A Taylor series approximation technique for self-interference cancellation in full-duplex radios

Full-duplex (FD) wireless communication is gaining increasing attention of the wireless industry because of the potential doubling of spectral efficiency. Radio design of an FD transceiver is a key aspect to its realization. The major impediment in realizing an FD radio is the self interference (SI). The received self interference is a filtered version of the transmitted signal, the filter (SI filter) being caused by the multiple transmit paths through the circuit board (or silicon substrate) and the wireless channel. Current techniques for suppressing SI rely on mimicking the SI filter partly in the RF domain (using multiple length RF traces on a PCB) and partly in the digital domain by adaptive techniques. This paper proposes a novel SI cancellation technique, based on Taylor series expansion of the delayed signal, that results in linearizing the delayed self-interference component of the transmitted signal. Linearization not only aids the practicality of analog cancellation by reducing the form factor, but also results in a simple SI filter model in the digital domain. In this paper, in addition to deriving the generic form of the SI filter, we provide experimental evidence for the same.