OTSA: Optimized Time Synchronization Approach for Delay-based Energy Efficient Routing in WSN

Distributed time synchronization is an important part of sensor networks. Due to the limited battery capacity of the sensor nodes, applicable schemes should concern the energy consumption of the networks. To achieve better efficiency, an event-triggered time synchronization scheme (ETTS) is presented, which aims at providing on-demand time synchronization in sensor networks. The scheme is composed of two phases: skew correction phase and estimation of offset phase. When timestamps from different clocks need to be compared, they can be reconciled after the event. ETTS removes the need to predict application requirements in advance, which means that the synchronization energy is only expended after an event has occurred. Compared to traditional schemes, for example, TPSN, simulation results show that ETTS achieves desired energy efficiency when the frequency of event is low.

Energy conservation and fault tolerance are the most two important challenging issues for the development of large scale wireless sensor networks (WSNs). Failure of cluster heads in a cluster based WSN is more catastrophic as they are responsible not only for data aggregation and transmission of the aggregated data to the base station but also relaying data for multi-hop communication. Therefore, a routing algorithm in WSNs should be energy aware as well as fault tolerant. In this paper, we present a distributed energy efficient and fault tolerant routing algorithm for WSNs. The algorithm selects next-hop cluster head in energy efficient manner in the data routing phase and carefully restores the connectivity of the neighbours of a cluster head in case of its failure. The algorithm is tested extensively by considering several scenarios of WSN. The experimental results are compared with the existing algorithms in terms of several metrics to show the effectiveness of the proposed algorithm.

Large-scale distribution, communication and processing of sensed information require the operation of a highly-dynamic, dense, and widely-distributed wireless sensor network. Existing centralized and decentralized solutions require the use of information that may not be readily available to the nodes in a timely fashion. Instead of seeking such techniques, in this paper we propose an evolutionary price-based routing and bandwidth allocation algorithm for the management of information in large-scale distributed wireless sensor networks that will be (1) adaptable and responsive to demands and seek delivery of information to desired nodes despite the fact that the source and destination are not globally known, (2) efficient in allocating bandwidth, and (3) decentralized.

Study of consensus-based time synchronization in wireless sensor networks

Landmark-based routing (LR) provides a promising approach for scalable point-to-point routing in wireless sensor networks (WSNs). Though various approaches have been proposed for landmark-based routing, they either introduce significant computational complexity or are inefficient in realistic, dynamic environments. In this paper, we identify three design principles that could form the basis of efficiency: algorithmic simplicity, update efficiency, and application awareness. Motivated by these principles, we present XLR, a new, flexible and comprehensive framework that tackles the inefficiency of landmark-based routing. XLR consists of four components: Relay Selection (RS), Parametric P-Norm distance function (PPN), Efficient Update with Coordinate Difference (EUCD) and General Forwarding (GF). The key advantage of XLR is that any subset of XLR's components can be independently incorporated into most landmark-based routing protocols.We perform extensive simulations to demonstrate that: (i) RS, a simple method, yields good performance comparable with previous methods, (ii) PPN increases LR performance considerably, (iii) EUCD reduces coordinate update overhead by up to 39%, and (iv) our GF outperforms previous approaches that consider factors such as link quality, delay and power consumption independently.

Energy efficiency is a critical problem for wireless sensor networks. In past decades, network coding has been proved as a promising technology to reduce the number of transmissions, save energy, and improve network throughput, especially suitable for the wireless network that motivates the emergence of network coding aware routings. However, existing network coding aware routings have the failure decoding problem, because of defective network coding conditions. On the other hand, existing network coding aware routings usually consider the ideal traffic scheduling and neglect nodes’ energy and load which are important to wireless sensor networks. Therefore, it is not appropriate to directly apply existing network coding aware routings in wireless sensor networks. Regarding the problems above problems, this paper proposes traffic-shaped network coding aware routing (TSCAR) for wireless sensor networks. In the TSCAR, a universal network coding condition is presented to solve the false decoding problem. And traffic shaping mechanism is proposed to shape the traffic of different flows to create more coding actions when coding opportunities exist. In addition, network calculus is used to analyze the delay of the TSCAR. Besides, a coding, load, and energy aware routing metrics are proposed to evaluate the discovered paths. Extensive simulation results demonstrate that the TSCAR increases the number of coding opportunities and the proportion of coded packets, improves network throughput, and extends the network lifetime of wireless sensor networks.

Wireless sensor networks require time synchronization, which is the coordination of events or actions to make a system operate in unison. In this work, real experiments and a theoretical analysis of the behavior of the clock sources, most used in wireless sensor networks, have been carried out. The experiments have been performed on two real platforms from two different manufacturers in real environments with sudden changes in temperature. Complementary metal-oxide-semiconductor oscillators have a low accuracy, bigger than 500 ppm, and a high dependency with temperature. External crystal oscillators have good accuracy, around 20 ppm, and are stable with temperature. Temperature-compensated crystal oscillators are very accurate, around 5 ppm, and the temperature has no influence in their drift. The use of phase-locked loop circuits minimizes the impact of temperature and stabilizes oscillators. We highlight and demonstrate the importance of the early stages of design, especially the selection of the clock source, because that decision has a great impact on the performance of the time synchronization in wireless sensor networks.

Routing algorithms for large-scale sensor networks should be capable of finding energy efficient paths to prolong the lifetime of the networks in a decentralized manner. With this respect, Ant System has several proper characteristics for routing algorithm in large-scale wireless sensor networks. First, its distributed mechanism enables routing algorithm to find a solution with only local information and be robust for uncertainties in wireless sensor networks. Second, the framework of the Ant System is proper to solve dynamic problems such as routing problem. Transition probability in Ant System can be used to estimate how good a given routing path is. Capturing these features, this work proposes two Ant Systems based routing algorithms, which are AS-RWSNs (Ant System for Routing in Wireless Sensor Networks) and SAAS-RWSN (Structure-Aware AS-RWSN). The AS-RWSN applies the original Ant System to routing algorithm for wireless sensor network and SAAS-RSN upgrades AS-RWSN with considering properties of network structure such as degree of node. In SAAS-RSN, sensors with high node degree have high data traffic since they have more routing paths. Consequently, SAAS-RSN achieves an energy balance over sensor network through this routing scheme. We demonstrate the effectiveness of the proposed algorithms by comparing three existing routing algorithms.

Routing in a wireless sensor network field requires significant resources. Computing optimal routes using graph theoretic algorithms becomes intractable as number of nodes become very large. In this paper, authors propose an alternative using a continuous function approximation for path cost. It is based on a fluid type approximation in which the whole network is replaced by a continuum plain - where the discrete graph describing the links and their cost is replaced by a cost density over the plain. The fluid limit approach does not depend on the number of nodes and hence the complexity of finding optimal routes does not grow with the number of nodes. The approach makes use of calculus of variations. Complexity analysis shows that this leads to a large saving in communication and computational overhead associated with routing. Two practical situations for possible application of this approach are identified. The computed path cost can also serve as the theoretical lower bound of cost for paths that can be computed by any routing algorithm. Preliminary simulation results are also reported.

Wireless sensor networks are generally composed of densely deployed sensor nodes that collaboratively sense, compute and communicate the sensed information. Routing in sensor networks is based on energy optimisation and quality of service. In this paper, a meta-heuristic technique comprising particle swarm optimisation and Tabu search (TS) is used for energy efficient routing in sensor network. The hybrid approach has better network performance compared with the traditional approaches, simple particle swarm algorithm and TS, respectively. Experimental results penlight the efficacy of the proposed approach.

Time synchronization, aiming to provide a common timescale among distributed sensor nodes, is a key enabling technology for many applications, such as collaborative condition monitoring and localization detection. Due to the complexity of time synchronization in wireless sensor networks, the Discrete Event Simulator is recommended to adopt resulting from the feature that the behavior of a complex is represented as an order sequence of well-defined event in time. In this paper, the PCO clock is firstly implemented into the open-source software simulator OMNeT++ by using desynchronization mechanism under a realistic scenario, and it can also be simulated at an adjustable and higher resolution. The developed relay node, can either be a Full Function Device or a Reduced Function Device, enables the high scalability for multi-node and multi-hop simulation. In addition, the shared code of this project on the GitHub directly benefits the researchers and engineers in communication.

A wireless sensor network is an enormous assortment of sensor nodes with inadequate power supply and self-conscious computational competence. Due to the circumscribed communication range and high density of sensor nodes, packet dispatching in sensor networks is usually performed through multi-hop data transmission. For that reason, routing in wireless sensor networks has been deliberated as an imperative field of research over the past decade. These days, multipath routing techniques is widely used in wireless sensor networks to improve network performance over and done with efficient utilization of accessible network resources. Consequently, the main intention of this review is to present the conception of the various routing approaches and its fundamental experiments, as well as the basic motivations for exploiting these techniques in wireless sensor networks. Routing procedures for WSNs are responsible for selecting and maintaining the routes in the network and ensure reliable and effective communication in inadequate periods. The energy constriction of WSNs make energy saving become the most significant objective of various routing algorithms. In this paper, a review of routing protocols and algorithms used in WSNs is presented with energy efficiency as the main goalmouth.

International audience

A common time reference across nodes is required in most Wireless Sensor Networks (WSNs) applications. Also many routing protocols require that nodes communicate according to some predefined schedule for reasons of energy efficiency. However, independent distribution of the time information, without considering the routing algorithm schedule or network topology, may lead to a failure of the synchronisation protocol. This can be avoided by integrating the synchronisation service into the network layer with a so-called cross-layer approach. We present two novel cross-layer routing algorithms, CLEAR and RISS. We implemented and tested the performance of these solutions in simulations and also deployed these routing techniques on sensor nodes using TinyOS. All proposed schemes extend the network lifetime and due to their lightweight architecture they are very efficient on WSN nodes with constrained resources. Hence, it is recommended that a cross-layer approach should be a feature of any routing algorithm for WSNs.

Time synchronization for wireless sensor networks (WSNs) has been studied in recent years as a fundamental and significant research issue. Many applications based on these WSNs assume local clocks at each sensor node that need to be synchronized to a common notion of time. Time synchronization in a WSN is critical for accurate time stamping of events and fine-tuned coordination among the sensor nodes to reduce power consumption. This paper proposes a bidirectional, reference based, tree structured time synchronization service for WSNs along with network evaluation phase. This offers a push mechanism for (i) accurate and (ii) low overhead for global time synchronization. Analysis study of proposed approach shows that it is lightweight as the number of required broadcasting messages is constant in one broadcasting domain.