Extension of an SDR UHF RFID Testbed for MIMO and Monostatic Time of Flight Based Ranging

This paper presents measurement results of a recently introduced time of flight (ToF) ranging method for backscattering radio frequency identification (RFID) tags. The measurements are done with off-the-shelf EPC Class1 Gen2 tags, an automated tag positioner, a modified software defined radio (SDR) platform as RFID reader, and a PC post-processing the ranging results. The structure of the multiple-input multiple-output (MIMO) enabled testbed is shown. A custom FPGA implementation was made to have access to the full potential of the used SDR platform. Furthermore, the synchronization of multiple SDRs to enable MIMO operation is discussed. The ranging error and its variance are measured and discussed for a monostatic ranging enabled RFID reader, using two USRPs. The results are compared to a bistatic setup which uses one USRP only. The underlying ranging principle is successfully verified, and its practical performance limitations, resulting from multipath propagation, are shown.