Cryptography Reference
In-Depth Information
ations. In the example of Figure 7.27(b), arrival at point (1,1) is performed in
3.5 iterations.
Figure 7.29 - Binary error rates of a 16-state (a) and 8-state (b) binary turbo code
with rate 2/3, with pseudo-random interleaving of 20000 bits. MAP decoding with 1,
3, 6, 10, 15 and 20 iterations and comparison with the convergence threshold estimated
by the EXIT method.
When the signal to noise ratio is too low, as in case
E
b
/N
0
=1
.
4
dB in
Figure 7.28(b), the curves have intersection points other than point
(1
,
1)
.The
iterative process starting from null MI at the input will therefore not be able to
lead to a perfectly determined message. The minimum signal to noise ratio for
which there is no intersection other than point (1,1) is the convergence threshold
of the turbo encoder. In the simulated example, this convergence can be esti-
