Enrico Del Re

Characterization of user mobility in low earth orbit mobile satellite systems

Future mobile communication networks will provide a global coverage by means of constellations with nongeosynchronous satellites. Multi‐spot‐beam antennas on satellites will allow a cellular coverage all over the Earth. Due to the unstationarity of satellites a call may require many cell changes during its lifetime. These passages will be managed by inter‐beam handover procedures. This paper deals with the modeling of the user cell change process during call lifetime in Low Earth Orbit‐Mobile Satellite Systems (LEO‐MSSs). The analytical derivations presented in this study can be also applied to different mobility models provided that basic assumptions are fulfilled. This paper evaluates the impact of user mobility on the blocking performance of channel allocation techniques. Moreover, the handover arrival process towards a cell has been characterized by using a usual statistical parameter for stationary point processes. Finally, a performance analysis has been carried out on the basis of the classic teletraffic theory for telephone systems.

Sleep mode management in cellular networks: a traffic based technique enabling energy saving

Because of the environmental policies that pursue a significant reduction of global greenhouse gas and to the ambition of the network operators to keep under control operational and maintenance expenditures, energy efficiency has recently become one of the most relevant issues for present and future research activities. This contribution deals with the management of the base station sleep mode in a cellular network. The forecasting based sleep mode algorithm, justified by daily and weekly periodic behaviour of traffic, is presented and evaluated for general deployments of second and third generation cellular networks. The energy consumption of each base station and the area power consumption are the metrics, which are considered for our simulations. The results show a significant increase of the energy efficiency during low traffic periods with respect to the usual scenario, thanks to the adoption of the proposed strategy. The forecasting based sleep mode algorithm has been also compared with a strategy based on real-time measurements and the results show similar performances while the number of updates of the network configuration and the global complexity are decreased. Copyright

Constant modulus blind equalization based on fractional lower-order statistics

The presence of non-Gaussian ambient channel noise in wireless systems can degrade the performance of existing equalizers and signal detectors. In this paper, we investigate the problem of blind equalization in noisy communication channels by addressing the negative effects of heavy-tailed noise to the original constant modulus algorithm (CMA). We propose a new CM criterion employing fractional lower-order statistics (FLOS) of the equalizer input. The associated FLOS-CM blind equalizer, based on a stochastic gradient descent algorithm, is able to mitigate impulsive channel noise while restoring the constant modulus character of the transmitted communication signal. We perform an analytic study of the lock and capture properties of the proposed adaptive filter and we illustrate its improved convergence behavior and lower bit error rate through computer simulations with various types of noise environments that include the Gaussian and the alpha-stable.

A rate adaptive bit-loading algorithm for in-building power-line communications based on DMT-modulated systems

This paper deals with a variable rate discrete multitone modulation system for broadband power-line communications, based on the bit-loading algorithm proposed by Leke and Cioffi. In the proposed system a suitable least mean square channel estimator is considered, which is based on the insertion of a training sequence (TS). The proposed approach will be compared with the ideal channel estimates, showing its effectiveness. Moreover, different TS lengths will be compared. The system performance, expressed in terms of bit rate and bit-error rate, is derived by simulation with and without estimation errors. The propagation environment has been assumed as a frequency-selective multipath fading channel with additive colored Gaussian noise, according to the in-building networks model

Improving cellular network energy efficiency by joint management of sleep mode and transmission power

Energy efficiency is one of the main challenges to be faced by mobile communications in the near future. The growth of the mobile communications market which is boosted by the increasing penetration of smartphones and laptops requires an increase of the network capacity and, consequently, a great leap forward also for the infrastructures. In this scenario, in order to reduce the operative expenditures, the network operators pay attention to energy saving strategies that may also contribute to the reduction of greenhouse emissions. In this paper the exponential smoothing technique is applied to forecast traffic in a given area considering daily and weekly variations. The availability of a reliable prediction of the future traffic values allows the adaptation of macro base station transmission power and the introduction of a sleep mode for micro base stations and permits to guarantee the requested network capacity while saving energy consumption. Results show the effectiveness of traffic forecast technique for capacity prediction and the usefulness of the proposed algorithms for energy efficiency maximization, affording very good performance, very close to the optimum one.

A power allocation strategy using Game Theory in Cognitive Radio networks

The Cognitive Radio approach can be considered as a promising and suitable solution to solve in an efficient and flexible way the increasing and continuous demand of services and radio resources. This paper investigates how the adoption of a cognitive radio strategy can help in the coexistence problem of two wireless networks operating on the same spectrum of frequencies. A DVB-SH based satellite network will be considered as primary system, while an infrastructured wireless terrestrial network will constitute the cognitive radio based secondary system. In this work it will be presented a power resource allocation technique based on Game Theory, considering mainly Potential Games. We will show the proposed approach is suitable for distributed implementation, furthermore it provides performances comparable to an heuristic allocation method representing the optimum allocation. The comparison between these two resource allocation methods will be provided as result of this work.

Resource Allocation in Cognitive Radio Networks: A Comparison Between Game Theory Based and Heuristic Approaches

Cognitive Radio (CR) approach can be considered as a promising and suitable solution to solve in an efficient and flexible way the increasing and continuous demand of services and radio resources. This paper shows the potential benefits of the adoption of a cognitive radio strategy to the coexistence problem. Two different approaches have been considered: the first one is based on the Game Theory while the second one is formalized as a constrained maximum search and represent the optimum solution. The Game theory approach, suitable for a distributed implementation, provides performances comparable to the heuristic one which is a centralized optimization problem. The paper analyzes the performances of both approaches in terms of secondary rates and spectral efficiency provided by the secondary system.

Physical Layer Cryptography and Cognitive Networks

AbstractRecently the huge development of different and heterogeneous wireless communication systems raises the problem of growing spectrum scarcity. Cognitive radio tends to solve this problem by dynamically utilizing the spectrum. Security in cognitive radio network becomes a challenging issue, since more chances are given to attackers by cognitive radio technology compared to conventional wireless network. These weaknesses are introduced by the nature itself of cognitive radio, and they may cause serious impact to the network quality of service. However, to the authors’ knowledge, there are no specific secure protocols for cognitive radio networks. This paper will discuss the vulnerabilities inherent to cognitive radio systems, identify novel types of abuse, classify attacks, and analyze their impact. Security solutions to mitigate such threats will be proposed and discussed. In particular, physical payer security will be taken into account. A new modulation technique, able to encrypt the radio signal without any a priori common secret between the two nodes, was previously proposed by the authors (Mucchi et al. 2009, WPC 51, 67–80; Mucchi et al. 2010, WPC 53, 329–347). The information is modulated, at physical layer, by the thermal noise experienced by the link between two terminals. A loop scheme is designed for unique recovering of mutual information. This contribution improves the previous works by proposing the noise loop modulation as physical layer security technique for cognitive radio networks.

SALICE - Satellite-Assisted LocalIzation and Communication systems for Emergency services

This paper describes the SALICE (Satellite-Assisted LocalIzation and Communication systems for Emergency services) project, an Italian National Research Project which has been recently funded by the Italian Ministry of Research; the SALICE project aims at identifying the solutions which can be adopted in an integrated reconfigurable NAV/COM device and studying its feasibility in realistic scenarios. The first goal of the SALICE project is the definition of the baseline scenarios and system architecture which will allow the design of new and effective solutions for what concerns integrated communications and localization techniques, Software Defined Radio (SDR) NAV/COM devices, satellite and HAPS integration in the rescue services, heterogeneous solutions in the area of intervention (IAN, Incident Area Network). Particular attention will be devoted to the optimization of the resources management strategies and to the cooperative localization of rescue entities (persons and means) that intervene in emergency situations.

Robust spatial filtering of coherent sources for wireless communications

This paper addresses the inter-signal coherence problem in mobile communications applications where multipath parameters, such as path angle of arrival, must be estimated with an array of sensors operating in impulsive interference. We reduce the measured coherence by using the spatial smoothing approach to the structure of the measurement matrix while at the same time we mitigate the e!ects of the heavy-tailed background noise by employing a signed-power nonlinearity to the array data. The combination of these two processing modules gives rise to a family of robust smoothed subspace array processing methods based on fractional lower-order statistics (FLOS), which are able to identify all incident angles regardless of their correlation structure. The improved performance of the proposed techniques is demonstrated via Monte Carlo simulations ( 2000 Elsevier Science B.V. All rights reserved.