Design Of A 6LoWPAN Wireless Sensors Network For SHM Application

Structural health monitoring(SHM)is one of the important means to inspect and evaluate the operational status of civil structures.In SHM,the collection and transmission of key information of the bridge is crucial.The accuracy of subsequent data evaluation and analysis can be guaranteed,only when the monitored data is transmitted accurately,reliably,in real time,and stably.Traditional wired monitoring systems for civil engineering have many disadvantages,such as complex wiring,poor flexibility and high cost.Wireless Sensor Network(WSN)effectively overcomes these deficiencies.But conventional wireless sensor networks for SHM suffers unbalanced energy consumption and non-uniform transmission protocol standard,resulting in information island and other issues.In this article,based on the 6LoWPAN WSN,a new wireless data acquisition system is proposed for structural monitoring applications,and the energy consumption of the network is balanced by improving the RPL routing protocol in 6LoWPAN network layer.The specific research work is as follows:The structure monitoring system based on 6LoWPAN WSN consists of wireless sensor nodes,border routing node and remote monitoring center.The hardware development of wireless sensor nodes and border routing node is based on the CC2538 wireless transceiver.The development of embedded software for these two types of nodes is mainly based on the Contiki3.0embedded operating system,including the operating system porting,sensor module drivers,Ethernet module driver and application software development.As the IPv6 terminal node,the wireless sensor nodes are based on the 6LoWPAN protocol stack.The wireless sensor node is used to acquire parameters such as temperature,humidity and acceleration of the bridge.In addition,an analog signal input channel is extended for other external sensors.The border routing node mainly collects and forwards the data of the sensor nodes in the monitoring area,and implements communication between the 6LoWPAN network and the IPv4 Internet by converting the IPv4 data packets and the IPv6 data packets.The development of the remote monitoring center includes user interface design and database design,which realizes the functions of monitoring data storage,processing and online real-time display.The user interface design is based on MATLAB GUIDE,and it includes user interface modules and data processing modules.The design of the databases is based on MySQL,and it realizes data storage and management.To address the issue of unbalanced network energy consumption caused by the single metric in the current RPL routing protocol,we proposed to add the energy metric to the OFO objective function.By this way,the child nodes can select parent nodes according to both node hop count and energy metrics,and thus the energy consumption among the network would be better balanced.The impro,ved protocol is simulated by the Cooja simulator that comes with the Contiki system.Simulation results show that the improved RPL routing protocol can improve the balance of network energy consumption.Finally,the performance and functions of the designed 6LoWPAN wireless sensor networic is comprehensively tested.The functional testing part of the system includes the connectivity of the border routing node and the Internet,the energy consumption of wireless sensor nodes,remote monitoring center and database.The performance testing part includes network throughput rate,packet loss rate and communication distance.Experimental testing results show that the system is stable and reliable,and the network performance is satisfactory.Besides,the system can realize interconnection between 6LoWPAN network and traditional IPv4 network,and it can accurately collect and transmit the sensing data.Therefore,the proposed wireless structural monitoring system has a certain practical engineering application value.