Full-Duplex Mobile Device - Pushing the Limits

TL;DR

This paper demonstrates the feasibility of full-duplex mobile devices by combining adaptive RF cancellation and nonlinear digital processing, achieving over 40 dB of self-interference suppression in a practical implementation.

Contribution

It introduces novel adaptive nonlinear DSP methods and a comprehensive RF cancellation approach for mobile full-duplex devices, validated through real-world measurements.

Findings

Achieved over 40 dB RF cancellation over 80 MHz bandwidth

Demonstrated effective self-healing against channel variations

Residual interference reduced to noise floor with nonlinear digital cancellation

Abstract

In this article, we address the challenges of transmitter-receiver isolation in \emph{mobile full-duplex devices}, building on shared-antenna based transceiver architecture. Firstly, self-adaptive analog RF cancellation circuitry is required, since the capability to track time-varying self-interference coupling characteristics is of utmost importance in mobile devices. In addition, novel adaptive nonlinear DSP methods are also required for final self-interference suppression at digital baseband, since mobile-scale devices typically operate under highly nonlinear low-cost RF components. In addition to describing above kind of advanced circuit and signal processing solutions, comprehensive RF measurement results from a complete demonstrator implementation are also provided, evidencing beyond 40~dB of active RF cancellation over an 80 MHz waveform bandwidth with a highly nonlinear transmitter power amplifier. Measured examples also demonstrate the good self-healing characteristics of the developed control loop against fast changes in the coupling channel. Furthermore, when complemented with nonlinear digital cancellation processing, the residual self-interference level is pushed down to the noise floor of the demonstration system, despite the harsh nonlinear nature of the self-interference. These findings indicate that deploying the full-duplex principle can indeed be feasible also in mobile devices, and thus be one potential technology in, e.g., 5G and beyond radio systems.