Anna Abbagnale

Gymkhana: A Connectivity-Based Routing Scheme for Cognitive Radio Ad Hoc Networks

The topology of a cognitive radio Ad Hoc network is highly influenced by the behavior of both licensed (primary) and unlicensed (secondary) users. In fact, the network connectivity could be impaired by the activity of primary users. This aspect has a significant impact on the design of routing protocols. We design a routing scheme for cognitive radio Ad Hoc networks, named Gymkhana, which is aware of the degree of connectivity of possible paths towards the destination. Gymkhana routes the information across paths that avoid network zones that do not guarantee stable and high connectivity. To this aim we use a mathematical framework, based on the Laplacian spectrum of graphs, that allows a comprehensive evaluation of the different routing paths of the cognitive radio network. Laplacian matrixes are used to compute the connectivity of the different network paths. Gymkhana uses a distributed protocol to collect some key parameters related to candidate paths from an origin to a destination. The parameters are fed into a basic mathematical structure which is used to compute efficient routing paths. Besides the basic idea of Gymkhana, the use of Laplacian matrixes to derive a closed formula to measure the path connectivity is another contribution of ours.

Performance analysis of IEEE 802.15.4 wireless sensor networks: An insight into the topology formation process

Topology formation is an important issue in a wireless sensor network. Performance parameters such as energy consumption, network lifetime, data delivery delay, sensor field coverage depend on the network topology. In this paper, we analyze the process of formation of a wireless sensor network according to the IEEE 802.15.4/ZigBee standards. We focus on both single-sink scenarios and multi-sink ones where: (i) we characterize the topology in terms of network depth and nodes distribution at different network levels; (ii) we analyze some network performance as a function of the number of sinks; (iii) we investigate the effects of some topology constraints on network performance; (iv) we study the effects of nodes mobility on the network formation. The whole study is performed by taking into account the specific features and recommendations of the IEEE 802.15.4/ZigBee standards; thus, our results can be used to configure IEEE 802.15.4/ZigBee procedures and set the related parameters, as a function of the desired application requirements.

Keeping the connectivity and saving the energy in the internet

Nowadays a big effort is spent to reduce the Internet energy consumption. Actual Internet topologies have space to power off some links and devices to reduce the energy consumed in off-peak periods still guaranteeing connectivity among terminals. In this work we leverage the algebraic connectivity of the graph modeling an ISP network in order to define the ESACON (Energy Saving based on Algebraic CONnectivity) algorithm. We then consider the network connectivity as a first target performance to be assured. To this aim we identify a metric based on the algebraic connectivity that, on one side, allows to switch off several links with the consequent significant energy saving and, on the other side, still preserves network connectivity and network performance for efficiently supporting the Internet traffic. We find that ESACON achieves better performance with respect to similar topology-aware approaches; moreover ESACON performance are comparable with ones of a complex traffic-aware solution.

Cross-layer network formation for energy-efficient IEEE 802.15.4/ZigBee Wireless Sensor Networks

In IEEE 802.15.4/ZigBee Wireless Sensor Networks (WSNs) a specific node (called the PAN coordinator or sink) controls the whole network. When the network operates in a multi-hop fashion, the position of the PAN coordinator has a significant impact on the performance: it strongly affects network energy consumption for both topology formation and data routing. The development of efficient self-managing, self-configuring and self-regulating protocols for the election of the node that coordinates and manages the IEEE 802.15.4/ZigBee WSN is still an open research issue. In this paper we present a cross-layer approach to address the problem of PAN coordinator election on topologies formed in accordance with the IEEE 802.15.4. Our solution combines the network formation procedure defined at the MAC layer by the IEEE 802.15.4 standard with a topology reconfiguration algorithm operating at the network layer. We propose a standard-compliant procedure (named PAN coordinator ELection -PANEL) to self-configure a IEEE 802.15.4/ZigBee WSN by electing, in a distributed way, a suitable PAN coordinator. A protocol implementing this solution in IEEE 802.15.4 is also provided. Performance results show that our cross-layer approach minimizes the average number of hops between the nodes of the network and the PAN coordinator allowing to reduce the data transfer delay and determining significant energy savings compared with the performance of the IEEE 802.15.4 standard.

Leveraging the Algebraic Connectivity of a Cognitive Network for Routing Design

In this paper, we consider the implications of spectrum heterogeneity on connectivity and routing in a Cognitive Radio Ad Hoc Network (CRAHN). We study the Laplacian spectrum of the CRAHN graph when the activity of primary users is considered. We introduce the cognitive algebraic connectivity, i.e., the second smallest eigenvalue of the Laplacian of a graph, in a cognitive scenario. Throughout this notion we provide a methodology to evaluate the connectivity of CRAHNs and consequently introduce a utility function that is shown to be effective in capturing key characteristics of CRAHN paths. This model provides a unique metric that captures network connectivity, path length, and impact of primary users. Moreover, the proposed metric penalizes paths where spectrum band switchings are highly probable. We design all the components of our routing framework, named Gymkhana, and we present a twofold performance verification: one from a topological perspective to show all the potentialities of the proposed routing approach, and the other considering network traffic to evaluate the performance in terms of end-to-end delay and packet delivery ratio.

ESOL: Energy saving in the Internet based on Occurrence of Links in routing paths

After the big Internet growing of the past decade, in the current decade a considerable effort is spent to reduce the Internet energy consumption. Actual Internet topologies have space to power off some links and devices in order to reduce energy consumed in off-peak periods still guaranteeing connectivity among terminals. In this paper we propose a methodology to identify less used links in the network in order to have the capability to switch off these network interfaces for energy saving purposes. We describe four different algorithms able to identify this set of links and we show the tradeoff between complexity, and the consequent execution time, and efficiency in powering off a great number of links. We find that, by using our solutions, it is possible to switch off a big percentage of links still keeping the network load under suitable thresholds and still guaranteeing topological characteristics of the resulting network topology.

Connectivity-Driven Routing for Cognitive Radio Ad-Hoc Networks

We design a routing scheme based on an extension of the algebraic connectivity for cognitive radio ad hoc networks. We observe that a cognitive radio network topology and its connectivity are highly influenced by the behavior of primary users. Even if the physical proximity of nodes would give rise to a connected topology, the primary user behavior could impact the network connectivity. In graph theory the second smallest Laplacian eigenvalue, i.e., the algebraic connectivity, has numerous relationships with the graph characteristics, including connectivity, diameter, mean distance of vertexes. We then propose to compute the algebraic connectivity in a cognitive scenario by deriving the average Laplacian matrix of the network, averaged over the random activity of the primary users, and compute the algebraic connectivity. On the basis of this mathematical model we build up an utility function which is shown to be effective for capturing some key characteristics of networks paths and can be used to compare them for routing purposes. We then design a routing scheme which, by modeling a path with a graph and its Laplacian, captures the connectivity characteristics of the path itself and suitably selects the best route in a uncertain and high variable connectivity scenarios.

Measuring the connectivity of a cognitive radio ad-hoc network

In Cognitive Radio Ad-Hoc Networks (CRAHN) the behavior of the primary users influences the secondary network connectivity and the relevant performance. The methodologies used to evaluate network connectivity have to be worked up to take into account this aspect. In this letter we propose the use of Laplacian matrix and its second smallest eigenvalue to measure the network algebraic connectivity of a CRAHN. We re-elaborate the Laplacian matrix in order to have in its second smallest eigenvalue a function of the primary users behavior expressed as an activity factor. In this way we are able to monitor the algebraic connectivity of CRAHNs. This metric can be a useful instrument for network planning, data routing and network maintenance. Performance results show how this methodology can be efficiently applied in this kind of networks.

Analysis of k-connectivity of a cognitive radio ad-hoc network

The cognitive radio paradigm will allow the formation of spontaneous wireless networks able to communicate in sectrum bands temporarily left free by licensed primary users. The behavior of the primary users has a high influence on the network connectivity and impacts the performance of the Cognitive Radio Network (CRN). When an ad-hoc network is established among cognitive radio nodes, not only the position of nodes but also the activity of the primary users impacts the network connectivity. The aim of this paper is twofold: on one side it provides a methodology to evaluate the

Constraining the network topology in IEEE 802.15.4

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