一、實(shí)驗(yàn)?zāi)康?、熟悉Matlab環(huán)境并編寫函數(shù)實(shí)現(xiàn)功能；2、掌握數(shù)字基帶傳輸系統(tǒng)基本知識(shí)。二、實(shí)驗(yàn)內(nèi)容1、產(chǎn)生一個(gè)長(zhǎng)度為1000的二進(jìn)制隨機(jī)序列，“0”的概率為0.7,”1”的概率為0.3；下面是產(chǎn)生的隨機(jī)序列前20個(gè)符號(hào)對(duì)應(yīng)的波形：2、對(duì)上述數(shù)據(jù)進(jìn)行歸零AMI編碼，脈沖寬度為符號(hào)寬度的50%，波形采樣率為符號(hào)率的8倍，話出前20個(gè)符號(hào)對(duì)應(yīng)的波形（同時(shí)給出前20位信源序列）；3、改用HDB3碼，畫出前20個(gè)符號(hào)對(duì)應(yīng)的波形；4、改用密勒碼，畫出前20個(gè)符號(hào)對(duì)應(yīng)的波形；5、分別對(duì)上述1000個(gè)符號(hào)的波形進(jìn)行功率譜估計(jì)，畫出功率譜；6、改變信源“0”的概率，觀察AMI碼的功率譜變化情況。原序列全為1時(shí)，功率譜為可以看到原序列中”0”的個(gè)數(shù)越少，在1/2碼速率處出現(xiàn)的尖峰會(huì)越高，也就說(shuō)能量會(huì)更集中。三、實(shí)驗(yàn)代碼clear;fs=8;%采樣率倍數(shù)X=ceil(rand(1,1000)-0.5)%長(zhǎng)度為1000的序列,"0"的概率為0.7,"1"的概率為0.3L=length(X);%AMIj=-1;%-1和1交替變換fori=1:LifX(i)==1y1(i)=-j;j=y1(i);elsey1(i)=X(i);endend%HDB3count=0%計(jì)算連"0"的個(gè)數(shù)y2=y1;sign=0;%標(biāo)志V碼極性交替V=zeros(1,L);%存儲(chǔ)破壞脈沖V的位置B=zeros(1,L);%存儲(chǔ)調(diào)節(jié)脈沖B的位置fori=1:Lify1(i)==0count=count+1;ifcount==4ifi>4y2(i)=y2(i-4);elsey2(i)=1;endV(i)=y2(i);ify2(i)==signy2(i)=-y2(i);y2(i-3)=y2(i);B(i-3)=y2(i-3);V(i)=y2(i);fork=i+1:Ly2(k)=-y2(k);endendsign=y2(i);endelsecount=0;endend%Milery3=zeros(1,2*L);sign1=0;%"10"和"01"交替表示sign0=1;%計(jì)算連"0"的個(gè)數(shù),1個(gè)"0"sign0=1,多個(gè)"0"sign0=0fori=1:LifX(i)==1y3(2*i-1)=sign1;y3(2*i)=abs(1-sign1);sign1=abs(1-sign1);sign0=1;elseifsign0==1y3(2*i-1)=sign1;y3(2*i)=sign1;sign0=0;elsesign1=abs(1-sign1);y3(2*i-1)=sign1;y3(2*i)=sign1;sign0=0;endendend%波形采樣y=zeros(1,L*fs);X_out=zeros(1,L*fs);y1_out=zeros(1,L*fs);y2_out=zeros(1,L*fs);y3_out=zeros(1,L*fs);fori=1:L*fsifmod(i-1,8)<=5&mod(i-1,8)>=2%50%脈沖寬度y(i)=1;elsey(i)=0;endX_out(i)=X(ceil(i/8));y1_out(i)=y(i)*y1(ceil(i/8));%歸零碼y2_out(i)=y(i)*y2(ceil(i/8));y3_out(i)=y3(ceil(i/4));end%畫出波形figure(1)plot(X_out(1:160));axis([1,160,-0.2,1.2]);title('原始序列');figure(2)subplot(311);plot(y1_out(1:160));axis([1,160,-1.2,1.2]);title('歸零AMI碼');subplot(312);plot(y2_out(1:160));axis([1,160,-1.2,1.2]);title('HDB3碼')subplot(313);plot(y3_out(1:160));axis([1,160,-0.2,1.2]);title('Miler碼');%功率譜密度C_y1=xcorr(y1_out);%求自相關(guān)函數(shù)C_y2=xcorr(y2_out);C_y3=xcorr(y3_out);S_y1=abs(fft(C_y1));%自相關(guān)函數(shù)作傅里葉變換S_y2=abs(fft(C_y2));S_y3=abs(fft(C_y3));figure(3)subplot(311);plot(10*log10(S_y1));ti