- 學位論文
頻率選擇性衰減通道下之合作式與感知通訊研究
Cooperative and cognitive communications over frequency-selective fading channels
摘要
現今的無線網路，有限頻譜的使用與高資料傳輸率已成為主要的研究議題。許多的解決方案，例如：合作式中繼傳輸與感知網路技術，其也是未來第五代行動通訊系統可能運用到的重要技術。為了提供未來無線通訊系統可供參考的研究報告，本論文，合作式傳輸與感知頻譜分享，將在頻率選擇性衰減通道下討論與分析。其內容，包含單向與雙向中繼傳輸之效能分析、低功率中繼傳輸討論，以及自適性中繼傳輸應用於感知頻譜分享之研究。 論文第一部分，主要分析單向與雙向中繼傳輸，透過放大再傳送模式，在頻率選擇性衰減通道下之效能。其中，特別針對兩種傳統型的放大再傳送模式進行討論，並推算接收訊雜比的機率密度函數，以及動差產生函數。在對稱與非對稱的Nakagami-m衰減中繼通道下，依據所推導的統計函數，對系統平均符元錯誤率進行數值分析，同時透過電腦模擬來驗證。 考量蓄電力有限的中繼裝置，其功率損耗將影響中繼網路的續航力。針對此問題，論文第二部分，將提出放大再傳送低功率的傳輸方法，並進一步推算接收訊雜比於Nakagami-m衰減通道下的機率密度函數。根據所推導的統計函數，分析中斷機率、中繼與接收端的通道容量，以及中繼站功率損耗的效能指標來驗證所提出的方法優於傳統型。 論文第三部分將雙向中繼傳輸運用在感知網路上，結合類比與數位網路編碼模式，提出自適性網路編碼。其中，具中繼轉傳能力的次要用戶，對主要用戶欲中繼服務的訊號進行解碼，並依據解碼結果來實行自適性網路編碼，同時夾帶本身欲傳輸的訊號一起傳輸。根據所提出的方法，將分別探討主要與次要用戶在Nakagami-m衰減通道下的中斷機率。
並列摘要
Nowadays the spectrum scarcity and high data rates in wireless networks become the major issues and have triggered a broad range of research activities. Several solutions including cooperative relaying and cognitive radio have been proposed, which are also the parts of key components of the next-generation (5G) wireless communications. To provide a referable study for 5G or the future wireless communications, in this thesis, the performance of cooperative relay systems over the practical frequency-selective fading channels is investigated. A power-efficient relay scheme is also proposed for green communications. In addition, to exploit the dual benefits of cooperative relaying and cognitive radio, the concept that integrating both techniques, named as cognitive relaying, is discussed. An adaptive cognitive relaying is presented for improving the system performance. The specific contents are as follows. 1.Taking the multipath spread of the channel into account, the performances of one-way and two-way amplify-and-forward (AF) relaying over frequency-selective fading channels are analyzed. Specifically, the exact probability density functions (PDFs) of the received signal-to-noise ratio (SNR) for semi-blind and channel state information assisted AF relaying are derived, respectively. Furthermore, the moment generating functions for both relay schemes are also presented. Based on these statistical characteristics, the average symbol error rate can be found, and then verified by computer simulations under Nakagami-$m$ frequency-selective fading channels. 2.The amplified power is actually an extra power consumption in the AF relay systems. For the battery-limited relay transmissions, the lifetime of the relay network depends on the power consumption of the relay terminal. In this thesis, a power-efficient AF relaying is proposed for the one-way and two-way transmissions. In accordance with the proposed amplification factor, the closed-form expression of the PDF of the received SNR is derived over the Nakagami-$m$ frequency-selective fading channels. Based on the derived PDF of the received SNR, the performance indexes are presented to show the merits of the proposed scheme, including the overall outage probability, the ergodic capacity between the relay node and the destination node, and the power consumption at the relay terminal. 3.Consider the overlay cognitive relaying, an adaptive cognitive relaying is proposed which integrates the digital and analog network coding methods. In the proposed scheme, the secondary relay user performs the adaptive relaying based on the result of decoding, and makes use of the broadcast phase to send his/her own information. The outage probabilities for both the primary and secondary users over the Nakagami-$m$ frequency selective fading channels are investigated.