Joint problem of power optimal connectivity and coverage in wireless sensor networks

This work considers a multi-hop sensor network and addresses the problem of minimizing power consumption in each sensor node locally while ensuring two global (i.e., network wide) properties: (i) communication connectivity, and (ii) sensing coverage. A sensor node saves energy by suspending its sensing and communication activities according to a Markovian stochastic process. We show that a power level to induce a coverage radius is sufficient for connectivity provided that w(n)→∞. The paper presents a Markov model and its solution for steady state distributions to determine the operation of a single node. Given the steady state probabilities, we construct a non-linear optimization problem to minimize the power consumption. Simulation studies to examine the collective behavior of large number of sensor nodes produce results that are predicted by the analytical model.     

Energy efficient collaborative communications in AWGN and Rayleigh fading channel in wireless sensor networks

Collaborative communication produces high power gain and significantly reduces bit error rate (BER) if both frequency and phase synchronization are achieved. In this paper, a novel collaborative communication system with imperfect phase and frequency synchronization that includes the influence of noise and fading is proposed, modeled, theoretically analyzed, and simulated. Mathematical expressions are derived for the received power as a function of number of collaborative nodes and BER as a function of signal to noise ratio (E_b ∕ N₀). To analyze the energy efficiency of our proposed collaborative communication system, energy consumption of the system is modeled, simulated, and analyzed by considering the parameters of the off‐the‐shelf products. Analytical and simulation results showed that the proposed system produces significant power gain and reduction in BER in the presence of phase errors, frequency errors, additive white Gaussian noise, and Rayleigh fading. A detailed theoretical analysis and Monte Carlo simulation revealed that the proposed collaborative communication system is an energy efficient communication system that can be implemented in sensor networks, as approximately N (number of collaborative nodes) times less total transmitted power is required than for the single input single output communication for a specifies transmission range. Copyright © 2012 John Wiley & Sons, Ltd.     

Energy-Efficient Routing Protocol for Wireless Sensor Networks with Static Clustering and Dynamic Structure

Data gathering is an essential operation in wireless sensor networks. For periodic data gathering applications, each sensor node has data that must be sent to a distant base station in a round of communication. Due to the limited battery power of sensor nodes, each sensor node transmitting its sensed data to the base station directly significantly consumes its energy. This work presents a hierarchical ring-based data gathering (HRDG) scheme for dense wireless sensor networks. A hierarchical grid structure is constructed, and only some sensor nodes are elected as grid heads for gathering data, subsequently reducing the total energy consumption per round. Grid heads are then organized into hierarchical rings to decrease the transmission delay of a round. The proposed HRDG scheme focuses on reducing the energy × delay cost in a round of data gathering. Moreover, the energy × delay cost of HRDG is analyzed. Simulation results indicate that the proposed HRDG scheme outperforms other data gathering schemes in terms of the number of rounds, the energy × delay cost and coverage ratio.     

Dynamic power management in new architecture of wireless sensor networks

Dynamic power management (DPM) technology has been widely used in sensor networks. Though many specific technical challenges remain and deserve much further study, the primary factor currently limiting progress in sensor networks is not these challenges but is instead the lack of an overall sensor network architecture. In this paper, we first develop a new architecture of sensor networks. Then we modify the sleep state policy developed by Sinha and Chandrakasan in (IEEE Design Test Comput. 2001; 18 (2):62–74) and deduce that a new threshold satisfies the sleep‐state transition policy. Under this new architecture, nodes in deeper sleep states consume lower energy while asleep, but require longer delays and higher latency costs to awaken. Implementing DPM with considering the battery status and probability of event generation will reduce the energy consumption and prolong the whole lifetime of the sensor networks. We also propose a new energy‐efficient DPM, which is a modified sleep state policy and combined with optimal geographical density control (OGDC) (Wireless Ad Hoc Sensor Networks 2005; 1 (1–2):89–123) to keep a minimal number of sensor nodes in the active mode in wireless sensor networks. Implementing dynamic power management with considering the battery status, probability of event generation and OGDC will reduce the energy consumption and prolong the whole lifetime of the sensor networks. Copyright © 2008 John Wiley & Sons, Ltd.     

Cache consistency in Wireless Multimedia Sensor Networks

The production of cheap CMOS cameras, which are able to capture rich multimedia content, combined with the creation of low-power circuits, gave birth to what is called Wireless Multimedia Sensor Networks (WMSNs). WMSNs introduce several new research challenges, mainly related to mechanisms to deliver application-level Quality-of-Service (e.g., latency minimization). Such issues have almost completely been ignored in traditional WSNs, where the research focused on energy consumption minimization. Towards achieving this goal, the technique of cooperative caching multimedia content in sensor nodes can efficiently address the resource constraints, the variable channel capacity and the in-network processing challenges associated with WMSNs. The technological advances in gigabyte-storage flash memories make sensor caching to be the ideal solution for latency minimization. Though, with caching comes the issue of maintaining the freshness of cached contents. This article proposes a new cache consistency and replacement policy, called NICC, to address the cache consistency issues in a WMSN. The proposed policies recognize and exploit the mediator nodes that relay on the most “central” points in the sensor network so that they can forward messages with small latency. With the utilization of mediator nodes that lie between the source node and cache nodes, both push-based and pull-based strategies can be applied in order to minimize the query latency and the communication overhead. Simulation results attest that NICC outperforms the state-of-the-art cache consistency policy for MANETs.     

Semijoin‐Based Spatial Join Processing in Multiple Sensor Networks

This paper presents an energy‐efficient spatial join algorithm for multiple sensor networks employing a spatial semijoin strategy. For optimization of the algorithm, we propose a GR‐tree index and a grid‐ID‐based spatial approximation method, which are unique to sensor networks. The GR‐tree is a distributed spatial index over the sensor nodes, which efficiently prunes away the nodes that will not participate in a spatial join result. The grid‐ID‐based approximation provides great reduction in communication cost by approximating many spatial objects in simpler forms. Our experiments demonstrate that the algorithm outperforms existing methods in reducing energy consumption at the nodes.     

Energy awareness workflow model for wireless sensor nodes

Before the development of a large‐scale wireless sensor network (WSN) infrastructure, it is necessary to create a model to evaluate the lifespan of the infrastructure, the system performance and the cost so that the best design solution can be obtained. Energy consumption is an important factor that influences the lifespan of WSNs. One of the ways to extend the lifespan of WSNs is to design wireless sensor nodes with low power consumption. This involves component selection and the optimisation of hardware architecture, monitoring software system and protocols to satisfy the requirements of the particular applications. This paper proposes a comprehensive model to describe the workflow of a wireless sensor node. Parameter setup and energy consumption calculation are demonstrated through the model simulation. It provides a mathematical approach to dynamically evaluate the energy consumption of a sensor node. This will benefit the development of wireless sensor nodes based on microprocessors with limited computational capability. Therefore, the model can be applied in dynamic power management systems for wireless sensor nodes or in wireless communication protocols with energy awareness, in particular, for WSNs with self‐organisation. More importantly, the generalisation of the model may be employed as a standard paradigm for the development of wireless sensor node with energy awareness. Copyright © 2012 John Wiley & Sons, Ltd.     

Securing sensor data storage and query based on k‐out‐of‐ n coding

With in‐network sensor data storage and query, sensed data are stored locally and further accessed by users on demand. Thus, without proper protection for sensor data and user queries, compromise of sensor nodes may reveal sensitive information about the sensed environment as well as users’ query patterns. Furthermore, the adversary can alter some stored data and prevent users from recovering information correctly. In this paper, we propose and analyze the use of maximum‐distance separable codes to address the problem. First, initial data is encoded in (n, k) maximum‐distance separable code and spread from a single data source to a set of storage nodes for higher survivability. Second, a blind signature‐based privacy scheme is explored to preserve user query, such that authorized user's identity and privacy interests are concealed from others. Finally, an efficient data retrieval scheme is carried out such that the redundancy symbols in the remaining nodes are accessed only if the user fails to decode the data, which reduces the communication and computation cost. Analysis and evaluation verify the efficiency of the proposed scheme. Copyright © 2011 John Wiley & Sons, Ltd.     

Energy Saving Electrochromic Polymer Windows with a Highly Transparent Charge‐Balancing Layer

Highly transparent TiO₂ nanoparticles are explored as a non‐electrochromic (non‐EC) charge‐balancing layer for a high color contrast, bistable electrochromic window (ECW). The TiO₂ nanoparticle (TNP) layer increases the potential at the EC polymer electrode, thereby lowering the working voltage of the ECW. This leads to lower the power consumption of ECWs without loss in the high color contrast (ΔT > 72%) and to remarkably improve the cyclability (ΔT change <1% over 3000 cycles), mainly due to the low overvoltage (<0.1 V) on the electrochromic polymer layer. Furthermore, the ECWs including the non‐EC TNP layer show long‐term bistability (>2.7 h, 40% increase) and UV stability (ΔT change <1%) to provide a low‐power automatic ECW. This finding shows that the charge balanced ECP window has the potential to be used for an energy saving ECW with low‐power consumption and will be widely applied in various ECWs as well as electrochemical devices with multiple functions.     

A new load balancing and data collection algorithm for energy saving in wireless sensor networks

Data gathering is a major function of many applications in wireless sensor networks. The most important issue in designing a data gathering algorithm is how to save energy of sensor nodes while meeting the requirements of special applications or users. Wireless sensor networks are characterized by centralized data gathering, multi-hop communication and many to one traffic pattern. These three characteristics can lead to severe packet collision, network congestion and packet loss, and even result in hot-spots of energy consumption thus causing premature death of sensor nodes and entire network. In this paper, we propose a load balance data gathering algorithm that classifies sensor nodes into different layers according to their distance to sink node and furthermore, divides the sense zone into several clusters. Routing trees are established between sensor node and sink depending on the energy metric and communication cost. For saving energy consumption, the target of data aggregation scheme is adopted as well. Analysis and simulation results show that the algorithm we proposed provides more uniform energy consumption among sensor nodes and can prolong the lifetime of sensor networks.     

A novel efficient power‐saving MAC protocol for multi‐hop MANETs

Following recent advances in the performance of ad hoc networks, the limited life of batteries in mobile devices poses a bottleneck in their development. Consequently, how to minimize power consumption in the Medium Access Control (MAC) layer of ad hoc networks is an essential issue. The power‐saving mode (PSM) of IEEE 802.11 involves the Timing Synchronization Function to reduce power consumption for single‐hop mobile ad hoc networks (MANETs). However, the IEEE 802.11 PSM is known to result in unnecessary energy consumption as well as the problems of overheating and back‐off time delay. Hence, this study presents an efficient power‐saving MAC protocol, called p‐MANET, based on a Multi‐hop Time Synchronization Protocol, which involves a hibernation mechanism, a beacon inhibition mechanism, and a low‐latency next‐hop selection mechanism for general‐purpose multi‐hop MANETs. The main purposes of the p‐MANET protocol are to reduce significantly the power consumption and the transmission latency. In the hibernation mechanism, each p‐MANET node needs only to wake up during one out of every N beacon interval, where N is the number of beacon intervals in a cycle. Thus, efficient power consumption is achieved. Furthermore, a beacon inhibition mechanism is proposed to prevent the beacon storm problem that is caused by synchronization and neighbor discovery messages. Finally, the low‐latency next‐hop selection mechanism is designed to yield low transmission latency. Each p‐MANET node is aware of the active beacon intervals of its neighbors by using a hash function, such that it can easily forward packets to a neighbor in active mode or with the least remaining time to wake up. As a consequence, upper‐layer routing protocols can cooperate with p‐MANET to select the next‐hop neighbor with the best forwarding delay. To verify the proposed design and demonstrate the favorable performance of the proposed p‐MANET, we present the theoretical analysis related to p‐MANET and also perform experimental simulations. The numerical results show that p‐MANET reduces power consumption and routing latency and performs well in extending lifetime with a small neighbor discovery time. Copyright © 2011 John Wiley & Sons, Ltd.     

Span: An Energy-Efficient Coordination Algorithm for Topology Maintenance in Ad Hoc Wireless Networks

This paper presents Span, a power saving technique for multi-hop ad hoc wireless networks that reduces energy consumption without significantly diminishing the capacity or connectivity of the network. Span builds on the observation that when a region of a shared-channel wireless network has a sufficient density of nodes, only a small number of them need be on at any time to forward traffic for active connections. Span is a distributed, randomized algorithm where nodes make local decisions on whether to sleep, or to join a forwarding backbone as a coordinator. Each node bases its decision on an estimate of how many of its neighbors will benefit from it being awake, and the amount of energy available to it. We give a randomized algorithm where coordinators rotate with time, demonstrating how localized node decisions lead to a connected, capacity-preserving global topology. Improvement in system lifetime due to Span increases as the ratio of idle-to-sleep energy consumption increases. Our simulations show that with a practical energy model, system lifetime of an 802.11 network in power saving mode with Span is a factor of two better than without. Additionally, Span also improves communication latency and capacity.     

Power‐aware range‐free wireless sensor network localization using neighbor distance distribution

In large‐scale wireless sensor networks, cost‐effective and energy‐efficient localization of sensor nodes is an important research topic. In spite of their coarse accuracy, range‐free (connectivity‐based) localization methods are considered as cost‐effective alternatives to the range‐based localization schemes with specialized hardware requirements.In this paper, we derive closed‐form expressions for the average minimum transmit powers required for the localization of sensor nodes, under deterministic path loss, log‐normal shadowing, and Rayleigh fading channel models. The impacts of propagation environment and spatial density of anchor nodes on the minimum transmit power for node localization are evaluated analytically as well as through simulations. Knowledge of the minimum transmit power requirements for localizability of a sensor node enables improving energy efficiency and prolonging lifetime of the network. We also propose a novel distance metric for range‐free localization in large‐scale sensor networks. The target and anchor nodes are assumed to be positioned according to two statistically independent two‐dimensional homogeneous Poisson point processes. Analytical expression for the average distance from a target node to its kth nearest neighbor anchor node is derived and is used for estimating the target‐to‐anchor node distances for localization. The Cramér–Rao lower bound on the localization accuracy for the new distance estimator is derived. Simulation results show the accuracy of the proposed distance estimate compared with some existing ones for range‐free localization. The results of our investigation are significant for low‐cost, energy‐efficient localization of wireless sensor nodes. Copyright © 2011 John Wiley & Sons, Ltd.     

A study of subdividing hexagon-clustered WSN for power saving: Analysis and simulation

Hexagons are an ideal shape for clustering sensor networks, for it can seamlessly divide clustered areas, and is the largest regular polygon (in terms of the number of sides) that has this property. In this paper, we analyze the benefit of subdividing a hexagonal cluster for the purpose of reducing the overall power consumption in the cluster. Assuming a spatial Poisson distribution of sensor nodes in the cluster, we propose a subdivision scheme, and perform a comprehensive analytical estimate of power savings brought about by the subdivision. The analytical results show that subdivision will yield considerable saving in overall power consumption of the cluster, and the saving is heavily dependent on the nodes’ transmission range and their deployment density. The limit on the depth of subdivision is also analyzed. Simulation results are presented, and their implication discussed.     

基于发布/订阅模型的WSN设计

为降低通信频率对节点能耗的影响同时提高大规模节点下传感器网络的连通率,本文设计了一种以发布/订阅模型作为应用层数据交互方式的无线传感器网络。该网络利用6LoWPAN技术实现组网,并以Contiki操作系统为平台完成了基于发布/订阅模型的MQTT-S应用层协议设计。测试结果表明,该设计能够有效降低节点的通信流量,实现对节点功耗以及网络通信优化,并能与互联网实现无缝连接减少开发成本,对大规模传感器网络的设计与应用具有重要意义。     

Power-aware single- and multipath geographic routing in sensor networks

Nodes in a sensor network, operating on power limited batteries, must save power to minimize the need for battery replacement. We note that the range of transmission has a significant effect on the power consumption of both the transmitting node and listeners. This paper first presents a Geographical Power Efficient Routing (GPER) protocol for sensor networks. Each sensor node makes local decisions as to how far to transmit: therefore, the protocol is power efficient, localized, highly distributed, and scalable. In GPER, given a final destination, each node first establishes a subdestination within its maximum radio range. The node, however, may decide to relay the packet to this subdestination through an intermediary node or alter the subdestination if this will preserve power. Traditional deterministic geographic routing algorithms aim at achieving close to the shortest weighted paths. However, they normally stick to the same paths for the same source/destination pairs. This may conversely drain the nodes on these paths and result in short network life when the communication in the network is unevenly distributed. Thus, we further investigate a set of probabilistic multipath routing algorithms, which generate braided multipaths based only on local information. The algorithms have less communication and storage overhead than conventional on-demand multipath routing algorithms, while providing greater resilience to node failures. Simulations on NS2 show that GPER almost halves the power consumption in the network relative to alternative geographic routing algorithms. Furthermore, in situations where the communication tasks are non-uniformly distributed, probabilistic multipath routing contributes up to an additional 30% to network lifetime.     

Demand‐based charging strategy for wireless rechargeable sensor networks

A wireless power transfer technique can solve the power capacity problem in wireless rechargeable sensor networks (WRSNs). The charging strategy is a widespread research problem. In this paper, we propose a demand‐based charging strategy (DBCS) for WRSNs. We improved the charging programming in four ways: clustering method, selecting to‐be‐charged nodes, charging path, and charging schedule. First, we proposed a multipoint improved K‐means (MIKmeans) clustering algorithm to balance the energy consumption, which can group nodes based on location, residual energy, and historical contribution. Second, the dynamic selection algorithm for charging nodes (DSACN) was proposed to select on‐demand charging nodes. Third, we designed simulated annealing based on performance and efficiency (SABPE) to optimize the charging path for a mobile charging vehicle (MCV) and reduce the charging time. Last, we proposed the DBCS to enhance the efficiency of the MCV. Simulations reveal that the strategy can achieve better performance in terms of reducing the charging path, thus increasing communication effectiveness and residual energy utility.     

Lead‐Free Polycrystalline Ferroelectric Nanowires with Enhanced Curie Temperature

Ferroelectrics are important technological materials with wide‐ranging applications in electronics, communication, health, and energy. While lead‐based ferroelectrics have remained the predominant mainstay of industry for decades, environmentally friendly lead‐free alternatives are limited due to relatively low Curie temperatures (T _C) and/or high cost in many cases. Efforts have been made to enhance T _C through strain engineering, often involving energy‐intensive and expensive fabrication of thin epitaxial films on lattice‐mismatched substrates. Here, a relatively simple and scalable sol–gel synthesis route to fabricate polycrystalline (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃ nanowires within porous templates is presented, with an observed enhancement of T _C up to ≈300 °C as compared to ≈90 °C in the bulk. By combining experiments and theoretical calculations, this effect is attributed to the volume reduction in the template‐grown nanowires that modifies the balance between different structural instabilities. The results offer a cost‐effective solution‐based approach for strain‐tuning in a promising lead‐free ferroelectric system, thus widening their current applicability.     

节能型单总线通信系统供电方法

针对单总线通信的特点,提出一种节能型单总线通信系统供电方法。该方法能降低电源在总线上传输的损耗,实现节能目的。在同等传输线条件下,可以延长通信节点之间的距离,增加通信节点数,有效解决了单总线通信系统节点功率大小、能量传输距离和传输电缆成本三者之间的矛盾。在单总线通信工程中应用该方法,可以提高通信节点功率、增加通信距离或降低传输电缆成本。     

无线传感器网络拓扑控制策略研究

节能设计是无线传感器网络的首要设计目标,拓扑控制是实现该目标的重要技术之一,其主要目标是在保证网络连通和覆盖的前提下剔除不必要的通信链路,降低节点能耗和减少通信干扰,为MAC协议和路由协议的顺利执行提供基础。文中对传感器网络拓扑控制策略进行了的分析。最后针对目前传感器节点成本仍然很高这一特点,通过仿真得出了在节点随机配置的情况下,保证网络连通和覆盖所需的至少节点数目。并通过仿真分析证明了方案的可行性。