隨著日常生活中智慧電錶，智慧停車和智慧交通系統等機器對機器通信應用的快速 增長，機器對機器通信將在5G以及未來B5G系統發揮至關重要的作用。與專注於提 供高數據速率和低延遲的常規人對人通信不同，機器對機器通信需要容納大量具有 各種服務品質要求的連接。現有的無線通信系統主要是為傳統的人對人通信設計 的，無法為大量的機器對機器通信設備提供服務。諸如3GPP和IEEE之類的國際標準 化組織一直在積極製定新的無線接入技術標準，包括NB-IoT和IEEE 802.11ah。
傳統的IEEE 802.11系統採用distributed coordination function (DCF)作為隨機接入技 術，DCF的性能隨著用戶數的增多而快速下降，因而無法支援大量物聯網設備。為了緩解這個問題，IEEE 802.11ah導入了restricted access window (RAW)的機制。與傳統的DCF機制相比，RAW機制只允許其組內的用戶在被分配的時隙內傳輸資料。現在關於IEEE 802.11ah RAW機制的研究聚焦於飽和流量下的吞吐量。然而物聯網應用常常會面對非飽和流量的情形，針對非飽和流量下RAW機制的研究卻沒有得到太多關注。本文主要研究於非飽和流量下IEEE 802.11ah RAW機制在非跨越時隙邊界以及 跨越時隙邊界下的性能分析與建模。本文提出了一種二維馬爾科夫模型來表徵IEEE 802.11ah在非飽和流量以及有限緩衝區下的RAW機制。為了反映封包到達泊松分佈 的特性，M/M/1/K排隊模型被整合進二維馬爾科夫模型中。本論文推導出了理論分析的結果，並與模擬結果比較。實驗結果表明我們提出的模型可以很好的表徵IEEE 802.11ah RAW在非飽和流量下的吞吐量特性。
關鍵字 ─ 機器對機器通信，人對人通信，IEEE 802.11ah，RAW，非飽和吞吐 量。

With the rapid growth of machine-to-machine (M2M) applications like smart metering, smart parking, and intelligent transportation systems in our daily life, M2M communications will play a vital role in 5G and beyond 5G (B5G) systems. Unlike the conventional human- to-human (H2H) communications that focus on providing high data rates with low latency, M2M communications are expected to accommodate a massive number of connections with diverse Quality-of-Service (QoS) requirements. Existing wireless systems are primarily de- signed for traditional H2H communications and can not serve a huge number of M2M de- vices. Different standardization organizations like 3GPP and IEEE have been active on new radio access technologies (RATs), i.e., narrowband IoT (NB-IoT) and IEEE 802.11ah.
As the performance of the conventional distributed coordination function (DCF) method in IEEE 802.11 systems degrades significantly with the increasing number of devices, IEEE 802.11ah introduces the restricted access window (RAW) to provide connectivity for a massive number of devices. Although the saturated throughput of RAW has been studied, RAW under unsaturated traffic does not be equally treated. In this dissertation, one two-dimensional Markov chain model is suggested to model RAW in IEEE 802.11ah under un- saturated traffic with finite buffer. Moreover, one M/M/1/K queueing model is integrated to character the buffer status of each station (STA). For both non-cross slot boundary and cross-slot boundary cases, the unsaturated throughput of RAW is derived. Analytical results of the proposed model are evaluated by simulations. Experimental results demonstrated the efficiency of the proposed approach in terms of throughput.
Index Terms – M2M Communications, H2H Communications, IEEE 802.11ah, Restricted Access Window, Unsaturated Throughput.

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