A New QoS-Aware Protocol Guaranteeing Lifetime in Wireless Sensor Networks
정보과학과 Department of Informatics, Major: Informatics
Wireless Sensor Networks Lifetime Coverage Real-Time;
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Wireless Sensor Networks (WSNs) are comprised of many low-cost sensor nodes with wireless communication capability, limited transmission power, resource constraints and limited battery energy. These large-scale WSN deployments require routing and scheduling protocols to scale the large networks in an energy-efficient way. WSNs have become a key technology for various applications due to their long-term and low-cost operations in different scenarios such as; disaster alerts, security surveillance, health monitoring, industrial automation, among others. Sensor energy conservation is one of the main goals for protocols which impose many fundamental design limitations in WSNs. For example, when the outdoor surveillance or target tracking systems are deployed in harsh and non-human operational remote environment, it is economically unfeasible to replace or recharge batteries of energy-depleted sensor nodes. Under such circumstances, due to the restriction of the environments, guaranteeing the network lifetime is mandatory to provide the WSN service. Since, WSNs are subject to failures, lifetime becomes an important requirement for many WSN applications where messages from all sensor nodes must be delivered to sink in a reliable and timely manner. Besides the energy constraint, real-time communication is another concern in emergency WSNs applications, such as radiation monitoring, security surveillance, among others. In many cases, real-time communication has tight deadline requirements due to its time and event critical applications in many WSNs scenarios, which demands the network to operate for a pre-configure lifetime. In a dynamic environment, it is very difficult to continually fulfill this requirement, since the sensor density may drop with the passage of time and the emergency duration may change unexpectedly. Therefore, the pre-planned strategy failed in such situation, as the sensor task should be dynamically adjusted according to the lifetime requirement and network conditions. Due to such critical and unbalanced situation, guaranteed lifetime for real-time applications is more important than prolonging network lifetime. To meet WSNs requirements, most research works have focused on how to reduce energy consumption of sensors to prolong network lifetime. Despite of the prolong, another research challenge related to energy, guaranteed network lifetime which is predictable as well as certain, has rarely been studied. If the network lifetime is guaranteed by the pre-determined time, many deployment problems can be easily solved. To design a guaranteed WSNs lifetime protocol to support real-time service, the communication protocols must adjust their routing performance based on the packet deadline. However, high complexity to find the adequate path between source and destination requires more battery on the sensor node. Eventually, it is demanded to control battery usage for guaranteed network lifetime to support real-time applications. Thus, both energy and QoS awareness are involved in different layers of the protocol stack of real-time applications and WSNs lifetime . Therefore, how to efficiently utilize the limited sensor nodes energy resource and packet routing to solve this problem has been the primary concern in this thesis. This thesis tackles the problem of real-time packets in a guaranteed WSNs lifetime while maintaining k-coverage of network field. The technique wisely combines energy and coverage aware scheduling scheme to power aware transmission for achieving the required challenges of real-time and guaranteed lifetime at once in WSNs. In order to guarantee network lifetime, each node are enforced to remain steadfast in the idle state for a known duration of its lifetime. To do so, the protocol periodically assigns each node role for next period by coupling residual energy, total active time and possible coverage area. In addition, the scheduling algorithms are extended to provide real-time service by adjusting dynamic transmission range according to the current energy state of a sensor node. These two core functions enable the unreliable WSNs to accomplish real-time routing for a guaranteed network lifetime. The performance of newly developed protocols have been evaluated by simulation in an extensive range of scenarios, and compared to existing algorithms. It is shown that the newly proposed algorithms allow long and defined-term continuous data collection in WSNs, offering greater network longevity than existing solutions. Simulation results show that the proposed schemes can achieve a 10% increase in real-time packets meeting their deadline and a significantly longer guaranteed network lifetime than protocols reported in the literature.