16QAM调制解调(MATLAB)(2)

end; end;

Pe(j)=numoferr/N; %统计误码率 end; figure;

semilogy(SNR_in_dB,Pe,'blue*-'); grid on;

xlabel('SNR in dB'); ylabel('Pe');

title('16QAM调制误码率');

bshape.m

%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);

four2two.m

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';

two2four.m

%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

random_binary.m

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;

qamdet.m

%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';

qam.m

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);

32QAM

M = 32;

k = log2(M);

x = randint(20000,1);

y = modulate(modem.qammod('M',32,'InputType','Bit'),x); EbNo = -5:1:10;

for n=1:length(EbNo)

snr(n) = EbNo(n) + 10*log10(k); ynoisy = awgn(y,snr(n),'measured');

zms = demodulate(modem.qamdemod('M',32,'OutputType','Bit'),ynoisy); z = de2bi(zms,'left-msb');

[nErrors(n), BITBER(n)] = biterr(x,z);

theo_err_prb(n)=(1/k)*3/2*erfc(sqrt(k*0.1*(10.^(EbNo(n)/10)))); end

disp (nErrors); disp (BITBER);

semilogy(EbNo,BITBER,'b*-',EbNo,theo_err_prb,'k*-'); title('32QAM误比特率性能'); xlabel('Eb/N0(dB)'); ylabel('误比特率');

legend('仿真误码率','理论误码率');