因為現今日益增長的用戶需求，D2D 多播通訊 (Device-to-Device multicast
communications) 作為加強傳統 D2D 通訊技術以提升頻譜效率的技術可以滿足
更大量的使用者需求而備受期待，我們考慮存在多個 Cache-Enabled D2D 裝置
的環境，每個 D2D 設備都配有有限容量的電池而且可以作為需求者 (demander)
要求下載檔案同時也能作為幫助者 (helper) 傳送存放在暫存中的檔案給需求
者。 為了提高在此 Cache-Enabled D2D 網路的頻譜效益，我們提出了一個方法
並分成三個步驟，第一個步驟的目的是使用最少數量的幫助者來滿足盡可能多
的需求者的需求，一個幫助者允許同時為多個需求者服務，我們將這個問題轉
化成最小集合覆蓋問題的變種並使用啟發式演算法來找出最小數量的幫助者集
合。 在取得幫助者集合後，由於每個幫助者都會服務多個需求者，所以第二個
步驟是要去決定每幫助者的功率分配，以便在最短時間內完成檔案傳輸，同時
也要滿足所有需求者的速率要求以及幫助者的功率限制。 第三個步驟目的是通
過讓多個幫助者共享一個頻譜資源來盡量減少使用的頻譜資源數量，實驗結果
表明，我們提出的方法可以顯著增加被良好服務的需求者數量 (由幫助者提供服
務)，並提高頻譜效益和幫助者的效益。

We consider a mobile network in which there exist multiple device-to-device
(D2D) multicast networks. Each D2D node is powered by finite-capacity battery
and can serve as a demander (which requests of downloading files) and/or a helper
(which sends files stored in its cache to demanders). This cache-enabled scenario
offloads data delivery (which is originally targeted for base stations) to helpers.
In order to improve spectral efficiency in this cache-enabled scenarios, we de-
velop a method, which could be divided into helper association, sum multicast
rate maximization, and channel-sharing scheduling.
The helper association process aims to satisfy the rate requirements of as many
demanders as possible by utilizing fewest helpers; a helper is allowed to serve
multiple demanders. We transfer this helper association problem into a variant
of the minimum set cover problem and use a heuristic algorithm to find out a
minimal set of helpers.
After obtaining a set of helpers, each of which serves multiple demanders, the
sum multicast rate maximization process decides power allocation for each helper
in order to finish file transmissions in the shortest time duration while satisfying
rate requirements of all these demanders and power constraints of the helpers
themselves.
The channel sharing scheduling process aims to minimize the number of chan-
nels in use by letting multiple helpers share the same channel if it can fit. The
experimental results show that our proposed method can significantly increase
the number of well-served demanders (that are served by helpers) and improve
per-channel efficiency and per-helper efficiency.
Keywords: D2D multicast communications, radio resource allocation, cache-
enabled D2D

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