almouti2x2.m

This is a code for 2X2 MIMO system using Alamouti code

clc;
clear all;
close all;
clf;

no_bit=input('Enter the no. of bits generated ');

actual_data=randint(1,no_bit);
in_data=2*actual_data-1; %bpsk mapping

linColor = 'b'; 
linSym1   = 'o'; 
linSym2   = 'x';

SNRdB    = 1:1:25;
 
% Memory allocation
errRate = zeros(size(SNRdB));

%% Alamouti Space Time Code
for i = 1 : length(SNRdB)
% Main Program
    % generating the data
    % splitting the data into two vectors (first transmition, second
    % transmition in time);
    
    actual_data=randint(1,no_bit);
    in_data=2*actual_data-1; %bpsk mapping

    temp = reshape(in_data,2,no_bit/2);
    
    H  = [randn(2,no_bit)] + [sqrt(-1)*randn(2,no_bit)];
     
    % transmitted data through channel
    
    Hoverall=[];
    Hnew=[];
    for j=1:no_bit/2;
        txMod(1,j)=H(1,2*j-1)*temp(1,j)+H(1,2*j)*temp(2,j);
        txMod(2,j)=H(2,2*j-1)*temp(1,j)+H(2,2*j)*temp(2,j);
        txMod(3,j)=conj(H(1,2*j))*temp(1,j)-conj(H(1,2*j-1))*temp(2,j);
        txMod(4,j)=conj(H(2,2*j))*temp(1,j)-conj(H(2,2*j-1))*temp(2,j);
        
        Hnew=[H(1,2*j-1) H(1,2*j);H(2,2*j-1) H(2,2*j);conj(H(1,2*j)) -conj(H(1,2*j-1)); conj(H(2,2*j)) -conj(H(2,2*j-1))];
        Hoverall=[Hoverall Hnew];
        [U,S,V]=svd(Hnew);
    end
    
    % adding noise 
    txMod = awgn(txMod,SNRdB(i),'measured');
    
    % receiving the data
     
    for j=1:no_bit/2;
        [U,S,V]=svd(Hoverall(1:4,(2*j-1):(2*j)));
        p=U^(-1)*txMod(:,j)
        S1=S(1:2,:)^(-1)*p(1:2,:);
        S2=(V')^(-1)*S1;
        data(1,j)=S2(1,1);
        data(2,j)=S2(2,1);
    end
    
    data=real(data);
    for j=1:length(data(1,:))
        if(data(1,j)>0)
            data(1,j)=1;
        else
            data(1,j)=-1;
        end
        
        if(data(2,j)>0)
            data(2,j)=1;
        else
            data(2,j)=-1;
        end
    end
    
    rxData=data;
    
   [numErr errRate(i)] = symerr(rxData,reshape(in_data,2,no_bit/2));
end

 f1 = figure(1);
    semilogy(SNRdB,errRate,[linColor,'-',linSym1]);
    xlabel('SNR in dB');
    ylabel('Symbol Error Rate');
    
% Without Almouti coding
for i = 1 : length(SNRdB)
    
    actual_data=randint(1,no_bit);
    in_data=2*actual_data-1; %bpsk mapping

    temp = reshape(in_data,no_bit/2,2);
    
    % Channel Definition
     H  = 1/sqrt(2) * (randn(no_bit/2,2) + sqrt(-1)*randn(no_bit/2,2));
    
    % passing through channel
    txMod = H.*temp;
    
    % adding noise
    txMod = awgn(txMod,SNRdB(i),'measured');
    
    % decoding
    temp = txMod./H;
    
    temp=real(temp);
    for j=1:length(temp(:,1))
        if(temp(j,1)>0)
            temp(j,1)=1;
        else
            temp(j,1)=-1;
        end
        
        if(temp(j,2)>0)
            temp(j,2)=1;
        else
            temp(j,2)=-1;
        end
    end
    rxData = temp;
    
    [numErr errRate(i)] = symerr(rxData,reshape(in_data,no_bit/2,2));
end


    figure(1);
    hold on
    semilogy(SNRdB,errRate,[linColor,':',linSym2]);
    xlabel('SNR in dB');
    ylabel('Symbol Error Rate');
    title(['SER evaluation of BPSK Modulation based on Alamouti STC'])
    legend('With Alamouti Coding','Without Almouti coding(2X2)')
    grid on