Localized algorithms in wireless ad-hoc networks

Wireless ad-hoc sensor networks will provide one of the missing connections between the Internet and the physical world. One of the fundamental problems in sensor networks is the calculation of coverage. Exposure is directly related to coverage in that it is a measure of how well an object, moving on an arbitrary path, can be observed by the sensor network over a period of time.In addition to the informal definition, we formally define exposure and study its properties. We have developed an efficient and effective algorithm for exposure calculation in sensor networks, specifically for finding minimal exposure paths. The minimal exposure path provides valuable information about the worst case exposure-based coverage in sensor networks. The algorithm works for any given distribution of sensors, sensor and intensity models, and characteristics of the network. It provides an unbounded level of accuracy as a function of run time and storage. We provide an extensive collection of experimental results and study the scaling behavior of exposure and the proposed algorithm for its calculation.

Topology control is an important problem in wireless ad-hoc sensor networks. The aim of the topology control is to maintain desired properties of the network topology to improve the performance of networking algorithms (e.g. routing). In this paper, we present a distributed algorithm for assigning minimum possible power to all the nodes in the wireless sensor networks, such that the network is K-connected. Extensive simulation has been performed to prove the optimality of the algorithm

In wireless mobile ad-hoc networks, data packets have to be relayed hop by hop from a given source node to a destination node. This means that some or all of the mobile nodes must accept to forward information for the benefit of other nodes. It has been shown by F. Nait-Abdesselam, et al., (2003) that this ability of forwarding packets leads to a new unfairness problem in wireless ad-hoc networks, where a node which is forwarding other node's packets gets less bandwidth, for its own use, than a node which is not participating to the routing service. The proposed RAMAC scheme by F. Nait-Abdesselam, et al., (2003), has shown all its effectiveness to cope with this unfairness problem. However, an extra bandwidth is sometimes allowed to the routing node's own traffic comparing to other nonrouting node's own traffics, and the routing node's routed traffic gets much less bandwidth. This is explained by the fact that at the upper layer (for instance the IP layer) does not differentiate between the routing and the own traffics, and that the multiplicative factor used to compute the new contention window is too aggressive. In this paper, an enhanced RAMAC scheme is proposed, by taking into account the differentiation on top of the MAC layer, between the and routed traffics within a routing node, and by smoothing the multiplicative factor used to compute the new contention window. The simulation results obtained showed a good improvement of the original RAMAC scheme, leading to better approximate equal bandwidth share among all the mobile nodes in the wireless ad-hoc network.

Wireless ad-hoc sensor networks have caught the fancy of many researchers through the world in a very small span of time. Although notable progress has been made in several key areas, several researchers falter in the way they look at sensor networks i.e. just another kind of wireless ad hoc networks, albeit one composed of energy constrained nodes. A key aspect that makes sensor networks different from traditional networks is their strong link to the physical world. We develop this perspective by studying an interesting class of sensor network applications called aggregation applications.We argue that when a user queries for aggregates like maximum, average etc., he is interested in knowing the statistics of the underlying physical process. In general, this is not equivalent to the statistics gathered from a bunch of nodes. We introduce a distinction between aggregates calculated over a region and aggregates calculated over a discrete set of nodes. We classify them as spatial and nodal aggregates respectively. Till now, researchers have followed the approach of doing nodal aggregation in response to every user query in sensor networks. For a continuous physical process and a random deployment of sensor nodes, which are a norm for sensor networks, the conventional approach of doing nodal aggregation produces inaccurate results.We verify our claim by studying a specific aggregation function namely the average over a region (spatial average) in detail. We use a voronoi-based approach to propose an algorithm for calculating spatial average in sensor networks. The algorithm can work in two modes -- centralized and distributed. The energy and accuracy tradeoff associated with each of the two modes is analyzed in detail. The efficacy of the proposed algorithm is tested over a wide variety of physical processes including real precipitation data of South America acquired over a span of past 50 years. We will show that our algorithm gives a 2-8 times performance gain as compared to the conventional approach of doing nodal aggregation. We further explore the robustness of our algorithm to link failures and channel impairments.Although not 100% accurate, our approach is a simple, efficient and a practical solution for calculating the spatial average. We have implemented our algorithm on Berkeley motes. Our first prototype implementation occupies less than 12K flash ROM and consumes less than 1.6K run-time memory. Our algorithm can be easily integrated with available frameworks for doing aggregation in sensor networks. For a minimal cost, our algorithm can be used to provide a spatial aggregation service on a network of motes.

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Recent development has a tremendous growth in the ad-hoc wireless networks. Ad-hoc wireless networks are dynamic topology networks organized by a collection of mobile nodes that utilize multi-hop radio relaying and are capable of operating without the support of any fixed infrastructure. Ad-hoc wireless networks are very useful in emergency operations, collaborative and distributed computing and military applications. Multicasting plays an important role in the ad-hoc wireless networks, where nodes form groups to carry out certain tasks that require point-to-multipoint and multipoint-to-multipoint voice and data communication. The biggest challenge in the ad-hoc wireless networks is to find an optimized path between the two nodes. In this paper, we present an ant colony based metaheuristic multicast routing protocol for ad-hoc wireless networks, in that we analyzed the performance of dynamic core based multicast routing protocol (DCMP). This approach maps the solution capability of swarm intelligence to mathematical and engineering problems. The DCMP is highly adaptive, efficient and scalable. The performance of these protocols has been examined under realistic scenarios using NS 2, the network simulator tool. Performance has been analyzed for the metrics packet delivery ratio and control overheads with the multicast routing protocol. The proposed ant colony based routing protocol reduce the overheads in routing.

In wireless, every device can moves anywhere without any infrastructure also the information can be maintained constantly for routing the traffic. The open issues of wireless Adhoc network the attacks which are chosen the forwarding attack that is dropped by malicious node to corrupt the network performance then the information integrity exposure. Aim of the problem that existing methods in Adhoc network for malicious node detection which cannot assure the traceability of the node as well as the fairness of node detection. In this paper, the proposed heterogeneous cluster based secure routing scheme provides trust based secure network for detection of attacks such as wormhole and black hole caused by malicious nodes presence in wireless Adhoc network. The simulation result shows that the proposed model is detect the malicious nodes effectively in wireless Adhoc networks. The malicious node detection efficiency can be achieved 96% also energy consumption also 10% better than existing method.

Minimizing interference of a wireless ad-hoc network in a plane

Geographic routing protocols establish scalable and robust routes for multi-hop trsdansmission in wireless mobile ad-hoc networks, where accurate location information of the mobile nodes is needed. Aiming to alleviate the influence of location errors, existing works focus on modifying routing protocols through modeling the error sources and mobility prediction. In this paper, we propose a cooperative cluster based geographic routing (CCGR) protocol, which views the cooperative cluster as one virtual relay node, and lessens the impact of location errors through opportunistic receiving and cooperative radio range extension. Opportunistic receiving achieves the link diversity and radio range extension enlarges the transmission distance of one hop. The performance of CCGR is analyzed under scenarios of both static and mobility location errors in terms of reliability index, which is defined to represent the link stability. Further more, numerical results demonstrate that our proposed transmission scheme CCGR outperforms non-cooperative routing schemes in terms of link error probability with location errors.

We present a protocol that manages wireless ad-hoc sensor networks in several scenarios including large scale, high density and high mobility deployments. One of the main applications is to communicate important information from inaccessible areas by spreading just "enough" mobile sensors which must self-configure and assemble. According to our protocol, connectionless probabilistic (CoP) routing, the information is routed in a multi-hop, cluster level fashion by enabling each sensor to make individual decisions regarding its mode of operation. The aim is to prolong the network's lifetime by minimizing the energy spent for each communication. CoP is capable of addressing high mobility requirements as it is completely independent of any kind of topological knowledge and control messages. We show by extended experiments that CoP performs very well in terms of consumed energy by comparing it to a standard directed flooding and a greedy forwarding protocol.

The emergence of wireless ad-hoc networks is considered extremely attractive in terms of new applications' enabler. The integration of reliable sensors in nodes of wireless ad-hoc networks has posed various interesting challenges to the community of researchers and engineers. We focus in this paper on two fundamental issues: supporting high mobility of sensors and guaranteeing continuity of sensing, while providing for the correlation of collected data. We propose an efficient scheme for the management of data, sensor mobility, and sensing security

Broadcasting is an essential operation for Wireless Ad Hoc Networks to perform routing path discovery, and it has become the predominant technology for message dissemination in Vehicular Ad Hoc Networks (VANETs). In the reactive routing schemes of wireless ad hoc network, Routing Request (RREQ) packets are broadcast from the source, and once received the destination traces back the broadcasting path to build an on-demand route. In VANETs, different broadcasting schemes have been proposed for safety, comfort, and commercial applications. However, broadcasting usually generates a lot of redundant messages which would cause excessive channel contention and packet collisions, especially when the density of the network becomes higher. In this survey article, we first introduce the most common data dissemination techniques used in wireless ad hoc networks. After that, we discuss techniques that have been proposed to mitigate the broadcast storm problem. Finally, we introduce an effective model for analyzing the broadcasting schemes, and based on the model we propose an adaptively adjusted probabilistic scheme that highly improves the reliability of broadcasting in dense ad hoc networks.

The sensor networks are characterized by tiny, inexpensive, and advanced communication technology. However, wireless ad-hoc sensor networks (WASNs) have some issues such as the limited amount of energy, multipath fading, and some other issues when they applied in disaster situations. For reducing power consumption, we show mathematical analysis of energy saving, and enhanced error symbol probability. The simulation results prove our analysis. As for the multipath fading, we also show the mathematical analysis of fading channel characteristics and channel model, as well as how to mitigate the multipath fading by modulation and diversity techniques. From the simulation results, we prove the proposed system with amplify-and-forward (AF) relaying can achieve a 2.5 dB performance gain the BER 10-4 whereas the achievable improvement is almost a 4 dB at the BER 10-5 when using maximal ratio combining.

Actuation ability introduces a fundamentally new design dimension in wireless ad-hoc sensor networks, allowing the network to adaptively reconfigure and repair itself in response to unpredictable run-time dynamics. One of the key network resources in these systems is energy and several uncontrollable factors lead to situations where a certain segment of the network becomes energy constrained before the remaining network. The performance gets limited due to the constrained sections. We argue that in this scenario, instead of rendering the complete network useless, the remaining energy resources should be reorganized to form a new functional topology in the network. We present methods for the network to be aware of its own integrity and use actuation to improve performance when needed. This capability of the system is referred to as self aware actuation. In this paper, we consider a network where nodes (or a subset of the nodes) have traction ability. The network uses mobility to repair the coverage loss in the area being monitored by it. We present a completely distributed energy aware algorithm (referred to as CO-Fi) for coordinated coverage fidelity maintenance in sensor networks. The energy overheads of mobility are incorporated in the algorithm, thus leaving no hidden costs. Our preliminary analysis shows that CO-Fi can significantly help improve the usable lifetime of these networks.

In the last decade, drones became frequently used to provide eye-in-the-sky overview in the outdoor environment. Their main advantage compared to the other types of robots is that they can fly above obstacles and rough terrains and they can quickly cover large areas. These properties also open a new application; drones could provide a multi-hop, line of sight communication for groups of ground users. The aim of this thesis is to develop a drone team that will establish wireless ad-hoc network between users on the ground and distributively adapt links and spatial arrangement to the requirements and motion of the ground users. For this application, we use fixed wing drones. Such platforms can be easily and quickly deployed. Fixed wing drones have higher forward speed and higher battery life than hovering platforms. On the other hand, fixed wing drones have unicycle dynamics with constrained forward speed which makes them unable to hover or perform sharp turns. The first challenge consists in bridging unicycle dynamics of the fixed wing drones. Some control strategies have been proposed and validated in simulations using the average distance between the target and the drone as a performance metric. However, besides the distance metric, energy expenditure of the flight also plays an important role in assessing the overall performance of the flight. We propose a new methodology that introduces a new metric (energy expenditure), we compare existing methods on a large set of target motion patterns and present a comparison between the simulation and field experiments on proposed target motion patterns. The second challenge consists in developing a formation control algorithm that will allow fixed wing robots to provide a wide area coverage and to relay data in a wireless ad-hoc network. In such applications fixed wing drones have to be able to regulate an inter-drone distance. Their reduced maneuverability presents the main challenge to design a formation algorithm that will regulate an inter-drone distance. To address this challenge, we present a distributed control strategy that relies only on local information. Each drone has its own virtual agent, it follows the virtual agent by performing previously evaluated and selected target tracking strategy, and flocking interaction rules are implemented between virtual agents. It is shown in simulation and in field experiments with a team of fixed wing drones that using this distributed formation algorithm, drones can cover an area by creating an equilateral triangular lattice and regulate communication link quality between neighboring drones. The third challenge consists in allowing connectivity between independently moving ground users using fixed wing drone team. We design two distributed control algorithms that change drones' spatial arrangement and interaction topology to maintain the connectivity. We propose a potential field based strategy which adapts distance between drones to shrink and expand the fixed wing drones' formation. In second approach, market-based adaptation, drones distributively delete interaction links to expand the formation graph to a tree graph. In simulations and field experiments we show that our proposed strategies successfully maintain independently moving ground users connected. Overall, this thesis presents synthesis of distributed algorithms for fixed wing drones to establish and maintain wireless ad-hoc communication networks.