無線感測網路(wireless sensor network; WSN)是由感測節點所組成，感測節點由於其運作環境之特性，故大多以電池為其主要能量之供應，因此其設計必須要符合簡單、便宜、低功率、長時間運作等考量。尤其是能量的使用效率，一直是很重要的研究議題。在IEEE 802.15.4標準中，MAC層使用修改過的碰撞避免式載波偵測多重存取(carrier sense multiple access with collision avoidance; CSMA/CA)來存取通道以達到較小的能量消耗，但是此一機制對於隱藏節點問題(hidden node problem; HNP)並無法防範。在先前的研究中發現，於一個節點隨機分佈的網路裡，節點間發生產生隱藏節點問題之機率高達41%。因此，此一問題將造成資料的碰撞，重複的傳送資料，使能量大量的消耗，因而降低無線感測網路的壽命。
　　有鑑於以往避免隱藏節點的方式，如RTS/CTS(request to send/clear to send)協定並不適合使用在IEEE 802.15.4標準之下，在不增加網路的額外負擔(overhead)之下，我們參考先前的研究使用分群的概念，將可傳輸的時間分成若干的區段，且將整個網路的成員分成若干群，最多六群。每個群有屬於自己的存取區段，群內的節點必須彼此互相不為隱藏節點。當協調者(coordinator)發現隱藏節點造成碰撞發生時，便會開始執行分群的機制，以避免隱藏節點碰撞的再度發生。
　　本論文有效改善先前分群策略的缺點；此外，我們的分群的演算機制可相容於僅支援IEEE 802.15.4標準的節點，使其能在適當的時間進行傳輸，且不會與使用分群機制的節點產生碰撞，並且可動態的調整各群的存取區間，以符合網路的使用效率。經由模擬的方式，我們將提出的方法與IEEE 802.15.4標準以及先前的分群機制比較，從模擬結果顯示，本論文的方法有較佳的結果。

　　Wireless sensor networks (WSN) is composed of by sensor nodes. Due to its operational environment of sensor nodes, the battery is used as its main energy source. Therefore its design must meet a simple, cheap, low-power, long-term operation considerations. In particular, the use of energy efficiency has been very important research topics. In the IEEE 802.15.4 standard, MAC layer include modified CSMA/CA algorithm to achieve smaller energy consumption. However, such an algorithm can't prevent hidden node problem(HNP). In previous studies have found that if the node distribution is uniform, the probability of occurrence of HNP is as high as 41%. So, this problem will results in data collision, repeated transmission of data, and a large amount of energy consumption, thus lowering wireless sensor networks lifetime.
　　In view of the past to avoid HNP, like RTS/CTS(request to send/clear to send) mechanism is not suitable for use under the IEEE 802.15.4 standard. Under the prerequisite of not increasing additional overhead of sensor network, we refer to the concept of group strategy. Grouping strategy divide the transmission time into several segments, and the entire network of nodes can be divided into several groups, the largest of six groups. Each group has its own access segments, and in the group HNP must not exist. When the coordinator found the HNP is exist, it will begin the implementation of a mechanism to avoid the recurrence of HNP.
　　In this thesis, we proposed the enhanced group strategy, it effectively improves the disadvantage of traditional grouping strategy. In addition, our strategy improves the compatibility with the standard IEEE 802.15.4 nodes, it can be made at the appropriate time transmission, and will not have a collision with the grouping node. It can also dynamically adjust the access time of each group, in line with the efficient use of the bandwidth. Through simulations, we compare our proposed strategy, previous grouping strategy, and the IEEE 802.15.4 standard. The simulation results show that our strategy has a better result.

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