用於決定多使用者多輸入多輸出系統中最優用戶數的算法和分析結果

Abstract

在本論文中，我們發現在多使用者多輸入多輸出的系統中有最優用戶數讓總傳輸量最大，在大部 分的例子中，滿載的傳輸不一定達到最大總傳輸量，有時候降低用戶數可以增加用戶的自由度和分集 增益，因此運用最優用戶數可以顯著增加總傳輸量的效能。我們可以使用窮舉搜尋找到最優用戶，但 隨著可選擇的用戶數增加，計算複雜度會令人卻步，因此為了確實地找到最優用戶，我們先分析系統 效能，並推導不同用戶數的平均總傳輸量的上下界來得到效能的解析解，同時，這有助於降低搜尋的 複雜度，因為只需要搜尋一些可能的用戶數即可，此外，我們提出兩個尋找最優用戶的次佳演算法， 這兩個演算法可以顯著降低計算複雜度，但與窮舉搜尋的效能相去不遠。模擬結果展現了分析結果的 正確性以及提出方案所降低的運算複雜度。

In this thesis, we nd that there exists an optimal number of active users that maximizes the sum rate in a MU-MIMO system. That is, in most cases, full-loaded transmission may not lead to the maximum sum rate. Instead, sometimes reducing the number of users increases the degree of freedom of the active users and thus the diversity gain. The sum rate performance can be signicantly improved by applying the optimal number of active users. This optimal number of active users can be search exhaustively. Unfortu- nately the computational complexity becomes prohibitive as the potential numbers of active users increases. To nd this optimal number feasibly, we analyze the performance of such systems and derived a lower and a upper bounds of the averaged sum rate. From these bounds, the performance of such systems can be represented in closed-forms. At the same time, they help in identifying some numbers that have potential to be optimal to avoid search exhaustively. As a results, the computational complexity can be greatly reduced. Moreover, we also propose two sub-optimal algorithms to nd the optimal number of active users. These two algorithms can also signicantly reduce the computational complexity; while the corresponding performance degradations are very small. Simulation results show the accu- racy of the proposed analytical results, as well as the complexity reductions of the proposed schemes.