Research On Capacity Problem In Chain-topology ZigBee Wireless Network

Zig Bee is a typical wireless communication technology, which is widely used in wireless sensor network. ZigBee has great advantages in terms of low cost, low power and low speed, so that be variously applied to industrial control, home automation, and transport management. However, affected by natural formation of landscape or manmade infrastructures, some monitoring areas present a chain characteristic, such as rivers, bridges, power lines, rode, etc. And nodes are in one-dimensional distribution. The mesh topology of ZigBee network becomes instability when capacity exists over thirty nodes in these field. Therefore, considering with application scenarios, the chain-type of Zig Bee network can be taken to solve the problem of capacity limitations.The Chain-type wireless network has the following characteristics: Firstly, single path, the nodes of network are distributed in a line, so it has a single path to transfer data; Secondly, multi-hop routing, the data of collection by nodes is transported to sink node, which through one-by-one; Thirdly, load imbalance in network, the less the distance between routing nodes and sink node, the more data should be transmitted, the farther routing nodes get away from sink node, the less data need to be transmitted. Therefore, in practice, as the network capability increases, the chain-type network will become instability, such as node offline, network crashes, higher data transmission delay.In response to the problem of network instability caused by increasing capacity, the research is carried out in two aspects, including how to improve the reliability of link and data transmission. In the study of link reliability, reconnection mechanism is carried out on offline-node to help them join the network again; Adaptive power control mechanism can adjust transmit power to skip the damaged node for data transmission; Redundancy node mechanism in dual-link can find an alternative route. These measures can improve the stability of the transmission link. In the study of data transmission reliability, scheduling mechanism, which based on a plurality of transceiver slots, is used to improve the accuracy of data transmission and reduce packet loss rate; The chain-type network is divided into a plurality of cluster group can reduce the number of routing and data forwarding; The data fusion in the cluster group can reduce the amount of data; Through adding error control to data transmission. These measures can improve the stability of data transmission.In order to verify the feasibility of scheme, a ZigBee chain-type wireless network system is designed and verified its functionality and performance. In terms of functional test, the nodes of network can still achieve data transmission when some nodes are offline or broken; Data fusion mechanism effectively reduces the amount of data and data transfer times. In the performance test, two hundred nodes in chain network can steady running, and the mitigate packet dropped ratio and the average end-to-end delay can meet the actual needs. The results of testing show that the stability and reliability of high-capacity network has been greatly improved, increasing the real value of chain-type ZigBee network.