课程设计报告——matlab瑞利衰落信道仿真

1、目录摘要 ·················································&

2、#183;·················································&

3、#183;························· 11、设计原理 ······················

4、3;·················································

5、3;······································ 21.1设计目的 ··········

6、··················································

7、··················································

8、· 21.2仿真原理 ···············································&#

9、183;·················································&#

10、183;············· 21.2.1瑞利分布简介 ··································

11、··················································

12、········· 21.2.2多径衰落信道基本模型 ······································

13、······································· 21.2.3产生服从瑞利分布的路径衰落r(t) ·······

14、;··················································

15、;··· 31.2.4产生多径延时 ············································

16、83;················································ 41.3仿真框架

17、 ··················································

18、;··················································

19、;··········· 42、设计任务 ·····································&#

20、183;·················································&#

21、183;······················· 42.1设计任务要求 ························&#

22、183;·················································&#

23、183;···························· 42.2 MATLAB 仿真程序要求 ··················

24、··················································

25、················ 43、DSB调制解调分析的MATLAB实现 ······························&

26、#183;································ 53.1 DSB调制解调的MATLAB实现 ·············&#

27、183;·················································&#

28、183;········ 53.2瑞利衰落信道的MATLAB实现 ······································

29、;··································· 64、模拟仿真及结果分析 ············

30、83;·················································

31、83;···························· 74.1模拟仿真 ····················

32、;··················································

33、;········································· 74.1.1多普勒滤波器的频响 ······

34、··················································

35、································ 74.1.2多普勒滤波器的统计特性 ···············

36、;··················································

37、;··············· 74.1.3信道的时域输入/输出波形 ·······························

38、83;··············································· 84.2仿真结果分析

39、83;·················································

40、83;·················································

41、83;·· 84.2.1时域输入/输出波形分析 ············································&#

42、183;······································ 84.2.2频域波形分析 ·········

43、··················································

44、········································· 84.2.3多普勒滤波器的统计特性分析 ·····

45、83;·················································

46、83;················ 95、小结与体会 ································

47、;··················································

48、;························· 96、参考文献 ·······················&#

49、183;·················································&#

50、183;····································· 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

51、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、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

52、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（02）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，在02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.

53、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TapRelative delay (ns)Average power (dB)1002310-1.03

54、710-9.041 090-10.051 730-15.062 510-20.01.3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。2.2 MAT

55、LAB 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3.1 DSB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

56、.*c;%调制delay=0 31 71 109 173 251;%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for i=1:6%图4 f=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)

57、/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_

58、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('

59、;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:LengthOfSi