Experimental study on the passive MIMO transmission

In the passive Multiple-Input Multiple-Output (MIMO) transmission scheme, load modulation is applied to the multi-antenna, and a number of signals can be transmitted in parallel. The tag has the multi-antenna terminated by variable reactances. The varactor diodes are used as the variable reactance element. We determine the set of the bias voltage of the varactor diodes so as that its reflection coefficients corresponding to the bias voltages are to be distant each other in complex number plane in the range of the varactor diode can take. This paper describes the characteristics of the 2 × 2 passive MIMO transmission in an actual indoor environment. Finally, we clarify the passive MIMO transmission with multi-level modulation can achieve high-speed data transmission without using the transmitter at the tag antenna.