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Broadcast is a fundamental operation in Wireless Sensor Networks (WSNs) and plays an important role in a communication protocol design. In duty-cycled scenarios, a sensor node can receive a message only in its active time slot, which makes it more difficult to design collision-free scheduling for broadcast operations. Recent studies in this area have focused on minimizing broadcast latency and guaranteeing that all nodes receive a broadcast message. This paper investigates the problem of Minimum Latency Broadcast Scheduling in Duty-Cycled (MLBSDC) WSNs. By using special geometric properties of independent sets of a broadcast tree, we reduce the number of transmissions, consequently reducing the possibility of collision. Allowing multiple transmissions in one working period, our proposed Latency Aware Broadcast Scheduling (LABS) scheme provides a latency-efficient broadcast schedule. Theoretical analysis proves that the scheme has the same approximation ratio and complexity as the previous best algorithm for the MLBSDC problem. Moreover, simulation shows that the new scheme achieves up to 34%, 37%, and 21% performance improvement over previous schemes, in terms of latency, number of transmissions, and energy consumption, respectively. [ABSTRACT FROM AUTHOR]

Recently, several multi-channel MAC protocols have been proposed for wireless sensor networks (WSNs) to improve network capacity and boost energy efficiency. In addition, cooperative multiple-input multiple-output (MIMO) technique has been shown to be able to significantly enhance the energy efficiency of WSNs if properly configured. However, these two promising techniques have not been jointly considered in clustered WSNs. In this paper, we explore such a joint design by proposing a novel MAC protocol for clustered WSNs that takes advantage of both multiple channels and cooperative MIMO to further boost network performance. Specifically, sensor nodes in a WSN are organized into clusters and each cluster head selects some cooperative nodes to help forward traffic to or receive from other clusters by utilizing a cooperative MIMO technique. For intra-cluster communications, different channels are assigned to adjacent clusters to reduce collisions, while for inter-cluster communications, cooperative MIMO links are scheduled to improve energy efficiency and concurrent transmissions are enabled by assigning different channels to them. We also provide a network-wide time synchronization approach to facilitating the functionality of this protocol. We carry out extensive simulations and the results demonstrate that the proposed protocol can significantly increase throughput and improve energy efficiency compared to other schemes. For example, for a WSN with 150 sensors in a 250 × 250 m 2 field, with five available channels, the protocol can achieve three times saturated throughput while saving 14 % energy per bit for inter-cluster communications. [ABSTRACT FROM AUTHOR]

Abstract: Automatic reprogramming is an important and challenging issue in wireless sensor networks (WSNs). A usual approach is the over-the-air programming (OAP), which is a fundamental service based on reliable broadcast for efficient code dissemination. However, existing OAP protocols do not enable the reprogramming of a subset of the sensor nodes in a WSN. Hence, in this work we propose a multicast-based over-the-air programming protocol that considers a small world infrastructure (MOAP-SW). The small world model is used to create shortcuts toward the sink in the communication infrastructure of sensor networks. The endpoints of these shortcuts are more powerful nodes, resulting in a heterogeneous wireless sensor network. Simulation results show the feasibility of the protocol regarding the number of messages transmitted, the energy consumption and the time to reconfigure the network. [Copyright &y& Elsevier]

Abstract: Time synchronization is a critical component in any wireless sensor network (WSN). In terms of energy consumption, on-demand time synchronization is better than continuous synchronization. However, currently existing on-demand time synchronization protocols have a very low accuracy and very strong spatial accumulative effect. These features are not suitable for several types of WSN applications, such as applications with stringent temporal requirements, or applications that have a large spatial region of interest. In this paper, we propose an on-demand time synchronization protocol, named AOTSP (Accurate On-demand Time Synchronization Protocol), which differs from other protocols of the same category by having the following advantages, as shown in our theoretical analysis and simulation results: (1) weak spatial accumulative effect; (2) fairly low communication cost; (3) low computational complexity; (4) high accuracy; (5) high scalability. Such features make AOTSP a suitable time synchronization protocol for a broad range of WSN applications. [Copyright &y& Elsevier]

Abstract: We propose an adaptive and energy-efficient TDMA-based MAC protocol that significantly reduces energy consumption in the network, while efficiently handling network traffic load variations and optimizing channel utilization through a timeslot stealing mechanism and a timeslot reassignment procedure. We have analytically derived the average delay performance of our MAC protocol, with and without the timeslot stealing mechanism. Our delay model, validated via simulations, shows that the timeslot stealing mechanism can substantially improve the protocol throughput in scenarios with varying and asymmetric traffic patterns. Evaluation results show that the timeslot reassignment procedure is efficient in handling the longer timescale changes in the traffic load, while the timeslot stealing mechanism is better in handling the shorter timescale changes in the traffic patterns. [Copyright &y& Elsevier]

Abstract: To promote commercial deployment of multihop wireless networks, the research/industry communities must develop new theories and protocols for flexible traffic engineering in these networks in order to support diverse user applications. This paper studies an important traffic engineering problem–how to support fair bandwidth allocation among all end-to-end flows in a multihop wireless network–which, in a more precise term, is to achieve the global maxmin fairness objective in bandwidth allocation. There exists no distributed algorithm for this problem in multihop wireless networks using IEEE 802.11 DCF. We have two major contributions. The first contribution is to develop a novel theory that maps the global maxmin objective to four local conditions and prove their equivalence. The second contribution is to design a distributed rate adjustment protocol based on those local conditions to achieve the global maxmin objective through fully distributed operations. Comparing with the prior art, our protocol has a number of advantages. It is designed for the popular IEEE 802.11 DCF. It replaces per-flow queueing with per-destination queueing. It achieves far better fairness (or weighted fairness) among end-to-end flows. [Copyright &y& Elsevier]

Abstract: Cluster based wireless sensor networks have been widely used due to the good performance. However, in so many cluster based protocols, because of the complexity of the problem, theoretical analysis and optimization remain difficult to develop. This paper studies the performance optimization of four protocols theoretically. They are LEACH (Low Energy Adaptive Clustering Hierarchy), MLEACH (Multi-hop LEACH), HEED (Hybrid Energy-Efficient Distributed Clustering Approach), and UCR (Unequal Cluster based Routing). The maximum FIRST node DIED TIME (FDT) and the maximum ALL node DIED TIME (ADT) are obtained for the first time in this paper, as well as the optimal parameters which maximize the network lifetime. Different from previous analysis of network lifetime, this paper analyzes the node energy consumption in different regions through the differential analysis method. Thus, the optimal parameters which maximize the lifetime can be obtained and the detailed energy consumption in different regions at different time can be also obtained. Moreover, we can obtain the time and space evolution of the network, from a steady state (without any death) to a non-steady state (with some death of nodes), and then to the final situation (all nodes die). Therefore, we are fully aware of the network status from spatial and temporal analysis. Additionally, the correctness of the theoretical analysis in this paper is proved by the Omnet++ experiment results. This conclusion can be an effective guideline for the deployment and optimization of cluster based networks. [Copyright &y& Elsevier]

Abstract: Recent deployments of wireless sensor networks have targeted challenging monitoring and surveillance applications. The medium access control being the main source of energy wastage, energy-efficiency has always been kept in mind while designing the communication stack embedded in spread sensors. Especially, versatile protocols have emerged to offer a suitable solution over multiple deployment characteristics. In this study, we observe to what extent versatility applies to dynamic scenarios in which communications do not respect specific communication paradigms. We first provide a performance evaluation of two well-reputed versatile protocols (B-MAC (Polastre et al., 2004 ) and X-MAC (Buettner et al., 2006 )) under the conditions of such a scenario. The obtained results convinced us to propose more than versatility and pre-configured solutions, that is auto-adaptation. We then introduce the main contribution of this paper, an auto-adaptive algorithm that allows one to adjust the previously mentioned protocols while the network is operating. We analyze to what extent it outperforms the previously obtained results. [Copyright &y& Elsevier]

Abstract: During the past five years, considerable research has been reported on the design of various coordination systems for Wireless Sensor and Actor Networks (WSANs). Though the coordination mechanism taxonomy was presented, there has been no work published for the performance comparison among these different strategies or protocols quantitatively. In this paper, we attempt to address this challenge. The contribution of this paper is as follows: (i) an approach for the performance comparison among different strategies of sensor–actor coordination in WSANs is proposed; (ii) analytical models to abstract the system characteristics and operation for each kind of solutions are developed; (iii) the performance of each individual strategy under various conditions is analysed; (vi) the performance among three typical strategies is compared. The results may be helpful for the users to understand the advantage of each strategy over others under a certain condition. [Copyright &y& Elsevier]

Abstract: In many wireless sensor network applications, nodes are mobile, while many protocols proposed for these networks assume a static network. Thus, it is important to evaluate if a traditional protocol designed for a static network can tolerate different levels of mobility. This paper provides an analytic model to investigate the effect of mobility on a well-known cluster-based protocol, LEACH. The model evaluates data loss after construction of the clusters due to node mobility, which can be used to estimate a proper update interval to balance the energy and data loss ratio. Thus, the results can help the network designer to adjust the topology update interval given a value of acceptable data loss threshold. A practical approach to increase the mobility tolerance of the protocol is applying a buffer zone to the transmission ranges of the nodes. The model is extended in order to consider the effect of buffer zone. To validate the analytic evaluations, extensive simulations are conducted and correctness of the evaluations is tightly verified. [Copyright &y& Elsevier]

Abstract: Random walk is one of the widely used techniques for information discovery in unstructured networks like Ad hoc Wireless Networks (AWNs) and Wireless Sensor Networks (WSNs). In a random walk, instead of taking all steps uniform randomly, our idea is to modify the random walk to take some level biased steps to improve its energy efficiency and latency which are important design parameters of protocols for WSNs. The level of a node is defined as the minimum number of hops in which it can reach the sink node. We propose three protocols viz., Several Short Random Walks (SSRW) search, Random Walk with Level Biased Jumps (RWLBJ) search, and Level Biased Random Walk (LBRW) search. The proposed protocols use a combination of random and level biased steps to search for the target information. As we move from SSRW to LBRW, the percentage of biased steps increases and the percentage of random steps decreases i.e., SSRW uses fewer biased steps compared to the other proposals, LBRW uses only biased steps, and the usage of biased steps in RWLBJ is somewhere in between. We show by extensive simulations and testbed experiments that SSRW, RWLBJ, and LBRW are better choices compared to that of a pure Random walk in terms of the energy consumption and latency of search, and we also show that among the proposed protocols, LBRW and RWLBJ are the best. [ABSTRACT FROM AUTHOR]

Abstract: Key management is an important building block for all security operations in sensor networks. Most existing key management schemes try to establish shared keys for all pairs of neighbor sensors; hence, a large number of keys need to be preloaded on each sensor, which necessitates a large key space for the nodes in the network. The recent trend in research is to mainly consider homogeneous sensor networks, and to a lesser degree heterogeneous sensor networks, for key management. In this paper, we propose a novel key agreement protocol which is based on pairing-based cryptography over an elliptic curve. Using this protocol, any two nodes that need to communicate can independently compute the same secret key by using pairing and identity-based encryption properties. The proposed protocol significantly reduces the key space of a node. Additionally, the security analysis of the proposed protocol shows that it is robust against a number of attacks including wormhole attack, masquerade attacks, reply attacks, and message manipulation attacks. [Copyright &y& Elsevier]

Abstract: Data forwarding is an essential function in wireless sensor networks (WSNs). It is well-known that geographic forwarding is an efficient scheme for WSNs as it requires maintaining only local topology information to forward data to a central gathering point, called the sink (or base station), for further analysis and processing. In this paper, we propose an energy-efficient data forwarding protocol for WSNs, called Weighted Localized Delaunay Triangulation-based data forwarding (WLDT), with a goal to extending the network lifetime. Specifically, WLDT selects as forwarders the sensors with high remaining energy and whose locations lie nearer the shortest path between source sensors and a single sink, thus helping the sensors minimize their average energy consumption. More precisely, WLDT defines checkpoints to build energy-efficient data forwarding paths and uses a 1-lookahead scheme to guarantee data delivery to the sink. We show that WLDT, which favors data forwarding through short Delaunay edges, achieves an energy gain percentage in the order of 55% for the free space model and close to 100% for the multi-path model compared to BVGF and GPSR, which forward data through long distances and which we have slightly updated to account for energy in the selection of next forwarders. We prove that these checkpoints yield an energy gain percentage in the order of 30% in comparison with a similar protocol, called WLDT-w/c (or WLDT without checkpoints), which forwards data via short distances but does not use checkpoints. [Copyright &y& Elsevier]

Abstract: The deployment of wireless sensor networks in many application areas requires self-organization of the network nodes into clusters. Clustering is a network management technique, since it creates a hierarchical structure over a flat network. Quite a lot of node clustering techniques have appeared in the literature, and roughly fall into two families: those based on the construction of a dominating set and those which are based solely on energy considerations. The former family suffers from the fact that only a small subset of the network nodes are responsible for relaying the messages, and thus cause rapid consumption of the energy of these nodes. The latter family uses the residual energy of each node in order to decide about whether it will elect itself as a leader of a cluster or not. This family’s methods ignore topological features of the nodes and are used in combination with the methods of the former family. We propose an energy-efficient distributed clustering protocol for wireless sensor networks, based on a metric for characterizing the significance of a node, w.r.t. its contribution in relaying messages. The protocol achieves small communication complexity and linear computation complexity. Experimental results attest that the protocol improves network longevity. [Copyright &y& Elsevier]

Abstract: With more and more real deployments of wireless sensor network applications, we envision that their success is nonetheless determined by whether the sensor networks can provide a high quality stream of data over a long period. In this paper, we propose a consistency-driven data quality management framework called Orchis that integrates the quality of data into an energy efficient sensor system design. Orchis consists of four components, data consistency models, adaptive data sampling and process protocols, consistency-driven cross-layer protocols and flexible APIs to manage the data quality, to support the goals of high data quality and energy efficiency. We first formally define a consistency model, which not only includes temporal consistency and numerical consistency, but also considers the application-specific requirements of data and data dynamics in the sensing field. Next, we propose an adaptive lazy energy efficient data collection protocol, which adapts the data sampling rate to the data dynamics in the sensing field and keeps lazy when the data consistency is maintained. Finally, we conduct a comprehensive evaluation to the proposed protocol based on both a TOSSIM-based simulation and a real prototype implementation using MICA2 motes. The results from both simulation and prototype show that our protocol reduces the number of delivered messages, improves the quality of collected data, and in turn extends the lifetime of the whole network. Our analysis also implies that a tradeoff should be carefully set between data consistency requirements and energy saving based on the specific requirements of different applications. [Copyright &y& Elsevier]