Study On Node Deployment Of The WSN Measuring And Controlling System In Greenhouse

Using the newly arisen wireless sensor networks for greenhouse measuring and controlling system has great practical significance for realizing agricultural modernization. Node deployment is the basic issue of wireless sensor networks. Deploy the sensor nodes reasonably can improve the performance of WSN on several aspect including network coverage, connectivity, the efficiency of routing protocols and MAC protocols, etc. In data gathering WSN, nodes closer to the base station have heavier load for data forwarding, and the energy consume faster than the outer nodes. This phenomenon which called funneling effect may cause network partition. So it is necessary to research the node deployment algorithm to balance the energy consumption and extend the lifetime of the network.According to the demand of greenhouse applications, a WSN measuring and controlling system in greenhouse based on virtual grid and cluster architecture is designed. The collected greenhouse environment information is submitted periodically to the control centre, so this kind of network is ascribed to data gathering WSN. In order to balance the energy consumption and solve the funnel effect problem in the measuring and controlling system, a redundant node deployment algorithm based on fuzzy graph theory is designed. The measuring and controlling area of the greenhouse is divided into several virtual grids in the algorithm, under the precondition of coverage and connectivity, some nodes are placed into each virtual grid, and then a cluster is formed in each grid. According to the load of clusters in WSN, a certain amount of redundant nodes are deployed to balance the energy consumption among clusters. As the fuzzy weight of the graph edge, the next hop route selection probability of the cluster head is introduced into fuzzy graph theory, and a theorem of calculating the probability that data transmits from source node to destination node with m hops is proposed. The theorem provides an effective way for researching the technology of data transmission in networks. In order to implement the node deployment algorithm, two routing protocols are designed by analyzing the characteristics of the data stream in the network. The Downlink data Routing Protocol DRP is used for forwarding the control and management commands ordered by the control center, while the Uplink data Routing Protocol URP is used for forwarding the uplink data which stay at cluster head according to the route selection probability which set preliminarily by the node deployment algorithm. Take CC2430 which support the IEEE 802.15.4 standard as the core component, the hardware of the sensor node is designed. By analyzing the function requirements of the system, the software system is designed according to the operating mechanism.A simulation for redundant node deployment algorithm and uniform node deployment algorithm is implemented. Then the performance of two algorithms is analyzed on three aspects: the number of virtual grids, the number of redundant nodes, data fusion coefficient. The results show that the network lifetime is shorted when increasing the number of virtual grids or data fusion coefficient, while the lifetime is prolonged when increasing the number of redundant nodes; as the energy consumption is effectively balanced, the redundant node deployment algorithm has a significant advantage over prolonging the network lifetime compared with purely uniform node deployment algorithm.