覆蓋率優先動態路由演算法應用於無線感測器網路之研究

Abstract

無線感測器網路因受到各感測器節點電量、通訊能力及運算能力的限制，使得無線感測器網路系統在實際應用中會有諸多問題需要考量。為改善無線感測器網路的使用壽命，過去許多研究學者利用各種路由演算法來調整節點間的資料傳遞。目前大多數演算法僅多半針對能量平衡、資料傳輸可靠度及節點分群調度方式加以探討。針對軍事偵測、保全系統及老人居家看護等應用，感測器節點在所欲監測的區域內應必須能達到100 % 覆蓋率才能準確偵測任一重要事件，因此覆蓋率因素應當納入感測器網路運作考量之中。因此，吾人提出一高覆蓋率動態路由演算法，透過模擬驗證此演算法能持續維持百分之百覆蓋率且增加網路的運作時間，並透過實作實驗驗證此演算法於實際網路應用之可行性。 在本研究中吾人提出一動態路由演算法，演算法針對能量均衡消耗及高覆蓋率的特性來進行群首挑選機制。利用經過覆蓋率考量後挑選出多餘的節點，讓這些節點主要用於群首節點運作及資料轉傳，藉以延長網路持續維持100 % 覆蓋率的運作時間，並依據傳輸能量消耗與節點剩餘能量來進行動態路由挑選機制。模擬中針對群首挑機制及動態路由挑選機制進行最佳參數分析，並與其他已經發表過的演算法進行性能比較，模擬結果顯示高覆蓋率動態路由演算法有效增加59 %的系統運作時間。 過去大多數所發表的演算法僅透過模擬方式分析性能，為了驗證本演算法確實可於實際應用中使用，本研究之演算法透過NesC語言撰寫，架構於TinyOS 系統上，實際在OctopusII節點上運作。為了驗證及分析本演算法的相關性能，分別於實驗室內及戶外環境進行相關實驗測試，實驗結果顯示動態路由機制確實能有效運作並提升資料回傳率。

There are a lot of issues which need to be considered due to the limited power, the communication range, and the programming ability of wireless sensor nodes. In order to improve the lifetime of wireless sensor networks (WSNs), a number of routing algorithms have been proposed to adjust the data transmission between sensor nodes. Besides the energy efficiency, however, reliability of data transmission and cluster forming method, maintenance of the sensing coverage over the entire monitored area are also essential. In construction of projects that involve operational strategies to responds to specific emergency events such as medical healthcare, battlefield surveillance, or illegal smuggling, the primary concern is to preserve all valuable data acquired from the targeted area without any losing. Hence, this work proposed a novel energy-aware coverage-preserving hierarchical routing (ECHR) algorithm. The performance of ECHR algorithm was evaluated by simulations. In simulations, the ECHR algorithm can maximize the on duty time of full coverage. This work also applied the ECHR algorithm in wireless sensor node with OctopusII platform. The basic idea of the proposed ECHR algorithm is to take the remaining energies of the nodes as well as the coverage redundancy of its sensing ranges into consideration while selecting cluster heads. Intuitively, the sensor nodes deployed in a densely populated area have the higher probability to be selected as cluster heads in each round. These nodes are frequently chosen to be cluster heads, because the loss of nodes from the densely populated area is not significant for the network coverage. In addition, an energy-aware hierarchical routing mechanism was also proposed to determine the optimal route. Extensive series simulations were conducted to analyze the performance of the ECHR algorithm applying to the network with different weight factors of the cluster head selection mechanism and the adaptive energy-aware hierarchical routing mechanism. The simulation results demonstrate that the proposed protocol is able to increase the duration of network on duty and provide up to 59 % of extra service time with 100% sensing coverage ratio comparing with other existing protocols. Most presented researches about routing algorithms only evaluated the performance under simulations. In order to evaluate the feasibility of ECHR algorithm in realistic applications, this work has developed the ECHR algorithm with NesC program on TinyOS. All of experimental tests in laboratory and outdoor environment used wireless sensor nodes, OcotpusII. The experimental results demonstrate that the adaptive routing mechanism of the ECHR algorithm is able to reduce the data loss rate.