course.m

用matlab编写的用于跳频技术的基于simulink环境的仿真程序

clc
clear all

%--------- 扩频通信过程 ---------------
%--------- 只仿真一个频点的情况 ---------------

%--------- 初始化 ---------------
Ts=0.00001; fs=1/Ts;
EndTime=2-Ts;  %2s

%--------- 产生信息序列(双极性不归零码) ---------------
Tm=0.25; fm=1/Tm;   %码率
[u,time] = gensig('square',2*Tm,EndTime,Ts);
y = 2*(u-0.5); 
figure(1)
plot(time,y);
title('信息序列')
xlabel('time (seconds)')
axis([0 2 -2 2])

%--------- FSK调制 ---------------
T0=0.1; f0=1/T0;
T1=0.2; f1=1/T1;
[u0,time] = gensig('sin',T0,EndTime,Ts);
[u1,time] = gensig('sin',T1,EndTime,Ts);
y0=u0.*sign(-y+1);
y1=u1.*sign(y+1);
SignalFSK=y0+y1;   % FSK信号
%--------- FSK调制的频谱 ---------------
nfft=fs+1;
Y = fft(SignalFSK,nfft);
PSignalFSK = Y.* conj(Y) / nfft;
f = fs*(0:nfft/2)/nfft;
figure(2);
plot(f,PSignalFSK(1:nfft/2+1))
title('FSK调制后的频谱')
xlabel('frequency (Hz)')
axis([0 100 -inf inf])
%--------- FSK调制后，低通滤波 ---------------
cof_low=fir1(64,25/fs);
SignalFSK_l=filter(cof_low,1,SignalFSK);
figure(3)
plot(time,SignalFSK_l);
title('FSK调制后经过低通滤波的波形')
xlabel('time (seconds)')
axis([0 2 -2 2])
YSignalFSK_l = fft(SignalFSK_l,nfft);
PSignalFSK_l = YSignalFSK_l.* conj(YSignalFSK_l) / nfft;
f = fs*(0:nfft/2)/nfft;
figure(4);
plot(f,PSignalFSK_l(1:nfft/2+1))
title('FSK调制后经过低通滤波的频谱')
xlabel('frequency (Hz)')
axis([0 100 -inf inf])

%--------- 混频 --------------
fc=1000;Tc=1/fc;    %频点: 1000
[Carrier,time] = gensig('sin',Tc,EndTime,Ts);   %产生扩频载波
MixSignal=SignalFSK_l.*Carrier;
figure(6)
plot(time,MixSignal);
title('混频后的波形')
xlabel('time (seconds)')
axis([0 2 -2 2])

%--------- 带通滤波 --------
cof_band=fir1(64,[fc-12.5,fc+12.5]/fs);
yMixSignal=filter(cof_band,1,MixSignal);
figure(7)
plot(time,yMixSignal);
title('经过带通滤波的混频信号')
xlabel('time (seconds)')
axis([0 2 -2 2])
YMixSignal = fft(yMixSignal,nfft);
PMixSignal = YMixSignal.* conj(YMixSignal) / nfft;
f = fs*(0:nfft/2)/nfft;
figure(8);
plot(f,PMixSignal(1:nfft/2+1))
title('经过带通滤波的混频信号频谱')
xlabel('frequency (Hz)')
axis([800 1200 -inf inf])

%---------- 传输信道 --------------
Sign_send=yMixSignal;
Sign_rec=Sign_send;
%---------- 传输信道 ---------------

%---------- 接收端 ---------------
%---------- 解扩 ----------------
fc=1000;Tc=1/fc;
[Carrier,time] = gensig('sin',Tc,EndTime,Ts);   %产生扩频载波
Sign_rec=Sign_send;
ySign_rec=Sign_rec.*Carrier;
figure(9)
plot(time,ySign_rec);
title('解扩后的信号')
xlabel('time (seconds)')
axis([0 2 -1 1])

%---------- 低通滤波,取下边频 ------------
yrr=ySign_rec;
cof_low=fir1(64,25/fs);
Sign_rec_l=filter(cof_low,1,ySign_rec);
figure(10)
plot(time,Sign_rec_l);
title('解扩后的下边频的信号')
xlabel('time (seconds)')
axis([0 2 -1 1])
YSign_rec_l = fft(Sign_rec_l,nfft);
PSign_rec_l = YSign_rec_l.* conj(YSign_rec_l) / nfft;
f = fs*(0:nfft/2)/nfft;
figure(11);
plot(f,PSign_rec_l(1:nfft/2+1))
title('解扩后的下边频频谱')
xlabel('frequency (Hz)')
axis([0 100 -inf inf])

%---------- FSK译码 --------------
cof_f0=fir1(64,[f0-0.25,f0+0.25]/fs);
cof_f1=fir1(64,[f1-0.25,f1+0.25]/fs);
DeFSK0=filter(cof_f0,1,Sign_rec_l);
DeFSK1=filter(cof_f1,1,Sign_rec_l);
rDeFSK0=DeFSK0.*u0;
rDeFSK1=DeFSK1.*u1;
rDeFSK=rDeFSK0-rDeFSK1;
figure(12);
plot(time,rDeFSK)
title('采样判决前的信号')
xlabel('time (seconds)')
axis([0 2 -2 2])

%----------- 采样判决 ---------------
Sampletime=0.25/Ts;
Message=[];
Num=0;

while(Num<2/Ts)
    if(mod(Num,Sampletime)==0)
        
        Message=[Message  ones(1,Sampletime+1)*sign(sum(rDeFSK((Num+1):(Num+Sampletime))))];
    end
    Num=Num+Sampletime;
end
figure(13);
plot((1:length(Message))/fs,Message)
title('恢复的信息')
xlabel('time (seconds)')
axis([0 2 -2 2])