近年來由於科技的日新月異，數位通訊技術儼然成為我們日常生活中不可或缺的一部份，而數位通訊技術的主要特點就是能有效降低接收的錯誤率以及提供迅速的傳收速度。然而近期由於環保意識的日漸茁壯，人們對於節能省碳的概念愈加重視，而在通訊領域則有所謂綠色通訊的概念被提出。目前已有許多在通訊系統使用能量和各式效能參數間相互取捨的相關探討，像是建置成本、頻寬效益與傳輸延遲等。
　　本篇論文中將在合作式通訊系統的場景下，以我們所提出的在中繼端協助下的封包傳輸機制，探討在傳輸過程中採用不同的傳輸模式時，系統傳輸的能量與其所花費時間的相對關係，此外，我們藉由系統工作轉移狀態所推導出的數學式，能快速地將系統預期的傳輸時間以及使用能量運算出來，且能迅速又方便的找出系統的最佳效能，使系統在面臨不同導向的傳輸環境下，也能立即找出其相對應的傳輸方式。
　　另外，我們也考量在路徑衰減會影響通道錯誤率的情況下，以能量分配的方式在訊號端及中繼端的部分做調整，在傳輸時間可允許的範圍內，盡量的把使用能量降低，以求得更好的傳輸效能，並嘗試在不同的場景下做模擬分析，觀察出最適當的傳輸場景。最後，再利用本文所提出的機制與Sohaib傳輸機制做比較，其中在Sohaib傳輸機制方面，我們對其傳輸通道錯誤率做進一步的推導及延伸，以便於比較各式實驗數據。實驗結果指出，在本文所提出之機制下的兩種傳輸模式，皆能在考量不同導向的傳輸環境下，優於Sohaib傳輸機制。

For many decades by now, digital communication is a technique that has been part of everyone’s daily life. The primary requirement on digital communication is that data transmission via it should be reliable (i.e. has a very low error probability at reception) and fast (i.e. has a high transmission speed in terms of bits per second). Recently, however, due to people’s consciousness for environmental protection, another issue has also become a big concern in digital communication – namely, efficient use of energy. Energy-efficient communication is also referred to as green communication. Developments of enabling technologies for achieving green communication have been actively conducted in the academic as well as in the industry. Various trade-offs are investigated between energy efficiency and other factors such as deployment cost, bandwidth efficiency, and transmission delay, etc.

In this thesis, a green (i.e. energy-efficient) scheme is proposed for a packet-oriented cooperative communication network wherein a source node sends data packets to a destination node with the aid of a relay node.When the destination node has successfully received the packet from the source node, the system operation is completed. Otherwise, retransmission of unsuccessful packet is performed, possibly by the source node, or the relay, or even both. There is a trade-off between the time taken and the energy consumed by the system to complete the data transmission. Closed-form equations that enable very fast computation of the expected cost in time and energy by the system are derived. With those equations, we can quickly and easily obtain the system setting that produces optimal performance (in the sense of being green or fast, depending on the user’s priority).

In this work, power allocation is part of the system setting. More specifically speaking, the power allocation between the source node and the relay node is investigated (via the afore-mentioned closed-form equations). The goal is to reduce the overall power consumption while in the meantime the transmission delay is still acceptable. For the evaluation of the effectiveness of the proposed scheme, simulation results are generated. The results are compared to results corresponding to a scheme found in the literature – namely, the paper of Sohaib, So, and Ahmed (for short, referred to as SSA). We want to emphasize, however, that we had significantly extended the SSA paper so that the comparison between our scheme and SSA’s scheme is meaningful. More specifically speaking, in the SSA paper, the bit error rate (BER) was derived for a source-relay-destination cooperative network (just like the one under this thesis’ consideration). The extension we made was to have derived the packet error rate (PER). A few scenarios of different fading (of transmission paths) and location (of relay node) are tested. Simulation results show that our scheme outperforms SSA.

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