QAM_QAM算法_QAM调制解调_数字信号处理课程实验_

clear;clc;echo off;close all; N=512; %设定码元数量 fb=2; %基带信号频率 fs=32; %抽样频率 fc=4; %载波频率,为便于观察已调信号，我们把载波频率设的较低 Kbase=2; % Kbase=1,不经基带成形滤波，直接调制; % Kbase=2,基带经成形滤波器滤波后，再进行调制 info=random_binary(N); %产生二进制信号序列 [y,I,Q]=qam(info,Kbase,fs,fb,fc); %对基带信号进行16QAM调制 y2=y;y1=y; %备份信号，供后续仿真用 T=length(info)/fb; m=fs/fb; nn=length(info); dt=1/fs; t=0:dt:T-dt; plot(t(1:1000),y(1:1000),t(1:1000),I(1:1000),t(1:1000),Q(1:1000),[0,35],[0,0],'b'); title('已调信号'); % figure(3) % plot(y);grid; % axis([0,100,-3,3]); % title('原信号时域波形'); % y=awgn(y2,-10); % figure(4) % plot(y);grid; % axis([0,100,-10,10]); % title('加入噪声的信号时域波形'); n=length(y); y=fft(y)/n; y=abs(y(1:fix(n/2)))*2; q=find(y<1e-04); y(q)=1e-04; y=20*log10(y); f1=m/n; f=0:f1:(length(y)-1)*f1; figure; plot(f,y,'r'); grid on; title('已调信号频谱'); xlabel('f/fb'); constel(y1,fs,fb,fc); title('星座图'); SNR_in_dB=-10:1:0; %AWGN信道信噪比 for j=1:length(SNR_in_dB) y_add_noise=awgn(y2,SNR_in_dB(j)); %加入不同强度的高斯白噪声 y_output=qamdet(y_add_noise,fs,fb,fc); %对已调信号进行解调 numoferr=0; for i=1:N if (y_output(i)~=info(i)) numoferr=numoferr+1; end end Pe(j)=numoferr/N; %统计误码率 end figure; semilogy(SNR_in_dB,Pe,'red*-'); grid on; xlabel('SNR in dB'); ylabel('Pe'); title('16QAM调制误码率'); figure; plot(t(1:1000),y_add_noise(1:1000)); title('已调信号加噪声信号'); figure; % plot(t(1:512),y_output(1:512)); stairs(y_output); axis([1 100 -1 3]); grid on title('解调信号'); %基带升余弦成形滤波器 function y=bshape(x,fs,fb,N,alfa,delay) %设置默认参数 if nargin<6 delay=8; end if nargin<5 alfa=0.5; end if nargin<4 N=16; end b=firrcos(N,fb,2*alfa*fb,fs); y=filter(b,1,x); end function xn=four2two(yn) y=yn; ymin=min(y); ymax=max(y); ymax=max([ymax abs(ymin)]); ymin=-abs(ymax); yn=(y-ymin)*3/(ymax-ymin); %设置门限电平，判决 I0=find(yn< 0.5); yn(I0)=zeros(size(I0)); I1=find(yn>=0.5 & yn<1.5); yn(I1)=ones(size(I1)); I2=find(yn>=1.5 & yn<2.5); yn(I2)=ones(size(I2))*2; I3=find(yn>=2.5); yn(I3)=ones(size(I3))*3; %一位四进制码元转换为两位二进制码元 T=[0 0;0 1;1 1;1 0]; n=length(yn); for i=1:n xn(i,:)=T(yn(i)+1,:); end xn=xn'; xn=xn(:); xn=xn'; end %二进制转换成四进制 function [y,yn]=two2four(x,m) T=[0 1;3 2]; n=length(x); ii=1; for i=1:2:n-1 xi=x(i:i+1)+1; yn(ii)=T(xi(1),xi(2)); ii=ii+1; end yn=yn-1.5; y=yn; for i=1:m-1 y=[y;yn]; end y=y(:)'; %映射电平分别为-1.5；0.5；0.5；1.5 end function [info]=random_binary(N) if nargin == 0 %如果没有输入参数，则指定信息序列为10000个码元 N=10000; end for i=1:N temp=rand; if (temp<0.5) info(i)=0; % 1/2的概率输出为0 else info(i)=1; % 1/2的概率输出为1 end end end %QAM信号解调 function [xn,x]=qamdet(y,fs,fb,fc) dt=1/fs; t=0:dt:(length(y)-1)*dt; I=y.*cos(2*pi*fc*t); Q=-y.*sin(2*pi*fc*t); [b,a]=butter(2,2*fb/fs); %设计巴特沃斯滤波器 I=filtfilt(b,a,I); Q=filtfilt(b,a,Q); m=4*fs/fb; N=length(y)/m; n=(.6:1:N)*m; n=fix(n); In=I(n); Qn=Q(n); xn=four2two([In Qn]); %I分量Q分量并/串转换，最终恢复成码元序列xn nn=length(xn); xn=[xn(1:nn/2);xn(nn/2+1:nn)]; xn=xn(:); xn=xn'; end function [y,I,Q]=qam(x,Kbase,fs,fb,fc) T=length(x)/fb; m=fs/fb; nn=length(x); dt=1/fs; t=0:dt:T-dt; %串/并变换分离出I分量、Q分量，然后再分别进行电平映射 I=x(1:2:nn-1); [I,In]=two2four(I,4*m); Q=x(2:2:nn); [Q,Qn]=two2four(Q,4*m); if Kbase==2 %基带成形滤波 I=bshape(I,fs,fb/4); Q=bshape(Q,fs,fb/4); end y=I.*cos(2*pi*fc*t)-Q.*sin(2*pi*fc*t); end function c=constel(x,fs,fb,fc) N=length(x); m=2*fs/fb; n=fs/fc; i1=m-n; i=1; ph0=(i1-1)*2*pi/n; while i<=N/m xi=x(i1:i1+n-1); y=2*fft(xi)/n; c(i)=y(2); i=i+1; i1=i1+m; end if nargout<1 cmax=max(abs(c)); ph=(0:5:360)*pi/180; plot(1.414*cos(ph),1.414*sin(ph),'c'); hold on; for i=1:length(c) ph=ph0-angle(c(i)); a=abs(c(i))/cmax*1.414; plot(a*cos(ph),a*sin(ph),'r*'); end plot([1.5 1.5],[0,0],'k:',[0,0],[-1.5,1.5],'k:'); hold off ; axis equal; axis([-1.5 1.5 -1.5 1.5]); end end