%實(shí)驗(yàn)四 多徑傳播誤碼率與信噪比%本程序中時間單位是微秒%頻率單位為MHz%碼速率單位是Mb/sglobal dt t f df Nclose allN=2^13; %采樣點(diǎn)數(shù)L=16;   %每碼元的采樣點(diǎn)數(shù)M=N/L   %碼元數(shù)Rb=2;		%碼速率是2Mb/sTs=1/Rb;        %碼元間隔dt=Ts/L;        %時域采樣間隔df=1/(N*dt)     %頻域采樣間隔T=N*dt          %截短時間Bs=N*df/2       %系統(tǒng)帶寬Na=6;           %示波器掃描寬度為6個碼元alpha=0.5;t=linspace(-T/2,T/2,N); %時域橫坐標(biāo)f=linspace(-Bs,Bs,N)+eps;   %頻域橫坐標(biāo)%升余弦hr1=sin(pi*t/Ts)./(pi*t/Ts);hr2=cos(alpha*pi*t/Ts)./(1-(2*alpha*t/Ts).^2);hr=hr1.*hr2;		 HR=t2f(hr);tao=0.5*Ts;C=1-0.5*exp(-j*(2*pi*f*tao)); %多徑信道的傳遞函數(shù) H=C.*HR; h=real(f2t(H));for loop1=1:20     Eb_N0(loop1)=(loop1-1); %分貝值變?yōu)榫€性值    eb_n0(loop1)=10^(Eb_N0(loop1)/10);     Eb=1;     n0=Eb/eb_n0(loop1); %信道噪聲譜密度     sita=n0*Bs; %噪聲功率     n_err=0; %誤碼計(jì)數(shù)       for loop2=1:10        a=sign(randn(1,M)); %發(fā)送碼元        imp=zeros(1,N);        imp(L/2:L:N)=a/dt;        IMP=t2f(imp);        n_ch=sqrt(sita)*randn(size(t)); %信道噪聲        nr=real(f2t(t2f(n_ch).*sqrt(HR)));        sr=real(f2t(IMP.*H))+nr; %多徑信道的接收信號        y=sign(sr(L*0.5:L:N));%取樣判決        n_err=n_err+length(find(y~=a)) ;%多徑信道誤碼     end    Pe(loop1)=n_err/(M*loop2); %誤碼率     eb_n0=10.^(Eb_N0/10); %還原為線性值     figure(1)     semilogy(Eb_N0,0.5*erfc(sqrt(eb_n0)),'r');     hold on;     semilogy(Eb_N0,Pe+eps,'g');    axis([0,9,1e-4,1]);     legend('紅色：理想誤碼率曲線', '綠色：通過多徑信道后的誤碼率曲線','Location','SouthWest');     title(['取樣時間偏差為0Ts，滾降系數(shù)為0.5的誤碼率曲線']);     xlabel('Eb/N0 (dB)')    ylabel('Pe') end