A Code-Domain, In-Band, Full-Duplex Wireless Communication Link with Greater Than 100-dB Rejection

This article presents a CMOS-based, code-domain (CD), full-duplex (FD) transceiver operating in a link at 1 GHz. The CD FD link rejects in-band transmitter self-interference (TX SI) by more than 100 dB through a combination of pseudo-noise (PN) code orthogonality, circulator, and digital cancellation algorithms. A nonmagnetic CMOS circulator based on switched transmission lines is used as an antenna interface with >40-dB maximum rejection. Then, transmitter (TX) and receiver (RX) modulators spread the TX SI and correlate the desired RX signal in the RF domain. Orthogonality between the PN codes allows an additional >40-dB maximum rejection relaxing the FD transceiver linearity requirements. Finally, digital self-interference cancellation (SIC) eliminates any residual TX SI in the digital domain using a least mean squares (LMS) estimation for the SI channel based on a nonlinear truncated Volterra series model. The digital SIC can have almost 40 dB of rejection depending on the SI power level. An implemented FD node leverages these techniques to achieve an overall rejection that is around 104 dB bringing the TX signal from 20 dBm to the noise floor of the RX at -85 dBm.