Self-calibrating indoor positioning system based on ZigBee® devices

This paper presents a positioning system based on the round-trip time-of-flight measurement of a sequence of Direct Sequence Spread Spectrum (DSSS) modulated pulses, propagating between several transceiver devices. The architectures of the implemented devices, referred to as mobile node, fixed nodes and calibration node, are described. The mobile device can perform time-interval measuring by means of a Time-to-Digital Converter (TDC) integrated circuit, while the slave acts as pulse repeater. A calibration node, constituted by a fixed node integrated with a commercial Time-to-Digital Converter chip, has been introduced for bias removal purpose. All the devices are suitable for low-cost realization and low-power operations. This paper also presents and discusses some experimental results obtained from the system prototype.