课程设计报告-matlab瑞利衰落信道仿真

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--内页可以根据需求调整合适字体及大小--课程设计报告——matlab瑞利衰落信道仿真(总15页)课程设计报告——matlab瑞利衰落信道仿真目录摘要·····························································································································11、设计原理···············································································································21.1设计目的···············································································································21.2仿真原理···············································································································2 1.2.1瑞利分布简介·····························································································2 1.2.2多径衰落信道基本模型·············································································2 1.2.3产生服从瑞利分布的路径衰落r(t)····························································3 1.2.4产生多径延时·····························································································41.3仿真框架···············································································································42、设计任务···············································································································42.1设计任务要求·······································································································42.2MATLAB仿真程序要求····················································································43、DSB调制解调分析的MATLAB实现·······························································53.1DSB调制解调的MATLAB实现········································································53.2瑞利衰落信道的MATLAB实现·········································································64、模拟仿真及结果分析···························································································74.1模拟仿真···············································································································74.1.1多普勒滤波器的频响························································································74.1.2多普勒滤波器的统计特性················································································74.1.3信道的时域输入/输出波形···············································································84.2仿真结果分析·······································································································84.2.1时域输入/输出波形分析···················································································84.2.2频域波形分析····································································································84.2.3多普勒滤波器的统计特性分析········································································95、小结与体会···········································································································96、参考文献···············································································································9MATLAB通信仿真设计摘要主要运用MATLAB进行编程，实现采用对输入信号进行抑制载波的双边带调幅；而后将调幅波输入信道，研究多径信道的特性对通信质量的影响；最后将信道内输出的条幅波进行同步解调，解调出与输入信号波形相类似的波形，观测两者差别。同时输出多普勒滤波器的统计特性图及信号时域和频域的输入、输出波形。关键字：双边带调幅 瑞利衰落 相干解调 MATLAB设计原理1.1设计目的由于多径和移动台运动等影响因素，使得移动信道对传输信号在时间、频率和角度上造成了色散，如时间色散、频率色散、角度色散等等，因此多径信道的特性对通信质量有着至关重要的影响，而多径信道的包络统计特性成为我们研究的焦点。根据不同无线环境，接收信号包络一般服从几种典型分布，如瑞利分布、莱斯分布和Nakagami-m分布。在设计中，专门针对服从瑞利分布的多径信道进行模拟仿真，进一步加深对多径信道特性的了解。1.2仿真原理1.2.1瑞利分布简介（1）环境条件：通常在离基站较远、反射物较多的地区，发射机和接收机之间没有直射波路径，存在大量反射波；到达接收天线的方向角随机且在（0~2π）均匀分布；各反射波的幅度和相位都统计独立。（2）幅度、相位的分布特性：包络r服从瑞利分布，θ在0～2π内服从均匀分布。瑞利分布的概率分布密度如图1所示：图1瑞利分布的概率分布密度1.2.2多径衰落信道基本模型根据ITU-RM.1125标准，离散多径衰落信道模型为(1)其中复路径衰落，服从瑞利分布；是多径时延。多径衰落信道模型框图如图2所示：图2多径衰落信道模型框图1.2.3产生服从瑞利分布的路径衰落r(t)利用窄带高斯过程的特性，其振幅服从瑞利分布，即（2）上式中，、、分别为窄带高斯过程的同相和正交支路的基带信号。首先产生独立的复高斯噪声的样本，并经过FFT后形成频域的样本，然后与S（f）开方后的值相乘，以获得满足多普勒频谱特性要求的信号，经IFFT后变换成时域波形，再经过平方，将两路的信号相加并进行开方运算后，形成瑞利衰落的信号r(t)。如下图3所示:图3瑞利衰落的产生示意图其中，（3）1.2.4产生多径延时多径/延时参数如表1所示：表1多径延时参数TapRelativedelay(ns)Averagepower(dB)1002310-1.03710-9.041090-10.051730-15.062510-20.01.3仿真框架根据多径衰落信道模型（见图2），利用瑞利分布的路径衰落（见图3）和多径延时参数（见表1），我们可以得到多径信道的仿真框图，如图4所示：图4多径信道的仿真框图设计任务2.1设计任务要求（1）查找资料，了解瑞利衰落信道模型的分类，结合某种模型，掌握瑞利分布的多径信道仿真原理，用MATLAB仿真实现瑞利分布的多径信道的仿真；（2）根据已学的知识，实现一种基带信号的模拟调制并做出仿真；（3）结合（1）（2）步，观察已调信号通过瑞利信道后的时域波形图和频谱图；（4）对仿真结果做适当分析。2.2MATLAB仿真程序要求（1）参数设计准确、合理；（2）关键语句加注释；（3）仿真结果正确，图形清晰。3、DSB调制解调分析的MATLAB实现3.1DSB调制解调的MATLAB实现%main.mclc;LengthOfSignal=10000;%信号长度fm=500;%最大多普勒频移？相关文献应该有估算公式

fc=5000;%信道载波频率t=1:LengthOfSignal;%SignalInput=sin(t/100);%DSB调制SignalInput=sin(t/50);%+cos(t/65);%调制信号c=cos(0.2*pi*t);%载波信号y_in=SignalInput.*c;%调制delay=[03171109173251];%10nspower=[0-1-9-10-15-20];%dBy_in=[zeros(1,delay(6))y_in];%为时移补零y_out=zeros(1,LengthOfSignal);%存放经信道未解调的信号（现为无输入信号%时的输出信号）%y_out_end最终解调后信号%多路径衰落fori=1:6%图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))%用一个低通滤波器将上式中的第一项和第二项分离，无失真的恢复出原始的调制信号。%这种调制方法又称为同步解调或相干解调%同步解调y_out_end=y_out.*c;%同步解调或相干解调%低通滤波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);%滤波y_out_end=2*y_out_end;%恢复幅度%原信号的频谱K=fft(SignalInput);%DSB调制后信号的频谱L=fft(y_in);%y_out的频谱（含包络）M=fft(y_out);%最终解调的频谱N=fft(y_out_end);%输出figure(1);subplot(4,2,1);plot(SignalInput(delay(6)+1:LengthOfSignal));axis([0,3000,-2,2]);title('原始输入信号');subplot(4,2,2);plot(abs(fftshift(K)));axis([4900,5100,0,6000]);title('原始输入信号的频谱');subplot(4,2,3);plot(y_in(delay(6)+1:LengthOfSignal));axis([0,3000,-2,2]);%去除时延造成的空白信号title('进入瑞利信道前，DSB调制后的信号');subplot(4,2,4);plot(abs(fftshift(L)));axis([3500,6500,0,3000]);title('进入瑞利信道前，DSB调制后的信号的频谱');subplot(4,2,5);plot(y_out(delay(6)+1:LengthOfSignal));axis([0,3000,-0.08,0.08]);%去除时延造成的空白信号title('经瑞利信道后，DSB解调前的信号');subplot(4,2,6);plot(abs(fftshift(M)));axis([3500,6500,0,100]);title('经瑞利信道后，DSB解调前的信号的频谱');subplot(4,2,7);plot(y_out_end(delay(6)+1:LengthOfSignal));axis([0,3000,-0.08,0.08]);%去除时延造成的空白信号title('最终解调后的信号');subplot(4,2,8);plot(abs(fftshift(N)));axis([4900,5100,0,200]);title('最终解调后的信号的频谱');figure(2);subplot(3,1,1);hist(r,256);%绘制直方图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('多普勒滤波器的频响特性');3.2瑞利衰落信道的MATLAB实现%Rayl.m参考【1】f=1:2*fm-1;%通频带长度y=1.5./((1-((f-fm)/fm).^2).^(1/2))/pi/fm;%多普勒功率谱(基带)图3Sf=zeros(1,LengthOfSignal);Sf1=y;Sf(fc-fm+1:fc+fm-1)=y;%(把基带映射到载波频率)x1=randn(1,LengthOfSignal);x2=randn(1,LengthOfSignal);nc=ifft(fft(x1+1i*x2).*sqrt(Sf));%同相分量%首先产生独立的复高斯噪声的样本，并经过FFT后形成频域的样本，%然后与S（f）开方后的值相乘，以获得满足多普勒频谱特性要求的信号，%经IFFT后变换成时域波形，再经过平方，将两路的信号相加并进行开方运算后，形成瑞利衰落的信号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));%瑞利信号r=abs(r0);%瑞利信号幅值（nc、ns分别为窄带高斯过程的同相和正交支路的基带信号）模拟仿真及结果分析4.1模拟仿真4.1.1多普勒滤波器的频响图5多普勒滤波器的频响4.1.2多普勒滤波器的统计特性图6多普勒滤波器的统计特性4.1.3信道的时域输入/输出波形图7信道的时域/频域输入/输出波形4.2仿真结果分析4.2.1时域输入/输出波形分析次实验主要是通过MATLAB仿真瑞利衰落信道的传输过程，通过双边带调幅的调制与解调实现信号的传输。正如右图所示：图中第一、第二个波形是在进入瑞利衰落前，第三、第四个波形是在进入瑞利衰落后，有明显的噪声的存在。由第一个图输入，第四个图输出，信号的传递在存在干扰的情况下基本实现。第一个波形到第二个波形是实现了抑制载波的双边带调幅；第三个波形到第四个波形是运用同步解调或相干解调实现对载波信号的解调功能。 图8信道的时域输入/输出波