Forward and reverse calibration for ground-based beamforming
Methods and systems for calibrating the return and forward links of a satellite communication system are provided according to embodiments of the invention. The phase and/or amplitude variations caused by the return and forward links are calculated and/or estimated to aid in beamforming, such as ground-based beamforming. Calibration earth stations, distributed within one or more beam patterns, may be used to transmit calibration codes to the gateway to calibrate the return link. Return links variations may be estimated using a weighted minimum mean square algorithm at the gateway. Forward links may be calibrated with calibration codes transmitted from the gateway through a hybrid matrix to at least one calibration station. Forward calibration links may also calibrate for temperature-dependent signal variations such as diplexer variations at the satellite.
1. A method for ground-based calibration of a satellite forward link, the method comprising:
transmitting a pseudo-noise (PN) code from a gateway to a satellite;
receiving the PN code from the gateway at the satellite;
transmitting the PN code from the satellite through a plurality of feeds to at least one calibration earth station, wherein the PN code is transmitted through each feed consecutively one after another;
receiving the PN code at the at least one calibration earth station; and
determining either or both of a phase shift or an amplitude shift of the PN code.
2. The method according to claim 1 , wherein each PN code is transmitted through one of the plurality of feeds for a period of time from 10 milliseconds to 10 seconds.
3. The method according to claim 1 , further comprising:
receiving signaling from the at least one calibration earth station comprising the received PN code; and
correlating the received PN code in the signaling with the PN code transmitted from the gateway to obtain either or both of the phase shift or the amplitude shift.
4. The method according to claim 1 , further comprising:
correlating, at the at least one calibration earth station, the received PN code with the PN code transmitted from the gateway to obtain either or both of the phase shift or the amplitude shift.
5. The method according to claim 4 , further comprising:
sending the PN code transmitted from the gateway to the at least one calibration earth station for use in the correlation to the received PN code.
6. The method according to claim 1 , further comprising:
determining beamforming parameters for forward link transmissions from the gateway to at least one spot beam via the satellite based on the either or both of the phase shift or the amplitude shift.
7. The method according to claim 1 , wherein the PN code is transmitted from the gateway at times when data is not being transmitted.
8. The method according to claim 1 , further comprising:
transmitting a plurality of PN codes from the gateway to the satellite, the plurality of PN codes comprising the PN code.
9. The method according to claim 1 , wherein transmitting the PN code comprises transmitting the PN code using one port of an input hybrid matrix at a time.
10. A method for ground-based calibration of a satellite forward link, the method comprising:
transmitting a signal including at least one predetermined code from a gateway to at least one calibration earth station through a satellite, wherein the signal includes a plurality of orthogonal calibration codes and is transmitted from the satellite to the at least one calibration earth station through at least one feed;
receiving the signal at the at least one calibration earth station;
comparing the code received in the signal with a predetermined code at the at least one calibration earth station; and
determining either or both of a phase shift or an amplitude shift of the code received in the signal.
11. The method according to claim 10 , further comprising:
calculating beamforming parameters based in part on either or both of the phase shift or the amplitude shift; and
transmitting the beamforming parameters to the satellite.
12. The method according to claim 10 , wherein the determining either or both of the phase shift or the amplitude shift of the code received in the signal occurs at the at least one calibration earth station.
13. The method according to claim 10 , wherein the determining either or both of the phase shift or the amplitude shift of the code received in the signal occurs at the gateway.
14. A system, comprising:
a gateway having a transmitter, wherein the transmitter is configured to transmit a pseudo-noise (PN) code to a satellite;
the satellite configured to transmit the PN code received by the satellite through a plurality of feeds to at least one calibration earth station, wherein the PN code is transmitted through each feed consecutively one after another;
the at least one calibration earth station configured to receive the PN code; and
a processor configured to determine either or both of a phase shift or an amplitude shift of the PN code.
15. The system of claim 14 , wherein the processor is further configured to:
correlate the PN code received by the at least one calibration earth station with the PN code transmitted from the gateway to obtain either or both of the phase shift or the amplitude shift.
16. The system of claim 15 , wherein the processor is further configured to:
receive signaling from the at least one calibration earth station comprising the PN code received by the at least one calibration earth station.
17. The system of claim 16 , wherein the processor is further configured to:
send the PN code transmitted from the gateway to the at least one calibration earth station for use in the correlation to the PN code received by the at least one calibration earth station.
18. The system of claim 14 , wherein the processor is further configured to:
determine beamforming parameters for forward link transmissions from the gateway to at least one spot beam via the satellite based on the either or both of the phase shift or the amplitude shift.
19. The system of claim 14 , wherein the gateway is further configured to:
transmit a plurality of PN codes to the satellite, the plurality of PN codes comprising the PN code.
20. The system of claim 14 , wherein the gateway is further configured to:
transmit the PN code using one port of an input hybrid matrix at a time.