function p=form_ref_matrix(P)

if P==1
    a=[-1 1];
    b=a;
elseif P==2
    bits_in=[1 0 1 1 0 1 0 0];
    full_len=length(bits_in);
    % Angle [pi/4 3*pi/4 -3*pi/4 -pi/4] corresponds to 
    % Gray code vector [00 10 11 01], respectively.
    table=exp(j*[-3/4*pi 3/4*pi 1/4*pi -1/4*pi]);  % generates QPSK symbols
    table=table([0 1 3 2]+1); % Gray code mapping pattern for QPSK symbols
    inp=reshape(bits_in,2,full_len/2);
    mod_symbols=table([2 1]*inp+1);  % maps transmitted bits into QPSK symbols
   a=mod_symbols;
   b=a;
end
p=[];;   
temp3=[];
for i=1:2*P
    for j=1:2*P
        temp2=[a(i); b(j)];
        temp3=[temp3 temp2];
        temp2=[];
    end
        p=[p temp3];
        temp3=[];
end