Radio Mobile Unit Location System

• US 20080287116A1
• Filed: 09/07/2005
• Published: 11/20/2008
• Est. Priority Date: 09/07/2004
• Status: Abandoned Application

• Current Assignee: Seeker Wireless Pty., Limited
• Original Assignee: Seeker Wireless Pty., Limited
• Inventors: Drane, Christopher R., Macnaughtan, Malcolm D.
• Application Number:
  US11/662,203
• Publication Number:
  US 20080287116A1
• Time in Patent Office: Days
• US Class Current: 455/423
• CPC Class Codes: G01S 5/0036 of measured values, i.e. measurement on mobile and position calculation on base station
• CPC Class Codes: G01S 5/021 Calibration, monitoring or correction G01S5/0252 takes precedence
• CPC Class Codes: G01S 5/10 Position of receiver fixed by co-ordinating a plurality of position lines defined by path-difference measurements , e.g. omega or decca systemsG01S5/12 takes precedence ; beacons and receivers cooperating therewith G01S1/306, G01S1/308
• CPC Class Codes: G01S 5/14 Determining absolute distances from a plurality of spaced points of known location
• CPC Class Codes: H04W 64/00 Locating users or terminals or network equipment for network management purposes, e.g. mobility management

Abstract

Disclosed is a method for locating a mobile radio unit within a mobile radio communications network. The method provides for the calculation of network variables such as a Real Time Difference (RTD) between network elements, from measurements already available to the network from, for example, handovers between network elements. The method provides for the location of radio mobile units without having to synchronise network elements such as BTSs or LMUs.

Claims

1. A method of determining a Real Time Difference (RTD) between respective clocks of a first network element and a second network element in a communications network, the method comprising:

measuring at least one parameter resulting from a first handover of a first mobile unit from the first network element to the second network element to provide a first measurement set;

measuring the at least one parameter resulting from a handover of at least one further mobile unit between the first network element and the second network element to provide a further measurement set; and

processing the first and further measurement sets to provide an estimate of a common RTD.

2. A method according to claim 1, wherein the first mobile unit and the further mobile unit are at different positions within the communications network.

3. A method according to claim 1 wherein the at least one parameter is an Observed Time Difference (OTD) and/or a Timing Advance (TA).

4. A method according to claim 1 wherein the first network element and the second network element are base transmitting stations (BTS).

5. A method according to claim 1 wherein the first and further measurement sets are processed by averaging.

6. A method according to claim 5 wherein the step of averaging comprises filtering the first and further measurement sets according to the formula:

$R<br><br><br><br>T<br><br><br><br>D_{\mathrm{ij}}^{\mathrm{\prime <br><br>}}=\frac{1}{n}<br><br>\underset{k=1}{\overset{n}{\sum <br><br>}}<br><br>R<br><br><br><br>T<br><br><br><br>D_{\mathrm{ij}}<br><br>\left(k\right)$

where RTD′

_ij is the estimate of the common RTD obtained by taking the numerical average of the previous n common RTD measurements denoted RTD_ij(k) and where i=an i^th sector, j=a j^th sector.

7. A method according to claim 6 wherein the step of averaging comprises filtering the first and further measurement sets according to the recursive formula:

$R<br><br><br><br>T<br><br><br><br>D_{\mathrm{ij}}^{\mathrm{\prime <br><br>}}<br><br>\left(k\right)=\frac{1}{k}<br><br>\left(R<br><br><br><br>T<br><br><br><br>D_{\mathrm{ij}}<br><br>\left(k\right)\left(k-1\right)<br><br>R<br><br><br><br>T<br><br><br><br>D_{\mathrm{ij}}^{\mathrm{\prime <br><br>}}<br><br>\left(k-1\right)\right)$

8. A method according to claim 1 wherein measurements of the at least one parameter from handovers occurring between co-sited sectors are analysed to determine whether the co-sited sectors derive their timing from a common source.

9. A method according to claim 8 wherein the measurements from the handovers occurring between co-sited sectors which have been determined to derive their timing from a common source are processed to provide the common RTD.

10. A method according to claim 5 wherein the step of averaging is performed by use of a filter having a time constant.

11. A method according to claim 10 wherein the time constant of the filter is determined by a rate of drift of a clock of the first or second network element.

12. A method according to claim 10 wherein the filter is a Kalman filter.

13. A method of averaging a plurality of RTD measurements taken in respect of a communications network clocked element which experiences clock drift, the method comprising:

averaging the plurality of RTD measurements over a given period of time.

14. A method according to claim 13, wherein the given period of time is determined by a rate of the clock drift of the clocked element.

15. A method according to claim 14 wherein the plurality of RTD measurements is averaged by use of a filter having a time constant.

16. A method according to claim 15 wherein the time constant of the filter is proportional to the rate of clock drift.

17. A method according to claim 16 wherein the time constant is proportional to a maximum tolerable synchronisation error divided by the differential clock drift between the clocked element and that of a second clocked element in the network.

18. A method according to claim 13 wherein RTD measurements taken towards the beginning of the given period of time are given progressively less weighting than RTD measurements taken towards the end of the given period of time.

19. A method according to claim 18 wherein the filter is an exponential filter operating according to the following formula:

RTD′

_ij(k)=α

RTD_ij(k) (1−

α

)RTD′

_ij(k−

1)

where

RTD′

_ij(k) is the filtered estimate of the RTD between BTS_i and BTS_j at time k

RTD_ij(k) is the computed RTD between BTS_i and BTS_j at time k and α

is the filter parameter determining the time constant of the filter.

20. A method according to claim 13 wherein the averaging is performed by a Kalman filter.

21. A method of calculating a real time difference (RTD) between respective clocks of a first network element and a second network element within a radio communications network, the method comprising;

estimating a position of a mobile element within the network to provide an estimated mobile element position;

calculating a distance (d₁) between the first network element and the estimated mobile element position;

calculating a distance (d₂) between the second network element and the estimated mobile element position;

measuring an Observed Time Difference (OTD_1,2) between the respective clocks of the first and second network elements; and

calculating the RTD according to the following formula;

RTD_1,2=OTD_1,2−

d₁ d₂

22. A method according to claim 21 wherein the step of estimating the position of the mobile element is performed using Cell ID.

23. A method according to claim 21 wherein the step of estimating the position of the mobile element is performed using a Global Positioning System (GPS).

24. A method according to claim 21 wherein the network elements are Base Transmitting Stations (BTS) and the mobile element is a mobile telephone handset.

25. A method of calculating a Real Time Difference (RTD) between respective clocks of a first network element and a second network element within a radio communications network, the method including;

estimating a position of a mobile element handing over from the first network element to the second network element, using a current value of the RTD found by the network;

estimating a subsequent RTD using the estimated position of the mobile element;

processing the subsequent RTD according to the first aspect of the present invention and using the processed subsequent RTD to again estimate the position of the mobile element; and

repeating the process for as many cycles as is required.

26. A method according to claim 25 wherein the initial RTD value used is calculated using the estimated position of the mobile element derived from Timing Advance plus NMR values in place of the current RTD held by the network.

27. A method for determining a position of a mobile unit within a mobile radio communications network, the method including the use of an Observed Time Difference (OTD) in conjunction with two or more time of arrivals (TA) and a current RTD held by the network to derive a Geometric Time Difference (GTD) describing a hyperbolic locus of position.

28. A method of estimating a position of a mobile unit between two network elements within a radio communications network, the method including:

measuring signal strength at the mobile unit to provide a first measurement;

obtaining a Timing Advance measurement at the mobile unit to provide a second measurement;

measuring an Observed Time Difference (OTD) between the two network elements at the mobile unit to provide a third measurement; and

combining and processing the three measurements to obtain an estimate of the position of the mobile unit.

29. A method according to claim 28 wherein the OTD is obtained as the mobile unit is handing over from a first to a second of the two network elements.

30. A method according to claim 28 wherein the network elements are BTSs.