Welfare Improvisation from the Receiving Waters of Urban Wastewater Systems in the Context of the Water Framework Directive

The compliance of wastewater authorities with the Water Framework Directive (WFD, 2000/60/EC) although may highly contribute to a “good” ecological status in aquatic ecosystems, is alleged to require disproportionally high costs in relevance to the anticipated benefits. This is mainly due to the limited yet research in the assessment of the economic welfare derived by the compliance with the WFD. In this light, the direct and indirect economic benefits emerged by the attaining of WFD are investigated. The wastewater treatment plant of Athens (Greece) is demonstrated as a comprehensive pilot case.     

User selection scheme with limited feedback processing and outdated CSI in multiuser relay networks

A new user selection strategy is investigated and analyzed in a multiuser relaying environment in the presence of co‐channel interference. The proposed selection scheme aims at avoiding unnecessary feedback load processing, in cases where a target threshold, in the received instantaneous signal‐to‐noise ratio, is exceeded. Assuming that perfect channel state information is available, closed‐form lower bound expressions are derived for the cumulative distribution function of the output signal to interference plus noise ratio. Moreover, the impact of outdated channel state information on the system's performance is also investigated. In addition, under the assumption of high signal‐to‐noise ratio conditions, simplified approximated expressions are also provided for the cumulative distribution functions of the output signal to interference plus noise ratio, which are employed to study the outage probability and bit error probability performance of the system. It is shown that with the proposed approach, a significant reduction in feedback load processing is achieved, with only a slight loss in performance. Copyright © 2016 John Wiley & Sons, Ltd.     

Performance analysis of a class of GSC receivers over nonidentical Weibull fading channels

The performance of a class of generalized-selection combining (GSC) receivers operating over independent but nonidentically distributed Weibull fading channels is studied. We consider the case where the two branches with the largest instantaneous signal-to-noise ratio (SNR), from a total of L available, GSC(2, L) are selected. By introducing a novel property for the product of moments of ordered Weibull random variables, convenient closed form expressions for the moments of the GSC(2,L) output SNR are derived. Using these expressions, important performance criteria, such as average output SNR and amount of fading, are obtained in closed form. Furthermore, employing the Pade/spl acute/ approximants theory and the moment-generating function approach, outage and bit-error rate performance are studied. An attempt is also made to identify the equivalency between the Weibull and the Rice fading channel, which is typically used to model the mobile satellite channel. We present various numerical performance evaluation results for different modulation formats and channel conditions. These results are complemented by equivalent computer simulated results which validate the accuracy of the proposed analysis.     

Diversity reception over generalized-K (KG) fading channels

A detailed performance analysis for the most important diversity receivers operating over a composite fading channel modeled by the generalized-K (Kg) distribution is presented. The Kg distribution has been recently considered as a generic and versatile distribution for the accurate modeling of a great variety of short term fading in conjunction with long term fading (shadowing) channel conditions. For this relatively new composite fading model, expressions for important statistical metrics of maximal ratio combining (MRC), equal gain combining (EGC), selection combining (SC) and switch and stay combining (SSC) diversity receivers are derived. Using these expressions and by considering independent but not necessarily identical distributed fading channel conditions, performance criteria, such as average output signal-to-noise ratio, amount of fading and outage probability are obtained in closed form. Moreover, following the moments generating function (MGF) based approach for MRC and SSC receivers, and the Pade approximants method for SC and EGC receivers, the average bit error probability is studied. The proposed mathematical analysis is complemented by various performance evaluation results which demonstrate the accuracy of the theoretical approach.     

Performance analysis of dual-diversity receivers over correlated generalised Gamma fading channels

The performance of dual-branch equal-gain combining (EGC) and maximal-ratio combining receivers operating over a composite correlated fading environment, modelled by the generalised Gamma (GG) distribution, is analysed. The moments of the output signal-to-noise ratio are derived in closed form for both types of receivers, and by employing the Pade approximants method, the average bit error probability is studied for a great variety of modulation schemes. Furthermore, based on the statistic of the product of two correlated GG random variables, a tight union upper bound for the outage probability of the EGC is obtained, whereas for the special case of Weibull fading a simpler bound is derived in closed form. The proposed mathematical analysis is complemented by various, numerically evaluated performance results, whereas simulations verify the correctness of the proposed analysis.     

Operationalizing sustainability in urban coastal systems: A system dynamics analysis

We propose a system dynamics approach for Ecologically Sustainable Development (ESD) in urban coastal systems. A systematic analysis based on theoretical considerations, policy analysis and experts' knowledge is followed in order to define the concept of ESD. The principles underlying ESD feed the development of a System Dynamics Model (SDM) that connects the pollutant loads produced by urban systems' socioeconomic activities with the ecological condition of the coastal ecosystem that it is delineated in operational terms through key biological elements defined by the EU Water Framework Directive. The receiving waters of the Athens Metropolitan area, which bears the elements of typical high population density Mediterranean coastal city but which currently has also new dynamics induced by the ongoing financial crisis, are used as an experimental system for testing a system dynamics approach to apply the concept of ESD. Systems' thinking is employed to represent the complex relationships among the components of the system. Interconnections and dependencies that determine the potentials for achieving ESD are revealed. The proposed system dynamics analysis can facilitate decision makers to define paths of development that comply with the principles of ESD.     

The bivariate generalized-Κ (ΚG) distribution and its application to diversity receivers

The correlated bivariate generalized-K (K_G) distribution, with not necessarily identical shaping and scaling parameters, is introduced and studied. This composite distribution is convenient for modeling multipath/shadowing correlated fading environments when the correlations between the signal envelopes and their powers are different. Generic infinite series expressions are derived for the probability density function (PDF), the cumulative distribution function (CDF) and the joint moments. Assuming identical shaping parameters, simpler expressions for the PDF, CDF and the characteristic function (CF) are provided, while the joint moments are derived in closed form. Furthermore, the PDFs of the product and ratio of two correlated K_G random variables are obtained. Capitalizing on these theoretical expressions for the statistical characteristics of the correlated K_G distribution, the performance analysis of various diversity reception techniques, such as maximal ratio combining (MRC), equal gain combining (EGC) and selection diversity (SD), over bivariate K_G fading channels is presented. For the SD, the outage probability is studied, while for the MRC and EGC the average bit error probability is obtained. The proposed analysis is accompanied by numerical results, clearly demonstrating the usefulness of the theoretical approach as well as the appropriateness of the K_G distribution to model multipath/shadowing fading channels.     

On the performance analysis of digital communications over generalized-K fading channels

The performance of digital communication systems over generalized-K (K/sub G/) fading channels is analyzed and evaluated. Novel closed form expressions for the SNR statistics, the average Shannon's channel capacity and the bit error rate (BER) are derived. These expressions are used to study important performance criteria such as the outage performance, the average capacity and the BER for a great variety of modulation formats in K/sub G/ fading channels. The proposed mathematical analysis is accompanied with various performance evaluation results, which demonstrate the usefulness of the proposed approach.