Index exceeds the number of array elements (4)

Hi all,

I try to run the code about Alamouti_scheme but I had an error "Index exceeds the number of array elements (4)", could you guys please help me find out my problem

Thank you very much

function [mod_symbols,sym_table,M] = modulator(bitseq,b)

%MIMO-OFDM Wireless Communications with MATLAB¢ç   Yong Soo Cho, Jaekwon Kim, Won Young Yang and Chung G. Kang
%2010 John Wiley & Sons (Asia) Pte Ltd

N_bits = length(bitseq);
sq10=sqrt(10);
if b==1      % BPSK modulation
   sym_table=exp(j*[0 -pi]);  sym_table=sym_table([1 0]+1);
   inp=bitseq;   mod_symbols=sym_table(inp+1);
   M=2;
 elseif b==2    % QPSK modulation
   sym_table = exp(j*pi/4*[-3 3 1 -1]); sym_table=sym_table([0 1 3 2]+1);
   inp=reshape(bitseq,b,N_bits/b);
   %mod_symbols=sym_table(565);
   mod_symbols=sym_table([2 1]*inp+1);
   M=4;
 elseif b==3    % generates 8PSK symbols
   sym_table=exp(j*pi/4*[0:7]); sym_table=sym_table([0 1 3 2 6 7 5 4]+1);
   inp=reshape(bitseq,b,N_bits/b); mod_symbols=sym_table([4 2 1]*inp+1);
   M=8;   
 elseif b==4    % 16-QAM modulation
   m=0;  sq10=sqrt(10);
   for k=-3:2:3
      for l=-3:2:3
         m=m+1; sym_table(m) = (k+j*l)/sq10; % power normalization
      end
   end
   sym_table = sym_table([0 1 3 2 4 5 7 6 12 13 15 14 8 9 11 10]+1); % Gray code mapping pattern for 8-PSK symbols
   inp = reshape(bitseq,b,N_bits/b);
   mod_symbols = sym_table([8 4 2 1]*inp+1);  % maps transmitted bits into 16QAM symbols
   M=16; %16 constellation points
 else
   error('Unimplemented modulation');
end


Alamouti_scheme.m

%MIMO-OFDM Wireless Communications with MATLAB¢ç   Yong Soo Cho, Jaekwon Kim, Won Young Yang and Chung G. Kang
%2010 John Wiley & Sons (Asia) Pte Ltd

clear; clf;
L_frame=130; N_Packets=4000; % Number of frames/packet and Number of packets 
NT=2; NR=1; b=2; 
SNRdBs=[0:2:30];  sq_NT=sqrt(NT); sq2=sqrt(2);
for i_SNR=1:length(SNRdBs)
   SNRdB=SNRdBs(i_SNR);  sigma=sqrt(0.5/(10^(SNRdB/10)));
   for i_packet=1:N_Packets
      msg_symbol=randi(L_frame*b,NT);
      tx_bits=msg_symbol.';  tmp=[];   tmp1=[];
      for i=1:NT
         [tmp1,sym_tab,P] = modulator(tx_bits(i,:),b); tmp=[tmp; tmp1];
      end
      X=tmp.'; X1=X; X2=[-conj(X(:,2)) conj(X(:,1))];
      for n=1:NT
         Hr(n,:,:)=(randn(L_frame,NT)+j*randn(L_frame,NT))/sq2;
      end
      H=reshape(Hr(n,:,:),L_frame,NT);  Habs(:,n)=sum(abs(H).^2,2);
      R1 = sum(H.*X1,2)/sq_NT + sigma*(randn(L_frame,1)+j*randn(L_frame,1));
      R2 = sum(H.*X2,2)/sq_NT + sigma*(randn(L_frame,1)+j*randn(L_frame,1));
      Z1 = R1.*conj(H(:,1)) + conj(R2).*H(:,2);
      Z2 = R1.*conj(H(:,2)) - conj(R2).*H(:,1);
      for m=1:P.
         tmp = (-1+sum(Habs,2))*abs(sym_tab(m))^2;
         d1(:,m) = abs(sum(Z1,2)-sym_tab(m)).^2 + tmp;
         d2(:,m) = abs(sum(Z2,2)-sym_tab(m)).^2 + tmp;
      end
      [y1,i1]=min(d1,[],2);   S1d=sym_tab(i1).';    clear d1
      [y2,i2]=min(d2,[],2);   S2d=sym_tab(i2).';    clear d2
      Xd = [S1d S2d];   tmp1=X>0;  tmp2=Xd>0;
      noeb_p(i_packet) = sum(sum(tmp1~=tmp2));% for coded
   end % End of FOR loop for i_packet
   BER(i_SNR) = sum(noeb_p)/(N_Packets*L_frame*b);
end    % End of FOR loop for i_SNR
semilogy(SNRdBs,BER), axis([SNRdBs([1 end]) 1e-6 1e0]); 
grid on;  xlabel('SNR[dB]'); ylabel('BER');

and the error is:

>> Alamouti_scheme
Index exceeds the number of array elements (4).

Error in modulator (line 16)
   mod_symbols=sym_table([2 1]*inp+1);

Error in Alamouti_scheme (line 16)
         [tmp1,sym_tab,P] = modulator(tx_bits(i,:),b); tmp=[tmp; tmp1];
 

[kris]

Did u solve it now?

Answer 1

[Bob Thompson]

The error is occuring because sym_table is a 1x4 complex double array, but in the particular line you are attempting to call element 357. I am not sure exactly what you're trying to do with this line, but perhaps indexing is not it? If you are actually trying to index here, you either need to change the value of bitseq, which is significantly greater than sym_table, or you need to make sym_table much much larger.

Answer 2

[Walter Roberson]

   msg_symbol=randi(L_frame*b,NT);

The code was improperly converted from earlier code that was written using randint(). randint() had the size first and the range after. The correct conversion should probably be something like

     msg_symbol = randi([0, NT-1], 1, L_frame*b);