Roman Khassraf | aa8fa99 | 2015-06-02 09:20:03 +0200 | [diff] [blame] | 1 | /* |
| 2 | * Copyright 2008, 2009, 2014 Free Software Foundation, Inc. |
| 3 | * Copyright 2014 Range Networks, Inc. |
| 4 | * |
| 5 | * This software is distributed under the terms of the GNU Affero Public License. |
| 6 | * See the COPYING file in the main directory for details. |
| 7 | * |
| 8 | * This use of this software may be subject to additional restrictions. |
| 9 | * See the LEGAL file in the main directory for details. |
| 10 | |
| 11 | This program is free software: you can redistribute it and/or modify |
| 12 | it under the terms of the GNU Affero General Public License as published by |
| 13 | the Free Software Foundation, either version 3 of the License, or |
| 14 | (at your option) any later version. |
| 15 | |
| 16 | This program is distributed in the hope that it will be useful, |
| 17 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 18 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 19 | GNU Affero General Public License for more details. |
| 20 | |
| 21 | You should have received a copy of the GNU Affero General Public License |
| 22 | along with this program. If not, see <http://www.gnu.org/licenses/>. |
| 23 | |
| 24 | */ |
| 25 | |
| 26 | #ifndef _VITERBIR204_H_ |
| 27 | #define _VITERBIR204_H_ 1 |
| 28 | |
| 29 | #include "Viterbi.h" |
| 30 | |
| 31 | |
| 32 | /** |
| 33 | Class to represent convolutional coders/decoders of rate 1/2, memory length 4. |
| 34 | This is the "workhorse" coder for most GSM channels. |
| 35 | */ |
| 36 | class ViterbiR2O4 : public ViterbiBase { |
| 37 | |
| 38 | private: |
| 39 | /**name Lots of precomputed elements so the compiler can optimize like hell. */ |
| 40 | //@{ |
| 41 | /**@name Core values. */ |
| 42 | //@{ |
| 43 | static const unsigned mIRate = 2; ///< reciprocal of rate |
| 44 | static const unsigned mOrder = 4; ///< memory length of generators |
| 45 | //@} |
| 46 | /**@name Derived values. */ |
| 47 | //@{ |
| 48 | static const unsigned mIStates = 0x01 << mOrder; ///< (16) number of states, number of survivors |
| 49 | static const uint32_t mSMask = mIStates-1; ///< survivor mask |
| 50 | static const uint32_t mCMask = (mSMask<<1) | 0x01; ///< candidate mask |
| 51 | static const uint32_t mOMask = (0x01<<mIRate)-1; ///< ouput mask, all iRate low bits set |
| 52 | static const unsigned mNumCands = mIStates*2; ///< number of candidates to generate during branching |
| 53 | static const unsigned mDeferral = 6*mOrder; ///< deferral to be used |
| 54 | //@} |
| 55 | //@} |
| 56 | |
| 57 | /** Precomputed tables. */ |
| 58 | //@{ |
| 59 | uint32_t mCoeffs[mIRate]; ///< polynomial for each generator |
| 60 | // (pat) There are 16 states, each of which has two possible output states. |
| 61 | // These are stored in these two tables in consecutive locations. |
| 62 | uint32_t mStateTable[mIRate][2*mIStates]; ///< precomputed generator output tables |
| 63 | // mGeneratorTable is the encoder output state for a given input state and encoder input bit. |
| 64 | uint32_t mGeneratorTable[2*mIStates]; ///< precomputed coder output table |
| 65 | //@} |
| 66 | int mBitErrorCnt; |
| 67 | |
| 68 | public: |
| 69 | |
| 70 | /** |
| 71 | A candidate sequence in a Viterbi decoder. |
| 72 | The 32-bit state register can support a deferral of 6 with a 4th-order coder. |
| 73 | */ |
| 74 | typedef struct candStruct { |
| 75 | uint32_t iState; ///< encoder input associated with this candidate |
| 76 | uint32_t oState; ///< encoder output associated with this candidate |
| 77 | float cost; ///< cost (metric value), float to support soft inputs |
| 78 | int bitErrorCnt; ///< number of bit errors in the encoded vector being decoded. |
| 79 | } vCand; |
| 80 | |
| 81 | /** Clear a structure. */ |
| 82 | void vitClear(vCand& v) |
| 83 | { |
| 84 | v.iState=0; |
| 85 | v.oState=0; |
| 86 | v.cost=0; |
| 87 | v.bitErrorCnt = 0; |
| 88 | } |
| 89 | |
| 90 | |
| 91 | private: |
| 92 | |
| 93 | /**@name Survivors and candidates. */ |
| 94 | //@{ |
| 95 | vCand mSurvivors[mIStates]; ///< current survivor pool |
| 96 | vCand mCandidates[2*mIStates]; ///< current candidate pool |
| 97 | //@} |
| 98 | |
| 99 | public: |
| 100 | |
| 101 | unsigned iRate() const { return mIRate; } |
| 102 | uint32_t cMask() const { return mCMask; } |
| 103 | uint32_t stateTable(unsigned g, unsigned i) const { return mStateTable[g][i]; } |
| 104 | unsigned deferral() const { return mDeferral; } |
| 105 | |
| 106 | |
| 107 | ViterbiR2O4(); |
| 108 | |
| 109 | /** Set all cost metrics to zero. */ |
| 110 | void initializeStates(); |
| 111 | |
| 112 | /** |
| 113 | Full cycle of the Viterbi algorithm: branch, metrics, prune, select. |
| 114 | @return reference to minimum-cost candidate. |
| 115 | */ |
| 116 | const vCand* vstep(uint32_t inSample, const float *probs, const float *iprobs, bool isNotTailBits); |
| 117 | |
| 118 | private: |
| 119 | |
| 120 | /** Branch survivors into new candidates. */ |
| 121 | void branchCandidates(); |
| 122 | |
| 123 | /** Compute cost metrics for soft-inputs. */ |
| 124 | void getSoftCostMetrics(uint32_t inSample, const float *probs, const float *iprobs); |
| 125 | |
| 126 | /** Select survivors from the candidate set. */ |
| 127 | void pruneCandidates(); |
| 128 | |
| 129 | /** Find the minimum cost survivor. */ |
| 130 | const vCand& minCost() const; |
| 131 | |
| 132 | /** |
| 133 | Precompute the state tables. |
| 134 | @param g Generator index 0..((1/rate)-1) |
| 135 | */ |
| 136 | void computeStateTables(unsigned g); |
| 137 | |
| 138 | /** |
| 139 | Precompute the generator outputs. |
| 140 | mCoeffs must be defined first. |
| 141 | */ |
| 142 | void computeGeneratorTable(); |
| 143 | |
| 144 | public: |
| 145 | void encode(const BitVector &in, BitVector& target) const; |
| 146 | void decode(const SoftVector &in, BitVector& target); |
| 147 | int getBEC() { return mBitErrorCnt; } |
| 148 | }; |
| 149 | #endif |