An in-band full-duplex transceiver prototype with an in-system automated tuning for RF self-interference cancellation

This paper presents a transceiver prototype capable of in-band full duplex communication. Apart from a conventional transceiver and antenna, this prototype relies on a tunable electrical balance duplexer to minimize the in-band self-interference at RF. Such duplexer however requires continuous-time tuning to ensure accurate impedance balancing with the antenna across different environmental conditions. An automatic tuning algorithm is presented which tracks antenna impedance variations and tunes the duplexer accordingly. This tuning operates on a standard compliant training sequence to minimize the overhead on the communication system. The implemented tuning mechanism does not require any additional RF or analog hardware, and maximally re-uses the digital resources of a conventional baseband processor. The full duplex prototype was validated in a wireless link for IEEE802.11 channels in the 2.4GHz ISM band, in which the error vector magnitude improves by 15dB as the RF self-interference cancellation increased from 25dB to 45dB.