A Taylor Series Approximation of Self-Interference Channel in Full-Duplex Radios

The fundamental problem in the design of a fullduplex radio is the cancellation of the self-interference (SI) signal generated by the transmitter. Current techniques for suppressing SI rely on generating a copy of the SI signal and subtracting it partly in the radio frequency (RF) and digital domains. A critical step in replicating the self-interference is the estimation of the multipath channel through which the transmitted signal propagates to the antenna. Since there is no prior model on the number of multipath reflections, current techniques assume a tap delay line filter (in the RF and digital domain) with a large number of taps, and estimate the taps in the analog and the digital domain. In this paper, using a linearization technique, we show that the self-interference channel in an indoor environment can be effectively modeled as H(f ) = C
₀
- C
₁
f in the frequency domain. Thus, the effective self-interference channel can be represented by two parameters C
₀
and C
₁
, irrespective of the multipath environment. We also provide experimental evidence to verify the above channel model and propose novel low-complexity designs for self-interference cancellation.