Abstract
The direct measurement of distance-dependent information between wireless units represents a challenge for wireless locating systems, because it requires the exact time synchronization of separate wireless units. To avoid these synchronization efforts, many wireless locating systems only evaluate phase difference of arrival (PDOA) measurements. While simple PDOA localization techniques rely on multiangulation, advanced PDOA concepts like the holographic extended Kalman filter (HEKF) directly evaluate the measured phases without non-linear preprocessing. However, these differential phase measurement approaches are less sensitive than systems that can measure absolute phase variations, which allow the tracking of much smaller position changes than the signal’s carrier wavelength. This paper proposes to extend the HEKF by the evaluation of absolute phases in an incoherent measurement setup, which consists of a continuous wave (CW) beacon and several receivers. The developed quasi-coherent holographic extended Kalman filter (QCHEKF) uses the overdetermined PDOA measurements to estimate the phase–frequency relation between each beacon–receiver pair. Then, the established phase–frequency relations allow the evaluation of absolute phase measurements and, thus, the accurate localization and tracking of a simple, unsynchronized, narrowband CW beacon, even under severe multipath conditions. This novel concept is experimentally validated via 3D localization results in a challenging indoor scenario using a 24 GHz CW measurement setup. Here, the QCHEKF improves the achieved localization accuracy in comparison to the HEKF by 35 % from 0.78 cm to 0.51 cm, while the maximum deviation from the trajectory reduces by 68 % from 5 cm to 1.6 cm. Furthermore, the QCHEKF enables the exact tracking of fast changes in direction, which is usually a significant challenge for standard wireless target tracking systems.
Highlights
N OWADAYS, positioning systems are used for many applications, such as logistics, automation, and autonomous driving [1]
To involve the time-dependency of the absolute phase measurements in the incoherent continuous wave (CW) measurement setup, the quasi-coherent holographic extended Kalman filter (QCHEKF) extends the holographic extended Kalman filter (HEKF)’s constant velocity model via a constant frequency model for each beacon–receiver pair. To estimate this phase–frequency relation between each beacon–RX pair, the QCHEKF inherently uses the absolute position information gathered from the phase differences
Afterwards, the constant frequency model provides absolute phase measurment estimations, which are used via the quasi-coherent phase evaluation to improve the localization in comparison to the pure phase difference-based HEKF
Summary
N OWADAYS, positioning systems are used for many applications, such as logistics, automation, and autonomous driving [1]. To involve the time-dependency of the absolute phase measurements in the incoherent CW measurement setup, the QCHEKF extends the HEKF’s constant velocity model via a constant frequency model for each beacon–receiver pair To estimate this phase–frequency relation between each beacon–RX pair, the QCHEKF inherently uses the absolute position information gathered from the phase differences. Afterwards, the constant frequency model provides absolute phase measurment estimations, which are used via the quasi-coherent phase evaluation to improve the localization in comparison to the pure phase difference-based HEKF. Due to the direct evaluation of phases, the QCHEKF completely omits hindering preprocessing steps, such as the AOA or the Doppler frequency estimation This novel concept is validated by 3D indoor localization results using a 24 GHz measurement setup with strong multipath propagation.
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