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。输入串川变换我波振蔻#sin/X-b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1代）和、代），经过抽样判决和并/用交换器，将上下支路得到的并行数据恢复成申行数据。输入A带通港波器sin co r位定L低通一抽样判决并7串变换载波恢复%调相法clearallt=-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);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(解调后序列);效果图:原序列2iiiI0102030I405060708090100解调后序列2iiIirrrrr_0-_U-1LI_LILILJULIUULJ_ULI_2-0102030406060708090100%设定T=1,不加噪声clearall#close all%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=1:1e4data_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;t3=0:0.1:1e3-0.1;#dafalrecover一；foriHEOIOOOOdafalrecoverdafalrecover-(z+19)Qz.+Igl;end;dddH2*brn+1;dddlHrepmaf(dd510,)；forli-eje4ddd2(iHddd1(D;endfigure(l)Subp_of(411)；p_of(f3)；a6争SNRindB1H021。；SNRindB2=0:0.1:10;fori=1:length(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;s00=10;s01=01;s11=-10;s10=0-1;fori=1:Ntemp=rand;if(temp0.25)dsource1(i)=0;dsource2(i)=0;el