040920317 张宇
附录 2:4ASK
fs=4000;
ts=1/fs;
ft=100;
f0=1000;
n=1000;
bit=randint(1,n,4);%%g 为比特流
N=40;
bits=[]; sig=[]; %%定义空矩阵 bits 用来存放 N 个 0,或 N 个 1;
for i=1:n
if bit(i)==0
bits=zeros(1,N);
elseif(bit(i)==1)
bits=ones(1,N);
elseif(bit(i)==2)
bits=2.*ones(1,N);
else
bits=3.*ones(1,N);
end
sig=[sig,bits];
end
t=ts:ts:1/ft*n;
subplot(2,1,1);
plot(t,sig);
axis([0 0.1 -0.5 3.5]);
title('信息信号波形');
subplot(2,1,2);
[Pxx,Pxxc,f] = pmtm(sig,3.5,1024,fs,0.99);%%X 为信号,fs 为信号采样率
hpsd = dspdata.psd(Pxx,'Fs',fs);
plot(hpsd) ;
title('信息信号功率谱');
figure;
t1=ts:ts:1/ft*n;
y1=cos(2*pi*f0*t1);
y2=y1.*sig;
t2=ts:ts:1/ft*n;
subplot(2,1,1);
plot(t2,y2);
axis([0 0.1 -3.5 3.5]);
title('调制后波形');