symbol_to_bit.m

瑞利衰落信道下

%symbols are de-mapped to the bits
%4PSK (Gray encoded) de-mapped to 2 bits
%inputs: in_vec (complex 4PSK vector), num_syms -- length of vector
%output: out_vec (binary -- 0/1 -- of length 2*num_syms
% demapping according to:
% 00 -- 1; 01 -- j; 11 -- -1; 10 -- -j

function [out_vec] = symbol_to_bit(in_vec, num_syms)

    const = 1/sqrt(2.)*(1+j);
    rotate_vec = const*(in_vec); 
    %phase rotated by pi/4 for ease of detecton
    re = real(rotate_vec); im = imag(rotate_vec);
    
    for ii=1:num_syms
        if((re(ii)>0)&(im(ii)>0)) 
            out_vec(2*ii-1)=0; out_vec(2*ii)=0;
        elseif((re(ii)<0)&(im(ii)>0)) 
            out_vec(2*ii-1)=0; out_vec(2*ii)=1;
        elseif((re(ii)<0)&(im(ii)<0)) 
            out_vec(2*ii-1)=1; out_vec(2*ii)=1;
        else
            out_vec(2*ii-1)=1; out_vec(2*ii)=0;
        end
    end