Accuracy assessment in assisted GPS positioning

• US 8,289,206 B2
• Filed: 02/15/2006
• Issued: 10/16/2012
• Est. Priority Date: 02/15/2006
• Status: Active Grant

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Wigren, Karl Torbjörn, Kangas, Ari
• Primary Examiner(s): Issing, Gregory C
• Assistant Examiner(s): Nguyen, Nga X
• Application Number:
  US12/279,807
• Publication Number:
  US 20080316091A1
• Time in Patent Office: 2,435 Days
• Field of Search: 3423572-35778, 342/357.64, 342/357.43, 342/357.46, 342463-464, 455/456.1
• US Class Current: 342/357.64
• CPC Class Codes: G01S 19/05 providing aiding data
• CPC Class Codes: G01S 19/256 relating to timing, e.g. time of week, code phase, timing offset

Abstract

Reliable and efficient search windows are provided by allowing the adaptation of the code search window to be dependent on inaccuracy measures of relations between a cellular frame time and a satellite reference time. This inaccuracy is calculated in a positioning node (21) of the cellular communications system (1), preferably by filtering of measurements received from user equipments. Linear trend Kalman filtering followed by post processing of estimation errors is presently preferred. In order to ensure non-ambiguous interpretation of the received time stamps of received satellite signals (55) provided by user equipments (10), a pseudo propagation delay is computed in both the user equipment (10) and the positioning node (21) based on GPS acquisition assistance data. The GPS time stamp is then defined referring to the determined pseudo propagation delay. In a preferred embodiment, the pseudo propagation delay is assured to be situated within a pre-determined time interval.

Claims

1. A method for providing assistance data when determining a position of a mobile terminal being connected to a cellular communication system via a base station, comprising the steps of:

providing satellite time reference data using a positioning node of the cellular communication system, said satellite time reference data comprising a relation between a frame time of said cellular communication system and a satellite reference time;

using the positioning node, adapting a search window to a specific satellite from which a satellite ranging signal emerges based at least on said satellite time reference data; and

,

using the positioning node, providing said search window to said mobile terminal;

wherein said step of providing satellite time reference data comprises the steps of;

the positioning node receiving, from a multitude of mobile terminals over time, measured quantities representing said relation;

the positioning node calculating an estimate of said relation from said received measured quantities representing said relation, as well as calculating an estimated inaccuracy of said estimate of said relation;

wherein said step of adapting said search window is based on said estimated relation and said estimated inaccuracy of said estimated relation.

2. The method according to claim 1, wherein said step of calculating comprises Kalman filtering.

3. The method according to claim 2, wherein said Kalman filtering is based on a linear trend model.

4. The method according to claim 2, wherein said step of calculating further comprises the positioning node estimating said inaccuracy from estimation errors of said Kalman filtering.

5. The method according to claim 1, wherein said step of calculating comprises estimation of said inaccuracy from a repeated differentiation of said measured quantities.

6. The method according to claim 1, applied to mobile terminal assisted positioning using the global positioning system - GPS, comprising the further steps of:

providing, in said positioning node, GPS acquisition assistance data comprising code phase, integer code phase and the GPS bit number for a list of GPS satellites expected at a reference site;

the positioning node transferring said GPS assistance data to said mobile terminal;

the mobile terminal receiving signals from a plurality of GPS satellites;

the mobile terminal determining a pseudorange to each of said plurality of GPS satellites and a GPS time stamp for the reception of respective said signals; and

the mobile terminal transferring said GPS time stamp and truncations of said pseudoranges to said positioning node;

whereby said received measured quantities representing said relation comprises said GPS time stamp and truncations of said pseudoranges;

said step of the mobile terminal determining a GPS time stamp and said step of the positioning node calculating an estimate of said relation both comprising the further step of computing a pseudo propagation delay based on said GPS acquisition assistance data;

said mobile terminal determining a GPS time stamp for a first of said plurality of GPS satellites based on said pseudorange to said first GPS satellite and said pseudo propagation delay; and

whereby the positioning node calculates an estimate of said relation based on said pseudo propagation delay and said received measured representation of said relation.

7. The method according to claim 6, wherein said computing of said pseudo propagation delay in turn comprises the steps of:

determining an apparent propagation delay;

establishing said pseudo propagation delay as said apparent propagation delay if said apparent propagation delay is larger than a predetermined minimum delay and as said apparent propagation delay plus 80 ms if said apparent propagation delay is smaller than said predetermined minimum delay.

8. The method according to claim 7, wherein said minimum delay is selected in the interval of 7 to 58 ms.

9. The method according to claim 8, wherein said minimum delay is selected in the interval of 30 to 45 ms.

10. The method according to claim 7, wherein said apparent propagation delay, τ

, being calculated as;

t_t1,ref =GPSBN ·

0.02 +ICP ·

0.001 +(1023−

CP) / 1.023·

10⁶, CP ≠

0

t_t1,ref =GPSBN ·

0.02 +ICP ·

0.001, CP =0

expressed in s, where GPSBN is the GPS bit number, ICP is the integer code phase and CP is the code phase for said first of said plurality of satellites;

said GPS time stamp for said first of said plurality of satellites being calculated as;

GPSTOW =floor {1000 * (t_t1+τ

*)}ms,

expressed in ms, where t_t1is a transmission time from said first of said plurality of satellites and τ

* is said pseudo propagation delay.

11. The method according to claim 10, wherein said calculation of said relations is based on a transmission time calculated as:

t_t1=[GPSTOW −

floor {1000*(δ

t_t1+τ

*)}]/1000+δ

t_t1

expressed in s, where δ

t_t1 is a truncated transmission time calculated according to the relation;

δ

ρ

₁ =c ·

(0.001-δ

t_t1)

where δ

ρ

₁ is said truncated pseudorange.

12. The method according to claim 6, further comprising the step of:

the positioning node calculating said position of said mobile terminal based on said transferred GPS time stamp, said transferred truncations of said pseudoranges and said pseudo propagation delay.

13. An assistance data providing arrangement, comprising:

means for providing satellite time reference data;

said satellite time reference data comprising a relation between a frame time of a cellular communication system and a satellite reference time;

means for adapting limits of a search window to a specific satellite from which a satellite ranging signal emerges based at least on said satellite time reference data, connected to said means for providing satellite time reference data; and

means for providing said limits of said search window to a mobile terminal;

said means for providing satellite time reference data in turn comprising;

means for receiving measured quantities representing said relation for a multitude of mobile terminals over time;

processor arranged for calculating an estimate of said relation from said received measured quantities representing said relation, as well as for calculating an estimated inaccuracy of said estimate of said relation;

wherein said means for adapting said search window is arranged to adapt said limits of said search window based on said estimated relation and said estimated inaccuracy of said estimated relation.

14. The arrangement according to claim 13, wherein said processor is arranged for performing Kalman filtering.

15. The arrangement according to claim 14, wherein said Kalman filtering is based on a linear trend model.

16. The arrangement according to claim 14, wherein said processor is further arranged for postprocessing estimating said inaccuracy from estimation errors of said Kalman filtering.

17. The arrangement according to claim 13, wherein said processor is arranged for estimation of said inaccuracy from a repeated differentiation of said measured quantities.

18. The arrangement according to claim 13, for application to mobile terminal assisted positioning using the global positioning system-GPS, further comprising:

means for providing GPS acquisition assistance data comprising code phase, integer code phase and the GPS bit number for a list of GPS satellites expected at a reference site;

means for transferring said GPS assistance data to a mobile terminal;

said means for receiving said measured quantities representing said relation being arranged for receiving data representing truncations of a pseudorange between a plurality of GPS satellites and said mobile terminal, and a GPS time stamp for the reception of signals from respective ones of GPS satellites in said mobile terminal;

said processor being further arranged for computing a pseudo propagation delay based on said assistance data;

whereby said processor is arranged for calculating said relations based on said pseudo propagation delay, said pseudorange and said time stamp.

19. The arrangement according to claim 18, wherein said processor is arranged for performing said computing of said pseudo propagation delay by:

determining an apparent propagation delay;

establishing said pseudo propagation delay as said apparent propagation delay if said apparent propagation delay is larger than a predetermined minimum delay and as said apparent propagation delay plus 80ms if said apparent propagation delay is smaller than said predetermined minimum delay.

20. The arrangement according to claim 19, wherein said minimum delay is selected in the interval of 7 to 58 ms.

21. The arrangement according to claim 20, wherein said minimum delay is selected in the interval of 30 to 45 ms.

22. The arrangement according to claim 19, wherein said apparent propagation delay, τ

, being calculated as;

t_t1,ref=GPSBN ·

0.02+ICP ·

0.001+(1023−

CP)/ 1.023·

10⁶, CP ≠

0

t_t1=GPSBN ·

0.02+ICP ·

0.001, CP =0

expressed in s, where GPSBN is the GPS bit number, ICP is the integer code phase and CP is the code phase for said first of said plurality of satellites.

23. The arrangement according to claim 22, wherein said calculation of said relations is based on a transmission time calculated as:

t_t1=[GPSTOW −

floor {1000*(δ

t_t1+τ

*)}]/1000+δ

t_t1

expressed in s, where δ

t_t1 is a truncated transmission time calculated according to the relation;

δ

ρ

₁−

c·

(0.001−

δ

t_t1)

where δ

ρ

₁ is said truncated pseudorange, GPSTOW_sv1 is said GPS time stamp and τ

* is said pseudo propagation delay.

24. Cellular communication system node comprising an arrangement according to claim 13.

25. The cellular communication system node according to claim 24, wherein said cellular communication system node being a radio network controller—

RNC—

or a serving mobile location centre—

SMLC.