Location Support in 802.11v

The IEEE is currently working on the inclusion of support for location information in the 802.11 protocols. Draft changes in 802.11v would allow wireless nodes to exchange location measurements and information using 802.11. The goal of these changes is to grant each wireless node the ability to determine its own location.

The protocol additions enable wireless nodes to report location measurements that can be sent to wireless peers, or request measurements from neighboring peers. The supported location measurements include timing and signal strength measurements. The timing measurement that is reported can be used to eliminate the fixed processing time mentioned previously, it provides a value for the fixed delay between receipt of a message and when the acknowledgment is sent in response. This removes the dependencies on having manufacturer- and model-specific data available to make use of timing measurements. The signal strength measurements include the signal to noise and RCPI, along with information about the transmission system of the node: transmit power and antenna gain.

Wireless nodes can also include location information; the current form contains a range of encodings for location information, including the formats defined by the IETF in References 2 and 3. A number of other parameters are provided, including speed, direction, and precision indicators.

A wireless node can use this information, along with measurements that it is able to make, to determine its own location. If the location of adjacent nodes is known from these reports, the timing information in these reports can be used as input to a trilateration algorithm.

For a device to determine its own location requires that the device has the processing and battery capacity available to perform the necessary calculations. Devices with limited processing or battery capacity are able to use the proposed method to regularly report location measurements.

From the perspective of the location architecture, the location measurements provided by wireless peers are the most interesting. An ALE within this network can use these messages to request information from its peers, thus being able to provide location measurements with greater precision than a passive receiver would be able to provide. The measurements that are reported can also be centrally combined to improve overall precision and accuracy.