1:  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%info%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

   2:  %author: Yang Li

   3:  %email: [email protected]

   4:  %data:2013/12/16

   5:  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%IF signal generation%%%%%%%%%%%%%%%%%%%%%%%%% 

   6:  b=2e6;

   7:  taup=50/1e6;

   8:  fc=20e6;

   9:   

  10:  n = fix(50 * taup * b);

  11:  t = linspace(-taup/2,taup/2,n);

  12:  s= exp(i * pi * (b/taup) .* t.^2 + i * 2 * pi * fc .* t);

  13:  figure(1)

  14:  subplot(4,1,1)

  15:  plot(t,real(s),'k')

  16:  ylabel('real part of IF signal s')

  17:  xlabel('time in seconds')

  18:  grid

  19:  subplot(4,1,2)

  20:  sampling_interval = 1 / 5 /fc;

  21:  freqlimit = 0.5/ sampling_interval;

  22:  freq = linspace(-freqlimit,freqlimit,n);

  23:  plot(freq,fftshift(abs(fft(real(s)))),'k');

  24:  ylabel('Spectrum of real part of s')

  25:  xlabel('Frequency in Hz')

  26:   

  27:  grid

  28:  subplot(4,1,3)

  29:  plot(t,imag(s),'k')

  30:  ylabel('imag part of IF signal s')

  31:  xlabel('time in seconds')

  32:  grid

  33:   

  34:  subplot(4,1,4)

  35:   

  36:  plot(freq,fftshift(abs(fft(imag(s)))),'k');

  37:  ylabel('Spectrum of imag part of s')

  38:  xlabel('Frequency in Hz')

  39:  grid

  40:  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%mixer%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

  41:  lo =   exp(i*2 * pi * fc .* t);

  42:  smi = real(s) .* real(lo);

  43:  figure(2)

  44:  subplot(4,1,1)

  45:  plot(t, smi,'k')

  46:  ylabel('real part of   signal sm after mixed')

  47:  xlabel('time in seconds')

  48:  grid

  49:  subplot(4,1,2)

  50:  sampling_interval = 1 / 5 /fc;

  51:  freqlimit = 0.5/ sampling_interval;

  52:  freq = linspace(-freqlimit,freqlimit,n);

  53:  plot(freq,fftshift(abs(fft( smi ))),'k');

  54:  ylabel('Spectrum of smi')

  55:  xlabel('Frequency in Hz')

  56:  grid

  57:   

  58:  smq = real(s) .* imag(lo);

  59:   

  60:  subplot(4,1,3)

  61:  plot(t, smq,'k')

  62:  ylabel('imap part of   signal sm after mixed')

  63:  xlabel('time in seconds')

  64:  grid

  65:  subplot(4,1,4)

  66:  sampling_interval = 1 / 5 /fc;

  67:  freqlimit = 0.5/ sampling_interval;

  68:  freq = linspace(-freqlimit,freqlimit,n);

  69:  plot(freq,fftshift(abs(fft( smq ))),'k');

  70:  ylabel('Spectrum of smq')

  71:  xlabel('Frequency in Hz')

  72:  grid

  73:   

  74:   

  75:  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%CIC filter %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

  76:  decf    = 10;  % Decimation Factor

  77:  diffd   = 1;   % Differential Delay

  78:  numsecs = 5;   % Number of Sections

  79:   

  80:  hm = mfilt.cicdecim(decf, diffd, numsecs);

  81:  sci=double(filter(hm,smi));

  82:  scq=double(filter(hm,smq));

  83:  n=length(sci);

  84:  t = linspace(-taup/2,taup/2,n);

  85:  figure(3)

  86:  subplot(4,1,1)

  87:  plot(t, sci,'k')

  88:  ylabel('real part of   signal smi after cic filter')

  89:  xlabel('time in seconds')

  90:  grid

  91:  subplot(4,1,2)

  92:  sampling_interval = 1 / 5 /fc;

  93:  freqlimit = 0.5/ sampling_interval;

  94:  freq = linspace(-freqlimit,freqlimit,n);

  95:  plot(freq,fftshift(abs(fft( sci ))),'k');

  96:  ylabel('Spectrum of sci')

  97:  xlabel('Frequency in Hz')

  98:  grid

  99:   

 100:   

 101:   

 102:  subplot(4,1,3)

 103:  plot(t, scq,'k')

 104:  ylabel('imap part of   signal sm after mixed')

 105:  xlabel('time in seconds')

 106:  grid

 107:  subplot(4,1,4)

 108:  sampling_interval = 1 / 5 /fc;

 109:  freqlimit = 0.5/ sampling_interval;

 110:  freq = linspace(-freqlimit,freqlimit,n);

 111:  plot(freq,fftshift(abs(fft( scq ))),'k');

 112:  ylabel('Spectrum of smq')

 113:  xlabel('Frequency in Hz')

 114:  grid

 115:   

 116:  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%lpf filter %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

 117:  Fs = 9.98;  % Sampling Frequency

 118:   

 119:  Fpass = 1;               % Passband Frequency

 120:  Fstop = 1.5;             % Stopband Frequency

 121:  Dpass = 0.057501127785;  % Passband Ripple

 122:  Dstop = 0.0001;          % Stopband Attenuation

 123:  dens  = 20;              % Density Factor

 124:   

 125:  % Calculate the order from the parameters using FIRPMORD.

 126:  [N, Fo, Ao, W] = firpmord([Fpass, Fstop]/(Fs/2), [1 0], [Dpass, Dstop]);

 127:   

 128:  % Calculate the coefficients using the FIRPM function.

 129:  b  = firpm(N, Fo, Ao, W, {dens});

 130:  Hd = dfilt.dffir(b);

 131:   

 132:  spi=double(filter(Hd,sci));

 133:  spq=double(filter(Hd,scq));

 134:  n=length(spi);

 135:  t = linspace(-taup/2,taup/2,n);

 136:  figure(4)

 137:  subplot(4,1,1)

 138:  plot(t, spi,'k')

 139:  ylabel('real part of   signal spi after lpf filter')

 140:  xlabel('time in seconds')

 141:  grid

 142:  subplot(4,1,2)

 143:  sampling_interval = 1 / 5 /fc;

 144:  freqlimit = 0.5/ sampling_interval;

 145:  freq = linspace(-freqlimit,freqlimit,n);

 146:  plot(freq,fftshift(abs(fft( spi ))),'k');

 147:  ylabel('Spectrum of spi')

 148:  xlabel('Frequency in Hz')

 149:  grid

 150:   

 151:   

 152:   

 153:  subplot(4,1,3)

 154:  plot(t, spq,'k')

 155:  ylabel('imap part of   signal sm after lpf filter')

 156:  xlabel('time in seconds')

 157:  grid

 158:  subplot(4,1,4)

 159:  sampling_interval = 1 / 5 /fc;

 160:  freqlimit = 0.5/ sampling_interval;

 161:  freq = linspace(-freqlimit,freqlimit,n);

 162:  plot(freq,fftshift(abs(fft( spq ))),'k');

 163:  ylabel('Spectrum of smq')

 164:  xlabel('Frequency in Hz')

 165:  grid