Keisuke Terasaki

Use of load modulation for interference control between primary and secondary systems

Controlling interference from the secondary system to the receiver of the primary system is important issues when the secondary system uses the same frequency band in the area of television broadcast system. The reason includes that the secondary system cannot know the interference channel to the primary receiver, which does not have a transmitter. In this paper, we propose the interference control method between primary receiver and secondary system, where a load modulation scheme is introduced to the primary receiver. In this method, the signal from the transmitter station is scattered by switching load impedance at the primary receiver. Also, the secondary system estimates the reflected wave from receiver and estimates the interference suppression weights. Based on the simulation, it is shown that the proposed method is effective in controlling interference between primary receiver and secondary system.

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).

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.