ROFA: An OFDMA system for Ultra-Reliable Wireless Industrial Networking

TL;DR

This paper introduces ROFA, a novel OFDMA-based PHY design for ultra-reliable wireless industrial networks, demonstrating significant power efficiency improvements and synchronization techniques on SDR hardware.

Contribution

ROFA presents a new PHY-layer design with synchronization and precoding mechanisms specifically optimized for ultra-reliable wireless communication in industrial settings.

Findings

ROFA achieves PER<10^-5 with 11.5dB less power than OFDM-TDMA.

The prototype demonstrates real-time ultra-reliable packet delivery.

Synchronization methods effectively reduce timing offsets and CFOs.

Abstract

This paper proposes and demonstrates a PHY-layer design of a real-time prototype that supports Ultra-Reliable Communication (URC) in wireless infrastructure networks. The design makes use of Orthogonal Frequency Division Multiple Access (OFDMA) as a means to achieve URC. Compared with Time-Division Multiple Access (TDMA), OFDMA concentrates the transmit power to a narrower bandwidth, resulting in higher effective SNR. Compared with Frequency-Division Multiple Access (FDMA), OFDMA has higher spectrum efficiency thanks to the smaller subcarrier spacing. Although OFDMA has been introduced in 802.11ax, the purpose was to add flexibility in spectrum usage. Our Reliable OFDMA design, referred to as ROFA, is a clean-slate design with a single goal of ultra-reliable packet delivery. ROFA solves a number of key challenges to ensure the ultra-reliability: (1) a downlink-coordinated time-synchronization mechanism to synchronize the uplink transmission of users, with at most $0.1us$ timing offset; (2) an "STF-free" packet reception synchronization method that makes use of the property of synchronous systems to avoid packet misdetection; and (3) an uplink precoding mechanism to reduce the CFOs between users and the AP to a negligible level. We implemented ROFA on the Universal Software Radio Peripheral (USRP) SDR platform with real-time signal processing. Extensive experimental results show that ROFA can achieve ultra-reliable packet delivery ($PER<10^5$) with $11.5dB$ less transmit power compared with OFDM-TDMA when they use $3$ and $52$ subcarriers respectively.