decoder.rst

|RSC| Decoder parameters

--dec-type, -D

Type:	text
Allowed values:	BCJR CHASE ML
Examples:	--dec-type BCJR

|factory::Decoder::parameters::p+type,D|

Description of the allowed values:

Value	Description
BCJR	Select the |BCJR| algorithm from :cite:`Bahl1974`.
CHASE	See the common :ref:`dec-common-dec-type` parameter.
ML	See the common :ref:`dec-common-dec-type` parameter.

--dec-implem

Type:	text
Allowed values:	GENERIC STD FAST VERY_FAST
Default:	STD
Examples:	--dec-implem FAST

|factory::Decoder::parameters::p+implem|

Description of the allowed values:

Value	Description
GENERIC	Select the generic |BCJR| implementation that can decode any trellis (slow compared to the other implementations).
STD	Select the |STD| |BCJR| implementation, specialized for the {013,015} polynomials (c.f. the :ref:`enc-rsc-enc-poly` parameter).
FAST	Select the fast |BCJR| implementation, specialized for the {013,015} polynomials (c.f. the :ref:`enc-rsc-enc-poly` parameter).
VERY_FAST	Select the very fast |BCJR| implementation, specialized for the {013,015} polynomials (c.f. the :ref:`enc-rsc-enc-poly` parameter).

--dec-simd

Type:	text
Allowed values:	INTER INTRA
Examples:	--dec-simd INTER

|factory::Decoder_RSC::parameters::p+simd|

Description of the allowed values:

Value	Description
INTER	Select the inter-frame strategy, only available for the |BCJR| STD, FAST and VERY_FAST implementation (see :cite:`Cassagne2016a`).
INTRA	Select the intra-frame strategy, only available for the |BCJR| STD and FAST implementations (see :cite:`Wu2013`).

Note

In the intra-frame strategy, |SIMD| units process several LLRs in parallel within a single frame decoding. In the inter-frame strategy, SIMD units decodes several independent frames in parallel in order to saturate the |SIMD| unit. This approach improves the throughput of the decoder but requires to load several frames before starting to decode, increasing both the decoding latency and the decoder memory footprint.

Note

When the inter-frame |SIMD| strategy is set, the simulator will run with the right number of frames depending on the |SIMD| length. This number of frames can be manually set with the :ref:`src-src-fra` parameter. Be aware that running the simulator with the :ref:`src-src-fra` parameter set to 1 and the :ref:`dec-polar-dec-simd` parameter set to INTER will completely be counterproductive and will lead to no throughput improvements.

--dec-max

Type:	text
Allowed values:	MAXS MAXL MAX
Examples:	--dec-max MAX

|factory::Decoder_RSC::parameters::p+max|

Description of the allowed values:

Value	Description
MAXS	\max^*(a,b) = \max(a,b) + \log(1 + \exp(-|a - b|)).
MAXL	\max^*(a,b) \approx \max(a,b) + \max(0, 0.301 - (0.5 |a - b|)).
MAX	\max^*(a,b) \approx \max(a,b).

MAXS for Max Star is the exact \max^* operator. MAXL for Max Linear is a linear approximation of the \max^* function. MAX for Max is the simplest \max^* approximation with only a \max function.

Note

The |BCJR| with the \max approximation is also called the max-log-|MAP| algorithm.

References

.. bibliography:: references.bib