IEEE 802.11 資訊新鮮度與能源效率的權衡分析：目標喚醒時間機制之資訊年齡效能分析

Abstract

IEEE 802.11 標準提出了目標喚醒時間（Target Wake Time, TWT）作為重要的省電機制，透過排程站台（STAs）的喚醒時間來接收封包，並在其他時間進入休眠模式（Doze State）以節省電力。雖然TWT可顯著降低能源消耗並緩解頻道競爭，但其對資訊新鮮度（information freshness）的影響尚未得到充分探討，而資訊新鮮度正是即時性和物聯網應用中的關鍵需求之一。尤其是用來量化數據即時性的資訊年齡（Age of Information, AoI），在現有的TWT分析中鮮少被考量。 據作者所知，本研究首次針對各種TWT設定，推導出資訊年齡（AoI）的期望值、峰值資訊年齡（peak AoI）的期望值，以及平均功耗之解析閉合式解。透過模擬驗證後的分析結果顯示，在固定喚醒比例（awake ratio）的情況下，提高喚醒頻率（亦即將偵聽間隔LI設為1）能有效降低資訊年齡的期望值與峰值資訊年齡，且不會增加功耗。這些結果提供了調整TWT參數的具體指引，並為改善網路效能提供了有價值的參考依據。

The IEEE 802.11 standard introduces Target Wake Time (TWT) as a crucial power-saving mechanism that schedules the wake-up times of stations (STAs) for receiving packets, while the remaining time is spent in a Doze State to conserve power. Although TWT significantly reduces energy consumption and mitigates channel contention, its impact on information freshness—a key requirement for real‑time and IoT applications—remains underexplored. In particular, Age of Information (AoI), which quantifies the timeliness of received data, has rarely been considered in existing TWT analyses. To the best of the authors’ knowledge, this work is the first to analytically derive closed-form expressions for expected AoI, expected peak AoI, and average power consumption under various TWT configurations. The analysis—validated by simulation—shows that frequent wake-ups (i.e., setting the listen interval LI to 1) yield the lowest expected and peak AoI without increasing power usage for a given awake ratio. These findings provide actionable guidelines for tuning TWT parameters and offer valuable insights for improved network performance.