Systems and methods of communication in an assisted navigation system
View Patent ↗Provided herein are methods and systems for efficient communication between a server and a client in an assisted navigation system. In one or more embodiments, the server transmits a set of parameters for a satellite to the client, e.g., a GPS receiver, via a wireless or wired connection. The set of parameters includes a force parameter, initial condition parameters and time correction coefficients for the satellite. The receiver uses the received parameters in a numerical integration to compute the position of the satellite at a desired time. The set of parameters needed for the integration is small. To further reduce the amount of data transmitted, reference parameters may be subtracted from the original parameters before transmission from the server. The receiver is able to reconstruct the original parameters from the received parameters and the identically computed reference parameters. The parameters may be further compressed using data compression techniques.
1. A method for reducing a data set of satellite parameters transmitted to a navigational receiver of a satellite navigation system to assist the navigation receiver in satellite navigation, the method comprising:
obtaining original satellite parameters corresponding to a satellite specific reference time for one or more satellites;
predicting reference satellite parameters corresponding to the satellite specific reference time from previous satellite parameters for the one or more satellites;
calculating differences between the original satellite parameters and their respective reference satellite parameters to generate delta satellite parameters corresponding to the satellite specific reference time for the one or more satellites; and
transmitting the delta satellite parameters corresponding to the satellite specific reference time for the one or more satellites to the navigational receiver.
2. The method of claim 1 , wherein the original satellite parameters corresponding to the satellite specific reference time for a satellite comprise an original position, an original velocity, and an original satellite clock of the satellite corresponding to the satellite specific reference time, and said predicting the reference satellite parameters corresponding to the satellite specific reference time from previous satellite parameters for the satellite comprises predicting a reference position, a reference velocity, and a reference satellite clock of the satellite corresponding to the satellite specific reference time from previous satellite parameters.
3. The method of claim 2 , wherein said predicting the reference position, the reference velocity, and the reference satellite clock of the satellite corresponding to the satellite specific reference time from previous satellite parameters comprises:
computing the reference position of the satellite based on a numerical integration from a previous time to the satellite specific reference time using solar radiation pressure parameters, a previous velocity, and a previous position corresponding to the previous time;
computing the reference velocity of the satellite based on a numerical integration from the previous time to the satellite specific reference time using the solar radiation pressure parameters, and the previous velocity corresponding to the previous time; and
computing the reference satellite clock of the satellite based on calculating a satellite clock bias using time correction coefficients, and a time difference between the previous time and the satellite specific reference time.
4. The method of claim 2 , wherein said predicting the reference position, the reference velocity, and the reference satellite clock of the satellite corresponding to the satellite specific reference time from previous satellite parameters comprises calculating the reference position, the reference velocity, and the reference satellite clock using an almanac corresponding to a previous time.
5. The method of claim 2 , wherein said predicting the reference position, the reference velocity, and the reference satellite clock of the satellite corresponding to the satellite specific reference time from previous satellite parameters comprises calculating the reference position, the reference velocity, and the reference satellite clock using an ephemeris corresponding to a previous time.
6. The method of claim 1 , wherein said predicting the reference satellite parameters corresponding to the satellite specific reference time from previous satellite parameters for a satellite comprises obtaining a reference velocity of the satellite from a reference altitude of the satellite using a fixed relationship between orbital altitude and orbital velocity.
7. The method of claim 1 , wherein the original satellite parameters corresponding to a first reference time for a first satellite comprise an original position of the first satellite corresponding to the first reference time, and wherein said predicting the reference satellite parameters corresponding to a second reference time from previous satellite parameters for a second satellite comprises predicting a reference position of the second satellite corresponding to the second reference time using the original position of the first satellite corresponding to the first reference time when the first satellite and the second satellite share an orbital plane.
8. The method of claim 1 , wherein said predicting the reference satellite parameters corresponding to the satellite specific reference time from previous satellite parameters for the one or more satellites further comprises determining common reference satellite parameters corresponding to a common reference time for the one or more satellites from the reference satellite parameters corresponding to the satellite specific reference time for the one or more satellites using orbital integrations, and using the common reference satellite parameters to generate the delta satellite parameters for the one or more satellites.
9. The method of claim 1 , further comprising determining a subset of satellites likely to be observable by the navigation receiver and using the subset of satellites as the one or more satellites for which the delta satellite parameters are transmitted.
10. The method of claim 1 , further comprising transmitting a satellite mask to the navigational receiver, wherein the satellite mask identifies the one or more satellites for which the delta satellite parameters are transmitted.
11. The method of claim 1 , wherein said predicting the reference satellite parameters corresponding to the satellite specific reference time from previous satellite parameters for the one or more satellites further comprises identifying model flags, using the model flags to select models used for predicting reference solar radiation parameters for the one or more satellites, and transmitting the model flags for the one or more satellites to the navigation receiver.
12. The method of claim 1 , wherein said predicting the reference satellite parameters corresponding to the satellite specific reference time from previous satellite parameters for the one or more satellites further comprises identifying model flags, using the model flags to select models used for predicting reference satellite clocks for the one or more satellites, and transmitting the model flags for the one or more satellites to the navigation receiver.
13. The method of claim 1 , further comprising:
compressing the delta satellite parameters to generate compressed delta satellite parameters corresponding to the satellite specific reference time for the one or more satellites; and
transmitting the compressed satellite parameters corresponding to the satellite specific reference time for the one or more satellites to the navigational receiver.
14. The method of claim 13 , wherein said compressing the delta satellite parameters comprises using historical trends of the delta satellite parameter over a time period to identify lower limits of the delta satellite parameters and normalizing the delta satellite parameters with respect to their lower limits to generate the compressed delta satellite parameters.
15. The method of claim 13 , wherein said compressing the delta satellite parameters comprises:
encoding data blocks of the delta satellite parameters with pre-coded data stored in a pre-coded data table, wherein the pre-coded data are referenced by flags; and
transmitting flags referencing the pre-coded data in the pre-coded data table corresponding to the delta satellite parameters to the navigation receiver.
16. The method of claim 13 , wherein said compressing the delta satellite parameters comprises:
Scanning the delta satellite parameters over a period of time to determine value range of the delta satellite parameters; and
adjusting number of bits used to transmit the delta satellite parameters responsive to the value range.
17. The method of claim 13 , wherein said compressing the delta satellite parameters comprises using run length encoding technique.
18. The method of claim 13 , wherein said compressing the delta satellite parameters comprises:
encoding data blocks of the delta satellite parameters having a high frequency of occurrence with pre-coded data stored in a pre-coded data table, wherein the pre-coded data are referenced by flags; and
transmitting the flags referencing the pre-coded data in the pre-coded data table corresponding to the delta satellite parameters to the navigation receiver.
19. The method of claim 1 , wherein said obtaining the original satellite parameters corresponding to the satellite specific reference time for a satellite comprises determining a minimum necessary precision for the original satellite parameters.
20. The method of claim 1 , further comprising determining groups of subsets of satellites wherein the groups are used independently by the navigation receiver for positioning, and transmitting the delta satellite parameters for each group of satellites to the navigation receiver on different days.