Optimization of 2D location system for smartphones using a single WiFi acces point with Frequency-Scanned Antenna for Real Time Location System

This work studies a WiFi 2D Real Time Location System (RTLS) requiring only one Access Point. The precise two-dimensional position is computed with a combination of the Direction-of-Arrival (DoA) estimated from the RSSI acquired by a frequency-scanned antenna, and the range distance obtained with the 802.11mc Fine-Time Measurement (FTM) Round Trip Time (RTT) protocol. The DoA is computed by acquiring the RSSI from several WiFi channels, and a heuristic algorithm is employed to determine the best channel for measuring the RTT. In this work, we investigate the effect of reducing the number of used WiFi channels and the number of RTT samples, in order to minimize the acquisition time. It is shown that by reducing the number of WiFi channels from eleven to three and acquiring half of the RTT samples, the localization latency is reduced from 3.4 sec. to 1.2 sec. On the other hand, the 2D location mean error increases only from 1.18 m to 1.49 m for an outdoor experiment, and from 2.27 m to 2.67 m for an indoor experiment. This time reduction is of key importance for RTLS, such as tracking moving devices.