SUMMARY
This paper presents a novel passive repeater that achieves enhanced Multiple-Input-Multiple-Output (MIMO) communication between two isolated terminals. The novel aspect of this work is an avoidance of the key-hole effect, which is normally caused by a repeater since all of the signal goes through the same point. Moreover, our idea uses electrical control, which is simply realized by only varactor diodes on the antennas, and this idea provides fast and low-cost control of the MIMO channel. This configuration allows the passive repeater to control the MIMO channel. MIMO channel capacity is maximized by controlling all repeater elements individually. The effectiveness of the passive repeater in enhancing MIMO channel capacity is verified by experiments. First of all, we obtained propagation data from field experiment, and propagation characteristics were evaluated using equations. The results show that the 10% value of MIMO channel capacity can be improved by 2.92 bits/s/Hz in an indoor propagation environment, which well confirms the effectiveness of the proposed method.