International Journal of Distributed Sensor Networks http://www.hindawi.com The latest articles from Hindawi Publishing Corporation © 2015 , Hindawi Publishing Corporation . All rights reserved. Analysis of College Classes Based on U-CLASS System Using Personal Mobile Nodes Sun, 24 May 2015 10:32:17 +0000 http://www.hindawi.com/journals/ijdsn/2015/493407/ The increase in mobile communications has led to advanced educational methods and technologies through accepting new technologies. A lot of studies have tried to overcome temporal and spatial limits on using personal mobile devices and have tried to increase learning effectiveness using various efficient educational methods. In this paper, U-CLASS, an interactive learning management system that provides interactive communications between a professor and students, is proposed and implemented. Monitoring of academic achievement after a real experiment with the proposed system and analysis of educational activities during the experimental class are important points. In order to achieve that, the proposed system was used in a practical class at a university, and educational activities from the classroom were gathered and analyzed. The data on the educational activities include frequency of questions, attendance rate, and seat positions of the students. Analysis results show that the average distance between professor and student in the classroom is strongly related to the grade of the student. Students who have a higher attendance rate and who ask more questions commonly show higher achievement. Chonggun Kim, Jeongmi Kim, Hohwan Park, and Ilkyu Ha Copyright © 2015 Chonggun Kim et al. All rights reserved. Design of a RSSI Location System for Greenhouse Environment Sun, 24 May 2015 09:16:21 +0000 http://www.hindawi.com/journals/ijdsn/2015/525861/ In order to improve the location accuracy in the complicated greenhouse environment, a positioning system is designed in this paper. According to RSSI data in the greenhouse, the parameters of the path-loss model are modified. Besides, least square estimation is used to filter RSSI data to eliminate random disturbance. Based on RSSI, the blind node is positioned by triangle centroid location method. Finally, to lessen the negative influence of steel pillars in the greenhouse, a region segmentation mechanism is introduced to the system. Experiments prove that our positioning system has higher accuracy in the greenhouse. Lihong Xu Copyright © 2015 Lihong Xu. All rights reserved. Propagation Analysis for Automated Switching of Embedded RFID with GPS in Wireless Sensor Network Platform Thu, 21 May 2015 13:00:40 +0000 http://www.hindawi.com/journals/ijdsn/2015/392385/ A 2.45 GHz active integrated ZigBee RFID system embedded with GPS is developed with an automated switching protocol algorithm utilizing wireless sensor network (WSN) platform to track the physical belongings or people in indoor and outdoor environments within a control area. In addition, to make the system contactless when the tag is not joining the network, the function of global system for mobile (GSM) communication is added to the integration. The communication between RFID reader and RFID tags is via WSN platform that supports mesh network and self-healing mechanism. Energy efficiency, robustness, and reliability are key factors in the design algorithm of the system. Comparisons are made between the existing active RFID system and the proposed active RFID system to study the performance of the proposed RFID system with an automated switching algorithm implemented on it. Based on the experimental study and statistical analysis done for all situations, a conclusion has been made where the proposed embedded RFID tag provided better signal propagation compared to the existing RFID tag and the battery lifetime for embedded RFID tag with switching mechanism is better than without switching mechanism. F. A. Poad and W. Ismail Copyright © 2015 F. A. Poad and W. Ismail. All rights reserved. A Novel ID-Based Authentication and Key Exchange Protocol Resistant to Ephemeral-Secret-Leakage Attacks for Mobile Devices Thu, 21 May 2015 07:16:06 +0000 http://www.hindawi.com/journals/ijdsn/2015/898716/ With the rapid development in wireless communications and cloud computing technologies, clients (users) often use handheld mobile devices to access remote servers via open network channels. To provide authentication and confidentiality between clients and servers, a large number of ID-based authentication and key exchange (ID-AKE) protocols have been proposed for mobile client-server environments. However, most of the existing ID-AKE protocols adopt the precomputation technique so that they become vulnerable to the ephemeral-secret-leakage (ESL) attacks, in the sense that an adversary could use the ephemeral secrets to reveal the private keys of clients from the corresponding exchange messages. In the paper, we propose a new ESL-secure ID-AKE protocol for mobile client-server environments. We formally prove that the proposed protocol satisfies the security requirements of both mutual authentication and key exchange while resisting the ESL attacks. When compared with previously proposed ID-AKE protocols, our protocol has higher security and retains computational performance, since it requires no bilinear pairing operation for mobile clients. Finally, we mention the possibility of adopting our protocol as an authentication method of the extensible authentication protocol (EAP) for wireless networks. Yuh-Min Tseng, Sen-Shan Huang, Tung-Tso Tsai, and Li Tseng Copyright © 2015 Yuh-Min Tseng et al. All rights reserved. Advanced Smoothing Approach of RSSI and LQI for Indoor Localization System Wed, 20 May 2015 14:26:40 +0000 http://www.hindawi.com/journals/ijdsn/2015/195297/ Ubiquitous indoor environments often contain substantial amounts of metal and other similar reflective materials that affect the propagation of radio frequency signals in important ways, causing severe multipath effects, including noise and interference, when measuring the signal strength between sender and receiver. To minimize the noise level, this study proposes advanced fusion filter (AFF) and improved fusion filter (IFF) using received signal strength indicator (RSSI) and link quality indicator (LQI) by using feedback filter. The aim of this research was to provide a low cost, simple technique based on RSSI and LQI values, provided by ZigBee module without considering needs to change the system according to specific indoor environments. The proposed technique could efficiently decrease huge amount of noise level from the original signal. To check the performance of the proposed technique, this study applied median filter and Savitzky-Golay filter to compare the performance of AFF and IFF. Further, the statistical analysis technique of cross-correlation method was used to check the similarity between original signal and filtered signal. The simulation results demonstrate the efficiency of the proposed RF-based indoor location determination. Sharly Joana Halder, Paritosh Giri, and Wooju Kim Copyright © 2015 Sharly Joana Halder et al. All rights reserved. EPPDC: An Efficient Privacy-Preserving Scheme for Data Collection in Smart Grid Wed, 20 May 2015 13:13:48 +0000 http://www.hindawi.com/journals/ijdsn/2015/656219/ Different from the traditional grid, smart grid builds a real-time connection network between the user and the grid company by smart terminals, which can achieve bidirectional data transmission and information control. In smart grid, the smart meters send various information to the power generators and substations. Frequent data collection meets real-time management, but it tends to raise privacy concerns from the users about privacy information leakage. Based on the blind signature and the key distribution scheme, an efficient and privacy-preserving data collection (EPPDC) scheme is proposed for smart grid to cope with the above problems. In EPPDC scheme, the users’ data information is transmitted to the local aggregator by building gateway with privacy preserving. In addition, the security analysis indicates that EPPDC scheme not only can resist replay attack, but also has source authentication and data integrity, confidentiality, unforgeability, nonrepudiation, and evolution of shared keys. Furthermore, performance analysis shows that EPPDC scheme has less computation cost than existing scheme. Jie Chen, Junping Shi, and Yueyu Zhang Copyright © 2015 Jie Chen et al. All rights reserved. Reliable and Swift Message Broadcast Method in Vehicular Ad Hoc Networks Wed, 20 May 2015 09:33:09 +0000 http://www.hindawi.com/journals/ijdsn/2015/219689/ A vehicular ad hoc network (VANET) could deliver safety-related messages reliably within a short time to increase road safety. Since safety-related messages should be sent to a set of unspecified receivers, they are delivered by broadcast method. However, the broadcast method specified in the IEEE 802.11p does not have a collision avoidance procedure and receivers do not acknowledge when they receive a broadcast frame. In addition, frames could be lost and corrupted. Therefore, as the portion of nodes that do not receive a broadcast frame increases, the effectiveness of a safety application decreases. To tackle the problem, we propose a reliable and swift message broadcast method (RSMB). In RSMB, to expedite message dissemination process, a relay node is selected in a distributed manner considering the progress made to a frame and the delay requirements of an application. In addition, a relay node broadcasts a message multiple times to assure that the probability that the other nodes successfully receive the message at least once is larger than a given threshold value. Since the number of rebroadcasts is regulated based on the successful message reception probability, the additional bandwidth needed to increase the reliability of broadcast is reasonably small. Jaesung Park and Yujin Lim Copyright © 2015 Jaesung Park and Yujin Lim. All rights reserved. System Architecture for Real-Time Face Detection on Analog Video Camera Tue, 19 May 2015 14:34:35 +0000 http://www.hindawi.com/journals/ijdsn/2015/251386/ This paper proposes a novel hardware architecture for real-time face detection, which is efficient and suitable for embedded systems. The proposed architecture is based on AdaBoost learning algorithm with Haar-like features and it aims to apply face detection to a low-cost FPGA that can be applied to a legacy analog video camera as a target platform. We propose an efficient method to calculate the integral image using the cumulative line sum. We also suggest an alternative method to avoid division, which requires many operations to calculate the standard deviation. A detailed structure of system elements for image scale, integral image generator, and pipelined classifier that purposed to optimize the efficiency between the processing speed and the hardware resources is presented. The performance of the proposed architecture is described in comparison with the detection results of OpenCV using the same input images. For verification of the actual face detection on analog cameras, we designed an emulation platform using a low-cost Spartan-3 FPGA and then experimented the proposed architecture. The experimental results show that the processing time for face detection on analog video camera is 42 frames per second, which is about 3 times faster than previous works for low-cost face detection. Mooseop Kim, Deokgyu Lee, and Ki-Young Kim Copyright © 2015 Mooseop Kim et al. All rights reserved. Pseudonyms in IPv6 ITS Communications: Use of Pseudonyms, Performance Degradation, and Optimal Pseudonym Change Tue, 19 May 2015 14:07:54 +0000 http://www.hindawi.com/journals/ijdsn/2015/189389/ IPv6 developed as a next generation Internet protocol will provide us with safer and more efficient driving environments as well as convenient and infotainment features in cooperative intelligent transportation systems (ITS). In this paper, we introduce the use of pseudonyms in IPv6 ITS communications for preserving location privacy. We conduct qualitative study on the performance degradation due to the use of pseudonyms and quantitative analysis on the optimal pseudonym change interval. Numerical results demonstrate that an appropriate pseudonym change interval should be changed depending on the packet arrival rate, mobility rate, and security level. Jong-Hyouk Lee, Giwon Lee, and Sangheon Pack Copyright © 2015 Jong-Hyouk Lee et al. All rights reserved. PAMTree: Partitioned Multicast Tree Protocol for Efficient Data Dissemination in a VANET Environment Tue, 19 May 2015 13:53:04 +0000 http://www.hindawi.com/journals/ijdsn/2015/431492/ The way to distribute a wide range of services on Vehicular Ad Hoc Networks is going to be a very interesting research topic, due to the willingness of the investors and the standardization institutions. In fact, the higher the number of available services is, the higher the impact and the market penetration of the considered technology will be. Also governance institutions appreciate the benefits of VANETs, having the possibility to increase safety level along the roads, saving lots of human lives, and reducing the severity of the collisions among vehicles. In this work we propose a multicast protocol, called partitioned multicast tree (PAMTree), which is suitable for spreading several kinds of services, increasing the reliability of the network, and giving the possibility to a higher number of users of having access to those services. The proposed protocol aims to exploit the characteristics of the VANET architecture in order to distribute services along the nodes of the network; owing to the high nodes mobility, several issues have to be faced to supply an optimal distribution, having a look at the quality of service (QoS) satisfaction. Amilcare Francesco Santamaria, Cesare Sottile, and Peppino Fazio Copyright © 2015 Amilcare Francesco Santamaria et al. All rights reserved. A Full-Duplex Relay Based Hybrid Transmission Mechanism for the MIMO-Capable Cooperative Intelligent Transport System Tue, 19 May 2015 12:59:25 +0000 http://www.hindawi.com/journals/ijdsn/2015/586040/ The goal of the cooperative intelligent transport system (C-ITS) is to provide a vehicular communication system that can enable quick, cost-effective means to distribute data in order to ensure safety, traffic efficiency, driver comfort, and so forth. The vehicular communication for C-ITS is composed of vehicle-to-infrastructure (V2I) and vehicle-to-vehicle (V2V) communications. In V2I, signals from roadside units (RSUs) often have to propagate through large buildings in urban areas, which can cause signal loss due to shadowing effects. V2V can provide video streaming capabilities to enable enhanced C-ITS services, but communication among vehicles may suffer from network congestion. Therefore, we propose a hybrid transmission mechanism in this paper based on full-duplex relay vehicles for MIMO-capable C-ITS. We adopt the use of full-duplex relay vehicles to enhance the reliability of seamless video stream transmission in V2I. For congestion resolution in V2V communications, the MIMO transmission mode is adapted according to the traffic situation and an extra detour path is used to satisfy various QoS requirements of multipriority video data. Simulations are also carried out to show that our mechanism improves the network throughput of MIMO-capable C-ITS with video streaming capability. Hayoung Oh and Sanghyun Ahn Copyright © 2015 Hayoung Oh and Sanghyun Ahn. All rights reserved. Asynchronous Scheme for Optical Camera Communication-Based Infrastructure-to-Vehicle Communication Tue, 19 May 2015 12:47:43 +0000 http://www.hindawi.com/journals/ijdsn/2015/908139/ This paper introduces infrastructure-to-vehicle (I2V) communication based on asynchronous optical camera communication (OCC), the transmitter of which can be an LED traffic light or electronic display, with the receiver being the existing front vehicle camera. In asynchronous OCC-based I2V communication, the key technique is an asynchronous scheme. An asynchronous scheme not only takes advantage of simplicity owing to the lack of an uplink or synchronization requirement, but is also the most feasible solution for communication to/from moving vehicles where synchronization is difficult to achieve within a short time. An asynchronous scheme for OCC-based I2V communication is proposed, and a performance evaluation shows its feasibility for use in a number of promising OCC-based wireless communication applications and services in a vehicular environment. Trang Nguyen, Nam Tuan Le, and Yeong Min Jang Copyright © 2015 Trang Nguyen et al. All rights reserved. Selective Random CDD Enhanced Joint Cooperative Relay and HARQ for Delay-Tolerant Vehicular Communications Tue, 19 May 2015 12:40:23 +0000 http://www.hindawi.com/journals/ijdsn/2015/657938/ We propose a selective random cyclic-delay diversity (CDD) enhanced joint cooperative relay and hybrid automatic repeat request (HARQ) scheme for two-hop vehicular communications. Our innovation mainly concentrates on design of the second-hop transmissions. On one hand, the CDD technique is applied across multiple relay nodes to artificially create frequency selectivity and then achieve diversity gain by applying channel coding. The employment of CDD does not necessarily require channel state information (CSI) at the transmitters and thus also decreases overhead caused by CSI feedback. On the other hand, retransmission for the second hop is performed based on relay selection. Particularly, the CDD is constructed only over selected relay nodes with qualified channel qualities to achieve a better frequency selective channel. As the selection results vary with random channel fading, our scheme is termed selective random CDD. Our scheme is presented based on a generic model and further applied into two scenarios, respectively: (1) car-to-car communications in high-way vehicular networks; (2) downlink transmission for the high velocity mobile station in cellular networks. Simulation results show that our proposed selective random CDD scheme can achieve higher throughput as well as lower transmission delay than the conventional cooperative beamforming based transmission scheme. Gang Wu, Qinghe Du, and Kun Hua Copyright © 2015 Gang Wu et al. All rights reserved. QoS Aware Service Scheduling Scheme for VANETs Tue, 19 May 2015 12:21:20 +0000 http://www.hindawi.com/journals/ijdsn/2015/282978/ People immediately want to access the required data in vehicular ad hoc networks (VANETs). They provide the requests to road side unit (RSU) while travelling. The job of RSU is to handle various requests in such a way so that the service ratio and the quality of service (QoS) is optimized. In this paper we present a mechanism to achieve this goal. Our proposed algorithm considers both data size and deadline and optimizes uploading/downloading based on number of requests to be handled. It also deals with the impact of missed upload operations to achieve maximum optimization. The proposed scheme categorizes data into two classes to assign weight according to their effect on QoS and assigns priorities to upload and download requests while maintaining common queue for both upload and download requests. Simulation results corroborate that the proposed algorithm provides better service ratio and QoS than existing techniques. Ajay Guleria, Kuldip Singh, and Narottam Chand Copyright © 2015 Ajay Guleria et al. All rights reserved. Hybrid Adaptive Beaconing in Vehicular Ad Hoc Networks: A Survey Tue, 19 May 2015 12:16:39 +0000 http://www.hindawi.com/journals/ijdsn/2015/390360/ Beacon or safety messages are broadcasted in vehicular ad hoc networks (VANETs) to disseminate network state or emergency incident information to other vehicles in the network. The freshness of information depends upon the frequent transmission of beacons. Similarly, to increase the awareness area or communicating with the distant nodes, beacons are disseminated with a high transmission power. However, increasing the beacon transmission power or rate has a negative effect on information communication efficiency because of the finite bandwidth of the wireless link. Therefore, different schemes have been proposed to individually control beacon’s transmission power, transmission rate, or contention window at the MAC layer, or any combination of those, to achieve quality beacon communication in VANETs. The latter case is called hybrid adaptive beaconing schemes. In literature, there are many hybrid adaptive beaconing schemes that control multiple communication parameters to efficiently broadcast beacon messages in VANETs. In this paper, we explicitly survey and summarized various aspects of those schemes. The open and challenging issues are also highlighted in this paper. Safdar Hussain Bouk, Gwanghyeon Kim, Syed Hassan Ahmed, and Dongkyun Kim Copyright © 2015 Safdar Hussain Bouk et al. All rights reserved. Phase-Sensitive Optical Time Domain Reflectometer with Dual-Wavelength Probe Pulse Mon, 18 May 2015 15:46:49 +0000 http://www.hindawi.com/journals/ijdsn/2015/624643/ A dual-wavelength pulse strategy is proposed to reduce the fading phenomenon in a phase-sensitive optical time domain reflectometer (-OTDR). The theoretical basis behind this dual-wavelength pulse strategy is presented and an experimental setup is described to help validate the proposed strategy. Through the experimental tests, a 37.79% improvement in detection for available points along the fiber is achieved when 1550.000 nm and 1550.138 nm wavelength signals are applied. The different wavelength tests show that at least a 0.012 nm or 1.498 GHz difference should be applied in a dual-wavelength pulse and an average 30% detecting improvement can be achieved when one wavelength changes from 1549.950 nm to 1550.100 nm. In addition, the dual-wavelength strategy makes the system response more stable and consistent along the sensing optical fiber. Yi Shi, Hao Feng, and Zhoumo Zeng Copyright © 2015 Yi Shi et al. All rights reserved. Adaptive Decision Fusion with a Guidance Sensor in Wireless Sensor Networks Mon, 18 May 2015 13:15:23 +0000 http://www.hindawi.com/journals/ijdsn/2015/643732/ In wireless sensor networks, the fusion center collects the dates from the sensor nodes and makes the optimal decision fusion, while the optimal decision fusion rules need the performance parameters of each sensor node. However, sensors, particularly low-cost and low-precision sensors, are usually displaced in harsh environment and their performance parameters can be easily affected by the environment and hardly be known in advance. In order to resolve this issue, we take a heterogeneous wireless sensor network system, which is composed of both low-quality and high-quality sensors. Low-quality sensors are inexpensive and consume less energy while high-quality sensors are expensive and consume much more energy but provide high accuracy. Our approach uses one high-quality sensor as the guidance sensor, which enables the fusion center to estimate the performance parameters of the low-quality sensors online during the whole sampling process, and optimal decision fusion rule can be used in practice. Through using the low-quality sensors rather than the high-quality sensor most of the time, the system can efficiently reduce the system-level energy cost and prolong the network lifetime. Zhaohua Yu, Qiang Ling, and Yi Yu Copyright © 2015 Zhaohua Yu et al. All rights reserved. A New Range-Free Localization Algorithm Based on Amendatory Simulation Curve Fitting in WSN Mon, 18 May 2015 12:07:30 +0000 http://www.hindawi.com/journals/ijdsn/2015/634153/ We analyze Range-free localization algorithms of WSN and propose a new localization algorithm based on amendatory simulation curve fitting theory. Firstly, we present the current research status of localization technology and some improved Range-free localization algorithms based on the modification of hop distance and selection of anchors. Secondly, we analyze the disadvantages of those algorithms. Thirdly, we propose a new algorithm based on amendatory simulation curve fitting (ASCF) through selecting more accurate reference distance and anchors. The new algorithm can improve the localization accuracy. At last, simulation experiments are conducted, and the experimental results indicate that the new algorithm can enhance the localization accuracy efficiently. Zhuang Liu, Xin Feng, Jingjing Zhang, Yanlong Wang, and Teng Li Copyright © 2015 Zhuang Liu et al. All rights reserved. HeadsUp: Keeping Pedestrian Phone Addicts from Dangers Using Mobile Phone Sensors Mon, 18 May 2015 12:03:23 +0000 http://www.hindawi.com/journals/ijdsn/2015/279846/ Walking while staring at the mobile phone is dangerous, and the danger mainly arises from distraction. While watching the mobile phone, one could fall into a deep well without noticing the manhole cover was missing, one could be hit by a rushing car without observing the traffic light, and so forth. Some mobile phone users are already aware of the crisis, and they keep looking up and down to allocate some focus to danger spying; however, the statistics data revealed by US government make such efforts frustrating: about 1,152 pedestrians are injured in US in the year 2010, while they were using mobile phones, and the number doubled in the year 2012. This paper identified the possibility of using mobile phone sensors to develop a walk pattern recognition system. By sampling from embedded sensor, such as accelerometer and gyroscope, the movement pattern of mobile phone users can be computed. We design and implement HeadsUp, a system that warns pedestrian and locks the screen when one looks at the mobile phone while walking. Evaluation results from experiments of 20 testers in real life situation show that, on average, the false negative rate is less than 3%. Zhengjuan Zhou Copyright © 2015 Zhengjuan Zhou. All rights reserved. An Anomaly Detection Based on Data Fusion Algorithm in Wireless Sensor Networks Mon, 18 May 2015 08:18:24 +0000 http://www.hindawi.com/journals/ijdsn/2015/943532/ In recent years, with the development of wireless sensor networks (WSN), it has been applied in more and more areas. However, energy consumption and outlier detection have been always the hot topics in WSN. In order to solve the above problems, this paper proposes a timely anomaly detection algorithm which is based on the data fusion algorithm. This algorithm firstly employs the piecewise aggregate approximation (PAA) to compress the original data so that the energy consumption can be reduced. It then combines an improved unsupervised detection algorithm of -Means and artificial immune system (AIS) to classify the compressed data to normal and abnormal data. Finally, relevant experiments on virtual and actual sensor databases show that our algorithm can achieve a high outlier detection rate while the false alarm rate is low. In addition, our detection algorithm can effectively prolong the life because it is based on data fusion algorithm. Xingfeng Guo, Dianhong Wang, and Fenxiong Chen Copyright © 2015 Xingfeng Guo et al. All rights reserved. Constrained Extended Kalman Filter for Target Tracking in Directional Sensor Networks Sun, 17 May 2015 06:35:56 +0000 http://www.hindawi.com/journals/ijdsn/2015/158570/ The target tracking problem in directional sensor networks (DSNs) is attracting increasing attention. Unlike the traditional omnidirectional sensor, a directional sensor has a special angle of view. It can offer direction information rather than just the sensing signal measurement with respect to the detected target. The existing tracking approaches in DSNs always separately consider the direction and measurement information; they hardly promise the tracking performance of minimum variance. In this paper, the field of view of directional sensor is approximated to a rectangle; as such the constrained area in which the target is bound to be is constructed. Then, the target tracking problem is formulated as a constrained estimation problem, and a constrained extended Kalman filter (CEKF) tracking algorithm integrating the direction and measurement information is presented; its structural and statistical properties are rigorously derived. It is proved that CEKF is the linear unbiased minimum variance estimator, and CEKF can yield a smaller error covariance than the unconstrained traditional extended Kalman filter using only sensor measurements. Simulation results show that the CEKF has superior tracking performance for directional wireless networks. Sha Wen, Zixing Cai, and Xiaoqing Hu Copyright © 2015 Sha Wen et al. All rights reserved. A Dynamic Virtual Force-Based Data Aggregation Algorithm for Wireless Sensor Networks Thu, 14 May 2015 16:20:32 +0000 http://www.hindawi.com/journals/ijdsn/2015/814184/ In wireless sensor networks (WSNs), energy efficiency is critical for increasing network lifetime. WSNs consist of low-cost nodes with constrained energy. Present study demonstrates that data aggregation is an effective approach to reduce energy consumption in WSNs. Current data aggregation algorithms, such as cluster-based, tree-based, and chain-based data aggregation algorithm, incur high overhead to maintain structures and in dynamic scenarios incur much more cost to continuously reconstruct aggregate route. In this paper, we propose a dynamic virtual force-based algorithm (VFE) for data aggregation which can adapt to different scenario changes. Inspired by the concept of cost field and virtual force, VFE constructs dynamic routing without structure overhead, which makes data aggregation more efficient. The simulations confirm that VFE achieves significant energy saving and prolongs network lifetime. Junhai Luo and Jiyang Cai Copyright © 2015 Junhai Luo and Jiyang Cai. All rights reserved. An Energy-Efficient and Relay Hop Bounded Mobile Data Gathering Algorithm in Wireless Sensor Networks Thu, 14 May 2015 13:13:36 +0000 http://www.hindawi.com/journals/ijdsn/2015/680301/ Recent studies reveal that great benefit can be achieved by employing mobile collectors to gather data in wireless sensor networks. Since the mobile collector can traverse the transmission range of each sensor, the energy of nodes may be saved near maximally. However, for directly receiving data packet from every node, the length of mobile collector route should be very long. Hence it may significantly increase the data gathering latency. To solve this problem, several algorithms have been proposed. One of them called BRH-MDG found that data gathering latency can be effectively shortened by performing proper local aggregation via multihop transmissions and then uploading the aggregated data to the mobile collector. But, the BRH-MDG algorithm did not carefully analyze and optimize the energy consumption of the entire network. In this paper, we propose a mathematical model for the energy consumption of the LNs and present a new algorithm called EEBRHM. The simulation results show that under the premise of bounded relay hop, compared with BRH-MDG, EEBRHM can prolong the networks lifetime by 730%. Ling Chen, Jianxin Wang, Xiaoqing Peng, and Xiaoyan Kui Copyright © 2015 Ling Chen et al. All rights reserved. On Tracking Dynamic Objects with Long Range Passive UHF RFID Using a Mobile Robot Thu, 14 May 2015 12:53:16 +0000 http://www.hindawi.com/journals/ijdsn/2015/781380/ Service robots have shown an impressive potential in providing assistance and guidance in various environments, such as supermarkets, shopping malls, homes, airports, and libraries. Due to the low cost and contactless way of communication, radiofrequency identification (RFID) technology provides a solution to overcome the difficulties (e.g., occlusions) that the traditional line-of-sight sensors (e.g., cameras and laser range finders) face. In this paper, we address the applications of using passive ultrahigh frequency (UHF) RFID as a sensing technology for mobile robots to track dynamic objects. More precisely, we combine a two-stage dynamic motion model with the dual particle filter to capture the dynamic motion of the object and to quickly recover from failures in tracking. The state estimation from the particle filter is used in combination with the VFH+ (Vector Field Histogram) to guide the robot towards the target. This is then integrated into a framework, which allows the robot to search for both static and dynamic tags, follow them, and maintain the distance between them. We finally tested our approach on a SCITOS G5 service robot through various experiments. Ran Liu, Goran Huskić, and Andreas Zell Copyright © 2015 Ran Liu et al. All rights reserved. Delay and Lifetime Performance of Underwater Wireless Sensor Networks with Mobile Element Based Data Collection Thu, 14 May 2015 09:52:38 +0000 http://www.hindawi.com/journals/ijdsn/2015/128757/ Underwater Wireless Sensor Networks (UWSNs) may be easily partitioned due to resource constraints and sparse deployment, and such UWSNs need to be treated as Delay/Disruption Tolerant Networks (DTN). The principal objective of DTN routing is to maximize the possibility of eventual data delivery, which can be achieved only at the cost of high energy consumption and/or increased message latency. The energy efficiency and network lifetime are more important than data collection latency for certain underwater applications. We consider energy-efficient data collection using mobile elements, which is suitable for long-term sensing applications that are not time-critical. Using different analytical models, we investigate energy efficiency, network lifetime, packet delivery ratio, and message latency in a mobility-assisted data collection framework for UWSNs. The analytical models are validated with the experimental setup developed using the NS-2 based Aqua-Sim simulator. The results demonstrate that the proposed framework shows superior performance in terms of energy efficiency, network lifetime, and packet delivery ratio at the cost of increased message latency. The analytical models for delay performance are compared to see that the polling model is more effective in modelling the mobility-assisted data collection framework for UWSNs and more flexible in implementing different service policies. Jalaja Janardanan Kartha and Lillykutty Jacob Copyright © 2015 Jalaja Janardanan Kartha and Lillykutty Jacob. All rights reserved. Towards a Secure Medium Access Control Protocol for Cluster-Based Underwater Wireless Sensor Networks Thu, 14 May 2015 09:34:36 +0000 http://www.hindawi.com/journals/ijdsn/2015/325474/ The unique characteristics of high bit error rate, low bandwidth, and long propagation delay in underwater environments pose significant challenges to the design of the medium access control (MAC) protocol for underwater wireless sensor networks (UWSNs). Clustering is an effective and practical way to enhance the performance of UWSNs. In this paper, we propose a secure MAC protocol for cluster-based UWSNs, called SC-MAC, which aims to ensure the security of data transmission. In SC-MAC, the clusters are formed and updated dynamically and securely. We leverage MAC layer information by considering the link quality as well as residual energy of the modem’s battery. After the successful mutual authentication, all sensor nodes from different clusters can protect the data transmission in the continuous communication. As the states of sensor nodes may not be observed accurately in a harsh underwater environment, we formulate the channel scheduling process as a stochastic partially observed Markov decision process (POMDP) multiarmed bandit problem and derive the optimal channel scheduling rules hereby. Simulation results show that SC-MAC can perform better than existing state-of-the-art MAC protocols in terms of network throughput, successful delivery ratio, and energy consumption in various circumstances. Ming Xu, Guangzhong Liu, and Jihong Guan Copyright © 2015 Ming Xu et al. All rights reserved. Scheduling and Power Control for Energy-Optimality of Low Duty Cycled Sensor Networks Thu, 14 May 2015 09:30:05 +0000 http://www.hindawi.com/journals/ijdsn/2015/432978/ The main limitation of operating sensor networks autonomously is the finite battery capacity of sensor nodes. Sensors are usually operated at low duty cycle; that is, they remain in active mode for short duration of time, in order to prolong the network lifetime. However, operating at low duty cycle may result in significant performance degradation in system operation. Hence, in this work, we quantitatively investigate the tradeoff between the duty cyle and network performance. Specifically, we address the design of efficient channel access protocol, by developing a scheduling algorithm based on well known Lyapunov optimization framework. Our proposed policy dynamically schedules transmissions of sensor nodes and their sleep cycles by taking into account the time-varying channel state information, traffic arrivals, and energy consumptions due to switching between operational modes. We analytically show that our policy is energy optimal in the sense that it achieves an energy consumption which is arbitrarily close to the global minimum solution. We use simulations to confirm our results. Nursen Aydin, Mehmet Karaca, and Ozgur Ercetin Copyright © 2015 Nursen Aydin et al. All rights reserved. Design and Optimization of Hierarchical Routing Protocol for 6LoWPAN Thu, 14 May 2015 06:50:37 +0000 http://www.hindawi.com/journals/ijdsn/2015/802387/ To build scalable and lightweight wireless sensor networks with energy saving devices, 6LoWPAN-based protocols become emergent technologies that successfully constructed ubiquitous networks and seamlessly connected the traditional Internet with WSNs. However, the existing researches cannot effectively maintain the routing and the network topology for the problems of low cost sensors’ malfunctions. In this paper, we improved the HiLow protocol in aspects of interconnection between the Internet and 6LoWPAN and designed a network routing path recovery approach. In addition, we designed and modified the address mapping table in gateway to store and map nodes’ EUI-64 address and 16-bit short address. Nodes from the Internet can access the 6LoWPAN nodes by an IPv6 address, which is generated by the EUI-64 address and IPv6 prefix. Due to the benefits of additional data structure and our designs, the simulation results manifested that our protocol improves the routing efficiency and can effectively reduce the cost for network reorganization caused by node failures and mobiles. Ming Liu, Yang Xu, Shuai Wu, and Tian Lan Copyright © 2015 Ming Liu et al. All rights reserved. Indoor Mobile Localization in Mixed Environment with RSS Measurements Thu, 14 May 2015 06:49:18 +0000 http://www.hindawi.com/journals/ijdsn/2015/106475/ Mobile localization is a significant issue for wireless sensor networks (WSNs). However, it is a problem for the indoor localization using received signal strength (RSS) measurements that the signal is contaminated by the anisotropy fading and interference due to walls and furniture. Standard schemes such as Kalman filter are inadequate as the random transition of line-of-sight (LOS)/non-line-of-sight (NLOS) conditions occurs frequently. This paper proposes an indoor mobile localization scheme with RSS measurements in a mixed LOS and NLOS environment. First, a new efficient composite measurement model is induced and validated, which approximates the complex effects of LOS and NLOS channels. Second, a greedy anchor sensor selection strategy is adopted to break through the constraints of hardware consistency and the multipath interference. Third, for the Markov transition between LOS and NLOS conditions, an effective unscented Kalman filter (UKF) based interactive multiple model (IMM) is proposed to estimate not only the posterior model probabilities but also a weighted-sum position estimation with the aid of likelihood function. To evaluate the proposed algorithm, a complete hardware and software platform for mobile localization has been constructed. The numerical study, relying on the actual experiments, illustrates that the proposed UKF based IMM achieves a substantial gain in precision and robustness, compared with other works. Zhengguo Cai, Lin Shang, Dan Gao, Kang Zhao, and Yingguan Wang Copyright © 2015 Zhengguo Cai et al. All rights reserved. Scheduling with Collaborative Mobile Chargers Inter-WSNs Wed, 13 May 2015 14:03:21 +0000 http://www.hindawi.com/journals/ijdsn/2015/921397/ Mobile charge problem describes a fleet of mobile chargers delivers energy to the sensor nodes periodically in wireless sensor networks (WSNs). In it, every sensor node has an asynchronous rest working time during a charging round. We consider the asynchronous rest working time and give the lower and upper bounds of the recharging cycle by the suitable total serving rate, to give the definition of time windows for the sensor nodes. In this paper, we model this problem in 2-dimensional WSNs as a vehicle routing problem with time windows (VRPTW). For solving the problem of multiple mobile chargers with different routing paths, we propose to transform the multiple routing problems into a single routing problem, by duplicating the sink into multiple virtual sinks. To optimize the routing path, we propose a local optimization algorithm by considering the collaborative charging among the mobile chargers. Through the simulations, we compare our proposed algorithm with the algorithm. We demonstrate the advantages of our collaborative scheduling algorithm in this problem. Jidong Zhao, Xili Dai, and Xiaomin Wang Copyright © 2015 Jidong Zhao et al. All rights reserved.