Design And Simulations Of MAC Protocols To Reduce Energy Consumption In Wireless Sensor Network

Recent years have seen a rapid development of Wireless Sensor Network (WSN) and also more and more WSN applications are being deployed. However, the energy consumption of sensor nodes is still a major limitation to the lifetime of each sensor and the performance of the network. Energy depleted nodes will cause degraded coverage, suboptimal routes or partitioned network that impairs the functionality of the WSN. In WSN, Medium Access Control (MAC) Protocol decides how the precious wireless communication resources such as energy and bandwidth are being distributed among sensor nodes, thus the MAC protocol is critical to the energy efficiency of the WSN.We analyze some present MAC protocols and discuss S-MAC protocol in detail. During the research, we find two limitations in S-MAC protocol. The first problem is the boundary nodes. There is no global synchronization of the schedules in S-MAC. So nodes form clusters, in which the nodes synchronize locally. The energy of boundary nodes between clusters is depleted faster than that of the inner nodes. They maybe die earlier and it may destroy the connectivity of the network. The second problem is the mechanism of collision-avoiding. S-MAC adapts the mechanism based on RTS/CTS frame. There is considerable protocol overhead and may cause new collision between RTS/CTS frame and other signal frames.For the first problem, we propose a mechanism to achieve a global synchronization by forming a spanning tree among the nodes, which will eliminate the boundary nodes. The resulting protocol is named as Synchronized S-MAC (SS-MAC). We carry out extensive simulations, which show that both energy efficiency and network connectivity are improved. Simulation results also demonstrate the scalability of the proposed scheme.For the second problem, we first discuss the efficiency of the collision-avoiding mechanism based RTS/CTS frame. Then we propose a position based scheme to avoid collisions between nearby nodes without using RTS/CTS handshakes. We make an improvement to S-MAC with the proposed mechanism and name the resulting protocol P-MAC. Although P-MAC introduces broadcasting position messages between neighboring nodes and may result more hops between source and destination, it is still beneficial of removing RTS/CTS exchanges. Simulations show the energy consumption of transmitting in P-MAC is lower than that in S-MAC. Besides, the medium access delay of P-MAC is lower than that of S-MAC, and P-MAC also achieves a higher throughput than S-MAC.