在此論文中，我們針對無線感測網路提出一個新的密度控制演算法，儘量使得較少的感測器進入活躍狀態，以對一個指定的監視區域，達成連通的完整覆蓋；而其他未進入活躍狀態的節點則進入休眠狀態，以節省電力資源，達到增長感測網路生命週期的效果。不像其他相關的演算法，本篇論文所提演算法不依賴感測器的位置資訊，它只要求處於活躍狀態的感測器週期性的發送兩個不同傳送距離的信標訊號(beacon)，而接收到這些信標訊號的感測器便可依據信標訊號中的資訊決定應該處於活躍狀態或者是休眠狀態。當有任何處於活躍狀態節點電力用盡或者是故障的時候，處於休眠狀態的節點即可立即進入活躍狀態，接替其感測工作，因而達到容錯機制的功能。在具有足夠高密度(sufficiently high density)感測器及感測器無線傳輸距離大於等於2倍感測距離的假設情況下，所提演算法在最佳情況下可以達到最佳連通完整覆蓋。我們並執行模擬實驗，探討a參數與節點密度對演算法效能的影響，其中a ((1/√3) < a < 1) 為兩個信標訊號傳送距離的比值。這些模擬實驗數據，讓我們可以根據給定的感測器密度，設定適當的 a 值以便得到較佳的演算法效能。 In this thesis, we propose a new density control algorithm for wireless sensor networks to keep as few as possible sensors in active state to achieve a connected coverage of a specific area of interest. Inactive sensors can turn off sensor modules to save energy for prolonging the network lifetime. Unlike other algorithms, the proposed algorithm does not rely on position information of sensors. It just requires each active sensor to send two beacons of distinct transmission ranges periodically. Sensors can then decide to stay in the active state or inactive state. When any active sensor runs out of energy or fails, one or more inactive sensors can switch to the active state to take over the surveillance responsibility. The proposed algorithm is thus of the capability of fault-tolerance. Under the assumption of sufficiently high density of sensors and the assumption of Rc > 2Rs, we show our algorithm can achieve optimal connected coverage in the best case, where Rc and Rs are the radio communication radius and the sensing radius of sensors, respectively. Furthermore, we perform simulation experiments to investigate the impact of the node density and the ratio a on algorithm performance, where a, (1/√3) < a < 1, is the ratio of the transmission ranges of the two beacons. By simulation results, we can set a to be proper values according to given node densities for better performance.
