Method and system for determining the location of a mobile computer

• US 6,664,925 B1
• Filed: 05/02/2002
• Issued: 12/16/2003
• Est. Priority Date: 05/02/2002
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Bahl, Paramvir, Polastre, Joseph, Barkley, Warren, Moore, Timothy M.
• Primary Examiner(s): Blum, Theodore M.
• Application Number:
  US10/137,912
• Publication Number:
  US 20030218570A1
• Time in Patent Office: 593 Days
• Field of Search: 342/463, 342/450, 342/451
• US Class Current: 342/451
• CPC Class Codes: G01S 5/02 using radio waves using satellite radio beacon systems for determining position G01S19/00
• CPC Class Codes: H04W 4/021 Services related to particular areas, e.g. point of interest [POI] services, venue services or geofences
• CPC Class Codes: H04W 4/024 Guidance services
• CPC Class Codes: H04W 4/33 for indoor environments, e.g. buildings
• CPC Class Codes: H04W 64/00 Locating users or terminals or network equipment for network management purposes, e.g. mobility management

Abstract

A mobile computer establishes a wireless communication session with a wireless access point of a computer network. The location of each wireless access point is known and obtainable either from a database on the network or from the access points themselves. The strengths of wireless signals passing between the mobile computer and multiple wireless access points of the network, including the access point with which the mobile computer has established the session are measured at multiple time intervals. The measurements may be taken at the mobile computer itself or at the wireless access points. The measured strength values are then weighted according to such factors as whether the mobile computer has already established a communication session with the access point from which the sample was taken, and how old the sample is. For each location, the weighted strength values obtained for access points in that location are summed. The location having the highest sum is deemed to be the location of the mobile computer.

Claims

1. A method for determining the location of a client computer, the client computer having an existing wireless communication session with a wireless access point of a computer network, the method comprising:

measuring the strength of signals received from a plurality of wireless access points of the computer network, including the wireless access point to which the client computer has established the existing wireless communication session, wherein each wireless access point is located at one of a plurality of locations, and each of the plurality of locations has one or more of the plurality of wireless access points;

repeating the measuring step to obtain a plurality of signal strength values from each of the plurality of wireless access points;

calculating the difference between each signal strength value and a threshold value to obtain a plurality of modified signal strength values for each of the plurality of wireless access points;

summing the modified signal strength sample values for each of the plurality of locations to obtain a plurality of summed values, each of the plurality of summed values corresponding to a location of the plurality of locations;

determining which of the plurality of summed values is the highest; and

designating the client computer to be located near the location for which the summed value is determined to be the highest.

2. A computer-readable medium having stored thereon computer-executable instructions for performing the method of claim 1.

3. The method of claim 1, further comprising:

weighting the summed value of the location having the wireless access point with which the client computer has established the existing wireless communication session, wherein the determining step is performed after the weighting step.

4. The method of claim 1, further comprising, prior to execution of the summing step, weighting each signal strength value by a factor that is inversely proportional to the time elapsed since the signal strength value was measured.

5. The method of claim 1, further comprising, prior to execution of the summing step, weighting each signal strength value such that the more time that has elapsed since the signal strength value was measured, the less weight the signal strength value receives.

6. The method of claim 1, wherein the calculating step comprises calculating the absolute difference between each signal strength value and the threshold value to obtain the plurality of modified signal strength values for each of the plurality of wireless access points.

7. The method of claim 1, further comprising determining the location of each of the plurality of wireless access points based on a location string received from each of the wireless access points.

8. The method of claim 1, wherein the measuring step is repeated over a time interval, the method further comprising, prior to execution of the summing step, weighting each signal strength value by a factor that is based on the difference between the number of time units that elapsed in the time interval when that the signal strength value was taken and the total number of time units in the time interval.

9. The method of claim 1, wherein the designating step further comprises estimating, based on the strength of the signal received from a wireless access point in the location in which the client is designated to be located, the radial distance between the client and the wireless access point.

10. The method of claim 1, further comprising informing a user of the network that the user of the client computer is in the location in which the client computer has been designated to be located.

11. The method of claim 10, further comprising:

receiving from the user of the network an inquiry as to where the user of the client computer is located; and

performing the informing step in response to the inquiry.

12. The method of claim 1, wherein each of the steps is performed without the use of a satellite positioning system.

13. The method of claim 1, further comprising discarding the oldest signal strength value from at least one of the access points.

14. The method of claim 1, wherein at least one of the steps is performed by a network interface card coupled to the client computer.

15. The method of claim 1, wherein at least one of the steps is performed by one or more of the plurality of wireless access points.

16. The method of claim 1, wherein at least one of the locations has a plurality of wireless access points, the method further comprising:

averaging the modified signal strength values obtained for all of the plurality of wireless access points of the at least one location; and

using the averaged value as the summed value for the location.

17. A method for determining the location of a client computer, the client computer having an existing wireless communication session with a wireless access point of a computer network, the method comprising:

measuring the strength of signals received at a plurality of wireless access points of the computer network from the client computer, including the wireless access point to which the client computer has established a communication session, wherein each wireless access point is located at one of a plurality of locations, and each of the plurality of locations has one or more of the plurality of wireless access points;

repeating the measuring step to obtain a plurality of signal strength values from each of the plurality of wireless access points;

calculating the difference between each signal strength value and a threshold value to obtain a plurality of modified signal strength values for each of the plurality of wireless access points;

for each location, summing the modified signal strength sample values that were based on signal strength values obtained from the one or more wireless access points at the location, thereby obtaining a summed value for each location;

weighting the summed value of the location having the wireless access point with which the client computer has a wireless communication session;

after the weighting step, determining which of the summed values is the highest; and

designating the client computer to be located in the location for which the summed value is determined to be the highest.

18. A computer-readable medium having stored thereon computer-executable instructions for performing the method of claim 17.

19. The method of claim 17, further comprising, prior to execution of the summing step, weighting each signal strength value by a factor that is inversely proportional to the time elapsed since the signal strength value was measured.

20. The method of claim 17, wherein the calculating step comprises calculating the absolute difference between each signal strength value and the threshold value to obtain the plurality of modified signal strength values for each of the plurality of wireless access points.

21. The method of claim 17, wherein the measuring step is repeated over a time interval, the method further comprising, prior to execution of the summing step, weighting each signal strength value by a factor that is based on the difference between the number of time units that elapsed in the time interval when that the signal strength value was taken and the total number of time units in the time interval.

22. A method for determining the location of a client computer, the method comprising:

measuring the strength of signals received from a plurality of wireless access points of the computer network, wherein each wireless access point is located at one of a plurality of locations, and each of the plurality of locations has one or more of the plurality of wireless access points;

repeating the measuring step to obtain a plurality of signal strength values from each of the plurality of wireless access points;

calculating the difference between each signal strength value and a threshold value to obtain a plurality of modified signal strength values for each of the plurality of wireless access points;

weighting each modified signal strength value by a factor that is inversely proportional to the time elapsed since the signal strength value was measured;

for each location, summing the modified signal strength values that were based on signal strength values obtained from the one or more wireless access points at the location, thereby obtaining a summed value for each location;

determining which of the summed values is the highest; and

designating the client computer to be located in the location for which the summed value is determined to be the highest.

23. A computer-readable medium having stored thereon computer-executable instructions for performing the method of claim 22.

24. The method of claim 22, further comprising:

weighting the highest summed value; and

performing the determining step after the step of weighting the highest summed value.

25. The method of claim 22, wherein each of the steps is performed without the use of a satellite positioning system.

26. The method of claim 22, further comprising discarding the oldest signal strength value from at least one of the access points.

27. The method of claim 22, wherein at least one of the steps is performed by a network interface card coupled to the client computer.

28. The method of claim 22, wherein at least one of the steps is performed by one or more of the plurality of wireless access points.

29. The method of claim 22, wherein at least one of the locations has a plurality of wireless access points, the method further comprising:

averaging the modified signal strength values obtained for all of the plurality of wireless access points of the at least one location; and

using the averaged value as the summed value for the location.

30. A system for determining the location of a user, the system comprising:

a computer network having a plurality of wireless access points, wherein each wireless access point is located at one of a plurality of locations, each of the plurality of locations has one or more of the plurality of wireless access points, each wireless access point broadcasts a location identifier identifying the location in which the wireless access point is located;

a client computer engaged in a wireless communication session with one of the plurality of wireless access points, wherein the user is associated with the client computer,

wherein the client computer performs steps comprising;

measuring the strength of signals received from the plurality of wireless access points of the computer network, including the wireless access point to which the client computer has established a communication session;

repeating the measuring step to obtain a plurality of signal strength values from each of the plurality of wireless access points;

calculating the difference between each signal strength value and a threshold value to obtain a plurality of modified signal strength values for each of the plurality of wireless access points;

for each location, summing the modified signal strength sample values that were based on signal strength values obtained from the one or more wireless access points at the location, thereby obtaining a summed value for each location;

weighting the summed value of the location having the wireless access point with which the client computer has a wireless communication session;

after the weighting step, determining which of the summed values is the highest; and

transmitting to the computer network the location identifier of the location determined to have the highest summed value.

31. A method for determining the location of a client computer, the method comprising:

establishing a wireless communication session with a wireless access point of a computer network;

detecting wireless signals being broadcast by a plurality of wireless access points of the computer network, including the access point with which a communication session has been established, wherein the signals from each of the plurality of wireless access points comprise a location identifier for the wireless access point, the location identifier being indicative of the location of the wireless access point;

taking samples of the signals from the plurality of wireless access points over a preset number of iterations;

for each of the number iterations, recording the values of the strength of the signal samples and the location identifiers for the access points from which the signal samples originated;

establishing a minimum signal strength value;

disregarding all signal samples whose strength is less than the minimum signal strength value;

modifying the value of the strength of each signal sample by;

weighting the value of the strength of the signal sample by the absolute value of the difference between the minimum signal strength value and the value of the strength of-the signal sample; and

weighting the value of the strength of the signal sample by a factor of the age of the signal sample;

if the signal sample was obtained from the wireless access point with which the client computer has established a communication session, further weighting the signal sample;

for each location identifier, summing the modified strength sample values of the wireless access points that are broadcasting that location identifier; and

returning the location identifier for which the summed modified strength sample values of the wireless access points having that location identifier is the highest.

32. A computer-readable medium having stored thereon computer-executable instructions for performing the method of claim 31.

33. A system for determining the location of a client computer, the client computer having an existing wireless communication session with a wireless access point of a computer network, the method comprising:

means for repeatedly measuring the strength of signals received from a plurality of wireless access points of the computer network to obtain a plurality of signal strength values from each of the wireless access points, including the wireless access point to which the client computer has established the existing wireless communication session, wherein each wireless access point is located at one of a plurality of locations, and each of the plurality of locations has one or more of the plurality of wireless access points; and

means for obtaining the signal strength values from the measuring means, calculating the difference between each signal strength value and a threshold value to obtain a plurality of modified signal strength values for each of the plurality of wireless access points, summing the modified signal strength sample values for each of the plurality of locations to obtain a plurality of summed values, and determining the location of the client computer based on which of the plurality of summed values is the highest.