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Unformatted text preview: ECE501 Introduction to Analog and Digital Communications Autumn 2011 Homework #4 October 28, 2011 HOMEWORK SOLUTIONS #4 1. The code and a plot for the audio frequency f c QPSK example appear below. 500 1000 1500 2000 2500 30000.30.250.20.150.10.05 0.05 0.1 0.15 Received bandpass signal, r(t) Amplitude time (msec) Keyboard clicks r(t) %define parameters fs = 44100; %44.1k samples per second for DAC and ADC fc = 12000;%carrier frequency at 12000 Hz P = ceil(fs/200); %oversampling factor to get 200Hz baud rate %P is number of samples per symbol interval g = srrc(3, 0.5, P);%pulse waveform; see srrc.m from course webpage %define symbols symbols = psk(100,4,1); %simple example with 100 QPSK symbols %the psk.m script is available at the course webpage a = symbols; %list of symbols %symbol period of P samples a_up = reshape([a;zeros(P1,length(x))],1,P*length(x)); %convolve symbols with pulse shape mbb = conv(a_up,g); %baseband message waveform, sampled % sample index (time) n=[0:length(mbb)1]; % upcovert to carrier frequency s = real(exp(j*2*pi*fc*n/fs).*mbb); % DAC conversion and transmit via soundcard and speakers wavplay(s,44100) ECE501, Au2011 1 (a) Use psk.m from the course webpage to generate QPSK symbols. Alternatively, make your own by selecting M ∈ { , 1 , 2 , 3 } and defining QPSK symbols e j ( 2 πM 4 + π 4 ) , yielding symbols of modulus 1 and phase 45 , 135 , 225, or 315 degrees. (b) See help wavplay . Select fs = 44100 so that the sampling rate is at least twice the desired carrier frequency, here listed at 12kHz (low enought that my aging ears could hear the signal)....
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This note was uploaded on 11/11/2011 for the course ECE 501 taught by Professor Schniter,p during the Fall '08 term at Ohio State.
 Fall '08
 Schniter,P
 Frequency

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