fade.m

OFDM multipath fading channel model jakes

% fade.m
% Generate Rayleigh fading
function [theta, ramp, xc, xs] = fade( nsamp, tstp, fm, N1, counter, flat)

%******************* variables *******************************
% nsamp         Number of samples to be simulated
% tstp          Minimum time resolution
% fm            Maximum doppler frequency (Hz)
% N1            Number of waves in order to generate fading
% counter       fading counter
% flat          flat fading or not
% theta         phase of fading channel impulse response (rad)
% ramp          Amplitude contaminated by fading
% xc            Cosine value contaminated by fading
% xs            Sine value contaminated by fading
%***************************************************************

ac0 = sqrt(1.0./(2.0.*(N1+1))); % power nomalized constant(ich)
as0 = sqrt(1.0./(2.0.*N1));    % power nomalized constant(qch)

% some parameters
wm = 2.0.*pi.*fm;
N = 4.*N1+2;
ts = tstp;
wmts = wm.*ts;
paino = pi./N1;

xc=zeros(1,nsamp);
xs=zeros(1,nsamp);
ic=[1:nsamp]+counter;

for nn = 1:N1
    cwn = cos(cos(2.0.*pi.*nn./N).*ic.*wmts);
    xc = xc+cos(paino.*nn).*cwn;

    xs = xs+sin(paino.*nn).*cwn;
end

cwmt = sqrt(2.0).*cos(ic.*wmts);
xc = (2.0.*xc + cwmt).*ac0;
xs = 2.0.*xs.*as0;

ramp=sqrt(xc.^2+xs.^2); % amplitude contaminated by fading

% calculate theta
for i=1:nsamp
    if xc(i)>0 & xs(i)>0       % the 1st quadrant
        theta(i) = atan(xs(i)/xc(i));
    elseif xc(i)<0 & xs(i)<0   % the 3st quadrant
        theta(i) = atan(xs(i)/xc(i)) + pi;
    elseif xc(i)<0 & xs(i)>0    % the 2nd quadrant
        theta(i) = atan(xs(i)/xc(i)) + pi;
    else                            % the 4nd quadrant
        theta(i) = atan(xs(i)/xc(i)) + 2*pi;
    end
end

end

%******************* end of file **********************************