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The low-rate denial of service (LDoS) attack mainly exploits security vulnerabilities of adaptive mechanisms in network protocols and application services. The high-rate attack pulses within a short time interval are sent periodically, which will result in the degradation of service quality. The attack traffic is similar to normal traffic from legitimate users in the network, consequently, it is easy to escape the traditional detection methods because of its intermittence. Research works have demonstrated that there are fractal characteristics (self-similarity) of the network traffic over the large scale of time. Although the fractal characteristics of the network traffic will be changed under the LDoS attack, the variations of the fractal characteristics in some network states are not apparent in real-time detection. Based on the fractal characteristics, the fractal residual of the network traffic is analyzed through the Hurst parameters calculating process by R/S algorithm in this article. It can be found that the fractal residual of the network traffic can better reflect the different states of the LDoS attack. Combining the idea behind the sliding window, a novel fractal residual based real-time detection (FR-RED) method of the LDoS attack is proposed. The effectiveness of the method in this article is verified by performing some experiments on two platforms, the NS2 and test-bed. The results manifest the beginning and end of the LDoS attack can be estimated in real-time with high detection accuracy. [ABSTRACT FROM AUTHOR]

A natural basis for the detection of a wireless random reactive jammer (RRJ) is the perceived violation by the detector [typically located at the access point (AP)] of the carrier sensing protocol underpinning many wireless random access protocols (e.g., Wi-Fi). Specifically, when the wireless medium is perceived by a station to be busy, a carrier sensing compliant station will avoid transmission, while an RRJ station will often initiate transmission. However, hidden terminals (HTs), i.e., activity detected by the AP but not by the sensing station, complicate the use of carrier sensing as the basis for RRJ detection since they provide plausible deniability to a station suspected of being an RRJ. The RRJ has the dual objectives of avoiding detection and effectively disrupting communication, but there is an inherent performance tradeoff between these two objectives. In this paper, we capture the behavior of both the RRJ and the compliant stations via a parsimonious Markov chain model and pose the detection problem using the framework of the Markov chain hypothesis testing. Our analysis yields the receiver operating characteristic (ROC) of the detector and the optimized behavior of the RRJ. While there has been extensive work in the literature on jamming detection, our innovation lies in leveraging carrier sensing as a natural and effective basis for detection. [ABSTRACT FROM AUTHOR]

Extending an Internet subnet by connecting resource-constrained nodes (e.g., embedded sensors and actuators) over multiple wireless hops is necessary to support the future Internet of Things (IoT). RPL, the IPv6 routing standard for low-power and lossy networks, tried to achieve this goal but has not seen wide adoption in practice. As an alternative, Thread is a recently standardized low-power network protocol for IoT, driven by the Thread group, an industry consortium led by Google/Nest. We provide a comparative analysis of the technical aspects of RPL and Thread based on their specifications, explaining why using Thread, as opposed to RPL, may make sense for the future Internet. Specifically, the fundamental differences between RPL and Thread are their respective scopes and multihop network architectures, which result in Thread's unique design and advantages over RPL. Lastly, we evaluate Thread in an indoor multihop wireless testbed using OpenThread, an official open source implementation of Thread. This work serves as the first analysis of the Thread protocol in academia. [ABSTRACT FROM AUTHOR]

Network latency and reliability are becoming critical performance indicators for future mission critical services based on wireless connectivity. In this article we present a portable and low-cost measurement framework for quantifying the endto- end (E2E) latency and reliability of communication systems based on single or multiple links. The proposed framework is tailored for characterization of access diversity mechanisms, for example, multi-connectivity or hybrid access methods, which are expected to be essential for ultra-reliable wireless communications in 4G and 5G networks. An active-probe measurement approach is adopted, consisting of a client that transmits timestamped packets to a server, and vice versa, via one or multiple communication links under test. The setup allows us to measure the one-way latency performance in uplink and downlink separately, and allows fully synchronized measurements of multiple links in parallel to understand the benefits of multi-connectivity mechanisms. Traffic generation is flexible in terms of packet size, transport protocol (TCP or UDP), and inter-arrival time interval of the generated packets, hence being a powerful tool for benchmarking the performance for different application-specific message flows. Special emphasis is put on the tail of the latency distribution, that is, the latency that can be achieved with a certain probability constraint, for example, 99.9 percent or beyond. Given the challenge of measuring such rare events, we measure and validate the stability of the measurement equipment to ensure that the observed performance is not compromised by undesired behavior or malfunction of the equipment. The system has a measurement error below 400 μs with 99.9 percent confidence and below 3.1 ms with 99.999 percent confidence. The capability and applicability of the measurement framework is illustrated by a measurement test of two simultaneous LTE connections that provide robust communications to an aerial drone. [ABSTRACT FROM AUTHOR]

The amazing proliferation of communication technologies for embedded systems opens the way for completely new applications but forces designers to adopt new methodologies to meet time-to-market constraints. Computer-Aided Design (CAD) has been traditionally applied to computers and embedded systems in isolation without considering them as a global inter-connected system. The paper contributes to fill this gap by proposing 1) a communication-aware design flow for network-interconnected embedded systems and 2) a formal framework to efficiently synthesize their network aspects by formulating and solving an optimization problem. Presented case studies show the potentiality of the proposed approach to address heterogeneous scenarios, e.g., related to smart spaces up to the ever-more-mentioned Internet-of-Things. [ABSTRACT FROM AUTHOR]

We consider a binary hypothesis testing problem in a wireless sensor network, where a fusion center (FC) makes a final decision about the underlying hypothesis. We assume under hypothesis ${\mathcal H}_0$ , sensors’ observations are uncorrelated and identically distributed Gaussian, however, under ${\mathcal H}_1$ they are correlated and nonidentically distributed Gaussian and sensors are unaware of this correlation when making decisions. Sensors send their local binary decisions over power constrained fading channels. We consider both parallel access channel (PAC) and multiple access channel (MAC) models. To obtain the detection statistic in PAC, we assume that the FC utilizes a linear fusion rule, which linearly combines the signals received from all sensors, while in MAC, the signal received at the FC is naturally the coherent sum of the transmitted signals. For both PAC and MAC, we derive modified deflection coefficient (MDC) of the detection statistic at the FC with coherent reception. Choosing MDC as the detection performance metric, we formulate several constrained transmit power optimization problems. In these problems, MDC is the objective function to be maximized and there are three different sets of transmit power constraints: total power constraint, individual and total power constraints, and individual power constraints only. We refer to the solutions of these constrained optimization problems as MDC-based transmit power allocation. When analytical solutions to these constrained optimization problems are elusive, we discuss how these problems can be converted to convex ones. Our results show that, compared with equal power allocation, detection performance improvement provided by our proposed MDC-based power allocation is more significant in MAC. We quantify the improvement in terms of several factors, including the degree of correlation among sensors’ observations, reliability of local decisions (local detection performance indices), communication channel properties, and the type of transmit power constraint. We also study how the power allocation among sensors varies as these factors change. [ABSTRACT FROM AUTHOR]

In this paper, we consider multichannel ALOHA for a wireless sensor network (WSN), where sensors’ signals are correlated. The impact of the number of channels on the length of information that an access point (AP) can collect is investigated. Under a certain distributed signal source model, in order for the AP to have a sufficiently long length of information, we show that the number of channels is to be larger than the square of the average number of active nodes. Thus, when the number of channels is limited, we need to use re-transmissions. To this end, we propose an adaptive transmission approach that can effectively exploit the correlation between the collected signals at the AP and nodes’ signals using Slepian–Wolf coding to shorten the total transmission time, which results in a more energy efficient WSN. [ABSTRACT FROM AUTHOR]

Opportunistic routing and network coding are two promising techniques that have been proposed for wireless networks. These techniques have significantly improved the performance of multi-hop wireless networks by utilizing the broadcast nature of wireless media and optimizing the capacity of lossy wireless networks. Recent research has shown that the combination of opportunistic routing and network coding in a single joint protocol outperforms each of them individually. This article explains the motivation and interaction effect of the joint protocols. We provide a taxonomy of joint protocols and illustrate the benefit and cost by highlighting their fundamental components and comparing different solutions. We also present a conclusion along with the outline of future research direction. [ABSTRACT FROM AUTHOR]

Fuel utilization efficiency and cost reduction are two major goals in designing in-vehicle networks. Aiming to address these two issues, we investigate in-vehicle networking protocols from both wired and wireless perspectives by first presenting representative solutions in each area, then identifying the challenges to current solutions, and finally advocating the use of the automotive Ethernet. Also, we propose a priority-based scheduler for the automotive Ethernet. Our preliminary experiments show that the proposed scheduler is effective and flexible, and thus is applicable to next-generation in-vehicle networks. We hope that further studies in this area can be inspired by our work and will be forthcoming in years to come. [ABSTRACT FROM AUTHOR]

Underwater sensor networks have enabled a new era in scientific and industrial underwater monitoring and exploration applications. However, these networks are energy-constrained and, more problematically, energy-hungry, as a consequence of the use of underwater acoustic links. In this work, we thoroughly review potential techniques for greening underwater sensor networks. In a top-down approach, we discuss the principal design and challenges of the appealing highlighted techniques. We also exemplify their use by surveying recent proposals in underwater sensor networks. Finally, we describe potential future research directions for energy conservation in underwater networks. [ABSTRACT FROM PUBLISHER]

We report the development of a network of wireless ultralow-power sensors to be deployed on freight railway cars, with the main purpose of detecting derailment events and alerting the engineer in the cab of the leading locomotive. Because no power bus is available on freight cars, we plan to rely on energy scavenging from vibrations; therefore, minimization of the power consumption has been one of our main priorities. We have, therefore, focused on ultralow-power hardware and strived to reduce the time intervals during which it is in active mode, achieving an average power consumption of $\sim 0.5$ mW with an active cycle of $\sim 20$ ms every 2 s. We discuss the overall concept that we propose, including the self-initialization protocol and the communication strategy that we have developed, and present the results of measurements on a prototype network that we have implemented. [ABSTRACT FROM AUTHOR]

Many people, especially technology historians, often ponder "Where would the world be without Ethernet?" Now, such a rhetorical question typically has no answer because you cannot rewind time, remove Ethernet from being invented, and let time fast forward to the present day. However, we have many active contributors amongst us who have been part of that history as it has evolved over the past 30 years. The Evolution of Ethernet Standards in 802.3 Working Group covers great details on the history of not just Ethernet standards development, but many dot standards that have led to support of wide-ranging applications. For me, just the first sentence captures the past, the present, and the future that I'd like to know more about: Ethernet is constantly evolving, adapting to the needs of the networking world, addressing the requirements of both operators and end-users, while making sure that the resulting technology is cost-efficient, reliable, and operates in a plug and play manner. [ABSTRACT FROM AUTHOR]

In the near future, wireless networks will be one of the key technologies for road traffic management in smart cities. Vehicles and dedicated roadside units should be interconnected through wireless technologies such as IEEE 802.11p (WAVE). Traffic lights and road signs may also take their place in this architecture, forming a large-scale network of small devices that report measurements, take orders from a control center, and are able to take decisions autonomously based on their local perception. Such a network shares many similarities with classical wireless sensor and actuator networks, starting with its distributed organization and with the role of the control center. However, its topology, and, subsequently, the appropriate selection of protocols and algorithms, will be strongly influenced by each city's characteristics. In this paper, we characterize and discuss probable topologies of these networks. The aim of this work is to provide network models that can be used to evaluate protocols and algorithms using realistic scenarios in place of generic random graphs. We deploy such networks over 52 city maps extracted from OpenStreetMap and characterize the resulting graphs, with particular focus on the connectivity aspects (degree distribution and connected components). The tools, the complete data sets, and OMNeT++ network models are freely available online. [ABSTRACT FROM AUTHOR]

Cyber-physical systems (CPSs) have recently become an important research field not only because of their important and varied application scenarios, including transportation systems, smart homes, surveillance systems, and wearable devices but also because the fundamental infrastructure has yet to be well addressed. Wireless sensor networks (WSNs), as a type of supporting infrastructure, play an irreplaceable role in CPS design. Specifically, secure communication in WSNs is vital because information transferred in the networks can be easily stolen or replaced. Therefore, this paper presents a novel distributed low-storage clone detection protocol (LSCD) for WSNs. We first design a detection route along the perpendicular direction of a witness path with witness nodes deployed in a ring path. This ensures that the detection route must encounter the witness path because the distance between any two detection routes must be smaller than the witness path length. In the LSCD protocol, clone detection is processed in a nonhotspot region where a large amount of energy remains, which can improve energy efficiency as well as network lifetime. Extensive simulations demonstrate that the lifetime, storage requirements, and detection probability of our protocol are substantially improved over competing solutions from the literature. [ABSTRACT FROM AUTHOR]

Buffer sizing is an important network configuration parameter that impacts the quality of service characteristics of data traffic. With falling memory costs and the fallacy that "more is better," network devices are being overprovisioned with large buffers. This may increase queueing delays experienced by a packet and subsequently impact stability of core protocols such as TCP. The problem has been studied extensively for wired networks. However, there is little work addressing the unique challenges of wireless environments such as time-varying channel capacity, variable packet inter-service time, and packet aggregation, among others. In this article we discuss these challenges, classify the current state-of-the-art solutions, discuss their limitations, and provide directions for future research in the area. [ABSTRACT FROM PUBLISHER]

Duty cycling mode is widely adopted in wireless sensor networks to save energy. Existing duty-cycling protocols cannot well adapt to different data rates and dynamics, resulting in a high energy consumption in real networks. Improving those protocols may require global information or heavy computation and thus may not be practical, leading to many empirical parameters in real protocols. To fill the gap between the application requirement and protocol performance, in this paper, we analyze the energy consumption for duty cycled sensor networks with different data rates. Our analysis shows that existing protocols cannot lead to an efficient energy consumption in various scenarios. Based on the analysis, we design a light-weight adaptive duty-cycling protocol (LAD), which reduces the energy consumption under different data rates and protocol dynamics. LAD can adaptively adjust the protocol parameters according to network conditions such as data rate and achieve an optimal energy efficiency. To make LAD practical in real network, we further pre-calculate optimal parameters offline and store them on sensor nodes, which significantly reduces the computation time. We theoretically validate the performance improvement of the protocol. We implement the protocol in TinyOS and extensively evaluate it on 40 TelosB nodes. The evaluation results show the energy consumption can be reduced by 28.2-40.1 percent compared with state-of-the-art protocols. Results based on data from a 1,200-node operational network further show the effectiveness and scalability of the design. [ABSTRACT FROM AUTHOR]

While energy consumption is widely considered the primary challenge of wireless networked devices, energy harvesting emerges as a promising way of powering the Internet of Things (IoT). In the Medium Access Control (MAC) layer of the communication stack, energy harvesting introduces spatial and temporal uncertainty in the availability of energy. In this context, this paper focuses on the design and implementation of the MAC layer of wireless embedded systems that are powered by energy harvesting; providing novel protocol features and practical experiences to designers of consumer electronics who opt for tailoring their own protocol solutions instead of using the standards. [ABSTRACT FROM AUTHOR]

A data discovery and dissemination protocol for wireless sensor networks (WSNs) is responsible for updating configuration parameters of, and distributing management commands to, the sensor nodes. All existing data discovery and dissemination protocols suffer from two drawbacks. First, they are based on the centralized approach; only the base station can distribute data items. Such an approach is not suitable for emergent multi-owner-multi-user WSNs. Second, those protocols were not designed with security in mind and hence adversaries can easily launch attacks to harm the network. This paper proposes the first secure and distributed data discovery and dissemination protocol named DiDrip. It allows the network owners to authorize multiple network users with different privileges to simultaneously and directly disseminate data items to the sensor nodes. Moreover, as demonstrated by our theoretical analysis, it addresses a number of possible security vulnerabilities that we have identified. Extensive security analysis show DiDrip is provably secure. We also implement DiDrip in an experimental network of resource-limited sensor nodes to show its high efficiency in practice. [ABSTRACT FROM AUTHOR]

Time synchronization is one of the most fundamental services for wireless sensor networks. Prior studies have investigated the clock stability due to environmental dynamics. In this paper, we demonstrate by experiment that in spite of the surrounding environment, time synchronization is unavoidably impacted by in-network energy heterogeneity, which may incur up to 30-40 ppm clock uncertainty. We mathematically analyze the root cause of such clock uncertainty and propose a protocol called EATS. Sensor nodes with EATS can intelligently select the best synchronization parents that minimize the negative impact of the energy heterogeneity. The selection is robust to multiple impacting factors in the network and provides fine-grained synchronization accuracy. In addition, nodes can make use of local energy information and further calibrate the clocks. In light of this, the logic time maintained among different nodes is more consistent and the synchronization can be performed with a longer re-synchronization interval and less energy consumption. We implement EATS with TelosB motes and evaluate the effectiveness and efficiency of our design through extensive experiments and simulations. [ABSTRACT FROM PUBLISHER]

As a key approach to achieve energy efficiency in sensor networks, sensing coverage has been studied extensively in the literature. Researchers have designed many coverage protocols to provide various kinds of service guarantees on the network lifetime, coverage ratio and detection delay. While these protocols are effective, they are not flexible enough to meet multiple design goals simultaneously. In this paper, we propose a unified sensing coverage architecture for duty cycled wireless sensor networks, called uSense, which features three novel ideas: Asymmetric Architecture, Generic Switching and Global Scheduling. We propose asymmetric architecture based on the conceptual separation of switching from scheduling. Switching is efficiently supported in sensor nodes, while scheduling is done in a separated computational entity, where multiple scheduling algorithms are supported. As an instance, we propose a two-level global coverage algorithm, called uScan. At the first level, coverage is scheduled to activate different portions of an area. We propose an optimal scheduling algorithm to minimize area breach. At the second level, sets of nodes are selected to cover active portions. Importantly, we show the feasibility to obtain optimal set-cover results in linear time if the layout of areas satisfies certain conditions. Through extensive testbed and simulation evaluations, we demonstrate that uSense is a promising architecture to support flexible and efficient coverage in sensor networks. [ABSTRACT FROM AUTHOR]

Wireless sensor networks with mobile sinks, mWSNs, have attracted a lot of attention recently. This is because sink mobility can greatly alleviate the hotspot issue in WSNs and further prolong the network lifetime. However, sink mobility also causes unexpected changes in network topology and data routing paths, which can largely affect the routing performance in such networks. Design of efficient routing protocols for mWSNs has been a critical issue, and much work has been carried out in this aspect. In this article, we first classify existing protocols based on different design criteria and then present a survey of the state-of-the-art routing protocols in this area. We illustrate how each of the protocols works, and discuss their advantages and disadvantages. Finally, we point out some future directions for efficient routing in mWSNs. [ABSTRACT FROM AUTHOR]

Wireless Access in Vehicular Environment (WAVE) dictates primitives for intelligent transportation system (ITS) applications and services. The medium access control (MAC) layer in WAVE facilitates service differentiation. This offers quality of service (QoS) by prioritizing traffic through different access categories (ACs), which are based on application-requested priorities. However, it is oblivious to network load, to delay requirements for ITS safety applications, and to the “severity” of vehicles. In this paper, we propose a novel opportunistic service differentiation (OSD) scheme as an enhancement to WAVE. We define a fuzzy inference system (FIS) to deduce a context severity metric (CSM) that relates the driving behavior of a vehicle to its environment. Our OSD traffic distribution heuristic prioritizes vehicle traffic, with respect to CSM, and accounts for network load and link layer bounds. Furthermore, the OSD scheme guarantees that ACs do not exceed maximum allowable delay for ITS applications. Our methodology entails defining and designing a linear programming (LP) model for verification and validation of the OSD scheme. We perform a comparative study of OSD-enhanced WAVE and classical WAVE analytically and in a vehicular ad hoc network (VANET) simulator. We show that both simulation and analytical results substantiate our claim of improvement in performance of OSD-enhanced WAVE over classical WAVE. [ABSTRACT FROM PUBLISHER]

Time synchronization is a fundamental requirement for the wide spectrum of applications with wireless sensor networks (WSNs). However, most existing time synchronization protocols are likely to deteriorate or even to be destroyed when the WSNs are attacked by malicious intruders. This paper is concerned with secure time synchronization for WSNs under message manipulation attacks. Specifically, the theoretical analysis and simulation results are first provided to demonstrate that the maximum consensus based time synchronization (MTS) protocol would be invalid under message manipulation attacks. Then, a novel secured maximum consensus based time synchronization (SMTS) protocol is proposed to detect and invalidate message manipulation attacks. Furthermore, we prove that SMTS is guaranteed to converge with simultaneous compensation of both clock skew and offset. Extensive numerical results show the effectiveness of our proposed protocol. [ABSTRACT FROM PUBLISHER]

Although the principles of gossip protocols are relatively easy to grasp, their variety can make their design and evaluation highly time consuming. This problem is compounded by the lack of a unified programming framework for gossip, which means developers cannot easily reuse, compose, or adapt existing solutions to fit their needs, and have limited opportunities to share knowledge and ideas. In this paper, we consider how component frameworks, which have been widely applied to implement middleware solutions, can facilitate the development of gossip-based systems in a way that is both generic and simple. We show how such an approach can maximize code reuse, simplify the implementation of gossip protocols, and facilitate dynamic evolution and redeployment. id="fnote1" asterisk="no"paraAlso known as “epidemic” protocols. para [ABSTRACT FROM PUBLISHER]

The accurate and efficient operation of many applications and protocols in wireless sensor networks require synchronized notion of time. To achieve network-wide time synchronization, a common strategy is to flood current time information of a reference node into the network, which is utilized by the de facto time-synchronization protocol Flooding Time-Synchronization Protocol (FTSP). In FTSP, the propagation speed of the flood is slow because each node waits for a given period of time to propagate its time information about the reference node. It has been shown that slow-flooding decreases the synchronization accuracy and scalability of FTSP drastically. Alternatively, rapid-flooding approach is proposed in the literature, which allows nodes to propagate time information as quickly as possible. However, rapid flooding is difficult and has several drawbacks in wireless sensor networks. In this paper, our aim is to reduce the undesired effect of slow-flooding on the synchronization accuracy without changing the propagation speed of the flood. Within this context, we realize that the smaller the difference between the speeds of the clocks, the smaller the undesired effect of waiting times on the synchronization accuracy. In the light of this realization, our main contribution is to show that the synchronization accuracy and scalability of slow-flooding can drastically be improved by employing a clock speed agreement algorithm among the sensor nodes. We present an evaluation of this strategy on a testbed setup including 20 MICAz sensor nodes. Our theoretical findings and experimental results show that employing a clock speed agreement algorithm among the sensor nodes drastically improves the synchronization accuracy and scalability of slow-flooding. [ABSTRACT FROM AUTHOR]

Smart homes and environments will consist of a large number of low power wireless devices such as sensors and actuators. Recently IETF standardized a network protocol called RPL that is designed to run on these nodes. In this article, we study the performance of RPL on a variety of scenarios that these nodes will encounter when they are deployed in practice. We deploy a network of 23 sensor nodes in a computer lab to monitor energy used by each computer across the applications and users. We subject the network to four different levels of interference that are representative of the types and levels of interference that these networks might encounter in deployment. Our study finds that RPL?s reliability degrades even with an access point in overlapping channel under normal network traffic. With high interference, the packet delivery reliability goes down to 10 percent. The scenario that resulted in this performance is not unimaginable in smart home or environment. This performance degradation is partly due to lack of coordination across the layers of the protocol stack: RPL is unaware of the changes in the wireless environment underneath and proceeds as usual. As other research has shown, coordination across the network stack is essential for network protocols to work reliably in the presence of interference. This will require a more coordinated approach to standards across the bodies. [ABSTRACT FROM PUBLISHER]

We address pairwise and (for the first time) triple key establishment problems in wireless sensor networks (WSN). Several types of combinatorial designs have already been applied in key establishment. A $(BIBD(v,b,r,k,\lambda ))$ (or $(t-(v,b,r,k,\lambda ))$ design) can be mapped to a sensor network, where $(v)$ represents the size of the key pool, $(b)$ represents the maximum number of nodes that the network can support, and $(k)$ represents the size of the key chain. Any pair (or $(t)$-subset) of keys occurs together uniquely in exactly $(\lambda)$ nodes; $(\lambda = 2)$ and $(\lambda = 3)$ are used to establish unique pairwise or triple keys. We use several known constructions of designs with $(\lambda =2)$, to predistribute keys in sensors. We also describe a new construction of a design called strong Steiner trade and use it for pairwise key establishment. To the best of our knowledge, this is the first paper on application of trades to key distribution. Our scheme is highly resilient against node capture attacks (achieved by key refreshing) and is applicable for mobile sensor networks (as key distribution is independent on the connectivity graph), while preserving low storage, computation and communication requirements. We introduce a novel concept of triple key distribution, in which three nodes share common keys, and discuss its application in secure forwarding, detecting malicious nodes and key management in clustered sensor networks. We present a polynomial-based and a combinatorial approach (using trades) for triple key distribution. We also extend our construction to simultaneously provide pairwise and triple key distribution scheme, and apply it to secure data aggregation. [ABSTRACT FROM AUTHOR]

Recent years have seen the emergence of wireless cyber-physical systems that must support real-time queries of physical environments through wireless sensor networks. This paper proposes Real-Time Query Scheduling (RTQS), a novel approach to conflict-free transmission scheduling for real-time queries in wireless sensor networks. First, we show that there is an inherent tradeoff between latency and real-time capacity in query scheduling. We then present three new real-time schedulers. The nonpreemptive query scheduler supports high real-time capacity but cannot provide low response times to high-priority queries due to priority inversions. The preemptive query scheduler eliminates priority inversions at the cost of reduced capacity. The slack stealing query scheduler combines the benefits of the preemptive and nonpreemptive schedulers to improve the capacity while meeting the end-to-end deadlines of queries. We provide schedulability analysis for each scheduler. The analysis and advantages of our approach are validated through NS2 simulations. [ABSTRACT FROM AUTHOR]

The resources especially energy in wireless sensor networks (WSNs) are quite limited. Since sensor nodes are usually much dense, data sampled by sensor nodes have much redundancy, data aggregation becomes an effective method to eliminate redundancy, minimize the number of transmission, and then to save energy. Many applications can be deployed in WSNs and various sensors are embedded in nodes, the packets generated by heterogenous sensors or different applications have different attributes. The packets from different applications cannot be aggregated. Otherwise, most data aggregation schemes employ static routing protocols, which cannot dynamically or intentionally forward packets according to network state or packet types. The spatial isolation caused by static routing protocol is unfavorable to data aggregation. To make data aggregation more efficient, in this paper, we introduce the concept of packet attribute, defined as the identifier of the data sampled by different kinds of sensors or applications, and then propose an attribute-aware data aggregation (ADA) scheme consisting of a packet-driven timing algorithm and a special dynamic routing protocol. Inspired by the concept of potential in physics and pheromone in ant colony, a potential-based dynamic routing is elaborated to support an ADA strategy. The performance evaluation results in series of scenarios verify that the ADA scheme can make the packets with the same attribute spatially convergent as much as possible and therefore improve the efficiency of data aggregation. Furthermore, the ADA scheme also offers other properties, such as scalable with respect to network size and adaptable for tracking mobile events. [ABSTRACT FROM AUTHOR]

Wireless sensor networks (WSNs) can be successfully applied in a wide range of applications. Efficient data dissemination is a fundamental service which enables many useful high-level functions such as parameter reconfiguration, network reprogramming, etc. Many current data dissemination protocols employ network coding techniques to deal with packet losses. The coding overhead, however, becomes a bottleneck in terms of dissemination delay. We exploit the concurrency potential of sensor nodes and propose MT-Deluge, a multithreaded design of a coding-based data dissemination protocol. By separating the coding and radio operations into two threads and carefully scheduling their executions, MT-Deluge shortens the dissemination delay effectively. An incremental decoding algorithm is employed to further improve MT-Deluge's performance. Experiments with 24 TelosB motes on four representative topologies show that MT-Deluge shortens the dissemination delay by 25.5-48.6 percent compared to a typical data dissemination protocol while keeping the merits of loss resilience. [ABSTRACT FROM PUBLISHER]

We present the Secure SOurce-BAsed Loose Synchronization (SOBAS) protocol to securely synchronize the events in the network, without the transmission of explicit synchronization control messages. In SOBAS, nodes use their local time values as a one-time dynamic key to encrypt each message. In this way, SOBAS provides an effective dynamic en-route filtering mechanism, where the malicious data is filtered from the network. With SOBAS, we are able to achieve our main goal of synchronizing events at the sink as quickly, as accurately, and as surreptitiously as possible. With loose synchronization, SOBAS reduces the number of control messages needed for a WSN to operate providing the key benefits of reduced energy consumption as well as reducing the opportunity for malicious nodes to eavesdrop, intercept, or be made aware of the presence of the network. Albeit a loose synchronization per se, SOBAS is also able to provide $(7.24 \mu)$s clock precision given today's sensor technology, which is much better than other comparable schemes (schemes that do not employ GPS devices). Also, we show that by recognizing the need for and employing loose time synchronization, necessary synchronization can be provided to the WSN application using half of the energy needed for traditional schemes. Both analytical and simulation results are presented to verify the feasibility of SOBAS as well as the energy consumption of the scheme under normal operation and attack from malicious nodes. [ABSTRACT FROM PUBLISHER]

A schedule-based approach, such as time division multiple access, is more efficient than a contention-based approach in terms of energy saving by switching sensors into sleeping mode. However, it does not use the transmission media effectively as each time slot is dedicated to a sensor and therefore cannot be used by others should it be idle. Moreover, a schedule-based approach requires a central node to manage and broadcast the schedule to other members, causing high delay and unscalability. On the other hand, contention-based protocols can be used in a distributed fashion. However, contention-based protocols such as IEEE 802.11 waste a lot of energy in idle listening. In this paper, we propose a hybrid approach between contention- and schedule-based protocols. The preliminary results using simulation and a test bed show that our proposed approach uses transmission media more efficiently, leading to lower delay while preserving energy for wireless sensor networks. [ABSTRACT FROM PUBLISHER]

In large-scale Wireless Sensor Networks (WSNs), leveraging data sinks' mobility for data gathering has drawn substantial interests in recent years. Current researches either focus on planning a mobile sink's moving trajectory in advance to achieve optimized network performance, or target at collecting a small portion of sensed data in the network. In many application scenarios, however, a mobile sink cannot move freely in the deployed area. Therefore, the precalculated trajectories may not be applicable. To avoid constant sink location update traffics when a sink's future locations cannot be scheduled in advance, we propose two energy-efficient proactive data reporting protocols, SinkTrail and SinkTrail-S, for mobile sink-based data collection. The proposed protocols feature low-complexity and reduced control overheads. Two unique aspects distinguish our approach from previous ones: 1) we allow sufficient flexibility in the movement of mobile sinks to dynamically adapt to various terrestrial changes; and 2) without requirements of GPS devices or predefined landmarks, SinkTrail establishes a logical coordinate system for routing and forwarding data packets, making it suitable for diverse application scenarios. We systematically analyze the impact of several design factors in the proposed algorithms. Both theoretical analysis and simulation results demonstrate that the proposed algorithms reduce control overheads and yield satisfactory performance in finding shorter routing paths. [ABSTRACT FROM AUTHOR]

Sleep scheduling is a widely used strategy for saving the energy of sensor nodes and prolonging the lifetime of a wireless sensor network (WSN). The lower the duty cycle is, the longer the network lifetime will be. However, sleep scheduling brings great challenges to the design of efficient distributed routing protocols for multi-hop duty-cycled WSNs. This issue has attracted much attention and various routing protocols have been proposed. In this article we first summarize the fundamental issues in the design of routing protocols for such networks, and then classify existing protocols based on different design criteria. We then present a survey of state-of-the-art routing protocols in this area. We illustrate how different protocols work and discuss their merits and deficiencies. Finally, we point out some future directions for routing in duty-cycled wireless sensor networks. [ABSTRACT FROM PUBLISHER]

RFID (Radio Frequency Identification) tags are small, wireless electronic devices that help identify objects and people. Privacy protection and integrity assurance become rather crucial in the RFID systems, because these RFID tags may have a wide transmission range, making them subject to unauthorized scanning by malicious readers and various other attacks. Hence, Ha et al. proposed an RFID protocol and proved that their protocol can provide the forward privacy service. However, in this paper, it is shown that an attacker can track a target tag by observing unsuccessful previous session of the tag. That is, Ha et al.'s RFID protocol fails to provide the forward privacy protection as claimed. Therefore, to overcome the privacy weaknesses of Ha et al.'s RFID protocol, an RFID protocol based on the cryptographic hash functions is proposed. Moreover, the proposed RFID protocol is evaluated according to both the privacy attribute and the implementation performance. [ABSTRACT FROM AUTHOR]

In-network aggregation reduces the energy cost of processing aggregate queries (such as SUM, MAX, etc.) in wireless sensor networks. Recently, research has focused on secure in-network aggregation, motivated by the following two scenarios: 1) the sensors are deployed in open and unsafe environments, and 2) the aggregation process is outsourced to an untrustworthy service. Despite the bulk of work on the topic, there is currently no solution providing both integrity and confidentiality in the above scenarios. Moreover, existing solutions either return approximate results, or have limited applicability to certain types of aggregate queries. Our paper is the first work that provides both integrity and confidentiality in the aforementioned scenarios, while covering a wide range of aggregates and returning exact results. We initially present SIES, a scheme that solves exact SUM queries through a combination of homomorphic encryption and secret sharing. Subsequently, we show how to adapt SIES in order to support many other exact aggregate queries (such as MAX, MEDIAN, etc.). Finally, we augment our schemes with a functionality that identifies malicious sensors, preventing denial-of-service (DoS) attacks and attributing robustness to the system. Our techniques are lightweight and induce very small bandwidth consumption. Therefore, they constitute ideal solutions for resource-constrained sensors. [ABSTRACT FROM AUTHOR]

In this work, we assume a geographic area populated by tiny sensors, each perhaps no larger than a dime. In order to save their energy, the sensors spend most of their lifetime in sleep mode and wake up for short periods of time to participate in various tasks supportive of the overall mission of the network. We assume that the tasks to be performed stipulate QoS parameters expressed in terms of the minimum number of sensors that need to monitor their sensing area. Since only awake sensors participate in tasks, the Effective Sensor Density (ESD), defined as the density of awake sensors, is an important network parameter that obviously depends on the sleep schedules adopted in the network. The first main contribution of this work is to provide a mathematical analysis of ESD from the perspective of the monitored events. We also provide design guidelines to determine deployment-time sensor density and an associated sleep schedule that probabilistically keeps the ESD at a level needed by QoS requirements. We also propose a fully distributed sleep schedule which adaptively adjusts the duty cycles of sensors within the same sensing area based on the relative difference in their remaining energy budget. The main advantage of the proposed adaptive scheme is to balance energy consumption among sensors, thus promoting the functional longevity of the sensor network without adversely affecting the ESD. [ABSTRACT FROM AUTHOR]

Wireless reprogramming of sensor nodes is an essential requirement for long-lived networks because software functionality needs to be changed over time. The amount of information that needs to be wirelessly transmitted during reprogramming should be minimized to reduce reprogramming time and energy. In this paper, we present a multihop incremental reprogramming system called Hermes that transfers over the network the delta between the old and new software and lets the sensor nodes rebuild the new software using the received delta and the old software. It reduces the delta by using techniques to mitigate the effects of function and global variable shifts caused by the software modifications. Then it compares the binary images at the byte level with a method to create a small delta that needs to be sent over the wireless network to all the nodes. For the wide range of software change scenarios that we experimented with, we find that Hermes transfers up to 201 times less information than Deluge, the standard reprogramming system for TinyOS, and 64 times less than an existing incremental reprogramming system by Jeong and Culler. [ABSTRACT FROM AUTHOR]

In this work, for a wireless sensor network (WSN) of n randomly placed sensors with node density \lambda \in [1,n], we study the tradeoffs between the aggregation throughput and gathering efficiency. The gathering efficiency refers to the ratio of the number of the sensors whose data have been gathered to the total number of sensors. Specifically, we design two efficient aggregation schemes, called single-hop-length (SHL) scheme and multiple-hop-length (MHL) scheme. By novelly integrating these two schemes, we theoretically prove that our protocol achieves the optimal tradeoffs, and derive the optimal aggregation throughput depending on a given threshold value (lower bound) on gathering efficiency. Particularly, we show that under the MHL scheme, for a practically important set of symmetric functions called divisible perfectly compressible (DPC) functions, including the mean, max, and various kinds of indicator functions, etc., the data from \Theta (n) sensors can be aggregated to the sink at the throughput of a constant order \Theta (1), implying that, our MHL scheme is indeed scalable. [ABSTRACT FROM AUTHOR]

A game-theoretic framework is introduced for studying selfish user behavior in shared wireless networks. The investigation treats an n-unicast problem in a wireless network that employs a restricted form of network coding called reverse carpooling. Unicast sessions independently choose routes through the network. The cost of a set of unicast routes is the number of wireless transmissions required to establish those connections using those routes. Game theory is employed as a tool for analyzing the impact of cost sharing mechanisms on the global system performance when each unicast independently and selfishly chooses its route to minimize its individual cost. The investigation focuses on the performance of stable solutions, where a stable solution is one in which no single unicast can improve its individual cost by changing its route. The results include bounds on the best- and worst-case stable solutions compared to the best performance that could be found and implemented using a centralized controller. The optimal cost sharing protocol is derived and the worst-case solution is bounded. That worst-case stable performance cannot be improved using cost-sharing protocols that are independent of the network structure. [ABSTRACT FROM AUTHOR]

Time-based localization approaches attract a lot of interest due to their high accuracy and potentially low cost for wireless sensor networks (WSNs). However, time-based localization is tightly coupled with clock synchronization. Thus, the reliability of timestamps in time-based localization becomes an important yet challenging task to deal with. In this paper, we propose robust time-based localization strategies to locate a target node with the help of anchors (nodes with known positions) in asynchronous networks. Two kinds of asynchronous networks are considered: one only with clock offsets, labeled quasi-synchronous networks, whereas the other with not only clock offsets but also clock skews, labeled fully asynchronous networks. A novel ranging protocol is developed for both networks, namely asymmetric trip ranging (ATR), to reduce the communication load and explore the broadcast property of WSNs. Regardless of the reliability of the timestamp report from the target node, closed-form least-squares (LS) estimators are derived to accurately estimate the target node position. As a result, we counter the uncertainties caused by the target node by ignoring the timestamps from this node. Furthermore, in order to simplify the estimator in fully asynchronous networks, localization and synchronization are decoupled. A simple yet efficient method is proposed to first Calibrate the Clock Skews of the anchors, and then Estimate the Node Position (CCS-ENP). Finally, Cramér-Rao bounds (CRBs) and simulation results corroborate the efficiency of our localization schemes. [ABSTRACT FROM AUTHOR]

This paper addresses a transmission energy problem for distributed (or decentralized) estimation in multihop wireless sensor networks (WSN). A primary advantage of distributed estimation is its energy efficiency when compared to centralized estimation. Two distributed estimation schemes are considered in this paper: progressive estimation and consensus estimation. We develop a generalized energy planning algorithm for a progressive estimation method which exploits routing tree and channel state information. We also analyze the energy cost for a consensus estimation method used in broadcast multihop WSN. We demonstrate by analysis and simulation that, subject to an equivalent performance, the total energy cost for consensus estimation is typically much higher than that for progressive estimation, but the peak energy for the former can be less than that for the latter. [ABSTRACT FROM PUBLISHER]

In many wireless systems, interference is the main performance-limiting factor, and is primarily dictated by the locations of concurrent transmitters. In many earlier works, the locations of the transmitters is often modeled as a Poisson point process for analytical tractability. While analytically convenient, the PPP only accurately models networks whose nodes are placed independently and use ALOHA as the channel access protocol, which preserves the independence. Correlations between transmitter locations in non-Poisson networks, which model intelligent access protocols, makes the outage analysis extremely difficult. In this paper, we take an alternative approach and focus on an asymptotic regime where the density of interferers \eta goes to 0. We prove for general node distributions and fading statistics that the success probability \\tt P\\tt s \sim 1-\gamma \eta^{\kappa} for \eta \rightarrow 0, and provide values of \gamma and \kappa for a number of important special cases. We show that \kappa is lower bounded by 1 and upper bounded by a value that depends on the path loss exponent and the fading. This new analytical framework is then used to characterize the transmission capacity of a very general class of networks, defined as the maximum spatial density of active links given an outage constraint. [ABSTRACT FROM PUBLISHER]

Nowadays, careful measurement applications are handed over to wireless sensor networks (WSNs). In most of these tasks, sensor nodes work together to recognize the data fusion process. Synchronization is a critical element in this scenario. Nodes have to be regulated to a common clock and regulated among them. Many synchronization algorithms can be found in literature, and some of them have been intentionally established for low-cost structural designing where efficient memory management and reduced computational burden are important constraints. The performance of these algorithms is usually evaluated either in simulation environments or by adopting ad hoc radio systems. Attention is rarely paid to the influence of factors, such as the following: clock stability, the dependence of the measurement application on the synchronization algorithm and vice versa, the effect of the limited bandwidth available on real radio systems, and the change of performance when common commercial wireless communication busses such as Wi-Fi, Bluetooth (BT), and ZigBee are adopted. This paper makes the first step toward this direction, proposing the experimental characterization of a small-scale WSN implementing some of these protocols versus common wireless busses such as BT, Wi-Fi, and ZigBee. [ABSTRACT FROM AUTHOR]

In this paper, we consider a cooperative network that is trying to reach consensus on the occurrence of an event, by communicating over time-varying network topologies with fast fading channels. We mathematically characterize both the asymptotic and transient behaviors of the network. We show that the network converges to a memoryless state asymptotically, which is undesirable. However, the network can still be in consensus for a long period of time. In order to characterize the transient behavior, we then derive a tight approximation for the second largest eigenvalue of the underlying average probability transition matrix in fading environments. We show the impact of channel unreliability and network topology on consensus performance and shed light on the underlying tradeoffs in terms of speed of convergence and memoryless asymptotic behavior. [ABSTRACT FROM AUTHOR]

Flood is a communication primitive that can be used by the base station of a sensor network to send a copy of a message to every sensor in the network. When a sensor receives a flood message, the sensor needs to check whether it has received this message for the first time and so this message is fresh, or it has received the same message earlier and so the message is redundant. In this paper, we discuss a family of four flood sequencing protocols that use sequence numbers to distinguish between fresh and redundant flood messages. These four protocols are: a sequencing free protocol, a linear sequencing protocol, a circular sequencing protocol, and a differentiated sequencing protocol. We analyze the self-stabilization properties of these four flood sequencing protocols. We also compare the performance of these flood sequencing protocols, using simulation, over various settings of sensor networks. We conclude that the differentiated sequencing protocol has better stabilization property and provides better performance than those of the other three protocols. [ABSTRACT FROM AUTHOR]

Many sensor network applications are tightly coupled with the geometric environment where the sensor nodes are deployed. The topological skeleton extraction for the topology has shown great impact on the performance of such services as location, routing, and path planning in wireless sensor networks. Nonetheless, current studies focus on using skeleton extraction for various applications in wireless sensor networks. How to achieve a better skeleton extraction has not been thoroughly investigated. There are studies on skeleton extraction from the computer vision community; their centralized algorithms for continuous space, however, are not immediately applicable for the discrete and distributed wireless sensor networks. In this paper, we present a novel Connectivity-bAsed Skeleton Extraction (CASE) algorithm to compute skeleton graph that is robust to noise, and accurate in preservation of the original topology. In addition, CASE is distributed as no centralized operation is required, and is scalable as both its time complexity and its message complexity are linearly proportional to the network size. The skeleton graph is extracted by partitioning the boundary of the sensor network to identify the skeleton points, then generating the skeleton arcs, connecting these arcs, and finally refining the coarse skeleton graph. We believe that CASE has broad applications and present a skeleton-assisted segmentation algorithm as an example. Our evaluation shows that CASE is able to extract a well-connected skeleton graph in the presence of significant noise and shape variations, and outperforms the state-of-the-art algorithms. [ABSTRACT FROM AUTHOR]

Wireless sensor networks are mainly designed for environment surveillance, wherein wireless sensor nodes cooperate to get their job done. Generally, wireless sensors are battery powered; therefore, it is crucial for them to efficiently use their battery resources. Most of the existing power-saving protocols achieve power savings by periodically putting sensor nodes to sleep. Such a regular sleep/awake mechanism fails to adjust a sensor node's sleep duration based on its traffic load, thus causing either lower power efficiency or higher latency. Furthermore, sensors may be deployed in hostile environments and may thus unexpectedly fail. Most power-saving protocols do not promptly react to such link breakage, resulting in long transmission delays. In this paper, we propose a quorum-basedmedium access control (QMAC) protocol that enables sensor nodes to sleep longer under light loads. Since traffic flows toward the sink node in wireless sensor networks, a new concept, i.e., the next-hop group, is also proposed to reduce transmission latency. Simulation results verify that the proposed QMAC saves more energy and keeps the transmission latency low. [ABSTRACT FROM AUTHOR]

In this paper, three clock-synchronization algorithms for wireless sensor networks (WSNs) under unknown delay are derived. They include the maximum-likelihood estimator (MLE), a generalization of the estimator of Noh et al., and a novel low-complexity estimator. Their corresponding performance bounds are derived and compared, and complexities are also analyzed. It is found that the MLE achieves the best performance with the price of high complexity. For the generalized version of the estimator of Noh et al., although it has low complexity, its performance is degraded with respect to the MLE. On the other hand, the newly proposed estimator achieves the same performance as the MLE, and the complexity is at the same level as that of the generalized version of the estimator of Noh et al. [ABSTRACT FROM AUTHOR]

This article presents an overview of the IEEE project 802.15.5 that targets providing mesh capabilities to both high-rate and low-rate wireless personal area networks. Low-rate mesh is built on IEEE 802.15.4 MAC, while high-rate mesh utilizes IEEE 802.15.3 MAC. We seek to share our insights and motivations of the approach adopted in the major components of the standard instead of presenting a Ia carte items drawn in the specification. We hope this article helps readers of the 802.15.5 standard to better understand the rationale and intent of the protocol design. [ABSTRACT FROM AUTHOR]