Exploiting Ultra-Wideband Channel Impulse Responses for Device-Free Localization

Abstract

In radio-frequency (RF)-based device-free localization (DFL), the number of sensors acting as RF transmitters and receivers is crucial for accuracy and system costs. Two promising approaches for DFL have been identified in the past: radio tomographic imaging (RTI) and multi-static radar (MSR). RTI in its basic version requires many sensors for high accuracy, which increases the cost. In this paper, we show how RTI benefits from multipath propagation. By evaluating the direct and echo paths, we increase the coverage of the target area, and by utilizing UWB signals, the RTI system is less susceptible to multipath propagation. MSR maps reflections that occur within the target area to reflectors such as persons or other objects. MSR does not require that the person is located near a signal path. Both suggested methods exploit ultra-wideband (UWB) channel impulse response (CIR) measurements. CIR measurements and the modeling of multipath effects either increase the accuracy or reduce the required number of sensors for localization with RTI. We created a test setup and measure UWB CIRs at different positions with a commercially available off-the-shelf UWB radio chip, the Decawave DW1000. We compare the localization results of RTI, multipath-assisted (MA)-RTI, and MSR and investigate a combined approach. We show that RTI is improved by the analysis of multipath propagation; furthermore, MA-RTI results in a better performance compared to MSR: with 50% of all cases, the localization error is better than 0.82 m and in 80% of all cases 1.34 m. The combined approach results in the best localization result with 0.64 m in 50% of all cases.

MA-RTI: Design and Evaluation of a Real-World Multipath-Assisted Device-Free Localization System

“…For the i -th MPC, the measurement vector for the i -th MPC is defined as: where is the signal power of the observed and idle CIR at , respectively [ 9 ].…”

“…When a person affects an MPC, either on the direct or an echo path, in comparison to an idle target area, MA-RTI assigns pixels in the proximity of the signal paths a high attenuation value. As in previous work, we used the absolute difference for each MPC as input for our system (see (3) [ 9 ]).…”

“…They deployed low-cost commercially off-the-shelf (COTS) UWB radio chips in [ 21 ]. COTS-available UWB radio chips enable access to UWB CIR measurements, where multiple complex-valued MPCs can be extracted from one measurement [ 7 , 9 , 22 ]. In addition to the magnitude of the MPCs, the phase of the complex-valued MPC can be modeled and exploited in MA-DFL systems [ 8 , 23 ].…”

“…Furthermore, UWB CIRs enable bi- and multi-static radar approaches that are able to localize a person by extraction of additional signal paths [ 24 , 25 , 26 ]. However, these approaches are again susceptible to multipath propagation [ 9 ]. In this work, we proposed applying an MA-RTI approach to our real-world indoor localization system.…”

“…Another recent approach is to exploit multipath propagation. Considering multipath propagation increases localization accuracy or reduces the number of physical sensors, as shown in [ 7 , 8 , 9 ].…”