| 摘要: | 無線感測器網路(Wireless Sensor Networks)是一門新興的無線網路技術，該技術可廣泛地使用於各種不同的領域。一般而言，無線感測器網路是由許多以電池作為能源供應的節點所組成。因此，如何節省能源便成為重要的問題之一。我們在媒介存取控制層中，設計兩個有效率的電量節省通訊協定。首先，我們提出一個有效率的時槽預約之媒介存取通訊協定(Efficient Slot Reservation Medium Access Control, ESR-MAC)，該協定結合了競爭模式、行程安排模式、及預留模式等特性，透過預約傳送時槽以達成無競爭與無碰撞的通訊連結，以增加網路流量、減少碰撞並降低傳送延遲。另外該協定保留了行程安排模式的優點，使網路節點週期性進入睡眠模式來節省電量的消耗，達到省電功能。模擬結果顯示，時槽預約媒介存取通訊協定能在省電的前提下，有效的改進網路流量並且減少傳送延遲。另外，我們提出一個非同步工作循環調整之媒介存取通訊協定。此協定透過使節點進入睡眠模式來保存能量，並採用兩個時間調整機制：延長工作循環調整機制及下次工作循環調整機制，來能增加通道使用率、網路流量並減少傳送延遲。在正常工作循環時，接收者的收發時間可能受到鄰居的佔用或干擾，因此，延長工作循環調整機制能新增一個工作時段以彌補接收者的損失，故能增加網路流量並減少傳送延遲。而下次工作循環調整機制則是經由接收者的收發器狀態，來預測目前網路交通量，並調整下次的工作循環，以求較高的通道使用率。實測與模擬結果顯示，我們的協定能有效的改進網路流量、減少傳送延遲並保存節點電量以延長網路存活時間。 Wireless sensor network (WSN) is an emerging technology that is expected to be used in a wide range of applications such as target tracking, environment monitoring, habitat sensing, and home security. Making energy conservation is one of the most important issues in WSNs. In the viewpoint of communication protocols, energy conservation can be addressed at each layer of the network protocol stack, but our researches are focused on the Medium Access Control (MAC) layer. Two energy efficient MAC protocols are designed in the dissertation. A good MAC protocol must always consider the following attributes: energy efficiency, scalability, fairness, latency, and throughput. We propose an Efficient Slot Reservation (ESR) MAC protocol which combines contention-based, scheduling-based, and reserving-based schemes to achieve energy efficiency, reduce transmission delay, and decrease collision probability of data transmission. In ESR-MAC, nodes periodically turn into sleeping mode to save energy and the reservation slots to provide collision-free transmissions between the senders and the receivers. Thus, channel utilization is greatly improved. The simulation results show that our protocol provides high throughput, low delivery latency and low energy consumption compared to other methods. In addition, we propose an Asynchronous Duty Cycle Adjustment (ADCA) MAC protocol. ADCA conserves energy by putting nodes into the sleeping mode. ADCA also increases the throughput and decreases the transmission delay by adjusting two time periods: the extended period and the next contention period. Furthermore, the asynchronous schedule of ADCA also increases the successful transmitting rate and channel utilization. We implement ADCA and T-MAC protocols on NCU Wireless Sensor Network TestBed (WSNTB) and simulate them by ns-2 simulator for the sake of performance evaluation. The experiment results show that ADCA has better performances in terms of energy saving, network throughput and transmission delay. The extra simulation results also show that ADCA improves throughput and decreases the transmission delay without scanting energy efficiency in a large wireless sensor networks. |
