仿真高斯白噪声信道下QPSK地EbN0与误比特率

1、QPSK调制与解调在MATLAB平台上的实现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，由丁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I(t)和Q(t)，经过抽样判决和并/申交换器，将上下支路得

2、到的并行数据恢复成申行数据。输入带通滤波器%调相法clearallcloseallt=-1:0.01:7-0.01;tt=length(t);x1=ones(1,800);fori=1:ttif(t(i)=-1&t(i)=5&t(i)=0&t1(i)=4&t1(i)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+1;ddd=dd;ddd1=repmat(ddd,20,1);fo

3、ri=1:2e4ddd2(i)=ddd1(i);endfori=1:1e3ifbit_recover(i)=ddd(i)error=error+1;endendp=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%设定T=1,不加噪声clearallcloseall%调制bit_in=randint(1e3,1,01);bit_I=bit_in(1:2

4、: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=1:1e4data_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=

5、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

6、-0.05;t3=0:0.1:1e3-0.1;data_recover=;fori=1:20:10000data_recover=data_recoverI(i:1:i+19)Q(i:1:i+19);end;ddd=-2*bit_in+1;ddd1=repmat(ddd,10,1);fori=1:1e4ddd2(i)=ddd1(i);endfigure(1)subplot(4,1,1);plot(t3,I);axis(020-66);subplot(4,1,2);plot(t3,Q);axis(020-66);subplot(4,1,3);plot(t2,data_recover);axis(

7、020-66);subplot(4,1,4);plot(t,ddd2);axis(020-66);效果图：%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(Q

8、PSK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;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;

9、s00=10;s01=01;s11=-10;s10=0-1;fori=1:Ntemp=rand;if(temp0.25)dsource1(i)=0;dsource2(i)=0;elseif(temp0.5)dsource1(i)=0;dsource2(i)=1;elseif(temp0.75)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)&(

10、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;end;symbolerror=0;if(decis1=dsource1(i)numofbiterror=numofbiterror+1;symbolerror=1;end;if(decis2=dsou