808 research outputs found
Optimal fault-tolerant placement of relay nodes in a mission critical wireless network
The operations of many critical infrastructures (e.g., airports) heavily depend on proper functioning of the radio communication network supporting operations. As a result, such a communication network is indeed a mission-critical communication network that needs adequate protection from external electromagnetic interferences. This is usually done through radiogoniometers. Basically, by using at least three suitably deployed radiogoniometers and a gateway gathering information from them, sources of electromagnetic emissions that are not supposed to be present in the monitored area can be localised. Typically, relay nodes are used to connect radiogoniometers to the gateway. As a result, some degree of fault-tolerance for the network of relay nodes is essential in order to offer a reliable monitoring. On the other hand, deployment of relay nodes is typically quite expensive. As a result, we have two conflicting requirements: minimise costs while guaranteeing a given fault-tolerance. In this paper address the problem of computing a deployment for relay nodes that minimises the relay node network cost while at the same time guaranteeing proper working of the network even when some of the relay nodes (up to a given maximum number) become faulty (fault-tolerance). We show that the above problem can be formulated as a Mixed Integer Linear Programming (MILP) as well as a Pseudo-Boolean Satisfiability (PB-SAT) optimisation problem and present experimental results com- paring the two approaches on realistic scenarios
Synchronization in complex networks
Synchronization processes in populations of locally interacting elements are
in the focus of intense research in physical, biological, chemical,
technological and social systems. The many efforts devoted to understand
synchronization phenomena in natural systems take now advantage of the recent
theory of complex networks. In this review, we report the advances in the
comprehension of synchronization phenomena when oscillating elements are
constrained to interact in a complex network topology. We also overview the new
emergent features coming out from the interplay between the structure and the
function of the underlying pattern of connections. Extensive numerical work as
well as analytical approaches to the problem are presented. Finally, we review
several applications of synchronization in complex networks to different
disciplines: biological systems and neuroscience, engineering and computer
science, and economy and social sciences.Comment: Final version published in Physics Reports. More information
available at http://synchronets.googlepages.com
Secure Integrated Routing and Localization in Wireless Optical Sensor Networks
Wireless ad hoc and sensor networks are envisioned to be self-organizing and
autonomous networks, that may be randomly deployed where no fixed infrastructure
is either feasible or cost-effective. The successful commercialization of such networks
depends on the feasible implementation of network services to support security-aware
applications.
Recently, free space optical (FSO) communication has emerged as a viable technology
for broadband distributed wireless optical sensor network (WOSN) applications.
The challenge of employing FSO include its susceptibility to adverse weather
conditions and the line of sight requirement between two communicating nodes. In
addition, it is necessary to consider security at the initial design phase of any network
and routing protocol. This dissertation addresses the feasibility of randomly deployed
WOSNs employing broad beam FSO with regard to the network layer, in which two
important problems are specifically investigated.
First, we address the parameter assignment problem which considers the relationship
amongst the physical layer parameters of node density, transmission radius
and beam divergence of the FSO signal in order to yield probabilistic guarantees on
network connectivity. We analyze the node isolation property of WOSNs, and its
relation to the connectivity of the network. Theoretical analysis and experimental
investigation were conducted to assess the effects of hierarchical clustering as well as fading due to atmospheric turbulence on connectivity, thereby demonstrating the
design choices necessary to make the random deployment of the WOSN feasible.
Second, we propose a novel light-weight circuit-based, secure and integrated routing
and localization paradigm within the WOSN, that leverages the resources of the
base station. Our scheme exploits the hierarchical cluster-based organization of the
network, and the directionality of links to deliver enhanced security performance including
per hop and broadcast authentication, confidentiality, integrity and freshness
of routing signals. We perform security and attack analysis and synthesis to characterize
the protocol’s performance, compared to existing schemes, and demonstrate its
superior performance for WOSNs.
Through the investigation of this dissertation, we demonstrate the fundamental
tradeoff between security and connectivity in WOSNs, and illustrate how the transmission
radius may be used as a high sensitivity tuning parameter to balance there
two metrics of network performance. We also present WOSNs as a field of study that
opens up several directions for novel research, and encompasses problems such as
connectivity analysis, secure routing and localization, intrusion detection, topology
control, secure data aggregation and novel attack scenarios
Reliable load-balancing routing for resource-constrained wireless sensor networks
Wireless sensor networks (WSNs) are energy and resource constrained. Energy limitations make it advantageous to balance radio transmissions across multiple sensor nodes. Thus, load balanced routing is highly desirable and has motivated a significant volume of research. Multihop sensor network architecture can also provide greater coverage, but requires a highly reliable and adaptive routing scheme to accommodate frequent topology changes. Current reliability-oriented protocols degrade energy efficiency and increase network latency. This thesis develops and evaluates a novel solution to provide energy-efficient routing while enhancing packet delivery reliability. This solution, a reliable load-balancing routing (RLBR), makes four contributions in the area of reliability, resiliency and load balancing in support of the primary objective of network lifetime maximisation. The results are captured using real world testbeds as well as simulations. The first contribution uses sensor node emulation, at the instruction cycle level, to characterise the additional processing and computation overhead required by the routing scheme. The second contribution is based on real world testbeds which comprises two different TinyOS-enabled senor platforms under different scenarios. The third contribution extends and evaluates RLBR using large-scale simulations. It is shown that RLBR consumes less energy while reducing topology repair latency and supports various aggregation weights by redistributing packet relaying loads. It also shows a balanced energy usage and a significant lifetime gain. Finally, the forth contribution is a novel variable transmission power control scheme which is created based on the experience gained from prior practical and simulated studies. This power control scheme operates at the data link layer to dynamically reduce unnecessarily high transmission power while maintaining acceptable link reliability
Utilizing ZigBee Technology for More Resource-efficient Wireless Networking
Wireless networks have been an essential part of communication in our daily life. Targeted at different applications, a variety of wireless networks have emerged. Due to constrained resources for wireless communications, challenges arise but are not fully addressed. Featured by low cost and low power, ZigBee technology has been developed for years. As the ZigBee technology becomes more and more mature, low-cost embedded ZigBee interfaces have been available off the shelf and their sizes are becoming smaller and smaller. It will not be surprising to see the ZigBee interface commonly embedded in mobile devices in the near future. Motivated by this trend, we propose to leverage the ZigBee technology to improve existing wireless networks. In this dissertation, we classify wireless networks into three categories (i.e., infrastructure-based, infrastructure-less and hybrid networks), and investigate each with a representative network. Practical schemes are designed with the major objective of improving resource efficiency for wireless networking through utilizing ZigBee technology. Extensive simulation and experiment results have demonstrated that network performance can be improved significantly in terms of energy efficiency, throughput, packet delivery delay, etc., by adopting our proposed schemes
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