WiFi Localization Based on IEEE 802.11 RTS/CTS Mechanism

Location Based Services are providing one of the fastest growing market segments today. While the most common technique for location determination is GPS, several alternative approaches have been proposed for Wi-Fi environments, based on time of flight, signal strength, etc. Time based techniques not only require accurate timestamping mechanisms, but also precise and synchronized clocks, which is quite difficult and expensive in industry. On the other hand, signal strength based methods need a lot of ground truth data. These method also require time consuming work and efforts before the system comes into use. In considerations of costs and time consumption, we present in this paper an approach for determining the location of a general Wi-Fi device combining RTS/CTS and TDoA techniques. The proposed model is deployable in various environments and contains two different methods, with clock mapping functions and asynchronized clocks. We also explain limitations of current round trip time (RTT) based RTS/CTS systems. Extensive experiments have been conducted and demonstrated how an accuracy of about one foot can be obtained and also the assumption of RTT measurements have been verified.