QPSK調(diào)制與解調(diào)在MATLAB平臺上的實現(xiàn)

1、QPSK調(diào)制與解調(diào)在MATLAB平臺上的實現(xiàn)QPSK即四進(jìn)制移向鍵控（QuaternaryPhaseShiftKeying,它利用載波的四種不同相位來表示數(shù)字信息，由于每一種載波相位代表兩個比特信息，因此每個四進(jìn)制碼元可以用兩個二進(jìn)制碼元的組合來表示。兩個二進(jìn)制碼元中的前一個碼元用a表示，后一個碼元用b表示。QPSK信號可以看作兩個載波正交2PSK信號的合成，下圖表示QPSK正交調(diào)制器。輸入串川變換我波振蔻3sin/X-b由QPSK信號的調(diào)制可知，對它的解調(diào)可以采用與2PSK信號類似的解調(diào)方法進(jìn)行解調(diào)。解調(diào)原理圖如下所示，同相支路和正交支路分別采用相干解調(diào)方式解調(diào)，得到1代）和、代），經(jīng)過抽樣

2、判決和并/用交換器，將上下支路得到的并行數(shù)據(jù)恢復(fù)成申行數(shù)據(jù)。輸入A帶通港波器sin co r位定L低通一抽樣判決并7串變換載波恢復(fù)%調(diào)相法clearallt=-1:0.01:7-0.01;tt=length(t);x1=ones(1,800);fori=1:ttif(t(i)>=-1&t(i)<=1)|(t(i)>=5&t(i)<=7);x1(i)=1;elsex1(i)=-1;endendt1=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

3、(t1);x2=ones(1,800);fori=1:tt1if(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).*I+s

4、qrt(1/2).*Q;QPSK_n=(sqrt(1/2).*I+sqrt(1/2).*Q)+n0;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;figuresubplot(4,1,1);plot(t3,i_rc);axis(-18-11);ylabel('a序列');subplot(4,1,

5、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('加入噪聲');效果圖：%設(shè)定T=1,加入高斯噪聲clearall%調(diào)制bit_in=randint(1e3,1,01);bit_I=bit_in(1:2:1e3);bit_Q=bit_in(2:2:1e3);data_I=-2*bi

6、t_I+1;data_Q=-2*bit_Q+1;data_I1=repmat(data_I',20,1);data_Q1=repmat(data_Q',20,1);fori=1:1e4data_I2(i)=data_I1(i);data_Q2(i尸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.

7、*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;%解調(diào)I_demo=QPSK_rc_n0.*cos(2*pi*f1*t1);Q_demo=QPSK_rc_n0.*sin(2*pi*f1*t1);%低通濾波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:

8、1e3-0.05;t3=0:0.1:1e3-0.1;%抽樣判決data_recover=;fo門=1:20:10000data_recover=data_recove門(i:1:i+19)Q(i:1:i+19);end;bit_recover=;fo門=1:20:20000ifsum(data_recover(i:i+19)>0data_recover_a(i:i+19)=1;bit_recover=bit_recover1;elsedata_recover_a(i:i+19)=-1;bit_recover=bit_recover-1;endenderror=0;dd=-2*bit_in

9、+1;ddd=dd'ddd1=repmat(ddd,20,1);fori=1:2e4ddd2(i尸ddd1(i);endfori=1:1e3ifbit_recover(i)=ddd(i)error=error+1;endendp=error/1000;figuresubplot(2,1,1);plot(t2,ddd2);axis(0100-22);title('原序歹U');subplot(2,1,2);plot(t2,data_recover_a);axis(0100-22);title('解調(diào)后序列');效果圖:原序列2iiiI'010203

10、0I405060708090100解調(diào)后序列2iiIirrrrr_0-_U-1LI_LILILJULIUULJ_ULI_2-0102030406060708090100%設(shè)定T=1,不加噪聲clearall5close all%調(diào)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=1:1e4dat

11、a_I2(i)=data_I1(i);data_Q2(i尸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);%解調(diào)I_demo=QP

12、SK_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;t3=0:0.1:1e3-0.1;7dafalrecover"一；foriHEOIOOOOdafalrecover"dafalrecover-(z+19)Qz.+Igl;end;dddH2*brn+1;dddlHrepmaf(dd510

13、,)；forli-eje4ddd2(iHddd1(D;endfigure(l)Subp_of(411)；p_of(f3)；a><.s(o20661)；subp_of?12)；p_of(f3o)；a><.s(o2。661)；subp-of?1oo)；p-of(55dafalrecover)；a><.s(o20061)；subp_of?14)；p_of(Lddd2)；a><.s(o2。661)；常米H一原始序列解調(diào)后序列解調(diào)后偶位解調(diào)后奇位%QPSK浙璋>6爭SNRindB1H021。；SNRindB2=0:0.1:10;fori=1:leng

14、th(SNRindB1)pb,ps=cm_sm32(SNRindB1(i);smld_bit_err_prb(i尸pb;smld_symbol_err_prb(i尸ps;end;fori=1:length(SNRindB2)SNR=exp(SNRindB2(i)*log(10)/10);theo_err_prb(i尸Qfunct(sqrt(2*SNR);end;title('QPSK誤碼率分析)；semilogy(SNRindB1,smld_bit_err_prb,'*');axis(01010e-81);holdon;%semilogy(SNRindB1,smld_s

15、ymbol_err_prb,'o');semilogy(SNRindB2,theo_err_prb);legend('仿真比特誤碼率,'理論比特誤碼率');holdoff;functiony=Qfunct(x)y=(1/2)*erfc(x/sqrt(2);functionpb,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:Ntemp=rand;if(temp<0.25)dsource

16、1(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;elsedsource1(i)=1;dsource2(i)=1;end;end;numofsymbolerror=0;numofbiterror=0;fori=1:Nn=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;elser=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;elsedecis1=1;decis2=1;e