2 × 2 MIMO In-Band Full-Duplex Radio Front-End With Delay Shapable Single-Tap RF Cancellers

This paper presents the experimental results of self-interference cancellation for a
$2\times 2$
multiple input multiple output (MIMO) in-band full-duplex radio front-end. The proposed radio-frequency (RF) front-end consists of two rat-race couplers and a four antennas network for passive suppression, and four self-interference active cancellation. The canceller generates an identical signal to the residual self-interference signal, and then subtracts it from the received signal. The RF canceller has a single signal path(tap) composed of attenuator, phase shifter, and time delay circuit which all are variable. To broaden the bandwidth of active cancellation, the time delay circuit is developed to have a wide delay variation range and to control the shape of the delay over the frequency. The experimental results demonstrate the 50-dB self-interference cancellation over the bandwidth of 90 MHz at the center frequency of 2.53 GHz.