文章目录

一、要求二、设计三、代码四、结果五、结论

一、要求

画出QPSK信号产生的信息、I路、Q路信号对比图以及接收端解调的I路,Q 路，信息恢复的对比图。

二、设计

三、代码

clear all; clc; N=20; T=1; fc=2; Fs=100; bitstream=randi([0,1],1,N); bitstream=2*bitstream-1; I=[];Q=[]; for i=1:N if mod(i,2)~=0 I=[I,bitstream(i)]; else Q=[Q,bitstream(i)]; end end bit_data=[]; for i=1:N bit_data=[bit_data,bitstream(i)*ones(1,T*Fs)]; end I_data=[]; Q_data=[]; for i=1:N/2 I_data=[I_data,I(i)*ones(1,T*Fs*2)]; Q_data=[Q_data,Q(i)*ones(1,T*Fs*2)]; end figure(); t=0:1/Fs:N*T-1/Fs; subplot(3,1,1) plot(t,bit_data);legend('Bitstream') subplot(3,1,2) plot(t,I_data);legend('Bitstream') subplot(3,1,3) plot(t,Q_data);legend('Bitstream') bit_t=0:1/Fs:2*T-1/Fs; I_carrier=[]; Q_carrier=[]; for i=1:N/2 I_carrier=[I_carrier,I(i)*cos(2*pi*fc*bit_t)]; Q_carrier = [Q_carrier, Q(i)*cos(2*pi*fc*bit_t+pi/2)]; end QPSK_signal=I_carrier+Q_carrier; figure(); subplot(3,1,1) plot(t,I_carrier);legend('I signal') subplot(3,1,2) plot(t,Q_carrier);legend('Q signal') subplot(3,1,3) plot(t,QPSK_signal);legend('QPSK signal') snr=1; QPSK_receive=awgn(QPSK_signal,snr); for i=1:N/2 I_output=QPSK_receive(1,(i-1)*length(bit_t)+1:i*length(bit_t)).*cos(2*pi*fc*bit_t); if sum(I_output)>0; I_recover(i)=1; else I_recover(i)=-1; end Q_output=QPSK_receive(1,(i-1)*length(bit_t)+1:i*length(bit_t)).*cos(2*pi*fc*bit_t+pi/2); if sum(Q_output)>0; Q_recover(i)=1; else Q_recover(i)=-1; end end bit_recover=[]; for i=1:N if mod(i,2)~=0 bit_recover=[bit_recover,I_recover((i-1)/2+1)]; else bit_recover=[bit_recover,Q_recover(i/2)]; end end recover_data=[]; for i=1:N recover_data=[recover_data,bit_recover(i)*ones(1,T*Fs)]; end I_recover_data=[];Q_recover_data=[]; for i=1:N/2 I_recover_data=[I_recover_data,I_recover(i)*ones(1,T*Fs*2)]; Q_recover_data=[Q_recover_data,Q_recover(i)*ones(1,T*Fs*2)]; end figure(); t=0:1/Fs:N*T-1/Fs; subplot(3,1,2) plot(t,I_recover_data);legend('I Bitstream') subplot(3,1,3) plot(t,Q_recover_data);legend('Q Bitstream') subplot(3,1,1) plot(t,recover_data);legend('Bitstream')

四、结果

五、结论

由上图所示，最后解调出来的信号图像，按照理论应该与原信号相同，但由于实际原因，可能混杂着其他的噪声信号，所以导致解调之后的图像并不能完全与原信号的图像一致。