Electrical balance duplexing for small form factor realization of in-band full duplex

Transceiver architectures utilizing various self-interference suppression techniques have enabled simultaneous transmission and reception at the same frequency. This full-duplex wireless offers the potential for a doubling of spectral efficiency; however, the requirement for high transmit-to-receive isolation presents formidable challenges for the designers of full duplex transceivers. Electrical balance in hybrid junctions has been shown to provide high transmit- to-receive isolation over significant bandwidths. Electrical balance duplexers require just one antenna, and can be implemented on-chip, making this an attractive technology for small form factor devices. However, the transmit-to-receive isolation is sensitive to antenna impedance variation in both the frequency domain and time domain, limiting the isolation bandwidth and requiring dynamic adaptation. Various contributions concerning the implementation and performance of electrical balance duplexers are reviewed and compared, and novel measurements and simulations are presented. Results demonstrate the degradation in duplexer isolation due to imperfect system adaptation in user interaction scenarios, and requirements for the duplexer adaptation system are discussed.