Design of Simulink Projects for an Undergraduate Communications Course

This paper describes a set of six Simulink based laboratory projects designed for a junior level undergraduate communications course. The course is traditionally a lecture course with no laboratory component. The authors aim to add a laboratory component to the course to help students to better understand and analyze the theory taught in lectures. The laboratory component is structured by following effective teaching strategies which aids reinforcement and retention of information. Background and Motivation An introductory communications course is the essential foundation to learn advanced communications topics. At Missouri University of Science and Technology, the Electrical and Computer Engineering (ECE) department offers a junior level undergraduate course: Communication Systems I. The course is presently a three hour lecture course with no laboratory component. As a first course in the communication series, it covers a review of linear systems and introduces analog communication systems as well as digital baseband communication systems. The course, first reviews important concepts of Fourier series, Fourier transforms, power spectral density and linear systems which students have learnt in their preliminary courses. Next, the students are introduced to basic analog modulation techniques of Amplitude Modulation (AM), Frequency Modulation (FM) and Phase Modulation (PM) along with feedback demodulators. They are also taught pulse modulation, digital signaling and multiplexing. Then, they are introduced to digital baseband transmission which covers the topics of line codes, pulse shaping, Inter-Symbol Interference (ISI), Zero Forcing (ZF) Equalizer and synchronization. This course structure is meant to provide students with a solid foundation for advanced courses such as Communication Systems II, Communication Circuits, and Wireless Communications. The lecture approach to teaching communication courses can be intimidating for many students because of the heavy theoretical and mathematical content, compounded by the lack of visual aids. The students find the aforementioned concepts difficult to grasp with block diagrams alone. The complexity increases as the course progresses and the authors wanted to help students cope with the complex theory without reducing the standard of the course content. Empirical studies advocate the need for innovative techniques to help students grasp the course material 1,2,3 . A number of course developments implement MATLAB based projects to simulate theoretical concepts 4,5,6,7 . Although the textbook 8 provides MATLAB examples and exercises in the form of script files, previous offerings of the course have found that the lecture-only format does not lend itself to teaching simulation. Besides, more than 50% of the students are not ready for the extensive MATLAB required by this approach. The authors hence decided to supplement the traditional lectures with hands on simulation experience using a model based Simulink approach. Simulink is a graphical environment provided by MathWorks to enable model-based design and simulation. It provides an extensive P ge 22436.2 set of pre-defined blocks for modeling continuous-time or discrete-time systems or a hybrid of the two. It is an easy tool for beginners since, once the user has conceived a system, it can be built into a model by a simple drag, drop and connecting of blocks and wires. The models can be organized into modules in a hierarchical manner and display blocks can be used to visualize the results as the simulation runs. The model can be simulated for different parameters and users can learn from a „what if‟ approach to such simulation. Simulink is integrated with the MATLAB environment and so the user may also utilize MATLAB features to define inputs, store results for analysis or post processing, or perform functions within a model. Overall, Simulink permits students to bring static representations of communication systems in textbooks to life. Thus, Simulink was chosen as a tool which could be used to make theory tangible. Thanks to its attractive features, Simulink has been identified as an ideal tool for laboratory projects and has hence been adopted for teaching a variety of courses by many instructors 9,10,11,12,13,14 . For example, in 13,14 digital communication theory is taught by using Simulink exercises. However, none have attempted to introduce Simulink for teaching analog communication theory in core level communication courses, where students do not necessarily have a strong programming capability. The benefits of such a laboratory course are twofold. Firstly, students learn simulation, which is widely used by engineers in the industry to verify and validate system designs. Secondly, these laboratory projects have been designed following the Gagne‟s nine events of instruction 15 which leads to an enhanced learning environment. Also, when compared to hardware based labs, such as with EMONA TIMS 16 , Mobile Studio 17 and Ettus USRP 18 , Simulink has the advantage of lower cost and ease of maintenance. Simulink Laboratory Projects for Communication Systems Course Six Simulink laboratory projects are constructed to teach Simulink skills in parallel with the theory. Table 1 enumerates topics covered in the six labs and the Simulink skills gained therein. The first two projects relate to the review of frequency domain analysis and linear system concepts to reinforce previously learnt basics. At this stage, students are introduced to the primary skill of building a model and creating subsystems and masks. The next two projects deal with analog communication systems. Here we introduce students to design techniques such as creating libraries and using model referencing. The last two projects are on digital baseband communication systems. The fifth lab also introduces the Stateflow tool of Simulink to implement complex control logic in Simulink and the sixth lab introduces integration of models with MATLAB scripts as a formative step towards more advanced implementations in Simulink. The projects have been designed with a gradually increasing complexity to provide the necessary confidence boost to students for subsequent projects. Lab Topics covered Simulink skill I Frequency Domain Analysis Building a Model II Linear Systems Subsystems & Masks III Amplitude Modulation Library Building IV Frequency & Phase Modulation Model Referencing V Pulse Code Modulation & Line Codes Using Stateflow VI Zero Forcing Equalizer Interacting with MATLAB Table 1. Simulink Laboratory Projects P ge 22436.3 In this paper we discuss two of the laboratory projects. Firstly, we discuss Lab III (AM lab) and how it implements the features of Simulink outlined earlier. This lab is split into two parts, one to implement the modulation techniques and one to implement the demodulation techniques. Typically, the equation for an AM signal is given by, xc(t) = Ac [ A + a m(t) ] cos(2 π fc t) (1) where , Ac is the amplitude of the unmodulated carrier wave Accos(2 π fc t), m(t) is the message signal, a is the modulation index and A is the DC bias. The inclusion of a DC bias results in the carrier component to be included in the AM signal. Further, the Double Sideband (DSB) modulation and Single Sideband (SSB) modulation are variations of AM itself. DSB can be achieved by simply multiplying the carrier with the message signal. xc(t) = Ac m(t) cos(2 π fc t) (2) The SSB signal can be generated from the DSB output by the method of sideband filtering. The illustration in Fig.1 shows a complete model of the modulation half of the lab. It includes a scope for visual comparison of the modulation techniques. As can be seen from the figure the model is a direct translation of the equations into an intuitive assembly of blocks. All the blocks have been taken from the variety of block libraries available in Simulink. Fig.1 Intuitive assembly of blocks for amplitude modulation lab The above model can be better organized by making subsystems for the individual modulation techniques and then combining them to form an AM techniques subsystem. This is an example of a two level hierarchy being designed in a bottom-up manner. Similarly, a top-down design is possible by making empty subsystems and entering constituent blocks into them individually. Fig.2 shows the final hierarchical model. The amplitude modulator can now be stored in a library to be used for other model designs, for example in the other half of this lab, AM demodulation Lab 3 Part A Comparison of Amplitude Modulation Techniques Multiplier 2 Multiplier 1 .5 Modulation index Input signal