60 GHz RSS localization with omni-directional and horn antennas

Abstract

Location estimation using RSSI has been attempted and studied extensively, but usually at the WiFi band, WiMax band and UWB. At 60 GHz, the studies are mostly simulations without much consideration of practical hardware constraints. In addition, the publications mainly show delay spread measurements which are only useful for systems utilizing the Time-of-Arrival (TOA), Time-Difference-of-Arrival (TDOA) and Angle-of-Arrival (AOA) methods. This research aims to develop a 60 GHz RSS-based localization system with commercially available transmitters, receivers and antennas. Preliminary RSSI measurements are obtained with omni-directional antennas over metal, various thicknesses of wood, mm-wave absorber from Siepel and on 20 cm high plastic stands. The conditions that result in minimal RSS fluctuations are chosen for the system. Initial development started with using omni-directional antennas at all the transmitters and receivers. Through measurements, RSS look-up tables are formed, and propagation models are created with spline approximations that represent the various transmitters. Various algorithms are developed surrounding the concept of trilateration. Together with the look-up tables, localization is shown to work at 60 GHz with mean accuracies of 2.2 cm to 3.1 cm, depending on the algorithm. The localization area is however, limited to a 60 cm by 60 cm area due to the high attenuation at this frequency. To increase the localization area of the system, the omni-directional antennas at the transmitters are replaced with directional antennas. This modification allows localization area to be increased to 1 m2. The trilateration method, however, is difficult to implement because of the radiation pattern belonging the directional antennas. Thus, the fingerprinting method is used instead. Three-dimensional look-up tables are measured and surface splines are generated to represent each transmitter. During localization, these tables are sifted through to obtain the distance and position estimates. It is found that the azimuth angle of the horn antennas contributes significantly to the overall accuracy of the localization system. In addition, surface splines generated from lower resolution measurements did not result in significant degradation of localization errors. This shows measurement effort in creating the look up tables can be reduced without compromising significantly on accuracy. The demonstrator developed in this work clearly demonstrates the feasibility of RSS localization at 60 GHz. While the system currently localizes on a planar surface, the experimental results paves the way for future development of a three-dimensional localization system.