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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]

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]

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]

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]

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]

In this paper, we consider security-related and energy efficiency issues in multihop wireless networks. We start our work from the observation, known in the literature, that shortest path routing creates congested areas in multihop wireless networks. These areas are critical—they generate both security and energy efficiency issues. We attack these problems and set out routing in outer space, a new routing mechanism that transforms any shortest path routing protocol (or approximated versions of it) into a new protocol that does not create congested areas, does not have the associated security-related issues, and does not encourage selfish positioning. Moreover, the network is more energy efficient than the same network using the original routing protocol (in spite of using more energy globally) and dies more gracefully. We also describe applications of our idea to mobility and to a security protocol for the detection of node replication attacks. [ABSTRACT FROM AUTHOR]

The establishment of a localization system is an important task in wireless sensor networks. Due to the geographical correlation between sensed data, location information is commonly used to name the gathered data and address nodes and regions in data dissemination protocols. In general, to estimate its location, a node needs the position information of at least three reference points (neighbors that know their positions). In this work, we propose a different scheme in which only two reference points are required in order to estimate a position. To choose between the two possible solutions of an estimate, we use the known direction of the recursion. This approach leads to a recursive localization system that works with low-density networks (increasing by 40 percent the number of nodes with estimates in some cases), reduces the position error by almost 30 percent, requires 37 percent less processor resources to estimate a position, uses fewer beacon nodes, and also indicates the node position error based on its distance to the recursion origin. No GPS-enabled node is required, since the recursion origin can be used as a relative coordinate system. The algorithm's evaluation is performed by comparing it with a similar localization system; also, experiments are made to evaluate the impact of both systems in geographic algorithms. [ABSTRACT FROM AUTHOR]

In this paper, we present the performance evaluation of an algorithm for preserving temporal relationships of events in Wireless Sensor Actor Networks (WSANs). The algorithm consists of two modules, which deal with the problems of temporal event ordering and time synchronization. These two problems are approached as a whole as they complement each other: in order to temporally order the events, the nodes must be synchronized. The goal of the proposed event ordering algorithm for WSANs is to reduce the overhead in terms of energy dissipation and delay. We also propose a tunable time synchronization algorithm employing a hybrid synchronization scheme suited for clustered topology. The proposed algorithm utilizes the message exchange necessary for event ordering and routing for synchronization purposes by piggybacking messages with synchronization pulses and replies to reduce the communication cost of synchronization. Simulation experiments showed that the event ordering algorithm is capable of reducing the overhead when compared to previously proposed algorithms. The synchronization algorithm demonstrated that the combination of synchronization techniques was well suited for the communication mode utilized in a clustered topology. The approach of piggybacking synchronization pulses and replies resulted in a considerable gain, which we demonstrated in the number of messages that were piggybacked for synchronization purposes. [ABSTRACT FROM AUTHOR]

Sensing coverage is an essential functionality of wireless sensor networks (WSNs). However, it is also well known that coverage alone in WSNs is not sufficient, and hence network connectivity should also be considered for the correct operation of WSNs. In this paper, we address the problem of k-coverage in WSNs such that in each scheduling round, every location in a monitored field (or simply field) is covered by at least k active sensors while all active sensors are being connected. Precisely, we study sensors duty-cycling strategies for generating k-coverage configurations in WSNs. First, we model the k-coverage problem in WSNs. Second, we derive a sufficient condition of the sensor spatial density for complete k-coverage of a field. We also provide a relationship between the communication and sensing ranges of sensors to maintain both k-coverage of a field and connectivity among all active sensors. Third, we propose four configuration protocols to solve the problem of k-coverage in WSNs. We prove that our protocols select a minimum number of sensors to achieve full k-coverage of a field while guaranteeing connectivity between them. Then, we relax some widely used assumptions for coverage configuration in WSNs, to promote the use of our proposed protocols in real-world sensing applications. Our simulation results show that our protocols outperform an existing distributed k-coverage configuration protocol. [ABSTRACT FROM AUTHOR]

In numerous applications of wireless sensor networks (WSN), the reliability of the data collected by sensors is cast as specific QoS requirements expressed in terms of the minimum number of sensors needed to perform various tasks. Designing a long-lived sensor network with reliable performance has always been challenging due to the modest nonrenewable energy budget of individual sensors. In such a context, energy-unaware task management protocols may result in uneven expenditure of sensor energy by assigning uneven workloads to sensors. This, in turn, often translates into reduced sensor density around those heavily loaded sensors and may, eventually, lead to the creation of energy holes that partition the network into disconnected islands. To avoid these problems and to promote network longevity, we propose two energy-aware task management protocols: our first protocol is centralized, while the second one is fully distributed. The proposed protocols assign tasks to sensors based on their remaining energy so that energy expenditure among neighboring sensors is almost even. We compare the reliable lifetime of the network achieved by assigning tasks to sensors using the proposed protocols against optimal task assignment and also against energy-unaware protocols. Extensive simulation results have revealed that the performance of the proposed protocols is very close to that of the optimal task assignment. Furthermore, our simulation has shown that the proposed protocols can increase the functional longevity of the network by about 16 percent. [ABSTRACT FROM AUTHOR]

Minimizing energy consumption is a fundamental requirement when deploying wireless sensor networks. Accordingly, various topology control protocols have been proposed, which aim to conserve energy by turning off unnecessary sensors while simultaneously preserving a constant level of routing fidelity. However, although these protocols can generally be integrated with any routing scheme, few of them take specific account of the issues which arise when they are integrated with geographic routing mechanisms. Of these issues, the dead-end situation is a particular concern. The dead-end phenomenon (also known as the "local maximum” problem) poses major difficulties when performing geographic forwarding in wireless sensor networks since whenever a packet encounters a dead end, additional overheads must be paid to forward the packet to the destination via an alternative route. This paper presents a distributed dead-end free topology maintenance protocol, designated as DFTM, for the construction of dead-end free networks using a minimum number of active nodes. The performance of DFTM is compared with that of the conventional topology maintenance schemes GAF and Span, in a series of numerical simulations conducted using the ns2 simulator. The evaluation results reveal that DFTM significantly reduced the number of active nodes required in the network and thus prolonged the overall network lifetime. DFTM also successfully constructed a dead-end free topology in most of the simulated scenarios. Additionally, even when the locations of the sensors were not precisely known, DFTM still ensured that no more than a very few dead-end events occurred during packet forwarding. [ABSTRACT FROM AUTHOR]

Recent years have witnessed a surge of interest in efficient data gathering schemes in wireless sensor networks (WSNs). In this paper, we address this issue by adopting mobility and space-division multiple access (SDMA) technique. Specifically, mobile collectors, called SenCars in this paper, work like mobile base stations and collect data from associated sensors via single-hop transmissions so as to achieve uniform energy consumption. We also apply SDMA technique to data gathering by equipping each SenCar with multiple antennas such that distinct compatible sensors may successfully make concurrent data uploading to a SenCar. To investigate the utility of the joint design of controlled mobility and SDMA technique, we consider two cases, where a single SenCar and multiple SenCars are deployed in a WSN, respectively. For the single SenCar case, we aim to minimize the total data gathering time, which consists of the moving time of the SenCar and the data uploading time of sensors, by exploring the trade-off between the shortest moving tour and the full utilization of SDMA. We refer to this problem as mobile data gathering with SDMA, or MDG-SDMA for short. We formalize it into an integer linear program (ILP) and propose three heuristic algorithms for it. In the multi-SenCar case, the sensing field is divided into several regions, each having a SenCar. We focus on minimizing the maximum data gathering time among different regions and refer to it as mobile data gathering with multiple SenCars and SDMA (MDG-MS) problem. Accordingly, we propose a region-division and tour-planning (RDTP) algorithm in which data gathering time is balanced among different regions. We carry out extensive simulations and the results demonstrate that our proposed algorithms significantly outperform single SenCar and non-SDMA schemes. [ABSTRACT FROM AUTHOR]