function  Pb=qostbc(SNR_dB)
%------------------------------------------------------------------------

%星座映射采用的是QPSK映射
% SNR_dB 接收天線上的接收信噪比，在仿真的過(guò)程中把接收信號(hào)的功率歸一化為1
% Pb是誤比特率
%-------------------------------------------------------------------------
SNR=10^(SNR_dB/10);
Cons=sqrt(1/2)*[1+j -1+j -1-j 1-j]; % QPSK星座
E=1; %接收端的信號(hào)功率
No=E/(SNR);%高斯白噪聲的功率譜密度
Frame=100000;
ErrorNum=0;
for i=1:1:Frame
    
            temp=rand(1);
            if (temp<0.25)
                x1=Cons((temp<0.25));
            else
                if (temp<0.5)
                    x1=Cons((temp<0.5)+1);
                else
                    if (temp<0.75)
                        x1=Cons((temp<0.75)+2);
                    else 
                        x1=Cons((temp<1)+3);
                    end
                end
            end
       
            temp=rand(1);
            if (temp<0.25)
                x2=Cons((temp<0.25));
            else
                if (temp<0.5)
                    x2=Cons((temp<0.5)+1);
                else
                    if (temp<0.75)
                        x2=Cons((temp<0.75)+2);
                    else 
                        x2=Cons((temp<1)+3);
                    end
                end
            end
        
            temp=rand(1);
            if (temp<0.25)
                x3=Cons((temp<0.25));
            else
                if (temp<0.5)
                    x3=Cons((temp<0.5)+1);
                else
                    if (temp<0.75)
                        x3=Cons((temp<0.75)+2);
                    else 
                        x3=Cons((temp<1)+3);
                    end
                end
            end
        
            temp=rand(1);
            if (temp<0.25)
                x4=Cons((temp<0.25));
            else
                if (temp<0.5)
                    x4=Cons((temp<0.5)+1);
                else
                    if (temp<0.75)
                        x4=Cons((temp<0.75)+2);
                    else 
                        x4=Cons((temp<1)+3);
                    end
                end
            end
     
    X=[x1 x2 x3 x4;-conj(x2) conj(x1) -conj(x4) conj(x3);-conj(x3) -conj(x4) conj(x1) conj(x2);x4 -x3 -x2 x1]; % 進(jìn)行空時(shí)編碼
    h1=sqrt(1/2)*(randn(1)+j*randn(1));  % 產(chǎn)生信道 
    h2=sqrt(1/2)*(randn(1)+j*randn(1));
    h3=sqrt(1/2)*(randn(1)+j*randn(1));  
    h4=sqrt(1/2)*(randn(1)+j*randn(1));
    H=[h1;h2;h3;h4];
    N=sqrt(No/2)*(randn(4,1)+j*randn(4,1));%接收端的噪聲
    bf1=sqrt(1/16)*[1;exp(j*pi*sin(0.1*pi));exp(j*2*pi*sin(0.1*pi));exp(j*3*pi*sin(0.1*pi));exp(j*4*pi*sin(0.1*pi));exp(j*5*pi*sin(0.1*pi));exp(j*6*pi*sin(0.1*pi));exp(j*7*pi*sin(0.1*pi))]'*h1*[1;exp(j*pi*sin(0.1*pi));exp(j*2*pi*sin(0.1*pi));exp(j*3*pi*sin(0.1*pi));exp(j*4*pi*sin(0.1*pi));exp(j*5*pi*sin(0.1*pi));exp(j*6*pi*sin(0.1*pi));exp(j*7*pi*sin(0.1*pi))];
    bf2=sqrt(1/16)*[1;exp(j*pi*sin(0.2*pi));exp(j*2*pi*sin(0.2*pi));exp(j*3*pi*sin(0.2*pi));exp(j*4*pi*sin(0.2*pi));exp(j*5*pi*sin(0.2*pi));exp(j*6*pi*sin(0.2*pi));exp(j*7*pi*sin(0.2*pi))]'*h2*[1;exp(j*pi*sin(0.2*pi));exp(j*2*pi*sin(0.2*pi));exp(j*3*pi*sin(0.2*pi));exp(j*4*pi*sin(0.2*pi));exp(j*5*pi*sin(0.2*pi));exp(j*6*pi*sin(0.2*pi));exp(j*7*pi*sin(0.2*pi))];
    bf3=sqrt(1/16)*[1;exp(j*pi*sin(0.8*pi));exp(j*2*pi*sin(0.8*pi));exp(j*3*pi*sin(0.8*pi));exp(j*4*pi*sin(0.8*pi));exp(j*5*pi*sin(0.8*pi));exp(j*6*pi*sin(0.8*pi));exp(j*7*pi*sin(0.8*pi))]'*h3*[1;exp(j*pi*sin(0.8*pi));exp(j*2*pi*sin(0.8*pi));exp(j*3*pi*sin(0.8*pi));exp(j*4*pi*sin(0.8*pi));exp(j*5*pi*sin(0.8*pi));exp(j*6*pi*sin(0.8*pi));exp(j*7*pi*sin(0.8*pi))];
    bf4=sqrt(1/16)*[1;exp(j*pi*sin(0.9*pi));exp(j*2*pi*sin(0.9*pi));exp(j*3*pi*sin(0.9*pi));exp(j*4*pi*sin(0.9*pi));exp(j*5*pi*sin(0.9*pi));exp(j*6*pi*sin(0.9*pi));exp(j*7*pi*sin(0.9*pi))]'*h4*[1;exp(j*pi*sin(0.9*pi));exp(j*2*pi*sin(0.9*pi));exp(j*3*pi*sin(0.9*pi));exp(j*4*pi*sin(0.9*pi));exp(j*5*pi*sin(0.9*pi));exp(j*6*pi*sin(0.9*pi));exp(j*7*pi*sin(0.9*pi))];
    R=X*[bf1;bf2;bf3;bf4]+N;
    %-----------------------------------------------進(jìn)行空時(shí)解碼
    A=(h1+h4)*conj(h1+h4)+(h2-h3)*conj(h2-h3);
    B=(h1-h4)*conj(h1-h4)+(h2+h3)*conj(h2+h3);
    C1=(conj(h1+h4)*R(1)+(h2-h3)*conj(R(2))+(h3-h2)*conj(R(3))+conj(h1+h4)*R(4))/A;
    C2=(conj(h2+h3)*R(1)+(h4-h1)*conj(R(2))+(h4-h1)*conj(R(3))-conj(h2+h3)*R(4))/B;
    C3=(conj(h2-h3)*R(1)-(h4+h1)*conj(R(2))+(h1+h4)*conj(R(3))+conj(h2-h3)*R(4))/A;
    C4=(conj(h1-h4)*R(1)+(h2+h3)*conj(R(2))+(h2+h3)*conj(R(3))+conj(h4-h1)*R(4))/B;
    X1=(C1+C4)/2;
    X4=C1-X1;
    X2=(C2+C3)/2;
    X3=C2-X2;
     if real(X1)>=0
        if imag(X1)>=0
            X1=Cons(1);
        else
            X1=Cons(4);
        end
    else
        if imag(X1)>=0
            X1=Cons(2);
        else
            X1=Cons(3);
        end
    end
     if real(X2)>=0
        if imag(X2)>=0
            X2=Cons(1);
        else
            X2=Cons(4);
        end
    else
        if imag(X2)>=0
            X2=Cons(2);
        else
            X2=Cons(3);
        end
    end
     if real(X3)>=0
        if imag(X3)>=0
            X3=Cons(1);
        else
            X3=Cons(4);
        end
    else
        if imag(X3)>=0
            X3=Cons(2);
        else
            X3=Cons(3);
        end
    end
     if real(X4)>=0
        if imag(X4)>=0
            X4=Cons(1);
        else
            X4=Cons(4);
        end
    else
        if imag(X4)>=0
            X4=Cons(2);
        else
            X4=Cons(3);
        end
    end
    ErrorNum=ErrorNum+(x1~=X1)+(x2~=X2)+(x3~=X3)+(x4~=X4);
end
Pb=ErrorNum/(Frame*4);