Prototype of Analog Self-interference Cancellation based on Super-heterodyne Architecture for In-band Full-duplex Cellular System

IBFD (In-Band Full-Duplex) cellular system is one of the promising approaches to enhance the efficiency of spectrum utilization. Meanwhile, SI (Self-Interference) induced by simultaneous transmission and reception impairs receiver performance, and it is important to reduce or isolate SI by any means. In general, SI cancellation circuit in the analog signal domain is implemented close to the final stage of the RF (Radio Frequency) front-end. However, this architecture requires a dedicated analog cancellation circuit for different frequency bands and impairs the extensibility with regard to the operation frequency. In this paper, we propose an analog SI cancellation circuit based on super-heterodyne architecture. Once an analog SI cancellation is implemented in the IF (Intermediate Frequency) circuit, the same architecture can be used for various frequency bands without an individual dedicated circuit design. We also prototype an RF front-end with our proposal and evaluate the performance of analog cancellation. As a result, we achieve a 35 dB SI cancellation at 4.5 GHz band with a 20 MHz LTE-based transmission signal.