Altera Viterbi Compiler - Manual (Page 24)

Figure 3-6: Conversion of Received Symbol into Four Branch Metrics and a Sector Number
Branch Metric 1
Branch Metric 3
Branch Metric 2
Branch Metric 0
Received Symbol
011
001
000
110
111
101
100
010
2
For example, consider a received symbol that lands in sector number 2 with the following distances to the
four nearest symbol map points:
• 1111
• 1101
• 1011
• 0001
Where the distance of the radius for 4 softbits is 1111. The distances are inverted to obtain the following
branch metrics:
• Branch metric 0 = 0000
• Branch metric 1 = 0010
• Branch metric 2 = 0100
• Branch metric 3 = 1110
The decoder uses the coded bits (c1, c0) to select the branch metric number, which it uses to decide where
to connect the branch metrics to the rr input of the Viterbi decoder. Branch metric 3 goes to the most
significant bits (MSB) of
rr
; branch metric 0 goes to the least significant bits (LSB) of
rr
.
3-6 About Converting Received Signals
UG-VITERBI
2014.12.15
Altera Corporation Viterbi IP Core Functional Description
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