NBLoc: A Narrowband RF Localization System for Wide-Area Indoor Applications

We introduce NBLoc, a narrowband frequency hopping, long-range localization system designed for low-power Internet of Things (IoT) devices. Traditional high-accuracy localization systems typically require wide-bandwidth and power-demanding radio frequency (RF) circuits, leading to limitations such as short operational range and high power consumption to achieve decimeter-level accuracy. NBLoc overcomes these challenges by using narrowband symbols with a frequency-hopping mechanism across a wide bandwidth, enabling the localization of low-power tags over large areas. NBLoc features a novel custom-designed RF analog frontend (AFE) integrated circuit (IC), that eliminates the need for a conventional phase-locked loop, significantly reducing the cost and power consumption of the receiving tag. This advancement is enabled by NBLoc's thoughtful waveform design and specialized signal processing algorithms, which mitigate phase noise and uncertainty. Compared to previous solutions, NBLoc achieves lower power consumption and extended operational range due to its narrowband symbols while maintaining high localization accuracy by leveraging a 100 MHz localization bandwidth through frequency hopping. In NBLoc, system anchors transmit narrowband orthogonal symbols, hopping across the localization bandwidth in a predetermined pattern known to the tag. The tag, equipped with the custom low-power RF AFE IC, dynamically tunes its local oscillator (LO) frequency to match the hop pattern and capture these symbols, which are then used to estimate the channel impulse response (CIR). The tag calculates the time difference of arrival (TDOA) for each anchor pair from the CIRs, and determines its 2D location via multilateration. The system was implemented and tested using the low-power RF AFE IC in both line-of-sight (LOS) and non-line-of-sight (NLOS) environments, achieving decimeter-level accuracy across areas as large as 269 × 125 m$^{2}$.