Research On MAC Layer Protocol Of Wireless Sensor Network

The Wireless Sensor Network(WSN)distributes many sensor nodes randomly within the monitoring area to complete the monitoring,collection,processing and transmission of the required information.Currently,because of its advantages on strong flexibility and less investment capital,it is widely used in many fields.The sensor nodes usually needs the battery to supply energy,but in some of the monitoring area away from the people,supply energy to the energy exhausted nodes timely is unrealistic,so designing a suitable network protocol to reduce energy consumption of the node during the communication process is really necessary.The Medium Access Control(MAC)protocol is at the bottom of the wireless sensor network protocol and has a great influence on the sensor network performance.It is one of the key network protocols to ensure the efficient communication of the wireless sensor network.In the MAC protocol,the Sensor-MAC(S-MAC)protocol adoped fixed duty cycle and a random backoff mechanism that can not adapt to the changes in network traffic,which will cause the degredation of network performance.Taking reduce the energy consumption of nodes and extend the network life as the primary goal,this thesis proposes a protocol named Dynamic Self-adaptive S-MAC(DSA-SMAC)based on S-MAC protocol.The new protocol mainly improved on two aspects.Firstly,the contention window in the S-MAC protocol is fixed,so the calculated value of the backoff time by a random selection in the competition window is also fixed,which makes it difficult to allocate the channel better during the data transfer.In this thesis,an improved backoff algorithm is proposed to solve this problem.In order to update the contention window in real time,the competition window field is added to the control frame,and the parameters like continuous successfully transfer number?continuous failure transfer number and thresholds are also be introduced,so the contention windows can be dynamically adjusted and the recurrence of conflicts also can be reduced;Secondly,the duty cycle of the S-MAC protocol is a value that does not vary with network traffic.Excessive duty cycle will lead to a waste of node energy.Low duty cycle will cause higher network end-to-end latency and low throughput.Therefore,based on the S-MAC protocol,a real-time adjustment strategy of the duty cycle algorithm is proposed.This strategy predicts the change of network load according to the number of queuing packets in the node buffer queue and dynamicly adjusts the duty cycle of the nodes.When the network has a lot of data to transmit,the S-MAC original listening / sleep cycle will be divided into several small cycle to adapt to the network better.When the network has few data to transmit,it does not have to divide the original cycle.The simulation experiments of DSA-SMAC,S-MAC and B-SMAC protocols are carried out under different network scenarios on NS2.The simulation results shows that the DSA-SMAC protocol has shown an absolute advantage in energy saving,which is the primary goal of wireless sensor network protocol design,and its end-to-end delay,throughput and packet successfully received ratio has also be improved in some extent.