function y = ppdec(x,h,M);

% Synopsis: y = ppdec(x,h,M).

% Convolution and M-fold decimation, by polyphase decomposition.

% Input parameters:

% x: the input sequence

% h: the FIR filter coefficients

% M: the decimation factor.

% Output parameters:

% y: the output sequence.



% Part of software package for the book:

% A Course in Digital Signal Processing

% by Boaz Porat, John Wiley & Sons, 1997



lh = length(h); lp = floor((lh-1)/M) + 1;

p = reshape([reshape(h,1,lh),zeros(1,lp*M-lh)],M,lp);

lx = length(x); ly = floor((lx+lh-2)/M) + 1;

lu = floor((lx+M-2)/M) + 1; % length of decimated sequences

u = [zeros(1,M-1),reshape(x,1,lx),zeros(1,M*lu-lx-M+1)];

u = flipud(reshape(u,M,lu)); % the decimated sequences

y = zeros(1,lu+lp-1);

for m = 1:M, y = y + conv(u(m,:),p(m,:)); end

y = y(1:ly);