Design And Implementation Of Warehousing Environment Monitoring System Based On ZigBee

In the past years,the business of warehousing has grown rapidly.And compared to the previous,there're some new special features appeared in the modern warehousing,including various storage materials,large throughout and frequent turnover.And always,for one certain area,it may be full of storage materials today,but empty tomorrow;and the current storage materials are sensitive to temperature while maybe the next ones to humidity.Obviously,the traditional method of sensor fixed settling cannot meet the latest requirement.On the other hand,traditional method to transfer signals via cables,which consumes not only material costs of cables and cable trays,but also time and workloads during the installation and maintenance.Except both two above,there're some signal errors due to signal attenuation and external noises if the traditional method used.Based on these reasons,wireless sensor network has been chosen to implement the warehousing environment monitoring system to avoid all of the problems caused by cable connections.Furthermore,considering the requirements of modern warehousing,such as larger amount of nodes,longer timer to sustain,frequent networking,ZigBee network has been selected finally,compared to the other popular wireless communication technologies.There're three different types of nodes in ZigBee network,including the Network Coordinator,the Router and the End Device.Specially,the Network Coordinator and the Routers take responsibility for transferring data,and work as fixed nodes.All of the End Devices with sensors are responsible to collect the environment information,and work as moving nodes,which always get in and out of the warehousing with the storage materials.The basic requirement of the warehousing environment monitoring system is to get the real-time data and avoid network delay.For this,it's better to choose the Star topology as the network topology,because every End Device talks to the Network Coordinator directly.But in this case,the Network Coordinator cannot work fine or make responses quickly due to its own limitation of access nodes and hardware performance.According to this analysis,Cluster-tree network has been selected.In this network topology,the transmission path is single and simple without any network delay,and the quantity of access nodes is numerous.In the following,the system needs to position the moving End Device to make the environment information corresponding to the unique area.Regarding the positioning of moving End Device,there are always two types of methods,based on measuring and without measuring.Balancing the cost and accuracy,the method of trilateral positioning based on RSSI(Received Signal Strength Indicator)measuring technology has been chosen.But in fact,the problem of unable to position the moving nodes due to no intersections of three circles always occurs.So an optimized trilateral positioning method has been made to solve the problem,in which the three distances should be enlarged to make sure there're intersections for any two of the three circles.Then the position of moving End Device can be got through the centroid method with mean value.