Multifrequency Phase Difference of Arrival Range Measurement: Principle, Implementation, and Evaluation

Abstract

Real-time location system (RLS) based on RFID is an effective indoor positioning system. The battery-free and low cost UHF passive tags can be attached on almost any objects, which are recognized as the best medium to achieve high precision ranging and positioning for large-scale objects. This paper proposes an indoor range measurement based on multifrequency phase difference of arrival (MF-PDoA) using UHF RFID passive tags and discusses the measurement principle, experiment implementation, and results evaluation in detail. After a theoretical overview of MF-PDoA range measurement principle, it introduces an experimental prototype under EPC C1G2 standard for range measurements. Both our prototype and a commercial off-the-shelf RFID reader have been used to verify the measurement method. We propose a Kalman filter and weighting method to process the measuring data. Experiment results indicate that, in a real environment, this method can effectively improve the ranging accuracy, which lays a foundation to extend the proposed measurement into two to three dimensions indoor object positioning.

Review of Indoor Positioning: Radio Wave Technology

“…The ranging measurement based on PDOA uses the phase difference of the propagation path between the anchor nodes or the reader to the tag to calculate its distance [80]. It is also mostly used in RFID and wireless sensor networks (WSNs) system.…”

A Joint TDOA-PDOA Localization Approach Using Particle Swarm Optimization

“…It is observed that the function is relatively flat around the global minimum, which makes the localization accuracy more susceptible to TDOA estimation errors. Existing methods for TDOA estimation are limited in their accuracy by the effect of noise, the sampling rate, time resolution and other factors [15], [17]- [19]. To enhance localization accuracy, our proposed approach leverages, in addition to TDOA, the more accurate estimates of PDOA.…”

“…This method requires the two received signals to be transferred to a central processor. Another method to estimate the PDOA is by recording the phase of arrival of the signal at each anchor independently and subtracting the two phases to obtain the PDOA [18], [19]. The method proposed in this paper does not depend on how the PDOA is obtained.…”

“…This is due to the phase wrapping problem [15], which results in an observed wrapped phase difference that cannot be directly used. Despite the phase wrapping issue, PDOA provides high measurement precision compared to TDOA [15], [17]- [19].…”

Memetic Chains for Improving the Local Wireless Sensor Networks Localization in Urban Scenarios

“…LPS consist on ad-hoc deployments of sensors which particularly adapt to the characteristics of the environment of application, improving the accuracy and stability of GNSS allowing the precise localization in complex conditions. LPS are classified depending on the physical property measured for determining the target location: Power [ 12 ], angle [ 13 ], time [ 14 ], phase [ 15 ], frequency [ 16 ], or even combinations of them, thus decreasing the percentage probability of error that each one have individually [ 17 , 18 ].…”