Cellular Radio Communications Engineering Education Through Laboratory Experimentation

Cellular Radio Communications Engineering Education through Laboratory Experimentation

G. LIODAKIS(1), E. KOKKINOS(1), I.O. VARDIAMBASIS(2), D. PATERAKIS(2), and M. MAVREDAKIS(2) (1) Laboratory of Telecommunication Systems, Networks and Applications (2) Microwave Communications and Electromagnetic Applications Laboratory Telecommunications Division, Department of Electronics, Technological Educational Institute (T.E.I.) of Crete - Chania Branch, Romanou 3, Chalepa, 73133 Chania, Crete, GREECE

Abstract: - This paper presents the issues related to the establishment of a series of laboratory experiments in the area of cellular radio communications at the Technological Educational Institute of Crete/ Department of Electronics (TEIoC/DoE), Greece. The experiments described here consist of hands-on experimentation, simulation work and small project-based activities, and complements the telecommunications engineering students’ theoretical knowledge in an effective manner. The overall laboratory course illustrates the complex tasks related to cellular radio engineering, can be regarded as a paradigm for an integrated approach for students’ experimentation in this area and as a case study for development of such a laboratory course with limited financial resources. The paper concludes with comments about the students’ attitude and experiences as well as with further directions for enhancing the laboratory curriculum, in line with the evolution of cellular communications area.

Keywords: - Cellular communications, Hands-on experimentation, Simulation.

1 Introduction program, including the conduction of a student thesis During the last decades, the telecommunications field and incorporating half a year of industrial placement experienced extraordinary development. The need to for workplace learning. As it concerns the exchange information with a user, anywhere and TEIoC/DoE, Greece, in particular, a new curriculum anytime, led to cellular mobile networks, which are is under implementation from the academic year wireless networks integrating several services. The 2002-3. The curriculum consists of a number of success of second generation (2G) mobile systems courses organized according to the European Credit prompted the development of third-generation (3G) Transfer System – ECTS (most of them taught in mobile systems for the provision of high data-rate combination with laboratory exercises) which leads services. Furthermore, research efforts are currently to a specialization in the areas of automation and th th developing frameworks for future 4G networks. The telecommunications (during the 6 and 7 aforementioned evolutions pose challenging semesters). The laboratory experiments presented in problems in issues such as, performance modeling, this paper are part of the whole series of experiments teletraffic analysis, mobility, radio propagation and carried out in the framework of the elective senior fading in reduced cell sizes, interference course “Mobile and Satellite Communication environment, dynamic resource assignment, Systems” (7th semester). For successful students’ modulation and multiple access schemes, multiple understanding and treatment of cellular mobile antenna techniques, etc. Therefore, as the landscape communication systems’ problems during of the profession is continuously changing, third experimentation, some theoretical knowledge is level educational institutes are realigning what they presumed. Students can obtain these theoretical teach in telecommunications engineering. knowledge in other courses (Telecommunication The electronics engineering programs at the Systems, Digital Tele-communication Systems, Technological Educational Institutes in Greece are, Theoretical and Computational Electromagnetics, after the reform of 2001, organized as a 4-year Antenna Analysis and Design, Microwave Theory and Applications), and the course under each Base Station (BS) the sufficient radio resources consideration. It should be noted that the and cope with the traffic demand in the cell under development of the experiments was from near- consideration. The traffic-handling capacity of a BS, scratch with limited financial resources. Furthermore, when expressed in statistical terms, is by defining an the overall design process of the experiments focused acceptable Grade of Service (GOS) or probability of on the integration of circuits and systems aspects of blocked calls. Another aspect that requires attention current cellular technology. is adequate selection of carrier frequencies used in A high percentage of papers in proceedings and every BS in order to keep interference below journals on education deal with laboratory acceptable limits. Finally, transceiver design issues implementation in various disciplines related to should be regarded when considering the integration electronics engineering: Electronics, Electric Power of circuits and systems aspects in a cellular Systems, Signal Theory, Wireless Communications, communications environment. Computer Networks, Information Technologies, and Taking into account all the aforementioned issues, so on. These laboratory implementations rely either the laboratory experiments implemented so far and on project-based experimentation [1], on hands-on presented here (as well as for the other parts of the experimentation [2], on simulation [3]-[4], or on whole course) are carried out through: virtual laboratory implementations [5]. However, to  Hands-on experimentation and emulation for the extent of the authors’ knowledge, an integrated understanding basic principles, propagation approach (relying on projects, hands-on, emulation effects and sources of interference in a cellular and simulation) to cover the practical issues of the system architecture, as well as for transmitter whole “Mobile and Satellite Communication design and performance evaluation. Systems” course (and of cellular communications  Simulation study of radio and traffic planning engineering, in particular) with an academic and aspects of a cellular system. research-oriented content, has not been achieved so far. The organization of the paper is as follows: In Section 2, background information about the laboratory experimentation activities and equipment used, is presented. In Section 3, a detailed description of four laboratory experiments in cellular radio communications engineering, is given. Finally, in Section 4, further development plans under examination and/or implementation for this part of the overall lab course as well as some concluding remarks are presented.

2 Background Figure 1. Laboratory Equipment: Spectrum Analyzer Cellular radio communication engineering is a rather and Educational Kits. complex task in which a large number of concepts must be mastered, in order to be able to optimize this The overall educational process is complemented type of systems. The overall optimization process by a small project-based laboratory-related activity should guarantee that an inadequate coverage, a high and is supported by the e-learning platform of probability of blocked or dropped-out calls, low TEIoC/DoE (for student reports submission, for transmission quality, etc., are to be avoided. In provision of additional educational material related to particular, cellular radio planning involves a the laboratory experiments, for the communication thorough knowledge of propagation effects in various between students and the instructors, etc.). Also, a environments (indoor, urban, suburban, open areas, lab manual containing description of the etc.). As propagation effects are extremely variable experimental procedures and selected theoretical along the Mobile Subscriber’s (MS) route, the use of issues related to each experiment, is available. The statistical definitions for both coverage quality and equipment and tools used during the laboratory interference levels, is necessary. Furthermore, traffic experimentation include (see Fig. 1): Oscilloscope, planning must be performed in order to allocate to Spectrum analyzer (HP 8594E), RF signal generator, two kits for Gaussian Minimum Shift Keying previous courses (see Section 1), is presumed. In (GMSK) and Direct Sequence (DS) spread spectrum addition, although the whole “Mobile and Satellite transmitters, walkie-talkies (operating at the 155MHz Communications” course is offered as an elective to frequency of range) for emulating a cellular system, a senior students, the enrollments are high and software tool developed at TEIoC/DoE for traffic increased since the introduction of lab calculations as well as simulation software (the EDX experimentation in the course (September 2003). It is SignalPro planning tool which is operational over a felt that these high enrollments are a result of the specific geographical area under study).Taking into strength and visibility of the telecommunications account that the oscilloscope, the spectrum analyzer, specialization in our Department as well as the strong and the RF generator were available at the job market in Greece for radio engineers. Such a Telecommunications Sector Labs of TEIoC/DoE and positive students’ feedback is also expressed in their that the kits were implemented free of charge by lab reports and by the motivation they apply the contacting chip manufacturers, we had to purchase theoretical concepts to a cellular communications only the set of walkie-talkies. environment. Finally, as it concerns the grading One of the difficulties of carrying out the policy, is as follows: lab reports (20%), small laboratory experiments (from both the students’ and project-based laboratory-related activity (20%), and instructors’ point of view), is the need to cover a final examination (60%). variety of topics about which most of the students have had little exposure. For example, although probability theory is known to the students, there 3 Lab Experiments Details exists some uniqueness to the application of the The six laboratory experimentation activities for concepts to issues concerning cellular radio cellular radio communications engineering are as communications (outage probabilities, queuing depicted in Fig. 2 and described as follows: theory as related to trunking, the statistical nature of fading, etc.). Therefore, as a prerequisite for the 3.1 Experiment 1: Traffic planning and whole course, knowledge and skills acquired at Resource allocation

Figure 2. Organisation of the cellular communications laboratory experimentation activities. The primary objective of any mobile communication planning are also examined by the use of the system is to provide coverage for a large number of software tool. users scattered over a wide geographic area, using Another set of issues that belong to radio resource the limited resources (like spectrum, transmitted allocation in cellular systems (spectrum efficiency, power) available. Furthermore, cellular radio systems multiple access schemes, fixed and dynamic channel rely on trunking which, in turn, exploits the statistical assignment algorithms), is also covered. Finally, the behavior of the users. Thus, we developed a software student is asked to carry out a cellular system design tool using the Visual Basic programming language from scratch with specified capacity, taking into and modeling the fundamentals of trunking theory, as account both performance and cost criteria. expressed by Erlang B formula which calculates the GOS = Probability of Blocking. 3.2 Experiment 2: Hands-on experimentation It should be noted that the Erlang B formula is on Interference and Indoor propagation used when the lost calls are cleared due to Reliability and performance in cellular radio systems unavailability of radio channels; in such a case the depend on proper deployment, which includes system does not have a mechanism to queue the call careful site survey and design, in order to provide request, and the user must retry initiating the call adequate coverage and capacity. However, both later. Other assumptions when using the Erlang B coherent and adjacent channel interference, are major formula include that there exists an infinite number limiting factors in the performance of cellular radio of users requesting the radio resources, calls arrive as systems. As implied by the frequency reuse concept, determined by a Poisson distribution, and that the in order to reduce cochannel interference, cochannel call holding time (in general it takes into account the cells must be physically separated by a minimum call length, the call overhead time, plus queueing distance to provide sufficient isolation. Also, as time, if any) is exponentially distributed. The adjacent channel interference results from imperfect software tool models, also, the case of a cellular receiver filters which allow nearby frequencies to system where the lost calls are queued. Then, as leak into the passband, it can be minimized through determined by the Erlang C formula, the likelihood careful channel assignments. Furthermore, when of a call not having immediate access to a radio considering radio propagation, propagation channel depends on the Probability [delay>0]. measurements in a mobile radio channel show that In such case, the GOS of the cellular system the average received signal strength at any point under study, where blocked calls are delayed more decays as a power law of the distance between the than t seconds, is given by, [6]: BS and the MS. In addition, when considering indoor Probability [delay>t] = radio propagation, the indoor radio channel is Probability [delay>0] * exp(-(C-A)t/H) different from the traditional mobile radio channel. In (C: number of trunked channels, A: total traffic load fact, it is influenced by local features, such as the (in Erlang), H: the holding time of a typical call in layout of the building, the construction materials, and seconds). The assumptions when using the Erlang C the building type. delay formula include a Poisson arrival process, an During this laboratory experiment, students have infinite number of traffic sources, exponential service a hands-on experience on interference and indoor times, and a First-in-First-out (FIFO) server queue radio propagation issues by means of walkie-talkies where no calls leave the queue and the waiting area which emulate a cellular system architecture and are (queue) is as large as necessary (i.e. infinite). used as a MS, respectively. The RF signal generator Therefore, during laboratory experimentation, we represents an adjacent channel interference source, assume that our cellular system is a circuit switched while the spectrum analyzer is used for power system following either Erlang B or Erlang C measurements. Following the guidelines in the lab models. Thus, the student is faced with various manual, the students have the opportunity to: scenarios regarding the callers’ density (in a) Understand basic cellular concepts (the cell radio callers/Km2), the average activity factor per user (in coverage, the frequency reuse distance and the Erlang), etc. for proper system design. Other cellular power control mechanism) concepts and design approaches (cell splitting, b) Carry out the Carrier-to-Interference (C/I) sectorization, densification of BSs, multilayer cell measurements, when cochannel and adjacent architecture, effect of channel bandwidth on the channel interference sources are present. traffic carried by the system) related to traffic c) Consider parameters (building penetration, floor attenuation, working frequency) that affects 3.4 Experiment 4: Cellular network quality pathloss, by taking the associated measurements. assessment d) Be familiar with methods used by cellular radio The versatility and efficiency of simulation for engineers (when conducting site surveys, for performance evaluation and tradeoff analysis is characterization of indoor radio wave exploited for the study of various cellular network propagation, etc.) architectures in this experiment. By the use of the same simulation software (as in Experiment 3.3) and During experimentation for (a) and (b), students the specific region under consideration, the student have to adjust the frequency and power transmitted makes assessment of the following aspects of cellular by the walkie-talkies for emulating the operation of network quality: BSs. Furthermore, the position of the “BSs” is a) Bit Error Rate (BER) predictions for various changing by students’ movements. In such a way, modulation schemes, receiver implementations, various C/I measurements are achieved, the power data rates, levels of cochannel interference and collected by the spectrum analyzer is varied, the Additive White Gaussian Noise (AWGN) and quality of voice communication is affected, the cell speeds of the MSs. Thus, for example, the student radius can be redefined, etc. Considering can get BER patterns for the area, where a GSM experimentation for (c) and (b), students are guided system will be potentially deployed for coherent by the lab manual to follow the required practical and differential detection receivers. steps and compare their measurements with other b) C/(I+N) predictions as well as the effect of fading, experimental results (in other testbed scenarios, for for a MS moving in the area under study. other than the 155 MHz frequency range of the Therefore, the student, by getting a quantified walkie-talkie frequencies, etc.), as derived from picture of the perceived QoS a user is research papers. Thus, the aforementioned real experiencing, can identify problematic parts of the measurements on real-world signals allow the student simulated region, investigate ways of quality to address practical issues and phenomena often not improvement and seek for the cellular network observed otherwise. quality optimization.

3.3 Experiment 3: Radio planning 3.5 Experiment 5: GMSK and DS-spread In this laboratory experiment, the student is spectrum transmitter issues confronted with radio planning issues on a specific In this experiment two kits developed at TEIoC/DoE region through simulation. Actually, by changing are used for educational purposes and laboratory various parameters and design assumptions, the experimentation. They include a GMSK transmitter student is involved in a trial and error procedure. The with a carrier frequency of 125MHz as well as a DS issues covered here include: spread spectrum transmitter operating in the 450MHz a) path loss calculations by employing different frequency region. As it concerns the implementation propagation models (Okumura, Hata, COST 231, of the DS spread spectrum transmitter, it is based on ITU-R, etc.), two PCBs in order to achieve a higher degree of b) statistical variables, such as the percentage of time modularity. The first PCB includes the Motorola and locations, where a prespecified received microcontroller MC68HC12 for controlling the power is exceeded, generation of the spreading code through a 15-bit c) environmental issues (atmospheric absorption, shift register and the modulation circuit at the base climate type, etc.), band. The chip rate can be chosen from 0.1536 d) terrain topography that affects the existence of a Mchips/sec to 1.2288 Mchips/sec, while the data rate line-of-sight (LOS) or non line-of-sight (NLOS) is 9600 baud. The second PCB contains a synthesizer communication path, for the carrier generation of the overall transmitter e) antenna design issues (employment of an and the frequency for the up-converter, the up- omnidirectional or a directional antenna, converter itself, as well as the band pass filter (BPF) exploitation of space or polarization diversity), and the high frequency amplifier. f) the locations where a handover occurs, The spectrum display is the most common method g) general cellular system’s design issues for viewing RF modulation. The major benefits of (frequency, the height of the BSs and MSs, the this technique are the ability to view and measure the transmitted power, etc.). overall channel bandwidth, center frequency and sidebands and gross out-of-band anomalies. the Push-to-talk service over cellular networks, by Therefore, the student by the use of the spectrum means of RPT/UDP/IP packet structures. analyzer can get the GMSK modulation output signal  Treatment of mobility management issues. As 3G spectrum, to observe the spread spectrum signal and 4G mobile networks are characterized by high spectrum by altering the chip rate, to measure the user density and high mobility as well as smaller power at the up-converter /BPF/RF amplifier outputs cell sizes, the number of location updates and of the DS spread spectrum transmitter etc. handovers is increasing. Therefore, simulation of Furthermore measurements at specific test points (at such issues should be useful for students’ the output of the Gaussian low-pass filter of the understanding of cellular systems operation. GMSK modulator, at the output of the spreading Other enhancements of the laboratory code generator of the DS spread spectrum experiments of Fig. 2, that are already under transmitter, etc.) of both kits in the time domain are implementation, include: taken by the students, letting them understand and  Hands-on experimentation for the cellular system study the architecture and design of both transmitters. architectures of Digital Audio Broadcasting (DAB) and Digital Video Broadcasting (DVB) 3.6 Experiment 6: Small project-based systems, [7]. laboratory-related activity  Hands-on experimentation with the GMSK and In this experimentation activity, students are DS-Spread Spectrum receivers, that are under encouraged to try their own variations of the implementation by students of TEIoC/DoE in the prescribed experiments or to deal with other issues framework of their thesis. that are related to one or more of the former five  Study of fading effects by means of simulation in experiments. Such issues include the experimentation an RF environment as well as by hands-on of various resource allocation algorithms for cellular experimentation in the baseband. In such a way, communication systems, the role of cellular radio students will be able to characterize the planning tools when engineering a mobile system, propagation effects of a naturally occurring the comparison of radiowave propagation environment and assess cellular network quality measurement results for various wireless channels issues. and cellular systems, the implementation issues of  Simulation of a cellular system using the transceiver designs for mobile communications, etc. COMNET software package in order to let the This experimentation activity takes place during the student examine the role and effects of signaling whole semester under the instructors’ guidance, traffic between key components of the system, followed by a presentation to all students at the end such as the Mobile Switching Centre (MSC), the of the semester. Home Location Register (HLR), the Visitor Location Register (VLR), etc. Concluding, the series of experiments developed 4 Further Directions and Conclusions on the basis of our findings in [8] and presented The evolution and deployment of mobile cellular here , has a positive effect on student motivation, systems is characterized by the dominant role of IP learning, and academic success, since its introduction series of protocols and the necessity for a cross-layer to the whole course. The students gain experience, design approach in order to let the mobile user access confidence and thorough understanding of concepts a broad range of services in a transparent way. Also, and design issues in cellular radio communication in alignment with research carried out at the systems. Telecommunications Division of TEIoC/DoE, and at Finally, as the purchase of professional tools used the Communication Network and Telematics by mobile operators (such as Erricsson’s TEMS Applications (COMNETTA) Group in particular, the Cellplanner Universal, Nokia’s TOTEM Vantage or “cell layout” organization of the laboratory AirCom’s ASSET radio network planning and experiments described in this paper could be optimization software) could not be afforded by enhanced by: TEIoC/DoE, the overall laboratory course  Traffic planning experimentation in a packet- development may be regarded as a case study when switched environment limited financial resources are available.  Simulation study for the provision of various services. As an example, we are now considering Acknowledgment This work was supported by the Greek Ministry of National Education and Religious Affairs and the European Union under the ΕΠΕΑΕΚ ΙΙ projects: “Archimedes – Support of Research Groups in TEI of Crete – Smart antenna study & design using techniques of computational electromagnetics and pilot development & operation of a digital audio broadcasting station at Chania (SMART-DAB)” and “Reformation of the Electronics Dept’s syllabus”.

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