ISSN 1000-1239 CN 11-1777/TP

Table of Content

15 January 2008, Volume 45 Issue 1
A Multi-Path Routing Protocol Based on Divide and Conquer Strategy in Ad Hoc Network
Wang Li, Zhang Suwei, Li Zhansheng, and Song Linjian
2008, 45(1):  . 
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Routing in MANETs can be accomplished through either single path or multiple paths. Multipath routing may be used for various other reasons such as load-balancing, congestion avoidance, lower frequency of route inquiries and to achieve a lower overall routing overhead and better fault-tolerance. However, multipath routing shows degraded performance with increased distance between the source node and the destination node. Following a policy of divide and rule, a node-balanced scheme is proposed to solve this problem. In the proposed scheme, first the unipath routing protocol is used to find the best routing path from the source node to the destination node; then the routing path is divided into several segments and every segment is traded with the multipath routing policy. As every segment has the best performance, the performance of the whole network is improved accordingly. Furthermore how the moderate node is chosen to replace the failed node between the two adjacent segments is also discussed. Simulation results show that the new scheme not only significantly improves the performance of the network , but also can find more number of routing paths when increasing the distance between the source nodes and the destination nodes. The new scheme is also very easy to implement.
Survey on Sensor Network Research
Li Jianzhong and Gao Hong
2008, 45(1):  1-15. 
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Recent advances in sensing techniques, embedded computing techniques, distributed information processing techniques and communication techniques have enabled the development of wireless sensor networks. As there is a bright future in their application, wireless sensor networks have become a new research area in the 21 century. There are large numbers of challenge problems in science and engineering in the wireless sensor network area. Since 2000, more and more researchers have been engaged in the research work on wireless sensor networks and a lot of research results have already been obtained. Suiveyed in this paper is the research work on wireless sensor networks, including the wireless sensor network communication techniques, infrastructure techniques, middleware techniques, data management techniques, sensor node and embedded software techniques. The existing problems in the current research work and the new research issues are also discussed. At the end of the paper, many significant references are listed for the researchers.
EasiCC:A Congestion Control Mechanism for WSN
Ju Hailing, , Cui Li, and Huang Changcheng
2008, 45(1):  16-25. 
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It's necessary for wireless sensor network(WSN) applications to deal with network congestion, because the channel bandwidth of WSN is usually narrow. However, existing congestion control mechanisms don't run well on WSN platforms. A practical congestion control mechanism for WSN should not only have good network performance but also have little control cost, the proposed EasiCC (EasiNet congestion control mechanism) is such a congestion control mechanism. In EasiCC, the source nodes prorate data packets into several transporting priorities, all the network nodes adjust in-phase packet filtering threshold to adapt network congestion status. With the help of filtering threshold and packet priority, network bandwidth is fairly allotted among data streams. EasiCC uses a stepwise and exponential method to adjust network traffic, so as to reduce control messages between network nodes. EasiCC uses network access waiting time and packet queue overflowing to detect network congestion, uses network admittance and queue dropping simultaneously to ensure the integral network performance. EasiCC has been implemented in wireless sensor network test-bed and costs little on the network bandwidth, communication energy and node memory. Simulation and experimental results indicate that EasiCC can limit transmission delay effectively, reduce packet loss ratio remarkably, and provide bandwidth fairness between data streams at the same time.
A Real-Time Energy-Aware Cluster-Based Routing Protocol for Wireless Sensor and Actor Networks
Li Fangmin, Xu Wenjun, Liu Xinhua, and Hu Siquan
2008, 45(1):  26-33. 
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Wireless sensor and actor networks (WSANs) are composed of sensors and actors to perform distributed sensing and acting tasks. Depending on the application of automation there may be a need to rapidly respond to sensor input. The issue of real-time communication is one of the most important challenges in wireless sensor and actor networks. Besides, the energy efficiency of network is also crucial. Although WSAN is derived from wireless sensor networks (WSNs), since the application requirements impose stricter constraints, many protocols and algorithms which have been proposed for WSNs may not be well-suited for the unique features and requirements of WSANs. A system model according to a real network situation is proposed. In this paper, the performance of clustering algorithms and a power control scheme in minimizing the network latency are studied, and a real-time energy-aware cluster-based routing protocol (RECRP) for WSANs is proposed and evaluated. A novel two-level clustering scheme based on power control technique is proposed in the algorithm to reduce the network latency, and cluster-heads are elected by an energy-efficient algorithm to increase the network lifetime. The experimental results demonstrate that the cluster could be formed stably by RECRP in WSANs, and it provides shorter latency and longer lifetime than the current typical routing protocols.
An Aggregate Contribution Based Delay-Time Allocation Algorithm for Wireless Sensor Networks
Duan Bin, Ke Xin, Huang Fuwei, Zhou Xinyun, and Sun Limin
2008, 45(1):  34-40. 
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A primary goal in the design of wireless sensor networks (WSNs) is lifetime maximization, constrained by the energy capacity of batteries. By introducing in-network processing technology, data aggregation has been recently proved to be an effective method to reduce the redundant energy consumption and prolong the network lifespan. Data aggregation can also improve the data accuracy and reliability. When applying specific aggregation schemes to reality, it is necessary to take into account the aggregation time factor, whose increase will improve the aggregation efficacy but deteriorate network transmission performance. And how to allocate the entire delay-time along each route to attain a balance between these two factors is significant. In this paper, a novel aggregate contribution based delay-time allocation algorithm (ACDA) is proposed, in which the impact on aggregation efficacy of different positions in the route tree is quantified first, then the aggregate contribution is gradually refined through an iterative update process, and finally the aggregation time of every node at sink is proportionally allocated. Since this scheme takes into full consideration of location discrepancy and interaction between nodes, The simulation results show that the ACDA achieves a better performance in both aggregation gain and transmission real-time property when compared with other present schemes, just shown in the simulation results.
Energy Level-Based Routing Algorithm of Multi-Sink Sensor Networks
Wu Zhongbo, Fan Xiaobo, and Chen Hong,
2008, 45(1):  41-46. 
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In the traditional single-sink sensor network, query dissemination and data collection are based on a fixed infrastructure. This infrastructure has some disadvantages, such as consuming energy of the nodes on the key path too quickly, the singleness of routing algorithm, the invalidation of the sink node, etc. To solve these problems, the research of multi-sink sensor networks is deployed. The system architecture of the multi-sink sensor network is proposed and a topology discovering and maintaining policy is provided. the system architecture includes task manager, proxy nodes, sink nodes and common nodes. Then a routing algorithm based on minimum energy consumption is provided. Because the minimum energy consumption routing algorithm consumes energy of the nodes on the key path too quickly, an energy level-based routing algorithm is put forward. The energy level-based routing algorithm will choose the path which has the highest energy level to deliver sample data to the sink nodes. The analysis shows that the minimum energy consumption routing algorithm adapts for data collection of sudden events and the energy level-based routing algorithm adapts for continuous query. Experiment results show that the energy level-based routing algorithm can keep the balance of energy consumption in the sensor network which can prolong the lifetime of the network.
A Practical Fairness Control Model in Wireless Sensor Networks
Li Shanshan, Liao Xiangke, Peng Shaoliang, Cheng Weifang, and Xiao Nong
2008, 45(1):  47-54. 
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Fairness is an important problem in congestion control, which is to ensure that all data sources have equal access to end-to-end network bandwidth. In wireless sensor network, nodes are always deployed randomly and redundantly, the effective amount of sensed information of different sensors may be different. In order to fit the characteristic of wireless sensor networks, the Ttraditional fairness definition is extended and a practical fairness control model CFRC is proposed. CFRC does not need knowledge of source distribution at prior, nor make restrictive assumptions on the routing structure, nor maintain any state information, instead, CFRC guarantees the fairness dynamically. In CFRC, a low-cost credit computation algorithm is proposed for each source node to compute its credit locally based on the sensed area of itself and its neighbors; Aggregation node computes the credit of aggregated packets using simple sum operation. Furthermore, an interferer aware fair rate allocation method is proposed in CFRC to allocate bandwidth among not only all upstream neighbors, but also congested node and its interferers based on the average credit. Simulation results show that CFRC can achieve fairness based on the credit of data sources, reduce the number of dropped packets and downgrade the reliability fairly and gracefully when congestion happens.
A Survey of Congestion Control Technology for Wireless Sensor Networks
Sun Limin, Li Bo, and Zhou Xinyun
2008, 45(1):  63-72. 
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In wireless sensor networks (WSNs), the many-to-one communication mode, mutual interference of wireless links, dynamic changes of network topology and the memory-restrained characteristic of node, all make network more vulnerable to congestion. Since network congestion may deteriorate the transmitting performance and network lifetime, congestion control has become one of the most important technologies to decrease such impact and guarantee the network quality of service (QoS). Because the energy supply, computational power and wireless communication capabilities of sensor nodes are all limited and the network scale is always very large, higher requirements are imposed on the congestion control technology and researches on congestion avoidance and congestion release are more challengeable. This paper is a survey of congestion control technology for wireless sensor networks. In this paper, the main characteristics of wireless sensor networks, and causes and damages of network congestion are presented, and then three kinds of congestion detection strategies based on data buffer length, wireless channel sampling and data transmitting rate, and two kinds of congestion avoidance mechanisms based on data rate allocation and buffer announcement are introduced. The classical congestion release algorithms based on rate control, flow schedule and transport schedule are analyzed, and finally the development trend and future prospect of congestion control technology for wireless sensor networks are presented.
An Approximate Query Processing Algorithm with Confidence Based on Model Fitting in Sensor Networks
Pan Liqiang, Li Jianzhong, and Luo Jizhou
2008, 45(1):  73-82. 
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With the development of communication techniques, nested computation techniques and sensor techniques, wireless sensor networks have been widely applied to many fields. They can be used for testing, sensing, collecting and processing information of monitored objects and transferring the processed information to users. Collecting data of the environments is an important application of the sensor networks. Most current researches mainly focus on querying the sensing data with low energy consumption by utilizing sensor nodes' temporal-spatial correlations. These methods can collect the data with low energy consumption, but in some scenarios their results could not satisfy the applications with high confidence about the error bounds pre-specified. Moreover, these methods are not adapted to the case that there are no spatial correlations in sensor nodes. To overcome these defaults, a new method named approximate query processing algorithm with confidence based on model fitting is proposed in this paper. The proposed method create fitting models with the lower data transfer ratio, and the models are sent back to sink node instead of sensing data themselves. The proposed method can not only return the users the data within the error bounds with low energy consumption, but also be adapted to actual sensor node for being of light-weight. Theoretical analysis and experimental results show that this method can return high confident querying results and is energy efficient.
An Energy-Aware Data Gathering and Routing Protocol for WSN
Liu Xin, Wang Quanyu, and Jin Xuliang
2008, 45(1):  83-89. 
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This paper presents a distributed, energy-efficient data gathering and routing protocol for wireless sensor network. In the algorithm, each sensor node is assigned a tier ID in according to the distance between the node and the base station. Nodes closer to the base station are assigned lower tier IDs. When gathering data, nodes with higher tier IDs send their data to their neighbors who have lower tier IDs where the data is aggregated and then forwarded to nodes with even lower tier IDs. Therefore, the communication is conducted at a low energy level, and the data travels, layer by layer, toward nodes with the lowest tier IDs. When the data reaches the nodes with the lowest tier ID, the system selects a node among them to directly communicate with the base station. Because long-distance communication with the base station is energy-consuming, the node sending data to the base station will have its energy drained off very fast so that it die much earlier than other nodes. A mechanism is proposed to shift the long-distance communication among all network nodes, which is called the top-tier shifting mechanism. Using this mechanism, energy consumption can be evenly distributed among all network nodes, and the network lifetime is prolonged.
A Node Number Constraint Query Processing Algorithm for Sensor Networks
Li Guilin and Li Jianzhong
2008, 45(1):  90-96. 
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An energy efficient query processing algorithm is proposed to process a new kind of query named node number constraint query for wireless sensor networks. The algorithm is mainly composed of two parts: query dissemination algorithm and result collection algorithm. The function of the query dissemination algorithm is to select an energy efficient way to disseminate the user's query into sensor networks. First a relevant node selection algorithm is proposed to select partial number of nodes from the network and a Steiner tree based algorithm is designed to disseminate queries to these relevant nodes. Then two energy cost models are built for the Steiner tree based query dissemination algorithm and an energy efficient flooding based query dissemination algorithm respectively. By comparing two energy consumption models, a suitable dissemination algorithm can be selected to send query to sensor networks. The energy efficient result collection algorithm presents two kinds of result collection strategy, which are direct and indirect collection strategy, and then the collection algorithm gives the condition, in which each strategy is suitable to collect results. By combining all the above mentioned algorithms, an energy efficient query processing algorithm for node number constraint query is proposed and the simulation results show that the algorithm proposed in this paper can not only guarantee the precision of the result but also save much more energy than other algorithms.
An Open Wireless Sensor Network Platform—OpenWSN
Zhang Wei, He Bin, Zhao Xia, and Chen Qijun
2008, 45(1):  97-103. 
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Most of the current WSN research platforms are based on Mica nodes and TinyOS. However, they're difficult to integrate with the existing mature source codes and difficult to port to other platforms. These micro-controller based solutions are also quite weak to fulfill high performance tasks such as image processing and PAN coordination. Furthermore, the new invented nesC language also holdback its acceptance among industry application developers. Considering the above shortcomings, an ARM7 based powerful WSN research platform, named OpenWSN, is designed and implemented. OpenWSN adopts bus architecture to connect different modules in hardware design and uses layered OOD/OOP in software design. The component-based and service-based architecture makes it easy to integrate with current mature resources. The node has 32KB SRAM and up to 512KB flash memory. It can run between 11-60MHz and using DMA to move data inside memory. These features enable OpenWSN run much faster than general Mica or Telos nodes. The power consumption is a bit higher than Mica's Atmega128L solution because ARM7 processor consumes more energy than Atmega128L micro processor. However, due to its high performance, OpenWSN node can finish more tasks and spend more time in sleep status. This in turn decreases the power consumption. The experiment verifies the solution and confirms OpenWSN's effectiveness in high performance applications such as vibration measurements.
An Aggregation Tree Constructing Algorithm Based on Energy Consumption Assessment
Sun Dayang, Liu Yanheng, and Wang Aimin,
2008, 45(1):  104-109. 
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This paper first gives an analysis of data aggregation and data compression based on energy consumption of sensor nodes, after which an approach is proposed to construct an aggregation tree in the case of non-perfect aggregation, since GIT considers only the case of perfect aggregation and it does not work well if the aggregation is non-perfect. An assessment scheme that can get the information of hops from the aggregation point to the sink and the hops from the aggregation point to the source node is used to construct such an aggregation tree. Moreover, the energy consumption of the aggregation is also considered. This scheme can be used when perfect aggregation cannot be performed. In this paper, an approach to reduce the cost of reinforcement is also proposed, in which the reinforcement work is done by the source nodes themselves, not by the sink node. Simulation result shows that this approach can save more energy than GIT when the aggregation ratio is small. This result also provides a theoretical limit of aggregation to tell when GIT will lose its superiority and thus gives a direction to choose among the aggregation algorithms. Another result shows that the further the sources are away from the sink, the less reinforcement messages are needed. Finally a guidance to tell when to use the ECA (energy consumption assessment) scheme is given.
WSN Nodes for Real-Time Traffic Information Detection
Zhang Yuhe, Huang Xi, and Cui Li
2008, 45(1):  110-118. 
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With the rapid development of modern cities and fast increasing amount of vehicles, ITS has become crucial nowadays. Many elements of ITS are based on the real-time road condition represented mainly by the traffic volume, velocity and lane occupancy. Traditional traffic information detection systems can't meet the requirements of deployment convenience, detection accuracy and overall cost. WSN technology has potential wide prospect of applications. In this paper, the network architecture of a WSN-based wireless traffic information detection system, the hardware design of the detection nodes, and a series of detection algorithms are presented. Two kinds of algorithms are developed for traffic volume detection, which are a digital filter based algorithm (DiFiA) and a matched filter based algorithm (MaFiA) respectively. Two nodes for velocity detection are adopted and a velocity detection algorithm, namely VeDA is proposed. An efficient vehicle/non-vehicle classification algorithm is also designed to improve the accuracy of traffic volume, which is called ReSDiRA. And a lightweight synchronization method between two nodes is described for both velocity detection and vehicle/non-vehicle classification. On-road experiments are carried out to test and verify the accuracy and efficiency of the proposed methods, and the power consumption of the node is analytically evaluated. Experimental results indicate potential promises that the developed sensor node may be used in real-time traffic information detection as a new technique.
A Novel Range Free Localization Scheme Based on Voronoi Diagrams in Wireless Sensor Networks
Wang Jichun, Huang Liusheng, Xu Hongli, Xu Ben, and Li Shanliang
2008, 45(1):  119-125. 
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Recently, the topic of wireless sensor networks has become a fast-growing research area. In wireless sensor networks, sensor location plays a crucial role in many applications. The global positioning system (GPS) solves the problem of localization in outdoor environments, but it is not suitable for wireless sensor networks. Having a GPS receiver on every sensor is always costly and not feasible. So, in the past, there are many localization procedures have been proposed in the literature. In this paper, a distributed, accurate and reliable Voronoi diagrams based localization scheme (VBLS) is introduced, which makes use of received signal strength indicator (RSSI) from anchors. First, VBLS sorts received signal strength indicator in descending order. Then unit disk graph is used to calculate the Voronoi area of anchors in turn. Finally, the overlapping region of different anchors' Voronoi area is identified as the possible region where sensor resides in. This work is compared via simulation with two other range-free localization schemes (W-Centroid and Centroid) to show the efficiency of VBLS. For random anchor placement, VBLS outperforms Centroid scheme and W-Centroid scheme significantly, estimation error decreases by 18% and 13%, respectively. For uniform anchor placement, VBLS gets a gain of 7% decrease and 2% increase of estimation error, respectively.
A Low Cost Time Synchronization Algorithm for Wireless Sensor Networks
Xiao Lin, Cheng Lijuan, and Wang Fubao
2008, 45(1):  126-130. 
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Tremendous advances in communication, embedded computation and sensor technology have occurred in the development of wireless sensor networks, which are made by sensors, microprocessor and wireless communication interface, and have integrated collecting, processing and communication all-in-one. Time synchronization is a fundamental service for both design and application of wireless sensor networks. However, the complexity, energy, cost and size conflicts between traditional algorithms, such as NTP and GPS, and WSN prohibit their use in WSN. Because of the cost, power and size constraints of individual nodes, there are many new challenges. Developing time synchronization methods suitable for wireless sensor networks have attracted wide attention. Recently, many new algorithms are presented. But most of them sacrifice a lot of messages or complex computing for a good precision, so that much energy is consumed and life time of the whole network is shortened. In order to reduce messages and save energy, a new simple and low cost time synchronization algorithm for wireless sensor networks is proposed. It combines unidirectional reference broadcast and pair-wise mechanism, so that only one node in broadcast domain needs time synchronization, and the messages for time synchronization are reduced greatly. Finally, the performance of this algorithm is simulated.
A Robust Ordered Localization Algorithm for Wireless Sensor Network
Ji Jian, Shi Shengfei, and Li Jianzhong
2008, 45(1):  131-137. 
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Proposed in this paper is a distributed localization algorithm for wireless sensor network, which takes advantage of the measured distance between neighbors and the coordinates of two-hop nodes. This algorithm is very robust, and it performs well even when the measured distance error is high, which is seldom possessed by localization algorithms under similar conditions. The main idea of this algorithm is to localize the node constrained by many conditions first, so the coordinates calculated are very accurate, after that, some constraints will be incorporated, and so on. It is verified in experiment that this technique can greatly enhance the localization accuracy. This algorithm is composed of three stages. In the first stage, a routing tree is set up, so each node can communicate with root; in the second stage, each node's coordinates are calculated by the order determined by localization priority; in the third stage, all nodes' coordinates are slightly altered to minimize error. The novelty of this localization algorithm explained, in detail, and the reason and effect of each optimization technique are evaluated. The experiments are conducted mainly about the influence of average neighbor number and the distance measurement error on localization accuracy.
New Time Synchronization Techniques for Wireless Sensor Networks
Xu Chaonong, , Xu Yongjun, and Li Xiaowei
2008, 45(1):  138-145. 
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Time synchronization is one of the basic middle-wares of wireless sensor networks. Many time synchronization protocols which are based on exchanging packets with timing information have been proposed in recent years. However, in large scale wireless sensor networks, the accumulation of synchronization error over hop distance and the demand for scalability challenge these traditional time synchronization techniques. To deal with these two challenges, researchers from the field of wireless sensor networks are beginning to pay attention to the old technique of firefly-inspired synchrony and the new emerging cooperative synchronization technique. Great progress has been made in the technique of firefly-inspired synchrony in recent years, especially in single-hop network after the model of Strogatz and Mirollo was proposed. However, although a great number of experiments and simulations have been conducted, its characteristics of convergence in multi-hop network still needs to be found in theory. Based on the novel idea of spatial averaging instead of the traditional idea of time averaging, the technique of cooperative synchronization presents another new solution to time synchronization in wireless sensor networks although it is still strolling on simulation stage at present. Its basic idea and research and application status in wireless sensor networks are introduced. Future research directions are also proposed.
A General Key Seed Management and Assignment Model for Wireless Sensor Networks and Application
Feng Tao and Ma Jianfeng
2008, 45(1):  146-153. 
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To achieve security in distributed wireless sensor networks, one of the most promising approaches is the so-called random pre-distribution of key seeds. Pair-wise secure communication channels between nodes were established or discovered by using key seeds information that were constructed and pre-distribution to each node in distributed wireless sensor networks. A general key seeds management and assignment (KSMA) model is proposed, which is used to study the security of key pre-distribution schemes with five attributes for requirement of confidentiality and authentication. New key pre-distribution schemes based on new types of key seed are constructed within the framework of one-way accumulators, and new shared-key discovery protocols are presented. The discovery protocols are provably secure against the active adversaries in universally composable model. It is also shown how to set the parameters (pool and key-ring size) in such a way that the network is not only connected with high probability via secure links, but also new schemes are against Sybil attacks by using identity witness validated technique and achieving node-to-node identity authentication. New key pre-distribution scheme improves the resilience of the network compared with previous schemes, and an analysis of the scheme is given in terms of network resilience and associated overhead.
A Key Pre-Distribution Scheme for Wireless Sensor Networks Based on the Symmetric Balanced Incomplete Block Design
Xia Geming, Huang Zunguo, and Wang Zhiying
2008, 45(1):  154-164. 
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This paper focuses on key pre-distribution, a foundational problem of security in wireless sensor networks. A novel key pre-distribution scheme named sBIBD\-{Hadamard} KPS was devised by authors based on combinatorial designs technique. The essence of sBIBD\-{Hadamard} KPS is constructing symmetric balanced incomplete block design with Hadamard matrix and mapping it to a key pre-distribution scheme. The derivation and data illuminated that sBIBD\-{Hadamard} KPS and its extended versions improvement themselves than the most scheme in existence, mainly on three facets. First, sBIBD\-{Hadamard} KPS make the pair sensor nodes to share common keys at a higher sharing probability with the same key chain size, and achieved a smaller average key path length, especially to do all of that without asking for a node neighbor degree more than 2. Second, sBIBD\-{Hadamard} KPS make the pair sensor nodes to share more than one keys, and by carrying out a particular method to compositing the common key in time, it enhanced the security by enlarged the key space in the face of attacks using key analyzing. Finally, sBIBD\-{Hadamard} KPS upgrade itself to support many more nodes by two means named complementary set design and key slicing, and optimize the energy expenditure at the same time.
A Key Management Scheme Based on Variable Transmission Range in Wireless Sensor Networks
Chen Haikun, Shi Shengfei, and Li Jianzhong
2008, 45(1):  165-171. 
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Establishing a pair-wise key between nodes is important to secure communications in wireless sensor networks. Because traditional solutions for key management are difficult to implement in a resource-constrained environment, several methods, such as key pre-distribution, have been proposed to achieve the goals of data secrecy and integrity. In this paper, a new key management scheme KMVTR based on variable transmission range of sensor nodes is proposed. This scheme uses group-based deployment method and pre-distributes keys in groups and between groups. In each group, there are certain special nodes which can assist nodes from adjacent groups in establishing a pair-wise key. The KMVTR scheme can use the powerful senior nodes act as such special nodes, and can also use normal nodes act as such special nodes. The theory analysis and simulation result shows that the connect probability of two adjacent groups will be high enough when using normal nodes act as special nodes. The analysis also shows the communication energy cost of the KMVTT scheme is acceptable for wireless sensor networks. Compared with other methods, the KMVTR scheme has several advantages such as providing perfect resilience against node capture, supporting larger network size, and doesn't have to know the expected locations of sensor nodes in key pre-distributed phase.
Data-Driven Sleeping Scheduling Mechanism in Sensor Networks
Zhu Jinghua, Li Jianzhong, Liu Yong, and Gao Hong
2008, 45(1):  172-179. 
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In wireless sensor networks that consist of a large number of low-cost, battery-powered sensors, one of the main challenges is to obtain long system lifetime without sacrifying quality of service such as sensing coverage and data integrity. Scheduling sensors to work alternatively can prolong lifetime efficiently. In this paper, a novel data-driven sleeping scheduling mechanism is proposed, which can extend lifetime by identifying redundant nodes based on time-spatial correlations among sensing data. The main idea is: first, a non-parametric regression method is exploited to develop prediction models for forecasting measurements of one sensor using data from other sensors; then the maximal number of node dominating sets is created; finally the sleep?duty cycles of these node dominating sets based on prediction models are scheduled. Data in each of the dominating set is sufficient to recover the measurements of the entire sensor network. We present the centralized, semi-distributed and distributed sleeping scheduling algorithm respectively, guaranteeing that values of sleeping nodes can be recovered from awake nodes within a user's specified error bound. It is known that this is the first work on data-driven sleeping scheduling for large scale sensor networks. Experiments results show that the proposed methods can prolong network lifetime substantially while maintaining data integrity under the user's error constraint.
A Subset-Based Coverage-Preserving Distributed Scheduling Algorithm
Li Xiaolong, Lin Yaping, Hu Yupeng, and Liu Yonghe
2008, 45(1):  180-187. 
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Recent research has found that management of node duty circles, termed sensor scheduling, is able to save significant energy and prolong the lifetime of sensor networks. Sensor scheduling schemes could be categorized into two types in terms of scheduling features: round-based scheduling scheme and subset-based scheduling scheme respectively. Compared with round-based scheduling scheme, subset-based scheduling scheme is an effective solution because it is only carried out once after deployment. When sensor nodes are randomly deployed to a target region, existing subset-based scheduling algorithms can not guarantee that any subset of sensor nodes is uniformly distributed over the target region. Motivated by these reasons, firstly a maximum similarity distribution model is set up and an approximation algorithm, the subset-based coverage-preserving distributed scheduling algorithm is proposed. The algorithm is robust to clock asynchrony of nodes in different clusters, hence it is applicable to large-scale sensor networks, for which precise time synchronization is very hard. In addition, the analytical results for the theoretical upper bound of average coverage rate are presented, while nodes are randomly distributed over the target region. The experimental simulations demonstrate that this algorithm has the ability that sensor nodes in each subset are rather uniformly distributed over the target area, and available coverage rate approaches the upper bound.
Dynamic Sensor Selection Optimization Strategy for Wireless Sensor Networks
Wang Sheng, Wang Xue, and Bi Daowei
2008, 45(1):  188-195. 
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Energy consumption and effective coverage rate are both significant problem in wireless sensor networks (WSNs). The dynamic sensor selection optimization strategy refers to the optimization of the tradeoff between energy consumption and effective coverage rate, which is adopted to enhance energy efficiency, enlarge the effective coverage rate and prolong the lifetime of WSN. A strategy for dynamic sensor selection optimization, called HN-GA, is proposed, which uses the genetic algorithm (GA) to implement global searching and adopts the Hopfield network (HN) to reduce the search space of genetic algorithm and ensure the validity of each gene. In terms of evaluating the optimized sensor selection results, a combined metric is introduced, which is based on several practically feasible measures of the energy consumption and the effective coverage rate. The simulation results verify that the proposed HN-GA algorithm performs well in dynamic sensor selection optimization strategy. Under the guidance of HN-GA based dynamic sensor selection optimization strategy, the lifetime and the effective coverage performance of WSN can be significantly improved. Compared with GA algorithm and HN, HN-GA has better performance on regional convergence and global searching. It can achieve dynamic sensor selection optimization more efficiently and rapidly.
EasiFCCT:A Fractional Coverage Algorithm for Wireless Sensor Networks
Liu Wei, Cui Li, and Huang Changcheng
2008, 45(1):  196-204. 
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Scheduling nodes to work alternately can prolong network lifetime effectively. Existing solutions usually depend on geographic information which may introduce extra costs and compromise the overall effectiveness. Other node density control algorithms without geographic information do not guarantee a certain effected coverage degree. Analysis on pure stochastic-sleep scheduling mechanism reveals that a certain coverage degree can be met when numbers of nodes are at a certain level. However, the mechanism does not consider network connectivity and therefore its applicability is limited. A new definition of effected coverage is proposed to describe the network coverage maintaining network connectivity at the same time. And based on the definition of effected coverage, a new fractional coverage algorithm is proposed. The algorithm proposed in this paper takes network connectivity into account while maintaining a certain degree of effective coverage. Simulation shows that the proposed algorithm is superior to some existing algorithms in effectiveness, especially in effected coverage. EasiFCCT is designed on the basis of stochastic-sleep scheduling mechanism; so the random property of the proposed algorithm enables an easy implementation. This work is on the assumption that the network system is synchronized, which can be met by using some other algorithm. And the application of this algorithm in asynchronized system remains to be studied in the future.