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ISSN 1000-1239 CN 11-1777/TP

Table of Content

15 December 2009, Volume 46 Issue 12
Paper
Design of a Cognition-Enhanced Wireless Sensor Node
Liu Zhiwu and Wu Wei
2009, 46(12):  1963-1970. 
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To improve throughput and spectrum utilization in wireless sensor network, the authors present design and implementation of an ARM9 based multi-interface cognition-enhanced wireless sensor node. The node adopts architecture of single processor multiple radios, which is different from the typical single processor single radio architecture. Based on STR911 processor, the node can support four interfaces, two of which are for the CC2420 radio, and the other two are for the nRF905 radio. With these four radios, the node can work on ISM 433/868/915MHz and 2.4GHz ZigBee band. The node is equipped with light and temperature sensors, which can be used as a light and temperature monitor. Compared with single interface sensor node, node with multi-interface provides more flexibility for wireless sensor network, for it can be used as a router between 2.4GHz and 433MHz sensor networks. Also multi-interface makes the design of MAC protocol for wireless sensor network easier. Experiments give the measurement and validation of the nodes throughput and cognitive capability. The results show that the throughput has increased by 68.41% than Atmega128 based node. Also the average sense delay is 1.4782ms shorter for each channel. Compared with the method of CSMA/CA, communication delay is 11.86% shorter with the cognitive method, which can avoid the impact of interference effectively.
Multi-Channel Reliability Modeling and Analysis for IEEE802.15.4 in Industrial Environment
Wang Qin, Wan Yadong, Li Lei, and Duan Shihong
2009, 46(12):  1971-1984. 
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Wireless sensor network protocol design is highly depended on the link characteristics of the network environment. In real application field, link reliability is vulnerable to environment interferences. But there are little works which reveal the temporal variation and multi-channel difference characteristics of the link reliability. The authors present a statistics approach according to the temporal and frequency characteristics of link reliability in industrial environment. Two variables, i.e. packet drop rate (PDR) and packet drop sequence (PDS) are introduced to describe the relationship of link reliability with time and frequency. Through the measurements in typical environments like iron and steel factory and experimental factory in USTB with IEEE 802.15.4 compliant transceivers, it is found that the PDR of a certain range follows logistic distribution or log-logistic distribution, and the interval between two dropped packets for a given PDR follows lognormal distribution as well. Furthermore, based on the analysis of the link reliability, a link layer statistical model is presented and two proposals for IEEE802.15.4e are evaluated on the new model. The simulation results show that the network reliability can be improved when taking the statistic characteristics of the link variations into consideration in the design of high reliable protocols.
A Model of Energy Consumption Based on Characteristic Analysis of Wireless Communication and Computation
Cheng Xiaoliang, Deng Zhidong, and Dong Zhiran
2009, 46(12):  1985-1993. 
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Wireless sensor network (WSN) is a resource-constrained network, especially, in terms of energy aspect. Hence, the goal of energy-efficiency should be achieved for WSN. For the reason that the WSN is application-oriented, the problem of energy consumption of WSN must be considered in an application-oriented way. It is necessary to get knowledge of the energy depletion of WSN in a real-time way. This requires that a reasonable model of energy consumption should be provided first. But the general assumption in the study of WSN energy consumption modeling is somehow not in accordance with the truth. For this reason, all the existing models of energy consumption are not available to real-world applications of WSN. To build up an application-oriented model of energy consumption, a comprehensive analysis of energy consumption is made, together with specific WSN applications. Specifically, the activities of wireless communication and computation, physical characteristics of WSN nodes, and the influence of all these factors on energy consumption are investigated. As a result, a model of energy consumption based on characteristic analysis of wireless communication and computation is proposed. Furthermore, a new energy consumption model is constructed practically, and the effectiveness of this model is validated. Finally, conclusion remarks are given.
An Energy-Efficient Task Assignment Algorithm of Wireless Sensor Network
Li Zhigang, Zhou Xingshe, Li Shining, and Ma Junyan
2009, 46(12):  1994-2002. 
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In-network processing methods are often adopted in wireless sensor network (WSN) to reduce data communication and prolong the lifetime of network, which enables a WSN application to be described as a set of tasks (sensing, processing) and dependencies among them. Task assignment has become an important problem which needs to be resolved, as different task assignments can cause different communication traffics, and then cause different energy consumption when performing the application. Based on the task graph of WSN described by DAG (directed acyclic graph), an energy-efficient task assignment framework is proposed. As an application can be decomposed into sensing tasks and processing tasks, the task assignment is presented as a process of sensing task assignment and processing task assignment. Sensing task assignment involves sensor selection in WSN and some work has been done for this problem. In this paper, the authors consider the problem of how to assign the processing tasks after the selection of sensors to make the application performed using minimum energy. The processing task assignment is formulated as a quadratic 0-1 programming problem, and a distributed OALL algorithm (optimizing assignment layer by layer) is proposed. With demonstrative example, the proposed algorithm has been evaluated, and the results of experiment has proved its effectiveness.
EasiTOD: A Detection and Adjustment Mechanism to Reduce the Interference of the Timeliness Obstacles in Sensor Networks
Zhang Le, Li Dong, and Cui Li
2009, 46(12):  2003-2013. 
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The obstacles which affect the link quality of wireless sensor network can be divided into two categories by the time characteristics: one is the timeliness obstacles and the other is the permanent obstacles. The timeliness obstacles are a kind of barriers which are caused by the changes of the environment factors, and they reduce the wireless link quality. According to the properties of change in environment factors, the timeliness obstacles can be divided into periodical timeliness obstacles and sudden obstacles. Considering the periodical impact on the wireless sensor network caused by the periodic timeliness obstacles, EasiTOD(EasiNet timeliness obstacle detection) mechanism is proposed. Because the timeliness obstacles have a periodical impact on the wireless sensor network’ link, EasiTOD divides the link period into two link states: stable period and fluctuant period. Based on previous two link states, EasiTOD adopts corresponding adjustment methods of detection. Experiments show that EasiTOD mechanism can detect timeliness obstacles of wireless sensor network. With the above mechanism, EasiTOD reduces the timeliness obstacles’ interference on the communication of the wireless sensor network. EasiTOD also reduces energy consumption as much as possible on the basis of high communication reliability of network. Therefore, EasiTOD improves the overall performance of sensor networks.
DSMAC: Media Access Control Protocol for Wireless Multimedia Sensor Network
Li Ruifang, Li Renfa, Luo Juan, and Wei Yehua
2009, 46(12):  2014-2023. 
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Wireless multimedia sensor network (WMSN), as a multimedia information acquiring and processing technology, make potential applications span a wide spectrum from military to industrial fields. Research on wireless multimedia sensor network relates to many techniques. Medium access control (MAC) is at the core of effective communication. Owing to the energy constraints of the small, battery-powered sensor nodes, it is desirable that the medium access control protocol enable reliable, error-free data transfer with minimum retransmissions while supporting application-specific QoS requirements. There is some type of traffic with different QoS requirement in WMSN. Real-time traffic services demand low-latency. And, non-real-time traffic services demand high reliability. A different service medium access control (DSMAC) is presented for wireless multimedia sensor network. The four-channel protocol can support different service between real-time traffic using TDMA and non real-time traffic using contention based technology. It can support transmission of burst multimedia traffic through insert random contention period into frame. And a multi-channel inter-cluster transmission to avoid hidden terminal problem is proposed. Simulation analysis results and experimental results of difference-service, real-time, throughput, energy-efficiency, etc. show DSMAC is more suitable for wireless multimedia sensor network than other MAC protocols. Preliminary performance of DSMAC in real world system is discussed at the end.
HM-MAC: A Multi-Channel MAC Protocol for Sensor Network with Broadcast Supporting
Zhang Desheng, Li Jinbao, Guo Longjiang, Ji Shouling, and Wang Yu
2009, 46(12):  2024-2032. 
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Aiming at single radio multi-channel MAC protocol’s problems, such as the requirement of time synchronization and lots of orthogonal channels, large number of multi-channel hidden terminals, loss of single-hop multi-channel broadcast data, etc, the authors propose a competition based multi-channel MAC protocol, called HM-MAC, to tackle those problems for wireless sensor network. In HM-MAC, all the nodes work without time synchronization, use few orthogonal channels and take advantage of handshake mechanism to reduce the number of multi-channel hidden terminals. Meanwhile, a probability based sender adjustment broadcast scheme is presented, which reduces the loss of data and improves broadcasting efficiency. By theoretical analysis of the unicast mode, the number of used channel as well as the number of multi-channel hidden terminals are obtained. And, via theoretical analysis of the broadcast mode, the broadcasting efficiency of HM-MAC broadcast scheme is also obtained. More importantly, broadcast efficiencies of current multi-channel broadcast scheme are analyzed theoretically. In addition, a detailed comparison between HM-MAC broadcast scheme and other multi-channel broadcast schemes is presented. Finally, the theoretical analysis is verified via simulation experiments. The results of simulation experiment show that HM-MAC reduces the number of multi-channel hidden terminals effectively, and improves broadcasting efficiency as well as network throughput significantly.
A Tree-Based Clustering Construction Algorithm (TBCCA) in Wireless Sensor Network
Huang Haiping, Wang Ruchuan, Jiang Hao, Sun Lijuan, and Li Jing
2009, 46(12):  2033-2043. 
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Aimed at the disadvantages on current clustered and topology control protocols in distributed wireless sensor network (WSN), such as high energy cost, non-balanced communication overhead, unsatisfactory computational complexity and extra consumption, etc., a novel tree based clustering construction algorithm (TBCCA) is presented. Firstly, it provides some premises and definitions about topologic model such as area radius, cluster radius and reachable adjacent domain, etc. Based on isosceles triangle clustered-tree structure, it proposes clustering strategy according to three types of threshold sets called near set, common set and medium set, and cluster radius controlled by RSSI (received signal strength indicator) value between neighboring nodes. Detailed procedures which contain cluster head selection and determination of candidate nodes are described in this paper, where some theorems about topology & coverage are in proof, and several optional strategies are provided in terms of different requirements on price of computation or communication. Performance analysis and simulation results illustrate that TBCCA has advantage over some existing algorithms in computational expense, for instance, TopDisc or DLMST; And compared with Leach protocol and HEED protocol, TBCCA is energy-efficient and energy-balanced, and expands the life-time of network while lower complexity, higher coverage and connectivity is guaranteed.
An Distributed and Directed Clustering Algorithm Based on Load Balance for Wireless Sensor Network
Liu Xinhua, Li Fangmin, Kuang Hailan, and Fang Yilin
2009, 46(12):  2044-2052. 
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Clustering routing protocol for wireless sensor network (WSN) have been growing in recent years. In view of the load balance problem during network clustering for WSN, a distributed and directed clustering algorithm based on load balance is proposed (DDC). In DDC, the pre-evaluation factors which are used for pre-evaluating the energy level and load ability for each node in the next round are presented. During the clustering per round, the whole network is firstly divided into appropriate subareas by the energy pre-evaluation factor, and then the cluster head of each subarea is selected according to the load balance pre-evaluation factor. DDC effectively ensures that the network energy consumption can be decentralized uniformly to every subarea, and that the load for each node in subarea can be balanced. Those characteristics of DDC can organically combine the network energy with the load of node so as to prolong the lifetime of WSN to the greatest extent. The simulation experiments demonstrate that DDC significantly outperforms some similar algorithms such as LEAH and DCHS in terms of energy efficiency, and the load of each node in WSN is more balanced. In the energy-heterogeneous network environments, DDC still has very good adaptability and expandability.
A Disjoint Multi-Path Routing Algorithm in Wireless Sensor Network
Fang Xiaolin, Shi Shengfei, and Li Jianzhong
2009, 46(12):  2053-2061. 
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Wireless sensor network (WSN) are usually used to monitor environment by collecting data from sensors deployed in a particular area. But the link quality of WSN is unstable and the network easily has nodes failures, so the data loss is an open problem in wireless sensor network. In order to achieve routing robustness in networks, people proposed multi-path routing (MPR) in sensor networks. But MPR fails when the common links or the common nodes in multiple paths fail. To solve the common-link and common-node problem, disjoint multi-path routing (DMPR) is employed where sensors send data to the sink through link-disjoint or node-disjoint path. In this paper, the authors develop a routing mechanism where sensor nodes can send data to sink through node-disjoint paths. And the algorithm is suited for multi-sink applications where every sensor node can forward the packets to any one of the sinks. The number of routing table entries of the algorithms at each node is |K|, where |K| denotes the number of multi-path. The running time complexity of the algorithm is O(|L|), where |L| denotes the number of links in the network. The experiment results show that the algorithm can effectively improve the routing reliability in sensor networks.
A V2V Broadcast Protocol for Chain Collision Avoidance on Highways
Zhou Huan, Xu Shouzhi, and Li Chengxia
2009, 46(12):  2062-2067. 
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As the speed of a vehicle on the highway can reach as high as over 100km an hour, so drivers on highways have less reaction time than drivers in other road situations. That’s why chain collision happens frequently on highways. In this paper, V2V (vehicle to vehicle) network is applied to solve the problem of chain collision on highways. Currently, the V2V network relies on periodic broadcast to disseminate the emergency warning messages (EWM) to locations beyond the transmission range of individual nodes on highways. But along with it, there comes the problem of broadcast redundancy, which reduces the reliability and efficiency of the warning system. In this paper, by studying different broadcast strategies, a new efficient IEEE 802.11 based broadcast protocol of communication in vehicle group is proposed for preventing chain collision on highways. The proposed protocol designs to figure out broadcast redundancy, transmission latency, reliability problems of multi-hop broadcast on highways, and achieves the purpose by sending the ACK frame to choose broadcast vehicles on the basis of directive broadcast. The simulation result shows that it can effectively handle the broadcast redundancy problem of EWM and achieve higher reliability but lower transmission latency of message dissemination among vehicles on highways.
A Message Transmission Scheme for Community-Based Opportunistic Network
Niu Jianwei, Zhou Xing, Liu Yan, Sun Limin, and Ma Jian
2009, 46(12):  2068-2075. 
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The proliferation of mobile devices has witnessed the extensive research on opportunistic network in both academia and industry. Community-based opportunistic network combine the social people and wireless communication devices so that characteristics from both the opportunistic network and social networking are inherited. However, the prevalent multi-copy message routing algorithms in opportunistic network will lead to long transmission delay and high message loss rate when deployed directly in the community-based opportunistic network. To tackle the above problems, a community-based message transmission scheme (CMTS) is proposed in utilizing the clustering characteristics of all the nodes in community-based opportunistic network. CMTS utilizes Newman’s weighted network analysis method to organize network nodes into different communities based on the contact frequencies among them. In dealing with intra-community communication, CMTS determines the number of message copies in the network and chooses more active nodes as the relays. For inter-community communication, messages are transmitted to target communities mainly relying on the nodes which have larger social degrees. Simulation results show that CMTS can balance well the tradeoff between delivery ratio and resource consumption in community-based opportunistic network. The evaluation results also show that CMTS can reduce the message forwarding times by about 20% when compared with Spray and Focus.
COBRA: A Collaboration Based Reinforcement Mechanism for Mass Transmission in VANETs
Tian Rui, Sun Limin, Liu Yan, and Ma Jian5
2009, 46(12):  2076-2084. 
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Vehicular ad hoc networks (VANETs) allow vehicles to form self-organized networks while driving, which can offer cheap methods to access the Internet for the passengers. When the scope of VANETs becomes larger, it’s often needed to forward massive data to some fixed Internet APs distributed in the city. There are a lot of routing algorithms proposed to reduce the message propagation delay and also reduce bandwidth consumption on VANETs, but most of which are under the assumption that the bandwidth between vehicles is unlimited so massive data can be forwarded instantaneously; it is verified that this can lead poor transmission performances when implemented. The authors propose a reinforcing mechanism COBRA to forward massive data in VANETs. The COBRA mechanism focuses on the incomplete data transmitting problem brought by high driving speed and limited wireless communication range. The mechanism utilizes the stable topology characteristic of vehicles running in the same directions to prolong the opportunistic transmitting time, and also use erasure coding technology to deal with the uncertain factors in the “meeting-forwarding” processes. The simulation results show that, when data are large, or when bandwidth is limited, the routing method with the reinforcing mechanism can outperform the existing VANET routing protocols.
A Wavelet Data Compression Algorithm with Memory-Efficiency for Wireless Sensor Network
Zhou Siwang, Lin Yaping, Ye Songtao, and Hu Yupeng
2009, 46(12):  2085-2092. 
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Wireless sensor network is becoming an important field in wireless network, and data compression is a key technique. Most existing data compression algorithms for wireless sensor network give only emphasis on reducing energy consumption, not considering the limited memory of sensor nodes. In this paper, a problem of memory-efficient data compression for wireless sensor network based on wavelet technique is addressed. A virtual grid-based ring topology and an overlapping clustering topology are firstly designed. Employing those two topologies to perform wavelet transform, border effect can be eliminated. Then, two dimensional and three dimensional data compression transmission algorithms are proposed. In those algorithms, the progressively transmitting data units are specified according to wavelet function and the memory of each cluster head. So, the needed memory of each cluster head doesnt depend on the size of sensory data. The proposed algorithms select sensor nodes to transmit data to cluster head based on spatial correlation among sensory data, and thus high compression efficiency is obtained. From the view points of memory, energy consumption and delay, the performance of those algorithms is analyzed. Theoretically and experimentally it is shown that the proposed algorithm doesnt consume much more energy compared with the existing ones. More importantly, it is memory-efficient.
A Secure and Efficient Data Survival Strategy in Unattended Wireless Sensor Network
Ren Wei, Ren Yi, Zhang Hui, and Zhao Junge
2009, 46(12):  2093-2100. 
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Unattended wireless sensor network (UWSN) have attracted more and more interests in recent research community. In UWSN, sensed data are stored locally for a long term, instead of being sent to a central sink immediately. It is motivated by certain applications that only digest information (e.g. historical information), not real-time data, are of interest. The digest information can be extracted on-site upon request and real-time data are avoided to be forwarded away in order to mitigate the communication overhead. As UWSN always confront many security risks and adversaries that result in nodes random failure or node compromise, such stored data need to be survived to the collecting moment. Therefore, the security problem arises: how to maximize the data survival till the data are collected, or to maximize the valid data upon data retrieval. In particular, the involved defense strategies need to be efficient due to the resource constraints. A family of strategies is proposed to improve the data survival in this paper. Some observations are proofed such as location entropy based hopping limited data moving strategy. The proposed advanced strategy makes use of such observation to achieve efficiency and takes the advantage of computational secret sharing to achieve both fault tolerance and compromise resilience. The analysis of the performance and security are also presented extensively.
A Multiple-Regression-Model-Based Missing Values Imputation Algorithm in Wireless Sensor Network
Pan Liqiang and Li Jianzhong
2009, 46(12):  2101-2110. 
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In wireless sensor network, the missing of sensor data is inevitable due to the inherent characteristic of wireless sensor network, and it causes many difficulties in various applications. To solve the problem, the best way is to estimate the missing data as accurately as possible. In this paper, a multiple-regression-model-based missing values imputation algorithm is proposed. It first adopts the multiple linear regression model to estimate the missing data both on temporal dimension and spatial dimension. Then, it assigns the weight coefficients to the two estimated values computed respectively on temporal dimension and spatial dimension according to the goodness-of-fit, and then uses the weighted average of the two values as the final estimated value. Since the algorithm estimates the missing data with the data of multiple neighbor nodes jointly rather than independently, its estimation performance is more stable and reliable. Experimental results on two real-world datasets show that the proposed algorithm can estimate the missing data accurately.
An EnergyEfficient Data Storage Method in Wireless Sensor Network
Fu Xiong, Wang Ruchuan, and Deng Song
2009, 46(12):  2111-2116. 
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Now in the various applications of wireless sensor network, a large amount of sensing data is generated by all kinds of sensors over a long period of time. All collected data must be stored for the future information query and data analysis, so how to efficiently store the data has become one of the biggest challenges in the applications of wireless sensor network. In this paper a distributed data storage method is proposed for the wireless sensor network which has organized in a tree rooted at the sink node with the predefined communication routes from each sensor to the sink node. This method makes use of a dynamic programming based algorithm to select some storage nodes from all nodes in wireless sensor network to make storage node energy balanced and to minimize the total energy of all sensors at the same time. Therefore this data storage method tends to make all wireless sensor network energy efficient and prolong the lifetime of all wireless sensor network. In the experiments, the data storage method is compared with two kinds of data storage methods, which show that this data storage method can not only achieve better energy balance but also reduce total energy cost.
A Faulty Sensor Node Tolerance Algorithm Based on Cut Point Set
Ye Songtao, Lin Yaping,, Hu Yupeng, Zhou Siwang, and You Zhiqiang
2009, 46(12):  2117-2125. 
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In many sensor network applications, sensor collects correlated measurements of a physical field, for example: temperature field in a greenhouse. However, due to nodes’ inherent instability and the severe environment, sensors are prone to fail. The measurements of a faulty sensor node will incur confusions in global readings, while turning them into sleeping mode will degrade network connectivity and overload balance. Therefore, it is significant to exploit residual energy of those faulty sensor nodes so as to obtain accurate integrated readings as well as overload balance. In this paper, a cut-point set based faulty sensor node tolerance algorithm is proposed by introducing the concepts of spatial correlation model, strong correlation graph and cut-point set. The algorithm first finds out a cut-point set, which has strong spatial correlation with faulty sensor node. According to the observations of the cut-point set, the faulty sensor node is able to predict its missing sensor readings by using orthogonal intersection estimation method. Analytic results show that the algorithm not only can tolerate the faulty sensor node, but also accurately predicts miss-readings, and keeps network connectivity and overload balance. The results of miss-readings estimation, obtained from simulations and greenhouse monitoring experiments, show that the methodology presented can successfully predict the missing sensor readings.
A Path Coverage-Enhancing Algorithm for Directional Sensor Network Based on Improved Potential Field
Xiao Fu, Wang Ruchuan, Ye Xiaoguo, and Sun Lijuan
2009, 46(12):  2126-2133. 
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Path coverage is one of the hot research topics in monitor area using wireless sensor network. Motivated by the directional sensing feature of wireless multimedia sensor network, a direction adjustable sensing model is analyzed firstly and an path coverage-enhancing algorithm for directional sensor network based on improved potential field (IPFPCA) is proposed in this paper. Traditional virtual potential field’s local minimum may lead to path coverage-enhancing failure. Aimed at this problem, an improved potential field function considering the joint coverage rate of adjacent sensor nodes is designed. In this improved potential fields two forces including exclusive force and attractive force are defined, and the exclusive force considering joint coverage rate of adjacent sensor nodes is calculated between sensor nodes while the attractive force is calculated between sensor nodes and discrete points in montior path. And then, the total force for each node is calculated by exclusive force and attractive force’s vector sum to achieve path coverage-enhancing efficiently by adjusting directions of sensor nodes seperately. Experimental results show that compared with the existing path cover-enhancing algorithm in directional wireless sensor network, sensation overlap area and blind spots may be eliminated by IPFPCA, and thus the whole path coverage performance of the wireless sensor network can be enhanced.
A Distributed Target Detection Algorithm Based on Credit-Degree in Wireless Sensor Network
Zou Liang, Huang Liusheng, Wang Gang, and Xu Hongli
2009, 46(12):  2134-2142. 
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Target detection in wireless sensor network is widely used in many fields, such as military, ecological, medical and security, and it has highly practical research significance. Traditional centralized algorithm relies on fusion nodes so much that the network built is not robust enough and high false alarm rate is caused by its binary decision. Traditional centralized algorithm’s dependence on network coverage will cause “blind holes” of detection alarm in the network. To solve these problems, a distributed target detection algorithm based on credit degree—k-CD algorithm is proposed. k-CD algorithm runs as follows: First, the algorithm adjusts each node’s credit degree using the neighbor automata with all its neighbors’ credit degrees as the input; then, the nodes which have detected the target form a virtual group and make decision fusions using the method of credit degree matching; Finally, the algorithm solves the “blind hole” problem caused by network coverage through triggered mobile nodes. The simulation results show that compared with the majority voting algorithm (MV), k-CD algorithm can increase an average of 35% of detection probability while reducing the false alarm rate by 62% and with different network coverage degrees, network life-cycle can be prolonged by 44% on the average.
An Effective Location Updating Mechanism for Tracking Systems in Wireless Sensor Network
Xu Xueyong, Huang Liusheng, Huo Yongkai, Xiao Mingjun, and Xu Hongli
2009, 46(12):  2143-2152. 
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In traditional tracking systems, the mobiles report their location to server periodically, which will result in high packet loss rate and rapid energy depletion as the number of mobiles increase. Actually, in practical tracking applications, it is observed that nodes are often close to others. Hence, it is conceived to pick out some nodes to report periodically as delegates for their adjacent ones. By exploiting this thought, an effective location updating mechanism (LUM) is proposed for tracking systems in wireless sensor network. In this method, mobiles update location information through two kinds of delegates: remote and nearby delegates. Remote delegates are infrastructure nodes appointed by server. Nearby delegates are heads of clusters constructed according to the RSSI (received signal strength indicator) values. In LUM, only delegates report location periodically instead of each mobile node. Therefore, LUM can save energy greatly through reducing the message complexity. However, in practical environment, signal fluctuations will affect the process of LUM. In order to solve this problem, the parameterized flip-flop filter and strap thresholds methods are developed to smooth and stabilize the RSSI values respectively. To demonstrate the performance of LUM, a prototype system with 38 Micaz nodes are deployed. The results show that LUM outperforms traditional approaches by at least 45% less message transmission and 48% fewer energy depletion on average.