Clock synchronization during global navigation satellite system holdover
Technologies directed to estimating global navigation satellite system (GNSS) holdover time solutions are described. At a first time, at least four navigation messages are received. These navigation messages are used to determine an Earth-Centered, Earth-Fixed (ECEF) position. At a second time after the first time, less than four navigation messages are received. The ECEF position and an amount of time elapsed between the first and second times are used to determine a time solution corresponding to the second time. This time solution is used to synchronize a pulse per second (PPS) system to GNSS time.
1 . A method of operating a first space vehicle (SV), the method comprising:
at a first time:
receiving a first navigation message from a second SV, a second navigation message from a third SV, a third navigation message from a fourth SV, and a fourth navigation message from a fifth SV, wherein the second, third, fourth, and fifth SVs are different;
determining, using the first, second, third, and fourth navigation messages, a first time solution, a first Earth-Centered, Earth-Fixed (ECEF) position, a velocity parameter, and an acceleration parameter of the first SV; and
synchronizing a pulse per second (PPS) system of the first SV to a global navigation satellite system (GNSS) time using the first time solution; and
at a second time after the first time:
receiving one or more of a fifth navigation message from a sixth SV, a sixth navigation message from a seventh SV, or a seventh navigation message from an eighth SV, wherein the first SV receives less than four navigation messages total at the second time, and wherein the sixth, seventh, and eighth SVs are different;
determining, using a first amount of time elapsed between the first and second times and the first ECEF position, a second time solution; and
synchronizing the PPS system to the GNSS time based on the second time solution.
2 . The method of claim 1 , wherein determining the second time solution is further based on the velocity parameter and the acceleration parameter.
3 . The method of claim 1 , further comprising, at a third time after the second time:
receiving less than four navigation messages total from different SVs during the third time; and
determining, using a second amount of time elapsed between the first and third times and the first ECEF position, a third time solution; and
synchronizing the PPS system to the GNSS time based on the third time solution.
4 . The method of claim 1 , wherein determining the second time solution is further based on the fifth navigation message.
5 . The method of claim 4 , wherein determining the second time solution is further based on the sixth navigation message.
6 . The method of claim 5 , wherein determining the second time solution is further based on the seventh navigation message.
7 . The method of claim 1 , wherein synchronizing the PPS system to the GNSS time based on the second time solution comprises disciplining an on-board clock based on a predetermined counter value.
8 . A first space vehicle (SV) comprising:
a global navigation satellite system (GNSS) receiver;
one or more processors; and
a memory storing instructions that, when executed by the one or more processors or the GNSS receiver, configure the SV to:
at a first time:
receive a first navigation message from a second SV, a second navigation message from a third SV, a third navigation message from a fourth SV, and a fourth navigation message from a fifth SV, wherein the second, third, fourth, and fifth SVs are different;
determine, using the first, second, third, and fourth navigation messages, a first time solution, a first Earth-Centered, Earth-Fixed (ECEF) position, a velocity parameter, and an acceleration parameter of the first SV; and
synchronize a pulse per second (PPS) system of the first SV to GNSS time using the first time solution; and
at a second time after the first time:
receive one or more of a fifth navigation message from a sixth SV, a sixth navigation message from a seventh SV, or a seventh navigation message from an eighth SV, wherein the first SV receives less than four navigation messages total at the second time, and wherein the sixth, seventh, and eighth SVs are different;
determine, using a first amount of time elapsed between the first and second times and the first ECEF position, a second time solution; and
synchronize the PPS system to the GNSS time based on the second time solution.
9 . The first SV of claim 8 , wherein determining the second time solution is further based on the velocity parameter and the acceleration parameter.
10 . The first SV of claim 8 , wherein the instructions further configure the first SV to, at a third time after the second time:
receive less than four navigation messages total from different SVs at the third time; and
determine, using a second amount of time elapsed between the first and third times and the first ECEF position, a third time solution; and
synchronize the PPS system to the GNSS time based on the third time solution.
11 . The first SV of claim 8 , wherein determining the second time solution is further based on the fifth navigation message.
12 . The first SV of claim 11 , wherein determining the second time solution is further based on the sixth navigation message.
13 . The first SV of claim 12 , wherein determining the second time solution is further based on the seventh navigation message.
14 . The first SV of claim 8 , wherein synchronizing the PPS system to the GNSS time based on the second time solution comprises disciplining an on-board clock based on a predetermined counter value.
15 . A global navigation satellite system (GNSS) receiver comprising:
one or more processors; and
a memory storing instructions that, when executed by the one or more processors or the GNSS receiver, configure the GNSS receiver to:
at a first time:
receive a first navigation message from a second SV, a second navigation message from a third SV, a third navigation message from a fourth SV, and a fourth navigation message from a fifth SV, wherein the second, third, fourth, and fifth SVs are different;
determine, using the first, second, third, and fourth navigation messages, a first time solution, a first Earth-Centered, Earth-Fixed (ECEF) position, a velocity parameter, and an acceleration parameter of a first SV; and
synchronize a pulse per second (PPS) system of the first SV to GNSS time using the first time solution; and
at a second time after the first time:
receive one or more of a fifth navigation message from a sixth SV, a sixth navigation message from a seventh SV, or a seventh navigation message from an eighth SV, wherein the first SV receives less than four navigation messages total at the second time, and wherein the sixth, seventh, and eighth SVs are different;
determine, using a first amount of time elapsed between the first and second times and the first ECEF position, a second time solution; and
synchronize the PPS system to the GNSS time based on the second time solution.
16 . The GNSS receiver of claim 15 , wherein determining the second time solution is further based on the velocity parameter and the acceleration parameter.
17 . The GNSS receiver of claim 15 , wherein the instructions further configure the GNSS receiver to, at a third time after the second time:
receive less than four navigation messages total from different SVs at the third time; and
determine, using a second amount of time elapsed between the first and third times and the first ECEF position, a third time solution; and
synchronize the PPS system to the GNSS time based on the third time solution.
18 . The GNSS receiver of claim 15 , wherein determining the second time solution is further based on the fifth navigation message.
19 . The GNSS receiver of claim 18 , wherein determining the second time solution is further based on the sixth navigation message.
20 . The GNSS receiver of claim 19 , wherein determining the second time solution is further based on the seventh navigation message.