System and method for Doppler frequency shift compensation in free space optical links
Systems and methods for Doppler frequency shift compensation in free space optical links include a modulator configured to modulate a transmitter laser; a receiver including a Local Oscillator (LO) laser configured to receive a coherent signal; and circuitry configured to tune a frequency of the transmitter laser and the LO laser based on an amount of Doppler frequency shift to be compensated. The systems and methods determine an amount of Doppler shift between a first and second satellite and tune the frequency of the transmitter and LO laser based on the determined amount of Doppler frequency shift.
1. A coherent transceiver for use in a first satellite comprising:
a transmitter including a modulator configured to modulate a light transmitted by laser;
a receiver including a Local Oscillator (LO) laser configured to provide a down conversion signal for received signal; and
circuitry configured to tune a frequency of the transmitter laser and the LO laser based on an amount of Doppler frequency shift to be compensated, wherein only the LO laser is tuned responsive to a maximum Doppler frequency shift not exceeding a maximum frequency tuning range of the LO laser.
2. The coherent transceiver of claim 1 , wherein the transmitter laser and the LO laser are tuned in opposite frequency directions.
3. The coherent transceiver of claim 1 , wherein the transmitter laser frequency is decreased in the first satellite and the LO laser frequency is increased in a second satellite by an amount equal to half of the amount of positive Doppler frequency shift to be compensated.
4. The coherent transceiver of claim 1 , wherein the transmitter laser frequency is increased in the first satellite and the LO laser frequency is decreased in a second satellite by an amount equal to half of the amount of negative Doppler frequency shift to be compensated.
5. The coherent transceiver of claim 1 , wherein responsive to the first satellite approaching a second satellite, the circuitry is further configured to:
set a transmitter laser frequency to a near lowest edge of a fine-tuning range for both satellites,
determine an LO laser setting, and
tune the transmitter laser and LO laser to maximize future tuning range.
6. The coherent transceiver of claim 1 , wherein responsive to the first satellite moving away from a second satellite, the circuitry is further configured to:
set a transmitter laser frequency to a near highest edge of a fine-tuning range for both satellites,
determine an LO laser setting, and
tune the transmitter laser and LO laser to maximize future tuning range.
7. The coherent transceiver of claim 1 , wherein the first satellite is configured to operate in a constellation of satellites.
8. The coherent transceiver of claim 7 , wherein the constellation of satellites is in one of a Low Earth Orbit (LEO) and a Middle Earth Orbit (MEO).
9. The coherent transceiver of claim 1 , wherein the coherent transceiver is configured to communicate with a ground station.
10. The coherent transceiver of claim 1 , further comprising
circuitry configured to detect a singularity where the first satellite and a second satellite simultaneously arrive close to an orbital crossing.
11. The coherent transceiver of claim 10 , wherein the circuitry configured to detect the singularity is further configured to switch the coherent transceiver to communicate with a third satellite based on the singularity.
12. A coherent transceiver for use in a first satellite comprising:
a transmitter including a modulator configured to modulate a light transmitted by laser;
a receiver including a Local Oscillator (LO) laser configured to provide a down conversion signal for received signal; and
circuitry configured to tune a frequency of the transmitter laser and the LO laser in a second satellite based on an amount of Doppler frequency shift to be compensated,
wherein one of
the transmitter laser frequency is decreased in the first satellite and a LO laser frequency is increased in the second satellite by an amount equal to half of the amount of positive Doppler frequency shift to be compensated, or
the transmitter laser frequency is increased in the first satellite and the LO laser frequency is decreased in the second satellite by an amount equal to half of the amount of negative Doppler frequency shift to be compensated.
13. The coherent transceiver of claim 12 , wherein the transmitter laser and the LO laser in the second satellite are tuned in opposite frequency directions.
14. The coherent transceiver of claim 12 , wherein the first satellite is configured to operate in a constellation of satellites with the second satellite.
15. The coherent transceiver of claim 12 , wherein the coherent transceiver is configured to communicate with a ground station.
16. The coherent transceiver of claim 12 , further comprising
circuitry configured to detect a singularity where the first satellite and the second satellite simultaneously arrive close to an orbital crossing.
17. A coherent transceiver for use in a first satellite comprising:
a transmitter including a modulator configured to modulate a light transmitted by laser;
a receiver including a Local Oscillator (LO) laser configured to provide a down conversion signal for received signal; and
circuitry configured to tune a frequency of the transmitter laser and the LO laser in a second satellite based on an amount of Doppler frequency shift to be compensated,
wherein one or more of
(1) responsive to the first satellite approaching a second satellite, the circuitry is further configured to
set a transmitter laser frequency to a near lowest edge of a fine-tuning range for both satellites,
determine an LO laser setting, and
tune the transmitter laser and LO laser to maximize future tuning range, and
(2) responsive to the first satellite moving away from a second satellite, the circuitry is further configured to
set a transmitter laser frequency to a near highest edge of a fine-tuning range for both satellites,
determine an LO laser setting, and
tune the transmitter laser and LO laser to maximize future tuning range.
18. The coherent transceiver of claim 17 , wherein the transmitter laser and the LO laser in the second satellite are tuned in opposite frequency directions.
19. The coherent transceiver of claim 17 , wherein the first satellite is configured to operate in a constellation of satellites with the second satellite.
20. The coherent transceiver of claim 17 , wherein the coherent transceiver is configured to communicate with a ground station.