Medium Access Control Protocol Research And Implementation Of Wireless Sensor Network Mixed Network Topology

As a new control network technology , wireless sensor network is a intelligent network can realize data collection, integration, and transmission application .It combines modern sensor technology , microelectronic technology , communication technology ,embedded computing technology and distributed information processing technology and so on. Wireless sensor network is composed of many small nodes which possess sensor , data progress and communication modules, form several hop networks by means of wireless communication .The nodes use the inside several sensors to apperceive ,gather and process several signals of the network covering. Then we can carry out real-time monitoring and remote control. The emergence of wireless sensor networks has aroused widespread concern around the world. At present, wireless sensor networks can be widely used in military, environmental science, home automation, health care, architecture and urban management and so on. It becomes a "ubiquitous" sensor technology.Wireless sensor network involves many important technology, include topology control, communication, meshwork, network security, time synchronization, orientation, data amalgamation and process, cooperation and so on. Based on the requirement of item, the content is the medium access control research and implement of wireless sensor network using mixed topology control. It did research and comparative analysis about typical MAC protocol of distribution , competition and mixed type, and pointed out the nodes'soft, hardware requires and application requires . The emphasis was the competitive protocol. The paper indicated that the CSMA/CA binary exponential back off retreat arithmetic of IEEE 802.15.4 standard used irrational update rule of competition window, then there were two limitations of BEB arithmetic, one is that it can't accurately reflect the situation of channel contention, the other is that it would create an unfair situation . It can't adapt the situation of runoff break out or several nodes transmit packets in several hop networks. The high lose rate aroses many repeat transmition. Based on already several update rules, it brought forward adaptive rapid access avoid collision arithmetic. It set two thresholds to distinguish low-flow and high-flow retreat, used different update rules to take into account the performance of low and high flow in order to nodes can adaptively access channel . Under low flow, setting small competition window can allow nodes to access rapidly and reduce the channel idle waste, and in the large flow competition window changing smoothly to avoid short-range unfair situation caused by big difference competition window of each node. When the node continuously sent three packets successfully, then the rough window was considered a optimize value. Between one hop every node's window was updated to reduce the degree of short-range unfair. Then the group nodes have a considerable competitive ability.Through the TOSSIM simulation platform, experiments were carried out among the ARAC algorithm, the prototype algorithm and LMILD algorithm. From the messages transmission delay and packets loss rate, the ARAC arithmetic all shows its advantage performance. Finally refer to the subject application, it set the wireless sensor network model, planned network and nodes, built software architecture, designed and implemented the PHY and MAC layer. Experiments and practice have proved that the system is running well.