臺灣博碩士論文加值系統

在無線感測網路的研究領域中，如何計算一個區域被多少感測器覆蓋，亦即覆蓋度(Coverage Degree)，是一項很重要的議題。在覆蓋度已經達到需求後，若能將覆蓋感測區域的多餘感測器關掉來節省能源，則當一些感測器工作一段時間之後，那些被關掉電源的感測器就可以醒來接續監測任務，可延長網路的壽命，上述的動作也就是所謂的休眠排程(Sleep Scheduling)。在一些已經被提出的方法中，都只考慮如何讓整個感測區域在感測時間中都被感測器所覆蓋，也就是感測區域達成完全覆蓋(Full Covered)，但是卻沒有考慮到感測區域中可能並不需要開啟如此大量的感測器亦可達成完全覆蓋的要求，因此經常造成感測區域被過高重疊覆蓋(Coverage Overlap)的問題，而浪費了感測器寶貴的電源。
本文針對改善重疊覆蓋過高的問題提出GHG (Grouping with Hexagonal Grid)演算法，盡量將所有感測器都分成不同群組，使群組輪流啟動監控感測區域。此方法將感測區域劃分為若干個正六角形的網格，在每一個網格中挑選一個最靠近中心位置的感測器，使得網路拓樸盡可能呈現正六角形排列，以改善重疊覆蓋過高的情形;但由於感測器位於網格正中心的機會不高，而產生感測漏洞(Sensing Hole)，因此需挑選一些額外的感測器來覆蓋此感測漏洞。最後，將這些感測器訂定為一個群組，並從尚未挑選出的感測器中繼續挑選出下一個群組，直到無法挑選出滿足完全覆蓋要求的群組為止。模擬實驗顯示，GHG在平均重疊覆蓋率以及所啟動的感測器數量均優於[16]中的網格演算法。

In the research field of wireless sensor networks, the issue of how to measuring the number of sensors for the coverage of a sensing area, in other words, the coverage degree, is very important. After the coverage degree has reached the requirement, the redundant sensors covering the sensing area can be switched off to save energy. Those that have been turned off can be woken up then to continue the monitoring task while some sensors have been active for a certain period of time. Thus, network lifetime can be prolonged. The above-mentioned procedure is also called sleep scheduling. Among some of the methods that have been proposed, the only issue being considered is how to make the entire sensing area covered by the sensors during the sensing time, namely, how to make the area full covered. However, the fact that it may not be necessary to turn on such a great number of sensors in the sensing area to achieve the requirement of full covered. Therefore, it often causes the problem of coverage overlap in the sensing area, and wastes the valuable energy for sensors.
This thesis proposes a scheme, called GHG (Grouping with Hexagonal Grid). The scheme aimed at the problem of coverage overlap, in which all sensors are divided into as many different groups as possible, and the groups will be turned on alternately to monitor the sensing area. This method divides the sensing area into several hexagonal grids. To improve the coverage overlap problem, the sensor that is closest to the center position in each grid will be selected to make the network topology present a hexagonal form as closely as possible. Nevertheless, due to the low chance of a sensor being right in the center of the grid, a sensing hole is accordingly created. Hence, it is necessary to select some additional sensors to cover this sensing vulnerability. Lastly, these sensors will be set as a group. And the next group will be selected from the sensors that have not been selected. The process will be continued until no group that meets the requirement of full coverage can be selected anymore. The simulation result indicates that GHG can reduce the average coverage overlap ratio and the number of active sensors compared to the grid algorithm in [16].

論文審定書 i
誌謝 ii
摘要 iii
Abstract iv
目錄 vi
圖次 ix
表次 xi
字母縮寫對照表 xii
第ㄧ章 導論 1
1.1 簡介 1
1.2 無線感測網路的設計議題 2
1.3 無線感測網路的覆蓋問題與休眠排程機制 4
1.3.1 無線感測網路的覆蓋問題與連結性之關係 4
1.3.2 無線感測網路的休眠排程機制 5
1.4 研究動機 5
1.5 論文架構 6
第二章 相關研究 7
2.1 無線感測網路的多餘感測器檢查機制 7
2.1.1 扇形偵測法 7
2.1.2 交點偵測法 8
2.1.3 圓周覆蓋偵測法 9
2.2 無線感測網路的休眠排程機制 11
2.2.1 週期性協商的休眠排程機制 11
2.2.2 非週期性決定的休眠排程機制 11
2.3 無線感測網路的正多邊形拓樸 17
第三章 系統之架構與運作 19
3.1 基本假設 20
3.2 初始階段 20
3.2.1 初始階段之功能與名詞解釋 21
3.2.2 子階段1的運作方式:計算圓周覆蓋 22
3.2.3 子階段1的終止條件 23
3.2.4 子階段1的演算法流程 24
3.3 子階段2:感測漏洞填補機制 25
3.3.1 子階段2之功能與名詞解釋 25
3.3.2 子階段2:最小圓覆蓋問題 25
3.3.3 子階段2:選擇額外的unSelected Node啟動 29
3.3.3.1 權重演算法 31
3.3.3.2 權重演算法的運作 33
3.3.4 子階段2的終止條件 38
3.3.5 子階段2的演算法流程 39
3.4 休眠分群演算法 40
第四章 模擬結果與討論 41
4.1 模擬環境假設 42
4.2 模擬環境參數設定 42
4.3 實驗數據分析與討論 44
4.3.1 感測半徑對於無線感測網路的重疊覆蓋率之影響 44
4.3.1.1 感測半徑對於無線感測網路的平均重疊覆蓋率之影響 47
4.3.2 感測器數量對於無線感測網路的重疊覆蓋率之影響 48
4.3.2.1 感測器數量對於無線感測網路的平均重疊覆蓋率之影響 51
4.3.3 在感測時間內啟動的感測器數量 52
4.3.4 單一感測器在感測時間中平均啟動之時間 54
第五章 結論 57
參考文獻 58

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