Full-duplex Radio with Two Receivers for Self-Interference Cancellation

The design and implementation of a full-duplex radio system capable of real-time analogue self-interference cancellation at radio frequency and baseband stages are presented. The system consists of a dual-patch three-port orthogonally linear polarised antenna system (without a circulator/duplexer), a homodyne dual receiver, and a differential amplifier at the baseband. The interference outputs from the two receivers are equalised using a fixed attenuator and when they are passed through the differential amplifier at the baseband they are effectively cancelled. For the system reported the antenna system provides 45.1 dB isolation between transmit and receive ports over 60 MHz bandwidth centred at the operating frequency of 3.2 GHz. Interference cancellation achieved by the differential amplifier at the baseband reduces the total selfinterference to 81.5 dB minimum at −5.6 dBm transmit power. Using the proposed system, the recovery of two different types of baseband signals in real time is demonstrated while the surrounding is multipath enabled. Since the self-interference at baseband is removed by the differential amplifier instead of a complex digital signal processing unit, it makes the proposed system suitable for broad-band millimetre-wave full-duplex transceivers where the use of analogue/digital converter is not an option.