保證無線感測網路中覆蓋及連結程度的分散式協定

Abstract

無線感測網路近年來受到眾多矚目，它是由許多價格便宜的感測器所組成，每一個感測器皆具有蒐集、儲存、及處理從環境中感測到的資料，並透過無線連結能和鄰近的感測器交換資訊。一個無線感測網路要能夠成功被應用在實際環境中，感測器必須要能同時能維持感測覆蓋率以及網路的連結性，這樣的研究議題已經在[24, 30]被提出來討論，在這兩篇論文中都達到相似的結論：只要感測器的通訊範圍不小於兩倍的感測範圍，那麼覆蓋程度同時也意味著相同的連結程度。而在這篇論文中，是從不同的角度來探討此議題，提出不依賴以上假設但是能夠同時保證無線感測網路之覆蓋性及連結性的必須及充要條。這篇論文是我們先前論文[9, 10]的重要延伸，在先前的論文中描述了如何決定給定的感測網路之覆蓋程度，但是並沒有考慮到網路之連結性議題。這篇論文是第一個淮許感測器的感測範圍及通訊範圍能夠是任意關係之研究，我們還利用提出來之同時保證無線感測網路之覆蓋性及連結性的條件發展出能夠決定，甚至進而調整網路中覆蓋性及連結性的分散式協定；當一個感測網路中有過多的感測器存在時，能夠調整無線感測網路之覆蓋性及連結性能夠延長網路的生命期，因此我們藉由讓一些感測器進入睡眠模式且調整通訊範圍來達到此目標。

Wireless sensor networks have attracted a lot of attention recently. Such environments may consist of many inexpensive nodes, each capable of collecting, storing, and processing environmental information, and communicating with eighboring nodes through wireless links. For a sensor network to operate successfully, sensors must maintain both sensing coverage and network connectivity. This issue has been studied in [24, 30], both of which reach a similar conclusion that coverage can imply connectivity as long as sensors’ communication ranges are no less than twice their sensing ranges. In this paper, without relying on this strong assumption, we investigate the issue from a different angle and develop several necessary and sufficient conditions for ensuring coverage and connectivity of a sensor network. Hence, the results significantly generalize the results in [24, 30]. This work is also a significant extension of our earlier work [9, 10], which addresses how to determine the level of coverage of a given sensor network, but does not consider the network connectivity issue. Our work is the first work allowing an arbitrary relationship between sensing ranges and communication distances of sensor nodes. We develop decentralized solutions for determining, or even adjusting, the levels of coverage and connectivity of a given network. Adjusting levels of coverage and connectivity is necessary when sensors are overly deployed, and we approach this problem by putting sensors to sleep mode and tuning their transmission powers. This results in prolonged network lifetime.