hold on
%SNR upto 20 dBs
EbNo=[0:2:20];

%N, M: number of transmit and receive antennas

N=3;
M=4;

%initialize packet_count
idx=1;

 Num=100;
K=1000;

for SNR=EbNo
    sigma=0.5/(10^(SNR/10));
       for packet_count=1:Num
% we are interested in transmitting 'K' SYMBOLS not bits. Hence, K*2 for QPSK
% etc.
                data=randint(K*2,4);
                BIT=2;
           
        
tx_bits=data.';
temp1=[];
temp=[];
for i=1:4 %N is actually 3, but we require 4 tx antenna coding to be transmitted from 3 antennas.
  %  [temp1 s P]=tx_modulate(tx_bits(i,:),modulation);
    %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
       bits_in(i,:)=tx_bits(i,:);
   full_len = length(bits_in(i,:));
   %QPSK modulation
   
   % Angle [pi/4 3*pi/4 -3*pi/4 -pi/4] corresponds to 
   % Gray code vector [00 10 11 01], respectively.
   table=exp(j*[-3/4*pi 3/4*pi 1/4*pi -1/4*pi]);  % generates QPSK symbols
   table=table([0 1 3 2]+1); % Gray code mapping pattern for QPSK symbols
   inp=reshape(bits_in(i,:),2,full_len/2);
   mod_symbols=table([2 1]*inp+1);  % maps transmitted bits into QPSK symbols
   P=4;% 4 constellation points
    %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
      temp1=mod_symbols;
   s=table;
    temp=[temp; temp1];
    temp1=0;
end

%ready to transmit symbols of length 'K'
X=temp.';
fr_length=length(X);
 
%block signals in the lth time slot-Block coding for G3 STBC 
 x0=X(:,1);
 x1=X(:,1:3);
 x2(:,1)=-X(:,2); x2(:,2)=X(:,1); x2(:,3)=-X(:,4);
 x3(:,1)=-X(:,3); x3(:,2)=X(:,4); x3(:,3)=X(:,1);
 x4(:,1)=-X(:,4); x4(:,2)=-X(:,3); x4(:,3)=X(:,2);
 x5=conj(x1);
 x6=conj(x2);
 x7=conj(x3);
 x8=conj(x4);
 
 % form the channel matrix
 for n=1:N
    % if channel_model=='AWGN    '
      %   Hr(n,:,:)=ones(fr_length,N);
     %else
         Hr(n,:,:)=(randn(fr_length,N)+j*randn(fr_length,N))/sqrt(2);
    % end
 end
        

for n=1:N
%transmission matrix   
H=reshape(Hr(n,:,:),fr_length,N);
Habs(:,n)=sum(abs(H).^2,2);

 %received signal per receiver antenna   
 r1(:,n)=sum(H.*x1,2)/sqrt(N)+sqrt(sigma)*(randn(fr_length,1)+j*randn(fr_length,1));
 r2(:,n)=sum(H.*x2,2)/sqrt(N)+sqrt(sigma)*(randn(fr_length,1)+j*randn(fr_length,1));
 
 r3(:,n)=sum(H.*x3,2)/sqrt(N)+sqrt(sigma)*(randn(fr_length,1)+j*randn(fr_length,1));
 r4(:,n)=sum(H.*x4,2)/sqrt(N)+sqrt(sigma)*(randn(fr_length,1)+j*randn(fr_length,1));
 
 r5(:,n)=sum(H.*x5,2)/sqrt(N)+sqrt(sigma)*(randn(fr_length,1)+j*randn(fr_length,1));
 r6(:,n)=sum(H.*x6,2)/sqrt(N)+sqrt(sigma)*(randn(fr_length,1)+j*randn(fr_length,1));
 
 r7(:,n)=sum(H.*x7,2)/sqrt(N)+sqrt(sigma)*(randn(fr_length,1)+j*randn(fr_length,1));
 r8(:,n)=sum(H.*x8,2)/sqrt(N)+sqrt(sigma)*(randn(fr_length,1)+j*randn(fr_length,1));

  % demodulate the received signals
  z1_1(:,n)=r1(:,n).*conj(H(:,1))+r2(:,n).*conj(H(:,2))+r3(:,n).*conj(H(:,3));
  z1_2(:,n)=conj(r5(:,n)).*H(:,1)+conj(r6(:,n)).*H(:,2)+conj(r7(:,n)).*H(:,3);
  z1(:,n)=z1_1(:,n)+z1_2(:,n);
  
  z2_1(:,n)=r1(:,n).*conj(H(:,2))-r2(:,n).*conj(H(:,1))+r4(:,n).*conj(H(:,3));
  z2_2(:,n)=conj(r5(:,n)).*H(:,2)-conj(r6(:,n)).*H(:,1)+conj(r8(:,n)).*H(:,3);
  z2(:,n)=z2_1(:,n)+z2_2(:,n);
  
  z3_1(:,n)=r1(:,n).*conj(H(:,3))-r3(:,n).*conj(H(:,1))-r4(:,n).*conj(H(:,2));
  z3_2(:,n)=conj(r5(:,n)).*H(:,3)-conj(r7(:,n)).*H(:,1)-conj(r8(:,n)).*H(:,2);
  z3(:,n)=z3_1(:,n)+z3_2(:,n);
  
  z4_1(:,n)=-r2(:,n).*conj(H(:,3))+r3(:,n).*conj(H(:,2))-r4(:,n).*conj(H(:,1));
  z4_2(:,n)=-conj(r6(:,n)).*H(:,3)+conj(r7(:,n)).*H(:,2)-conj(r8(:,n)).*H(:,1);
  z4(:,n)=z4_1(:,n)+z4_2(:,n);
  
  
end

%uncoded(1,1)
r01=H(:,1).*x0+sqrt(sigma)*(randn(fr_length,1)+j*randn(fr_length,1));

  
%form estimates
for m=1:P
   d01(:,m)=abs(r01-H(:,1)*s(m)).^2; %uncoded signal
%coded signals       
   d1(:,m)=abs(sum(z1,2)-s(m)).^2+(-1+sum(Habs,2))*abs(s(m))^2;
   d2(:,m)=abs(sum(z2,2)-s(m)).^2+(-1+sum(Habs,2))*abs(s(m))^2;
   d3(:,m)=abs(sum(z3,2)-s(m)).^2+(-1+sum(Habs,2))*abs(s(m))^2;
   d4(:,m)=abs(sum(z4,2)-s(m)).^2+(-1+sum(Habs,2))*abs(s(m))^2;
end
% determine the minimum of estimates      

%decision for detecting uncoded
      [y0,i0]=min((d01),[],2);
      s0d=s(i0).';
      
      clear d01 
      
%decision for detecting s1     
      [y1,i1]=min(d1,[],2);
      s1d=s(i1).';
      
      clear d1
%decision for detecting s2     
      [y2,i2]=min(d2,[],2);
      s2d=s(i2).';
      
      clear d2
%decision for detecting s3     
      [y3,i3]=min(d3,[],2);
      s3d=s(i3).';
      
      clear d3
%decision for detecting s4     
      [y4,i4]=min(d4,[],2);
      s4d=s(i4).';
      
      clear d4

% form received symbols    
    Xd=[s1d s2d s3d s4d];
%determine symbol errors   
error_un(packet_count)=sum(X(:,1)~=s0d);% for uncoded
temp1=X>0;
temp2=Xd>0;
error(packet_count)=sum(sum(temp1~=temp2));% for coded
       end% end of FOR loop for "packet_count"
%calculate FER, SER and BER for current idx

%for uncoded signal
  SER_uncoded(idx)=sum(error_un)/(Num*K);
  BER_uncoded(idx)=SER_uncoded(idx)/BIT;
  FER_uncoded(idx)=SER_uncoded(idx)*K;

%for coded signal
  SER(idx)=sum(error)/(Num*K);
  BER(idx)=SER(idx)/BIT;
  FER(idx)=SER(idx)*K;
  
%increment idx  
  idx=idx + 1;
end% end of FOR loop for SNR
%semilogy(EbNo,SER,'g')
%hold on
semilogy(EbNo,BER,'-^')
%legend('SER','BER')
clc
clear