On the Analog Self-interference Cancellation for In-band Full-duplex Radio with Compensation for Inherent Frequency Response

In-band full-duplex (IBFD) has the potential to double spectrum efficiency by simultaneous transmission and reception at the same frequency. Meanwhile, simultaneous operation of the transmitter and receiver induces significant self-interference (SI) and degrades communication quality. In general, in the analog domain, the antenna isolation and analog cancellation circuit reduces the SI signal level and facilitates the SI cancellation in the digital domain. For the stable SI cancellation, a dedicated analog cancellation circuit is implemented in the analog radio frequency (RF) front-end circuit according to the characteristics of the antenna and analog circuit. The author has prototyped multi-band analog RF front-end for IBFD based on the super-heterodyne architecture. An analog SI cancellation circuit is implemented in an intermediate frequency (IF) circuit to support various frequency bands by connecting different analog RF front-end circuits and antennas according to the operation frequency. However, the frequency response of the antenna and analog circuit vary depending on the frequency band and needs to be flexibly compensated by the SI cancellation circuit. This paper describes a prototype multi-band analog RF front-end that can support various frequency bands with the compensation for the frequency response. Then, the SI cancellation performance is evaluated by connecting a prototype two-element integrated small antenna. From the result, more than 65 dB SI cancellation is obtained in the analog domain for the transmission signal with a 20 MHz bandwidth at 3.85 GHz.