Altera Viterbi Compiler - Manual (Page 27)

Figure 3-8: Graph Comparing Actual BER with Estimated BER
3.00 3.50 4.00 4.50 5.00 5.50 6.00
Signal-to-Noise Ratio
BER
Actual BER
Estimated BER
1.00e-03
1.00e-02
1.00e-01
Node Synchronization
If you are not using external synchronization, you may not know the order of your N bits. The node
synchronization option allows you to rotate the rr inputs until the decoder is in synchronization. To use
node synchronization, you observe the BER and keep changing state_node_sync to rotate the rr inputs
until you get the correct value for the BER.
Figure 3-9: Node Synchronization Block Diagram
state_node_sync
Barrel
Rotator
rr(1)
rr(2)
...
RR(1)
RR(2)
...
rr(N) RR(N)
The following equation represents node synchronization:
RR[i]
=
rr
[(
(state_node_sync
+
i
– 1) mod
N
) + 1]
where
i
is 1 to
N
.
RR
and
rr
are treated as an array of width
N
of busses
softbits
wide. The range of valid values for
state_node_sync
is 0 to (
N
– 1).
Code Sets
UG-VITERBI
2014.12.15
Node Synchronization 3-9
Viterbi IP Core Functional Description Altera Corporation
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