Analysis of Transmit and Receive Implementation Losses in Full Duplex Wireless Transceivers

This work studies transmit (TX) and receive (RX) power losses in single antenna in-band full duplex transceiver architectures employing passive self-interference cancellation (SIC) filters. Three different RF front-end (RFFE) approaches to realize passive primary TX-RX isolation - a circulator, an electrical-balanced duplexer (EBD), and quadrature balanced power amplifiers (QBPA), are considered and analyzed. The analysis assumes the SIC stage is implemented as a dual delay-line FIR filter with adjustable delay and amplitude. Closed-form expressions are derived to describe the accuracy of this filter in approximating frequency-selective channels over a wide bandwidth. System-level simulations at the frequency range between 5 and 6 GHz demonstrate that all three RFFEs can provide more than 60 dB isolation over 80 MHz of bandwidth for antenna reflections as high as 14 dB. TX and RX losses vary depending on the RFFE architecture and the insertion loss of the FIR filter.