Design And Implementation Of Time Synchronization And Dormancy Scheduling Method Used In Wireless Sensor Network

With the rapid development of microelectronic systems (MEMS), system-on-chip (SOC), wireless communications and low-power embedded technology, wireless sensor networks (WSN) is considered one of the most important technology in the 21st century for its low power, low cost, distributed and self-organizing features. In recent years, WSN attracts considerable attention and investment of the international community. Besides, the development of WSN is related to the national security, economic development, and other important fields. Therefore it has been used widely in military affairs, industry, transportation, security, medical, detection, family, office environment etc.Time synchronization and dormancy scheduling method play significant roles in the overall control of the whole wireless sensor networks. In traditional time synchronization method RBS and DMTS are used more widely than others. For one thing, RBS method is very easy to operate, but has too many messages between sinks in time synchronization process. Also, it usually makes the massages delay, for the reason that it is required to waiting free channel before sending messages. Hence, the accuracy can not be guaranteed. On the other hand, DMTS method could guarantee the accuracy of time synchronization. However, it is required to recording timestamps directly by hardware when sending synchronization information. Unfortunately, the general hardware could not complete this operation, and that is the great limitations of this method. Sinks in traditional wireless sensor network neither use dormancy scheduling method nor cluster dormancy scheduling method. As the equipment start, it will work without stopping and waste a lot of power, so that there is huge impact on the capacity of battery and the applications on wireless sensor network technology. On the other hand, at present, some network which using dormancy scheduling method, usually use cluster dormancy scheduling method to maintain several number of sinks continue to work, and to awake the others by turns. When the sink works, it firstly sends data to the cluster. Then the cluster will keep this data until the sink awaken and transmit it. However, firstly, under this method, cluster could not stop working, and its life will impact the entire network directly. Secondly, all the data is transmitted by the cluster, and this requires the cluster to receive a large amount of data. It means that the data may easily to be lost and be in a state of insecurity for the over loading by the cluster. Finally, the cluster needs to monitor the ordinary sinks and wait for their awakening. Also, this may waste a lot of resources. Thus, we need a better dormancy scheduling method, which using in wireless sensor networks, to make the wireless network more energy-efficient.According to this requirement, this report will give a new implementation method. It will be introduced in two aspects.The first one is time synchronization. In wireless sensor networks (Distributed System), each sink has its own independent clock. It is necessary to use the time synchronization technology to maintain the unity of the time of entire wireless sensor networks. This new method includes the design of the clock, timestamp method and time synchronization method. The design of the clock makes the clock more suitable for wireless sensor network, more commonly to popularize, and more easily to achieve time synchronization. Furthermore, timestamp method gives the message on the sink timestamps when the sinks send and receive data in the network, as the basis for the time synchronization and providing the logo for the upper services at the same time. Last, time synchronization method provides a simple and efficient method to make sinks in the network time synchronization.Another one is the dormancy scheduling, and it is based on time synchronization. This method makes the entire wireless sensor networks use a unified dormancy scheduling strategy. That is, there is a unified time to control sinks dormancy. When the clock reached a dormancy point-in-time, sinks enter dormancy state unified. Also, when the clock reached a work point-in-time, sinks enter work state unified. The overall clock enters sleep point-in-time and work point-in-time uninterrupted by cycle. This method requires several hardware equipments, such as at clock module in wireless sensor network sink and the data storage module.By researching of time synchronization, as well as comparing with other methods, it can be found a more suitable, simple and cost-effective way to improve the accuracy of time synchronization and flexibility and to reduce the limitations of time synchronization. Meanwhile, a dormancy scheduling method will be designed to conserve energy in wireless sensor network, which is based on time synchronization, to keep sinks working and sleeping regularly, in addition to making sinks self-regulated and live without depending on the data flow. Therefore, there will be a full use of network resources to avoid the excessive load of individual sinks. Even in bad network conditions, data also can be re-issued regularly to ensure the security of data transmission. Consequently, there will be an achievement in collecting data effectively, supporting various types wireless network sinks in various areas, and increasing versatility.