Altera Viterbi Compiler Bedienungsanleitung PDF herunterladen (Seite 29)

Parameter Value Description

ACS Units (A) 1, 2, 4, 8, or 16 The number of ACS units, which

adds a degree of parallelism

(hybrid architecture only). The

range of values available depends

upon the value of maximum

constraint length L

MAX

Traceback (v) 8 (minimum) The traceback length, which is

the number of stages in the trellis

that are traced back to obtain a

decoded bit. It is typically set to 6

× L for unpunctured codes, and

up to 15 × L for highly

punctured codes.

Softbits (softbits) 1 to 16 The number of soft decision bits

per symbol. When softbits is set

to 1 bit, the decoder acts as a

hard decision decoder, and still

allows for erased symbols to be

entered using the eras_sym

input.

Bmgwide – The precision of the state metric

accumulation. The parameter

editor selects and displays the

optimum value, which depends

on N

MAX

, L

MAX

and, softbits.

Soft Symbol Input

The number of soft decision bits per symbol, softbits, represent 2

softbits – 1

soft 0s and 2

softbits – 1

soft 1s. The

input values represent received signal amplitudes. If the input is in log-likelihood format, a transforma‐

tion is required and you must use extra softbits to retain signal integrity. The decoder marks depunctured

values separately. The decoder allows a hard-decision input when softbits = 1.

Table 3-3: Soft Symbol Input Representation

softbits = 3

Soft Symbol Meaning

011 Strongest '0'

010 Strong '0'

001 Weak '0'

000 Weakest '0'

111 Weakest '1'

110 Weak '1'

101 Strong '1'

UG-VITERBI

2014.12.15

Soft Symbol Input

3-11

Viterbi IP Core Functional Description

Altera Corporation

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