Location determination for mobile units

• US 20040169603A1
• Filed: 02/28/2003
• Published: 09/02/2004
• Est. Priority Date: 02/28/2003
• Status: Active Grant

• Current Assignee: Motorola Solutions, Inc.
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Olds, Keith A., Gustafson, David T., Armbruster, Peter J.
• Granted Patent: US 6,819,286 B2
• Time in Patent Office: Days
• US Class Current: 342/463
• CPC Class Codes: G01S 5/0226 Transmitters
• CPC Class Codes: G01S 5/0289 of multiple transceivers, e.g. in ad hoc networks
• CPC Class Codes: G01S 5/14 Determining absolute distances from a plurality of spaced points of known location

Abstract

A method for location determination using Bluetooth techniques is applicable within buildings, underground or within other structures. A mobile unit (10) seeks the location of a cell from location master (20). Location master (20) and a number of location subsidiaries (21-24) determine ranging information with regard to the mobile unit (10) using Bluetooth techniques. The location master (20) then determines the mobile unit location using least squares estimation or other triangulation methods (50). In an alternate embodiment, ranging information is fine tuned for noise and error measurements between the location master and the location subsidiaries (51, 53) are used.

Claims

1. A location determination method for a mobile unit using Blutooth, the location determination method performed by a location master and a plurality of location subsidiaries, the location determination method comprising the steps of:

measuring a first elapsed time, by the location master, between sent and received messages to the mobile unit;

measuring at least one of second elapsed times, by the plurality of location subsidiaries, between sent and received messages to the mobile unit; and

processing by the location master the first and second elapsed times to determine a location of the mobile unit.

2. The location determination method as claimed in claim 1, wherein there is further included a step of sending by the location master a paging message to the mobile unit.

3. The location determination method as claimed in claim 2, wherein there is further included a step of responding by the mobile unit to the location master using Bluetooth timing.

4. The location determination method as claimed in claim 3, wherein the step of measuring a first elapsed time further includes a step of recording the first elapsed time between a paging message sent by the location master and the responding by the mobile unit.

5. The location determination method as claimed in claim 4, wherein there is further included steps of:

transferring control by the location master to one of the plurality of location subsidiaries; and

sending a paging message by the one of the plurality of location subsidiaries to the mobile unit.

6. The location determination method as claimed in claim 5, wherein there is further included the step of responding by the mobile unit to the one of the plurality of location subsidiaries using Bluetooth timing.

7. The location determination method as claimed in claim 6, wherein there is further included the steps of:

recording by the one of the plurality of location subsidiaries one of the at least one of second elapsed times between the paging message and the responding by the mobile unit; and

forwarding by the one of the location subsidiaries the one of the at least one of second elapsed times to the location master.

8. The location determination method as claimed in claim 7, wherein there is further included a step of determining whether a sufficient number of the plurality of location subsidiaries have been used for the location determination method.

9. The location determination method as claimed in claim 8, wherein if an insufficient number of location subsidiaries have been used then there is further included the steps of:

selecting another location subsidiary of the plurality of location subsidiaries; and

iterating the steps of claims 5 through 8.

10. The location determination method as claimed in claim 8, wherein if a sufficient number of the plurality of location subsidiaries have been used, there is further included the steps of:

processing the first elapsed time and the plurality of second elapsed times by at least one of;

a trigonometric, analytical geometry or least squares error estimation method to produce a location of the mobile unit; and

transmitting the location of the mobile unit to the mobile unit by the location master.

11. A location determination method for a mobile unit using Bluetooth, the location determination method performed by a location master and a plurality of location subsidiaries, the location determination method comprising the steps of:

measuring by the location master a clock timing between the location master and each of the plurality of location subsidiaries;

measuring a first elapsed time by the location master between sent and received messages to the mobile unit;

measuring a at least one of second elapsed times by the plurality of location subsidiaries, between sent and received messages to the mobile unit; and

processing by the location master the first and second elapsed times to determine a location of the mobile unit.

12. The location determination method as claimed in claim 11, wherein there is further included the step of paging each subsidiary of the plurality of location subsidiaries by the location master.

13. The location determination method as claimed in claim 12, wherein there is further included a step of responding by each location subsidiary of the plurality of location subsidiaries using Bluetooth timing.

14. The location determination method as claimed in claim 13, wherein there is further included a step of determining elapsed time between the steps of paging and responding for each of the plurality of location subsidiaries.

15. The location determination method as claimed in claim 14, wherein there is further included the step of adjusting clock timings for each of the plurality of location subsidiaries relative to the location master.

16. The location determination method as claimed in claim 14, wherein the step of measuring a first elapsed time includes the steps of:

sending a paging message by the location master to the mobile unit;

responding by the mobile unit to the paging message using Bluetooth timing; and

recording by the location master the first elapsed time.

17. The location determination method as claimed in claim 16, wherein the step of measuring a plurality of second elapsed times includes the steps of:

transferring control by the location master to one location subsidiary of the plurality of location subsidiaries;

sending a paging message by the one location subsidiary to the mobile unit;

responding to the paging message by the mobile unit using Bluetooth timing;

recording by the one location subsidiary one of the at least one of second elapsed times; and

transmitting one of the at least one of second elapsed times to the location master.

18. The location determination method as claimed in claim 17, wherein there is further included the steps of:

determining whether a sufficient number of the plurality of location subsidiaries has been used for measuring the plurality of second elapsed times;

if an insufficient number of the plurality of location subsidiaries has been used, there is further included the steps of;

selecting another location subsidiary; and

iterating the steps of claims 17 and 18.

19. The location determination method as claimed in claim 18, wherein the step of processing by the location master includes the step of for each location subsidiary, finding a range R where:

R_i²=Δ

x_i²+Δ

y_i² 

 

(1)

Δ

x, Δ

y equal coordinates from location subsidiary to the mobile unit.

20. The location-determination method as claimed in claim 19 wherein the step of processing by location master further includes the steps of:

adjusting the range R for noise and error according to

$\begin{array}{cc}{R}_i=c<br><br>\left(\frac{\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>t_i-625<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\mu <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>s-d_{t_i}}{2}\right)& \left(2\right)\end{array}$

where c equals an identity of the one of the plurality of location subsidiaries and

R_i is the range between the mobile unit 10 and the i^th pico-net master (either the location master or the designated location subsidiary for a particular range measurement) and

Δ

x_i and Δ

y_i are the differences in the coordinates between the location of the mobile unit and the i^th pico-net master unit.

d_ti is the timing measurement noise that is assumed to be a zero mean random variable and independent from pico-net to pico-net. This noise is primarily caused by timing errors due to time reference offsets or frequency errors relative to the location master'"'"'s time and frequency reference in the location subsidiaries or mobile unit; and

transmitting the location to the mobile unit.

21. The location determination method as claimed in claim 11 wherein there is further included steps of:

fixing a location of the location master; and

providing the location to the mobile unit relative to the location master.