Altera Viterbi Compiler - Manual (Page 28)

Table 3-2: Code Sets Parameters
Parameter Value Description
Number of
Code Sets
1 to 8 The Viterbi IP core supports multiple code definitions. The multiple
code set option allows up to eight code sets, where a code set comprises
a code rate and associated generating polynomials.
Number of
coded bits.
(N)
2 to 7 (hybrid)
2 to 4 (parallel)
For every bit to be encoded, N bits are output. With the multiple code
set option there are up to 5 different N parameters, which can be in any
order. Valid only for Viterbi mode. For TCM mode only N = 2 is
supported
Constraint
length (L)
3 to 9 The constraint length. Defines the number of states in the convolu‐
tional encoder, where number of states = 2(L – 1). You can choose
different values of L for each code set.
Decimal or
Octal
– Decimal or octal base representation for the generator polynomials.
The design file representation is decimal, but you have the option of
entering in either decimal or octal base.
Mode V or T Viterbi (V) or TCM mode (T).
GA, GB, GC,
GD, GE, GF,
GG
– The generator polynomials. If you use the multiple code set option, the
wizard enters a different set of polynomials in the respective gi group.
The wizard provides default values that you can overwritte by any valid
polynomial. (The wizard does not check whether the entered values are
valid.) The parallel architecture uses only GA, GB, GC, and GD.
For multiple code sets, the first code definition corresponds to the first line and is selected with
sel_code
input = 0; the second line is selected with
sel_code
= 1; the third with
sel_code
= 2 and so on. For each
code definition you can select N, the polynomials, the constraint length L, and the mode (Viterbi or
TCM). You can mix different constraint lengths with different TCM and Viterbi modes. The test data,
which the wizardr creates, tests each of the code definitions. You can see these tests in the simulation with
the testbench or if you look at the block_period_stim.txt file.
In hybrid mode, for constraint lengths of 3 and 4, the bitwidth of
tr_init_state
is 4, but the MegaCore
function ignores the redundant higher bits.
For multiple constraint lengths, some of the last decoded bits may be incorrect, becauset of the Viterbi
algorithm. To avoid this effect, give a lower BER, and reduce the probability of being on the wrong trellis
path, set Optimization to None and turn on Best State Finder.
Viterbi Parameters
Parameter Value Description
Maximum constraint length
(L
MAX
)
5 to 9 (hybrid)
3 to 9 (parallel)
The maximum constraint length
L
MAX
. .
3-10 Viterbi Parameters
UG-VITERBI
2014.12.15
Altera Corporation Viterbi IP Core Functional Description
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