Digitally Controlled Analog Wideband Interference Cancellation for In-Device Spectrum Sharing and Aggregation

In this paper, we present a feasibility of wideband analog self-interference cancellation with a newly proposed digitally controlled analog adaptive filter. We analyze the key existing issues and concerns in analog interference cancellation and propose novel solutions to cancel the self-interference with a simple 1-tap cancellation circuit. The proposed solution conducts a blind estimation of optimal analog filter coefficients in the digital domain without requiring a pilot signal. We present an end-to-end system analysis and 1-tap adaptive filter circuit analysis to show the feasibility of wideband cancellation. We then propose a few novel blind coefficient estimation algorithms and show their cancellation performance by both simulations and measurements from an actual prototype. The results suggest that our self-interference approach enables the simultaneous operation of the licensed and unlicensed technologies in the adjacent spectrum within a single device, which, in turn, facilitates graceful spectrum sharing and bandwidth aggregation between the licensed and unlicensed technologies.