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1、《概率論與隨機(jī)信號(hào)分析》實(shí)驗(yàn)報(bào)告實(shí)驗(yàn)名稱:窄帶系統(tǒng)特性指導(dǎo)教師:張正明成績(jī):姓名:班級(jí):學(xué)號(hào):一.實(shí)驗(yàn)?zāi)康暮腿蝿?wù)1.了解窄帶系統(tǒng)的特性2.了解信號(hào)和噪聲經(jīng)過窄帶系統(tǒng)前后的統(tǒng)il?性二.實(shí)驗(yàn)原理介紹如果帶通信號(hào)的帶寬與中心頻率相比非常小,即1
2、<(0]V(Z)=5(Z)+/?(Z)v(z)=<(Ocos(obO-%(,)siii(呀f)n(0=(z)cos(^0-(/)siii(obO/.(Z)=z4cosO(0+<,(0^,(0=Asina>(/)+^,(/)rAonOnZ>o只有噪聲時(shí),
3、輸出噪聲幅度服從正態(tài)分布,而包絡(luò)服從瑞利分布。三.實(shí)驗(yàn)設(shè)備介紹1.IBMPC機(jī)一臺(tái);2.MATLAB工具軟件。pq.實(shí)驗(yàn)內(nèi)容和步驟%噪盧經(jīng)過窄帶系統(tǒng)closeallclearall%信號(hào)、噪聲產(chǎn)生和濾波器沒計(jì)f0-30e+6:%系統(tǒng)中心頻率fs=5.7*f0;%采樣頻率bb=3e+6;%濾波器帶寬%巴菲奧斯濾波器設(shè)計(jì)[bOaO]=butter(2,[(fO-bb/2)/(fs/2),(fO+bb/2)/(fs/2)]):%帶通Butterworth波波器系數(shù)[bvav]=butter(2,bb/2/(fs/2)):%低通Butterworth波波器系數(shù)[hff]=fre
4、qz(bO,aO,100,fs);%帶通濾波器頻率響應(yīng)plot(ff,abs(h))title(’系統(tǒng)頻率響應(yīng)’);gridon%信號(hào)及其頻譜figuretl=10e-6;%信號(hào)時(shí)寬t=0:1/fs:tl;ss=sin(2*pi*f0*t):%信號(hào)時(shí)域表示subplot(2,3,1)plot(t,ss)title(’輸入信號(hào)’):gridonsubplot(2,3,4):n=length(ss);fl=(0:(n-l)/2)/n*fs;%頻域頻率點(diǎn)nl=length(fl):fss=abs(fft(ss));plot(fl,fss(1:nl))titleC輸入信號(hào)頻譜’
5、);gridon;%信號(hào)經(jīng)過系統(tǒng)ys=filter(bO,aO,ss);%信號(hào)經(jīng)過BPF后輸出subplot(2,3,2)plot(t,ys)title(’輸入信號(hào)’);gridonsubplot(2,3,5);fys=abs(fft(ys)):%中頻輸出后FFTplot(f1,fys(1:nl))title(’輸入信號(hào)頻譜’);gridon;%信號(hào)直方閣統(tǒng)計(jì)subplot(2,3,3)hs=ss;hist(hs,20);title(’濾波前信兮人小直方圖’)subplot(2,3,6)hs=ys;hist(hs,20):title(’濾波后信號(hào)大小直方圖’)%噪聲及其
6、功率譜figure;sn=rand(l,n);%U(0,l)噪聲sn=2*sn-l;%U(-1,1)噪聲subplot(2,3,1)plot(t,sn);titleC輸入噪聲U(-l,1)’);gridon;subplot(2,3,4);rn二xcorr(sn,sn,’biased’);%噪聲的相關(guān)函數(shù)fn=abs(fft(rn));f2=(0:n-l)/(2*n+l)*fs;plot(f2,fn(l:n));title(’輸入噪聲功率譜’);gridon;%噪聲經(jīng)過系統(tǒng)yn=filter(bO,aO,sn);subplot(2,3,2)plot(t,yn);title
7、(’輸出噪聲’);gridonsubplot(2,3,5)rn=xcorr(yn,yn,'biased’);fn=abs(fft(rn));plot(f2,fn(l:n))title(’輸出噪聲功率譜gridon;%噪盧直方圖統(tǒng)計(jì)subplot(2,3,3)hs二sn;hist(hs,20);titleC濾波前噪聲大小直方閣’)subplot(2,3,6):hs=yn;hist(hs,20);%信號(hào)+噪聲figure;x=ss+sn;subplot(2,3,1)plot(t,X)title(’輸入信號(hào)+噪聲’);gridon;rn=xcorr(x,x,’biased’)
8、;%相關(guān)函數(shù)fn=abs(fft(rn));subplot(2,3,4)plot(f2,fn(1:n))title(’輸入信號(hào)+噪聲功率譜’);gridon;%濾波后的信號(hào)+噪聲y=filter(b0,a0,x);subplot(2,3,2)plot(t,y)title(’輸出信號(hào)+噪聲’);gridonsubplot(2,3,5)fy=xcorr(y,y,’biased’);fy=abs(fft(fy)):plot(f2,fy(1:n))title(’輸入信號(hào)+噪聲功率譜’);gridon;%信號(hào)+噪聲莨方圖統(tǒng)計(jì)subplot(2,3,