function X = QAM_Mod(x,Nbits);
% X = QAM_Mod(x,Nbits);
%

Lx = length(x);

i = x(1:2:Lx);
q = x(2:2:Lx);

for n = 1:Lx/2,
   i(n) = GrayCoding(i(n),Nbits);
   q(n) = GrayCoding(q(n),Nbits);
end;

Levels = 2^Nbits;
i = i - (Levels-1)/2;
q = q - (Levels-1)/2;

X = i + sqrt(-1)*q;

% scaling for uniform bit distribution
Scale = 1./[0.7071; 
   1.5811;
   3.2404;
   6.5192];

X = X*Scale(Nbits);