function y = QAM_Demod(Y,Nbits);
% y = QAM_Demod(Y,Nbits);
%

Ly = length(Y);
Levels = 2^Nbits;

% rescaling
Scale = [0.7071;
   1.5811;
   3.2404;
   6.5192];
Y = Y*Scale(Nbits);


% **** decision slicer ****
i = round(real(Y)+(Levels-1)/2);
i(i<0) = 0;
i(i>(Levels-1)) = Levels-1;

q = round(imag(Y)+(Levels-1)/2);
q(q<0) = 0;
q(q>(Levels-1)) = Levels-1;

% **** Gray decoding ****
for n = 1:Ly,
   i(n) = GrayDecoding(i(n),Nbits);
   q(n) = GrayDecoding(q(n),Nbits);
end;

% **** interleaving ****

y = zeros(1,2*Ly);
y(1:2:2*Ly) = i;
y(2:2:2*Ly) = q;