Double Balanced Feed Network for the Self-Interference Cancellation in Full Duplex Communication System

Recently, there have been hot issue and many research activities on the In-band full duplex (IBFD) for the spectral efficiency improvement in wireless and mobile communication system. In IBFD system, it is very important to cancel self-interference (SI). Especially SI cancellation of RF-stage is important because high power SI causes the saturation of ADC and the desired signal from the transmitter cannot be processed to recover the information. In this paper, we propose an RF cancellation method using the double balanced feed network (BFN) for the IBFD system, which is the main contribution of this paper. So, at first we introduce the conventional RF cancellation using BFN. Next we will show the proposed RF cancellation using double BFN. And then, we evaluate performance of the proposed circuits. As results of simulation, we can confirm that conventional RF cancellation using single BFN has 45-47 dB of SI cancellation. However, we can confirm that the proposed RF cancellation using double BFN has 72 dB of SI cancellation. This performance of SI cancellation is around 25 dB higher than conventional RF cancellation using single BFN.