| The basic unit of Wireless Sensor Networks(WSNs)is sensor nodes.The size of WSNs may be large or small,which may include thousands of or several nodes in WSNs respectively.Sometimes these nodes are randomly deployed in a certain area and form a variety of data streams by self-organization.Sometimes they are deployed in a certain area and only need to collect information in a fixed location.Each node has a set sensing area,collects various information related to or irrelevant to the task in its responsible area and then transmits the information to the sink node hop by hop.The sink node transmits the information to the user after the information processing.Therefore,the nodes in the WSNs should not only have their own characteristics,but also stick to the same goal and complete the information collection process together.In WSNs,the Medium Access Control(MAC)protocol is responsible for the channel access of nodes,which is one of the important guarantees of information transmission and can affect the lifetime of WSNs.The sensor node is a battery-powered node with limited energy.When energy runs out,the sensor node located in the position where the battery is not easily to replace will die.An energy-efficient MAC protocol can reduce battery power consumption and prolong the network's life cycle as much as possible.The outline of this thesis is as follows:Firstly,the basic structure of WSNs is summarized.The current MAC protocols are classified and discussed and the design goal of MAC protocol is put forward.Secondly,this thesis analyzes the backoff mechanism in synchronous protocol and the shortcomings are pointed out.A new backoff mechanism is put forward after discussing several typical backoff mechanisms.The performance of the new mechanism is compared with the traditional mechanism through NS2 simulation platform.The results show that the network energy consumption of the new mechanism is reduced and the throughput is improved.Thirdly,the asynchronous protocol RI-MAC(Receiver Initiated-MAC)is discussed and a new TQ-MAC(Transmission Quick-MAC)protocol aiming at improving low energy efficiency and long time channel occupation is proposed.The performance test between RI-MAC protocol and TQ-MAC protocol shows that TQ-MAC protocol has more advantages.The throughput,time delay and energy efficiency are all improved. |
