Design and Characterization of a Full-duplex Multi-antenna System for WiFi networks (1210.1639v2)

Abstract: In this paper, we present an experimental and simulation based study to evaluate the use of full-duplex as a mode in practical IEEE 802.11 networks. To enable the study, we designed a 20 MHz multi-antenna OFDM full-duplex physical layer and a full-duplex capable MAC protocol which is backward compatible with current 802.11. Our extensive over-the-air experiments, simulations and analysis demonstrate the following two results. First, the use of multiple antennas at the physical layer leads to a higher ergodic throughput than its hardware-equivalent multi-antenna half-duplex counterparts, for SNRs above the median SNR encountered in practical WiFi deployments. Second, the proposed MAC translates the physical layer rate gain into near doubling of throughput for multi-node single-AP networks. The two combined results allow us to conclude that there are potentially significant benefits gained from including a full-duplex mode in future WiFi standards.

• The paper demonstrates a multi-antenna full-duplex PHY that significantly improves throughput using self-interference cancellation up to 100 dB.
• It employs passive suppression along with active analog and digital cancellation techniques to optimize performance in standard WiFi SNR ranges.
• The adapted MAC protocol effectively translates PHY gains into nearly double throughput for single-access point networks while ensuring backward compatibility.

Full-Duplex Multi-Antenna System for WiFi Networks: An Overview

The paper presents a comprehensive paper evaluating the feasibility of implementing full-duplex communication in practical IEEE 802.11, or WiFi, networks through a multi-antenna system. It builds a case for integrating a full-duplex mode into future WiFi standards by designing and assessing both physical layer (PHY) and medium access control (MAC) protocols compatible with existing 802.11 networks.

Key Contributions

The research yields two significant findings:

1. Enhanced Throughput: The multi-antenna full-duplex PHY achieves higher ergodic throughput than its half-duplex counterparts for signal-to-noise ratios (SNRs) prevalent in indoor WiFi environments.
2. MAC Efficiency: The proposed MAC layer successfully converts PHY layer rate gains into nearly double the throughput for single-access point (single-AP) networks.

Design and Implementation

PHY Layer Design

The paper introduces a 20 MHz multi-antenna orthogonal frequency-division multiplexing (OFDM) full-duplex system, employing various self-interference cancellation strategies:

• Passive Suppression: Effective antenna placement to reduce self-interference.
• Active Analog Cancellation: Subcarrier-by-subcarrier cancellation is applied to maintain high cancellation precision across frequency-selective self-interference channels.
• Digital Cancellation: Further reduction of self-interference through baseband digital processing.

A notable achievement is the self-interference cancellation reaching a median of 85 dB, with the documentation of up to 100 dB — the highest reported thus far in similar systems.

MAC Layer Design

The MAC layer remains largely unchanged from standard 802.11 to ensure backward compatibility but adapts to support full-duplex communication. Innovations include handling collisions during full-duplex exchanges and ACK management to cope with asymmetric data packet sizes in bidirectional transfers.

Numerical Results and Analysis

Substantial experimental validation shows:

• Passive Suppression Impact: Device-based antenna placement improved cancellation by approximately 10-15 dB, indicating a pragmatic path toward reducing self-interference.
• Full-Duplex Throughput: Full-duplex systems often outperform half-duplex systems in common WiFi SNR ranges (~20-30 dB), showcasing potential real-world performance advantages.
• MAC Protocol Coexistence: The full-duplex MAC improves overall throughput significantly over legacy systems while maintaining fairness across full- and half-duplex nodes.

Implications and Future Work

The implications of this work are multifold:

• Practical Deployment: Full-duplex WiFi can improve spectral efficiency and network capacity, primarily in crowded indoor environments.
• Standardization Potential: By demonstrating backward compatibility and practical gains, this research paves the way for incorporating full-duplex into future WiFi standards.
• Research Directions: Further exploration is warranted to optimize full-duplex designs across various antenna configurations and environmental conditions, including outdoor scenarios.

In conclusion, this paper presents a substantial advancement in realizing practical full-duplex WiFi systems, illustrating tangible benefits that might propel future developments in wireless communications technology.