diff options
Diffstat (limited to 'macros/ssbdemod.sci')
| -rw-r--r-- | macros/ssbdemod.sci | 160 |
1 files changed, 160 insertions, 0 deletions
diff --git a/macros/ssbdemod.sci b/macros/ssbdemod.sci new file mode 100644 index 0000000..7271cf9 --- /dev/null +++ b/macros/ssbdemod.sci @@ -0,0 +1,160 @@ +function z = ssbdemod(y, Fc, Fs, varargin) + +// This function performs Single Side Band Amplitude Demodulation + +// Calling Sequence +// Z = SSBDEMOD(Y,Fc,Fs) +// Z = SSBDEMOD(Y,Fc,Fs,INI_PHASE) +// Z = SSBDEMOD(Y,Fc,Fs,INI_PHASE,NUM,DEN) + +// Description +// Z = SSBDEMOD(Y,Fc,Fs) +// demodulates the single sideband amplitude modulated signal Y +// with the carrier frequency Fc (Hz). +// Sample frequency Fs (Hz). zero initial phase (ini_phase). +// The modulated signal can be an upper or lower sideband signal. +// A lowpass butterworth filter is used in the demodulation. +// +// Z = SSBDEMOD(Y,Fc,Fs,INI_PHASE) +// adds an extra argument the initial phase (rad) of the modulated signal. +// +// Z = SSBDEMOD(Y,Fc,Fs,INI_PHASE,NUM,DEN) +// adds extra arguments about the filter specifications +// i.e., the numerator and denominator of the lowpass filter. +// +// Fs must satisfy Fs >2*(Fc + BW), where BW is the bandwidth of the +// modulating signal. + + +// Examples + +// Fs =200; +// t = [0:2*Fs+1]'/Fs; +// ini_phase = 5; +// Fc = 20; +// fm1= 2; +// fm2= 3 +// x =sin(2*fm1*%pi*t)+sin(2*fm2*%pi*t); +// y = ssbmod(x,Fc,Fs,ini_phase); +// o = ssbdemod(y,Fc,Fs,ini_phase); +// z = fft(y); +// zz =abs(z(1:length(z)/2+1 )); +// axis = (0:Fs/length(zz):Fs -(Fs/length(zz)))/2; +// +// figure +// subplot(3,1,1); plot(x); +// title(' Message signal'); +// subplot(3,1,2); plot(y); +// title('Amplitude modulated signal'); +// subplot(3,1,3); plot(axis,zz); +// title('Spectrum of amplitude modulated signal'); +// z1 =fft(o); +// zz1 =abs(z1(1:length(z1)/2+1 )); +// axis = (0:Fs/length(zz1):Fs -(Fs/length(zz1)))/2; +// figure +// subplot(3,1,1); plot(y); +// title(' Modulated signal'); +// subplot(3,1,2); plot(o); +// title('Demodulated signal'); +// subplot(3,1,3); plot(axis,zz1); +// title('Spectrum of Demodulated signal'); + +// See also +// ssbmod + +// Authors +// Pola Lakshmi Priyanka, IIT Bombay// + +//*************************************************************************************************************************************// + +// Check number of input arguments +[outa,inpa]=argn(0) +if(inpa > 6) + error("comm:ssbdemod:Too Many Input Arguments"); +end +//funcprot(0) //to protect the function + +//Check y,Fc, Fs. +if(~isreal(y)| ~or(type(y)==[1 5 8]) ) + error("comm:ssbdemod: Y must be real"); +end + +if(~isreal(Fc) | ~isscalar(Fc) | Fc<=0 | ~or(type(Fc)==[1 5 8]) ) + error("comm:ssbdemod:Fc must be Real, scalar, positive"); +end + +if(~isreal(Fs) | ~isscalar(Fs) | Fs<=0 | ~or(type(Fs)==[1 5 8]) ) + error("comm:ssbdemod:Fs must be Real, scalar, positive"); +end + +// Check if Fs is greater than 2*Fc +if(Fs<=2*Fc) + error("comm:ssbdemod:Fs<2Fc:Nyquist criteria"); +end + +// Check initial phase + +if(inpa<4 ) + ini_phase = 0; +else + ini_phase = varargin(1); +end +if(~isreal(ini_phase) | ~isscalar(ini_phase)| ~or(type(ini_phase)==[1 5 8]) ) + error("comm:ssbdemod:Initial phase shoould be Real"); +end + +// Filter specifications +if(inpa<5) + H = iir(5,'lp','butt',[Fc/Fs,0],[0,0]); + + num = coeff(H(2)); + den = coeff(H(3)); + num = num(length(num):-1:1); + den = den(length(den):-1:1); + +// Check that the numerator and denominator are valid, and come in a pair +elseif( (inpa == 5) ) + error("comm:ssbdemod:NumDenPair: Filter error :Two arguments required"); + +// Check to make sure that both num and den have values +elseif( bitxor( isempty(varargin(1)), isempty(varargin(2)))) + error(message('comm:ssbdemod:Filter specifications')); +elseif( isempty(varargin(1)) & isempty(varargin(2)) ) + H = iir(7,'lp','butt',[Fc/Fs*2*%pi,0],[0,0]); + + num = coeff(H(2)); + den = coeff(H(3)); + num = num(length(num):-1:1); + den = den(length(den):-1:1); +else + num = varargin(1); + den = varargin(2); +end + + + +// check if Y is one dimensional +wid = size(y,1); +if(wid ==1) + y = y(:); +end + +// Demodulation +t = (0 : 1/Fs :(size(y,1)-1)/Fs)'; +t = t(:, ones(1, size(y, 2))); +z = y .* cos(2*%pi * Fc * t + ini_phase); +for i = 1 : size(z, 2) + z(:, i) = filter(num, den, z(:, i)) ; + z=z(length(z):-1:1) + z(:, i) = filter(num, den, z(:, i)) ; + z=z*-2; +end; + +// restore the output signal to the original orientation +if(wid == 1) + z = z'; +end + +endfunction + +// End of function |