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function en_output = encoderm( x, g, alpha, puncture ) 
% Copyright Nov. 1998 Yufei Wu 
% MPRG lab, Virginia Tech. 
% for academic use only 
 
% uses interleaver map 'alpha' 
% if puncture = 1, unpunctured, produces a rate 1/3 output of fixed length 
% if puncture = 0, punctured, produces a rate 1/2 output  
% multiplexer chooses odd check bits from RSC1  
% and even check bits from RSC2 
 
% determine the constraint length (K), memory (m)  
% and number of information bits plus tail bits. 
 
[n,K] = size(g);  
m = K - 1; 
L_info = length(x);  
L_total = L_info + m;   
 
% generate the codeword corresponding to the 1st RSC coder 
% end = 1, perfectly terminated; 
input = x; 
output1 = rsc_encode(g,input,1);    % why 1? terminated?  --yzh 
 
% make a matrix with first row corresponing to info sequence 
% second row corresponsing to RSC #1's check bits. 
% third row corresponsing to RSC #2's check bits. 
 
y(1,:) = output1(1:2:2*L_total);    % y: unpuncture output of encoder; y(1,:) has m bits more than input bits   -yzh 
y(2,:) = output1(2:2:2*L_total); 
 
 
% interleave input to second encoder 
for i = 1:L_total 
   input1(1,i) = y(1,alpha(i));     %alpha--index of interleaver,   --yzh 
end 
output2 = rsc_encode(g, input1(1,1:L_total), -1 );  %input has been interleaved. L_total bits already.(see y(1,:)) so unterminated  --yzh 
y(3,:) = output2(2:2:2*L_total); 
 
% paralell to serial multiplex to get output vector 
% puncture = 0: rate increase from 1/3 to 1/2; 
% puncture = 1; unpunctured, rate = 1/3; 
 
 
if puncture > 0		% unpunctured 
   for i = 1:L_total 
       for j = 1:3 
           en_output(1,3*(i-1)+j) = y(j,i); % put the 3 bits of the same colomn to a sequential outputs  -yzh 
       end 
   end 
else			% punctured into rate 1/2 
   for i=1:L_total 
       en_output(1,n*(i-1)+1) = y(1,i); 
       if rem(i,2)  % output check bits by turns    -yzh 
      % odd check bits from RSC1 
          en_output(1,n*i) = y(2,i); 
       else 
      % even check bits from RSC2 
          en_output(1,n*i) = y(3,i); 
       end  
    end   
end 
 
% antipodal modulation: +1/-1 
en_output = 2 * en_output - ones(size(en_output));