Full-Duplex Mobile Device - Pushing the Limits (1410.3191v3)

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.

• The paper demonstrates a novel full-duplex design by integrating adaptive RF cancellation with digital nonlinear cancellation to effectively mitigate self-interference.
• It introduces a multi-tap RF cancellation mechanism that achieves over 40 dB attenuation across an 80 MHz bandwidth using a closed-loop LMS algorithm.
• Lab experiments validate the approach by reducing interference to the noise floor, paving the way for practical 5G mobile full-duplex implementations.

Overview of "Full-Duplex Mobile Device -- Pushing the Limits"

In the domain of wireless communications, the potential of full-duplex technology to enhance spectral efficiency is widely acknowledged. The paper "Full-Duplex Mobile Device -- Pushing the Limits" explores the technical challenges and solutions associated with implementing full-duplex operation in mobile devices. Unlike traditional systems that rely on half-duplex communication, this work focuses on facilitating simultaneous transmission and reception over the same frequency band, thus doubling the effective data rate without additional bandwidth.

Key Contributions

The primary challenge addressed in this work is the significant self-interference (SI) generated in full-duplex systems, particularly in mobile-scale devices. The authors propose an architecture based on shared-antenna transceiver design coupled with advanced self-interference cancellation mechanisms. Key elements of their approach include:

1. Adaptive RF Cancellation: The paper introduces a self-adaptive multi-tap RF cancellation architecture. This wideband RF canceller, demonstrated to provide more than 40 dB of interference cancellation over an 80 MHz bandwidth, employs a closed-loop LMS-based adaptation mechanism to dynamically adjust to time-varying SI channel characteristics. This ensures robust performance in highly dynamic mobile environments.
2. Digital Baseband Nonlinear Cancellation: Given the prevalent nonlinearities in the transmitter power amplifier, especially in mobile devices using cost-effective RF components, the authors emphasize the necessity of nonlinear DSP techniques. By implementing a parallel Hammerstein model, their digital cancellation method compensates for transmitter-induced nonlinearities, further reducing SI to the noise floor level.
3. Real-world Demonstration: Extensive lab measurements using a prototype implementation validate the proposed methodology. The results highlight the efficacy of combining sophisticated RF and digital cancellation techniques, showcasing their practical viability in mobile applications. Specifically, the integrated system demonstrates an aggregate self-interference attenuation reaching the receiver noise floor.

Implications and Future Directions

The work has several implications for the design and deployment of mobile full-duplex systems in future wireless networks such as 5G and beyond. The advancement of efficient interference cancellation directly impacts achievable network capacity and throughput. The rigorous demonstration of cancelling SI with a nonlinear digital framework is particularly promising, as it suggests a pathway toward widespread deployment using commercially viable components.

From a theoretical standpoint, the integration of adaptive learning algorithms into hardware designs paves the way for dynamic system adaptation. The self-calibration and self-healing characteristics discussed are crucial for real-world deployments, where environmental factors are unpredictable.

Future research could focus on scaling these solutions to accommodate higher power levels and further increase bandwidth while maintaining energy efficiency. Additionally, exploring the integration of machine learning techniques for further optimization of adaptive cancellation systems might provide new insights and performance enhancements.

In conclusion, the paper makes significant advancements towards realizing mobile full-duplex technology. Though challenges remain, particularly in sustaining performance at larger scales and higher powers, the solutions proposed by the authors mark a substantial step forward in overcoming practical deployment barriers for full-duplex mobile devices.