a_u_law.m

北邮《通信原理基于Matlab的计算机仿真》书的源码 m文件 好不容易弄来的

%demo for u and A law for quantize，filename: a_u_law.m
%u=255   y=ln(1+ux)/ln(1+u)
%A=87.6  y=Ax/(1+lnA) (0<x<1/A)   y=(1+lnAx)/(1+lnA)
clear all
close all
dx=0.01;
x=-1:dx:1;
u=255;
A=87.6;
 
%u Law
yu=sign(x).*log(1+u*abs(x))/log(1+u);
%A Law
for i=1:length(x)
   if abs(x(i))<1/A
      ya(i)=A*x(i)/(1+log(A));
   else
      ya(i)=sign(x(i))*(1+log(A*abs(x(i))))/(1+log(A));
   end
end
 
figure(1)
plot(x,yu,'k.:');
title('u Law')
xlabel('x');
ylabel('y');
grid on
hold on
xx=[-1,-127/255,-63/255,-31/255,-15/255,-7/255,-3/255,-1/255,1/255,3/255,7/255,15/255,31/255,63/255,...
      127/255,1];
yy=[-1,-7/8,-6/8,-5/8,-4/8,-3/8,-2/8,-1/8,1/8,2/8,3/8,4/8,5/8,6/8,7/8,1];
plot(xx,yy,'r');
stem(xx,yy,'b-.');
legend('u律压缩特性','折线近似u律');
 
 
figure(2)
plot(x,ya,'k.:');
title('A Law')
xlabel('x');
ylabel('y');
grid on
hold on
xx=[-1,-1/2,-1/4,-1/8,-1/16,-1/32,-1/64,-1/128,1/128,1/64,1/32,1/16,1/8,1/4,1/2,1];
yy=[-1,-7/8,-6/8,-5/8,-4/8,-3/8,-2/8,-1/8,1/8,2/8,3/8,4/8,5/8,6/8,7/8,1];
plot(xx,yy,'r');
stem(xx,yy,'b-.');
legend('A律压缩特性','折线近似A律');