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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

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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