Water Distribution Networks Resilience Analysis: a Comparison between Graph Theory-Based Approaches and Global Resilience Analysis

Water Resources Management - The structure and connectivity of infrastructure systems such as water distribution networks (WDNs) affect their reliability, efficiency and resilience. Suitable...     

Downlink cross‐layer scheduling strategies for long‐term evolution and long‐term evolution‐advanced systems

The most recent trend in the Information and Communication Technology world is toward an ever growing demand of mobile heterogeneous services that imply the management of different quality of service requirements and priorities among different type of users. The long‐term evolution (LTE)/LTE‐advanced standards have been introduced aiming to cope with this challenge. In particular, the resource allocation problem in downlink needs to be carefully considered. Herein, a solution is proposed by resorting to a modified multidimensional multiple‐choice knapsack problem modeling, leading to an efficient solution. The proposed algorithm is able to manage different traffic flows taking into account users priority, queues delay, and channel conditions achieving quasi‐optimal performance results with a lower complexity. The numerical results show the effectiveness of the proposed solution with respect to other alternatives. Copyright © 2013 John Wiley & Sons, Ltd.     

Performance evaluation of a reservation TDMA protocol for voice/data transmissions in a LEO satellite communication system

In this paper, the capability is investigated of a reservation TDMA‐based protocol to support constant bit rate and best‐effort traffics in Low Earth Orbit (LEO) satellite communication systems under typical propagation conditions. Differently from several previous papers on the same subject, we focus here on a communication channel affected by multipath fading and characterized by a high round trip delay. In our protocol, a higher priority is given to constant bit rate terminals with respect to best‐effort data terminals. The performance for constant bit rate and best‐effort terminals was derived by means of a suitable analytical approach and computer simulations. The results shown herein permits to evaluate the influence of the channel propagation conditions on the system performance. Moreover, they highlight that the reservation TDMA protocol exhibits a good behaviour for the communication channel under consideration and in comparison with a recent protocol based on the classical PRMA scheme. Copyright © 2003 John Wiley & Sons, Ltd.     

Cadenus: creation and deployment of end-user services in premium IP networks

Current trends in the information and communications technology industry clearly indicate the existence of a business requirement for a market-enabling technology that allows network operators to interact with users in a seamless, transparent manner for the sale and delivery of a wide range of services with guaranteed quality of service. In this context the need arises for the dynamic creation, configuration and delivery of services with QoS guarantees via the automated management of service level agreements. The aim of the Cadenus project is to bring theoretical and practical contributions to this area by defining a framework for the provisioning of advanced communication services in premium IP networks. Such networks might be characterized by a high degree of complexity, in terms not only of scale, but also of number of operators and technological heterogeneity. Our contribution is twofold, comprising both the design of the proposed framework and its actual implementation. An innovative approach was taken to framework design, based on the concept of mediation. With respect to the framework implementation, an example illustrating the realization of a virtual private network scenario is presented.     

Comparative analysis of yield optimized pulsed flip-flops

In this paper, the influence of random process variations on pulsed flip-flops is analyzed. Monte Carlo simulation results demonstrate that using transistor reordering and dual threshold voltage transistors timing, energy and energy-delay-product yields of more than 1.98, 1.62 and 1.99 times higher are obtained, without requiring architectural modifications and without increasing silicon area requirement. Several flip-flops optimized as described here are compared taking into account the effects due to random process variations and to environmental variations (caused by power supply voltage and temperature fluctuations). Obtained results show that among the compared circuits the Conditional Precharge Flip-Flop achieves the highest delay, energy and energy-delay-product yields.     

Structure and Morphology of PDI8‐CN2 for n‐Type Thin‐Film Transistors

A multiscale investigation of N,N′‐bis(n‐octyl)‐x:y, dicyanoperylene‐3,4:9,10‐bis(dicarboximide), PDI8‐CN2, shows the same molecular arrangement in the bulk and in thin films sublimated on SiO₂/Si wafers. Non‐conventional powder diffraction methods and theoretical calculations concur to provide a coherent picture of the crystalline structure. X‐ray diffraction (XRD) and atomic force microscopy (AFM) analyses of films of different thickness deposited at different substrate temperatures indicate the existence of two temperature‐dependent deposition regimes: a low‐temperature (room temperature) regime and a high‐temperature (80–120 °C) one, each characterized by different growth mechanisms. These mechanisms eventually result in different morphological and structural features of the films, which appear to be highly correlated with the trend of the electrical parameters that are measured in PDI8‐CN2‐based field‐effect transistors.     

Joint end-to-end loss-delay hidden Markov model for periodic UDP traffic over the Internet

Performance of real-time applications on network communication channels is strongly related to losses and temporal delays. Several studies showed that these network features may be correlated and exhibit a certain degree of memory such as bursty losses and delays. The memory and the statistical dependence between losses and temporal delays suggest that the channel may be well modeled by a hidden Markov model (HMM) with appropriate hidden variables that capture the current state of the network. In this paper, an HMM is proposed that shows excellent performance in modeling typical channel behaviors in a set of real packet links. The system is trained with a modified version of the Expectation-Maximization (EM) algorithm. Hidden-state analysis shows how the state variables characterize channel dynamics. State-sequence estimation is obtained by the use of Viterbi algorithm. Real-time modeling of the channel is the first step to implement adaptive communication strategies.     

An interconnected type-1 fuzzy algorithm for impulsive noise cancellation in multicarrier-based power line communication systems

This paper introduces an interconnected type-1 fuzzy algorithm which is trained by a modified version of the Scaled Conjugated Gradient method for impulsive noise cancellation in discrete multitone/orthogonal frequency-division multiplexing (DMT/OFDM)-based systems for broadband power line communications. The advanced algorithm makes use of the fuzzy systems capacity of dealing with uncertainties to reduce the presence of high-power impulsive noises while the DMT/OFDM technique copes with the severe intersymbol interference observed in power line channels. As a result, for a given error probability, a high number of bits can be allotted to each subchannel due to the signal-to-noise ratio enhancements achieved by the proposed fuzzy algorithm. The simulation results show that the novel fuzzy algorithm not only achieve a high data rate, but it also outperforms the standard impulsive noises techniques and other computational intelligence-based techniques, especially in the presence of additive and high-power impulsive noises.     

Detection and Mitigation of Impulsive Interference on OFDM Signals Based on Spectrum Sensing,Blanking and Symbol Retransmission

The increasing number of wireless devices and systems operating on the same area leads to significant interference problems that need to be solved. This paper deals with detection and mitigation of the interference generated by an impulsive noise source on an orthogonal frequency division multiplexing system. The idea proposed here is to overcome the interference problem by exploiting the transmission of two replicas of the symbol affected by interference, that are suitably combined at the receiver after a blanking operation of the corrupted samples. An energy detection based sensing scheme is used to reveal the presence of interference. The proposed method allows to efficiently remove the interference without affecting the useful information and exploiting profitably the diversity gain against noise through the soft combining approach. Performance in terms of bit error rate and throughput is compared with the case without mitigation and with the classical blanking method showing a significant improvement. The reduction of the transmission rate, due to the retransmissions, is well compensated by the improvement of the data reliability that leads to an increase of useful data correctly received.     

Efficient integration of isochronous and data bursty traffics in low earth orbit‐mobile satellite systems

This paper focuses on the radio resource management in low earth orbit‐mobile satellite systems (LEO‐MSSs) based on a time division multiple access (TDMA) air interface. A novel demand–assignment medium access control (MAC) protocol, named DRAMA+ (dynamic resource assignment multiple access—enhanced version), is proposed, where voice and Web traffic sources obtain transmission slots through requests sent by means of a random access phase. The round‐trip propagation delay (RTD) of LEO‐MSSs prevents an immediate feedback for each transmission attempt. Therefore, the main concern of the DRAMA+ scheme is to realize an efficient access phase. All the transmission requests successfully received at the satellite are managed by an on board scheduler. We have shown that DRAMA+ outperforms other techniques appeared in the literature in terms of voice quality, transmission delays for bursty data traffics and resource utilization. Moreover, a performance analysis of an ideal version of the DRAMA+ scheme has permitted us to prove the potentialities of the proposed DRAMA+ technique. Stability issues have been addressed as well as the impact on the DRAMA+ performance of the LEO satellite constellation RTD value. Copyright © 2002 John Wiley & Sons, Ltd.