Francesco Delli Priscoli

The geometric dynamic channel allocation as a practical strategy in mobile networks with bursty user mobility

In this paper we refer to a specific class of Dynamic Channel Allocation (DCA) strategies, namely the interferencefree, timid, not-conditioned class. The main concern of this work is to verify if and to what extent strategies belonging to this class can offer better performance than Fixed Channel Allocation (FCA). The interest in this kind of strategies is motivated by their feasibility with current TDM technologies, the limited amount of information required to carry out channel assignments and their intrinsic stability. In this framework we present a simple, but very attractive DCA strategy, the so-called Geometric DCA (GDCA). A performance evaluation is carried out to compare some representative DCA strategies of the considered class, by using a user mobility model that accounts for the large fluctuations of the number of users in a cell coverage area expected in a microcellular environment. The effect of the non-null propagation time required by the information exchange in the DCA strategies is also taken into account. It emerges that the proposed GDCA allows better performance than more sophisticated strategies already proposed, at the expense of a frequency planning carried out only at network configuration. This is due to the ability of GDCA to exploit the a priori information to maintain a tight geometric packing of used carriers. The reported results also show that DCA strategies in the considered class cope with large and sudden traffic fluctuations remarkably better than the FCA scheme does and that the advantage becomes more evident as the burstiness of the user mobility process (hence of the offered traffic) increases.

Output regulation with nonlinear internal models

This paper addresses the problem of semi-global nonlinear output regulation for a class of nonlinear systems possessing a nonlinear internal model. It is shown that, under appropriate (and verifiable) hypotheses, the standard assumption that the feed-forward inputs needed to keep the zero error manifold invariant satisfy a linear differential equation can be weakened.

Design of a bandwidth-on-demand (BoD) protocol for satellite networks modelled as time-delay systems

Bandwidth-on-demand (BoD) access protocols address the problem of guaranteeing a high exploitation of the valuable satellite bandwidth in the presence of large amount of data traffic accessing the satellite network. The novelty of the proposed BoD scheme consists in the use of control theory concepts to model the satellite network as a time-delay system and to generate the bandwidth requests. The proposed scheme, based on the internal model control and on the Smiths principle, yields the following advantages: (i) when the network is not congested, it provides upper-bounds to the queue lengths and to the queuing delays of the satellite terminal buffers; (ii) it is capable of recovering from congested states; (iii) it is independent of the statistical characteristics of the traffic entering the satellite network; (iv) the requests are such that the satellite terminals have always enough traffic to use all the requested bandwidth (so that no bandwidth is wasted). The paper includes simulations showing the effectiveness of the proposed BoD scheme. The work underlying this paper has been performed within the GEOCAST project belonging to the fifth framework Information Society and Technology programme of the European Union.

Resource management for ATM-based geostationary satellite networks with on-board processing

This paper deals with medium access control (MAC) and congestion control protocols for ATM-based geostationary satellite networks, where some demand assignment multiple access (DAMA) functionalities are performed on-board. The proposed resource management has been designed for the lower priority ATM traffic categories, which have to adapt themselves to the traffic conditions. The novelties proposed in this paper consist of a resource management strategy based on two levels of aggregations of the virtual channel connections and of a DAMA algorithm for generating the terminal bandwidth requests exploiting control theory concepts. These two innovative features are combined with an existing congestion control algorithm and an existing DAMA algorithm for assigning the capacity based on terminal requests. The resulting resource management achieves the goals of avoiding on-board congestion situations, guaranteeing an efficient use of the satellite resources and limiting the on-board processing complexity. Software simulations have been performed with the OPNET tool, in order to test the effectiveness of the proposed protocols.

Effects of imperfect power control and user mobility on a CDMA cellular network

Code-division multiple-access (CDMA) is one of the major candidate access techniques for third generation systems. A great deal of effort has been devoted to the study of the capacity it can support. This paper presents analytical derivations which allow the determination of the link availability in the presence of user mobility and power control imperfections in a CDMA network; moreover, it provides the guidelines which permit the implementation of a simple and flexible simulation tool which is independent of the specific CDMA implementations. As a matter of fact, the reported concepts can be applied to any asynchronous CDMA system, i.e., they hold both for the American Standard IS-95 and for the European Community Standard developed in the framework of the RACE CODIT Project.

A cognitive future internet architecture

This Chapter proposes a novel Cognitive Framework as reference architecture for the Future Internet (FI), which is based on so-called Cognitive Managers. The objective of the proposed architecture is twofold. On one hand, it aims at achieving a full interoperation among the different entities constituting the ICT environment, by means of the introduction of Semantic Virtualization Enablers, in charge of virtualizing the heterogeneous entities interfacing the FI framework. On the other hand, it aims at achieving an inter-network and inter-layer cross-optimization by means of a set of so-called Cognitive Enablers, which are in charge of taking consistent and coordinated decisions according to a fully cognitive approach, availing of information coming from both the transport and the service/content layers of all networks. Preliminary test studies, realized in a home environment, confirm the potentialities of the proposed solution.

Improving Resilience of Interdependent Critical Infrastructures via an On-Line Alerting System

This paper illustrates the activities under development within the FP7 EU MICIE project. The project is devotedto design and implement an on-line alerting system, able toevaluate, in real time, the level of risk of interdependent Critical Infrastructures (CIs). Such a risk is generated by undesired events and by the high level of interconnection of the different infrastructures. Heterogeneous models are under development to perform short term predictions of the Quality of Service (QoS) of each CI according to the QoS of the others, to the level of interdependency among the Infrastructures, and according to the undesired events identified in the reference scenario.

A robust adaptive congestion control for communication networks with time-varying delays

This work presents a congestion control for high-speed networks in the single bottle-neck case with time-varying multiple delays, aimed at avoiding congestion by setting the rates of the traffic flows. The novelty of this paper is that the controller explicitly deals with saturated (i.e., non persistent) sources. The controller consists in a main controller based on classical control theory coupled with a controller based on fuzzy logic: the former works properly when the sources are not saturated; the latter provides a saturation compensation by setting an adaptive multiplicative gain which acts on the rate command. The scheme provides also robust stability to time-delay uncertainties. Simulations prove its effectiveness.

Effects of user mobility on the capacity of a CDMA cellular network

In the recent technical literature on cellular networks Code Division Multiple Access (CDMA) has received a large attention as a promising radio interface access technique. Many studies. are devoted to the capacity evaluation of the radio interface adopting CDMA, but seemingly none of them accounts for the variability of the user spatial density due to user mobility. This should be a concern especially in a microcellular environment, where it cannot be relied upon a significant spatial average over the radio coverage area of a Base Station. The major aim of this work is a preliminary assessment of the effects of “bursty” user mobility on the capacity of the CDMA radio interface. To this end. we introduce a user mobility model apt to describe large fluctuations of the number of users in a radio cell area. A reference model of a CDMA network is used to evaluate the effects of user mobility on the capacity for a wide range of the model parameters, by means of simulations accounting for shadowing, call attempt process, voice activity and antenna directivity and assuming perfect power control. We show that user mobility can remarkably affect the CDMA capacity, mainly because of the resulting highly bursty behaviour of self-noise. A simple traffic control scheme is devised to increase the capacity of the CDMA network, under a joint constraint on link availability, call blocking and call dropping probabilities. It is pointed out that the concepts introduced in this paper are independent of the specific CDMA implementation, i.e. they hold for any asynchronous CDMA based cellular network.

Resilient planning of PowerLine Communications networks over Medium Voltage distribution grids

In this paper a network planning problem aiming to enable underground Medium Voltage (MV) power grids to resilient PowerLine Communications (PLCs) is faced. The PLC network is used to connect PLC End Nodes (ENs) located into the secondary substations to the energy management system of the utility by means of PLC network nodes enabled as Access Points. An optimization problem is formulated, aiming to optimally allocate the Access Points to the substations and the repeaters to the MV feeders. A multi-objective optimization approach is used, in order to keep in balance the needs of minimizing the cost of equipment allocation and maximizing the reliability of PLC network paths. Resiliency and capacity constraints are properly modeled, in order to guarantee the communications even under faulted link conditions. As a byproduct, the optimization algorithm also returns the optimal routing. Simulations performed on a realistic underground MV distribution grid validate the proposed approach.