A Multipath Mitigation Localization Algorithm Based on MDS for Passive UHF RFID

Traditional localization algorithms are vulnerable in multipath environment for passive UHF RFID tag localization. To improve the localization accuracy, this letter proposes a robust algorithm named residual weighted multidimensional scaling (RWMDS) based on the multipath channel model. The RWMDS algorithm first utilizes reader-to-tag distances derived from received signal phase. To obtain the squared distance matrix required in the algorithm, the inter-tag distances are estimated using a few reference tags by establishing the relationship between inter-tag distance and phase information vectors measurement. Based on the modeling of ranging error in multipath environment, the RWMDS lgorithm can be applied to determine the estimated locations of the tags through a few iterations. Simulation results show that the RWMDS algorithm achieves higher localization accuracy than traditional algorithms in multipath environment.

I. Introduction

With the increasing use of RFID-based devices, passive UHF RFID indoor localization technology has been widely concerned [1]. However, due to the influence of multipath channel characteristics [2], [3], localization parameters cannot be accurately extracted and positioning accuracy declines greatly. In the indoor localization, the ranging techniques include time of arrival (TOA) [4], time difference of arrival (TDOA) [5], phase of arrival (POA) [6], received signal strength (RSS) [7], or some combination of these methods. However, the extraction of the main path is rarely possible by TOA method with low bandwidths. The POA method has a problem of having whole-cycle phase ambiguity in calculation. Since signal strength is affected easily by various environment factors, such as multipath, the RSSI method suffers from poor accuracy. So, the influence of wireless channel on received signals is greatly significant. In RFID indoor localization, the multifrequency-based technique is used [8] for robust range estimation.