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.

翻译：本文提出并展示了无线基础设施网络中支持超可靠通信(URC)的实时原型的PHY级设计,该原型在无线基础设施网络中支持超可靠通信(URC)的实时原型设计。设计将OFDMA(OFDMA)作为实现无线基础设施网络的一种手段。与时司多存(TDMA)相比,ODMA(DMA)将电力输送到一个较窄的带宽,从而产生更有效的SNR。与频率司多存(FDMA)相比,ODMA(ODMA)的频谱效率较高。虽然ODMA(ODA)已在802.11ax中引入,但目的是增加频谱使用的灵活性。我们可靠的ODMA(ODMA)设计被称为RODMA(ODMA)设计,是一个清洁过时的设计,其单一的目标是交付超易燃的包。 ROFA(DA)解决了一系列关键挑战,以确保超可靠性:(1) 下行协调的时间同步时间同步机制,使用户的上下调传输同步,而最多为SUFO(S-R-RFI)的交付(OFADR-RFA(W)在S(ODFADFA(W)之前,时,可以降低运行)运行(O-R-R-R-R-R-R-R-R-R-R-R-R-RDFA-R-R)的交付)使用一个最低运行(RDFA(R)系统之间,可以降低一次。