5 Bursty error example.
As mentioned earlier, multipath fading can
produce strong correlation from one symbol time
to the next, especially for low Doppler spreads. It
is for this reason, as well as the type of demodulator
used in the receiver, that the errors tend to be
bursty in nature. The receiver takes the data and
writes them into columns. In this particular example
shown in Fig. 5.5, there is a burst of N bits.
Hence a complete column consists of erroneous
(or unreliable) data bits. As the de-interleaver
matrix is complete, the data is read out in rows as
shown in Fig. 5.6.
The de-interleaver data output bit stream will
resemble as shown in Fig. 5.7.
Here we can clearly see that a burst of N errors
was redistributed to having a single error, every
228 CHAPTER FIVE
Data Out
Data In
M
N
X
X
X
X
..
.
. . .
FIGURE 5.6 De-interleaving the bursty error example.
X11 C21 . . . CM1 X12 C12 . . . CM2 C13 C23 . . . CM3
FIGURE 5.7 De-interleaver output data stream for the bursty error example.
M bits apart. Hence using a simple single error correcting FEC code would correct and compensate
the channel burst of errors. We have redistributed the bursty channel errors into random errors in the
code words.
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