5.11).
Interleave
De-interleave
(B ??“ 1)N
B
FIGURE 5.10 Convolutional interleaver
decomposition.
230 CHAPTER FIVE
2
3
1
Interleaving De-interleaving
1
2
3
1
NA
NA
NA
NA
NA
(a)
5
6 3
2
4 1 4
5
6
4
2
NA
NA
NA
NA
(b)
8
9 6
5
7 4 7
8
9
7
5
3
1
2
3
(c)
11
12 9
8
10 7 10
11
12
10
8
6
5
6
(d)
4
FIGURE 5.11 N 3 symbol example of convolutional interleaving.
5.1.2 Block Codes
We will begin the discussion of block codes starting with linear block codes [4]. Here we group the
incoming bits into ???words??? which then enter what is commonly called a FEC encoder. This coder
essentially treats the input word as a vector (of size k bits) and applies an encoding rule across this
vector to produce an output ???code word.??? The FEC encoder has the following notation (n,k), where k
is the number of input bits that make up a word entering the FEC encoder and n is the number of output
bits representing the error protected code word. Here the integer value of n is always greater than that
of k (see Fig. 5.12) [5].
Hence the FEC encoder provides a mapping of the 2k possible k-tuple words to the 2n possible
n-tuple code words. The FEC encoder rule has each one of the 2k words assigned to one of the 2n code
words.
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