ETTC'2003 - SEE

free space in output buffer(s). Sizes of input
buffers depend on operation performed by
other modules and cannot be foreseen.
Taking into account amount of data that can
be read and free available space, the module is
able to operate some computations. In
general, it does not consume all input data nor
use all available output space. If any data
located in input buffer is not consumed, it will
be processed in a prior way at next module
call.
This operating mode ensure the data
continuity between modules: There is no loss
of data.
Data and free space management in a
JUZZLE module is as follows
input buffer 'A'
Free space
Data
APPLICATIONS
Module
Figure 5 : Module buffers
Coding / Decoding
output buffer 'A'
output buffer 'B'
The specificity of coding or decoding modules
is rate change. The size of the buffer has to be
chosen equal to the minimum in bits of the
data available at input and the free space
available at output, taking into account bit
rate ratio.
For convolutional codes, delays appear at
transmitter (code memory) and at receiver
(Viterbi path length). These delays are
undertaken by a shorter first amount of
produced data in the output buffer.
Modulation / Demodulation
As the previous modules, the modulation and
demodulation modules introduce rate
changes.
Filtering
Filtering modules introduce not only but also
processing constraints especially when
developed for accelerating computations.
One of available techniques is to use fast
convolution ‘Overlap And Add’ method.
Principle of this method is to perform
convolution by signal blocks constituted of 2 n
samples.
Let us consider, for instance, that filtering
module needs to operate blocks of 1024
samples. Noting ‘Nin’ the number of samples
available in input buffer and ‘Nout’ the number
of samples available in output buffer. As
module can only process blocks of 1024
samples, the number of blocks that can be
processed is the minimum of Nin/1024 and
Nout/1024 .
Obviously, some of input samples may not be
processed and all free space in output buffer
may not be used.
Hereafter figure describes an example with
numerical data
Before filtering
After filtering
7153 samples Filter
[1024]
9654 free positions
MIN [ 7153 / 1024 , 9654 / 1024 ] = 6
module can process 6 blocks of 1024 (=6144) samples
1009 samples Filter
[1024]
3510 free positions
Figure 6 : Buffering example for filtering module
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