实训四 数字信号频带传输的仿真设计

一、实验内容

1、基带信号采用不归零矩形脉冲，生成２ＰＳＫ信号的时域波形和功率谱密度。 2、生成ＱＰＳＫ信号的时域波形和功率谱密度。 3、ＱＰＳＫ接收信号的星座图。 4、仿真ＱＰＳＫ系统的误码率。 二、程序与仿真图 1.

clc;clear all; tm=1; fc=3;

Nsample=100; Nnum=1000; dt=tm/Nsample; N=Nsample*Nnum; t=0:dt:Nnum*tm-dt; NFFT=2.^16; Nloop=50; st1=0;st2=0; %%%%

for i=1:Nloop;

d=2*randint(1,Nnum)-1; st_bb=rectpulse(d,Nsample); st_2psk=st_bb.*sin(2*pi*fc*t); window=boxcar(length(st_bb));

[pxx1,f]=periodogram(st_bb,window,NFFT,1/dt); [pxx2,f]=periodogram(st_2psk,window,NFFT,1/dt); st1=st1+pxx1;st2=st2+pxx2; end

st1=st1/Nloop; st2=st2/Nloop;

%%%%%%%%%%%%%% figure(1);

subplot(211);plot(t,st_bb);axis([0 10 -1.5 1.5]);

xlabel('t');ylabel('幅度');title('双极性基带信号的时域波形'); subplot(212);plot(t,st_2psk);axis([0 10 -1.5 1.5]);grid on; xlabel('t');ylabel('幅度');title('2PSK已调信号波形'); figure(2);

subplot(211);plot([-1*flipud(f);f],0.5*[flipud(st1);st1]);axis([-15 15 0 1]); xlabel('f');ylabel('频谱');title('双极性基带信号的频谱');grid on;

subplot(212);plot([-1*flipud(f);f],0.5*[flipud(st2);st2]);axis([-10 10 0 0.5]); xlabel('f');ylabel('频谱');title('2PSK已调信号的频谱');grid on;

2.

clear all; N=10^6;

d1=randint(1,N).*2-1; d2=randint(1,N).*2-1; d=d1+j*d2;

Es=mean(abs(d).^2); Eb=Es./2;snr_db=-2:10; for snr=-2:10;

n0=Eb/(10^(snr/10)); sigma=sqrt(n0/2);

n=sigma*randn(size(d))+j*sigma*randn(size(d)); rt=d+n;

y1=sign(real(rt)); y2=sign(imag(rt));

ber(1,snr+3)=((length(find(y1~=d1)))+(length(find(y2~=d2))))/(2.*N); ber1(1,snr+3)=berawgn(snr,'qam',4); end

semilogy(snr_db,ber,'b- *');hold on; semilogy(snr_db,ber1,'r- ');grid on; xlabel('Eb/N0');ylabel('wumalv');

legend('ber','ber-theory');title('QPSK系统性能曲线');

3. Qm=2;

N_num=10^5;

d1=sign(randn(1,N_num)); d2=sign(randn(1,N_num)); d=d1+d2*j;

Es=mean(abs(d).^2); Eb=Es/Qm; EbN0_dB=10;

ebn0=10.^(EbN0_dB/10); sigma=sqrt(Eb/ebn0/2);

n=sigma*randn(size(d))+j*sigma*randn(size(d)); rt=d+n; plot(rt,'.');

axis([-2.5 2.5 -2 2]);grid on; xlabel('I');ylabel('Q');

title('信噪比为10dB的QPSK星座图');

4. Qm=2;

N_num=10^5;

d1=sign(randn(1,N_num)); d2=sign(randn(1,N_num)); d=d1+d2*j;

Es=mean(abs(d).^2); Eb=Es/Qm; EbN0_dB=5;

ebn0=10.^(EbN0_dB/10); sigma=sqrt(Eb/ebn0/2);

n=sigma*randn(size(d))+j*sigma*randn(size(d)); rt=d+n; plot(rt,'.');

axis([-3 3 -3 3]);grid on; xlabel('I');ylabel('Q');

title('信噪比为5dB的QPSK星座图');