Balanced RF-circuit based self-interference cancellation for full duplex communications

Self-interference cancellation in the analog domain is critical to achieve full duplex wireless communications. However, the capability of analog self-interference cancellation is not fully explored. To this end, a new approach of analog self-interference cancellation is developed in this paper. More specifically, a balanced RF frond-end circuit is designed to allow a signal to propagate through symmetrical paths such that: (1) transmit signals taking different paths to arrive at the receiver can be cancelled; (2) receive signals from different paths are simply added at the receiver. As a result, self-interference is gracefully cancelled without impacting the normal operation of transmission and reception. Furthermore, this new approach includes several distinct features. First, it can achieve high analog self-interference cancellation. Implementation and experiments are conducted to validate the new approach, and experimental results show that it can achieve more than 65 dB of self-interference cancellation over 5 MHz bandwidth and 52 dB cancellation over 100 MHz bandwidth with a flat frequency response. Second, the new approach can be easily integrated with existing analog self-interference cancellation schemes to deliver much higher self-interference cancellation. Third, it can be easily extended to MIMO communications in a scalable way. Experiments show that our proposed antenna cancellation schemes are sufficient to achieve the goal of analog self-interference cancellation for MIMO communications.