数字通信作业(2)

1、作业2.1.1 匹配滤波器的性能(方波脉冲信号)源代码：% 程序功能：画出误比特曲线clear all;close all;clcN = 1000;SNRindB = 0:6;% 理论曲线echo on;for i=1:length(SNRindB), SNR=exp(SNRindB(i)*log(10)/10); theo_err_awgn(i)=0.5*erfc(sqrt(SNR); echo off;end % 高斯信道 echo on;for i=1:length(SNRindB) smld_bit_awgn_err(i)=(y(N,i)/N; echo off;end;figure(

2、5)semilogy(SNRindB,theo_err_awgn,'r'),title('误码率曲线');hold on;semilogy(SNRindB,smld_bit_awgn_err,'r*');hold on;xlabel('Eb/No');ylabel('BER');legend('理论AWGN','仿真AWGN');% 程序功能：产生基带信号、发送机、接收机function Awgn_num = y(N,SNR) %N = 100;M = 4;Tb = 1;Ts = 2

3、*Tb;m = log2(M);dt = Tb/32;fs = 1/dt;t = 0:dt:N-dt;fc = 1; %基带信号的产生data = sign(randn(1,N);nrz = zeros(1,length(data)/dt);for i = 1:N if(data(i)=1) nrz(i-1)/dt+1:i/dt) = 1; else nrz(i-1)/dt+1:i/dt) = -1; endend %串并变换idata = data(1:m:(N-1);qdata = data(2:m:N);j = 1;for i = 1:N/2 inrz(j-1)/dt+1:(j+1)/d

4、t) = idata(i); qnrz(j-1)/dt+1:(j+1)/dt) = qdata(i); j = j+2;end %QPSK调制si = zeros(1,N/dt);sq = zeros(1,N/dt);s = zeros(1,N/dt);j = 1;for i = 1:N/2 si(j-1)/dt+1:(j+1)/dt) = idata(i)*cos(2*pi*fc*(j-1)/dt+1:(j+1)/dt)*dt); sq(j-1)/dt+1:(j+1)/dt) = qdata(i)*sin(2*pi*fc*(j-1)/dt+1:(j+1)/dt)*dt); s(j-1)/dt

5、+1:(j+1)/dt) = si(j-1)/dt+1:(j+1)/dt) + sq(j-1)/dt+1:(j+1)/dt); j = j+2;end %高斯信道s_w = channelAWGN(s,SNR); %解调部分idata_1 = s_w.*cos(2*pi*fc*t(1:length(t);qdata_1 = s_w.*sin(2*pi*fc*t(1:length(t); %匹配滤波imatch_filter = zeros(N/2);qmatch_filter = zeros(N/2);j = 1;for i = 1:N/2 imatch_filter(i) = sum(ida

6、ta_1(j-1)/dt+1:(j+1)/dt); qmatch_filter(i) = sum(qdata_1(j-1)/dt+1:(j+1)/dt); j = j+2;endimatch_filter = imatch_filter/max(abs(imatch_filter);qmatch_filter = qmatch_filter/max(abs(qmatch_filter); %抽样判决idata_3 = zeros(1,N/2);qdata_3 = zeros(1,N/2);for i = 1:N/2 if(imatch_filter(i)>0) idata_3(i) =

7、1; else idata_3(i) = -1; end if(qmatch_filter(i)>0) qdata_3(i) = 1; else qdata_3(i) = -1; endendj = 1;for i = 1:N/2 idata_3_1(j-1)/dt+1:(j+1)/dt) = idata_3(i); qdata_3_1(j-1)/dt+1:(j+1)/dt) = qdata_3(i); j = j+2;end %并串转换demodata = zeros(1,N);for i = 1:N if(mod(i,2)=1) data_3(i-1)/dt+1:i/dt) = id

8、ata_3_1(i/dt); demodata(i) = idata_3_1(i/dt); else data_3(i-1)/dt+1:i/dt) = qdata_3_1(i/dt); demodata(i) = qdata_3_1(i/dt); endend %累计误码个数Awgn_num = 0;for i = 1:N if(demodata(i)=data(i) Awgn_num = Awgn_num+1; endend %Drawfigure(1)subplot(311)plot(t,nrz(1,:);axis(0 N -1.5 1.5);title('基带信号');s

9、ubplot(312)plot(t,inrz(1,:);axis(0 N -1.5 1.5);title('I支路信号');subplot(313)plot(t,qnrz(1,:);axis(0 N -1.5 1.5);title('Q支路信号'); figure(2)subplot(311)plot(t,s(1,:);axis(0 N -1.5 1.5);title('QPSK已调信号');subplot(312)plot(t,si(1,:);axis(0 N -1.5 1.5);title('I路载波调制后的信号');subp

10、lot(313)plot(t,sq(1,:);title('Q路载波调制后的信号');axis(0 N -1.5 1.5); figure(3)subplot(211)plot(t,s(1,:);axis(0 N -1.5 1.5);title('QPSK已调信号');subplot(212)plot(t,s_w(1,:);title('经过高斯信道后的信号'); figure(4)subplot(211)plot(t,nrz(1,:);axis(0 N -1.5 1.5);title('原始发送信号');subplot(212)

11、plot(t,data_3(1,:);axis(0 N -1.5 1.5);title('解调后的信号');% 程序功能：加入高斯白噪声function signal_awgn=channelAWGN(signal,snr)snr_lin =10(snr/10);%计算信号功率和噪声功率signal_power=sum(signal.2)/length(signal);noise_power=signal_power/snr_lin;noise_std=sqrt(noise_power);noise=noise_std*randn(1,length(signal);signal

12、_awgn=signal+noise; 仿真波形：当N=10，SNR = 0时，调制解调波形作业2.1.2 接收端使用巴特沃斯低通滤波器的性能源代码与2.1.1不同的地方：%巴特沃斯低通滤波n,Wn = buttord(0.001,1/8,2,20);b,a = butter(n,Wn);ilow_filter = filter(b,a,idata_1);qlow_filter = filter(b,a,qdata_1);实验结果：结论：综合两种实验结果得出，匹配滤波器可以得到最佳性能。2.1.3匹配滤波器的性能(三角脉冲信号)源代码与2.1.1不同的地方：%基带信号的产生data = sig

13、n(randn(1,N);nrz = zeros(1,length(data)/dt);for i = 1:N if(data(i)=1) nrz(i-1)/dt+1:(i-0.5)/dt)= 2*dt*(i-1)/dt+1:(i-0.5)/dt)-2*(i-1); nrz(i-0.5)/dt+1:i/dt) = -2*dt*(i-0.5)/dt+1:i/dt)+2*i; else nrz(i-1)/dt+1:(i-0.5)/dt) = -2*dt*(i-1)/dt+1:(i-0.5)/dt)+2*(i-1); nrz(i-0.5)/dt+1:i/dt) = 2*dt*(i-0.5)/dt+1

14、:i/dt)-2*i; endend %串并变换idata = data(1:m:(N-1);qdata = data(2:m:N);j = 1;for i = 1:N/2 if(idata(i)=1) inrz(j-1)/dt+1:j/dt) = dt*(j-1)/dt+1:j/dt)-(j-1); inrz(j/dt+1:(j+1)/dt) = -dt*(j/dt+1:(j+1)/dt)+j+1; else inrz(j-1)/dt+1:j/dt) = -dt*(j-1)/dt+1:j/dt)+(j-1); inrz(j/dt+1:(j+1)/dt) = dt*(j/dt+1:(j+1)/

15、dt)-j-1; end if(qdata(i)=1) qnrz(j-1)/dt+1:j/dt) = dt*(j-1)/dt+1:j/dt)-(j-1); qnrz(j/dt+1:(j+1)/dt) = -dt*(j/dt+1:(j+1)/dt)+j+1; else qnrz(j-1)/dt+1:j/dt) = -dt*(j-1)/dt+1:j/dt)+(j-1); qnrz(j/dt+1:(j+1)/dt) = dt*(j/dt+1:(j+1)/dt)-j-1; end j = j+2;end当N=10，SNR = 0时，调制解调波形结论：由仿真结果得出，脉冲信号波形对匹配滤波器的性能是没有

16、影响的。作业2.2源代码：clear allclose allclc%Fc=10; %载频Fs=40; %系统采样频率Fd=1; %码速率N=Fs/Fd;df=10;numSymb=25;%进行仿真的信息代码个数M=4; %进制数SNRpBit=60;%信噪比SNR=SNRpBit/log2(M);seed=12345 54321;numPlot=15;%产生25个二进制随机码x=randsrc(numSymb,1,0:M-1);%产生25个二进制随机码figure(1)stem(0:numPlot-1,x(1:numPlot),'bx');title('二进制随机序列

17、')xlabel('Time');ylabel('Amplitude');%调制y=dmod(x,Fc,Fd,Fs,'fsk',M,df);numModPlot=numPlot*Fs;t=0:numModPlot-1./Fs;figure(2)plot(t,y(1:length(t),'b-');axis(min(t) max(t) -1.5 1.5);title('调制后的信号')%在已调信号中加入高斯白噪声randn('state',seed(2);y=awgn(y,SNR-10*log

18、10(0.5)-10*log10(N),'measured','dB');%在已调信号中加入高斯白噪声figure(3)plot(t,y(1:length(t),'b-');%画出经过信道的实际信号axis(min(t) max(t) -1.5 1.5);title('加入高斯白噪声后的已调信号')%相干解调figure(4)z1=ddemod(y,Fc,Fd,Fs,'fsk/eye',M,df);title('相干解调后的信号的眼图')%带输出波形的相干M元频移键控解调figure(5)stem(0:numPlot-1,x(1:numPlot),'bx');hold on;stem(0:numPlot-1,z1(1:numPlot),'ro');hold off;axis(0 numPlot -0.5 2);title(