課程設(shè)計報告-matlab瑞利衰落信道仿真

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--內(nèi)頁可以根據(jù)需求調(diào)整合適字體及大小--課程設(shè)計報告——matlab瑞利衰落信道仿真(總15頁)課程設(shè)計報告——matlab瑞利衰落信道仿真目錄摘要·····························································································································11、設(shè)計原理···············································································································21.1設(shè)計目的···············································································································21.2仿真原理···············································································································2 1.2.1瑞利分布簡介·····························································································2 1.2.2多徑衰落信道基本模型·············································································2 1.2.3產(chǎn)生服從瑞利分布的路徑衰落r(t)····························································3 1.2.4產(chǎn)生多徑延時·····························································································41.3仿真框架···············································································································42、設(shè)計任務(wù)···············································································································42.1設(shè)計任務(wù)要求·······································································································42.2MATLAB仿真程序要求····················································································43、DSB調(diào)制解調(diào)分析的MATLAB實現(xiàn)·······························································53.1DSB調(diào)制解調(diào)的MATLAB實現(xiàn)········································································53.2瑞利衰落信道的MATLAB實現(xiàn)·········································································64、模擬仿真及結(jié)果分析···························································································74.1模擬仿真···············································································································74.1.1多普勒濾波器的頻響························································································74.1.2多普勒濾波器的統(tǒng)計特性················································································74.1.3信道的時域輸入/輸出波形···············································································84.2仿真結(jié)果分析·······································································································84.2.1時域輸入/輸出波形分析···················································································84.2.2頻域波形分析····································································································84.2.3多普勒濾波器的統(tǒng)計特性分析········································································95、小結(jié)與體會···········································································································96、參考文獻(xiàn)···············································································································9MATLAB通信仿真設(shè)計摘要主要運用MATLAB進(jìn)行編程，實現(xiàn)采用對輸入信號進(jìn)行抑制載波的雙邊帶調(diào)幅；而后將調(diào)幅波輸入信道，研究多徑信道的特性對通信質(zhì)量的影響；最后將信道內(nèi)輸出的條幅波進(jìn)行同步解調(diào)，解調(diào)出與輸入信號波形相類似的波形，觀測兩者差別。同時輸出多普勒濾波器的統(tǒng)計特性圖及信號時域和頻域的輸入、輸出波形。關(guān)鍵字：雙邊帶調(diào)幅 瑞利衰落 相干解調(diào) MATLAB設(shè)計原理1.1設(shè)計目的由于多徑和移動臺運動等影響因素，使得移動信道對傳輸信號在時間、頻率和角度上造成了色散，如時間色散、頻率色散、角度色散等等，因此多徑信道的特性對通信質(zhì)量有著至關(guān)重要的影響，而多徑信道的包絡(luò)統(tǒng)計特性成為我們研究的焦點。根據(jù)不同無線環(huán)境，接收信號包絡(luò)一般服從幾種典型分布，如瑞利分布、萊斯分布和Nakagami-m分布。在設(shè)計中，專門針對服從瑞利分布的多徑信道進(jìn)行模擬仿真，進(jìn)一步加深對多徑信道特性的了解。1.2仿真原理1.2.1瑞利分布簡介（1）環(huán)境條件：通常在離基站較遠(yuǎn)、反射物較多的地區(qū)，發(fā)射機和接收機之間沒有直射波路徑，存在大量反射波；到達(dá)接收天線的方向角隨機且在（0~2π）均勻分布；各反射波的幅度和相位都統(tǒng)計獨立。（2）幅度、相位的分布特性：包絡(luò)r服從瑞利分布，θ在0～2π內(nèi)服從均勻分布。瑞利分布的概率分布密度如圖1所示：圖1瑞利分布的概率分布密度1.2.2多徑衰落信道基本模型根據(jù)ITU-RM.1125標(biāo)準(zhǔn)，離散多徑衰落信道模型為(1)其中復(fù)路徑衰落，服從瑞利分布；是多徑時延。多徑衰落信道模型框圖如圖2所示：圖2多徑衰落信道模型框圖1.2.3產(chǎn)生服從瑞利分布的路徑衰落r(t)利用窄帶高斯過程的特性，其振幅服從瑞利分布，即（2）上式中，、、分別為窄帶高斯過程的同相和正交支路的基帶信號。首先產(chǎn)生獨立的復(fù)高斯噪聲的樣本，并經(jīng)過FFT后形成頻域的樣本，然后與S（f）開方后的值相乘，以獲得滿足多普勒頻譜特性要求的信號，經(jīng)IFFT后變換成時域波形，再經(jīng)過平方，將兩路的信號相加并進(jìn)行開方運算后，形成瑞利衰落的信號r(t)。如下圖3所示:圖3瑞利衰落的產(chǎn)生示意圖其中，（3）1.2.4產(chǎn)生多徑延時多徑/延時參數(shù)如表1所示：表1多徑延時參數(shù)TapRelativedelay(ns)Averagepower(dB)1002310-1.03710-9.041090-10.051730-15.062510-20.01.3仿真框架根據(jù)多徑衰落信道模型（見圖2），利用瑞利分布的路徑衰落（見圖3）和多徑延時參數(shù)（見表1），我們可以得到多徑信道的仿真框圖，如圖4所示：圖4多徑信道的仿真框圖設(shè)計任務(wù)2.1設(shè)計任務(wù)要求（1）查找資料，了解瑞利衰落信道模型的分類，結(jié)合某種模型，掌握瑞利分布的多徑信道仿真原理，用MATLAB仿真實現(xiàn)瑞利分布的多徑信道的仿真；（2）根據(jù)已學(xué)的知識，實現(xiàn)一種基帶信號的模擬調(diào)制并做出仿真；（3）結(jié)合（1）（2）步，觀察已調(diào)信號通過瑞利信道后的時域波形圖和頻譜圖；（4）對仿真結(jié)果做適當(dāng)分析。2.2MATLAB仿真程序要求（1）參數(shù)設(shè)計準(zhǔn)確、合理；（2）關(guān)鍵語句加注釋；（3）仿真結(jié)果正確，圖形清晰。3、DSB調(diào)制解調(diào)分析的MATLAB實現(xiàn)3.1DSB調(diào)制解調(diào)的MATLAB實現(xiàn)%main.mclc;LengthOfSignal=10000;%信號長度fm=500;%最大多普勒頻移？相關(guān)文獻(xiàn)應(yīng)該有估算公式

fc=5000;%信道載波頻率t=1:LengthOfSignal;%SignalInput=sin(t/100);%DSB調(diào)制SignalInput=sin(t/50);%+cos(t/65);%調(diào)制信號c=cos(0.2*pi*t);%載波信號y_in=SignalInput.*c;%調(diào)制delay=[03171109173251];%10nspower=[0-1-9-10-15-20];%dBy_in=[zeros(1,delay(6))y_in];%為時移補零y_out=zeros(1,LengthOfSignal);%存放經(jīng)信道未解調(diào)的信號（現(xiàn)為無輸入信號%時的輸出信號）%y_out_end最終解調(diào)后信號%多路徑衰落fori=1:6%圖4f=1:2*fm-1;Rayl;y_out=y_out+r.*y_in(delay(6)+1-delay(i):(delay(6)+LengthOfSignal-delay(i)))*10^(power(i)/20);end;%S(t)*cos(w*t)=m(t)*cos(w*t)*cos(w*t)=0.5*m(t)*(1+cos(2*w*t))%用一個低通濾波器將上式中的第一項和第二項分離，無失真的恢復(fù)出原始的調(diào)制信號。%這種調(diào)制方法又稱為同步解調(diào)或相干解調(diào)%同步解調(diào)y_out_end=y_out.*c;%同步解調(diào)或相干解調(diào)%低通濾波wp=0.1*pi;ws=0.12*pi;Rp=1;As=15;[N,wn]=buttord(wp/pi,ws/pi,Rp,As);[b,a]=butter(N,wn);y_out_end=filter(b,a,y_out_end);%濾波y_out_end=2*y_out_end;%恢復(fù)幅度%原信號的頻譜K=fft(SignalInput);%DSB調(diào)制后信號的頻譜L=fft(y_in);%y_out的頻譜（含包絡(luò)）M=fft(y_out);%最終解調(diào)的頻譜N=fft(y_out_end);%輸出figure(1);subplot(4,2,1);plot(SignalInput(delay(6)+1:LengthOfSignal));axis([0,3000,-2,2]);title('原始輸入信號');subplot(4,2,2);plot(abs(fftshift(K)));axis([4900,5100,0,6000]);title('原始輸入信號的頻譜');subplot(4,2,3);plot(y_in(delay(6)+1:LengthOfSignal));axis([0,3000,-2,2]);%去除時延造成的空白信號title('進(jìn)入瑞利信道前，DSB調(diào)制后的信號');subplot(4,2,4);plot(abs(fftshift(L)));axis([3500,6500,0,3000]);title('進(jìn)入瑞利信道前，DSB調(diào)制后的信號的頻譜');subplot(4,2,5);plot(y_out(delay(6)+1:LengthOfSignal));axis([0,3000,-0.08,0.08]);%去除時延造成的空白信號title('經(jīng)瑞利信道后，DSB解調(diào)前的信號');subplot(4,2,6);plot(abs(fftshift(M)));axis([3500,6500,0,100]);title('經(jīng)瑞利信道后，DSB解調(diào)前的信號的頻譜');subplot(4,2,7);plot(y_out_end(delay(6)+1:LengthOfSignal));axis([0,3000,-0.08,0.08]);%去除時延造成的空白信號title('最終解調(diào)后的信號');subplot(4,2,8);plot(abs(fftshift(N)));axis([4900,5100,0,200]);title('最終解調(diào)后的信號的頻譜');figure(2);subplot(3,1,1);hist(r,256);%繪制直方圖title('瑞利信道的幅度分布')subplot(3,1,2);hist(angle(r0));title('瑞利信道的相位分布');subplot(3,1,3);plot(Sf1);title('多普勒濾波器的頻響特性');3.2瑞利衰落信道的MATLAB實現(xiàn)%Rayl.m參考【1】f=1:2*fm-1;%通頻帶長度y=1.5./((1-((f-fm)/fm).^2).^(1/2))/pi/fm;%多普勒功率譜(基帶)圖3Sf=zeros(1,LengthOfSignal);Sf1=y;Sf(fc-fm+1:fc+fm-1)=y;%(把基帶映射到載波頻率)x1=randn(1,LengthOfSignal);x2=randn(1,LengthOfSignal);nc=ifft(fft(x1+1i*x2).*sqrt(Sf));%同相分量%首先產(chǎn)生獨立的復(fù)高斯噪聲的樣本，并經(jīng)過FFT后形成頻域的樣本，%然后與S（f）開方后的值相乘，以獲得滿足多普勒頻譜特性要求的信號，%經(jīng)IFFT后變換成時域波形，再經(jīng)過平方，將兩路的信號相加并進(jìn)行開方運算后，形成瑞利衰落的信號r(t)x3=randn(1,LengthOfSignal);x4=randn(1,LengthOfSignal);ns=ifft(fft(x3+1i*x4).*sqrt(Sf));%正交分量r0=(real(nc)+1i*real(ns));%瑞利信號r=abs(r0);%瑞利信號幅值（nc、ns分別為窄帶高斯過程的同相和正交支路的基帶信號）模擬仿真及結(jié)果分析4.1模擬仿真4.1.1多普勒濾波器的頻響圖5多普勒濾波器的頻響4.1.2多普勒濾波器的統(tǒng)計特性圖6多普勒濾波器的統(tǒng)計特性4.1.3信道的時域輸入/輸出波形圖7信道的時域/頻域輸入/輸出波形4.2仿真結(jié)果分析4.2.1時域輸入/輸出波形分析次實驗主要是通過MATLAB仿真瑞利衰落信道的傳輸過程，通過雙邊帶調(diào)幅的調(diào)制與解調(diào)實現(xiàn)信號的傳輸。正如右圖所示：圖中第一、第二個波形是在進(jìn)入瑞利衰落前，第三、第四個波形是在進(jìn)入瑞利衰落后，有明顯的噪聲的存在。由第一個圖輸入，第四個圖輸出，信號的傳遞在存在干擾的情況下基本實現(xiàn)。第一個波形到第二個波形是實現(xiàn)了抑制載波的雙邊帶調(diào)幅；第三個波形到第四個波形是運用同步解調(diào)或相干解調(diào)實現(xiàn)對載波信號的解調(diào)功能。 圖8信道的時域輸入/輸出波