Dimitrios Zevgolis

Site-specific validation of indoor RF models for commercial propagation topologies at 2.4 GHz

This paper features a site-specific validation of indoor RF models for a commercial topology with an installed Wi-Fi system operating at 2.4 GHz (802.11g protocol). Based on extensive measurements acquired at the Athens International Airport, the efficiency of existing indoor RF models was validated in terms of signal prediction. Usage of different APs as transmitters allowed for more accurate results. Our work confirms the practical significance of the One-Slope model that calculates measurement-based values for the path loss exponent. These values are very useful for further studies of such complex indoor propagation environments at 2.4 GHz. In addition, it provides a numerical correction to the original formula of the ITU indoor RF model for commercial topologies at 2.4 GHz, with significantly increased precision in its predictions for all APs.

The alpha-lambda-mu-eta: A General Fading Distribution

In this paper, a general fading model for wireless communications is introduced describing the nonlinearity, and at the same time the non-homogeneous nature of the propagation medium. Namely, the a - lambda - mu - eta includes the a - mu , the lambda - mu, the eta - mu, the gamma, the exponential, the Weibull, the Hoyt, the Nakagami-m, the Rayleigh, and the one-sided Gaussian distributions as special cases. Field measurements and Monte Carlo simulation have been used to validate the proposed distribution. An outperformance has been shown among the widely known fading distributions by fitting to the experimental data.

Seniors' experiences with online banking

Older adults are the fastest growing segment of the population worldwide. This paper presents a evaluation of the user experience of two online web-banking sites from an older users point of view. We therefore conducted a usability testing employing 12 older participants, in order to analyze the needs and issues faced by this user group when performing real-world tasks. The study involved six tasks which users were required to complete within a specific time. Most of the participants were interested in learning to use online banking. Our results show that older persons do not find web-banking sites easy or user-friendly. Our qualitative findings revealed that both of the web-banking sites we examined presented problems. Implications for the future include the need to redesign bank websites so as to include guidelines and other suggestions made in this study.

Exploring users' experience with e-reading devices

New e-book readers and multifunctional mobile tablet devices are currently emerging, so bringing about a transition from printed to the electronic books. It is important to learn how usable these mobile devices are, by testing them on real users from various backgrounds. The paper presents a study which explores the perceived usability of two electronic reading devices, one dedicated reader and one multifunctional device. More specifically, the study employs eight tasks which users were required to complete within a specific time with two devices. Our results show that users functioned better on the multifunctional device in terms of performance measures, such as navigation, task difficulty and satisfaction.

HOW DO WE VISUALIZE MOBILE DEVICES’ CONTENT FORINEXPERIENCED USERS: A TASK FOR DESIGNERS

The purpose of the present study concerns the examination of a scenario involving the visualizing of content at mobile devicesplatforms and their respective applications. The scenario follows certain design principles that cater for interaction with inexperienced users within the interface of mobile devices. The visual design of an artifact obviously influences the way in which a user will interact with it. Gestalt laws and principles form one possible framework for the collection of helpful design guidelines. Based on field research, a prototype has been developed according to these principles. The results of a evaluation by users on the proposed visualization of content, are finally discussed.

An example of multimedia application for introducing renewable energy sources (RES) in an office environment

The creation of a simple or an interactive multimedia (MM) system can improve the presentation of a project and, in the case of the conservation of energy, it can highlight the numerous possibilities of the RES and help non-expert users be acquainted with them. The use of text, graphics, images, animations, video, and sound provides a more impressive and more complete way of presentation. This paper focuses on the development and implementation of an MM application for the saving of energy in a working place through the use of photovoltaic elements, a wind generator and geothermal heat exchanger. In particular, the mentioned RES, the MM applications together with all the special features that safeguard their proper function are illustrated and included in the present application. The study reveals: - The importance of RES. - The appropriateness of the MM presentation for informing potential users. - The appropriateness of the MM application in physics classes related to RES resources and RES exploitation.