clear all;
SNR=0:1:30;
snr=10.^(SNR/10);
sigma=sqrt(2./snr);%噪聲與信號的幅度比值
K=400000;           %未調制信號長度，信號越長，曲線越精確
data=randint(1,K);
%%%%%%%%%%%%%%%%%%%%設置參數%%%%%%%%%%%%%%%%%%%%%%%%
nt=4;%發射天線數
nr=1;%接收天線數
n=4; %調制方式QPSK

%%%%%%%%%%%%%%%%%%%%QPSK信號調制%%%%%%%%%%%%%%%%%%%%

npskdata=npsk(n,data);%調用調制方式子函數
x=npskdata;           %調制后信號

%%%%%%%%%%%%%%%%%%%Alamouti%%%%%%%%%%%%%%%%%%%%%%%%
for k=1:length(SNR)
    error_symbol=0;%對每一個信噪比下的誤符號率清零
	for i=1:length(npskdata)/4
    	x1=x(4*i-3);
        x2=x(4*i-2);         %對信源進行空時操作，每兩個數據符號一起
     	x3=x(4*i-1);
        x4=x(4*i);         %對信源進行空時操作，每兩個數據符號一起
        X=[x1 -x2 -x3 -x4 x1' -x2' -x3' -x4'
           x2  x1  x4 -x3 x2'  x1'  x4' -x3'
           x3 -x4  x1  x2 x3' -x4'  x1'  x2'
           x4  x3 -x2  x1 x4'  x3' -x2'  x1'];%空時發射信號矩陣
		h=rey(nt,nr);      %調用信道子函數
		noise=sigma(k).*rey(8,nr);
        R=sqrt(1/2).*h*X+noise;%接收信號矩陣
        
%         y=zeros(1,nt);
%         y(1)= r(1,1)*H(1,1)'+r(1,2)*H(1,2)'+r(1,3)*H(1,3)'+r(1,4)*H(1,4)'+r(1,5)'*H(1,1)+r(1,6)'*H(1,2)+r(1,7)'*H(1,3)+r(1,8)'*H(1,4);
%         y(2)= r(1,1)*H(1,2)'-r(1,2)*H(1,1)'-r(1,3)*H(1,4)'+r(1,4)*H(1,3)'+r(1,5)'*H(1,2)-r(1,6)'*H(1,1)-r(1,7)'*H(1,4)+r(1,8)'*H(1,3);
%         y(3)= r(1,1)*H(1,3)'+r(1,2)*H(1,4)'-r(1,3)*H(1,1)'-r(1,2)*H(1,2)'+r(1,5)'*H(1,3)+r(1,6)'*H(1,4)-r(1,7)'*H(1,1)-r(1,8)'*H(1,2);
%         y(4)=-r(1,1)*H(1,4)'-r(1,2)*H(1,3)'+r(1,3)*H(1,2)'-r(1,2)*H(1,1)'-r(1,5)'*H(1,4)-r(1,6)'*H(1,3)+r(1,7)'*H(1,2)-r(1,8)'*H(1,1);
        H=[h(1)   h(2)   h(3)   h(4)
           h(2)  -h(1)   h(4)  -h(3)
           h(3)  -h(4)  -h(1)   h(2)
           h(4)   h(3)  -h(2)  -h(1)
           h(1)'  h(2)'  h(3)'  h(4)'
           h(2)' -h(1)'  h(4)' -h(3)'
           h(3)' -h(4)' -h(1)'  h(2)'
           h(4)'  h(3)' -h(2)' -h(1)'];
        r=zeros(1,8);
        r=[R(1) R(2) R(3) R(4) R(5)' R(6)' R(7)' R(8)'];
        y=zeros(nt,1);
        y=H'*r.';
        y=y.';
	    %進行最大似然檢測
	    DEC_X=judge(y);

        %統計符號錯誤的總數
	    if DEC_X(1)~=x1
	    error_symbol=error_symbol+1;
	    end
	    if DEC_X(2)~=x2
	    error_symbol=error_symbol+1;
        end
        if DEC_X(3)~=x3
	    error_symbol=error_symbol+1;
	    end
	    if DEC_X(4)~=x4
	    error_symbol=error_symbol+1;
	    end
	end
     SER(k)=error_symbol/length(npskdata);
end
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%畫圖%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
semilogy(SNR,SER,'b*-');
grid on
legend('STBC4C QPSK(4TX 1RX)')
title('QPSK調制下的速率為1/2的4天線復信號STBC在慢瑞利衰減信道上的誤符號率性能')
xlabel('信噪比/dB');
ylabel('誤符號率');
hold on