Enhancing Channel Estimation in Cognitive Radio Systems by means of Bayesian Networks

This paper proposes enhancements to the channel(-state) estimation phase of a cognitive radio system. Cognitive radio devices have the ability to dynamically select their operating configurations, based on environment aspects, goals, profiles, preferences etc. The proposed method aims at evaluating the various candidate configurations that a cognitive transmitter may operate in, by associating a capability e.g., achievable bit-rate, with each of these configurations. It takes into account calculations of channel capacity provided by channel-state estimation information (CSI) and the sensed environment, and at the same time increases the certainty about the configuration evaluations by considering past experience and knowledge through the use of Bayesian networks. Results from comprehensive scenarios show the impact of our method on the behaviour of cognitive radio systems, whereas potential application and future work are identified.

Emerging,Self-Management Functionality for Introducing Cognition in the Wireless,B3G World

The unparalleled evolution of wireless communications is reflected in the tremendous investments on research and development, targeted at the continuous introduction of innovations that could serve the information society. This has led to the coexistence and complementary exploitation of versatile, legacy and also emerging Radio Access Technologies (RATs). At the same time, the continuously varying environment/users requirements impose the adaptation of those technologies to external stimuli, through reconfiguration (reconsideration) of their infrastructure and/or operating parameters. One feasible option to tackle the increased complexity of such environments, is to design wireless infrastructures with learning capabilities, thus forming cognitive networks. Cognitive networks are able to retain information from their interactions with the environment and intelligently adapt to any requirements. A prerequisite to facilitate operability of cognitive networks is the development of novel management mechanisms, which need to, distributively (centralized approaches would get even more complex), evaluate changes in external conditions and determine the way in which the network will properly respond to them. To this effect, this paper presents a complete framework under which Cognitive Access Points (CgAPs) could be managed and analyzes the functionality of its entities. Moreover, it also provides an approach for managing Cognitive Wireless Network Segments (CgWNSs).

The Stochastic Quasi-chemical Model for Bacterial Growth: Variational Bayesian Parameter Update

We develop Bayesian methodologies for constructing and estimating a stochastic quasi-chemical model (QCM) for bacterial growth. The deterministic QCM, described as a nonlinear system of ODEs, is treated as a dynamical system with random parameters, and a variational approach is used to approximate their probability distributions and explore the propagation of uncertainty through the model. The approach consists of approximating the parameters’ posterior distribution by a probability measure chosen from a parametric family, through minimization of their Kullback–Leibler divergence.     

On the security of the Feng–Liao–Yang Boolean functions with optimal algebraic immunity against fast algebraic attacks

In the past few years, algebraic attacks against stream ciphers with linear feedback function have been significantly improved. As a response to the new attacks, the notion of algebraic immunity of a Boolean function f was introduced, defined as the minimum degree of the annihilators of f and f + 1. An annihilator of f is a nonzero Boolean function g, such that fg = 0. There is an increasing interest in construction of Boolean functions that possess optimal algebraic immunity, combined with other characteristics, like balancedness, high nonlinearity, and high algebraic degree. In this paper, we investigate a recently proposed infinite class of balanced Boolean functions with optimal algebraic immunity, optimum algebraic degree and much better nonlinearity than all the previously introduced classes of Boolean functions with maximal algebraic immunity. More precisely, we study the resistance of the functions against one of the new algebraic attacks, namely the fast algebraic attacks (FAAs). Using the special characteristics of the family members, we introduce an efficient method for the evaluation of their behavior against these attacks. The new algorithm is based on the well studied Berlekamp–Massey algorithm.     

Optimum frequency reuse in mobile telephony systems

The reason why cellular mobile telephony systems exist is that they allow frequency reuse. Dynamic allocation algorithms improve the network efficiency and the service quality. Dynamic allocation is closely related to the following instantaneous allocation problem: given a number of channels (frequencies), a cell structure and the number of calls to be accommodated in each cell, find the optimum allocation of channels to cells subject to restrictions concerning the distance of cells, where the same frequency can be reused. In this paper we formulate and solve this problem by showing that it can be reduced to a 0–1 programming problem. Finally we present results, and draw subsequent conclusions.     

A robustness approach to international sourcing

An important advantage of the use of international sourcing networks (i.e. selection of suppliers in various countries to support the demands of the firm's international factory network) is the resulting hedging power against real exchange rate changes in the international environment. Due to the uncertainty of future real exchange rate changes, the international manager wants to develop a sourcing network that is relatively insensitive (i.e. robust) to the potential changes of the macroeconomic parameters over a planning horizon. In our paper, we formally develop arobust approach to international sourcing. This approach develops the international supplier network in a way that adequately hedges the firm's performance against the worst contingency in terms of realizable real exchange rate shocks over a planning horizon. We present an algorithm to obtain theN best robust solutions (i.e. sourcing networks) to the international sourcing problem. Some computational results on the effectiveness of the approach are provided. We also demonstrate how the approach can be used to evaluate various sourcing strategies.     

Unitary treatment of infrared singularities

Infrared singularities are treated to all orders by a unitary approximation of the time-evolution operator. The method allows the renormalization of the ultraviolet divergencies. It has been tested in QED bremsstrahlung processes.     

Exploring the intra-frame energy conservation capabilities of the horizontal simple packing algorithm in IEEE 802.16e networks: an analytical approach

The power saving capabilities of the mobile devices in broadband wireless networks constitute a challenging research topic that has attracted the attention of researchers recently, while it needs to be addressed at multiple layers. This work provides a novel analysis of the intra-frame energy conservation potentials of the IEEE 802.16e network. Specifically, the power saving capabilities of the worldwide interoperability for microwave access downlink sub-frame are thoroughly studied, employing the well-known simple packing algorithm as the mapping technique of the data requests. The accurate mathematical model, cross-validated via simulation, reveals the significant ability to conserve energy in this intra-frame fashion under different scenarios. To the best of our knowledge, this is the first work providing intra-frame power-saving potentials of IEEE 802.16 networks. Additionally, this is the first study following an analytic approach.