lab2_modulation_filtering

lab2_modulation_filtering - Massachusetts Institute of...

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6.02 Spring 2008 1 of 29 Lab #2 Massachusetts Institute of Technology Dept. of Electrical Engineering and Computer Science Spring Semester, 2008 6.02 Introduction to EECS 2 Lab #2: Modulation and Filtering Goal:. ................................................................................................................................... 2 Instructions:. ........................................................................................................................ 2 Prelab: . ................................................................................................................................ 3 A. Understanding Modulation . ....................................................................................... 3 B. Understanding Demodulation . ................................................................................... 7 C. Low Pass and Band Pass Filter Design. ..................................................................... 9 D: Exercises: Filtering and Modulating Signals With Nonzero Bandwidth. ............... 17 Lab Exercises (9am - noon and 2pm – 5pm, Wed., February 20, 2008):. ........................ 18 A. Objectives. ................................................................................................................ 18 B. Introduction. ............................................................................................................. 18 C. Building a FDM Receiver . ....................................................................................... 20 D. Exercises . ................................................................................................................. 21 Example Interview Questions. .......................................................................................... 27 Check-off for Lab 2 . ......................................................................................................... 29
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6.02 Spring 2008 2 of 29 Lab #2 Goal: Learn principles of modulation and filtering through hands on interaction with Matlab and the USRP board. In particular, you will become familiar with a wireless communication scheme known as frequency division multiplexing, and will write Matlab code to receive voice signals that have been modulated to different frequency bands. You will also examine the issue of frequency offset in demodulation. Instructions: 1. Complete the Prelab exercises BEFORE Wednesday’s lab (February 20, 2008). Complete Tasks 1-6, and for each task save the plots that you produce and hand- in the plots at the beginning of the lab. 2. Complete the activities for Wednesday’s lab (see below) and get checked off by one of the TAs. Be sure to work in pairs. 3. Look over the example interview questions, and be prepared to answer questions similar to them after you finish the lab on Wednesday.
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6.02 Spring 2008 3 of 29 Lab #2 Prelab: Modulation , demodulation , and filtering are integral to the frequency division multiplexing (FDM) communication system you will be building in Lab 2. The purpose of these prelab exercises is to familiarize you with the implementation of these signal processing operations using simple sinusoidal signals. A. Understanding Modulation The purpose of this exercise is to understand the mechanics of modulation and demodulation as well as to study the effects of these operations on signals in the time and frequency domains. We will study the modulation and demodulation of a 1 Hz sinusoid by 10 Hz. Consider the signal ) * 2 cos( ) ( t t x π = . This is a sinusoid with amplitude of 1 and frequency of 1 Hz. Create a Matlab file called “modulation.m” and enter the following commands to create and visualize x( t ) in the time domain. Your code should generate Figure 1. Fs = 1000; % Sample Frequency in Hz t = 0:1/Fs:5; % Time vector from 0-5 seconds in increments of % 0.001 seconds (eg. 0 0.001, 0.002, 0.003 . ..) x = cos(2*pi*1*t); % Cosine with amplitude 1 and frequency 1 Hz figure(1) % Create Figure 1 plot(t,x) % Plot Signal x(t) in Figure 1 title( 'Time-Domain' ); % Add Title Time-Domain to Figure 1 xlabel( 'Time (sec)' ); % Add Time (sec) as x-axis label of Figure 1 ylabel( 'Amplitude' ); % Add Amplitude as y-axis label of Fig. 1 axis([0 1 -2 2]) % Set x-axis range [0-1] sec and % y-axis range [-2 2] Figure 1
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6.02 Spring 2008 4 of 29 Lab #2 Now lets visualize the magnitude of the spectrum of x( t ). Since x( t ) is a real signal, the magnitude of its spectrum is an even function (symmetric about 0 Hz). We expect to see
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This note was uploaded on 08/23/2009 for the course EECS 6.02 taught by Professor Terman during the Spring '08 term at MIT.

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lab2_modulation_filtering - Massachusetts Institute of...

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