The latency gap between wired and wireless networks poses a challenge in the adoption of wireless technologies in latency-sensitive scenarios. The gap is especially notable in multi-hop communication typical for industrial sensor networks and robotic swarms. The main reason behind it is that commonly used wireless protocols rely on store-and-forward routing and costly overhead procedures to avoid interference. This article introduces RF-Zero-Wire, an RF-based symbol-synchronous communication protocol. Instead of relaying the whole frame per hop in a store-and-forward manner, nodes concurrently relay the frame symbol by symbol, without the need for tight time synchronization. Based on data collected in real-world experiments, we reveal that the inevitable carrier frequency offsets (CFOs) introduced by imperfect crystal oscillators cause a beating effect under concurrent symbol transmissions. This is characterized by periodic constructive and destructive interference, which significantly affects reliability. Subsequently, a thorough simulation study shows how the beating problem can be overcome with error correction codes. RF-Zero-Wire allows achieving an end-to-end latency of less than 1ms for a small 4-byte frame transmitted across 5 hops. Moreover, latency is shown to increase only by 0.16% per extra hop for 16-byte frames, which is negligible compared to the over 100% per-hop latency increase observed in store-and-forward protocols. The trade-offs between network reliability and CFO range, communication distance, node density, and achievable data rate are studied in large-scale experiments based on simulation.

翻译：有线与无线网络之间的延迟差距对延迟敏感场景中无线技术的采用构成了挑战。在工业传感器网络和机器人集群典型的多跳通信中，这种差距尤为显著。其主要原因是，常用的无线协议依赖存储转发路由和昂贵的开销机制来避免干扰。本文介绍了RF-Zero-Wire，一种基于射频的符号同步通信协议。该协议并非以存储转发方式逐跳中继整个帧，而是逐符号并发中继帧，无需严格的时间同步。基于实际实验收集的数据，我们发现由非理想晶体振荡器引入的不可避免的载波频率偏移（CFOs）会在并发符号传输中引发拍频效应。其特征为周期性的相长和相消干扰，显著影响可靠性。随后，一项全面的仿真研究表明，如何利用纠错码克服拍频问题。RF-Zero-Wire能够在5跳传输一个4字节小帧时实现低于1ms的端到端延迟。此外，对于16字节帧，延迟每增加一跳仅增加0.16%，与存储转发协议中观察到的每跳延迟增加超过100%相比，可忽略不计。基于仿真的大规模实验研究了网络可靠性与CFO范围、通信距离、节点密度以及可达数据速率之间的权衡。