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Low-Cost Vector Signal Analyzer for Communication Experiments

Abstract

Vector signal analyzers (VSA) are systems that provide real-time analysis of in-phase and quadrature components of RF signals, as well as providing spectral analysis and other signal measurement features. VSA’s would be an ideal addition to any undergraduate communications laboratory because of their ability to investigate the many types of signals prevalent today. Unfortunately, most VSA’s are priced well beyond the budgets of typical undergraduate ECE departments. This paper describes a novel low-cost VSA that uses basic PC data acquisition (DAQ) cards to capture signals of interest and real-time processing of signals with LabVIEW and MATLAB. This VSA system provides a user interface that has much of the basic functionality of standard hardware VSAs, but with the limitation that bandwidth is constrained by the sampling rate of the DAQ. The system provides real-time plots of I/Q constellations. We describe the user interface as well as example laboratory experiments, where students get hands- on experience with a variety of signals such as BPSK, QPSK, and QAM. Any undergraduate lab with workbenches outfitted with standard PC and data acquisition equipment will be able to make use of this novel VSA.

1. Introduction

Many universities offer a laboratory component as part their introductory digital and analog communication course. In traditional undergraduate teaching laboratory environments, many communication topics are difficult to convey because of their complexity in implementation. In the first reference1, a framework for meaningful hands-on undergraduate communication laboratories was introduced using a set of LabVIEW-based exercises that interact with computer- controlled industry-standard test and measurement equipment. This environment allows the students to explore a wide range of communication concepts using actual real-world signals and a balance between what is provided for the students and what the students need to design and implement to reinforce a particular concept. This paper expands on previous work1 by introducing a low-cost vector signal analyzer (VSA) built around a PC based data-acquisition (DAQ) card using LabVIEW and MATLAB. The second reference2 describes the use of hardware VSA’s in undergraduate labs. This paper goes on to describe a number of student laboratory exercises which use this VSA.

Most undergraduate textbooks3-6 do an excellent job of describing signal constellations that would be observed for signals such as QPSK and QAM, but few mention VSA’s as the test equipment used to measure these constellations. By introducing VSA’s in the laboratory, students get exposure to equipment used in the communication industry and hands on experience with real-time I/Q techniques. Many students find I/Q concepts to be difficult to understand. By having the students work with real-time I/Q signals in the laboratory, a goal is to make these concepts less abstract and more meaningful to the students.

Many test instruments can be created for undergraduate laboratories using a data acquisition card and LabVIEW. While the speed of operation of these instruments is usually limited by the acquisition rate of the data acquisition card and the computing power of the PC, the basic

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Tuffner, F., & Catellier, A., & Kubichek, R., & Pierre, J. (2007, June), Low Cost Vector Signal Analyzer For Communication Experiments Paper presented at 2007 Annual Conference & Exposition, Honolulu, Hawaii. 10.18260/1-2--3041