Indoor Localization based on Wireless LAN

Location awareness is a basic need for future wireless systems.  We present an indoor localization approach for high-performance wireless communication systems. The basic idea of the system is the measurement of DTDOA (Differential Time Differences Of Arrival) from a mobile terminal to more than 4 fixed base stations. By using the DTDOA scheme the base stations do not need a synchronisation in time. All base stations are equipped with an add-on fast correlator chip, whereas the mobile terminal doesn't need any special hardware. We show simulation results based on IEEE 802.11a wireless communication standard. The results demonstrate that carefully selected patterns and small modifications of the OFDM receiver would allow the implementation of the entire localization procedure. It has been demonstrated that a position estimation based on IEEE 802.11a wireless LAN with an accuracy of < 2 m is possible using the DTDOA principle. This can even be further improved by accumulation of multiple measurements. The problem of missing frequency synchronization can be solved using a ternary correlation pattern. In particular, localization-friendly training sequences can significantly enhance the performance of the algorithms. The simulation results yield localization accuracies of about 2 m for indoor purposes. This can be achieved without use of the received signal strength indication (RSSI).