合作式通訊為透過佈建在網路中的中繼站轉傳訊號達到分集增益以抵抗多路徑衰減，然而中繼站需仰賴額外固定電源供電，增加佈建中繼站的成本與複雜度，獵能技術是一個可行的解決方案來克服這項問題，中繼站使用獵能技術利用週遭環境資源獲取能量並轉換成電能，可延長系統的生命期及降低佈線、維護成本。相較於傳統固定電源供電，基於無線獵能的中繼站之效能主要受限於採集能量之轉換效率與充電電池容量，同時，中繼站亦受限半雙工機制，必須在充電模式與轉傳資料間取得良好的平衡。本篇論文為選擇一個最佳轉傳中繼站，其餘中繼站進行採集能量，針對最佳轉傳中繼站的選擇，除了根據通道狀況也將中繼站的電量納入考量。根據模擬結果，所提出的選擇機制能使採用能量採集技術的中繼站達到全分集增益，並藉由理論分析，得到所提方法的中斷機率。

The use of energy harvesting (EH) nodes as cooperative relays is a promising and emerging solution for energy limited wireless systems, rendering the network self-sustaining with significantly prolonged lifetime. In this thesis, we consider multiple EH relay nodes harvesting energy from the radio frequency (RF) signal received from the source and use that harvested energy to forward the source information to the destination. Unlike conventional wireless nodes relied on fixed power supplies, EH relays may not be permanently available to assist the source transmission due to the limited energy conversion efficiency, the mismatch between the charging and discharging profiles, and the finite energy storage capacity. Our objective is to improve the reliability of EH relays by properly selecting one relay to perform data forwarding while the remaining relays perform energy harvesting. We propose the ``battery-aware relay selection (BARS)', which jointly considers the channel condition and the buffer status for relay selection. The outage probability of the proposed scheme is analyzed based on a Markov chain model. Simulations are performed to validate the analysis accuracy. The proposed scheme is compared with the ``CSI-based relay selection scheme', which selects the cooperating relay only based on the channel condition. Through numerical results, we show that the CSI-based scheme suffers error floor while the propose BARS scheme can achieve the full diversity order equal to the number of relays without the need of fixed power cables.

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