alupcm.m

低通抽样定理程序有课程设计的要用的自己看看吧

clear all 
close all  
t=0:0.01:10; 
vm1=-70:1:0;                        % 输入的正弦信号幅度不同 
vm=10.^(vm1/20); 
figure(1) 
for k=1:length(vm)     
for m=1:2         
x=vm(k)*sin(2*pi*t+2*pi*rand(1));         
v=1;        
xx=x/v;                     % normalize         
sxx=floor(xx*4096);         
y=pcm_encode(sxx);         
yy=pcm_decode(y,v);                  
nq(m)=sum((x-yy).*(x-yy))/length(x);
sq(m)=mean(yy.^2);         
snr(m)=(sq(m)/nq(m));         
drawnow         
subplot(211)         
plot(t,x);         
title('sample sequence')         
subplot(212)         
plot(t,yy)         
title('pcm decode sequence')     
end     
snrq(k)=10*log10(mean(snr)); 
end figure(2) 
plot(vm1,snrq) 
xlabel('输入正弦信号幅度的dB值') 
ylabel('量化信噪比') 
axis([-60 0 0 60]) 
grid  
****************************************     
其中编码函数为pcm_encode.m。 
*********************************** 
function [out]=pcm_encode(x) 
n=length(x); 
for i=1:n     
if x(i)>0         
out(i,1)=1;     
else         
out(i,1)=0;     
end    
if abs(x(i))>=0 & abs(x(i))<32 
out(i,2)=0; out(i,3)=0;out(i,4)=0; step=2; st=0; 
elseif 32<=abs(x(i)) & abs(x(i))<64           
out(i,2)=0; out(i,3)=0; out(i,4)=1; step=2; st=32;    
elseif 64<=abs(x(i)) & abs(x(i))<128        
out(i,2)=0; out(i,3)=1; out(i,4)=0; step=4; st=64;    
elseif 128<=abs(x(i)) & abs(x(i))<256        
out(i,2)=0; out(i,3)=1; out(i,4)=1; step=8; st=128;    
elseif 256<=abs(x(i)) & abs(x(i))<512       
out(i,2)=1; out(i,3)=0; out(i,4)=0; step=16; st=256;    
elseif 512<=abs(x(i)) & abs(x(i))<1024        
out(i,2)=1; out(i,3)=0; out(i,4)=1; step=32; st=512;    
elseif 1024<=abs(x(i)) & abs(x(i))<2048        
out(i,2)=1; out(i,3)=1; out(i,4)=0; step=64; st=1024;    
elseif 2048<=abs(x(i)) & abs(x(i))<4096        
out(i,2)=1; out(i,3)=1; out(i,4)=1; step=128; st=2048;    
else         
out(i,2)=1; out(i,3)=1; out(i,4)=1; step=128; st=2048;    
end    
if(abs(x(i))>=4096)       
out(i,2:8)=[1 1 1 1 1 1 1];    
else       
tmp=floor((abs(x(i))-st)/step);       
t=dec2bin(tmp,4)-48;         % 函数dec2bin输出的是ASCII字符串，48对应0       
out(i,5:8)=t(1:4);    
end 
end 
out=reshape(out',1,8*n);   
***********************************     
其中解码函数为pcm_decode.m。 
******************************* 
function [out]=pcm_decode(in,v) 
n=length(in); 
in=reshape(in',8,n/8)'; 
slot(1)=0;  
slot(2)=32;  
slot(3)=64;   
slot(4)=128; 
slot(5)=256;  
slot(6)=512; 
slot(7)=1024;  
slot(8)=2048;  
step(1)=2;  
step(2)=2;  
step(3)=4;  
step(4)=8; 
step(5)=16; 
step(6)=32;  
step(7)=64;  
step(8)=128;  
for i=1:n/8     
ss=2*in(i,1)-1;     
tmp=in(i,2)*4+in(i,3)*2+in(i,4)+1;     
st=slot(tmp);     
dt=(in(i,5)*8+in(i,6)*4+in(i,7)*2+in(i,8))*step(tmp)+0.5*step(tmp);     
out(i)=ss*(st+dt)/4096*v; 
end 
*******************************


序列Lloyd算法，对一个正弦信号数据进行标量量化
clear all 
clear close  
N=2^3; 
t=[0:100]*pi/20;                      % 以3比特传输信道 
u=cos(t); 
[p,c]=lloyds(u,N);                    % 生成分界点矢量和编码手册 
[index,quant,distor]=quantiz(u,p,c);      % 量化信号 
plot(t,u,t,quant,'*') 
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