Improvement of S-MAC Protocol in Wireless Sensor Network
1 Introduction With the development of computers, sensors and wireless communications, a new computer network wireless sensor network has emerged . Due to its wide application prospects, wireless sensor networks are favored by more and more researchers. The medium access control (MAC) protocol determines the way the wireless channel is used, and the limited communication resources are allocated between sensor nodes. 1 Introduction With the development of computers, sensors and wireless communications, a new type of computer network has emerged—— Wireless sensor network . Due to its wide application prospects, wireless sensor networks are favored by more and more researchers. The medium access control (MAC) protocol determines the way the wireless channel is used, and allocates limited communication resources between sensor nodes to build the underlying infrastructure of the sensor network system. The MAC protocol has a greater impact on the performance of sensor networks, and is one of the key network protocols to ensure efficient communication in wireless sensor networks. The S-MAC  protocol is a typical random access MAC protocol based on competition. It is based on the IEEE802.11MAC  protocol and is a sensor network MAC protocol proposed for the energy-saving requirements of sensor networks. . This protocol has good scalability and does not require strict time synchronization, but it also has the problem of delay caused by node activity time that cannot be dynamically changed according to the communication load and node sleep. This article first analyzes the mechanism adopted by the S-MAC protocol, points out its existing problems, and then combines the T-MAC protocol and the D-MAC protocol to propose an improvement method. Finally, through simulation analysis, it is proved that the improved method can make the node activity time flexibly adapt to the change of network communication load, further save energy, and at the same time can greatly reduce the delay caused by node sleep. 2 S-MAC protocol adopts mechanism analysis S-MAC protocol is a control protocol based on competition. It mainly uses the following mechanisms: 'virtual cluster' mechanism: each node broadcasts its own scheduling information at the beginning of each time slot Synchronous data packet, the node that receives the synchronous data packet adjusts the clock as needed. In this way, nodes with the same schedule form a 'virtual cluster'. In principle, the entire network should work in the same 'time slot structure Periodic activity and dormancy mechanism: The S-MAC protocol divides time into multiple frames, and each frame consists of two parts: an active state and a dormant state. In the active state, the node communicates with neighboring nodes, receives or sends data, and the active state is usually fixed at 300ms. In the dormant state, the node turns off its transmitter and receiver to reduce energy consumption. If there is data to be processed at this time, it is cached and processed after the node is in an active state. The idleness is greatly reduced through periodic activity/sleep. Energy loss caused by monitoring. 3 Problems with S-MAC protocol S-MAC protocol adopts periodic activity/sleep scheduling mechanism. The active time is usually fixed and the message rate is variable. The length of time the protocol is active cannot be based on the traffic volume in the network. The dynamic adjustment of the change of the power supply cannot effectively save energy. If the communication module is in the sleep state, if an event is detected, it must wait until the communication module switches to the active cycle to send data. When the intermediate node wants to forward data, the next hop node may be in sleep state, and it must also wait until it switches to Active period, this delay caused by node sleep will increase proportionally with the increase of the number of hops on the path. 4 The improvement of S-MAC protocol For the wireless sensor network S-MAC protocol, the active time of the node cannot be dynamically changed according to the communication load and the delay caused by the sleep of the node. Let us first analyze the pair of T-MAC and D-MAC protocols. Improve it, and then propose your own improvement methods. The T-MAC protocol is mainly proposed for the problem that the S-MAC protocol has a fixed active time and cannot adapt to changes in the communication load. It dynamically adjusts the activity time according to the communication flow on the basis of keeping the period length unchanged. In the active state, if the period timer overflows or the perception network conflict occurs within a given time TA, it ends the active state and enters the dormant state, but the problem of early going to bed is introduced. D-MAC protocol is mainly proposed for the delay problem caused by node sleep. It uses a staggered scheduling mechanism to divide the node period into receiving time, sending time and sleep time. The receiving time and the sending time are equal, and both are the time for sending a data packet. The scheduling of each node has a different offset, and the sending time of the lower node corresponds to the receiving time of the upper node. In this way, data can be continuously transmitted from the data source node to the sink node, reducing transmission delay, but the D-MAC protocol requires strict time synchronization.
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