In order to estimate the signal parameters accurately for mobile systems, it is necessary to estimate a system's propagation characteristics through a medium. Propagation analysis provides a good initial estimate of the signal characteristics. The ability to accurately predict radio-propagation behavior for wireless personal communication systems, such as cellular mobile radio, is becoming crucial to system design. Since site measurements are costly, propagation models have been developed as a suitable, low-cost, and convenient alternative. Channel modeling is required to predict path loss and to characterize the impulse response of the propagating channel. The path loss is associated with the design of base stations, as this tells us how much a transmitter needs to radiate to service a given region. Channel characterization, on the other hand, deals with the fidelity of the received signals, and has to do with the nature of the waveform received at a receiver. The objective here is to design a suitable receiver that will receive the transmitted signal, distorted.due to the multipath and dispersion effects of the channel, and that will decode the transmitted signal. An understanding of the various propagation models can. actually address both problems. This paper begins with a review of the information available on the various propagation models for both indoor and outdoor environments. .The existing models can be classified into two major classes: statistical models and site-specific models. The main characteristics of the radio channelsuch as path loss, fading, and time-delay spreadare discussed. Currently, a third alternative, which includes many new numerical methods, is being introduced to propagation prediction. The advantages and disadvantages of some of these methods are summarized. In'addition, an impulse-response characterization for the propagation path is also presented, including models for small-scale fading. Finally, it is shown that when two-way communication ports can be defined for a mobile system, it is possible to use reciprocity to focus the energy along the direction of an intended user without any explicit knowledge of the electromagnetic environment in which the system is operating, or knowledge of the spatial locations of the transmitter and the receiver.

Abstract-Nowadays, the Web has revolutionized our vision as to how deliver courses in a radically transformed and enhanced way. Boosted by Cloud computing, the use of the Web in education has revealed new challenges and looks forward to new aspirations such as MOOCs (Massive Open Online Courses) as a technology-led revolution ushering in a new generation of learning environments. Expected to deliver effective education strategies, pedagogies and practices, which lead to student success, the massive open online courses, considered as the "linux of education", are increasingly developed by elite US institutions such MIT, Harvard and Stanford by supplying open/distance learning for large online community without paying any fees, MOOCs have the potential to enable free university-level education on an enormous scale. Nevertheless, a concern often is raised about MOOCs is that a very small proportion of learners complete the course while thousands enrol for courses. In this paper, we present LASyM, a learning analytics system for massive open online courses. The system is a Hadoop based one whose main objective is to assure Learning Analytics for MOOCs' communities as a mean to help them investigate massive raw data, generated by MOOC platforms around learning outcomes and assessments, and reveal any useful information to be used in designing learning-optimized MOOCs. To evaluate the effectiveness of the proposed system we developed a method to identify, with low latency, online learners more likely to drop out.

Abstract-Current marine wireless communication systems used for monitoring applications based on buoys suffer from lots of weakness. Many research works concern the design and development of new technological applications to improve marine communications. Particularly, a wireless communication system based on WiMAX standard at the 5.8 GHz band (license-exempt band) could be a good candidate. As an initial task, a propagation channel measurement campaign in maritime environments was carried out to investigate the impact of the wireless channel in different situations. This work provides large scale path loss measurements over sea around urban environments. In particular, a radio link between a buoy and a ship at 5.8 GHz is studied. NLOS (Non-Line-Of-Sight) paths are investigated in depth and they are compared to LOS (Line-Of-Sight) paths. The designed measurement system is described and the experimental measurements are shown. An empirical model is obtained using these experimental data and the key wireless channel parameters are analyzed. In addition, the empirical model is compared to the free space and two-ray theoretical models. This investigation is useful, among others, for planning Worldwide Interoperability for Microwave Access (WiMAX) networks offshore around these challenge environments.Propagation channel measurements; Sea; WiMAX; urban environments;

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