u_pcm.m

用MATLAB实现PCM（脉冲调制）的编码

function [sqnr,a_quan,code]=u_pcm(a,n)
%U_PCM        Uniform PCM encoding of a sequence.
%             [SQNR,A_QUAN,CODE]=U_PCM(A,N)
%             a=input sequence.
%             n=number of quantization levels(even).
%             sqnr=output SQNR(in dB).
%             a_quan=quantized output before encoding.
%             code=the encoded output.

amax=max(abs(a));
a_quan=a/amax;
b_quan=a_quan;
d=2/n;
q=d.*[0:n-1];
q=q-((n-1)/2)*d;
for i=1:n
    a_quan(find((q(i)-d/2<=a_quan)&(a_quan<=q(i)+d/2)))=q(i).*ones(1,length(find((q(i)-d/2<=a_quan)&(a_quan<=q(i)+d/2))));
    
    b_quan(find(a_quan==q(i)))=(i-1).*ones(1,length(find(a_quan==q(i))));
end
a_quan=a_quan*amax;
nu=ceil(log2(n));
code=zeros(length(a),nu);
for i=1:length(a)
    for j=nu:-1:0
        if(fix(b_quan(i)/(2^j))==1)
            code(i,(nu-j))=1;
            b_quan(i)=b_quan(i)-2^j;
        end
    end
end
sqnr=20*log10(norm(a)/norm(a-a_quan));