Mihael Mohorcic

Trends in the development of communication networks: Cognitive networks

One of the main challenges already faced by communication networks is the efficient management of increasing complexity. The recently proposed concept of cognitive network appears as a candidate that can address this issue. In this paper, we survey the existing research work on cognitive networks, as well as related and enabling techniques and technologies. We start with identifying the most recent research trends in communication networks and classifying them according to the approach taken towards the traditional layered architecture. In the analysis we focus on two related trends: cross-layer design and cognitive networks. We classify the cognitive networks related work in that mainly concerned with knowledge representation and that predominantly dealing with the cognition loop. We discuss the existing definitions of cognitive networks and, with respect to those, position our understanding of the concept. Next, we provide a summary of artificial intelligence techniques that are potentially suitable for the development of cognitive networks, and map them to the corresponding states of the cognition loop. We summarize and compare seven architectural proposals that comply with the requirements for a cognitive network. We discuss their relative merits and identify some future research challenges before we conclude with an overview of standardization efforts.

Routing in ISL networks considering empirical IP traffic

Next-generation satellite networks are expected to provide a variety of applications with diverse performance requirements, which will call for the development of adaptive routing procedures supporting different levels of services. In this paper, we propose traffic class dependent (TCD) routing, which has the potential to differentiate between traffic classes using different optimization criteria in route calculation. The performance of TCD routing is evaluated for different traffic scenarios using an empirical traffic source model derived from the real backbone Internet traffic trace and compared with results obtained with equivalent Poisson traffic as a reference point. In addition, TCD routing is compared with a simple single service routing procedure, which does not make any distinction between traffic classes. Performance analysis, in terms of average packet delay, normalized data throughput, and normalized link load, reveals improved routing resulting from traffic class differentiation, regardless of the traffic scenario considered. The performance measures based of aggregate traffic flow show no significant difference between routing of empirical and equivalent Poisson traffic.

Adaptive routing for packet-oriented intersatellite link networks: performance in various traffic scenarios

Regular mesh topologies typical for satellite communication networks comprised of intersatellite links provide high network flexibility and reliability, but due to dynamic changing of traffic load and interorbit link distance variation, adaptive routing is an absolute requirement for optimizing the network utilization. In this article, we address adaptive routing in the intersatellite link (ISL) segment of nongeostationary packet-switched satellite communication systems, focusing on the relative impacts of traffic load and propagation delay on the link cost. We consider four reference traffic flow scenarios with different levels of traffic concentration. he network performance is evaluated in terms of routing performance measures important from both the end user and the network operator perspectives. Using an ISL network simulator, we reveal some intrinsic effects of the selected constellation and effects introduced with different assumptions regarding the traffic model.

Demographically weighted traffic flow models for adaptive routing in packet-switched non-geostationary satellite meshed networks

In this paper, a performance analysis of adaptive routing is presented for packet-switched inter-satellite link (ISL) networks, based on shortest path routing and two alternate link routing forwarding policies. The selected routing algorithm and link-cost function are evaluated for a low earth orbit satellite system, using a demographically weighted traffic flow model. Two distinct traffic flow patterns are modelled: hot spot and regional. Performance analysis, in terms of quality of service and quantity of service, is derived using specifically developed simulation software to model the ISL network, taking into account topology adaptive routing only, or topology and traffic adaptive routing.

Airborne Base Stations for Emergency and Temporary Events

This paper introduces a rapidly deployable wireless network based on Low Altitude Platforms and portable land units to support disaster-relief activities, and to extend capacity during temporary mass events. The system integrates an amalgam of radio technologies such as LTE, WLAN and TETRA to provide heterogeneous communications in the deployment location. Cognitive radio is used for autonomous network configuration. Sensor networks monitor the environment in real-time during relief activities and provide distributed spectrum sensing capacities. Finally, remote communications are supported via S-band satellite links.

Performance evaluation of adaptive routing algorithms in packet-switched intersatellite link networks

This paper addresses the performance evaluation of adaptive routing algorithms in non-geostationary packet-switched satellite communication systems. The dynamic topology of satellite networks and variable traffic load in satellite coverage areas, due to the motion of satellites in their orbit planes, pose stringent requirements to routing algorithms. We have limited the scope of our interest to routing in the intersatellite link (ISL) segment. In order to analyse the applicability of different routing algorithms used in terrestrial networks, and to evaluate the performance of new algorithms designed for satellite networks, we have built a simulation model of a satellite communication system with intersatellite links. In the paper, we present simulation results considering a network-uniform source/destination distribution model and a uniform source–destination traffic flow, thus showing the inherent routing characteristics of a selected Celestri-like LEO satellite constellation. The updates of the routing tables are centrally calculated according to the Dijkstra shortest path algorithm. Copyright

Alternate link routing for traffic engineering in packet-oriented ISL networks

The implementation of a satellite communication network consisting of intersatellite links provides a highly interconnected backbone in the space segment, increasing the network flexibility and reliability, while, on the other hand, introducing numerous issues related to network dimensioning, efficient resource management, adaptive routing, etc. In this paper we study two forwarding policies based on alternate link routing (ALR) and compare their performance with that of a simple forwarding policy employing shortest path routing (SPR) without options. All forwarding policies compared in this study are operating on routing tables calculated with the Dijkstra shortest path algorithm, capable of adapting to traffic load and propagation delay on the links through the appropriately selected link cost metric. Using an ISL network simulator, we demonstrate that both ALR forwarding policies can efficiently handle traffic load sharing among alternative routes, significantly reducing peak values of link load which is a central goal of ISL network dimensioning.

Adaptive Coding and Modulation for Mobile Wireless Access Via High Altitude Platforms

In this paper we are concerned with broadband wireless access via high altitude platform system, providing the Internet access and broadband multimedia services to passengers equipped with WLAN terminals connecting through a collective terminal mounted on the train. The main challenge in such scenario is the development of efficient and reliable radio interface for the broadband communication link in the mobile wireless access segment. We are focusing on performance analysis of the adaptive coding and modulation scheme in the communication link between a high altitude platform and a collective terminal on-board moving train. In order to increase the reliability of the communication system in a fading environment we also exploit space and platform diversity. The proposed approach significantly increases the throughput of the wireless access system, while bit error rate remains below the target value regardless of the considered propagation environment.

Exposing real world information for the web of things

In this paper, we propose SemSense architecture for collecting real world data from a physical system of sensors and publishing it on the Web, thus contributing to the Web of Things. SemSense comprises of four components: (1) the data collection component, (2) the storage component (3) the semantic enrichment component and (4) the publishing component, which are described and implemented for an existing deployment of a sensor network. Through these components, the real world data is collected from the physical devices, processed, equipped with semantic information and published on the Web. The paper addresses challenges of efficiently collecting data and meta-data from sensors and publishing it following the linked data principles.

Evaluation of Wavelength Requirements for Stratospheric Optical Transport Networks

This paper addresses the concept of optical transport network based on high altitude platforms (HAPs) flying in lower stratosphere and equipped with optical communications payload. The stratospheric transport network is formed of optical links between HAPs and optical backhaul uplinks and downlinks between HAPs and ground stations (GSs) hosting gateways to the backbone network. In order to consider limitations of free space optics (FSO) for the dimensioning of stratospheric optical transport network (OTN), we investigate the physical layer aspects for a DWDM based optical interplatform link (IPL). Taking into account the physical constraints imposed by FSO, we estimate the number of wavelengths required for full interconnectivity without wavelength conversions. We are using an analytical approach for bus and full mesh regular topologies, and a numerical approach for circumcircled star, ring and star regular topologies. We also evaluate the performance of a representative network with irregular topology using different routing and wavelength assignment algorithms. We show that the number of wavelengths needed to achieve full interconnectivity strongly depends on the physical topology of the network, and that adaptive routing yields better overall performance of the network compared to fixed and fixed alternate routing. The analysis also shows that resources in realistic network topologies tend to be used very inefficiently, which could be improved by traffic engineering solutions or wavelength conversions.