Design Of High-performance MAC Protocol In Wireless Sensor Network

Wireless Sensor Networks(WSNs)are wireless networks with large-scale,self-organizing,low-cost,multi-hop routing and other features,which have been widely used in environmental monitoring,defense,military,public safety and other areas.Communication ways of sensor nodes directly affect overall performance of wireless sensor networks.In most cases,factors affecting network performance mainly include energy efficiency,collision,interference,latency and others.Medium Access Control(MAC)protocols decide a way that multiple nodes how to obtain a shared channel,coordinate nodes time to use the shared channel to transmit data,and simultaneously avoid conflicts,so that the communications between nodes become reasonable and ordered,and finally which ensure efficient operations of networks.Therefore,it is very necessary to design a high-performance MAC protocol.As the result of sensor nodes are likely to be battery powered and the energy is limited,most MAC protocols of the WSNs adopt a Duty Cycle mechanism that allows nodes in the network to periodically sleep to reduce extra energy that consumed by idle listening and to prolong lifetime of networks.However,this mechanism results in increasing significant sleep latency and reducing real-time performance in data transmission process.Especially,the greater number of hops that in the data transmission process,the greater impact of sleep latency.In addition,the periodic sleep of nodes also result in a shorter time for nodes to be active state,which largely limit throughput of the networks.Therefore,in this thesis,we focus on how to reduce the latency in multi-hop transmission of data and improve the throughput of networks simultaneously,and finally we proposed some related solutions,including:We proposed a synchronous RM-MAC protocol that can reserve future multi-hop nodes.Nodes in the RM-MAC who obtain the channel by a CSMA/CA competition mechanism and whose latter nodes will send several small control frames and use a virtual carrier sensing mechanism to reserve their future multi-hop nodes,so that the nodes were reserved will wake up at appropriate time to receive and forward data from their upstream nodes,thereby reduce the latency and quickly forward the data in transmission process and improve the throughput of networks.Theoretical analysis and simulation experiments results show that,the RM-MAC protocol is better than the S-MAC protocol in reducing the latency and improving the real-time performance,and it is more suitable for applications those are sensitive to latency.We proposed a asynchronous ALT-MAC protocol that has the low latency and the high throughput characteristics.ALT-MAC designs a reservation communication mechanism which makes a current sender node add addresses of remaining standby nodes to a data packet to reserve their a common receiver node,so that the receiver node can keep waking up on demand after completing the current communication,waiting for other nodes to transfer data to it.This mechanism effectively improves the throughput of the networks.ALT-MAC also designs an adaptive transmission mechanism which makes the receiver node adaptively keep awakening according to congestion of its internal message queue,so that the receiver node can forward its internal message to its next hop node as quickly as possible and avoid data overflow and reduce latency.In addition,ALT-MAC designs a node invalid notification mechanism which through operations from three aspects including the sender node,the receiver node and neighbor nodes to effectively avoid occurrence of that the receiver node had invalid,but the sender node still transmits preamble frames to it.Theoretical analysis and simulation experiments results show that,the ALT-MAC protocol is better than the X-MAC protocol in reducing the latency and improving the throughput of the networks,and it is more suitable for applications those have dynamic loads and large-scale features.