An Indoor Localization System Based on DTDOA for Different Wireless LAN Systems

Location awareness is a basic need for future wireless systems. In this paper we use the time measurement principle DTDOA and discuss a solution of time measurement based on an add-on correlator module in an IEEE 802.11a receiver. Furthermore, we investigate the performance of an indoor localization system for a Gbit/s, 60 GHz high-performance wireless LAN, currently under development. Simulation results demonstrate that carefully selected patterns and small modifications of the OFDM receiver would allow the implementation of the entire localization procedure using existing hardware. 1 Principles of differential time difference of arrival (DTDOA) The localization is based on distance measurements between a point at an unknown position of a mobile transceiver (MT) and points at known positions (access point, receiver base station BS). In practice, the propagation time of an electromagnetic wave is measured to calculate the distance. It requires the knowledge of the starting time at the transmitter and of the time of arrival (TOA) at the receiver. Our setup consists basically of at least four base stations and one or more mobile transceivers. Fig. 1 gives an impression of the setting. By using the DTDOA scheme the base stations do not need a costly synchronisation in time. The master base station sends a request using a pseudo noise (PN) data sequence, the mobile transceiver react with a response using the same PN sequence. Afterwards the host PC collects the measured time differences of the arrival of the request and the response data of all base stations to calculate the position of the mobile transceiver.