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lab4

Apr 27th, 2018
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  1. % 12619250 The Duc Vu & Chun Wa Lee
  2.  
  3. clear all;
  4. close all;
  5.  
  6. fs = 500e3;
  7. Ts = 1/fs;
  8. N = 50e3;
  9.  
  10. t = 0:Ts:(N-1)*Ts;
  11.  
  12.  
  13.  
  14. fc = 6e3;
  15. Tg = 1/fc;
  16. gt = 2+cos(2*pi*fc*t);
  17. %plot(t, gt)
  18.  
  19. % FFT calculation
  20. [~,G,f] = myfft(gt,fs);
  21.  
  22. figure('name','message signal, g(t)')
  23. plotscript(t,gt,f,G);
  24.  
  25.  
  26. fc1 = 100e3;
  27. Tc1 = 1/fc1;
  28. fc1t = 2*cos(2*pi*fc1*t);
  29.  
  30.  
  31. % FFT calculation
  32. [~,G,f] = myfft(fc1t,fs);
  33.  
  34. figure('name','carrier 1 signal, l_1(t)')
  35. % plot the time domain and frequency domain signals
  36. plotscript(t,fc1t,f,G);
  37.  
  38. %% modulated signal g,AM
  39. A = 0.5;
  40. gAM = A*gt.*fc1t;
  41.  
  42. % FFT calculation
  43. [~,G,f] = myfft(gAM,fs);
  44.  
  45. figure('name','gAM, g_AM(t)')
  46. plotscript(t,gAM,f,G);
  47.  
  48. %% demodulation
  49.  
  50. [b,a] = ellip(5,0.1,50,60000/(fs/2));
  51.  
  52. %% scenario 1: l_2(t) = 2*cos(2*pi*fc21*t)
  53.  
  54. fc21 = 100e3;
  55. Tc21 = 1/fc21;
  56. fc21t = 2*cos(2*pi*fc21*t);
  57.  
  58. A = 0.5;
  59. gdemod = A*gAM.*fc21t;
  60. gdemod = 2*filter(b,a,gdemod);
  61.  
  62.  
  63. % compute FFT, take the RMS amplitude and frequency vector
  64. [~,G,f] = myfft(gdemod,fs);
  65.  
  66. figure('name','Demodulated Signal, scenario 1')
  67. % plot the time domain and frequency domain signals
  68. plotscript(t,gdemod,f,G);
  69.  
  70. %% scenario 2: l_2(t) = 2*cos(2*pi*fc21*t)
  71.  
  72. fc21 = 100e3;
  73. Tc21 = 1/fc21;
  74. phasedeg = 45;
  75. fc21t = 2*cos(2*pi*fc21*t - (phasedeg*pi/180));
  76.  
  77. A = 0.5;
  78. gdemod = A*gAM.*fc21t;
  79. gdemod = 2*filter(b,a,gdemod);
  80.  
  81.  
  82. % FFT calculation
  83. [~,G,f] = myfft(gdemod,fs);
  84.  
  85. figure('name','Demodulated Signal, scenario 2')
  86. % plot the time domain and frequency domain signals
  87. plotscript(t,gdemod,f,G);
  88.  
  89. %% scenario 3: l_2(t) = 2*cos(2*pi*fc21*t)
  90.  
  91. fc21 = 100e3;
  92. Tc21 = 1/fc21;
  93. phasedeg = 90;
  94. fc21t = 2*cos(2*pi*fc21*t - (phasedeg*pi/180));
  95.  
  96. A = 0.5;
  97. gdemod = A*gAM.*fc21t;
  98. gdemod = 2*filter(b,a,gdemod);
  99.  
  100.  
  101. % FFT calculation
  102. [~,G,f] = myfft(gdemod,fs);
  103.  
  104. figure('name','Demodulated Signal, scenario 3')
  105. % plot the time domain and frequency domain signals
  106. plotscript(t,gdemod,f,G);
  107.  
  108. %% scenario 4: l_2(t) = 2*cos(2*pi*fc21*t)
  109.  
  110. fc21 = 96e3;
  111. Tc21 = 1/fc21;
  112. phasedeg = 0;
  113. fc21t = 2*cos(2*pi*fc21*t - (phasedeg*pi/180));
  114.  
  115. A = 0.5;
  116. gdemod = A*gAM.*fc21t;
  117. gdemod = 2*filter(b,a,gdemod);
  118.  
  119.  
  120. % FFT calculation
  121. [~,G,f] = myfft(gdemod,fs);
  122.  
  123. figure('name','Demodulated Signal, scenario 4')
  124. % plot the time domain and frequency domain signals
  125. plotscript(t,gdemod,f,G);
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