Research On Reliable Transmission Technology For Event Monitoring In Wireless Sensor Networks

Wireless sensor networks (WSNs) have broad market prospects of applications in event monitoring due to its characteristics of large scale, low cost and self-organization. However, for the severe condition and limited resources, the reliable transmission is a major challenge in developing system of WSNs. Besides, the features of event monitor-ing applications bring out an even higher demand for the protocol design, requiring not only the accurate detection of event, but also the reliable and timely transmission of event notification. Therefore, the information reliable transmission is one of the most important subjects in WSNs.In this dissertation, the key problem about the reliable transmission for event monitoring in WSNs is studied and the contents arc organized as follows:Firstly, we summarize the present resource literatures of relevant technologies and point out their shortcomings. And then, we carry out the research on four aspects:composite event detection and reliable notification, reliability of transmission for urgent information, burstiness-aware congestion control, and timeliness of transmission with sleep-wake scheduling. Meanwhile, relevant protocols and algorithms are presented and analyzed. The main contributions of this dissertation can be summarized as follows:(1) In this dissertation, a novel method for detecting composite event using multiple properties is proposed. The final decision node is not only the sink node, but any other nodes participating in forwarding primary decision packets. They could make final decision as soon as obtaining enough information. And then, the final decision node sends the alarm information to the sink to inform users, as well as the event source nodes to stop sending primary decision packets to save energy. As for the reliable notification of the alarm information, a k-copy reliable transmission scheme is designed to improve the reliability by copying the alarm packet on demand to reduce the risk of transmission failure of single packet.(2) Most of traditional congestion detection schemes do not take the dynamic change of load into consideration. Besides, they reduce the source rate of nodes to alleviate congestion at the cost of fidelity of event. To address this problem, a new concept of queue fluctuation is used to evaluate congestion by combining queue length. Based on the congestion evaluation results, nodes can be divided into different states and then a multistage rate adjustment scheme is proposed. Each node could adjust its rate depending on the different states. Furthermore, we use the idea of priority queue and assign a higher priority for the urgent information to further guarantee the reliability of transmission.(3) To deal with the temporary congestion due to the occurrence of event, a burstiness aware congestion control protocol is proposed. When the network load is low, sensor nodes use CSMA/CA-based MAC protocol to save energy. However, the event occurring might generate a large amount of traffic in network, resulting in the increasing load and congestion. The previous CSMA/CA-based media access scheme is not suitable under the heavy network due to the serious collision. In this dissertation, a TDMA-based media access scheme is used around the congestion area to avoid disorder contention when congestion occurs. As soon as the congestion is alleviated, the previous CSMA/CA-bascd scheme is active again.(4) For the severe cumulative latency in the asynchronous sleep-wake scheduling, a scout-based low latency MAC protocol is proposed. Initially, the sender transmits a serial of scout packets to wake up the receiver and then the receiver adjusts its sleep time to shorten the waiting time of next packet according to the scout packets. Besides, the other nodes not on the routing path overhearing the scout packets will adjust their sleep-wake scheduling to reduce the idle listening.