由於行動通訊快速的發展，使得在我們生活的環境中有很多射頻電波(radio frequency)訊號。這些射頻電波除了用來傳遞訊息之外，近年來逐漸也被當作能量應用在能量採集(energy harvesting)上，這種能量採集的緣起是因為隨著無限通訊設備的快速發展，智慧型手機、平板及各種行動裝置越來越普及，人們在日常生活中逐漸依賴於行動應用軟體，例如通訊軟體、照相及遊戲，但這些功能對於智慧型手機來說非常耗電，雖然目前有行動電源可以延長行動裝置的使用時間，但是行動電源的供應是有限的，當電源耗盡時，仍會造成相當大的不便。有介於此科技始終來自於人性，希望行動裝置可以無時無刻的持續運作，不需要擔心電池能量耗盡，射頻能量採集因應而生。利用能量採集電路，蒐集環境中射頻電波訊號產生電能；不僅如此，近年來在文獻中也針對同時處理資料訊號和能量採集提出探討。在本論文中，我們將探討在雙向放大後傳送中繼傳輸通道(two-way amplify-and-forward relaying)中，兩個使用者端彼此經由中繼點交換資訊，而此中繼點藉由採集使用者傳送訊號的射頻能量，提供給下個階段所轉傳訊息所用。系統中我們假設中繼點具備兩根天線，兩個使用者端分別為單天線。考慮完美通道資訊下，中繼點可以調整兩天線的接收訊號，使其產生建設性干涉，讓裝置可以採集到更多的能量。本論文在中繼點有功率限制的條件下，設計預編碼(precoder)矩陣，使得系統的總通道容量(sum-rate)達到最大，但由於此最佳化問題既不是凸函數(convex)也不是凹函(concave)，以至於無法使用常見的最佳化工具求解，所以我們會先將問題拆成兩個子問題，先以窮舉演算法及梯度演算法來找出能量分流比例(power splitting ratio)，再利用次方疊代演算法找出波束賦形(beamforing)矩陣，將兩個子問題得到的次佳解互相疊代後，逐漸收斂至最佳的能量分流比例及最佳的波束賦形矩陣，以增進兩使用者的總通道容量。

Due to rapid development of mobile communications, radio-frequency signals are surrounded in our environment. Besides conveying information, the ambient radio-frequency signal has gradually been utilized for energy harvesting. Radio Frequency energy harvesting begins from the fact that people gradually rely on mobile applications, such as communication apps., picturing software, and games, in their daily life. However, these applications are energy consuming. Although these devices can be charged through portable power bank, the energy stored in the power bank is still limited, which leads to inconvenience when the power bank is in outage. To provide further convenience, RF energy harvesting has been developed to avoid mobile devices suffering power outage by gathering energy from from the ambient radio frequency signals and transferring into electricity. Furthermore, simultaneously processing information and harvesting energy from the RF signal has been studied extensively in recent years. In this thesis, we will employ this technique in two-way amplify-and-forward relay system, where two users exchange information under assistance of an energy-harvesting relay node. Specifically speaking, transmission power of the relay node depends on the electrical energy harvested in previous phase. We assume that the relay node is equipped with two antennas, while the users are equipped with a single antenna. With perfect channel information, the relay node can coherently combines the signals received at two antennas, so that the relay node is able to gather more energy. In this thesis, we proposed a joint design of a precoding matrix and power-slitting ratios for the relay node to maximize the sum-rate of two users under a constraint that the transmission power of the relay node cannot exceed the harvested energy. However, this optimization problem is neither convex nor concave, and it can’t be solved by CVX tool. Thus, we divide the problem into two sub-problems to approach a locally-optimal solution of the precoding matrix and power-splitting ratios in an iterative manner. Specifically, we employ gradient algorithm to obtain power-splitting ratios with initial value obtained by exhaustively searching over a rough grid. Then, the beamforming matrix is obtained using power iteration algorithm. After several iterations, two subproblems get converged and we can find the set of suboptimal solutions. It shows through simulation results that the proposed scheme can effectively improve the spectrum efficiency of the system.

論文審定書 i
致謝 ii
摘要 iii
Abstract iv
目錄 vi
圖索引 vii
第一章簡介 1
第二章相關背景 5
2.1完美通道情況下的波束賦形設計 5
2.2雙向中繼點傳輸結合能量採集技術 8
第三章系統模型 11
第四章 中繼端能量限制下的波束賦型設計 15
4.1 調整天線方向下中繼點所能收到的最大能量 15
4.2 給定波束賦形矩陣 求出最佳的能量分流比例 及 18
4.3 給定分流比例 及 求出最佳的波束賦形矩陣 20
第五章 模擬結果與討論 23
第六章 結論 29
參考文獻 30

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