QPSK调制与解调在MATLAB平台上的实现.docx
《QPSK调制与解调在MATLAB平台上的实现.docx》由会员分享,可在线阅读,更多相关《QPSK调制与解调在MATLAB平台上的实现.docx(10页珍藏版)》请在冰豆网上搜索。
QPSK调制与解调在MATLAB平台上的实现
QPSK调制与解调在MATLAB平台上的实现
李悦
QPSK即四进制移向键控(QuaternaryPhaseShiftKeying,它利用载波的四种不同相位来表示数字信息,由于每一种载波相位代表两个比特信息,因此每个四进制码元可以用两个二进制码元的组合来表示。
两个二进制码元中的前一个码元用a表示,后一个码元用b表示。
QPSK信号可以看作两个载波正交2PSK信号的合成,下图表示QPSK正交调制器。
由QPSK信号的调制可知,对它的解调可以采用与2PSK信号类似的解调方法进行解调。
解调原理图如下所示,同相支路和正交支路分别采用相干解调方式
解调,得到l(t)和Q(t),经过抽样判决和并/串交换器,将上下支路得到的并行数据恢复成串行数据。
载波恢复
%调相法clearallcloseall
t=[-1:
0.01:
7-0.01];tt=length(t);x1=ones(1,800);fori=1:
tt
if(t(i)>=-1&t(i)<=1)|(t(i)>=5&t(i)<=7);x1(i)=1;
elsex1(i)=-1;endend
t1=[0:
0.01:
8-0.01];t2=0:
0.01:
7-0.01;t3=-1:
0.01:
7.1-0.01;t4=0:
0.01:
8.1-0.01;
tt1=length(t1);x2=ones(1,800);fori=1:
tt1
if(t1(i)>=0&t1(i)<=2)|(t1(i)>=4&t1(i)<=8);x2(i)=1;
elsex2(i)=-1;endendf=0:
0.1:
1;
xrc=0.5+0.5*cos(pi*f);
y1=conv(x1,xrc)/5.5;
y2=conv(x2,xrc)/5.5;
n0=randn(size(t2));
f1=1;
i=x1.*cos(2*pi*f1*t);q=x2.*sin(2*pi*f1*t1);
I=i(101:
800);
Q=q(1:
700);
QPSK=sqrt(1/2).*l+sqrt(1/2).*Q;
QPSK_n=(sqrt(1/2).*l+sqrt(1/2).*Q)+nO;
n1=randn(size(t2));i_rc=y1.*cos(2*pi*f1*t3);q_rc=y2.*sin(2*pi*f1*t4);
I_rc=i_rc(101:
800);
Q_rc=q_rc(1:
700);
QPSK_rc=(sqrt(1/2).*I_rc+sqrt(1/2).*Q_rc);
QPSK_rc_n1=QPSK_rc+n1;
figure
(1)
subplot(4,1,1);plot(t3,i_rc);axis([-18-11]);ylabel('a序列');subplot(4,1,2);plot(t4,q_rc);axis([-18-11]);ylabel('b序列');subplot(4,1,3);plot(t2,QPSK_rc);axis([-18-11]);ylabel('合成序列');subplot(4,1,4);plot(t2,QPSK_rc_n1);axis([-18-11]);ylabel('加入噪声');
效果图:
%设定T=1,加入高斯噪声
clearall
closeall
%调制
bit_in=randint(1e3,1,[01]);
bit_I=bit_in(1:
2:
1e3);
bit_Q=bit_in(2:
2:
1e3);
data_I=-2*bit_I+1;
data_Q=-2*bit_Q+1;
data_I1=repmat(data_I',20,1);
data_Q1=repmat(data_Q',20,1);
fori=1:
1e4
data_I2(i)=data_I1(i);data_Q2(i)=data_Q1(i);
end;
f=0:
0.1:
1;
xrc=0.5+0.5*cos(pi*f);
data_I2_rc=conv(data_I2,xrc)/5.5;
data_Q2_rc=conv(data_Q2,xrc)/5.5;
f1=1;
t1=0:
0.1:
1e3+0.9;
n0=rand(size(t1));
I_rc=data_I2_rc.*cos(2*pi*f1*t1);
Q_rc=data_Q2_rc.*sin(2*pi*f1*t1);
QPSK_rc=(sqrt(1/2).*I_rc+sqrt(1/2).*Q_rc);
QPSK_rc_n0=QPSK_rc+n0;
%解调
I_demo=QPSK_rc_n0.*cos(2*pi*f1*t1);
Q_demo=QPSK_rc_n0.*sin(2*pi*f1*t1);
%低通滤波
I_recover=conv(I_demo,xrc);
Q_recover=conv(Q_demo,xrc);
I=I_recover(11:
10010);
Q=Q_recover(11:
10010);
t2=0:
0.05:
1e3-0.05;
t3=0:
0.1:
1e3-0.1;
%抽样判决
data_recover=[];
fori=1:
20:
10000
data_recover=[data_recoverI(i:
1:
i+19)Q(i:
1:
i+19)];end;
bit_recover=[];
fori=1:
20:
20000
ifsum(data_recover(i:
i+19))>0data_recover_a(i:
i+19)=1;bit_recover=[bit_recover1];
else
data_recover_a(i:
i+19)=-1;
bit_recover=[bit_recover-1];
end
end
error=0;
dd=-2*bit_in+1;
ddd=[dd'];
ddd1=repmat(ddd,20,1);
fori=1:
2e4
ddd2(i)=ddd1(i);
end
fori=1:
1e3
ifbit_recover(i)~=ddd(i)error=error+1;
end
end
p=error/1000;
figure
(1)subplot(2,1,1);plot(t2,ddd2);axis([0100-22]);title('原序列');subplot(2,1,2);plot(t2,data_recover_a);axis([0100-22]);title('解调后序列');
效果图:
原序列
解调后序列
%设定T=1,不加噪声clearallcloseall
%调制bit_in=randint(1e3,1,[01]);bit_I=bit_in(1:
2:
1e3);bit_Q=bit_in(2:
2:
1e3);
data_I=-2*bit_I+1;data_Q=-2*bit_Q+1;
data_I1=repmat(data_I',20,1);data_Q1=repmat(data_Q',20,1);
fori=1:
1e4
data_I2(i)=data_I1(i);data_Q2(i)=data_Q1(i);
end;
t=0:
0.1:
1e3-0.1;
f=0:
0.1:
1;xrc=0.5+0.5*cos(pi*f);
data_I2_rc=conv(data_I2,xrc)/5.5;data_Q2_rc=conv(data_Q2,xrc)/5.5;
f1=1;t1=0:
0.1:
1e3+0.9;
I_rc=data_I2_rc.*cos(2*pi*f1*t1);Q_rc=data_Q2_rc.*sin(2*pi*f1*t1);
QPSK_rc=(sqrt(1/2).*I_rc+sqrt(1/2).*Q_rc);
%解调I_demo=QPSK_rc.*cos(2*pi*f1*t1);Q_demo=QPSK_rc.*sin(2*pi*f1*t1);
I_recover=conv(I_demo,xrc);Q_recover=conv(Q_demo,xrc);
I=I_recover(11:
10010);Q=Q_recover(11:
10010);t2=0:
0.05:
1e3-0.05;
dafalrecove卫一八
for耳20=0000
dafalrecove卫daQrlrecover-(s+19)Q(z」+19)r
end八
dddH—2*brn+l八
ddchHrepmasdd二03-
forIi'」=e4
ddd2(illddd二三
end
figures
subpof(411)八p-ofsDaxisao20—06一)八subpof(4L2)八pof(®Q)oi><.s(o20—06一)八subpof(4L3)八pof(N5daQrlrecover)Qi><.s(o20—06三subpof(4L4)八pof(Lddd2)oi><.s(o20—06一)八
解调后奇位
解调后偶位
解调后序列
原始序列
%QPSK误码率分析
SNRindB1=0:
2:
10;
SNRindB2=0:
0.1:
10;
fori=1:
length(SNRindB1)[pb,ps]=cm_sm32(SNRindB1(i));smld_bit_err_prb(i)=pb;smld_symbol_err_prb(i)=ps;
end;
fori=1:
length(SNRindB2)
SNR=exp(SNRindB2(i)*log(10)/10);theo_err_prb(i)=Qfunct(sqrt(2*SNR));
end;
title('QPSK误码率分析');
semilogy(SNRindB1,smld_bit_err_prb,'*');
axis([01010e-81]);
holdon;
%semilogy(SNRindB1,smld_symbol_err_prb,'o');semilogy(SNRindB2,theo_err_prb);
legend('仿真比特误码率','理论比特误码率');
holdoff;
function[y]=Qfunct(x)y=(1/2)*erfc(x/sqrt
(2));
function[pb,ps]=cm_sm32(SNRindB)
N=10000;
E=1;
SNR=10A(SNRindB/10);
sgma=sqrt(E/SNR)/2;
s00=[10];
s01=[01];
s11=[-10];
s10=[0-1];
fori=1:
N
temp=rand;
if(temp<0.25)
dsource1(i)=0;
dsource2(i)=0;
elseif(temp<0.5)dsource1(i)=0;dsource2(i)=1;
elseif(temp<0.75)dsource1(i)=1;dsource2(i)=0;
else
dsource1(i)=1;dsource2(i)=1;end;
end;numofsymbolerror=0;numofbiterror=0;
fori=1:
N
n=sgma*randn(size(s00));
if((dsource1(i)==0)&(dsource2(i)==0))r=s00+n;
elseif((dsource1(i)==0)&(dsource2(i)==1))r=s01+n;
elseif((dsource1(i)==1)&(dsource2(i)==0))r=s10+n;
else
r=s11+n;
end;
c00=dot(r,s00);
c01=dot(r,s01);
c10=dot(r,s10);
c11=dot(r,s11);
c_max=max([c00c01c10c11]);
if(c00==c_max)
decis1=0;decis2=0;
elseif(c01==c_max)
decis1=0;decis2=1;
elseif(c10==c_max)
decis1=1;decis2=0;
else
decis1=1;decis2=1;
end;
symbolerror=0;
if(decis1~=dsource1(i))numofbiterror=numofbiterror+1;symbolerror=1;
end;
if(decis2~=dsource2(i))
numofbiterror=numofbiterror+1;symbolerror=1;
end;
if(symbolerror==1)
numofsymbolerror=numofsymbolerror+1;end;
end;
ps=numofsymbolerror/N;
pb=numofbiterror/(2*N);
效果图
QF^K误码率分析
10
012346678910