实训二 信源编码和信道编码(2)

stem(t1,y1,'b');

title('A律压缩信号样值'); hold on;grid on; %%

[index,y2]=quantiz(y1,-6/8:2/8:6/8,-7/8:2/8:7/8); stem(t1,y2,'r','filled');

title('A律压缩信号样值和8级均匀量化的样值'); xlabel('t(s)');

ylabel('幅值');

legend('A律压缩信号样值','8级均匀量化样值'); %%%%%%%%% subplot(3,1,3);

stem(t1,y2-y1,'r','filled'); xlabel('t(s)'); title('量化误差'); grid on;

6.

close all; A=1;

L1=[8,12]; tc=1/200000; t=0:tc:1;

x0=sin(2*pi*t);

r=0:5:50;

sqnr=zeros(1,length(r)); for j=1:2 L=L1(j);

for i=1:length(r) A1=1/(10^(r(i)/20)); x=A1*x0; f=1/2000; t1=0:f:1;

y1=downsample(x,f/tc); M=2^L;

[index,y2]=quantiz(y1,-(M-1)/M:2/M:(M-1)/M, -1:2/M:1); sqnr(i) =10*log10(mean(y1.^2)./mean((y1-y2).^2)); end if j == 1

plot(r,sqnr,'r o --'); hold on; else

plot(r,sqnr,'r o -');

title('量化信噪比随信号衰减变化的曲线'); hold on; end end

%%%%%%%%

snr1 = 6.02*8+1.76; snr2 = 6.02*12+1.76; for i = 1:11

s1(i)=snr1-5*(i-1); end

for i = 1:11

s2(i)=snr2-5*(i-1); end

plot (r,s1,'k :'); grid on; hold on;

plot (r,s2,'k--'); grid on;

%%%%%%%%%%%% L=L1(1); A1=87.6;

for i=1:length(r)

x=x0/(10^(r(i)/20)); xmax=max(abs(x)); x1=zeros(1,200001);

for j=1:200001

if abs(x(j))<=1/A1

x1(j)=A1*x(j)/(1+log(A1)); else

x1(j)=sign(x(j))*(1+log(A1*abs(x(j))))/(1+log(A1)); end end

f=1/2000; t1=0:f:1;

y1=downsample(x1,f/tc); yy=downsample(x,f/tc); M=2^L;

[index,y2]=quantiz(y1,-(M-1)/M:2/M:(M-1)/M, -1:2/M:1); x2=zeros(1,2001); for k=1:2001

if abs(y2(k))<=1/(1+log(A1))

x2(k)=y2(k)*(1+log(A1))/A1; else

x2(k)=sign(y2(k))/A1*exp(abs(y2(k))*(1+log(A1))-1); end end

sqnr(i)=10*log10(mean(yy.^2)./mean((yy-x2).^2)); end

plot(r,sqnr,'b*-');grid on;

title('量化信噪比随信号衰减变化的曲线'); xlabel('信号的衰减dB');ylabel('量化信噪比'); axis([0,50,0,80]);

legend('均匀量化(8bits)','均匀量化(12bits)','均匀量化理论值(8bits)','均匀量化理论值(8bits)','A律压缩量化(8bits)' );