Self-interference cancellation

Self-interference cancellation (SIC) is a signal processing technique that enables a radio transceiver to simultaneously transmit and receive on a single channel, a pair of partially-overlapping channels, or any pair of channels in the same frequency band. When used to allow simultaneous transmission and reception on the same frequency, sometimes referred to as “in-band full-duplex” or “simultaneous transmit and receive,” SIC effectively doubles spectral efficiency. SIC also enables devices and platforms containing two radios that use the same frequency band to operate both radios simultaneously. Self-interference cancellation has applications in mobile networks, the unlicensed bands, cable TV, mesh networks, the military, and public safety. In-band full-duplex has advantages over conventional duplexing schemes. A frequency division duplexing (FDD) system transmits and receives at the same time by using two (usually widely separated) channels in the same frequency band. In-band full-duplex performs the same function using half of the spectrum resources. A time division duplexing (TDD) system operates half-duplex on a single channel, creating the illusion of full-duplex communication by rapidly switching back-and-forth between transmit and receive. In-band full-duplex radios achieve twice the throughput using the same spectrum resources. A radio transceiver cannot cancel out its own transmit signal based solely on knowledge of what information is being sent and how the transmit signal is constructed. The signal that the receiver sees is not entirely predictable. The signal that appears at the receiver is subject to varying delays. It consists of a combination of leakage (the signal traveling directly from the transmitter to the receiver) and local reflections. In addition, transmitter components (such as mixers and power amplifiers) introduce non-linearities that generate harmonics and noise. These distortions must be sampled at the output of the transmitter.