Rearch On The MAC Protocol In Wireless Sensor Networks With Variable Load

Applying WSN (Wireless Sensor Networks) in those monitoring systems with variable load will upgrade the safety level and reduce the hidden accident significantly. Compared to traditional networks, the MAC technology of WSN faces more problems, especially the problem of limited-energy. Therefore, the sticking point to solve in these monitoring systems is how to enhance energy-efficiency and reduce delay of the correspondence time as more as possible.Firstly, with this research and application background, this thesis first establishes a system layered model of WSN applied in monitoring system whose load is variable, and analyzes the different layers of the model. Then proposes a new MAC protocol ASMAC (Adaptive Sensor MAC) of lications of WSN. ASMAC is on the base of SMAC and proposes two improvements of SMAC.(1) The backoff scheme of SMAC uses a Contention-Windows (CW) of constant which is difficult to adapt the dynamic load. When the load of network is too heavy, this constant CW could not meet the requirement of network. It can not solve the growing delay and the declining throughput which are as the results of collision. This paper proposes an adaptive slow backoff scheme (Adaptive Increment Adaptive Decrement, AIAD) which can dynamicly adjust the CW based on the failure times. AIAD can solve some collision in effect which is as a result of the growing load. In addition, it can reduce the delay and enhance the throughput.(2) The low-duty-cycle scheme of SMAC can make the node sleep most of the time on the purpose of saving energy. But this constant low-duty-cycle could not adapt to heavy load. When the load is too heavy, the sender could not send data until the receiver wake up. This results in growing delay and declining throughput. If using bigger duty-cycle, when the load is light, there is too much unwanted listening. This paper proposes an adaptive duty-cycle scheme (Adaptive DutyCycle, ADC) which can dynamically periodically adjust the duty-cycle based on the load of the last period. ADC can efficiently reduce the delay and enhance the throughput. Finally, this paper implements simulation in NS2. The results prove that compared to SMAC, ASMAC has better performance in delay and throughput in the WSN applied in monitoring system whose load is variable.