Simulation Study on Wireless Sensor Network

[[abstract]]由於無線感測網路的應用是由許多微型感測器所組成，其數量的多寡依據環境來決定，管理起來有一定的困難度。而當電池耗盡時，通常都無法以更換電池的方式繼續運作，所以，如何降低能量的消耗，是無線感測網路研究上的一大課題。 S-MAC是無線感測網路中一個常見的媒體存取協定。S-MAC把每個循環分成兩個部分：監聽與睡眠週期，在監聽週期中，透過RTS/CTS交換機制進行封包交換。而我們發現，在網路負載較輕時節點在監聽週期間會一直保持監聽狀態，造成額外的能量消耗。假設鄰近節點沒有封包要傳送，則節點在這個循環就不會收到任何RTS，這使得節點必須持續感測通道直到監聽週期結束。 這篇論文提出了一個新的機制，當節點一進入監聽週期時，如果有封包需要傳送，便會發出一個Announce To Send (ATS)封包，而沒有封包要傳送的節點則進行通道感測。如果感測節點無法偵測到能量，它就會立刻進入睡眠模式。模擬結果顯示出我們提出的機制可以有效的減少在輕載時的能量消耗，並且延遲也只有輕微的增加。[[abstract]]The design of Wireless Sensor Networks (WSN) is application-specific and the number of sensor nodes depends on the environment. The network management is difficult and it is hard to replace the battery in the field. As a result, reducing the energy consumption is a major issue for WSNs. S-MAC is a popular MAC protocol for WSNs. A fixed time cycle is divided into two parts: the listen period and the sleep period. Typically packets are exchanged in the listen period based on the well-known RTS/CTS handshake mechanism. We found that a sensor node waste its energy during the listen period when the traffic is light. Suppose that its neighbors have no packet to transmit, it does not receive any RTS packet in this cycle. As a result, it needs to sense the channel until the listen period ends. This thesis proposes a new mechanism by which a node with packets sends an Announce To Send (ATS) packet at the beginning of the data period and a node without any packet senses the channel. If a sensing node fails to detect the energy, it can enter the sleep mode immediately. Simulation results show that the proposed scheme significantly reduce the consumed energy at light loads with slightly increase in packet delay.[[note]]碩