考量未來的頻譜需求不斷增加，頻譜資源日益短缺，一種短距離傳輸的Device-to-Device(D2D)通訊技術可以不需透過基地台(base station, BS)達到設備之間資料交換的技術，可以大大降低BS的負載。一般D2D研究文獻區分成了單播(unicast)與多播(multicast)通訊，為因應未來環境，本論文專注於多播D2D通訊之研究。一般多播D2D通訊的關鍵問題為如何分群和選擇群組頭(group head, GH)來幫助BS轉發多播資訊給群組內的用戶。
針對上述問題，多跳方式可以提高多播D2D群組整體覆蓋率；另外針對多播D2D群組內的用戶都是請求重複的資料，故利用社群關係幫助用戶分群亦可增加整體系統效率。故本論文所提出Social-aware Multi-hop Multicast (SMHM)分群方案，基於社群活躍度、物理位置及SINR等綜合考量因素的GH選取策略，制定衡量用戶活躍度和周圍成員密集程度之權重函數計算出合適的GH及相對應的群組成員。解決邊緣用戶無法有效加入多播D2D群組的問題，並在多播D2D群組選擇GH時根據用戶密集度與活躍度之權衡機制來協助分配，以例子說明，概念評估結果得知SMHM方法比之前的方法Multicast Tx user selection algorithm (MTSA)之整體吞吐量可提升約42.43%。

Considering the increasing demands of spectrum in the future, spectrum resources are getting less and less, a short-distance transmission Device-to-Device (D2D) communication technology can realize the technology of data exchange between devices without using a base station (BS), and greatly reduce the load of the BS. General D2D researches are of two sorts, unicast and multicast communication. In order to respond to the future environment, this paper focuses on the research of multicast D2D communication. The key issue of general multicast D2D communication is how to group and select the group head (GH) to help the BS forward the multicast information to the users in the group.
To solve the above problem, the multi-hop mode can increase the overall coverage of the multicast D2D group; in addition, the users in the multicast D2D group are all requests for duplicate data, so using the community relationship to help the users to group can also increase the overall system efficiency. Therefore, the Social-aware Multi-hop Multicast (SMHM) grouping scheme proposed in this paper is based on the GH selection strategy of comprehensive considerations such as community activity, physical location, and SINR, and formulates a weighting function to measure user activity and the density of surrounding member, and Calculate the appropriate GH and the corresponding group members. The proposed SMHM method solves the problem that edge users can’t effectively join the multicast D2D group. When selecting GH for the multicast D2D group, assigning GH through the trade-off mechanism which is based on the user density and activity. For instance, the result of the concept evaluation shows that the SMHM method can increase the overall throughput by about 42.43% compared to the previous method Multicast Tx user selection algorithm (MTSA).

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