Congestion Control Scheme Design And Research In Wireless Sensor Network Of Star-Structure

The technology of Wireless Sensor Network (WSN) has developed rapidly in recent years, and its application prospect is more and more broad. WSN is closely associated with specific application, the congestion of WSN will seriously affect the QoS performance and data transmission of the network. Thus the congestion control is a key technology to WSN. Star-structure network is a common topology in WSN, which can compose others topology such as tree-structure, mesh-structure or cluster-structure. In star-structure network, the child node is responsible for collecting the event, and transmitting it to the coordinator. When emergency event occurred, the collecting rate of sensor is increased and an increasing traffic flow into the network, which causes the rapid growth of the buffer queue, the increase of package loss and delay. It is the node-level congestion that is very harmful for application of a star-structure WSN, thus some measure must be taken.This thesis designed a novel congestion control scheme for the node-level caused by buffer overflow in star-structure WSN. This scheme controls the congestion periodically using three mechanisms which are detection, notification and relieving. The scheme uses the combination of queue length and queue congestion index with a state machine to judge the congestion condition. Each period coordinator and child nodes detected their own congestion state. The congestion relieve is performed in the child nodes. When the network is congested, the child nodes reduced the collecting rate gradually using an iteration approach, which is destined for reducing the congestion index. In this thesis, two models which consider that the serve rate is greater or less than the sending rate are built, which calculated the sending rate and collecting rate directing to congestion state. The simulation result shows that the congestion control scheme proposed in this thesis can effectively slowdown the growth of buffer queue after network congestion,prevent the overflow of queue, improve the throughput to relieve the congestion.In order to verify the congestion control scheme of the thesis, a star network platform is used to implement this scheme. The platform uses IEEE802.15.4protocol to form a beacon network of star-structure. Some congestion control models are adding to the specific MAC layer, including a buffer queue, congestion detection model, rate adjusting model. Different input rate is tested to observe the change situation of buffer queue, and the result of test is compared with the simulation result. The test result shows that the proposed congestion control scheme can effectively relieve the node-level congestion in the platform. There is a highly goodness of fit between the test result and simulation result, which is effectively verified the usefulness of the proposed scheme to the star-structure network.