Evaluating impact of tag element spacing on bit-error-rate performance using passive MIMO testbed

In this study, we experimentally assessed the impact of tag element spacing on Bit-Error-Rate (BER) performance of passive Multiple-Input Multiple-Output (MIMO), which uses multiple antennas at both Radio Frequency Identification (RFID) tag and its reader to improve data-rate of the backscattering load modulation. Since a small RFID tag needs miniaturized multiple antennas, the antenna element spacing must be narrow. However, no studies have evaluated the effect of the element spacing in passive MIMO. This paper experimentally reveals the relationship between the BER and the element spacing using own-developed passive MIMO testbed. From the experimental result, it is shown that the passive MIMO with 0.2-wavelength spacing yields feasible BER (<; 10^-2) at 1 m communication distance even with realistic noise power (> -90 dBm).