Indoor positioning utilizing fractional-N PLL synthesizer and multi-channel base stations

An indoor positioning system operating in the 5.8 GHz ISM-band is presented. The system principle is based on time-difference of arrival (TDoA) measurements by means of frequency modulated continuous wave (FMCW) signals. We briefly outline the measurement principle and system topology. Furthermore, we present a localizable tag hardware that features a novel integrated fractional-N PLL synthesizer for frequency ramp generation. The synthesizer IC has been designed within the Resolution project with the objective of low-power and inexpensive signal generation. The second focus of this paper is on measurement results that have been obtained using the integrated synthesizer in combination with a 4-channel base station. Due to the constricted signal bandwidth of 150 MHz, multipath propagation sets tight limits on ranging accuracy. By application of digital beam-forming techniques on the infrastructure side, we could significantly decrease the impact of channel echoes on accuracy compared with conventional single-channel systems.