| Wireless Sensor Network(WSN),which is composed of the convergence of sensor, nested computation, networks and wireless communication technologies. As a new research field, WSN provides lots of challengeable projects to the domestic and international scholars.Medium Access Control(MAC)protocol is an important foundation technology of network architecture. In WSN, its main function is to establish a data transmission network connecting and allocate the communication resources reasonable and efficiently. The main objective of the traditional network is to access resources on the premise of fair use, improve throughput and bandwidth utilization. There are some new requires because of the characteristics of WSN, including high throughput, low latency and dynamically extensible etc.This paper describes the design of MAC protocols in wireless sensor networks in recent years and carries out a comparative analysis. Although some of the MAC protocols have achieved many successes, but also have some problems, there are too many assumptions were made in the design of the model of WSN. The application environments of WSN are often very complicated, many factors will make sensor nodes move from the original position, and these MAC protocols are difficult to adapt to these topological structure changes. We discuss the mobility in WSN, and give the definition of weak mobility and strong mobility respectively. In addition, energy efficiency is one of the major factors constraining WSN, but it does not mean to all. For application-oriented WSN, to design MAC protocol to meet the various requirements is unrealistic and we should address the different needs of the application. In practical application, sensors send data is different, because different nodes have different data rates, and the urgency of data is also different. Distributing different nodes in the same time slot will lower WSN Channel utilization and fairness obviously. Due to the above reasons, we present a new MAC protocol (Adaptive MAC protocol based on Clustering for Wireless Sensor Networks, AMAC). It draws on the idea of clustering, and uses LEACH as the mechanism of clustering, cluster head selection and rotation. It also integrates the advantage of scheduled-based MAC protocols with the advantage contention-based MAC protocols. The using of slot applying by the cluster members and mediating the applications by the cluster head makes it avoid the waste caused by the traditional fixed time slot allocation, so improves the real-time of the data transmission. There are no packet collisions and retransmissions because of the using of slot allocation in data transmission and mediation broadcasting. Although it is taken on the form of contention-based in the random access time, results in the energy loss because of the transmission of conflict. However, this time is smaller compare with the frame time, and it will not affect the overall energy saving effect. Meanwhile, re-clustering and rotating cluster head periodically would make a balance use of the energy, there are no nodes dead earlier because of energy exhaust, so it extends the life time of the WSN. The simulation results show that AMAC outperforms other MAC protocols in the real-time and mobility wireless sensor networks. |
