What are the challenges in implementing full-duplex wireless communication?

Full-duplex (simultaneous transmit and receive on same frequency) doubles spectral efficiency but faces severe self-interference. Self-interference cancellation (SIC) required in three domains: Antenna domain: Isolation through antenna separation, polarization, and directional patterns; ~40-50 dB achievable. Analog domain: RF canceller samples Tx signal, adjusts delay/amplitude, and subtracts; handles PA nonlinearity; ~40-50 dB. Digital domain: Adaptive filters cancel residual interference; ~30-40 dB. Total ~110-130 dB cancellation needed (Tx power vs noise floor gap). Challenges include: Tx signal dynamics across bandwidth, PA nonlinearity modeling, ADC dynamic range requirements, phase noise, and real-time adaptation. Applications include relays, small cells, and radar. Full-duplex gains diminished by increased network interference in cellular deployments.