Study On A Query Qos Mechanism In Wireless Sensor Networks

Quality of Service (QoS) guarantee is a critical problem in Wireless Sensor Network (WSN) applications. Effective evaluation of query quality is an essential prerequisite to query optimization. In most of the existing research work, energy efficiency is taken as the evaluation metric for query optimization and results in that users'requirements cannot be met well. This thesis makes an intensive study on query QoS evaluation and QoS guaranteeing issues in WSNs.Firstly, this thesis introduces a query QoS evaluation method. Based on the analysis of query QoS requirement in WSNs, some important metrics are introduced as well as the methods to estimate them. Then, a simple and effective query QoS evaluating model is established and a dynamic adjustment strategy for this model is introduced noticing the dynamic nature of the WSNs. Finally, a sample QoS-based optimization is proposed to show the practicality of this model.In order to guarantee the QoS in the query result return process, a QoS supported, energy efficient data forwarding strategy—ERSPEED (Energy and Reliability aware SPEED) is proposed. In ERSPEED, the QoS provisioning is performed in two quality domains, namely, timeliness and reliability. ERSPEED first classifies the data into two classes, urgent and non-urgent data, and takes different strategy for these two classes of data in order to provide more reasonable service differentiation. For timeliness part, ERSPEED selects the next hop node based on the cost model introduced in this thesis, which is aware of both energy cost and transmission speed, so that ERSPEED can provide network-wide energy efficiency. For the reliability part, ERSPEED considers both multi-path forwarding and retransmission strategy to provide end-to-end reachability guarantee. To save energy consumption, ERSPEED consider the retransmission strategy first, unless the timeliness requirement is violated. ERSPEED is a localized strategy, which makes it scalable for large area, dense deployed and dynamic changing sensor network environment.The experimental results prove that the proposed query QoS evaluation method can reflect the features of WSNs and evaluate query quality of WSNs effectively; ERSPEED protocol can provide probabilistic QoS guarantee as well as network-wide energy effectively.