論在固定能量及異質鏈路狀態下之中繼站選取

Abstract

在傳統的中繼站輔助通訊的系統中，一般討論課題不外是如何提高系統的效 率(throughput) 、有待傳序列的中繼站(Relays with queues)或用戶的公平性(Fairness)等等。然而對於有多中繼站、感測器的各種感測及無線通訊網路之節能傳輸措施則較少著墨。這類網路或供緊急救難時使用，或設置於土質敏感區，於溪流沿岸、橋邊或環境保護區內以偵測水位、風速、溫度、氣壓或異常氣體等都是位在比較偏遠，電力不便或無法到達之處，中繼站或感測器之電源只能仰賴電池供應，其電能的使用效率遂格外重要。

本論文便是考慮這類有固定能量中繼站(Fixed-Energy Relays)的無線網路環 境下的中繼站選擇。我們提出有效率運用這些固定能量中繼站以傳送最大量資訊 的中繼站選擇方案。由於各中繼站離傳輸端與目的端之距離不一，選擇通道狀況 最好的鏈路此即許多文獻使用或提及的BRS (Best Relay Selection) 選擇法通常無法達到此目標。我們選擇依據統計的相對鏈路增益(relative equivalent end-to-end link gain)最好的中繼站反而有較BRS為佳的總傳輸量。為防止因要等待較佳的鏈路（通道）狀況而延宕中繼站的選擇（因統計上未來一定有更佳的鏈路狀況出現）並考量每次傳輸前的通道估計與回報所耗損的能量，我們因此設定了最低的單次傳輸量，只要所選擇的中繼站其等效鏈路增益足夠支持此最低傳輸量即必須進行傳輸。

我們針對上述選擇策略詳細分析了其統計行為，以估測相關的網路生命期與 總傳輸量。這個部份在中繼點的研究中非常少見，但如此分析可以避免耗時的電 腦模擬式預測，也方便瞭解各種系統及通道參數如何影響系統性能表現。事實上 我們的電腦模擬也證明我們的分析的確可以提供非常準確的性能預測。

Relay assisted network has been a very popular and important issue recently, and various selection methods have been put forth by other fellow researchers. The main topic discussed includes the throughput improvement, the fairness awareness, even MIMO can sometimes be involved. Recently, there are a group of researchers start to consider a new and more practical scenario, the energies on the relays are limited. The energy-limited relay scheme can be adopted in the area where it is hard to provide a constant power supply, for example, in the dessert, in the middle of Pacific ocean, or in the mountains. It is very difficult and not economical profitable to assume the relays to have constant power supply in the above mentioned areas, and thus energylimited relay schemes must be considered. In addition, energy-limited relay scheme is also suitable to provide essential emergency communications when either a natural or a human-made disaster strikes. In this study, we propose and analyze a highly-efficient and excellent-performance relay selection method. We compare our proposed algorithm to both the well-known conventional BRS (Best Relay Selection) algortihm and a rather trivial Max-Life algorithm, and we can see in the simulation part that our proposed algorithm is better. Moreover, since the total energy is fixed for the network and our scheme uses this energy more efficiently than BRS, we will call ourself a greener technology.