diff_enc.m

瑞利衰落信道下

%generates the 4PSK Gray encoded symbols
%inputs/outputs
%input -- binary (0,1) vector 
%num_bits -- length of input (make it even)
%c_vec -- 4PSK output of length num_bits/2
% 00 -- 1; 01 -- j; 11 -- -1; 10 -- -j

function [out_vec] = diff_enc(in_vec, num_sym)

    initial=1/sqrt(2)*(1+j);

    for ii=1:num_sym
        if(ii==1) 
            out_vec(ii)=in_vec(ii)*initial;
        else
            out_vec(ii)=in_vec(ii)*out_vec(ii-1);
        end
        
        % do the quantization of out_vec to 
        % overcome any prevision errors
        if(mod(ii,1000)==0)
            ang=(angle(out_vec(ii)))/(pi/4);
            ang=round(ang);
            out_vec(ii)=exp(j*ang*pi/4);
        end
            
    end