AUTONOMOUS WI-FI BASED RANGING DEVICE

1 . A method of operating a mobile device, the method comprising:

transmitting a first probe request to a target mobile device via a wireless channel;

receiving a first probe response from the target mobile device, wherein the probe response includes identification information associated with the target mobile device;

transmitting a first data packet to the target mobile device, via the wireless channel and using the identification information;

receiving a first reply packet from the target mobile device; and

determining a first distance to the target mobile device based, at least in part, on a round trip time (RTT) between the transmission of the first data packet and the reception of the first reply packet.

2 . The method of claim 1 , wherein the mobile device transmits the first data packet to the target mobile device without communicating with any wireless access points.

3 . The method of claim 1 , wherein the first data packet is a NULL frame and the first reply packet is an acknowledgement frame.

4 . The method of claim 1 , further comprising:

selectively triggering an alarm based on the first distance to the target mobile device.

5 . The method of claim 4 , wherein the selectively triggering comprises triggering the alarm if the first distance is less than or equal to a threshold distance.

6 . The method of claim 4 , wherein the alarm includes at least one of a visual, audible, or physical notification.

7 . The method of claim 4 , wherein the alarm intensifies as the first distance decreases.

8 . The method of claim 1 , wherein the mobile device does not pair or handshake with the target mobile device.

9 . The method of claim 1 , further comprising:

recording a transmit time when the mobile device transmits the first data packet;

recording a receive time when the mobile device receives the first reply packet; and

determining the RTT based on the transmit time and the receive time.

10 . The method of claim 1 , wherein the identification information includes at least a media access control (MAC) address of the target mobile device.

11 . The method of claim 1 , further comprising:

transmitting a second data packet to the target mobile device;

receiving a second reply packet from the target mobile device; and

determining a second distance to the target mobile device based, at least in part, on a RTT between the transmission of the second data packet and the reception of the second reply packet.

12 . The method of claim 11 , further comprising:

determining a velocity of the target mobile device based, at least in part, on a difference between the first distance and the second distance.

13 . A mobile communication device, comprising:

means for transmitting a first probe request to a target mobile device via a wireless channel;

means for receiving a first probe response from the target mobile device, wherein the probe response includes identification information associated with the target mobile device;

means for transmitting a first data packet to the target mobile device, via the wireless channel and using the identification information;

means for receiving a first reply packet from the target mobile device; and

means for determining a first distance to the target mobile device based, at least in part, on a round trip time (RTT) between the transmission of the first data packet and the reception of the first reply packet.

14 . The device of claim 13 , wherein the mobile device transmits the first data packet to the target mobile device without communicating with any wireless access points.

15 . The device of claim 13 , wherein the first data packet is a NULL frame and the first reply packet is an acknowledgement frame.

16 . The device of claim 13 , further comprising:

means for selectively triggering an alarm based on the first distance to the target mobile device.

17 . The device of claim 16 , wherein the means for selectively triggering is configured to trigger the alarm if the first distance is less than or equal to a threshold distance.

18 . The device of claim 13 , wherein the alarm includes at least one of a visual, audible, or physical notification.

19 . The device of claim 13 , wherein the mobile device does not pair or handshake with the target mobile device.

20 . The device of claim 13 , further comprising:

means for recording a transmit time when the mobile device transmits the first data packet;

means for recording a receive time when the mobile device receives the first reply packet; and

means for determining the RTT based on the transmit time and the receive time.

21 . The device of claim 13 , wherein the identification information includes at least a media access control (MAC) address of the target mobile device.

22 . The device of claim 13 , further comprising:

means for transmitting a second data packet to the target mobile device;

means for receiving a second reply packet from the target mobile device; and

means for determining a second distance to the target mobile device based, at least in part, on a RTT between the transmission of the second data packet and the reception of the second reply packet.

23 . The device of claim 22 , further comprising:

means for determining a velocity of the target mobile device based, at least in part, on a difference between the first distance and the second distance.

24 . The device of claim 13 , further comprising:

a GPS component configured to determine an absolute position of the mobile communication device.

25 . The device of claim 24 , further comprising:

means for communicating the absolute position of the mobile communication device to the target device.

26 . The device of claim 25 , wherein the absolute position of the mobile communication device is communicated to the target device by embedding the absolute position within the first data packet.