Self-assisted fast acquisition and first fix for a standalone GNSS receiver
A Global Navigation Satellite System (GNSS) positioning techniques is provided. A method to improve the time required to compute a position measurement in a GNSS receiver, and the time required to make this position measurement accurate is also provided. The method comprises computing a snapshot PVT (Position Velocity and Time) measurement, and use it to reduce the time required to acquire new signals to compute a conventional PVT measurement. A receiver implementing the method is further provided.
1. A device configured to calculate a first Position, Velocity and Time (PVT) measurement from Global Navigation Satellite System (GNSS) signals broadcasted by a plurality of transmitters of a GNSS constellation, the device comprising:
at least a first acquisition engine, configured to determine a code phase delay and a Doppler frequency shift value from a plurality of digitized GNSS signals respectively, by exploring a grid of possible code phase delays and Doppler frequency shift values for each digitized GNSS signal considered,
a tracking engine configured to retrieve clock and ephemeris data from navigation messages comprised into the digitized GNSS signals,
a first calculation device configured to compute said first PVT measurement from code phase delays determined by the first acquisition engine and clock and ephemeris data retrieved by the tracking engine for the corresponding GNSS signals, and
a second calculation device configured to compute a second PVT measurement from code phase delays determined by an acquisition engine, a coarse position of the receiver, a coarse time and coarse ephemerides, wherein the second calculation device performs the second PVT measurement through a snapshot PVT calculation, and wherein the device is configured to adapt the size of the grid of possible code phase delays and Doppler frequency shift values explored by the first acquisition engine using the value of the second PVT measurement computed by the second calculation device.
2. The device of claim 1 , wherein the position and the velocity of the second PVT measurement are used along with the coarse ephemerides to reduce the number of Doppler frequency shift values of the grid explored by the first acquisition engine.
3. The device of claim 1 , wherein the position and the time of the second PVT measurement are used along with the coarse ephemerides to reduce the number of code phase delays values of the grid explored by the first acquisition engine.
4. The device of claim 1 , wherein the first acquisition engine is configured to perform correlations between the digitized GNSS signals and local replicas of said GNSS signals generated considering code phase delays and Doppler frequency shift values from said grid of possible code phase delays and Doppler frequency shift values.
5. The device of claim 1 , further configured to use the second PVT measurement and the coarse ephemerides to select the GNSS signals considered in priority by the first acquisition engine.
6. The device of claim 1 , wherein the device is configured to further adapt the size of the grid of possible code phase delays and Doppler frequency shift values explored by the first acquisition engine using the value of the first PVT measurement computed by the first calculation device.
7. The device of claim 1 , wherein the tracking engine tracks the variations of code phase delay and Doppler frequency shift determined by the first acquisition engine.
8. The device of claim 1 , wherein the first calculation device is configured to compute pseudo-range measurements from code phase delays determined by the first acquisition engine and the clock and ephemeris data retrieved by the tracking engine from the corresponding signals, and to use said pseudo-range measurements to compute said first PVT measurement.
9. The device of claim 1 , wherein the second calculation device is configured to compute pseudo-range residual measurements from at least four code phase delays.
10. The device of claim 1 , wherein the coarse position of the receiver used by the second calculation device is calculated through a Doppler positioning.
11. The device of claim 1 , wherein the coarse ephemerides are Long Term Ephemeris.
12. The device of claim 11 , further comprising a calculation device configured to compute Long Term Ephemeris from the clock and ephemeris data retrieved by the tracking engine.
13. A Global Navigation Satellite System (GNSS) receiver, comprising:
an antenna and a Radio Frequency (RF) chain to receive and digitize GNSS signals, and a device according to claim 1 .
14. A method for calculating a first Position Velocity and Time (PVT) measurement in a device from Global Navigation Satellite System (GNSS) signals broadcasted by a plurality of transmitters of a GNSS constellation, the method comprising the steps of:
a. receiving and digitizing said GNSS signals through an antenna and a Radio Frequency (RF) chain,
b. determining a code phase delay and a Doppler frequency shift value associated to the digitized GNSS signals received respectively by exploring a grid of possible code phase delays and Doppler frequency shift values,
c. computing a second PVT measurement from code phase delays determined in step b, a coarse position of the receiver, a coarse time and coarse ephemerides through a snapshot PVT calculation,
d. using the second PVT measurement to adapt the size of the grid of possible code phase delays and Doppler frequency shift values explored in step b,
e. retrieving clock and ephemeris data from navigation messages comprised into the GNSS signals, and
f. computing said first PVT measurement from the code phase delays determined in step b, and the clock and ephemeris data retrieved in step e.