Demonstration of Self-Interference Antenna Suppression and RF Cancellation for Full Duplex MIMO Communications

This paper presents methods to design RF front-ends of the MIMO in-band full duplex radio (FDR). The RF front-end reduces the level of the self-interference(SI) using an passive suppression in the antenna domain and an active cancellation in the RF circuit. Three possible methods for the antenna suppression is introduced for M×M MIMO applications, which are separation, circulator, and dual-polarized antenna. In this demonstration, the antenna separation and the reflection-controlled circulator are used for the 2×2 MIMO FDR. A RF board for the active cancellation is designed to make the identical signal with residual SI, which consists of four self-interference reference generators subtracting SIs of two transmitters from two receivers. The reference generators are composed with three taps which are composed of attenuators, phase shifters and true time delays, each, to achieve the cancellation bandwidth of 100 MHz at 3.55 GHz. Experimental results show the passive antenna suppression of >30 dB and total SI isolation with the active cancellation of 60 dB over the bandwidth.