Method and system for providing timing and frequency synchronization for satellite diversity
View Patent ↗An approach facilitates synchronization by providing: (i) a method to analyze the two-satellite synchronization problem in time-frequency domain; and (ii) a two-stage estimation method to accomplish timing and frequency synchronization. The embodiment facilitates satellite diversity. The embodiment applies to a system involving two or more geosynchronous satellites.
1. A method comprising:
determining, by a processor of a communications device, a timing and a frequency for a data transmission associated with a communications terminal over a channel within a beam of a first satellite of a communications network, wherein the determinations of the timing and frequency for the data transmission over the channel of the first satellite are based on a first position within the beam of the first satellite;
determining, by the processor of the communications device, a timing and a frequency for the data transmission associated with the communications terminal over a channel within a beam of a second satellite of the communications network, wherein the determinations of the timing and frequency for the data transmission over the channel of the second satellite are based on a second position within the beam of the second satellite;
determining a timing estimate and a frequency estimate for the data transmission over the channel of the second satellite, wherein the determinations of the timing and frequency estimates are respectively based on timing and frequency relationships between the first satellite and the second satellite;
adjusting a receive window of a secondary receiver of the communications device based on the determined timing and frequency estimates for the data transmission over the channel of the second satellite;
receiving the data transmission over the channel of the second satellite, wherein the data transmission is received within the receive window of the secondary receiver and reflects a received timing and a received frequency relative to the receive window of the secondary receiver;
determining a secondary timing delta and a secondary frequency delta reflecting respective offsets of the received timing and received frequency relative to the receive window of the secondary receiver; and
acquiring synchronization for subsequent data transmissions associated with the communications terminal over the channel of the second satellite based on the determined secondary timing and frequency deltas.
2. The method of claim 1 , wherein the first position comprises a location approximately co-located with the second position.
3. The method of claim 1 , wherein the first position comprises an approximate center position within the beam of the first satellite, and the second position comprises an approximate center position within the beam of the second satellite, and wherein the beam of the first satellite overlaps with the beam of the second satellite.
4. The method of claim 1 , wherein the timing and frequency relationships between the first satellite and the second satellite comprise respective offsets between the determined timing and frequency for the data transmission associated with the communications terminal over the channel of the first satellite, and the determined timing and frequency for the data transmission associated with the communications terminal over the channel of the second satellite.
5. The method of claim 1 , wherein the secondary receiver of the communications device comprises a random access channel (RACH) receiver, and the receive window is approximately centered based on the timing and frequency estimates for the data transmission over the channel of the second satellite.
6. The method of claim 1 , further comprising:
adjusting a receive window of a primary receiver of the communications device based on the determined timing and frequency for the data transmission over the channel of the first satellite;
receiving the data transmission over the channel of the first satellite, wherein the data transmission is received within the receive window of the primary receiver and reflects a received timing and a received frequency relative to the receive window of the primary receiver;
determining a primary timing delta and a primary frequency delta reflecting respective offsets of the received timing and received frequency relative to the receive window of the primary receiver; and
acquiring synchronization for subsequent data transmissions associated with the communications terminal over the channel of the first satellite based on the determined timing and frequency deltas.
7. The method of claim 6 , wherein the first position comprises a location approximately co-located with the second position.
8. The method of claim 6 , wherein the first position comprises an approximate center position within the beam of the first satellite, and the second position comprises an approximate center position within the beam of the second satellite, and wherein the beam of the first satellite overlaps with the beam of the second satellite.
9. The method of claim 6 , wherein:
the primary receiver of the communications device comprises a random access channel (RACH) receiver, and the receive window is approximately centered based on the determined timing and frequency for the data transmission over the channel of the first satellite; and
the secondary receiver of the communications device comprises a random access channel (RACH) receiver, and the receive window is approximately centered based on the timing and frequency estimates for the data transmission over the channel of the second satellite.
10. An apparatus comprising:
a processor configured to determine a timing and a frequency for a data transmission associated with a communications terminal over a channel within a beam of a first satellite of a communications network, wherein the determinations of the timing and frequency for the data transmission over the channel of the first satellite are based on a first position within the beam of the first satellite, to determine a timing and a frequency for the data transmission associated with the communications terminal over a channel within a beam of a second satellite of the communications network, wherein the determinations of the timing and frequency for the data transmission over the channel of the second satellite are based on a second position within the beam of the second satellite, and to determine a timing estimate and a frequency estimate for the data transmission over the channel of the second satellite, wherein the determinations of the timing and frequency estimates are respectively based on timing and frequency relationships between the first satellite and the second satellite; and
a secondary receiver configured to receive the data transmission over the channel of the second satellite, wherein the data transmission is received within a receive window of the secondary receiver and reflects a received timing and a received frequency relative to the receive window of the secondary receiver, and wherein the receive window of the secondary receiver is adjusted based on the determined timing and frequency estimates for the data transmission over the channel of the second satellite; and
wherein the processor is further configured to determine a secondary timing delta and a secondary frequency delta reflecting respective offsets of the received timing and received frequency relative to the receive window of the secondary receiver, and to acquire synchronization for subsequent data transmissions associated with the communications terminal over the channel of the second satellite based on the determined secondary timing and frequency deltas.
11. The apparatus of claim 10 , wherein the first position comprises a location approximately co-located with the second position.
12. The apparatus of claim 10 , wherein the first position comprises an approximate center position within the beam of the first satellite, and the second position comprises an approximate center position within the beam of the second satellite, and wherein the beam of the first satellite overlaps with the beam of the second satellite.
13. The apparatus of claim 10 , wherein the timing and frequency relationships between the first satellite and the second satellite comprise respective offsets between the determined timing and frequency for the data transmission associated with the communications terminal over the channel of the first satellite, and the determined timing and frequency for the data transmission associated with the communications terminal over the channel of the second satellite.
14. The apparatus of claim 10 , wherein the secondary receiver of the communications device comprises a random access channel (RACH) receiver, and the receive window is approximately centered based on the timing and frequency estimates for the data transmission over the channel of the second satellite.
15. The apparatus of claim 10 , further comprising:
a primary receiver configured to receive the data transmission over the channel of the first satellite, wherein the data transmission is received within a receive window of the primary receiver and reflects a received timing and a received frequency relative to the receive window of the primary receiver, and wherein the receive window of the primary receiver is adjusted based on the determined timing and frequency for the data transmission over the channel of the first satellite; and
wherein the processor is further configured to determine a primary timing delta and a primary frequency delta reflecting respective offsets of the received timing and received frequency relative to the receive window of the primary receiver, and to acquire synchronization for subsequent data transmissions associated with the communications terminal over the channel of the first satellite based on the determined timing and frequency deltas.
16. The apparatus of claim 15 , wherein the first position comprises a location approximately co-located with the second position.
17. The apparatus of claim 15 , wherein the first position comprises an approximate center position within the beam of the first satellite, and the second position comprises an approximate center position within the beam of the second satellite, and wherein the beam of the first satellite overlaps with the beam of the second satellite.
18. The apparatus of claim 15 , wherein:
the primary receiver of the communications device comprises a random access channel (RACH) receiver, and the receive window is approximately centered based on the determined timing and frequency for the data transmission over the channel of the first satellite; and
the secondary receiver of the communications device comprises a random access channel (RACH) receiver, and the receive window is approximately centered based on the timing and frequency estimates for the data transmission over the channel of the second satellite.