Mobile terminal with frequency lock loop
View Patent ↗A mobile terminal for satellite communications receives communication, e.g., from a gateway via a satellite link. A frequency lock loop unit locks to the carrier frequency of the received communication. The mobile terminal includes a global positioning system for receiving global positioning data. The mobile terminal determines the Doppler frequency shift of the received communications based on the global positioning data. The mobile terminal generates a reference clock for return transmissions based on the frequency of the frequency lock loop, corrected for the Doppler shift. A correction factor of two times the determined Doppler frequency shift is used, to compensate for both a forward and return transmission link.
1. A mobile terminal comprising a computer including a processor and a memory, the memory storing instructions such that the processor is programmed to:
cause a reference signal that has been extracted from a received signal to be provided to a frequency lock loop to generate an output reference clock based on the reference signal;
determine an estimated Doppler shift of the received signal based at least in part on a velocity of the mobile terminal;
instruct a frequency synthesizer to generate a return carrier based at least in part on the output reference clock and the estimated Doppler shift; and
instruct a transmitter to transmit a return transmit signal based at least in part on the return carrier.
2. The mobile terminal of claim 1 , wherein the processor is further programmed to:
determine the estimated Doppler shift of the received signal based in part on a position of the mobile terminal.
3. The mobile terminal of claim 2 , wherein the frequency of the return carrier is compensated for a first Doppler shift of the received signal from a gateway to the mobile terminal, and a second Doppler shift of the return transmit signal from the mobile terminal to the gateway.
4. The mobile terminal of claim 2 , wherein the processor is further programmed to:
receive positioning data of the mobile terminal; and
determine the position and the velocity of the mobile terminal based on the positioning data.
5. The mobile terminal of claim 4 , wherein the Doppler shift is determined based on the positioning data at a first time and a second time.
6. The mobile terminal of claim 1 , wherein the frequency lock loop locks to the frequency of the reference signal.
7. The mobile terminal of claim 1 , wherein the processor is further programmed to instruct the frequency synthesizer to scale the return carrier to a return frequency band.
8. A method, comprising:
causing a reference signal that has been extracted from a received signal to be provided to a frequency lock loop to generate an output reference clock based on the reference signal;
determining an estimated Doppler shift of the received signal based at least in part on a velocity of the mobile terminal;
instructing a frequency synthesizer to generate a return carrier based at least in part on the output reference clock and the estimated Doppler shift; and
instructing a transmitter to transmit a return transmit signal based at least in part on the return carrier.
9. The method of claim 8 , further comprising;
determining the estimated Doppler shift of the received signal based in part on a position of the mobile terminal.
10. The method of claim 9 , wherein the frequency of the return carrier is compensated for a first Doppler shift of the received signal and a second Doppler shift of the return transmit signal.
11. The method of claim 9 , further comprising:
receiving positioning data of the mobile terminal; and
determining the position and velocity of the mobile terminal based on the positioning data.
12. The method of claim 11 , wherein the Doppler shift is determined based on the positioning data at a first time and a second time.
13. The method of claim 8 , wherein the frequency lock loop locks to the frequency of the reference signal.
14. The method of claim 8 , further comprising:
instructing the frequency synthesizer to scale the return carrier to a return frequency band.
15. A system comprising:
a mobile receiver that is programmed to:
receive a radio frequency signal,
extract a reference signal from the radio frequency signal, and
output the reference signal;
a frequency lock loop that is programmed to generate an output reference clock based on the reference signal;
a Doppler correction unit programmed to determine an estimated Doppler shift of the received signal based at least in part on a velocity of the mobile terminal;
a frequency synthesizer programmed to generate a return carrier based at least in part on the output reference clock and the estimated Doppler shift; and
a transmitter configured to transmit a return transmit signal based at least in part on the return carrier.
16. The system of claim 15 , wherein the Doppler correction unit is further programmed to determine the estimated Doppler shift of the received signal based in part on a position of the mobile terminal.
17. The system of claim 16 , wherein the frequency of the return carrier is compensated for a first Doppler shift of the received signal and a second Doppler shift of the return transmit signal.
18. The system of claim 16 , further comprising:
a global positioning system programmed to receive positioning data of the mobile terminal; wherein the determination of the Doppler shift is based at least in part on the positioning data.
19. The system of claim 18 , wherein the Doppler shift is determined based on the positioning data at a first and a second time.
20. The system of claim 15 , wherein the frequency lock loop locks to the frequency of the reference signal.
21. The system of claim 15 , wherein the frequency synthesizer is further programmed to scale the return carrier to a return frequency band.