Digitally assisted RF filter Self Interference cancellation system

In FDD radios, the problem of Self Interference, where the transmitter´s own noise and distortion can desensitize the receiver is traditionally solved by RF filtering. For bands with narrow duplex spacing, this selectivity comes at the cost of bulky filters and insertion loss with an associated power loss in the front end. Moreover, with the drive towards, cheaper, smaller, integrated duplexers and ultimately towards Full Duplex systems, conventional RF filtering is becoming less viable. In this paper, we described a digitally assisted RF filter system that addresses the isolation problem by means of a novel, sub band, self interference cancellation system. Sub band adaptation allows the canceller train in the presence of both blockers and on-channel wanted signals. Lab bench proof-of-concept results showing desense levels better than 0.1dB and cancellations gains > 35dB are presented for a 3GPP Band 1 cellular base station radio incorporating a ceramic duplexer with ~55dB isolation.