行動收集點與代理節點改善無線感測網路中次能量洞問題

無線感測網路乃依監控之需而大量、快速部署節點所形成的網路拓墣，可部署於待持續偵測的環境中，將偵測到的資料以多重跳躍方式回傳至後端資訊收集點(Sink)。為維續感測網路之運作，節點耗電能的問題是項重要的考慮，倘若節點喪失正常運作所需之電能時，則節點無法再偵測其周圍內的環境物理量，當然也喪失與鄰近節點通訊的能力。上述感測節點失能的問題，以位於距離Sink較近的環型區域內(Ring-0層)之節點最為嚴重，因其經常代轉遞感測訊息至Sink而致快速耗能，於電能消耗殆盡後便易於Sink周圍逐漸形成所謂的”能量洞”。於Sink周圍部署代理節點後雖可解決Ring-0層能量洞，惟位於代理節點之一次跳躍範圍內Ring-2層感測節點，亦需承擔轉送更外層之資料，如此易使Ring-2層之感測節點因頻於轉送資料而消耗過多電能，若網路感測區域更廣泛時(層數較多時)，勢必在該層易造成感測節點能量快速耗盡導致失效，形成”次能量洞”問題。為此，本文提出以行動收集點與行動代理節點機制(MSMA)，且行動收集點與行動代理節點之相對部署距離與位置不因移動而改變。此外，將依據感測資料之傳遞路徑以及各感測節點轉送封包之次數等資訊，以決定行動收集點下一步之移動方位。藉此行動收集點與行動代理節點之佈署有效改善感測網路中次能量洞問題，藉以降低至Sink 的路由距離與特定感測節點的能量消耗，來延長感測節點與無線感測網路總體的存活時間。最後，針對行動收集點與代理節點機制，以不同的事件分佈及網路負載平衡作效能評估，並以網路存活時間、路由平均跳躍數與SN剩餘電能作為量測標的。規劃模擬實驗以比較MSMA、RDM及STC等策略之效能優劣。由實驗結果得知，當網路區域越大時，MSMA比STC可在延長網路存活時間上獲得較大的改善幅度。在事件集中式分佈產生於網路區域實驗中，MSMA較STC提升了88.2%的存活時間、較RDM提升了77.3%；在事件分散式分佈產生於網路區域實驗中，MSMA較STC提升了64.8%的存活時間、較RDM提升了52%。因此，當事件發生集中於一區塊時，MSMA可準確移動靠近負載較重的SN，直接避免特定SN電能快速消耗，更有效率的延長網路存活時間。

關鍵字

無線感測網路；次能量洞；行動代理節點；行動收集點；網路存活時間。

並列摘要

In general, WSN contains of hundreds or thousands of sensor nodes for long-term monitoring and detecting dynamic environmental data in the sensed areas. Each deployed node can detect and forward the sensed data via a hop-to-hop route to the data sink. For prolonging the lifetime of WSN, how to effectively save power energy for nodes becomes one important research issue. When a node almost ran out of power energy, it cannot sense and forward data to others as usual. Since the sensor node consumes all energy, its status becomes “invalid” or “dead”. When a lot of neighboring nodes are dead gradually in WSN, the situation forms a “hole” in the topology. Most of the dead nodes are around at the Ring-0 layer nearest to the sink node, because they consumed more power for forwarding data to sink than others in outer layers. The area occupied by those dead nodes that cannot detect and communicate is called “Energy Hole”. Deploying the agent nodes around the sink can improve the energy-hole problem. However, SNs located at Ring-2 still waste extra energy on forwarding data from outer layer to ANs. When the coverage range of WSN is widen, the problem of “Sub-energy holes” could easily from and become a critical problem in WSN. We proposed a mobile mechanism for sink and agent nodes. That is, sink and ANs can move to the target and keep the relative distance. Besides, mobile sink can decide the next target area according to the data routes and the number of SN forwarding data packets. By mobile sink and agent nodes solving the Sub-energy holes problem, WSN can shorten the route to sink and the power consumption of SNs; hence, prolong the lifetime of WSN. Finally, we utilize different event distributions and load balance of the network to measure the network survival time, average number of hops and the residual power of SN. A simulation was conducted to evaluate the performances of MSMA, RDM and STC. The simulation results showed that when the network gets larger, MSMA outperformed STC in prolonging the network lifetime. In event-centralized distribution in the network, MSMA outperformed STC and RDM by 88.2% and 77.3% in survival time, respectively; in event-random distribution in the network, MSMA outperformed STC and RDM by 64.8% and 52%, respectively. When the sensed events gather in some area, MSMA could move close to the SN with a higher forwarding load, directly reduce the power exhaustion of the SN, and prolong the network survival time more efficiently.

並列關鍵字

WSN ； Sub-Energy Holes ； Mobile Agent Node ； Mobile Sink ； Lifetime.

參考文獻

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行動收集點與代理節點改善無線感測網路中次能量洞問題

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