Client location in 802.11 networks

Abstract

Location awareness is invaluable to the military commander. Any application that can accurately deliver this service is highly desirable. Being able to extract accurate distances is the first step towards developing a proposed 802.11 local area positioning system. This thesis explores a number of different methods of using 802.11 to capture physical distance separation between mobile stations. The first method of measuring distance, involves using 802.11 round trip signal times. Round trip signal times are determined from a transmitter to a receiver and back, and are used with the speed of light to measure distance between the nodes. Another method of using 802.11 to measure distance involves using signal strength measurements and a client-server arrangement. Distances can be extracted by extrapolating through a range of signal strength measurements. Because signal strength is a measurement of power, its behavior is governed by the inverse-square law. If environmental variables, such as humidity and RF interference do not significantly change, a line graph of signal strength measurements versus distance can be used to determine positions under these constant conditions.