Antenna/RF design and analog self-interference cancellation

The main obstacle to full-duplex radios is self-interference (SI). To overcome SI, researchers have proposed several analog and digital domain self-interference cancellation (SIC) techniques. Digital cancellation has the following limitations: (1) It is only possible if the SI is sufficiently removed in the analog domain to fall within the dynamic range of an analog-to-digital converter (ADC). (2) It cannot mitigate the transmitter noise. Thus, analog cancellation plays an important role in a SIC scenario. This chapter provides an overview of current research activities on the analog cancellation scheme. Analog cancellation can be categorized into two classes-passive and active. In the passive analog cancellation, an RF component suppresses the SI. This can be implemented using a circulator or antenna separation. Leakages are cancelled by the active analog cancellation, which is based on a channel estimation of residual SI channel. The leakage from the passive cancellation can be matched by a signal generated from a tunable circuit or an auxiliary transmit chain. A key issue then in active analog cancellation is designing a circuit and optimization algorithm.