Enhancing information freshness in wireless networks has gained significant attention in recent years. To optimize or analyze information freshness, which is often characterized by the age of information (AoI) metric, extensive theoretical studies have been conducted on various wireless networks. Early research has demonstrated the significance of last-come-first-served (LCFS) packet scheduling and controlled status sampling (i.e., packet generation) in improving information freshness. These mechanisms have been widely adopted in subsequent studies. However, the effective implementation of these mechanisms in commercial off-the-shelf (COTS) wireless devices has not been thoroughly investigated, which could limit the practical application of information freshness-oriented protocols in real-world systems. Our work aims to address the gap by exploring the effective implementation of the information freshness-oriented mechanisms mentioned above in COTS WiFi devices that use the Linux operating system. Our attempts reveal that implementing these mechanisms in COTS systems is not a straightforward task. Specifically, we found that the physical layer queue of WiFi devices operates on a first-come-first-served (FCFS) basis, and the packet generation process cannot be precisely controlled by default. To overcome these challenges, we develop Fresh-Fi, an information freshness-oriented protocol stack that involves careful customization to the lower layers of the Linux networking protocol stack. Fresh-Fi mainly incorporates a mac80211 subsystem-based LCFS queue and a real-time kernel-based cross-layer tunnel between the mac80211 subsystem and the application layer for triggered packet generation.

翻译：近年来，提升无线网络中的信息新鲜度引起了广泛关注。为优化或分析通常以信息年龄（AoI）为度量的信息新鲜度，研究者针对各类无线网络开展了大量理论工作。早期研究已证实，后到先服务（LCFS）数据包调度机制与受控状态采样（即数据包生成）对改善信息新鲜度具有关键意义，这些机制在后续研究中得到广泛应用。然而，上述机制在商用现成（COTS）无线设备中的有效实现尚未得到充分探究，这可能限制面向信息新鲜度的协议在实际系统中的工程应用。本研究旨在填补这一空白，探索在采用Linux操作系统的COTS WiFi设备中有效实现上述信息新鲜度优化机制。实验表明，在COTS系统中实现这些机制并非易事——具体而言，我们发现WiFi设备物理层队列采用先到先服务（FCFS）策略，且默认状态下无法精确控制数据包生成过程。为攻克这些挑战，我们开发了Fresh-Fi——一种通过深度定制Linux网络协议栈底层实现的面向信息新鲜度的协议栈。Fresh-Fi主要包含基于mac80211子系统的LCFS队列，以及用于触发式数据包生成的跨层通道（该通道基于实时内核在mac80211子系统与应用层间建立）。