function s = qam (M,N_s,sigma,sd1,sd2) % =====================================================================% function s = qam (M,N_s,sigma,sd1,sd2)% ---------------------------------------------------------------------%% creates a sequence of N_s samples of M-QAM with variance sigma^2,% where M is of the form 4*N^2 (for integer N).%% ===================================================================== clear j % a convenient quantity N = sqrt(M/4);					% M = 4N^2 % check if valid M (via checking if N is an integer) if N ~= floor(N),   error('M must be of the form 4*N^2 for integer N');  end % generate M-QAM with constellation points at +/-{1,3,5,7,etc.} rand('seed',sd1); sr = 2*(floor(2*N*rand(1,N_s))-N+0.5); rand('seed',sd2); si = 2*(floor(2*N*rand(1,N_s))-N+0.5); s = sr + j*si;  % adjust variance  var_cur = 2/N*sum((1+2*[0:N-1]).^2);		% current variance s = s*(sigma/sqrt(var_cur));