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Abstract: In Cognitive Radio (CR) systems, the fluctuating nature of the available frequency resource due to Primary Users (PUs) activity necessitates the introduction of admission and eviction measures at the CR system if a guaranteed Quality of Service (QoS) is required by Real Time (RT) Secondary Users (SUs). This problem has been recently addressed in the literature with simplified assumptions that might become unrealistic in practical system setups. In this paper, we tackle the problem of admission and eviction control of RT SUs in multiple-user Orthogonal Frequency Division Multiple Access (OFDMA) CR systems and propose new solutions that are practical and efficient at the same time. In particular, we propose three different ways to install a Resource Buffer Zone (RBZ) at the time of admission to limit future call drops resulting from fluctuating PU activity. We also study the effect of PU activity on the feasibility of the resource allocation problem and propose three different methods to resolve system outages once they occur. Numerical results obtained through Monte Carlo simulations demonstrate the efficacy of the proposed techniques. [Copyright &y& Elsevier]

Abstract: Low-frequency narrowband (LF NB) power line communications (PLC) is an old data-communication concept that has received renewed interest in industry, standardization, and academia for its potential to become an important element of the communication infrastructure supporting Smart Grid applications. In this paper, dedicated to Prof. Johannes Huber on the occasion of his 60th birthday, we review and discuss channel modeling and cooperative coding methods for LF NB PLC systems operating in low-voltage access networks. [Copyright &y& Elsevier]

Automatic modulation recognition (AMR) enables the detection of different data-transmission formats sharing the same frequency band. One such band is the European 868 MHz band that is dedicated for short-range devices. Recently, an AMR method that applies a feature-based tree has been proposed for this band. In this paper, we present alternative feature-based classifiers that enable a more accurate AMR. In particular, we propose the use of classification tree and random forest classifiers, and we devise an extended set of features for the modulation classification problem at hand. Through simulation experiments we demonstrate a significant improvement in recognition success rate for typical transmission types in the 868 MHz band. [ABSTRACT FROM AUTHOR]

The placenta is the interface between the fetus and the mother and is vital for fetal development. Ultrasound elastography provides a non-invasive way to examine in vivo the stiffness of the placenta; increased stiffness has previously been linked to fetal growth restriction. This study used a previously developed dynamic elastography method, called shear wave absolute vibro-elastography, to study 61 post-delivery clinically normal placentas. The shear wave speeds in the placenta were recorded under five different low-frequency mechanical excitations. The elasticity and viscosity were estimated through rheological modeling. The shear wave speeds at excitation frequencies of 60, 80, 90, 100 and 120 Hz were measured to be 1.23 ± 0.44, 1.67 ± 0.76, 1.74 ± 0.72, 1.80 ± 0.78 and 2.25 ± 0.80 m/s. The shear wave speed values we obtained are consistent with previous studies. In addition, our multi-frequency acquisition approach enables us to provide viscosity estimates that have not been previously reported. [ABSTRACT FROM AUTHOR]