dpcmenco.m

数字通信第四版原书的例程

function [indx, quant] = dpcmenco(sig, codebook, partition, predictor)
%DPCMENCO Encodes a signal using differential pulse code modulation method.
%       INDX = DPCMENCO(SIG, CODEBOOK, PARTITOIN, PREDICTOR) produces
%       differential pulse code modulation (DPCM) encoded index INDX. The
%       signal to be encoded is SIG. The predictive transfer function is
%       provided in PREDICTOR. The predictive-error quantization partition
%       and code book are given in PARTITION and CODEBOOK respectively. In
%       general, a M-th order transfer function numerator has the form of 
%       [0, n1, n2, ... nM].
%
%       [INDX, QUANT] = DPCMENCO(SIG, CODEBOOK, PARTITION, PREDICTOR) outputs
%       the quantized value in QUANT.
%
%       The input parameters CODEBOOK, PARTITION,  and PREDICTOR can be 
%       estimated by using DPCMOPT.
%
%       See also QUANTIZ, DPCMOPT, DPCMDECO.

%       Wes Wang 10/13/94, 10/5/95
%       Copyright (c) 1995-96 by The MathWorks, Inc.
%       $Revision: 1.1 $  $Date: 1996/04/01 17:57:06 $

if nargin < 4
    error('Not enough input variable for DPCMENCO.');
end;

% The structure of the DPCM is as follows:
%                       e                   quant
%   Input signal   -->+-----Quantization------|-------
%                     ^-                      V
%                     |---------------------->+
%                 out |<----Predictor<--------| inp

len_predictor = length(predictor) - 1;
predictor = predictor(2:len_predictor+1);
predictor = predictor(:)';
len_sig = length(sig);

x = zeros(len_predictor, 1);
for i = 1 : len_sig;
    out = predictor * x;
    e = sig(i) - out;
    % index
    indx(i) = sum(partition < e);
    % quantized value
    quant(i) = codebook(indx(i) + 1) + out;
    % renew the estimated output
    x = [quant(i); x(1:len_predictor-1)];
end;

% -- end of dpcmenco --