MIMO FMCW Reader Concept for Locating Backscatter Transponders

This paper presents a multiple-input multiple-output (MIMO) frequency-modulated continuous-wave (FMCW) reader concept for locating backscatter radio-frequency identification (RFID) transponders. The proposed MIMO concept enables transmitter sided digital beamforming after a measurement has been executed. An algorithm is presented to decompose the MIMO response to match a digital beamforming input matrix. A 2.4-GHz experimental reconfigurable localization system based on FMCW technology was set up to demonstrate the concept. Multichannels are implemented to allow the possibility of testing the MIMO concept. A frequency-division multiplexing was implemented into an MIMO FMCW RFID reader and successful tested. Moreover, the system is able to locate multiple transponders simultaneously. Measurements confirm the functionality of the concept. The implementation of a digital beamforming algorithm shows the possibility of transmitting and receiving sided spatial filtering. Angle and distance precision were determined in an antenna chamber as well as in a harsh multipath environment. To help readers to compare the system with others, the mean absolute error of the position shows the system accuracy in a laboratory environment. Finally, an error analysis of the decomposition algorithm verified its robustness.