals that coherently combine via the satellite. Scintillation and/or other atmospheric irregularities can degrade phase synchronization at the access nodes. Accordingly, embodiments can monitor phase tracking performance of the access nodes to detect when a phase tracking error occurs in at least one of the access nodes. In response to detecting the phase tracking error, embodiments can inhibit transmitting of forward uplink data signals by at least that access node.

First claim

What is claimed is:

1. A beamforming satellite communications system, the system comprising:
a satellite access node (SAN) comprising:
a transceiver subsystem to transmit a loopback signal to a bent-pipe satellite and to receive the loopback signal from the satellite in response thereto, and to transmit forward uplink data signals to the satellite;
a phase tracker subsystem and having:
a phase reference port to receive a phase reference signal;
a loopback port coupled with the transceiver subsystem to receive the loopback signal as received from the satellite; and
a monitoring port to output a phase stability signal that indicates a present phase stability of a tracking loop of the SAN between the phase reference signal received at the phase reference port and the loopback signal received at the loopback port; and

a signal conditioning subsystem coupled with the transceiver subsystem and the phase tracker subsystem and having:
a forward input port to receive forward signals from a ground network, the forward signals generated in accordance with dynamically computed beamforming weights; and
a forward output port to transmit the forward uplink data signals to the transceiver subsystem, the forward uplink data signals generated from the forward signals to be transmitted in a phase-synchronized manner in accordance with the phase stability signal, such that transmission of the forward uplink data signals is inhibited in response to detecting a phase stability insufficiency in the phase stability signal.

2. The system of claim 1 , wherein:
the SAN further comprises a phase error detector coupled with the phase tracker subsystem to receive the phase stability signal, the phase error detector having a trigger port to output an inhibit signal in response to detecting the phase stability insufficiency; and
the signal conditioning subsystem further comprises an inhibitor coupled with the trigger port to autonomously cease transmission of the forward uplink data signals in response to the inhibit signal.

3. The system of claim 1 , wherein:
the phase stability signal is generated by the phase tracker subsystem as a function of a lock state of the phase tracking loop; and
the phase stability insufficiency is detected in response to the lock state indicating the phase tracking loop is out of lock.

4. The system of claim 1 , wherein:
the phase stability signal is generated by the phase tracker subsystem as a function of estimating a loop tracking error variance of the phase tracking loop; and
the phase stability insufficiency is detected in response to the loop tracking error variance being outside of a predetermined tolerance level.

5. The system of claim 1 , wherein:
the phase stability signal is generated by the phase tracker subsystem as a function of a phase error of the phase tracking loop; and
the phase stability insufficiency is detected in response to the phase error being outside of a predetermined tolerance level.

6. The system of claim 1 , wherein:
the phase stability signal is generated by the phase tracker subsystem as a function of a loop tracking quality of the phase tracking loop; and
the phase stability insufficiency is detected in response to the loop tracking quality being below a predetermined threshold.

7. The system of claim 1 , wherein:
the signal conditioning subsystem further comprises an inhibitor coupled with the ground network to autonomously cease transmission of the forward uplink data signals in response to receiving an inhibit signal from the ground network, the inhibit signal generated by the ground network in response to detecting the phase stability insufficiency by the ground network.

8. The system of claim 1 , wherein:
the forward signals are generated by the ground network in accordance with the dynamically computed beamforming weights to remove beamforming contributions by the forward uplink data signals from the SAN in response to the ground network detecting the phase stability insufficiency, thereby ceasing transmission of the forward uplink data signals by the SAN.

9. The system of claim 1 , wherein:
the SAN is one of a plurality of geographically distributed SANs of the beamforming satellite communications system; and
each SAN generates respective forward uplink data signals to be transmitted in a phase-synchronized manner in accordance with a respective phase tracking signal, such that the plurality of forward uplink data signals are transmitted in a mutually phase-synchronized manner to coherently combine at the satellite.

10. The system of claim 1 , wherein:
the phase tracker subsystem further comprises a phase-lock loop (PLL) having PLL inputs to receive the phase reference signal and the loopback signal; and
the phase stability insufficiency is detected when an output of the PLL manifests an out-of-tolerance variance over time.

11. The system of claim 1 , wherein the SAN further comprises:
a phase reference generator to generate the phase reference signal from the loopback signal as transmitted to the satellite.

12. The system of claim 1 , wherein the SAN further comprises:
a phase reference generator to generate the phase reference signal from a synchronization beacon signal received via the transceiver subsystem from the satellite.

13. The system of claim 1 , further comprising:
the ground network, communicatively coupled with a plurality of SANs, the SAN being one of the plurality of SANs.

14. The system of claim 1 , further comprising:
the bent-pipe satellite in communication with the SAN.

15. A beamforming satellite communications system, the system comprising:
a ground network node comprising:
a SAN tracker subsystem having:
a satellite access node (SAN) input port to receive, from each of the plurality of SANs, a respective SAN tracking signal that corresponds to a present phase stability of a tracking loop of the SAN between a respective phase reference signal of the SAN and a respective loopback signal of the SAN; and
a tracking output port to transmit an inhibit signal associated with at least one of the plurality of SANs in response to detecting that the at least one SAN is presently manifesting a phase stability insufficiency according to the SAN tracking signals; and

a forward communications subsystem having:
a tracking input port coupled with the tracking output port to receive the inhibit signal; and
a plurality of forward signal output ports, each to communicate to a respective one of the plurality of SANs respective forward signals generated in accordance with dynamically computed beamforming weights and the inhibit signal, such that transmission of the respective forward signals by the at least one SAN is inhibited in accordance with the inhibit signal.

16. The system of claim 15 , wherein:
each SAN tracking signal is a phase stability signal generated by a respective SAN to indicate the present phase stability of the SAN; and
the inhibit signal is generated, at the SAN tracker subsystem, by detecting, for each SAN, whether the SAN is manifesting the phase stability insufficiency according to the phase stability signal generated by the SAN.

17. The system of claim 15 , wherein:
the SAN tracking signal for each SAN comprises the inhibit signal, the inhibit signal generated by the SAN to directly indicate whether the SAN is manifesting the phase stability insufficiency.

18. The system of claim 15 , wherein:
the present phase stability of each SAN is a function of a lock state of the phase tracking loop of the SAN; and
the at least one

Assignees

• Viasat Inc

Inventors

• Dankberg Mark

Classifications

• H04B7/2041 Primary

  Spot beam multiple access · CPC title

• H04B7/18517

  Transmission equipment in earth stations · CPC title

• H04B7/18519

  Operations control, administration or maintenance · CPC title

• H04B7/18515

  Transmission equipment in satellites or space-based relays · CPC title

• H04B7/18513 Primary

  Transmission in a satellite or space-based system · CPC title