Determining position of a GNSS receiver using fractional signalling event period times

Patent metadata

Field	Value
Publication number	US-9322922-B2
Application number	US-201213344297-A
Country	US
Kind code	B2
Filing date	Jan 5, 2012
Priority date	Jan 5, 2011
Publication date	Apr 26, 2016
Grant date	Apr 26, 2016

Abstract

Apparatus for calculating the position of a receiver in dependence on the time it takes signalling events to travel from a plurality of satellites to the receiver, obtains an indication of a transit time for a signalling event to travel from each satellite to the receiver, and forms an indication of an expected transit time for a signalling event to travel from the satellite to the receiver. The obtained indication of the transit time and the indication of the expected transit time for each non-reference satellite are compared with the obtained indication of the transit time and the indication of the expected transit time for the reference satellite to form residuals that are representative of a combined error in those indications of expected transit time; and the position of the receiver is calculate without calculating the integer ambiguities in the obtained transit times, in dependence on the residuals.

First claim

The invention claimed is:

1. An apparatus for calculating a position of the apparatus by using a time for periodic signalling events to travel from a plurality of satellites to the apparatus, the apparatus including:
a global navigation satellite system (GNSS) receiver configured to receive one of the periodic signalling events from each satellite, respectively;
a processor configured to:
determine, for each of the plurality of satellites, an initial estimate of a transit time for a periodic signalling event to travel from a respective satellite to the GNSS receiver; and
determine, for each of the plurality of satellites, an expected transit time for the periodic signalling event to travel from the respective satellite to the GNSS receiver based on an estimated current position of the GNSS receiver and a predetermined estimate of a position of the respective satellite;
designate one of the plurality of satellites as a reference satellite;
compare the initial estimate of the transit time and the expected transit time for each non-reference satellite with the initial estimate of the transit time and the expected transit time for the reference satellite, respectively, to form respective residuals that are representative of a combined error in the expected transit times; and
calculate the position of the GNSS receiver, without calculating an integer part of the initial estimates of the transit times based on the periodic signalling events, using the residuals.

2. The apparatus as claimed in claim 1 , wherein the processor is configured to use a time-of-arrival of the periodic signalling event at the GNSS receiver as the initial estimate of the transit time for that signalling event.

3. The apparatus as claimed in claim 1 , wherein the processor is configured to use a fractional part of a time-of-arrival of the periodic signalling event at the GNSS receiver as the initial estimate of the transit time for that periodic signalling event, wherein the time-of-arrival includes a fractional portion based on the periodic signalling event and the fractional part is the fractional portion of the period of the periodic signalling event.

4. The apparatus as claimed in claim 1 , wherein the processor is configured to compare the initial estimates of the transit times for the reference satellite and each non-reference satellite by measuring a respective time difference between an arrival at the GNSS receiver of the periodic signalling event transmitted by the reference satellite and an arrival at the GNSS receiver of the periodic signalling event transmitted by each of the non-reference satellites.

5. The apparatus as claimed in claim 1 , wherein the processor is configured to determine the expected transit times by estimating, for each satellite, a distance between that satellite and the GNSS receiver.

6. The apparatus as claimed in claim 1 , wherein the processor is configured to determine the expected transit time for each of the plurality of satellites by:
estimating the position of the GNSS receiver;
estimating the position of a satellite using an estimated absolute time and ephemeris information; and
computing the expected transit time of the satellite using the estimated positions of the GNSS receiver and the satellite.

7. The apparatus as claimed in claim 1 , wherein the processor is configured to calculate adjusted transit times by removing, from each initial estimate of the transit time for one periodic signalling event of the periodic signalling events, a clock bias associated with the satellite that transmitted the one periodic signalling event.

8. The apparatus as claimed in claim 7 , wherein the processor is configured to represent both the adjusted transit times and the expected transit times in units of one of distance or time, the apparatus being arranged to form the residuals by, for each non-reference satellite:
subtracting the representation of the expected transit time for a non-reference satellite from the representation of the adjusted transit time for the non-reference satellite;
subtracting the representation of the expected transit time for the reference satellite from the representation of the adjusted transit time for the reference satellite;
calculating a difference between the result of the subtraction in respect of the non-reference satellite and the result of the subtraction in respect of the reference satellite.

9. The apparatus as claimed in claim 1 , wherein the processor is configured to form each residual by calculating:
({tilde over (τ)} j −{circumflex over (d)} j /c )−({tilde over (τ)} 0 −{circumflex over (d)} 0 /c )

in which:
{tilde over (τ)} j is a fractional part of a time-of-arrival of the periodic signalling event transmitted by a non-reference satellite minus a clock bias associated with the non-reference satellite, wherein {tilde over (τ)} j is the fractional portion of the period of the signalling event of the non-reference satellite;
{tilde over (τ)} 0 is a fractional part of a time-of-arrival of the periodic signalling event transmitted by the reference satellite minus a clock bias associated with the reference satellite, wherein {tilde over (τ)} 0 is the fractional portion of the period of the signalling event of the reference satellite;
{circumflex over (d)} j is an estimated distance between the GNSS receiver and the non-reference satellite;
{circumflex over (d)} 0 is an estimated distance between the GNSS receiver and the reference satellite; and
c is the speed of light.

10. The apparatus as claimed in claim 9 , wherein the processor is configured to perform a modulo operation using the periodic signalling event on each residual to calculate the fractional part of that residual, the processor being configured to calculate the position of the GNSS receiver using the calculated fractional parts.

11. The apparatus as claimed in claim 1 , wherein each of the plurality of satellites is arranged to transmit respective periodic signalling events at time instants separated by a repetition interval t c , the apparatus is arranged to adjust a range of values of the residuals to a range t c /2 by identifying a sub-t c part of each residual and, if that result is greater than t c /2, subtracting t c from that sub-t c part.

12. The apparatus as claimed in claim 1 , wherein the processor is configured to adjust a range of values of the residuals in the range of −0.5 ms to 0.5 ms by identifying a sub-millisecond part of each residual and, if sub-millisecond part is greater than one-half millisecond, subtracting one millisecond from that sub-millisecond part.

13. The apparatus as claimed in claim 12 , wherein the processor is configured to represent the range-adjusted residuals in units of distance and calculate the position of the GNSS receiver using those distances.

14. The apparatus as claimed in claim 1 , wherein the processor is configured to determine the expected transit time for each of the non-reference satellites by predicting a time-of-arrival at the GNSS receiver of the periodic signalling event transmitted by each non-reference satellite.

15. The apparatus as claimed in claim 14 , wherein the processor is configured to form the prediction using a time-of-arrival at the GNSS receiver of the periodic signalling event transmitted by the reference satellite.

16. The apparatus as claimed in claim 14 , wherein the periodic signalling events are transmitted at regular intervals by the plurality of satellites and the processor is configured to determine the initial estimates of the transit time for each of the non-reference sat

Assignees

• Pratt Anthony Richard
• Jarvis Murray Robert
• Qualcomm Technologies Int Ltd

Inventors

• Pratt Anthony Richard
• Jarvis Murray Robert

Classifications

• G01S19/40

  Correcting position, velocity or attitude · CPC title

• G01S19/43

  using carrier phase measurements, e.g. kinematic positioning; using long or short baseline interferometry · CPC title

• G01S19/28 Primary

  Satellite selection · CPC title