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Using Real RF Signals Such as FM Radio to Teach Concepts in Communication Systems

Abstract

The theory of communication systems can be made more concrete and interesting by using real- world signals to illustrate the various theoretical concepts. The FM radio signal is, in many ways, an ideal signal to illustrate many of the concepts that are taught in communication system courses. This radio frequency (RF) signal is readily available in most populated areas, the students are familiar with the signal, and most FM stations broadcast both analog audio signals and digital Radio Data System (RDS) signals which can be used to illustrate digital receivers. The RDS signal contains auxiliary information such as the radio station identification, type of program, name of the current song, artist name, current time, traffic reports, etc. The RF signal that is broadcast from local FM radio stations, as well as most other RF signals, can be captured with hardware such as a real-time spectrum analyzer, a vector signal analyzer, or the Universal Software Radio Peripheral (USRP). The analog audio signals can be demodulated in software and used to demonstrate FM demodulation, frequency division multiplexing, double sideband suppressed carrier demodulation, mixing, and filtering. The digital RDS signal can be demodulated using a relatively simple software defined receiver which consists of a Costas loop, matched filter, timing recovery algorithm, and slicer. The FM radio signal can be used in classroom demonstrations or in student projects or homework assignments to enhance a communication systems course, motivate the students with a real-world system, and to provide students with the practical experience of creating and testing a software defined radio receiver.

Introduction

Some students are more motivated to learn material when it is clear that the material is useful in real systems. One way to show how concepts are used in practice is to examine existing commercial systems, but gaining access to commercial systems is impractical in many cases. However, capturing the wireless signals generated by real systems is often possible with commercially available test equipment, and these captured signals can be used to teach many of the concepts commonly found in communication systems courses. These signals can also be decoded in software to demonstrate concepts in software defined radio.

The FM radio signal is an excellent candidate for use in communication system courses because it (usually) contains both analog and digital signals, is widely available, and the students are familiar with the FM radio system. The digital signal is fairly easy to demodulate because it is a low bit rate system that does not necessarily require an adaptive equalizer, the bits are not interlaced, and it uses a fairly simple error control coding scheme. This paper explains how the FM radio signal can be used to teach many of the concepts in a communication system course.

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Hoffbeck, J. (2008, June), Using Real Rf Signals Such As Fm Radio To Teach Concepts In Communication Systems Paper presented at 2008 Annual Conference & Exposition, Pittsburgh, Pennsylvania. 10.18260/1-2--3129