Methods and apparatus for improved locationing in a wireless network
Methods and systems are provided for determining the location of a first wireless device (e.g., a mobile unit) within a wireless network comprising a second wireless device (e.g., an access point). The method includes determining a signal strength contour associated with RF communication between the access point and the mobile unit, and adding a correction factor to the signal strength contour to produce a corrected signal strength contour, wherein the correction factor includes the sums of the differences between the transmit power and the antenna gain associated with the mobile unit and the access point. In an alternate scheme involving stored fingerprint data, a correction factor is introduced based on the differences between antenna gains and transmit power associated with the mobile unit under consideration and the mobile unit used for generating the fingerprint data. The systems and methods disclosed herein are applicable, for example, to networks operating in accordance with 802.11, RFID, WiMax, WAN, Bluetooth, Zigbee, UWB, and the like.
1. A method for locating a first wireless device within a wireless network comprising a second wireless device, wherein each of the first and second wireless devices have respective antenna gains and transmit powers, the method comprising the steps of:
determining a signal strength contour associated with RF communication between the first wireless device and the second wireless device;
adding a correction factor to the signal strength contour to produce a corrected signal strength contour, wherein the correction factor includes a sum of both the difference between the transmit powers of the wireless devices and the difference between the antenna gains of the wireless devices; and
locating the wireless device with respect to the access point using the corrected signal strength contour.
2. The method of claim 1 , wherein the first wireless device is a mobile unit, and the second wireless device is an access port.
3. The method of claim 2 , wherein the method is performed individually for each access point.
4. The method of claim 2 , wherein the step of determining the signal strength contour includes:
generating a predetermined set of fingerprint data comprising receiver signal strength indicator (RSSI) values determined by a test mobile device interacting with the first wireless device, wherein the test mobile device has an associated antenna gain and transmit power.
5. The method of claim 4 , wherein the step of adding a correction factor includes adding, to the fingerprint data, the sum of the difference between the transmit powers of the test mobile device and second wireless device and the difference between the antenna gains of the test mobile device and the second wireless device.
6. The method of claim 1 , wherein the first wireless device is a mobile unit, and the second wireless device is a second mobile unit.
7. The method of claim 1 , wherein the contour of the first wireless devices is not congruent with a signal strength contour of the second wireless device.
8. The method of claim 1 , wherein the first wireless device is instructed to operate at a specific transmit power level for location modeling.
9. The method of claim 1 , wherein the step of determining the signal strength contour includes:
determining a first receiver signal strength indicator (RSSI) contour for the first wireless device as the sum of the transmit power of the second wireless device, the antenna gain of the second wireless device, and a path loss;
determining a second RSSI contour for the second wireless device as the sum of the transmit power of the first wireless device, the antenna gain of the first wireless device, and the path loss.
10. A wireless network system comprising:
a first wireless device;
a second wireless device, wherein a signal strength contour of the first wireless device is not coextensive with a signal strength contour of the second wireless device; and
a locationing module configured to identify a location of the second wireless device with respect to the first wireless device, the locationing module configured to determine a signal strength contour associated with RF communication between the first wireless device and the second wireless device, and add a correction factor to the first signal strength contour to produce a corrected signal strength contour, wherein the correction factor includes a sum of both the difference between the transmit powers of the first and second wireless devices and the difference between the antenna gains of the first and second wireless devices.
11. The system of claim 10 , wherein the first wireless device is a mobile unit, and the second wireless device is an access port.
12. The method of claim 11 , wherein the locationing module computes the signal strength contour by generating a predetermined set of fingerprint data comprising receiver signal strength indicator (RSSI) values determined by a test mobile device interacting with the first wireless device, wherein the test mobile device has an associated antenna gain and transmit power.
13. The method of claim 12 , wherein the correction factor includes adding, to the fingerprint data, the sum of the difference between the transmit powers of the test mobile device and second wireless device and the difference between the antenna gains of the test mobile device and the second wireless device.
14. The system of claim 10 , wherein the first wireless device is a mobile unit, and the second wireless device is a second mobile unit.
15. The system of claim 10 , wherein the contour of the first wireless devices is not congruent with a signal strength contour of the second wireless device.
16. The system of claim 10 , wherein an access point associated with the locationing module instructs the first wireless device to operate at a specific transmit power level for location modeling.
17. The system of claim 10 , wherein the locationing module computes the signal strength contour by determining a first receiver signal strength indicator (RSSI) contour for the first wireless device as the sum of the transmit power of the second wireless device, the antenna gain of the second wireless device, and a path loss; and determining a second RSSI contour for the second wireless device as the sum of the transmit power of the first wireless device, the antenna gain of the first wireless device, and the path loss.
18. The system of claim 17 , wherein contours are determined individually for each access point.
19. A locationing module for determining a location of a mobile unit with respect to an access point associated therewith, the locationing module configured to determine a signal strength contour associated with RF communication between the access point and the mobile unit, and add a correction factor to the signal strength contour to produce a corrected signal strength contour, wherein the correction factor includes a sum of both the difference between the transmit powers of the mobile unit and access point and the difference between the antenna gains of the mobile unit and the access point, wherein the locationing module uses the corrected signal strength contour to locate the mobile unit.
20. The module of claim 19 , wherein the mobile unit and access point are configured to operate within a 802.11 environment.