%gives the complex fade coefficients
%output power is approximately unity
%inputs:max_doppler_freq (Hz); sample_freq (Hz); num_samples

function [c_vec] = 4PSK_Gray(input, num_bits)

    for ii=1:num_bits/2
        if((input(2*ii-1)==0)&(input(2*ii)==0))
            c_vec(ii)=1;
        elseif((input(2*ii-1)==0)&(input(2*ii)==1))
            c_vec(ii)=i;
        elseif((input(2*ii-1)==1)&(input(2*ii)==1))
             c_vec(ii)=-1;
        else
             c_vec(ii)=-i;
        end
end