Research Of Real-time MAC Protocols In Event-driven Wireless Sensor Networks

The Wireless Sensor Networks(WSNs) typically consists of a large number of inexpensive, small, low-power communication devices called sensor nodes and one or more computing centers. The nodes detect and send the massages to the observers through the WSNs. Advances in energy-efficient design and wireless technologies have enabled the manufacture of the small devices to support several important wireless applications, including national defense military, environmental monitoring, target tracking, anti-terrorism disaster relief and medical application.In the architecture of wireless sensor networks, medium access control(MAC) protocol which lies below other network protocols, controls the usage mode of wireless channel is used and nodes share network media access. The MAC protocol assigns the wireless resources to nodes and decides the performance of network throughput, delay, and lifetime and so on. The simple and robust MAC protocol ensures the effective communication. The MAC protocol is widely researched in the field of WSNs; however, the existing MAC protocols are less designed for real-time of message. So in this paper, we propose a dynamic event driven real-time MAC(DEDR-MAC) protocol. The main contributions of my paper include:Firstly, based on the design target of event-driven wireless sensor network, this paper proposed a dynamic real-time event-driven wireless sensor networks MAC protocol(DEDR–MAC). DEDR-MAC is based on the idea of reservation scheme, and a reservation time slots assignment algorithm and scheduling time slots adjustment algorithm are presented. The reservation time slots assignment algorithm build reservation plan based on the current network topology for sending reservation request by nodes, so slots in scheduling phase can be reserved. This algorithm builds reservation plan as far as possible let nodes which do not conflict can send in parallel. The algorithm reduces transmission delay and avoids booking requests the data conflict. In the scheduling time slots adjustment algorithm, the event with the highest priority is chosen as a standard to prevent the competition of lower priority event. This algorithm can effectively reduce the collisions and adjust the time slot number in scheduling phase. Therefore this algorithm can confirm integrity and real time of the data transmission and reduce the number of nodes in the idle listening time as well as effectively reduce the energy consumption of nodes.Secondly, I simulated and verified the DEDR-MAC protocol in the open-source software simulation platform NS2. After we introduced the principle and implementation mechanism of NS2, we analyzed and evaluated the performance of DEDR-MAC protocol from four aspects: sensor fairness, real-time, throughput and energy consumption. And we compared performance with the typical WSNs MAC protocols..