Lattice Semiconductor
Figure 2-5. Trellis Tree
Functional Description
00
01
10
11
0/00
1/00
0/01
1/01
0/10
1/10
0/11
1/11
0/00
1/00
0/01
1/01
0/10
1/10
0/11
1/11
0/00
1/00
0/01
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1/11
Trellis for 3 stages and constraint length = 3
Branches corresponding to input seq. 101 is highlighted
In the above trellis, the branches for three transitions are drawn. The path of the trellis for a typical input sequence,
101, is highlighted in the figure. Any transmission error alters the path traversed in the trellis. In Viterbi decoding,
such a trellis is formed in memory, where the metrics corresponding to all paths are recorded. After constructing
the trellis for a sufficient length (called the traceback length, L), the traceback process starts from node 0 in the last
state. During the traceback process, the original sequence is reconstructed from the trellis. In error-prone applica-
tions, however, a trellis of length 2L is constructed and two traceback processes are employed. The first traceback
starts from node 0, traces back L stages of the trellis, and ends up in a node which is more likely to be the right
starting point for the second traceback. The second traceback starts from this reliable starting point and traces
back another L nodes. The data corresponding to the second traceback are decoded to result in the original data
stream.
Functional Description
A simplified implementation of the Lattice Block Viterbi Decoder IP is shown in Figure 2-6 . A brief description of the
modules is given below.
Figure 2-6. Internal Architecture of the Viterbi Decoder
BER
BER
din
BMU
ACS
TBU
dout
MMU
MEM
Branch Metric Unit (BMU)
This module takes in the input data from the channel and computes a metric for each state and input combination.
The metric is the Hamming distance for hard-decision encoded data and l1 norm (sum of absolute values) for soft
decision encoded data. The BMU also includes a depuncturing unit for punctured codes. This module has three
major sub-modules: state encoder, metric computer, and de-puncture unit.
IPUG32_02.7, June 2010
9
Block Viterbi Decoder User’s Guide
相关PDF资料
VTERB-DECO-XP-N1 IP CORE VITERBI DECODER XPGA
VTP110F POLYSWITCH PTC RESET 1.1A STRAP
VTP175LF POLYSWITCH PTC RESET 1.75A STRAP
VTP210GF POLYSWITCH PTC RESET 2.1A STRAP
VTP210SF POLYSWITCH PTC RESET 2.1A STRAP
W51-A121B1-10 CIRCUIT BREAKER THERM 10A ILLUM
W54-XC2A4B10-40 CIRCUIT BREAKER THERMAL 40AMP
WV-089047-10-9 LABEL ID PRODUCTS
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