[Paper Review] Measurement-driven Evaluation of All-digital Many-antenna Full-duplex Communication.

Evan Everett, Clayton Shepard+2 more|arXiv (Cornell University)|Aug 15, 2015

Full-Duplex Wireless Communications34 references3 citations

TL;DR

This paper proposes SoftNull, an all-digital full-duplex method for many-antenna systems that uses digital transmit beamforming to suppress self-interference, followed by digital cancellation of residual interference. Evaluated on a 72-element array, SoftNull significantly outperforms half-duplex in small cells with many-antenna configurations by efficiently managing dynamic range and enabling simultaneous uplink and downlink transmission.

ABSTRACT

In this paper, we present and study an all-digital method, called \softNull, to enable full-duplex in many-antenna systems. Unlike most designs that rely on analog cancelers to suppress self-interference, SoftNull relies on digital transmit beamforming to reduce self-interference. SoftNull does not attempt to perfectly null self-interference, but instead seeks to reduce self-interference sufficiently to prevent swamping the receiver's dynamic range. Residual self-interference is then cancelled digitally by the receiver. We evaluate the performance of SoftNull using measurements from a 72-element antenna array in both indoor and outdoor environments. We find that SoftNull can significantly outperform half-duplex for small cells operating in the many-antenna regime, where the number of antennas is many more than the number of users served simultaneously.

Motivation & Objective

• To address the challenge of self-interference in full-duplex many-antenna systems, particularly in small cells with high user density.
• To eliminate reliance on analog cancelers, which are complex and area-intensive in large-scale antenna arrays.
• To develop a scalable, all-digital solution that reduces self-interference to a level manageable by digital processing.
• To evaluate the performance of the proposed method in realistic indoor and outdoor propagation environments.
• To demonstrate that full-duplex operation can achieve higher spectral efficiency than half-duplex in many-antenna systems when self-interference is effectively managed.

Proposed method

• SoftNull employs digital transmit beamforming to shape the radiation pattern such that self-interference power is reduced at the receiver's array.
• Instead of perfect nulling, SoftNull aims to suppress self-interference sufficiently to prevent saturation of the receiver’s dynamic range.
• Residual self-interference is digitally canceled at the baseband receiver using adaptive filtering techniques.
• The method is implemented entirely in the digital domain, avoiding the need for analog cancelers or complex RF calibration.
• The system is evaluated using real-world channel measurements from a 72-element massive MIMO array in both indoor and outdoor environments.
• Performance is assessed by comparing spectral efficiency and user throughput against half-duplex operation under identical conditions.

Experimental results

Research questions

• RQ1 Can an all-digital beamforming approach effectively suppress self-interference in a many-antenna full-duplex system without analog cancellation?
• RQ2 How does the performance of SoftNull compare to half-duplex operation in small-cell environments with high-antenna-density arrays?
• RQ3 To what extent can digital beamforming reduce self-interference to a level where residual interference can be digitally canceled?
• RQ4 How does the system perform across diverse propagation environments, including indoor and outdoor scenarios?
• RQ5 What is the achievable spectral efficiency gain of full-duplex over half-duplex when using SoftNull in a many-antenna setup?

Key findings

• SoftNull successfully reduces self-interference to a level where the receiver’s dynamic range is not saturated, enabling reliable full-duplex operation.
• In both indoor and outdoor environments, SoftNull achieves significant spectral efficiency gains over half-duplex operation in small cells.
• The method outperforms half-duplex in scenarios with many-antenna arrays where the number of antennas greatly exceeds the number of simultaneous users.
• Residual self-interference after digital beamforming is effectively canceled using digital signal processing, confirming the feasibility of the hybrid approach.
• The all-digital implementation avoids the hardware complexity and calibration challenges of analog cancelers, enabling scalability.
• Measurement results from a 72-element array validate the robustness and performance of SoftNull across real propagation conditions.