% BPSK modulation, 2 X Nr antenna arrayclear all;%% initialztionNr=2; % Modify here!M=2;% M-QAM,can't be modifieddata_length=500000;% there are data_length*Nt bits at allNt=2; % can't be modified!EbNo=(0:3:18);BER=zeros(size(EbNo));fr_length=data_length/(log2(M));h=waitbar(0,'Percentage Completed');set(h,'name','Alamouti STBC 2XNr...');step_wb=100/(length(EbNo)-1);wb=0;%% QAM modulationdata=randint(data_length,Nt);X=[];for n=1:Nt    temp=qammod(data(:,n),M); %M-QAM    X=[X temp];endclear temp;constellation=qammod((0:M-1),M);%%  Alamouti STBCx0=X;x1(:,1)=-conj(X(:,2));x1(:,2)=conj(X(:,1));% x1 and x2 are consecutive symbols%% channel matrixfor n=1:Nr  % rx_antennas    H(n,:,:)=(randn(fr_length,Nt)+j*randn(fr_length,Nt))/sqrt(2); %Raylaigh channelend%% transmit and receiveSNR=EbNo;for ii=1:length(SNR)    for n=1:Nr  %received signal per receiver antenna          Hn=reshape(H(n,:,:),fr_length,Nt);        Habs(:,n)=sum(abs(Hn).^2,2);        r0(:,n)= sum(Hn.*x0,2)/sqrt(Nt)  +  sqrt(0.5/(10^(SNR(ii)/10)))*(randn(fr_length,1)+j*randn(fr_length,1));% AWGN        r1(:,n)= sum(Hn.*x1,2)/sqrt(Nt)  +  sqrt(0.5/(10^(SNR(ii)/10)))*(randn(fr_length,1)+j*randn(fr_length,1));% Alamouti's paper (14)        % combine the received signals        z0(:,n)= r0(:,n).*conj(Hn(:,1))  +  conj(r1(:,n)).*Hn(:,2);        z1(:,n)= r0(:,n).*conj(Hn(:,2))  -  conj(r1(:,n)).*Hn(:,1);   % Alamouti's paper (15)    end    Xe(:,1)=sum(z0,2);    Xe(:,2)=sum(z1,2); % esitmation of X    % Maximum Likelihood Decision    for p=1:M        d0(:,p)=(sum(Habs,2)-1)*abs(constellation(p))^2  +  abs(sum(z0,2)-constellation(p)).^2;        d1(:,p)=(sum(Habs,2)-1)*abs(constellation(p))^2  +  abs(sum(z1,2)-constellation(p)).^2; % Alamouti's paper (7)    end    [y0,i0]=min(d0,[],2);    y0=constellation(i0);    [y1,i1]=min(d1,[],2);    y1=constellation(i1);    Xd=[y0.' y1.'];    % QAM demodulation    Xd_bit=[];    for n=1:Nt        temp=qamdemod(Xd(:,n),M); %M-QAM         Xd_bit=[Xd_bit temp];    end    [errnum,BER(ii)]=biterr(data,Xd_bit);    %update the waitbar    str_bar=[num2str(wb) '% Completed'];    waitbar(wb/100,h,str_bar);    wb=wb+step_wb;endclose(h);semilogy(EbNo,BER,'b-v');xlabel('Eb/No');ylabel('Bit Error Rate');grid on;