Active Learning of Radiocommunication Systems with the ... - wseas.us

Recent Researches in Educational Technologies

Active Learning of Radiocommunication Systems with the Help of Radio Planning Tools ˜ M. J. MADERO-AYORA, M.A. SARMIENTO-VEGA, J.J. MURILLO-FUENTES, L. SALAMANCA-MINO Universidad de Sevilla Dept. Teor´ıa de la Se˜nal y Comunicaciones Escuela T´ecnica Superior de Ingenieros, Camino de los Descubrimientos s/n, 41092 Sevilla, SPAIN [email protected] Abstract: In this paper, two exercises are proposed in order to promote the active learning of radiocommunication systems in the framework of a graduate or master program. These exercises are based on the use of Xirio Online, a web-based tool for the design of radiocommunication networks that allows a free access mode. This software is presented as a flexible and comprehensive tool to support the teaching of different concepts on radio propagation, communications systems, radio planning and the basis of radiocommunication standards. It provides a wide range of wireless technologies, adjustable parameters and types of simulations, similar to any professional tool, while being an affordable alternative for academic institutions. Although the free-access mode only allows low-resolution calculations, it is not an obstacle to present practical cases to the students that enable a better learning. Key–Words: radio planning, educational software tool, fixed service radio link, cellular systems, radio broadcasting.

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Introduction

Furthermore, the computation of the methods must be theoretically presented to teach the students the most important concepts involved. The radio engineer normally uses some software tool to run the algorithms. These software tools help the engineer in the radio planning and deployment of a system. Therefore, the study of radiocommunication systems should not be made from a theoretical point of view only [4]. Although this theoretical study is essential, since it provides the foundations to understand the real problem and to solve practical cases, the students should know the software tools that are employed for the radio planning by professionals [5]. Radio planning software tools carry out simulations of radio propagation, coverage of a radio link, cell planning, traffic studies,. . . These applications use elevation maps (topographic or urban) and different radio propagation models to produce accurate results. Therefore, they are useful tools that allow the students to evolve in the reasonings and to find the solution to different cases. In this way, students are involved in an active learning process which helps them getting a better understanding of all the concepts, at the same time that serves to motivate them. However, the problem faced by lecturers nowadays is the unfeasibility to use these applications for simulation in the classroom due to their usually expensive licenses, as it is the case of the softwares ICS or

Since 1895, with the first radio transmission, the technologies for wireless communications have developed at a rapid pace [1]. They have marked the current technological development and have favored what is known as “information society”. Nowadays, it is possible to be connected anywhere around the globe, and to access any information in a few seconds. Therefore, wireless communication systems are essential in our present society. The International Telecommunication Union, national agencies, companies, research groups,... provide a vast set of laws, methods and recommendations on every topic of propagation. These tools are then exploited in the radio planning of every radio system; including cellular communications, broadcasting, wireless local area network, etc. For the design of these systems, it is necessary to study different topics: radio propagation, radio links and cellular communication systems, among others. Theory of radio propagation and radio planning is difficult to understand as it is grounded on empirical knowledge. Hence, this theory usually translates into a set of recipes. The role of the radio engineer is twofold. First, the correct method or recipe has to be chosen according to the characteristics of the system. Then, the recipe or method has to be run. As a result, the radio engineer needs a solid knowledge of the theory and methods [2, 3].

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• Several types of simulations that allow to create different scenarios and network topologies.

Atoll. In this paper, it is proposed to use the software Xirio Online, which is an excellent option for practical teaching because it provides a free access mode keeping characteristics of a professional tool. It will be shown that Xirio Online is a good alternative to expensive commercial applications in the framework of a graduate or master program. The remaining of the paper is structured as follows. Throughout Section 2, the possibilities of the software Xirio Online are enumerated. In Section 3, the utility of the simulation software as a support to the theoretical learning is set out and then, two practical examples are developed. Finally, the conclusions drawn are given in Section 4.

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• A broad range of technologies can be adopted: public (GSM, DCS, UMTS, LTE, . . . ) and private mobile communications systems (PMR, TETRA, . . . ), radio broadcasting systems (TV, DVB-T, FM, DAB, DVB-H, . . . ), broadband access systems (LMDS, WiMAX, WiFi, . . . ), etc. • A wide range of adjustable parameters, such as transmission power, sensitivity, antenna type, . . . • A powerful computation engine, updated with the most widely-used propagation methods, such as those coming from Recommendations of the Radiocommunication Section of the International Telecommunication Union (ITU-R) and semi-empirical models like Okumura-Hata or COST-231.

Xirio Online

Xirio Online is a web-based tool developed by the Spanish company Aptica [6]. It is composed by two modules with different functionality. The main module, PlanningTool, is a generic radio planning tool that allows different types of radio electrical coverage simulations for a wide range of wireless technologies. Xirio Online offers also the possibility to publish and share the simulated results with other users by means of the module SharePlace.

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For each of the selected technologies, the software applies default settings with the suggested transmitter and receiver parameters and the recommended computation method. Nevertheless, these settings can be modified by the user so that the flexibility of the simulation is almost unlimited. In addition to this, it is worth noticing that it is possible to freely access to results published by professional users that advertise their services in this way. This feature is interesting from the lecturer’s point of view, since the student can complement its training by studying professional designs and achieve a clearer notion of the magnitudes and characteristics employed in practice. Therefore, Xirio Online offers a wide range of features that make it an interesting and useful tool for lecturers. To better illustrate the utility of this software, a brief description of the workspace and tools of Xirio Online will be made and the different stages that must be followed to perform the simulations will be presented. However, we should not forget the restrictions imposed by the free access to Xirio: the resolution for the calculations will be limited (only altimetry maps with resolution 400 m are considered) and the results can be stored in the platform only for three days, after which the studies need to be computed again to analyze their results. Also, some studies of radio link quality cannot be performed.

Features

Xirio Online is a professional radio planning tool that follows a commercial pay-per-use model on the Internet. Similarly to other online applications, Xirio is based on a slim client that provides users with immediate and secure access to their information and services from any location and just requiring an Internet connection. As the use of the Internet becomes massive, there is an increasing acceptance of this kind of tools, mainly amongst young people. This fact, together with the possibility of performing free lowresolution calculations, make Xirio Online a useful software for teaching. Among its features, it is possible to highlight the following: • Simplicity of use, which allows an intuitive and brief learning process that is supported by a quite comprehensive online help. • The database of digital cartography is provided by the online platform, without being necessary to store large files in the user’s computer. This database includes altimetry, elevation, tridimensional urban and morphographic maps, and all of them can be combined with satellite photographs for visualization purposes (Fig. 1).

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Description of the workspace and tools

Fig. 2 shows how the workspace of Xirio Online is distributed. The main element is the cartographic viewer, where the maps and other elements such as

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Figure 2: Distribution of the workspace in Xirio Online.

Figure 1: Example of the radio electrical coverage of a transmitter illustrated over a satellite view of the area under study.

• Profile: A transmitter and a receiver with fixed geographic coordinates take part in this kind of study. The result of the simulation will be the signal level received for the propagation path connecting both elements. By default, such level will be plotted in a different color according to the clearance of the first Fresnel zone. In addition to this, a graph of the profile (see Fig. 3) and a report are provided, which can be printed in the paid version of the software.

transmitters, receivers, points of interest, . . . are represented together with the radio coverage footprints. This part of the workspace is based on the Google Maps viewer and, therefore, inherits its simplicity and facilitates the navigation through the maps. The toolbar allows to manage the studies, results, visualization users, templates, etc. It is interesting to know the functionality of each available tool in order to take better advantage of the software. For instance, under certain circumstances, tools to calculate distance, to calculate the orographic profile between two points or to consult the altitude of a location can be found of great usefulness. Other parts in the workspace are:

By means of this type of study, it is possible to evaluate the feasibility of a fixed service terrestrial radio link, calculating its rates of availability and error performance. In order to do it, the selected calculation method should be that of the ITU-R P. 530 Recommendation [7], which includes losses due to free space propagation, diffraction, reflections, rain attenuation, absorption by atmospheric gases, and an estimation of the statistics in reception. Despite the free version of Xirio allows to set all the parameters for a study of availability and fidelity, the results provided correspond to a demo digital hop instead of the designed one. Therefore, it is suggested to analyze radio links just in terms of the signal levels and obstruction of their profile when using free low-resolution calculations with Xirio.

• Legend panel, where the open elements of the present session are displayed in a tree diagram. • Actions panel, where the possible actions to realize with the selected element are listed. • Information panel, where some information is given about the selected element of the legend window. • Tasks panel, where the information about the state and progress of the launched calculations is shown.

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• Coverage: A transmitter and a receiver take also part in this study, although in this case the receiver has not a fixed position but it moves through the selected calculation area. Its result is a color footprint that represents the radio electrical coverage of the transmitter and indicates the

Creation of Studies

The basic work unit in Xirio Online is a study, which is constituted of different radio electrical elements: transmitters, receivers, calculation methods, etc. There are four different types of studies:

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elements. The process to set these general parameters starts by selecting the category and subcategory of the desired service, which will be associated to an operating frequency band. Once the service is fixed, many parameters of the transmitters and receivers will be fixed to the recommended values for the service. 2. Parameterization of the stations: In this stage, specific parameters for each transmitter or receiver station are given. In Xirio Online, a transmitter or receiver contains not only the transmitter or receiver equipment, but also the radiating system or antenna and their specific behavior parameters. The location for each station is determined by the geographical coordinates of its site, that can be specified manually or be obtained by the position of the cursor on the map. Some of the characteristics to be defined are the transmission power, polarization, reception threshold, antenna type, height, gain or azimuth, losses, mean time between failures, mean time to repair, diversity technique, modulation, etc.

Figure 3: Propagation path of a link between two stations for a received signal level below the threshold. zone where the signal level is over the reception threshold. • Multi-coverage: It consists of a combination of individual coverage studies in the same calculation area. Its result is a color footprint that represents the best signal level received for each calculation point, the best server or the number of overlapping transmitters.

3. Calculation: Once all the parameters of the study are defined, the area for the study should be limited. Note that in the paid version of the software, the price of the simulation will be determined by the size of the calculation area and the resolution of the cartography. Then, we proceed to click on the Free low-resolution calculation option contained in the actions panel. While the calculation is in progress, the tasks panel shows a table with the state, progress and actions performed.

• Effective height: In this kind of study, only one transmitter is involved. Its result is a report with the effective transmitter heights for each azimuth, as defined in ITU-R Recommendations P. 370 and P. 1546 [8].

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Radio Planning Process

4. Analysis of the results: After calculating the study, its results can be observed by opening the Results folder. The radio engineer should analyze at this point whether the achieved performance meets the requirements for the design. Two interesting tools for it are the action that let us read the value in a point of the map and the information panel that shows the color code associated to the depicted result. The results obtained with Xirio can also be saved in KMZ format and opened with Google Earth for a better analysis.

Prior to the development of any radiocommunication network, a thorough radio planning is necessary in order to satisfy all its requirements. This planning process is usually performed in the following stages: 1. Analysis of the requirements and configuration: The radio engineer should clearly determine the technology to be used, the coverage or performance objectives to be achieved and the methodology to employ to design the network. With these data, the appropriate templates are defined and basic simulation parameters are set up. Among these parameters, we can include the cartography, the calculation method, the radio service, the operating frequency band, the type of antennas, the transmitter and receiver equipments and the location of the sites. For a more efficient usage of the simulation software, it is suggested to create templates for repeatedly used

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Teaching with Xirio Online in a Graduate Program

As it has been shown in Section 2, Xirio Online is a powerful tool that can be employed to make the students face different practical exercises that will promote their active learning of basic concepts in ra-

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using omnidirectional antennas with the same gain as the original ones, i.e. 35.5 dBi. Finally, the student is asked to introduce a repeater station with the same characteristics as the other stations and to analyze two profile studies, one for each hop. The option Duplicate study might be found of interest for this task. After the proper reorientation of the antennas, the design of the radio link will be completed. Fig. 4 shows a possible configuration for the radio link where, thanks to the repeater, the received power level at each station is high enough. Fig. 3 corresponds to the profile graphic for the case in which the repeater is not used. As it can be observed, the received power level in that case was below the minimum threshold to establish a communication.

dio propagation, communication systems, propagation models, radio planning, and the basis of standards as GSM, UMTS, DVB, etc. As examples of the options that Xirio Online provides in the field of education, we present two case studies. These eminently practical exercises offer the students a more realistic and deep comprehension of the fundamental concepts explained and reinforce their learning. In addition to this, these practices involve a basic training with some of the simulation tools employed to solve problems in real scenarios by radio engineers [2]. During the course 2010/2011, the following exercises with Xirio Online have been included as a part of the teaching in the subject “Radiation and radiocommunication”, of the fourth year of Telecommunications Engineering at the University of Seville. The main objective of these exercises is to improve the learning of some important topics, thus showing the usefulness of Xirio Online in a graduate or master program.

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Radio link

This exercise proposes the design of a radio link between two Spanish cities, Seville and Monesterio, for a fixed service in the frequency band 10,7-11,7 GHz. It is suggested to start creating templates for the sites, transmitters and receivers. For the transmitter, the following parameters will be set: the transmission power will be 30 dBm given to a point-to-point antenna with 35.5 dBi (that is provided as a default template by Xirio) and a height of 20 m; cable and connector losses will be 0.5 dB. For the receiver, a reception threshold of −83 dBm will be selected, losses of 0.5 dB and the same antenna with height of 20 m. Once the templates are defined, a profile study will be created for the aforementioned service. The same transmitter and receiver equipments will be used in both terminals of the radio link. A calculation method based on the ITU-R P. 526 Recommendation will be used, since the free version of the software does not allow to obtain availability results. Then, the students are asked to perform a first calculation of the radio link, whose results are expected to be wrong, and to correct this simulation by carrying out an automatic orientation of the antennas with the suitable action. However, it can be checked that this first attempt for the design of the radio link is not feasible due to its long distance and the topography of the terrain, which produces a received signal level below the required threshold. As a possible solution of this problem, the use of a repeater station is proposed in a second part of the exercise. The location of the repeater station is done by studying the areas in which the coverage from both cities overlaps. This verification must be done by

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Figure 4: Design of the proposed radio link composed by two hops and a repeater.

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Planning of a GSM network

The planning of a GSM 900 network providing service to a rural area between the Spanish provinces of Seville and Cordoba is presented as a second exercise. Xirio Online only allows to carry out coverage studies, so the planning neither includes the traffic study that is usually made in cellular systems nor the frequency allocation strategy. The selection of an urban area for the planning of a mobile communications network has been discarded due to the low-resolution available in the free access version of Xirio, despite its being very attractive for educational purposes. For the base stations (BTSs), macrocellullar equipment will be employed providing the antenna with a transmission power of 1 Watt and having −110 dBm of sensitivity, 1.95 dB of losses. We will select an omnidirectional antenna with a gain of 11 dB and 30 m high. On

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versities and other teaching institutions. In this paper it has been proposed to use Xirio Online as a free and useful tool for the teaching of radio planning. It has been explained that this tool presents some limitations, the most important ones being that not traffic or interference simulations are available and the fact that only low-resolution calculations are provided for the free access option. However, the description of the main characteristics of this software and the exercises included in this paper, that can be easily extended as projects or case-studies to be developed and solved by the students, show the benefits of this application. Therefore, it is possible to conclude that Xirio Online has the potentials to be used to promote the active learning of the main concepts on radio planning by the students, and to make them familiar with the way radio planning is performed in practice at radio planning departments. We can consider this free software as a highly suitable choice to present real cases to the students, and to raise practical problems that enable a better and more complete learning.

Figure 5: Multi-coverage study results for the proposed rural GSM network: best server results (left) and best signal level results (right). the other hand, the mobile stations will have a transmission power of 0.5 Watts, −102 dBm of sensitivity, an omnidirectional antenna with 2 dBi and no losses will be considered for them. Additionally, a margin of 15 dB is considered for simulations. Despite being given enough data for the study of both the uplink and the downlink, the students are asked to focus on the downlink only. In this way, they need to reason which station plays the role of the transmitter and which one acts as the receiver in order to take into account the downlink. It is suggested to create templates for the antennas and transmitters to avoid reintroducing repeated parameters. The students are asked to create a multi-coverage study for the mobile service category, P-GSM 900 mobile service. The mobile network will be designed with the previously indicated characteristics, that must include an individual coverage study for each omnidirectional BTS defined. It is suggested to use the Okumura-Hata calculation method for a rural environment, obtaining the results of Fig. 5 for the best server and the best signal level. Since Xirio Online does not provide an specific tool for the analysis of interferences, it is proposed to analyze them by adequately adjusting the representation signal levels in the individual coverage studies. A realistic objective for the co-channel carrier-to-interference ratio can be a value over 12 dB. With this exercise, the performance of Xirio Online for planning cellular networks is illustrated. However, in this case, some limitations have been found in this tool, for example, the fact that it is not possible to make traffic or interference studies.

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Acknowledgements: This work was supported by the University of Seville under a grant for the publicity of projects on research, innovation and improvement of the teaching activity. References: [1] G. R. M. Garratt, The Early History of Radio from Faraday to Marconi. Inst. Electr. Eng., 1994. [2] T. W. Hissey, ”Education and careers 2000: Enhanced skills for engineers”, Proc. IEEE, vol. 88, no. 8, Aug. 2000, pp. 1367-1370. [3] Committee on Science, Engineering and Public Policy (COSEP), Careers in Science and Engineering. Nat. Academy Press, 1996. [4] J. D. Bransford, A. L. Brown, and R. R. Cocking, How People Learn: Brain, Mind, Experience, and School, Nat. Academy Press, 2001. [5] R. F. Schwartz, “Laboratory: Its scope and philosophy”, IRE Trans. on Educ, vol.2, no.4, pp.120122, Sept. 1959. R [6] Webpage of Xirio Online, http://www.xirioonline.com [7] International Telecommunication Union, Radiocommunication Sector, Recommendation P.530: Propagation data and prediction methods required for the design of terrestrial line-of-sight systems. [8] International Telecommunication Union, Radiocommunication Sector, Recommendation P.1546: Method for point-to-area predictions for terrestrial services in the frequency range 30 MHz to 3000 MHz.

Conclusion

Most of the radio planning software tools are quite expensive products, usually unaffordable by the uni-

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