PT  - JOURNAL ARTICLE
AU  - Blay, Ryan
AU  - Wang, Boyi
AU  - Akos, Dennis M.
TI  - Deriving Accurate Time from Assisted GNSS Using Extended Ambiguity Resolution
AID  - 10.1002/navi.412
DP  - 2021 Mar 20
TA  - NAVIGATION: Journal of the Institute of Navigation
PG  - 217--229
VI  - 68
IP  - 1
4099  - https://navi.ion.org/content/68/1/217.short
4100  - https://navi.ion.org/content/68/1/217.full
SO  - NAVIGATION2021 Mar 20; 68
AB  - The advent of assisted GPS/GNSS can reduce the time to first fix (TTFF) dramatically and still provide sufficient positioning accuracy. However, many applications utilize GNSS for timing and assisted GPS/GNSS does not always provide the accurate nanosecond synchronization. Accurate timing is challenging for assisted GNSS due to the lack of diversity in the solution over short time periods. The relatively short ambiguities of the GPS L1 C/A code signal, one millisecond and twenty milliseconds, are too coarse to resolve accurate time reliably. In this paper, the impact of different ambiguity times has been derived/computed and validated. Experimental results show that when the ambiguity time is 200 milliseconds or longer, the least squares process will reliably converge and the typical nanosecond-level timing can be achieved. An example shows how the GPS L1 C/A data parity word (provided every 600 milliseconds) can be used, demonstrating nanosecond-level timing from assisted GPS.