Estimation of speed of travel using the dynamic signal strength variation of multiple WLAN access points
A method for estimating the speed and bearing of a Wi-Fi enabled device using WLAN radio signals in a WLAN based location service is provided. A method used to estimate a speed of travel of a Wi-Fi enabled device comprises the Wi-Fi enabled device receiving signals transmitted by Wi-Fi access points in range of the Wi-Fi enabled device, and using the signals to estimate the speed of and/or direction of travel of the Wi-Fi enabled device.
1. A method used to estimate a speed of travel of a Wi-Fi enabled device without requiring position estimates of the Wi-Fi enabled device, the method comprising:
the Wi-Fi enabled device receiving all signals from detected Wi-Fi access points in range of the Wi-Fi enabled device;
measuring a power value for each of the received signals, the measuring occurring from individual Wi-Fi access points during a window of time;
calculating an amount of variation between the power values measured from the individual Wi-Fi access points during the window of time; and
using the amount of variation of the power values to estimate a speed of travel of the Wi-Fi enabled device so that the speed of travel can be estimated without requiring position estimates of the Wi-Fi enabled device.
2. The method of claim 1 , wherein the Wi-Fi enabled device communicates with at least one of the Wi-Fi access points to cause the Wi-Fi access point to transmit signals.
3. The method of claim 1 , wherein at least one of the calculating the amount of variation between the power values and estimating the speed of travel of the Wi-Fi enabled device is performed by the Wi-Fi enabled device.
4. The method of claim 1 , further comprising using the estimated speed of travel to estimate a subsequent position of the Wi-Fi enabled device.
5. The method of claim 1 , wherein at least one of the Wi-Fi access points is not in a reference database.
6. The method of claim 1 , wherein a length of time over which the individual Wi-Fi access points during the window of time are measured varies according to the rate of change of speed of travel of the Wi-Fi enabled device.
7. The method of claim 1 , wherein a Fourier Transform is performed to calculate the amount of variation between the power values.
8. The method of claim 1 , wherein a standard deviation of power values is used to calculate the amount of variation between the power values.
9. The method of claim 1 , wherein the speed of travel of the Wi-Fi enabled device is mapped as zero when the amount of variation between the power values is below a threshold value.
10. The method of claim 1 , wherein the amount of time over which the individual Wi-Fi access points during the window of time are measured is about 20 seconds and the power measurements are taken at a rate of about one per second.
11. The method of claim 1 , wherein the amount of time over which the individual Wi-Fi access points during the window of time are measured is about 15 seconds and the power measurements are taken at a rate of about one per second.
12. The method of claim 1 , wherein the amount of time over which the individual Wi-Fi access points during the window of time are measured is about 10 seconds and the power measurements are taken at a rate of about one per second.
13. The method of claim 1 , wherein the amount of time over which the individual Wi-Fi access points during the window of time are measured is about 5 seconds and the power measurements are taken at a rate of about one per second.
14. A method used to estimate a speed of travel of a Wi-Fi enabled device without requiring position estimates of the Wi-Fi enabled device, the method comprising:
the Wi-Fi enabled device receiving all signals from detected Wi-Fi access points in range of the Wi-Fi enabled device;
measuring a power value for each of the received signals, the measuring occurring from individual Wi-Fi access points during a window of time, wherein a length of time over which the individual Wi-Fi access points occur varies according to the speed of travel of the Wi-Fi enabled device;
calculating an amount of variation between the power values measured from the individual Wi-Fi access points during the window of time; and
using the amount of variation of the power values to estimate a speed of travel of the Wi-Fi enabled device so that the speed of travel can be estimated without requiring position estimates of the Wi-Fi enabled device.
15. The method of claim 14 , wherein a length of time over which the individual Wi-Fi access points during the window of time are measured decreases as the speed of travel of the Wi-Fi enabled device increases.