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···············································································································21.2.1瑞利分布简介·····························································································21.2.2多径衰落信道基本模型·············································································21.2.3产生服从瑞利分布的路径衰落r(t)····························································31.2.4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···············································································································714.1.1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2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MATLAB1、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、3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)(~)()(~tNkkktxtrty(1)其中)(trk复路径衰落，服从瑞利分布；k是多径时延。多径衰落信道模型框图如图2所示：4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22)()()(tntntrsc（2）上式中，、)(tnc、)(tns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，2)(15.1)(mcmfffffS（3）1.2.4产生多径延时k多径/延时参数如表1所示：表1多径延时参数TapRelativedelay(ns)Averagepower(dB)1002310-1.03710-9.041090-10.0551730-15.062510-20.01.3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)(tr（见图3）和多径延时参数k（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2、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6delay=[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_en