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Abstract-Nowadays, several systems are available for outdoor localization, such as GPS, assisted GPS and other systems working on cellular networks. However, there is no proper location system for indoor scenarios. Research into designing location systems for 802.11 networks is being carried out, so locating mobile devices on global networks (GSM/cellular + GPS + WLAN) finally seems feasible. The technique presented in this paper uses existing wireless LAN infrastructure with minor changes to provide an accurate estimation of the location of mobile devices in indoor environments. This technique is based on round-trip time (RTT) measurements, which are used to estimate distances between the device to be located and WLAN access points. Each RTT measurement estimates the time elapsed between the RTS (Request-to-Send) and the CTS (Clear-to-Send) frame of the 802.11 standard. By applying trilateration algorithms, an accurate estimation of the mobile position is calculated.

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Authors presented recently an indoor location technique based on Time Of Arrival (TOA) obtained from Round-Trip-Time (RTT) measurements at data link level and trilateration. This new approach uses the existing IEEE 802.11 WLAN infrastructure with minor changes to provide an accurate estimation of the position of static wireless terminals. This paper presents advances on how to incorporate tracking capabilities to this approach in order to achieve a noticeable enhancement in the positioning accuracy while maintaining the computational cost low, both essential requirements in some critical applications of indoor pedestrian navigation in which people carrying light mobile devices has to be tracked with precision. Taking as a basis the Discrete Kalman Filter, customizations and optimizations have been designed and presented. Results obtained after conducting extensive simulations fed with actual ranging observables demonstrate the validity and suitability of the researched algorithms and its ability to provide very high performance level in terms of accuracy and robustness.