Abstract:

The increasing interest in radio over fibre systems in the last years has motivated the inclusion of a new subject devoted to their study in the recent master degree in telecommunication engineering at the Universidad Politecnica de Valencia. Basically, the operation of an hybrid fibre-radio system relies on using optical fibre networks to distribute the RF signals of current and future wireless communication systems. In such systems, the signals are distributed from a central exchange or office to the remote antenna base-stations via low-loss optical fibre links. The propagation of high-frequency subcarriers through dispersive and nonlinear optical fibres adds a new insight into fibre modelling, as analogue signals suffer from different effects than optical pulses as they propagate through the transmission medium. Computer simulations are useful techniques to analyze the performance of these systems, as the influence of different parameters can be addressed quickly. So practice-oriented virtual laboratories comprise 1/3 of the subject contents, where students can assess the theory of fibre-radio systems by means of the results and conclusions obtained from the simulations. Virtual labs are not actually real-world experiments in a physical laboratory but are simulations – mathematical models implemented on a computer. However, they are still very useful to provide learning experiences similar to their in-class analogues, can facilitate deep learning in model-based knowledge domains, and can enable learning without most of the overhead inherent in traditional lab experiments. To date most virtual labs available through Internet are based on Java applets. Java is a powerful tool to implement complex numerical calculations because of its high speed. On the other hand, Matlab has a wider deployment in telecommunication engineering due to its rich and powerful library of signal processing functions available. However, a disadvantage of Matlab is that a license is required to execute the simulation files. In this paper, the advantage of joining both simulation worlds is shown. Dispersive and nonlinear optical fibres were modelled in Matlab using the split-step Fourier method. This model was then used to implement several HTML and Java-based virtual labs of fibre-radio systems which are free accessible through Internet. As an example, the following virtual labs were developed: frequency response of dispersive and nonlinear fibres (carrier suppression effect), harmonic RF generation through phase-modulation to intensity-modulation conversion in optical fibres, and fibre-induced nonlinear distortions in multichannel systems. They can simply be executed from a web browser, whereas the Matlab functions run on a server at university where the license is installed. So students can access the virtual labs from any PC without the need of having a Matlab license, thus making distance e-learning more comfortable.

Keywords:

virtual laboratories, digital learning objects, online repository, e-learning, distance learning, optical.