面臨行動通訊技術的日新月異，頻譜已成為無線通訊系統的重要資源，雖然4G(4th generation)行動系統已在全球被廣泛地使用，技術上仍有改善的空間，而5G(5th generation)的發展也已經是近年來全球的熱門研究議題。 5G行動系統的一個關鍵特性是基地台使用大量天線的大規模多重輸入多重輸出技術。大規模多輸出多輸入技術使基地台能夠同時服務多個用戶從而提高系統容量。藉由使用大規模多輸出多輸入技術，基地台可以在不同方向上形成多個正交波束。當基地台底下服務的用戶數量增加且波束數量太過龐大時，如果對所有用戶和波束做聯合檢測 (joint detection)，則最大相似度接收機的複雜度非常高。因此，我們嘗試設計用於上行鏈路的用戶分群演算法，為了讓只有在同一群組的用戶在基地台被共同檢測到。對群組的最大用戶數量設限，從而可以減少檢測器的複雜度。本篇論文我們提出了一種用戶分群和波束選擇演算法。主要是利用用戶的通道投影來評估用戶間的正交性，以此作為分群的依據。模擬結果顯示該演算法能有效提高系統和率。 Facing the ever-changing mobile communication technology, the spectrum has become an important resource in wireless communication systems. Although 4G (4th generation) mobile system has been widely used around the world, there is still room for improvement in technology. The development of 5G (5th generation) mobile communication system has also been a hot topic in recent years around the world. A key feature of 5G mobile system is the massive MIMO technology of which the base station equips with a large number of antennas. Massive MIMO technology enable the base station to serve multi-users at the same time so that the system capacity can be increased. By using the massive MIMO technology, the base station can form many orthogonal beams in different directions. When the number of users to be served under the base station is increased and the number of beams is too large, the complexity of the maximum-likelihood (ML) receiver is extremely high if all users and beams are joint detected. Therefore, we try to design a user grouping algorithm for up-link, so that only users in the same group are jointly detected in the base station. The maximum number of users in a group is limited by a predefined value so that the complexity of the detector can be reduced.In this paper, we propose a user grouping and beam selection algorithm. The major idea is to use the user's channel projection to assess the orthogonality between users, as a metric for grouping. Simulation results show that the proposed algorithm can effectively increase the system sum rate.