隨著未來5G與物聯網蓬勃發展的趨勢，同時間連網設備的數量將會大幅增加，現有的無線傳輸技術將無法乘載同時間龐大的連線請求，導致隨機接入頻道壅塞問題的發生，此問題發生在隨機接入機制的第一步：設備隨機選取前導碼傳送至基地台來競爭傳輸資源，當過多設備同時競爭資源，會導致碰撞的機率大幅提高，使得存取網路的成功率非常低，且因應頻譜資源不足的現象，本研究結合新一代NOMA技術，此技術能在同一份頻譜資源裡透過不同功率大小來區分設備，意旨能在同一份資源裡令多個設備傳輸，本方法將使用者根據其信噪比大小分為兩組，能有效減少同時間存取的設備數量，並能有效的利用頻譜資源，實驗結果證明系統的容量相較傳統方法有效增加，而碰撞機率則會有效減少。

In the future Internet of Things (IoT) scenario, the number of connected devices will grow rapidly. Existing wireless transmission technologies will not be able to handle large connection requests at the same time, resulting in the problem of random access channel congestion problem. This problem occurs in the first step of the random access procedure: a device randomly selects one preamble from those available and transmits to the base station. Collision occurs if more than one device selects the same preamble at the same time. When collision occurs, the data delivery fails. This thesis proposed a non-orthogonal multiple access (NOMA) based uplink access control method for massive IoT devices. NOMA serves multiple devices simultaneously using the same spectrum resource. The method divides the user into two groups according to signal-to-noise ratio, which can effectively reduce the number of devices accessed at the same time and can effectively utilize the spectrum resources. The experimental results show that the capacity of the proposed method is effectively increased compared with the traditional method, and the collision probability will be reduced.

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