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Abstract-How to sense and monitor the environment with high quality is an important research subject in the Internet of Things (IOT). This paper deals with an important issue of the balance between the quality of target detection and lifetime in Wireless Sensor Networks (WSNs). Two target monitoring schemes are proposed. One is TDSFK (Target Detection with Sensing Frequency K) which distributes the sensing time that currently is only on a portion of the sensing period into the entire sensing period. That is, the sensing frequency increases from 1 to K. The other scheme is TDASF (Target Detection with Adjustable Sensing Frequency) which adjust the sensing frequency on those nodes which have residual energy. The simulation results show that the TDASF scheme can improve the network lifetime by more than 17.4%, and can reduce the weighted detection delay by more than 101.6%.

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Cooperative sensing and monitoring event is one of the important applications of sensor networks. Node deployment and duty cycle configuration of event detection in a large wireless sensor networks is an enormous challenge. In this paper, through in-depth analysis we find that there is a tradeoff between node duty cycle and event quality monitoring. That is, adopting larger duty cycle enables network to deploy fewer nodes. Or deploying more nodes can reduce their duty cycle. Both of them can reach the event detecting quality requirement of application. Based on the above findings, a novel subtraction deployment strategy (SDS) combined with the unequal node duty cycle in the network is presented. This strategy improves the duty cycle of nodes in non-hotspots area when reduces the number, thereby minimizing the deployment cost on the premise of meeting the detecting quality of application. We introduce a formal model to indicate the tradeoff between deployment cost and the quality of event detection. Subsequently, we present a heuristic algorithm to find nearoptimal deployment solutions for practical scenarios. Both theoretical and experimental simulation results show that the proposed scheme SDS for event detection can reduce the deployed number of nodes by 11.49% and do no harm to detecting quality. In the deployment of the same node number, the weighted delay of detection can be reduced as much as 47%, and the weighted detection percentage can be increased by 1.56 times without reducing the network lifetime compared with those in uniform deployment scheme.

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As a way of lifetime extension, the energy efficiency has become a crucial criterion in the design of object tracking sensor networks (OTSN). In this paper, we propose a sentinel based sleep scheduling called Sleep Scheduling Protocol (SSP) to reduce the number of the awakened sensor nodes with less performance loss while existing solutions either suffer from increasing of event detecting delays or computing overhead. SSP is built upon cluster based network structure. Each cluster contains group of sensor nodes divided in terms of geometric information. Sentinels will be selected from each cluster for probing object moving trajectory and maintaining communication routes. In the approach, sentinels will remain active or be scheduled to periodic sleep. The rest of the nodes remain sleeping until being waked up by sentinels and only maintain low communication power to stay accessible for energy saving. We compare SSP with three sleep based scheduling protocols via simulation. The results show that SSP can reduce average energy consumption but with reasonable detection probability and delay.