隨著世界對網路的需求增加，網路的資源也愈加的珍貴。為了支援如此龐大的需求，如何去適當利用可用的頻譜變得十分重要。第五代行動通訊技術 (5-th Generation Mobile Network)需要達到比現在的 4G更高的系統效能，因此需要針對 如何 更有效率的 利用 資源 的多重存取 (Multiple Access)技術進行重大改進。具體而言， ，4G主要使用正交頻分多址 (Orthogonal Frequency Division Multiple Access, OFDMA)技術。而 5G則使用擺脫正交限制的非正交多址 (Non-Orthogonal Multiple Access, NOMA)技術來進一步提升頻譜效率。 NOMA跟 OFDMA最大的不同為多了功率域(Power Domain)的利用，並透過不同的功 率分配來區分用戶。在 NOMA中 發射端首先會將多個用戶訊號進行疊加，然後在接收端透過串行干擾消除 (Successive Interference Cancellation, SIC)技術逐一進行訊號解調。這其中有兩個因素會影響到 NOMA系統的資料傳輸率 (Data Rate)，分別為 用戶分組(User Grouping)和 功率分配 (Power Allocation)。 由於 NOMA系統中的非正交特性會使用戶之間存在干擾 ，無法供應所有用戶同時使用 ，因此 使用適當的用戶 分組策略可以減少多路復用用戶的數量 和 增加系統 總資料傳輸率 。而藉由不同的功率分配方案能使 NOMA系統達到不同要求的系統性能。而本篇論文 在 NOMA的基礎下， 將根據用戶的 需求 對用戶進行優先級排序，並 依據 優先級的考慮因素 進行用戶分組。 然而受限於用戶本身的通道狀態影響，在高優先權用戶具有極低通道狀態的情況下難以只透過使用用戶分組的方式進行改善。因此 ，提出 了一種 功率分配方法為每個用戶保留了 基於優先權的 比例公平性和 QoS。 在模擬結果中從所提出基於優先權的用戶分組中 可以看出在不同的情況下皆可以使較多具有高優先權的用戶擁有較高的 資料 傳輸率。並且再加入了所提出相應的功 率分配之後，所有用戶皆依據優先 權比例分配，且具有較低優先的用戶也比較其他方法獲得較多的資料傳輸率 。此外，為了驗證系統是否具有依據優先權為用戶分配資料傳輸率的能力 我們定義了一項指標 Ω。 Ω是一個用來 表達用戶可達到的數據傳輸率以及用戶的目標數據傳輸率的差異輸率以及用戶的目標數據傳輸率的差異。。當當Ω越大越大，，代表用戶可達到的數據傳代表用戶可達到的數據傳輸率以及用戶的目標數據傳輸率的差異越大輸率以及用戶的目標數據傳輸率的差異越大；；當當Ω越越小小，，代表用戶可達到的數代表用戶可達到的數據傳輸率以及用戶的目標數據傳輸率的差異越小，也代表系統依據優先權比例為據傳輸率以及用戶的目標數據傳輸率的差異越小，也代表系統依據優先權比例為用戶分配數據傳輸率的性能越高。在模擬報告中顯示，本論文中所提出的用戶分用戶分配數據傳輸率的性能越高。在模擬報告中顯示，本論文中所提出的用戶分組暨功率分配方案較其他方法的組暨功率分配方案較其他方法的Ω值值低低52%~76%。。

As the demand for the Internet increases, the resources of the Internet become much more precious. In order to support such a huge demand, the question of how to make appropriate use of the available spectrum becomes very important. To be specific, the 5-th Generation (5G) mobile network is expected to achieve much enhanced performance than the 4G network. As a result, the multiple access technology which aims to allocate spectrum efficiently requires a significant improvement. In 4G, the orthogonal multiple access scheme such as orthogonal frequency division multiple access (OFDMA) is primarily employed. However, the orthogonal technology results in a disadvantage where the available spectrums cannot be used efficiently. On the other hand, the non-orthogonal multiple access (NOMA) technology is proposed in 5G to relax the strict orthogonality limitation for further enhancing the spectrum efficiency. In particular, in the power-domain NOMA scheme, the users are distinguished by allocating different power levels. In such system, multiple user signals are allocated with different power levels and are superimposed at the transmitter. The mixed signals are transmitted over the wireless channel and are demodulated subsequently using a successive interference cancellation (SIC) technology at the receiver. There are two essential factors for designing the NOMA system, namely user grouping and power allocation. Due to the non-orthogonal characteristic of the NOMA system, the interference between users is caused and the number of users that can be transmitted simultaneously is limited. Using a proper user grouping strategy can reduce the number of multiplexed users and increase the system throughput. In addition, with different power distribution schemes, NOMA system can achieve different system performance requirements. In this paper, a priority-based joint user grouping and power allocation scheme for NOMA system is presented. In the proposed approach, users are prioritized based on their importance and are grouped with the considerations of the priorities. Furthermore, the proposed power allocation approach preserves the certain data rate under user priority constraint and QoS for each user. The detailed outline of the proposed schemes is presented in this paper. In the simulation results, it can be seen from the proposed grouping of users based on priority that under different circumstances, more users with high priority can have a higher data rate. And after adding the corresponding power allocation proposed, all users are allocated power according to the priority ratio, and users with lower priority also obtain more data transmission rates than other methods. In addition, this paper defines an index Ω to measure the difference between the user’s achievable data rate and target rate. The higher the system's ability to allocate rates based on priority, the smaller the Ω value. The simulation report shows that the Ω of the proposed priority-based joint user grouping and power allocation scheme is 52%~76% lower than other schemes.

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