Pushing the limits of Full-duplex: Design and Real-time Implementation (1107.0607v1)

Abstract: Recent work has shown the feasibility of single-channel full-duplex wireless physical layer, allowing nodes to send and receive in the same frequency band at the same time. In this report, we first design and implement a real-time 64-subcarrier 10 MHz full-duplex OFDM physical layer, FD-PHY. The proposed FD-PHY not only allows synchronous full-duplex transmissions but also selective asynchronous full-duplex modes. Further, we show that in over-the-air experiments using optimal antenna placement on actual devices, the self-interference can be suppressed upto 80dB, which is 10dB more than prior reported results. Then we propose a full-duplex MAC protocol, FD-MAC, which builds on IEEE 802.11 with three new mechanisms -- shared random backoff, header snooping and virtual backoffs. The new mechanisms allow FD-MAC to discover and exploit full-duplex opportunities in a distributed manner. Our over-the-air tests show over 70% throughput gains from using full-duplex over half-duplex in realistically used cases.

• The paper introduces a 64-subcarrier FD-PHY that achieves up to 80 dB self-interference cancellation, marking a significant advancement in full-duplex communication.
• The paper develops an innovative FD-MAC protocol featuring shared random backoff and header snooping, which delivers over 70% throughput improvements in real-world scenarios.
• The paper demonstrates the feasibility of both synchronous and selective asynchronous full-duplex operations, paving the way for practical and scalable wireless networks.

Design and Implementation of Full-Duplex Systems: A Detailed Exploration

The paper, "Pushing the limits of Full-duplex: Design and Real-time Implementation" by Achaleshwar Sahai, Gaurav Patel, and Ashutosh Sabharwal, presents a comprehensive paper on full-duplex wireless communication systems. This work explores both the Full-Duplex Physical Layer (FD-PHY) and Full-Duplex Medium Access Control (FD-MAC) protocols. The focus is on the design, real-time implementation, and performance evaluation of these systems on a Wireless Open-Access Research Platform (WARP)-based testbed. The results showcased offer promising insights into the feasibility and performance benefits of full-duplex systems over traditional half-duplex systems.

Overview of Full-Duplex Design and Implementation

The key contribution of the research is the development of a 64-subcarrier, 10 MHz full-duplex OFDM physical layer termed FD-PHY. The innovation doesn't end with mere synchronous full-duplex communication but extends to enabling selective asynchronous full-duplex modes. In comprehensive over-the-air experiments, the authors demonstrated a self-interference cancellation of up to 80 dB, which is unprecedented and significantly advances previous works that capped at 70 dB. This advancement is primarily attributed to optimal antenna placement on devices and innovative interference cancellation techniques.

Full-Duplex Medium Access Control (FD-MAC)

Building upon the physical layer achievements, the authors propose FD-MAC, a full-duplex MAC protocol tailored for infrastructure-based WiFi-like networks. This protocol innovatively integrates three critical mechanisms: shared random backoff, header snooping, and virtual backoffs. The FD-MAC strategy is grounded in the IEEE 802.11 framework and leverages novel duplexing opportunities in distributed environments. The reported results manifest throughput gains of over 70% in realistic usage scenarios when shifting from half-duplex to full-duplex systems.

Technical Contributions and Results

1. FD-PHY Implementation: The FD-PHY layer effectively addresses the chief challenge of self-interference in full-duplex communication by utilizing subcarrier-based active analog cancellation. This technique ensures compatibility with any OFDM PHY, extending the potential applicability across a range of bandwidths and configurations.
2. Self-Interference Suppression: The paper's experimental work on antenna placement, particularly on mobile devices like tablets, finds that device-induced attenuation combined with analog cancellation can achieve 80 dB self-interference suppression. This milestone does not necessitate additional baseband cancellation, marking a significant leap towards practical deployment of full-duplex communication.
3. Asynchronous Full-Duplex Operations: While conventional wisdom has limited full-duplex scenarios to synchronized operations, this work explores asynchronous capabilities, albeit with some trade-offs like a 3 dB degradation in bit error rates in certain asynchronous operations.
4. FD-MAC Mechanisms: The innovative MAC layer mechanisms like shared random backoff and virtual contention resolution balance the full-duplex capabilities with fair access for all nodes. These facilitate near-seamless transitions between full and half-duplex modes, maintaining system efficiency and fairness.

Implications and Future Directions

The research substantiates the feasibility of deploying real-time full-duplex systems with significant throughput gains, paving the way for more efficient wireless networks. By resolving major technical hurdles like self-interference cancellation and proposing robust MAC protocols, this work lays foundational stones for future exploration in the domain.

Theoretical implications include potential adaptations of these principles in refining MIMO systems or integrating these strategies into emerging 5G technologies. Practically, real-world deployment in mobile networks could see vast improvements, particularly in urban environments burdened by spectrum congestion.

Future developments might focus on refining asynchronous capabilities and further minimizing BER impacts, exploring more sophisticated adaptive algorithms for MAC enhancements, and optimizing device-level implementations for broader operability.

This paper delivers substantive progress in the domain of full-duplex communication, showcasing potential transitions from theoretical models to viable, high-performing real-world systems. The use of real-time testbeds like WARP substantiates its findings, offering a tangible roadmap for future wireless communication innovations.