International Journal of Distributed Sensor Networks The latest articles from Hindawi Publishing Corporation © 2014 , Hindawi Publishing Corporation . All rights reserved. Underwater Wireless Sensor Networks Wed, 16 Apr 2014 07:01:11 +0000 Dongkyun Kim, Juan Carlos Cano, Wei Wang, Floriano De Rango, and Kun Hua Copyright © 2014 Dongkyun Kim et al. All rights reserved. An Improved Group-Based Neighbor Discovery Algorithm for Mobile Sensor Networks Tue, 15 Apr 2014 16:36:18 +0000 Wireless sensor networks have been widely used in a variety of commercial and military applications, which often require neighbor nodes to establish connection quickly. Due to high mobility of nodes, it is a challenging issue to reduce discovery delay. Most discovery designs are based on pairwise and fixed duty cycle, in which discovery is passively achieved when two nodes wake up at the same time. In order to further improve the efficiency of neighbor discovery in mobile sensor networks, this paper proposes an improved group-based neighbor discovery algorithm (IGND) which dynamically adjusts the nodes’ active time based on spatial properties. This paper describes the network model and the algorithm implementation in detail. Simulation results show that the improved algorithm has a good effect in reducing discovery latency and promoting discovery efficiency. Qiang Niu, Weiwei Bao, and Shixiong Xia Copyright © 2014 Qiang Niu et al. All rights reserved. Sensor Resource Sharing Approaches in Sensor-Cloud Infrastructure Tue, 15 Apr 2014 16:29:43 +0000 Generally, wireless sensor networks have been designed to support predefined application services. The tight coupling between a network and application limits the usability of sensor data. To increase the utilities of wireless sensor networks, sensor-cloud infrastructure has been proposed to provide an open and flexible platform to gather, store, use, and share data from heterogeneous sensors. In this paper, we introduce sensor-cloud infrastructure and present not only comprehensive technical issues like sensor description and publish/subscribe middleware but also applications using sensor-cloud infrastructure. When the issues are tackled in the development of sensor-cloud system, the attractiveness of new applications and services will considerably be increased for end users. Yujin Lim and Jaesung Park Copyright © 2014 Yujin Lim and Jaesung Park. All rights reserved. Semisupervised Location Awareness in Wireless Sensor Networks Using Laplacian Support Vector Regression Tue, 15 Apr 2014 16:17:32 +0000 Supervised machine learning has been widely used in context-aware wireless sensor networks (WSNs) to discover context descriptions from sensor data. However, collecting a lot of labeled training data in order to guarantee good performance requires much cost and time. For this reason, the semisupervised learning has been recently developed due to its superior performance despite using only a small amount of the labeled data. In this paper, we extend the standard support vector regression (SVR) to the semisupervised SVR by employing manifold regularization, which we call Laplacian SVR (LapSVR). The LapSVR is compared with the standard SVR and the semisupervised least square algorithm that is another recently developed semisupervised regression algorithm. The algorithms are evaluated for location awareness of multiple mobile robots in a WSN. The experimental results show that the proposed algorithm yields more accurate location estimates than the other algorithms. Jaehyun Yoo and H. Jin Kim Copyright © 2014 Jaehyun Yoo and H. Jin Kim. All rights reserved. Using Traffic Light Signal to Enhance Intersection Foreground Detection Based on Video Sensor Networks Tue, 15 Apr 2014 14:05:10 +0000 Foreground detection plays an important role in the traffic surveillance applications, especially in urban intersections. Background subtraction is an efficient approach to segment the background and foreground with static cameras from video sensor networks. But when modelling the background, most statistical techniques adjust the learning rate only based on the changes from video sequences, which is a crucial parameter controlling the updating speed. This causes a slow adaptation to sudden environmental changes. For example, a stopped car fuses into background before moving again, and it lowers the segmentation performance. This paper proposes an efficient way to address the problem by accounting for the physical world signal in traffic junctions. It assigns an adaptive learning rate to each pixel by integrating traffic light signal obtained from sensor networks.Combined with abundant physical world signals, background subtraction method is able to adapt itself to the outside world changes instantly. We test our approach in real urban traffic intersection; experimental results show that the new method increases the accuracy of detection and has a promising future. Rong Ding, Shunli Wang, and Xu Liu Copyright © 2014 Rong Ding et al. All rights reserved. Activity Graph Feature Selection for Activity Pattern Classification Tue, 15 Apr 2014 14:01:38 +0000 Sensor-based activity recognition is attracting growing attention in many applications. Several studies have been performed to analyze activity patterns from an activity database gathered by activity recognition. Activity pattern classification is a technique that predicts class labels of people such as individual identification, nationalities, and jobs. For this classification problem, it is important to mine discriminative features reflecting the intrinsic patterns of each individual. In this paper, we propose a framework that can classify activity patterns effectively. We extensively analyze activity models from a classification viewpoint. Based on the analysis, we represent activities as activity graphs by combining every combination of daily activity sequences in meaningful periods. Frequent patterns over these activity graphs can be used as discriminative features, since they reflect people’s intrinsic lifestyles. Experiments show that the proposed method achieves high classification accuracy compared with existing graph classification techniques. Kisung Park, Yongkoo Han, and Young-Koo Lee Copyright © 2014 Kisung Park et al. All rights reserved. Implementation and Evaluation of Large-Scale Video Surveillance System Based on P2P Architecture and Cloud Computing Tue, 15 Apr 2014 11:27:46 +0000 Video surveillance system (VSS) is increasingly becoming important part in daily life. For traditional VSS, each camera stores streaming data to a centralized server. It will create a great volume of video data for a large VSS and may raise some issues in keeping daily video data to centralized server, such as limited bandwidth and storage insufficiency of server and lower reliability and scalability. In order to solve the problem, we have proposed an architecture for VSS based on well-developed peer-to-peer technique and emerging cloud computing. In this paper, we implement a large-scale VSS (LVSS) and propose an evaluation framework based on the proposed architecture. We implement the LVSS exploits inherent characteristics of P2P and cloud computing to provide an economic, scalable, reliable, and efficient approach to store streaming video. We conducted some experiments to evaluate effectiveness and efficiency of the system. The result shows that the proposed architecture outperforms traditional VSS in terms of effectiveness, efficiency, reliability, and scalability. Win-Tsung Lo, Yue Shan Chang, Ruey-Kai Sheu, Chao-Tung Yang, Tong-Ying Juang, and Yu-Sheng Wu Copyright © 2014 Win-Tsung Lo et al. All rights reserved. Associated Clustering Strategy for Wireless Sensor Network Tue, 15 Apr 2014 08:14:05 +0000 We consider the soil moisture monitoring problem and propose a WSN associated clustering strategy based on spatiotemporal data correlation, which ensures that the nodes within each cluster can share a good data correlation and consequently makes the cluster head do the data fusion more efficiently. As a result, the energy of each node will be saved and the lifetime of the whole sensor network will be extended. In the associated clustering strategy, the different clusters can be divided by the correlation characteristics of nodes data, which is based on a dynamic model and a correlation characteristics model after the correlation coefficient analysis. Simulation results show that our proposed associated clustering strategy works very well in soil moisture measurement. Moreover, as compared with the traditional random clustering, the associated clustering strategy based on data correlation achieves better performance for each cluster, and will be more efficient in data fusion at the cluster heads. Yajuan Sun, Huanzhao Wang, Kewang Zhang, and Xudong Yang Copyright © 2014 Yajuan Sun et al. All rights reserved. Proposed M-Payment System Using Near-Field Communication and Based on WSN-Enabled Location-Based Services for M-Commerce Tue, 15 Apr 2014 06:59:16 +0000 Advances in mobile communication and information technology have resulted in wireless sensor network (WSN) systems in which mobile phones (smart phones) can be used to conduct a wide variety of commercial, social, entertainment, and file-sharing transactions. In particular, mobile commerce (m-commerce) allows users to conduct payment, business, and service transactions over portable mobile devices. This trend has been enhanced by the development of near-field communication (NFC) technology and the increased market for NFC-embedded (smart phones). NFC technology is a standards-based wireless communication technology that allows data to be exchanged between devices located a few centimeters apart, such as radio-frequency identification (RFID tags and readers). To refine the m-commerce process in the NFC-based mobile environment, we study NFC and location-based services propose a WSN-hosted m-payment system based on these technologies. Sun-Kuk Noh, Seong-Ro Lee, and DongYou Choi Copyright © 2014 Sun-Kuk Noh et al. All rights reserved. Integration of Energy Harvester for Self-Powered Wireless Sensor Network Nodes Mon, 14 Apr 2014 16:07:24 +0000 This paper reports an energy harvester suitable for self-powered wireless sensor network (WSN) nodes consisting of a piezoelectric cantilever, an energy harvesting circuit, and a storage capacitor. Having the same size as a credit card, the proposed WSN nodes can be easily integrated into various applications, such as motor and air conditioning equipment. The WSN node is powered by an integrated bimorph piezoelectric generator that harvests energy from ambient vibration. The paper has developed a method to optimize the harvester parameters to attune it to the dominant vibration frequency. Tests carried out on the proposed harvester show that the proposed design can meet the energy requirements of a WSN node and achieve an efficiency of 79%. Lijuan Chen, Xiaohui Xu, Pingliang Zeng, and Jianqiang Ma Copyright © 2014 Lijuan Chen et al. All rights reserved. A Novel 3D Indoor Localization Scheme Using Virtual Access Point Mon, 14 Apr 2014 12:44:20 +0000 The global positioning system (GPS) is a popular choice for accurate location sensing and is often used in navigation systems. However, GPS fails to operate inside buildings because satellite signals are blocked. Thus, GPS cannot be used for localization indoors. Moreover, it is difficult to distinguish between the different floors. Research to overcome this problem using the ultrawideband (UWB), radio frequency identification (RFID), and infrared ray (IR) has been conducted. These methods, however, have drawbacks, such as the need for an additional communication module and database. Wireless local area network (WLAN) access point (AP) is widely installed at various locations, and using these WLAN APs can be a viable alternative. The proposed system in this paper indicates the location information in the service set identifier (SSID) of virtual AP. Therefore, merely by scanning the WLAN signals, mobile users can detect their location indoors. Taekook Kim and Eui-Jik Kim Copyright © 2014 Taekook Kim and Eui-Jik Kim. All rights reserved. Ubiquitous Data-Centric Sensor Networks Mon, 14 Apr 2014 09:00:32 +0000 Ting Yang, Peng-Yung Woo, Zhaoxia Wang, Javid Taheri, Chin Hoong Choor, and Guoqiang Hu Copyright © 2014 Ting Yang et al. All rights reserved. Side Information Generation for Distributed Video Coding Using Spatiotemporal Joint Bilinear Upsampling Mon, 14 Apr 2014 08:02:29 +0000 Distributed video coding presents a viable solution for power-constrained multimedia communication. However, its relatively low coding efficiency compared to the conventional video coding schemes remains a challenging issue. The rate-distortion performance of distributed video coding is highly dependent on the quality of side information generated at the decoder and various techniques have been proposed to improve the side information quality in block-based and frame-based distributed video coding architectures. In this paper, a robust spatiotemporal joint bilateral upsampling based side information generation method is proposed. The proposed side information generation method is based on a block-based low-complexity distributed video coding architecture with adaptive block coding mode classification. A partially reconstructed Wyner-Ziv (WZ) frame with skip and key blocks is downsampled and spatiotemporal error concealment and joint bilateral upsampling are used to generate the side information. Simulation results show that the proposed method improves the quality of side information significantly while keeping low computational complexity. Wenhui Liu, Krishna Rao Vijayanagar, and Joohee Kim Copyright © 2014 Wenhui Liu et al. All rights reserved. Protocol and Architecture to Bring Things into Internet of Things Sun, 13 Apr 2014 13:00:31 +0000 The Internet of Things (IoT) concept proposes that everyday objects are globally accessible from the Internet and integrate into new services having a remarkable impact on our society. Opposite to Internet world, things usually belong to resource-challenged environments where energy, data throughput, and computing resources are scarce. Building upon existing standards in the field such as IEEE1451 and ZigBee and rooted in context semantics, this paper proposes CTP (Communication Things Protocol) as a protocol specification to allow interoperability among things with different communication standards as well as simplicity and functionality to build IoT systems. Also, this paper proposes the use of the IoT gateway as a fundamental component in IoT architectures to provide seamless connectivity and interoperability among things and connect two different worlds to build the IoT: the Things world and the Internet world. Both CTP and IoT gateway constitute a middleware content-centric architecture presented as the mechanism to achieve a balance between the intrinsic limitations of things in the physical world and what is required from them in the virtual world. Said middleware content-centric architecture is implemented within the frame of two European projects targeting smart environments and proving said CTP’s objectives in real scenarios. Ángel Asensio, Álvaro Marco, Rubén Blasco, and Roberto Casas Copyright © 2014 Ángel Asensio et al. All rights reserved. A Novel Mobile Localization Method for Distributed Sensor Network with Non-Line-of-Sight Error Mitigation Sun, 13 Apr 2014 00:00:00 +0000 Mobile localization using distributed sensor network has attracted significant research interest in recent years. One of the main challenges for mobile location estimation is the presence of the non-line-of-sight (NLOS) propagation. It results in erroneous measurements containing NLOS error due to the reflection and diffraction. The NLOS error could seriously reduce the localization accuracy. This paper presents a novel mobile localization method for distributed sensor network in NLOS propagation scenarios. The aim of the method is to mitigate the NLOS error and enhance the localization accuracy. The transition between the LOS and NLOS is described by two-state Markov model. The interacting multiple model frame is employed to estimate the position of unknown node. The probability data association algorithm is used to filter the estimated location. The simulation results show that the proposed method outperforms the traditional filter method in NLOS scenarios. Nan Hu, Hao Wu, Chengdong Wu, and Yuan Gao Copyright © 2014 Nan Hu et al. All rights reserved. Prediction-Based Filter Updating Policies for Top- Monitoring Queries in Wireless Sensor Networks Sun, 13 Apr 2014 00:00:00 +0000 Processing top- query in an energy-efficient manner is an important topic in wireless sensor networks. Redundant data transmitting between base station and sink node is avoided by installing filters on sensor nodes; thus, communication overhead between base station and sensor nodes is decreased. However, existing algorithms such as FILA, and DAFM consume much energy when updating the filter window. In this paper, we propose a new top- algorithm named PreFU which is based on prediction models to update window parameters of filters. PreFU can predict the next step sensor values based on time series predicting models which can be built by historical data. By estimating the cost of updating window parameters based on predicted sensor values, updates of filter window parameters can be reduced. Thus, the cost of updating window parameters is decreased. Experimental results show that our PreFU algorithm is more energy-efficient than existing algorithms while guaranteeing the accuracy of top- query results. Jiping Zheng, Hui Zhang, Baoli Song, Haixiang Wang, and Yongge Wang Copyright © 2014 Jiping Zheng et al. All rights reserved. Geometric Range-Free Localization Algorithm Based on Optimal Anchor Node Selection in Wireless Sensor Networks Thu, 10 Apr 2014 17:40:37 +0000 In range-free localization scheme of wireless sensor networks, estimating the distance to the anchor nodes having the actual location is common to compute the position of unknown node. Since the range-free scheme is based on the topology information, the accuracy of distance estimation is considerably affected by node density or node deployment. In this paper, we propose a geometric range-free localization algorithm which estimates the unknown positions geometrically by topological information without considering the distance estimation. To achieve this, we propose an optimal anchor node selection algorithm which selects the anchor nodes connected topologically well for the geometrical location estimation. Simulation results show that the proposed algorithm offers considerably an improved performance compared to the other existing studies. Hyunjae Woo and Chaewoo Lee Copyright © 2014 Hyunjae Woo and Chaewoo Lee. All rights reserved. Consensus Target Tracking in Switching Wireless Sensor Networks with Outliers Thu, 10 Apr 2014 17:25:22 +0000 The problem of consensus-based distributed tracking in wireless sensor networks (WSNs) with switching network topologies and outlier-corrupted sensor observations is considered. First, to attack the outlier-corrupted measurements, a robust Kalman filtering (RKF) scheme with weighted matrices on innovation sequences is introduced. The proposed RKF possesses high robustness against outliers while having similar computational burden as traditional Kalman filter. Then, each node estimates the network-wide agreement on target state using only communications between one-hop neighbors. In order to improve the convergent speed of the consensus filter in case of switching topologies, an adaptive weight update strategy is proposed. Note that the proposed algorithm relaxes the requirement of Gaussian noise statistics in contrast to the decentralized/distributed Kalman filters. Besides, unlike the existing consensus-based filters, we do not need to perform consensus filtering on the covariance matrices, which will reduce the computational and communicational burden abundantly. Finally, simulation examples are included to demonstrate the robustness of the proposed RKF and effectiveness of adaptive consensus approach. Yan Zhou, Dongli Wang, Yonghong Lan, and Qingzhen Wen Copyright © 2014 Yan Zhou et al. All rights reserved. Design and Implementation of File Deduplication Framework on HDFS Thu, 10 Apr 2014 12:32:03 +0000 File systems are designed to control how files are stored and retrieved. Without knowing the context and semantics of file contents, file systems often contain duplicate copies and result in redundant consumptions of storage space and network bandwidth. It has been a complex and challenging issue for enterprises to seek deduplication technologies to reduce cost and increase the storage efficiency. To solve such problem, researchers proposed in-line or offline solutions for primary storages or backup systems at the subfile or whole-file level. Some of the technologies are used for file servers and database systems. Fewer studies focus on the cloud file system deduplication technologies at the application level, especially for the Hadoop distributed file system. It is the goal of this paper to design a file deduplication framework on Hadoop distributed file system for cloud application developers. The architecture, interface, and implementation experiences are also shared in this paper. Ruey-Kai Sheu, Shyan-Ming Yuan, Win-Tsung Lo, and Chan-I Ku Copyright © 2014 Ruey-Kai Sheu et al. All rights reserved. An Energy-Efficient Outlier Detection Based on Data Clustering in WSNs Thu, 10 Apr 2014 12:11:19 +0000 Sensor nodes in wireless sensor networks are prone to malfunction because they are exposed to the nearby environment directly. Consequently, wrong sensor readings occurred from sensor nodes and these readings are called an outlier. Commonly, since an outlier deviates from normal sensor readings and it can bring about some problems, various techniques to detect the outliers have been proposed. In this paper, we propose an efficient outlier detection technique based on data clustering. In order to decide the width of the cluster that consists of the sensor readings, we applied the Pigeonhole Principle and then detected the outliers based on clusters. In experiments, we demonstrate the efficiency of our proposed technique compared to other outlier detection techniques. Hongyeon Kim and Jun-Ki Min Copyright © 2014 Hongyeon Kim and Jun-Ki Min. All rights reserved. Gradient Based Multipath Reliable Transmission Strategy with Fault Tolerance for Wireless Sensor Networks Thu, 10 Apr 2014 09:07:02 +0000 Fault tolerance and reliable transmission are hot issues in wireless sensor networks. For the problems that the fault of nodes or links will affect the transmission stability and reliability of the network, a gradient based multipath reliable transmission strategy with fault tolerance is presented for wireless sensor networks. Firstly nonuniform clustering topology is established in nonequal clustering probability based on twice -means algorithm. Then it calculates the comprehensive measurements (CM) of cluster heads by the quality evaluation function and establishes the contour lines. Finally gradient based multiple disjoint transmission paths are established by the mechanisms of load balance and linear erasure coding. It also establishes the transmission mathematical model to analyze the performance of the network. Simulation shows that this strategy has good performance of fault tolerance. It improves the transmission reliability of the network and energy efficiency. Hongbing Li, Qingyu Xiong, Weiren Shi, Cheng Zeng, and Min Fan Copyright © 2014 Hongbing Li et al. All rights reserved. Development of Underwater Monitoring Wireless Sensor Network to Support Coral Reef Observation Wed, 09 Apr 2014 12:22:26 +0000 We have been developing a wireless sensor network system to support coral ecological system survey activities. This paper studies the required functions of a wireless sensor node for gathering information on underwater environmental conditions. For this purpose, a prototype sensor node is developed to clarify necessary functions through a practical experiment. In this paper, the hardware configuration of a latest prototype of wireless sensor node is described. The design of this prototype was based on our previous experiments and the comments of coral reef researchers. We conducted practical field experiments to observe the coral reefs along the Okinawa coast in Japan by using the prototype. Moreover, a browsing system of gathered information by the sensor network is described. Finally, we discuss the experimental results and the required functions of the sensor node for the future research. Tsuyoshi Suzuki, Kazuki Kato, Emi Makihara, Takafumi Kobayashi, Hitoshi Kono, Kei Sawai, Kuniaki Kawabata, Fumiaki Takemura, Naoko Isomura, and Hideyuki Yamashiro Copyright © 2014 Tsuyoshi Suzuki et al. All rights reserved. An Intelligent Guardrail Context-Awareness System Based on Acceleration Sensors in Ubiquitous Sensor Networks Wed, 09 Apr 2014 12:16:21 +0000 A ubiquitous city (u-City) is a next-generation information-based city that combines state-of-the-art IT (information technology) infrastructures and ubiquitous information services. In general, the urban facilities of a u-City can be categorized into ground and underground facilities. This paper proposes a guardrail context-awareness system based on the analysis of acceleration sensors to manage guardrails systematically. Guardrails are one of the major ground facilities in a u-City. The suggested system generates alarms when acceleration sensors on guardrails recognize a certain level of physical shock. General information on the size and direction from the acceleration sensors is transmitted to the context-awareness system. The context-awareness system analyzes the scalar magnitude of the impacted shock, acceleration values to the x, y, and z directions, gravity direction of the sensors, and threshold values. It then determines if there is pronounced physical activity on the guardrail. Experimental results show that the suggested guardrail context-awareness approach accurately recognizes guardrail shock events that occur in various environments. Seok-Woo Jang, Sung-Youn Cho, and Gi-Sung Lee Copyright © 2014 Seok-Woo Jang et al. All rights reserved. RGB Color Model Based the Fire Detection Algorithm in Video Sequences on Wireless Sensor Network Wed, 09 Apr 2014 08:51:06 +0000 Since the fire causes serious disasters, fire detection has been an important study to protect human life. Based on the deficiencies of existing fire detection on real-time and monitoring accuracy, the wireless sensor network technique for fire detection was introduced and needed. In this paper, we proposed the fire detection algorithm in video sequences on wireless sensor network. The proposed fire detection algorithm processes visual information acquired through static camera that lets us incorporate the algorithm to CCTV surveillance system, and therefore does not require an additional expanses on conventional fire sensors. Fire detection method based on motion information, any input image, is compared to background in order to identify foreground. Background is statistically modeled by mixture of Gaussians. To detect the foreground of video sequences, the proposed color detection algorithm was performed in RGB space. The procedure of algorithm eliminates all objects that do not fulfill color requirements without fire-like objects. And the change map and blob’s area are computed, change map shows temporal variation of pixel between two consecutive binary frames, and percentage area increase or decrease characterizes a fire property for swinging. Yoon-Ho Kim, Alla Kim, and Hwa-Young Jeong Copyright © 2014 Yoon-Ho Kim et al. All rights reserved. Divisible Load Theory Based Active-Sleep Workload Assignment Schemes for Wireless Sensor Networks Wed, 09 Apr 2014 08:38:09 +0000 Wireless sensor networks (WSNs) have been widely applied in many monitoring and surveillance processes. Due to the limited onboard energy resources, the operation of a WSN is severely hindered by its shortened lifespan arising from energy depletion. In order to alleviate this problem, and with the possibility of partitioning sensing workloads, the divisible load theory (DLT) can be adopted to derive a proper workload assignment scheme. However, special considerations have to be paid for its generic applicability in feasible workload assignment for WSNs. In this paper, an examination of DLT based WSN operations including the effect of assignment, measurement, and report times is presented, and the problem of negative workloads inherently generated in some schemes is revealed. Furthermore, by making use of the negativity phenomenon, an active-sleep scheme is proposed for the WSN such that sensor energy consumptions can be reduced and consequently extend the WSN operation lifespan. Specifically, sensors with smaller amount of residual energies are put into the sleep mode when the assigned workloads are negative. On the other hand, positive workloads are normalized and reassigned to sensors with larger amount of onboard energies. Simulation studies are carried out to demonstrate the negative workload phenomenon, and satisfactory performances of the proposed active-sleep scheme are verified. Haiyan Shi, Ngaiming Kwok, Wanliang Wang, and Shengyong Chen Copyright © 2014 Haiyan Shi et al. All rights reserved. Antistray, Learning Smart: Creating Indoor Positioning Learning Environment for Augmenting Self-Regulated Learning Tue, 08 Apr 2014 09:29:23 +0000 With the rapid development of augmented reality (AR) technology, the combination of reality and virtual learning material finally came true. This study adopts AR technology to enrich learning environment and students' learning experience at the same time. Furthermore, to passively avoid students being lost while they were learning in a real environment and to actively channel students into ideal learning topic, this study proposes an indoor positioning algorithm which is able to calculate the current position of the learner and further enables learners to find out where he/she is and which learning subjects he/she will learn. The experiment is carried out to demonstrate the accuracy of the proposed indoor positioning algorithm. The results show that the proposed algorithm has a higher accuracy and lower error. Meanwhile, the algorithm is able to eliminate the anomalous RSSI signals, which is the main reason for improving the positioning accuracy. The maximum error is improved by 51.22%. From the application aspect, we elaborate the implications of this study which present the substantial contributions and educational values of the system. We expect that the smart learning can be made via the system establishment in near future. Tien-Chi Huang Copyright © 2014 Tien-Chi Huang. All rights reserved. Achieving Distributed Consensus in UWB Sensor Networks: A Low Sampling Rate Scheme with Quantized Measurements Tue, 08 Apr 2014 00:00:00 +0000 Distributed consensus in sensor networks has received great attention in the last few years. Most of the research activity has been devoted to study the sensor interactions that allow the convergence of distributed consensus algorithms toward a globally optimal decision. On the other hand, the problem of designing an appropriate radio interface enabling such interactions has received little attention in the literature. Motivated by the above consideration, in this work an ultrawideband sensor network is considered and a physical layer scheme is designed, which allows the active sensors to achieve consensus in a distributed manner without the need of any admission protocol. We focus on the class of the so-called quantized distributed consensus algorithms in which the local measurements or current states of each sensor belong to a finite set. Particular attention is devoted to address the practical implementation issues as well as to the development of a receiver architecture with the same performance of existing alternatives based on an all-digital implementation but with a much lower sampling frequency on the order of MHz instead of GHz. Lorenzo Taponecco and Luca Sanguinetti Copyright © 2014 Lorenzo Taponecco and Luca Sanguinetti. All rights reserved. A Cluster-Based Secure Synchronization Protocol for Underwater Wireless Sensor Networks Tue, 08 Apr 2014 00:00:00 +0000 Secure time synchronization is one of the key concerns for Underwater Wireless Sensor Networks (UWSNs). This paper presents a CLUster-based Secure Synchronization (CLUSS) protocol that ensures the security of synchronization under harsh underwater environments against various attacks, including Sybil attack, replay attack, message manipulation attack, and delay attack. The time synchronization process of CLUSS is divided into three phases: authentication phase, intercluster synchronization phase, and intracluster synchronization phase. During the authentication phase, cluster heads are authenticated to beacons and ordinary nodes are authenticated to cluster heads. During the process of intercluster and intracluster synchronization phases, CLUSS distinguishes the propagation delay of downlink from that of uplink caused by node movement in order to improve time synchronization accuracy. Moreover, part of these two phases can be executed concurrently for reducing the number of messages generated in synchronization. We demonstrate through simulations that CLUSS can reduce synchronization errors as well as energy consumption compared to traditional protocols in various circumstances. Ming Xu, Guangzhong Liu, Daqi Zhu, and Huafeng Wu Copyright © 2014 Ming Xu et al. All rights reserved. Adaptive Compensation for Time-Slotted Synchronization in Wireless Sensor Network Mon, 07 Apr 2014 15:41:54 +0000 Since time division multiple access (TDMA) is employed to reduce power consumption, time synchronization is critically important for wireless sensor networks. Packet-based clock correction is one of main methods to maintain synchronization among nodes. However, in many real cases, such as industrial equipment monitoring and diagnosis, there is no need to exchange messages during relatively long time, while highly accurate time synchronization has to be maintained, which results in that additional packets have to be exchanged specifically for synchronization purpose. For addressing this problem, an adaptive compensation method is proposed in this paper to achieve a high synchronization precision without exchanging message frequently. We proved that the adaptive compensation method can achieve a high synchronization precision with much fewer packet exchanges. In addition, the performance of the proposed scheme has been evaluated in three different experimental settings. In the indoor experiment, compared with the synchronization method without using compensation, 98% of the synchronizing packets can be eliminated while maintaining synchronization precision at 100 s. In the outdoor experiment with higher temperature fluctuation, 80% of the packets can be eliminated with 100 s synchronization precision. In the case of sudden temperature changes of more than C, the proposed compensation packet frequency regresses to the frequency of the synchronization method without compensation. Tengfei Chang and Qin Wang Copyright © 2014 Tengfei Chang and Qin Wang. All rights reserved. Social Contribution-Based Routing Protocol for Vehicular Network with Selfish Nodes Mon, 07 Apr 2014 14:00:21 +0000 Routing in vehicular network is a challenging task due to the characteristic of intermittent connectivity, especially when nodes behave selfishly in the real world. Previous works usually assume that all nodes in the network are willing to forward packets for others, which is impractical in real world. Selfish behaviors of nodes would degrade network performance greatly. In this paper, we propose SCR, a social contribution-based routing protocol, for selfish vehicular network. When making forwarding decision, SCR considers both the delivery probability to the destination and the social contributions of the relay node. The delivery probability is determined by the social relations among nodes and social contribution is used as the incentive to stimulate selfish nodes to be more cooperative, which consists of reciprocal contribution and community contribution. The node with higher delivery probability and lower social contributions is the preferred candidate for the next hop. Simulation results show that SCR achieves better performance than other social routing protocols with the incentive scheme. Haigang Gong, Lingfei Yu, and Xue Zhang Copyright © 2014 Haigang Gong et al. All rights reserved.