| 摘要: | 無線感測網路係指由數百至數千個微小的感測器所組成之網路系統。此系統中的感測器有二個任務，一個是收集自己周圍環境中，我們所需要的資料，另一個則是利用無線網路將收集到的資料傳至基地台。
因為該網路中的感測器是利用電池作為電力來源，且感測網路的主要用途是在於觀測不易實地探查之環境，故散佈之後往往難以回收，就算可以回收，要為此數量龐大的感測器充電或是更換電池也不是件易事，所以對感測器的各個組成部份而言，能源消耗都是重要考量。在此論文中，我們將探討的重心放在無線感測網路中的資料收集架構上，因為對感測器而言，其能源花費的最主要因素就是在於資料傳輸所耗去的部份。所以若能在此部份有所突破，則感測器網路的生命期將會有顯著的提升。
在感測網路中主要有兩種資料收集方法，一種是感測器定期回報資料給基地台，稱之為data gathering，另一種則是每當基地台需要資料時，再發送要求至網路中，這稱之為data dissemination。其中前者的代表有LEACH (Low Energy Adaptive Clustering Hierarchy)及PEGASIS (Power Efficient GAthering in Sensor Information Systems)等，而後者的代表有Directed Diffusion及SEAD (Scalable Energy-efficient Asynchronous Dissemination)等。在論文中，我們將對這兩種資料收集方法作各別的探討。
我們以節省能源為出發點，參考過去所提出之資料收集架構的優缺點，提出適合於不同需求的資料收集架構，並在能源之外，再加入新的考量，比如減少收集資料所需之時間(transmission delay)、以分散式來建構、及為此網路加入容錯(fault-tolerant)等，以建出合於感測器網路之需求，且強健之資料收集架構。
從研究的結果中，我們可以得知，我們的方法能夠將我們所考量到的各個要素達成平衡，取得最佳化。利用這些資料收集架構將可以使感測器網路的應用層面更為廣闊。
Wireless sensor networks consist of hundreds or thousands of sensor nodes. These nodes have two tasks, the first is to collect information we want, and the second is to transmit the sensed data to the base station.
The power of the nodes is limited battery, and nodes are always deployed to gather information in inhospitable or dangerous environment, so it is difficult to recharge their power. Even if nodes are rechargeable, the hung number of nodes will also make recharge inefficient. So in each component of sensor node, energy dispassion is the important consideration.
In this paper we focus on the point of transmission schemes for wireless sensor networks because the transmission is the main consumer of battery power. If we can make good progress on them, we will also bring significant improvement on the life time of the sensor network.
There are two kinds of schemes to collect sensed data, one is that nodes periodically report their collected data to the base station, which is named data gathering, like LEACH (Low Energy Adaptive Clustering Hierarchy) and PEGASIS (Power Efficient GAthering in Sensor Information Systems), another is that nodes transmit their gathered data only when the base station transmits its interest, which is named data dissemination, like directed-diffusion and SEAD (Scalable Energy-efficient Asynchronous Dissemination). In this paper, we will discuss these two kinds of schemes separately.
We propose several data gathering schemes for wireless sensor networks, which not only takes energy efficiency for consideration but also other important terms into account, like efficiency of transmission delay, distributed way of construction schemes, and fault tolerant. After balancing these considerations, we can produce power efficient, robust and fast data gathering schemes for wireless sensor networks. |
