Cost Efficiency of Anycast-Based Forwarding in Duty-Cycled WSNs with Lossy Channel

Anycasting has been proposed recently as an efficient communication method for asynchronous duty-cycled wireless sensor networks. However, the interdependencies between end-toend communication cost and the anycasting design parameters have not been systematically studied. In this paper, a statistical endtoend cost model is presented to capture the end-to-end latency and energy consumption of anycasting operation under a realistic wireless channel model. By exploring the relationship between the end-to-end cost efficiency and the forwarding decision dependent anycasting design parameters, two anycasting forwarding metrics are proposed for fully distributed forwarding decision. By exploring the relationship among the preamble length, the size of the forwarding set and the achievable end-to-end cost efficiency, a series of preamble length control guidelines are proposed for low and extremely low duty-cycled WSNs. According to our analytical results and simulation validation, the proposed forwarding metrics help reduce the end-toend latency and energy consumption by about 55% for anycasting with moderate preamble length, compared with the existing heuristic forwarding metrics. The proposed preamble length control guidelines help reduce, by more than half, the end-to-end energy and latency costs in low and extremely-low duty-cycled WSNs

A Security Framework for Wireless Sensor Networks Utilizing a Unique Session Key

Key management is a core mechanism to ensure the security of applications and network services in wireless sensor networks. It includes two aspects: key distribution and key revocation. Many key management protocols have been specifically designed for wireless sensor networks. However, most of the key management protocols focus on the establishment of the required keys or the removal of the compromised keys. The design of these key management protocols does not consider the support of higher level security applications. When the applications are integrated later in sensor networks, new mechanisms must be designed. In this paper, we propose a security framework, uKeying, for wireless sensor networks. This framework can be easily extended to support many security applications. It includes three components: a security mechanism to provide secrecy for communications in sensor networks, an efficient session key distribution scheme, and a centralized key revocation scheme. The proposed framework does not depend on a specific key distribution scheme and can be used to support many security applications, such as secure group communications. Our analysis shows that the framework is secure, efficient, and extensible. The simulation and results also reveal for the first time that a centralized key revocation scheme can also attain a high efficiency

Service-differentiated and reliable communication in event-based wireless sensor networks

Wireless Sensor Networks (WSNs) consist of low-power embedded devices with integrated sensing, computing and wireless communication capabilities. These devices, called sensor nodes or motes, are often battery-powered and deployed in a distributed manner to provide observations on the physical world. Reliably and promptly collecting the sensing data to convey the features of a surveillance area, especially the events of interest, to the sink is one of the most critical requirements of WSN design. However, dynamic wireless channel conditions and the constrained energy resources make it a challenging task to provide the end-to-end performance guarantees in multi-hop WSNs. The objective of this research is to develop new communication protocols that provide soft Quality of Service (QoS) guarantees for event-based WSNs in terms of latency, reliability and service-differentiation capability. By examining the application-specific end-to-end communication requirements and the fundamental resource limitations of WSNs, cross-layer solutions are developed in this work, to support Service-Differentiated Real-time Communication through an integrated MAC and network layer protocol, SDRCS, and to support Loss-Tolerant Reliable Event Sensing through a transport layer protocol, LTRES. An analytical framework based on a realistic log-normal channel model is also developed to quantitatively analyze how the end-to-end latency and energy efficiency can be improved by tuning the MAC and network layer protocol parameters. Besides the theoretical research, the design, implementation, and deployment details of a state-wide real-time groundwater monitoring network in Nebraska are provided at the end, to demonstrate the advantages of wireless communication and networking technologies in improving the accuracy, coverage, and cost efficiency of real world environmental monitoring applications

uKeying: A Key Management Framework for Wireless Sensor Networks Utilizing a Unique Session Key

Key management is a core mechanism to ensure the security of applications and network services in wireless sensor networks. Key management includes two aspects: key distribution and key revocation. The goal of the key distribution is to establish the required keys between sensor nodes which must exchange data. Key revocation is used to remove compromised sensor nodes from the network. Although many key distribution schemes and key revocation schemes have been proposed in the literature, there is a lack of a framework which can integrate the schemes. In this paper, we propose a key management framework, uKeying, for wireless sensor networks using a globally distributed session key. uKeying includes three parts: a security mechanism to provide secrecy for the communication in the sensor network, an efficient session key distribution scheme, and a centralized key revocation scheme. The proposed framework does not depend on a specific key distribution scheme and can support many key distribution schemes. We further demonstrate how to use the framework to support secure group communication protocols in wireless sensor networks. Our analysis shows that the framework is secure, efficient, and extensible. The simulation and results reveal for the first time that a centralized key revocation scheme can also attain a high efficiency

The Effect of Implicit and Explicit Semiartificial L2 Learning on Motion Event Conceptualization: Recognition Memory and Similarity Judgment

This study trained participants with no prior Verb-framed language knowledge on a semiartificial L2 consisting of English lexicon and motion event lexicalization rules based on Uyghur the Satellite-framed language in either implicit or explicit manner. The main research questions were: whether learning this semiartificial L2 in implicit and explicit manner would lead to different L2 learning effects and different motion event conceptualization patterns; whether the effect on motion event conceptualization patterns was mediated by L2 learning effect and/or moderated by motion event encoding conditions (free versus verbal encoding). There were two target L2 rules for learning: a non-adjacent dependency rule between Uyghur dative/ablative case markers and motion event Path types, and a form-meaning mapping rule that mapped motion event Path and Manner onto the main verb and converb respectively. The implicit group was exposed to 120 L2 sentences and were asked to do semantic plausibility judgment and dative/ablative case marker recall after each sentence; the explicit group was provided with metalinguistic explanations of the two rules and were exposed to another 87 L2 sentences while attending to how the sentences conformed to the two rules and doing the same semantic plausibility judgment and case marker recall tasks. Motion event conceptualization pattern was measured using video-based recognition memory and similarity judgment tasks. L2 grammaticality judgment test showed that the L2 training only brought overall L2 learning effect in the explicit group who acquired some rule knowledge; while the implicit group very likely only memorized chunks formed by adjacent elements without generalizing or acquiring any rules. Regarding the relationship between L2 learning and non-linguistic motion event conceptualization, the only L2-specific effect found was that under verbal encoding, the explicit group showed significantly poorer recognition memory than the control group when Path was different between the target and alternative motion events. This effect was not mediated by overall L2 learning effect. This finding suggested that, after semiartificial L2 training, the explicit group’s memory of the core of the L2 lexicalization pattern may be less resilient to distraction than the memory of the detail of the L2 lexicalization pattern. The absence of L2-specific effects in motion event conceptualization in the implicit group suggested that mere L2 chunk memorization may not be sufficient to be transmitted into shifts in non-linguistic conceptualization pattern

Loss-Rate Based Reliable Data Transport Mechanism for Dynamic Event Sensing in Wireless Sensor Networks

Many wireless sensor network (WSN) transport protocols proposed in recent studies focus on providing end-to- end reliability as in TCP. However, traditional end-to-end reliability is energy and time consuming for common loss tolerant applications in WSNs. In this paper, we propose a Loss Tolerant Reliable (LTR) data transport mechanism for dynamic Event Sensing (LTRES) in WSNs. In LTRES, a reliable event sensing requirement at the transport layer is dynamically determined by the sink. A distributed source rate adaptation mechanism is designed, incorporating a loss rate based lightweight congestion control mechanism, to regulate the data traffic injected into the network so that the reliability requirement can be satisfied. An equation based fair rate control algorithm is used to improve the fairness among the LTRES flows sharing the congestion path. The performance evaluations show that LTRES can provide LTR data transport service for multiple events with short convergence time, low lost rate and high overall bandwidth utilization

Group Rekeying Schemes for Secure Group Communication in Wireless Sensor Networks

Wireless sensor networks are promising solutions for many applications. However, wireless sensor nodes suffer from many constraints such as low computation capability, small memory, limited energy resources, and so on. Grouping is an important technique to localize computation and reduce communication overhead in wireless sensor networks. In this paper, we use grouping to refer to the process of combining a set of sensor nodes with similar properties. We propose four centralized group rekeying (CGK) schemes for secure group communication in sensor networks. The lifetime of a group is divided into three phases, i.e., group formation, group maintenance, and group dissolution. We demonstrate how to set up the group and establish the group key in each phase. We further analyze and evaluate the performance of the proposed schemes in different scenarios