四川大学信号与系统实验报告

实验报告

课程名称信号与系统

实验名称信号与LTI系统的时频域分析

实验时间2017 年 6 月15 日学院电子信息学院

指导教师周新志

学生班级学号

学院(系) 电子信息学院专业信息安全

实验报告

（2）a．

clear;

h1=[0.0031,0.0044,-0.0031,-0.0272,-0.0346,0.0374,0.1921,0.3279,0.3279,0.192 1,0.0374,-0.0346,-0.0272,-0.0031,0.0044,0.0031];

k1=0:15;

n=-4:4;

x1=cos(0.25*pi*n);

y1=conv(h1,x1);%计算序列f1与f2的卷积和f

k0=k1(1)+n(1);%计算序列f非零样值的起点位置

k3=length(x1)+length(h1)-2;%计算卷积和f的非零样值的宽度

k=k0:k0+k3;%确定卷积和f非零样值的序号向量

subplot(2,2,1);

stem(k,y1);

title('x1[n]与h1[n]的卷积和y1[n]');

xlabel('k');

ylabel('y1[k]');

x2=cos(1.25*pi*n);

y2=conv(h1,x2);

subplot(2,2,2);

stem(k,y2);

title('x2[n]与h1[n]的卷积和y2[n]');

xlabel('k');

ylabel('y2[k]');

x3=x1+x2;

y3=conv(h1,x3);

subplot(2,2,3);

stem(k,y3);

title('x3[n]与h1[n]的卷积和y3[n]');

xlabel('k');

ylabel('y3[k]');

b.

clear;

h2=[-0.0238,0.0562,-0.0575,-0.1302,0.5252, -0.6842,-0.3129,5.6197,5.6197, -0.3129,-0.6842,0.5252,-0.1302,-0.0575,0.0562,-0.0238];

k1=0:15;

n=-4:4;

x1=cos(0.25*pi*n);

y1=conv(h2,x1);%计算序列f1与f2的卷积和f

k0=k1(1)+n(1); %计算序列f非零样值的起点位置

k3=length(x1)+length(h2)-2; %计算卷积和f的非零样值的宽度

k=k0:k0+k3; %确定卷积和f非零样值的序号向量

subplot(2,2,1);

stem(k,y1);

title('x1[n]与h2[n]的卷积和y1[n]');

xlabel('k');

ylabel('y1[k]');

x2=cos(1.25*pi*n);

y2=conv(h2,x2);

subplot(2,2,2);

stem(k,y2);

title('x2[n]与h2[n]的卷积和y2[n]');

xlabel('k');

ylabel('y2[k]');

x3=x1+x2;

y3=conv(h2,x3);

subplot(2,2,3);

stem(k,y3);

title('x3[n]与h2[n]的卷积和y3[n]'); xlabel('k');

ylabel('y3[k]');

3.(a)

fs=128;

t=1/fs;

L=256;

n=0:1:L-1;

x1=cos(0.25*pi*n);

x2=cos(1.25*pi*n);

x3=x2+x1;

N = 2^nextpow2(L);

X1=fft(x1,N)/N*2;

X2=fft(x2,N)/N*2;

X3=fft(x3,N)/N*2;

f=fs/N*(0:1:N-1);

figure;

subplot(2,1,1);

plot(f,abs(X1));

title('幅值频谱');

xlabel('频率(HZ)');

ylabel('幅值');

subplot(2,1,2);

plot(f,angle(X1));