Prediction refresh method for ephemeris extensions
Systems, methods and devices for using ephemeris data in GNSS receivers and systems are provided. Receivers using synthetic ephemeris data for longer ephemeris availability under poor reception conditions are updated using a variety of techniques that allow for the transfer of accurate information onto degraded synthetic ephemeris information.
1. A method comprising
obtaining, by an end user GNSS receiver, a broadcast ephemeris data set associated with a GNSS;
obtaining, by the end user GNSS receiver, a current position;
measuring, by the end user GNSS receiver, a range to a first satellite to obtain a first pseudorange;
determining, by the end user GNSS receiver, based on the current position and a synthetic ephemeris data set, an expected range to the first satellite to obtain a second pseudorange;
determining, by the end user GNSS receiver, based on the first pseudorange and the second pseudorange, an error in the first pseudorange;
attributing, by the end user GNSS receiver, the error only to clock error in the synthetic ephemeris data set;
determining, by the GNSS receiver, whether the synthetic ephemeris data set is valid or invalid based, at least in part, on the broadcast ephemeris data set and a predefined criterion of acceptability, wherein determining whether the synthetic ephemeris data set is valid or invalid includes performing statistical analysis of clock differences between the broadcast ephemeris data set and the synthetic ephemeris data set according to the predefined criterion of acceptability; and
in response to determining that the synthetic ephemeris data set is invalid, recalibrating, by the GNSS receiver, a clock correction parameter included in the synthetic ephemeris data set based on the clock error.
2. The method of claim 1 , wherein determining whether the synthetic ephemeris data set is valid or invalid further includes performing statistical analysis of position differences between the broadcast ephemeris data set and the synthetic ephemeris data set according to the predefined criterion of acceptability.
3. The method of claim 1 , further comprising:
accessing stored data representing the updated synthetic ephemeris data set; and
determining an estimated position based, at least in part, on the updated synthetic ephemeris data set.
4. An apparatus comprising:
an end user GNSS receiver comprising:
a receiver section configured to receive GNSS signals; and
a processor configured to:
obtain a broadcast ephemeris data set associated with a GNSS;
obtain a current position;
measure a range to a first satellite to obtain a first pseudorange;
determine, based on the current position and a synthetic ephemeris data set, an expected range to the first satellite to obtain a second pseudorange;
determine, based on the first pseudorange and the second pseudorange, an error in the first pseudorange;
attribute the error only to clock error in the synthetic ephemeris data set;
determine whether the synthetic ephemeris data set is valid or invalid based, at least in part, on the broadcast ephemeris data set and a predefined criterion of acceptability by performing statistical analysis of clock differences between the broadcast ephemeris data set and the synthetic ephemeris data set according to the predefined criterion of acceptability; and
in response to determining that the synthetic ephemeris data set is invalid, recalibrating a clock correction parameter included in the synthetic ephemeris data set based on the clock error.
5. The apparatus of claim 4 , wherein the processor is further configured to further perform statistical analysis of position differences between the broadcast ephemeris data and the synthetic ephemeris data set according to the predefined criterion of acceptability.
6. An apparatus comprising:
means for obtaining a broadcast ephemeris data set associated with a GNSS;
means for obtaining a current position;
means for measuring a range to a first satellite to obtain a first pseudorange for an end user GNSS receiver;
means for determining, based on the current position and a synthetic ephemeris data set, an expected range to the first satellite to obtain a second pseudorange for the end user GNSS receiver;
means for determining, based on the first pseudorange and the second pseudorange, an error in the first pseudorange;
means for attributing the error only to clock error in the synthetic ephemeris data set;
means for determining whether the synthetic ephemeris data set is valid or invalid based, at least in part, on the broadcast ephemeris data set and a predefined criterion of acceptability, wherein the means for determining whether the synthetic ephemeris data set is valid or invalid includes means for performing statistical analysis of clock differences between the broadcast ephemeris data set and the synthetic ephemeris data set according to the predefined criterion of acceptability; and
means for recalibrating a clock correction parameter included in the synthetic ephemeris data set based on the clock error in response to determining that the synthetic ephemeris data set is invalid.
7. The apparatus of claim 6 , wherein the means for determining whether the synthetic ephemeris data set is valid or invalid further includes means for performing statistical analysis of position differences between the broadcast ephemeris data and the synthetic ephemeris data set according to the predefined criterion of acceptability.
8. The apparatus of claim 6 , further comprising:
means for accessing stored data representing the updated synthetic ephemeris data set; and
means for determining an estimated position based at least in part on the updated synthetic ephemeris data set.