1、通信原理報告qpsk仿真系統qpsk調制與解調在matlab平臺上的實現qpsk即四進制移向鍵控（quaternary phase shift keying），它利用載波的四種不同相位來表示數字信息，由于每一種載波相位代表兩個比特信息，因此每個四進制碼元可以用兩個二進制碼元的組合來表示。兩個二進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正交調制器。由qpsk信號的調制可知，對它的解調可以采用與2psk信號類似的解調方法進行解調。解調原理圖如下所示，同相支路和正交支路分別采用相干解調方式解調，得到和，經過抽樣判決和并/

2、串交換器，將上下支路得到的并行數據恢復成串行數據。% 調相法clear allclose allt=-1:0.01:7-0.01;tt=length(t);x1=ones(1,800);for i=1:tt if (t(i)=-1 & t(i)=5& t(i)=0 & t1(i)=4& t1(i)0 data_recover_a(i:i+19)=1; bit_recover=bit_recover 1; else data_recover_a(i:i+19)=-1; bit_recover=bit_recover -1; endenderror=0;dd = -2*bit_in+1;ddd=d

3、d;ddd1=repmat(ddd,20,1);for i=1:2e4 ddd2(i)=ddd1(i);endfor i=1:1e3 if bit_recover(i)=ddd(i) error=error+1; endendp=error/1000;figure(1)subplot(2,1,1);plot(t2,ddd2);axis(0 100 -2 2);title(原序列);subplot(2,1,2);plot(t2,data_recover_a);axis(0 100 -2 2);title(解調后序列);效果圖：% 設定 t=1, 不加噪聲clear allclose all% 調

4、制bit_in = randint(1e3, 1, 0 1);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);for i=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(

5、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

6、);i=i_recover(11:10010);q=q_recover(11:10010);t2=0:0.05:1e3-0.05;t3=0:0.1:1e3-0.1;data_recover=;for i=1:20:10000 data_recover=data_recover i(i:1:i+19) q(i:1:i+19);end;ddd = -2*bit_in+1;ddd1=repmat(ddd,10,1);for i=1:1e4 ddd2(i)=ddd1(i);endfigure(1)subplot(4,1,1);plot(t3,i);axis(0 20 -6 6);subplot(4,1

7、,2);plot(t3,q);axis(0 20 -6 6);subplot(4,1,3);plot(t2,data_recover);axis(0 20 -6 6);subplot(4,1,4);plot(t,ddd2);axis(0 20 -6 6);效果圖：% qpsk誤碼率分析snrindb1=0:2:10;snrindb2=0:0.1:10;for i=1:length(snrindb1) pb,ps=cm_sm32(snrindb1(i); smld_bit_err_prb(i)=pb; smld_symbol_err_prb(i)=ps;end;for i=1:length(sn

8、rindb2) snr=exp(snrindb2(i)*log(10)/10); theo_err_prb(i)=qfunct(sqrt(2*snr);end;title(qpsk誤碼率分析);semilogy(snrindb1,smld_bit_err_prb,*);axis(0 10 10e-8 1);hold on;% semilogy(snrindb1,smld_symbol_err_prb,o);semilogy(snrindb2,theo_err_prb);legend(仿真比特誤碼率,理論比特誤碼率);hold off;functiony=qfunct(x)y=(1/2)*erf

9、c(x/sqrt(2);functionpb,ps=cm_sm32(snrindb)n=10000;e=1;snr=10(snrindb/10);sgma=sqrt(e/snr)/2;s00=1 0;s01=0 1;s11=-1 0;s10=0 -1;for i=1:n temp=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; else dsource1(

10、i)=1; dsource2(i)=1; end;end;numofsymbolerror=0;numofbiterror=0;for i=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(c00 c01 c10 c11); 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=dsour