合作式通訊（Cooperative Communications）技術協調多個中繼節點進行資料傳輸，可達到空間分集（Spatial Diversity）的效益來提升傳輸效能與信號覆蓋範圍，因此受到學界與業界廣泛的討論以及高度的重視；此技術可大略分為單向中繼轉送（One-Way Relaying）及雙向中繼轉送（Two-Way Relaying）。針對於進行信息交換而言，單向中繼轉送相對於傳統點對點傳輸需要多耗費一倍的頻譜資源，因此降低了頻譜使用率；然而，雙向中繼轉送不僅可得到空間分集的好處，亦能提供與點對點傳輸近似相同的頻譜使用率，因此具有相當大的發展潛力。雙向中繼轉送主要是利用多個中繼節點來協助兩訊號源進行資料的交換；因此，如何有效的使用中繼節點來提升雙向中繼轉送系統的傳輸效能是一關鍵的議題。
在本論文中，我們針對雙向放大轉送中繼（Two-Way Amplify-and-Forward Relaying）系統提出有效之功率分配（Power Allocation；簡稱PA）以及中繼點選擇（Relay Selection；簡稱RS）演算法基於符元錯誤率（Symbol Error Probability；簡稱SEP）。首先，我們先針對系統推導出一使用M-ary Quadrature Amplitude Modulation 與M-ary Phase-Shift Keying 之整體SEP（Overall SEP；簡稱OSEP）；且根據最小化此OSEP，我們發展出一基於統計通道狀態資訊（Statistical Channel State Information-Based；簡稱SCSI-based）PA方法，並且，在使用SCSI-based PA方法下，我們亦提出了一SCSI-based RS方法其選擇一最佳中繼節點來進行傳送且可達到最小OSEP效能；此外，在透過使用SCSI-based PA方法，兩訊號源將會有相同的SEP效能，也就是SEP Balancing。為了進一步提升系統效能且透過使用SEP Balancing方法，我們跟著提出了一基於瞬時通道狀態資訊（Instantaneous Channel State Information-Based；簡稱ICSI-based）PA方法，ICSI-based PA方法可使得兩訊號源有著相同的瞬時接收訊雜比（Signal-to-Noise Ratio；簡稱SNR），也就是SNR Balancing；根據此結果，我們接著發展了一ICSI-based RS方法選擇一最佳中繼節點來進行傳送且可達到最大平衡SNR效能，此外，我們亦提供了一分集增益分析透過推導整體中斷機率（Overall Outage Probability）。另一方面，透過使用路徑衰減模型（Path-Loss Model）來估測 SCSI，我們發展了一基於地理資訊（Geographic Information-Based；簡稱GI-based）之PA及RS方法；此外，根據GI-based OSEP的結果，我們也探討了在給定一OSEP值，其所對應之最大傳輸範圍（Maximum Transmission Coverage）以及對應之中繼轉送區域（Relaying Area）。
此外，我們將所提出基於不同通道或地理資訊所發展出來的PA及RS演算法運用於無線多重跳躍網絡下進行雙向式資料交換，以改善網路之效能。首先，我們提出一合作式傳輸架構，此架構能將無線多重跳躍網路分解成多個獨立的雙向放大轉送中繼系統；因此，根據此傳輸架構的特性，我們在之前所提出的有效PA及RS演算法則可以直接應用於此架構，進而來改善網路的傳輸效能；此外，此架構相較於一相關之方法，有較高的有效吞吐量（Effective Throughput）及相近的Frame Error Rate。除此之外，我們亦提出一合作式路由協定來建立雙向式傳輸路徑，此協定包含一轉送點選擇（Forwarder Selection）及一RS並且透過一競爭計時器設定（Contention-Timer Setting）來選擇最佳轉送點及中繼點；對於最佳轉送點是用來降低傳輸跳躍次數（Hops），另一方面，最佳中繼點則是用來增強網路傳輸效能。

Two-way relaying, using relays to accomplish information exchange between two source nodes, has been extensively investigated in recent years because it not only can obtain spatial diversity gain but also can provide the same channel utilization efficiency as end-to-end transmission. Because building communication links between the two sources in two-way relaying depends on the relays, system performance in turn depends on using the relays as efficiently as possible.
In this dissertation, we develop efficient power allocation (PA) and relay selection (RS) schemes based on overall symbol error probability (OSEP) for two-way amplify-and-forward (AF) relay systems, in which multiple single-antenna relays and reciprocal channels are considered and only one relay will cooperate with two source nodes. We first analyze an asymptotic OSEP (AOSEP) with closed-form in terms of second-order channel statistics and the transmit power of each participating node with M-ary quadrature amplitude modulation (M-QAM) and M-ary phase-shift keying (M-PSK) modulation schemes, and then introduce a statistical channel state information (SCSI)–based PA scheme by minimizing the AOSEP with a total transmit power constraint. In addition, using the SCSI-based PA, we propose a RS scheme by selecting one relay for cooperation in achieving the minimum OSEP value, which has diversity order one. Note that both the individual symbol error probabilities (SEPs) at the two sources are the same when using the SCSI-based PA; that is SEP balancing. To further improve system performance in terms of OSEP, we then present an instantaneous channel state information (ICSI)–based PA scheme using the SEP balancing approach; the PA scheme leads to the instantaneous received signal-to-noise ratios (SNRs) at the two sources being balanced. Following this observation, we then develop an ICSI-based RS scheme that finds one relay for transmission that has the maximum balanced received SNR and provide an achieved diversity order analysis of the ICSI-based schemes by deriving the lower and upper bounds of asymptotic overall outage probability. We also provide simplified PA-RS schemes by incorporating a path-loss model into the SCSI-based schemes, i.e., geographic information (GI)–based PA-RS schemes. Using the GI-based PA-RS schemes, we then study the maximum transmission coverage and the relaying area under a given OSEP requirement; the results show that the optimal relay location for maximizing the transmission coverage is at the center coordinates of the two sources, and that the relaying area shrinks as the geographic distance between the two sources increases.
Furthermore, we apply the proposed PA-RS schemes to wireless two-way multihop AF relay networks. We first propose a cooperative multihop transmission structure for the networks, in which a number of single-antenna relays are addressed and distributed between two sources. The proposed transmission structure can decompose the multihop networks to several independent two-way two-hop AF relay systems; therefore, the proposed PA-RS schemes can be adopted for use in the systems to enhance the transmission reliability of the networks. Our data show that the proposed transmission structure provides more effective throughput performance than a related method with almost the same frame error rate, whether or not the proposed PA-RS schemes are used. Moreover, according to the structure characteristics, we present a cooperative two-way routing protocol that consists mainly of a GI-based forwarder selection part and a SCSI/ICSI/GI-based RS part, where the forwarder selection part is used to reduce the number of transmission hops, and the RS part is applied for enhancing the reliability of the communication links.

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