IEEE 802.11無線區域網路已經廣泛被使用於各通訊服務領域，其媒介存取層主要依據分散式協調功能(distributed coordination function, DCF)協定處理。依DCF協定定義，當有多個用戶同時傳輸時，就會發生碰撞而致失敗重傳；然而從實體層觀點，假如最強訊號大於其他訊號超過一定門檻值(Threshold)，接收端就能成功接收此最強訊號，這個現象稱為捕獲效應(Capture Effect)。為了充分利用此特性，本論文提出利用傳輸功率控制以差別化不同用戶於接收端(AP)的接收功率，使接收端更有機會捕獲訊號。由於捕獲效應影響，接收功率較高的用戶相對接收功率較低的用戶會有較大的機會成功傳輸訊號，造成用戶間的不公平性，所以我們也藉由調整每個用戶的傳送機率以解決捕獲效應造成的不公平性。最後我們也將傳輸功率控制與非正交多重址接(NOMA)技術結合運用，以更進一步提升系統性能。模擬結果顯示我們所提的方法相較於IEEE 802.11DCF可以提升系統吞吐量(Throughput)，也不會失去公平性。

IEEE 802.11 wireless local area networks (WLANs) have been widely used in various communication domains, and the media access (MAC) layer is mainly based on the distributed coordination function (DCF) protocol. In DCF protocol, collision and transmission failure will happen when multiple stations launch transmissions simultaneously. However, from physical layer perspective, if the received signal strength of one transmission is much higher than others, then the receiver (AP) will be able to decode the corresponding data successfully. This is called capture effect. In order to exploit this effect, this thesis proposes a transmission power control method to differentiate the received powers of different transmissions. So that the receiver has the opportunity to capture the strongest signal. Due to the capture effect, the user with higher received power has a greater chance of successful transmission, which results in unfairness. Hence, this thesis also proposes various ways to solve this unfairness problem by adjusting the transmission probability of each users. Finally, we combine the proposed power control scheme with the NOMA mechanism to improve system performance. Simulation results show that our proposed scheme compared to IEEE 802.11 DCF can improve the system throughput without much loss on fairness.

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