Time-based localisation in unsynchronized wireless LAN for industrial automation systems

In the recent years, the term wireless factory automation began raising interest. Its probably most appreciated feature, mobility, is yet acknowledged as the key for new applications. Nevertheless, this apparent freedom comes with a palette of requirements, whereof one is localisation. Although locating systems have been an extensive research topic for years, industrial systems impose additional constraints, both in terms of accuracy and scalability. Typically, for state-of-the-art time-based locating systems one assumes that the network infrastructure is perfectly synchronized. However, in large-scale cellular wireless industrial networks this is not achievable without redesigning the complete infrastructure. This paper proposes a differential time difference of arrival based localisation system using IEEE802.11, which eliminates the need for clock synchronization.