ViterbiR204.h
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/*
* Copyright 2008, 2009, 2014 Free Software Foundation, Inc.
* Copyright 2014 Range Networks, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
* This use of this software may be subject to additional restrictions.
* See the LEGAL file in the main directory for details.
*/
#ifndef _VITERBIR204_H_
#define _VITERBIR204_H_ 1
#include "Viterbi.h"
/**
Class to represent convolutional coders/decoders of rate 1/2, memory length 4.
This is the "workhorse" coder for most GSM channels.
*/
class ViterbiR2O4 : public ViterbiBase {
private:
/**name Lots of precomputed elements so the compiler can optimize like hell. */
//@{
/**@name Core values. */
//@{
static const unsigned mIRate = 2; ///< reciprocal of rate
static const unsigned mOrder = 4; ///< memory length of generators
//@}
/**@name Derived values. */
//@{
static const unsigned mIStates = 0x01 << mOrder; ///< (16) number of states, number of survivors
static const uint32_t mSMask = mIStates-1; ///< survivor mask
static const uint32_t mCMask = (mSMask<<1) | 0x01; ///< candidate mask
static const uint32_t mOMask = (0x01<<mIRate)-1; ///< ouput mask, all iRate low bits set
static const unsigned mNumCands = mIStates*2; ///< number of candidates to generate during branching
static const unsigned mDeferral = 6*mOrder; ///< deferral to be used
//@}
//@}
/** Precomputed tables. */
//@{
uint32_t mCoeffs[mIRate]; ///< polynomial for each generator
// (pat) There are 16 states, each of which has two possible output states.
// These are stored in these two tables in consecutive locations.
uint32_t mStateTable[mIRate][2*mIStates]; ///< precomputed generator output tables
// mGeneratorTable is the encoder output state for a given input state and encoder input bit.
uint32_t mGeneratorTable[2*mIStates]; ///< precomputed coder output table
//@}
int mBitErrorCnt;
public:
/**
A candidate sequence in a Viterbi decoder.
The 32-bit state register can support a deferral of 6 with a 4th-order coder.
*/
typedef struct candStruct {
uint32_t iState; ///< encoder input associated with this candidate
uint32_t oState; ///< encoder output associated with this candidate
float cost; ///< cost (metric value), float to support soft inputs
int bitErrorCnt; ///< number of bit errors in the encoded vector being decoded.
} vCand;
/** Clear a structure. */
void vitClear(vCand& v)
{
v.iState=0;
v.oState=0;
v.cost=0;
v.bitErrorCnt = 0;
}
private:
/**@name Survivors and candidates. */
//@{
vCand mSurvivors[mIStates]; ///< current survivor pool
vCand mCandidates[2*mIStates]; ///< current candidate pool
//@}
public:
unsigned iRate() const { return mIRate; }
uint32_t cMask() const { return mCMask; }
uint32_t stateTable(unsigned g, unsigned i) const { return mStateTable[g][i]; }
unsigned deferral() const { return mDeferral; }
ViterbiR2O4();
/** Set all cost metrics to zero. */
void initializeStates();
/**
Full cycle of the Viterbi algorithm: branch, metrics, prune, select.
@return reference to minimum-cost candidate.
*/
const vCand* vstep(uint32_t inSample, const float *probs, const float *iprobs, bool isNotTailBits);
private:
/** Branch survivors into new candidates. */
void branchCandidates();
/** Compute cost metrics for soft-inputs. */
void getSoftCostMetrics(uint32_t inSample, const float *probs, const float *iprobs);
/** Select survivors from the candidate set. */
void pruneCandidates();
/** Find the minimum cost survivor. */
const vCand& minCost() const;
/**
Precompute the state tables.
@param g Generator index 0..((1/rate)-1)
*/
void computeStateTables(unsigned g);
/**
Precompute the generator outputs.
mCoeffs must be defined first.
*/
void computeGeneratorTable();
public:
void encode(const BitVector &in, BitVector& target) const;
void decode(const SoftVector &in, BitVector& target);
int getBEC() { return mBitErrorCnt; }
};
#endif
Viterbi.h
BitVector
Definition BitVector.h:116
SoftVector
Definition BitVector.h:328
ViterbiBase
Definition Viterbi.h:26
ViterbiR2O4::stateTable
uint32_t stateTable(unsigned g, unsigned i) const
Definition ViterbiR204.h:99
ViterbiR2O4::getBEC
int getBEC()
Definition ViterbiR204.h:143
ViterbiR2O4::decode
void decode(const SoftVector &in, BitVector &target)
ViterbiR2O4::vitClear
void vitClear(vCand &v)
Definition ViterbiR204.h:78
ViterbiR2O4::deferral
unsigned deferral() const
Definition ViterbiR204.h:100
ViterbiR2O4::vstep
const vCand * vstep(uint32_t inSample, const float *probs, const float *iprobs, bool isNotTailBits)
ViterbiR2O4::iRate
unsigned iRate() const
Definition ViterbiR204.h:97
ViterbiR2O4::initializeStates
void initializeStates()
ViterbiR2O4::encode
void encode(const BitVector &in, BitVector &target) const
ViterbiR2O4::ViterbiR2O4
ViterbiR2O4()
ViterbiR2O4::vCand
struct ViterbiR2O4::candStruct vCand
ViterbiR2O4::cMask
uint32_t cMask() const
Definition ViterbiR204.h:98
ViterbiR2O4::candStruct
Definition ViterbiR204.h:70
ViterbiR2O4::candStruct::cost
float cost
cost (metric value), float to support soft inputs
Definition ViterbiR204.h:73
ViterbiR2O4::candStruct::oState
uint32_t oState
encoder output associated with this candidate
Definition ViterbiR204.h:72
ViterbiR2O4::candStruct::iState
uint32_t iState
encoder input associated with this candidate
Definition ViterbiR204.h:71
ViterbiR2O4::candStruct::bitErrorCnt
int bitErrorCnt
number of bit errors in the encoded vector being decoded.
Definition ViterbiR204.h:74