软件无线电实验matlab程序

附录

(1)、SDR低通采样理论

%parameters

fs = 5e4;%采样频率注意fs至少是f的2倍或2倍以上

f = 5e3;%信号的频率

N = 1024;

n = 1:1024;

t= n/fs;

deta_t = 1/fs;%采样间隔

%signals

sn = sin(2*pi*f*t);%时域采样后的信号

w = hanning(N);%加汉宁窗

sn1 = sn.*w';%加窗减少频率泄露

Sn_fft = fft(sn1);%频域信号

Sn = abs(Sn_fft);

%figures

figure(1);

plot(t,sn);

title('s(n)的时域波形');

grid on;

xlabel('t');

xlim([0 0.021]);

ylabel('幅度');

figure(2);

xax = [-N/2:N/2-1]/N*fs/1000;%将f轴单位变为kHz

plot(xax,20*log10(fftshift(Sn)));

title('s(n)的频域波形');

grid on;

xlabel('f(kHz)');

ylabel('幅度(dB)');

ylim([-200 100]);

(2)、SDR带通采样理论

%parameters

f = 1.3e3;%基频

fo = 100e6;%载波频率

N = 1024;

n = 1:1024; fs = 4e3;%采样频率

t= 0:0.001:2;

st = cos(2*pi*(f+fo)*n/fs);%带通抽样信号St1 = fft(st);

St = abs(St1);

st0 = cos(2*pi*(f+fo)*t);

St0 = fft(st0);

St2 = abs(St0);

figure(1);

plot(n,st);

title('带通抽样信号时域图像');

xlabel('n');

xlim([0 1026]);

ylabel('幅度');

grid on;

figure(2);

plot(t,st0);

title('带通原始信号时域图像');

xlabel('t');

ylabel('幅度');

grid on;

figure(3);

xax =[-N/2:N/2-1]/N*fs/1000;

plot(xax,20*log10(fftshift(St)));

title('带通信号抽样后频域图像');

xlabel('f(kHz)');

ylabel('幅度(dB)');

grid on;

(3)、频率调制信号

%频率调制

%parameters

fs = 1e3;%抽样频率

ts = 1/fs;%采样率

N = 1024;

n = 0:1:N-1;

t = n/fs;

kf = 100.1;

A = 100;

Aw = 10;

fc = 10000;%载波频率

fm = 10;%调制信号频率

mf = kf*Aw/(2*pi*fm);

%signals

s1 = A*cos(2*pi*fc*t).*cos(mf*sin(2*pi*fm*t)); s2 = A*sin(2*pi*fc*t).*sin(mf*sin(2*pi*fm*t));

s = s1-s2;%频率调制信号

S0 = fft(s);

S1 = fftshift(S0);

S_0 = abs(S1);

%figures

figure(1);

plot(t,s);

title('频率调制信号时域图像');

xlim([0,0.5]);

xlabel('t(s)');

ylabel('幅度');

grid on;

figure(2);

xax = [-N/2:N/2-1]/N*fs/1000;

plot(xax,20*log10(S_0));

title('频率调制信号频域图像');

xlabel('f(kHz)');

ylabel('幅度(dB)');

grid on;

(4)、幅度调制信号、DSB信号、USB信号%parameters

clear all;clc;close all;

fs = 1e3;%抽样频率

ts = 1/fs;%采样间隔

N = 10000;

n = 1:N;

t = n/fs;

ma = 0.5;

fc = 200;%载波频率

x = cos(2*pi*fc*t);%生成载波fm = 1;%调制信号频率

m = cos(2*pi*fm*t);%基带信号

%signals

s = (1+ma*m).*x;%幅度调制信号

s1= m.*x;%双边带信号DSB

s2 = cos(2*pi*(fc+fm)*t);%SSB信号中的USB

S1 = fft(s);

S_1 = abs(S1);

S2 = fft(s1);

S_2 = abs(S2);

S3 = fft(s2);

S_3 = abs(S3);

%figures

figure(1);

plot(t,s);

title('幅度调制信号时域图像');

xlim([0 1.5]);

xlabel('t(s)');

ylabel('幅度');

grid on;

figure(2);

xax = [-N/2:N/2-1]/N*fs/1000;

plot(xax,20*log10(fftshift(S_1)));

title('幅度调制信号频域图像');

xlim([0.19 0.21]);

xlabel('f(kHz)');

ylabel('幅度(dB)');

grid on;

figure(3);

plot(t,s1);

title('双边带调制信号时域图像');

xlim([0 1.5]);

xlabel('t(s)');

ylabel('幅度');

grid on;