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.