GNU Radio's GSM Package: ViterbiR204.h Source File

GNU Radio's GSM Package

ViterbiR204.h
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1 /*
2 * Copyright 2008, 2009, 2014 Free Software Foundation, Inc.
3 * Copyright 2014 Range Networks, Inc.
4 *
5 * This program is free software: you can redistribute it and/or modify
6 * it under the terms of the GNU Affero General Public License as published by
7 * the Free Software Foundation, either version 3 of the License, or
8 * (at your option) any later version.
9 *
10 * This program is distributed in the hope that it will be useful,
11 * but WITHOUT ANY WARRANTY; without even the implied warranty of
12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 * GNU Affero General Public License for more details.
14 *
15 * You should have received a copy of the GNU Affero General Public License
16 * along with this program. If not, see <http://www.gnu.org/licenses/>.
17 *
18 * This use of this software may be subject to additional restrictions.
19 * See the LEGAL file in the main directory for details.
20 */
21
22 #ifndef _VITERBIR204_H_
23 #define _VITERBIR204_H_ 1
24
25 #include "Viterbi.h"
26
27
28 /**
29 Class to represent convolutional coders/decoders of rate 1/2, memory length 4.
30 This is the "workhorse" coder for most GSM channels.
31 */
32 class ViterbiR2O4 : public ViterbiBase {
33
34 private:
35 /**name Lots of precomputed elements so the compiler can optimize like hell. */
36 //@{
37 /**@name Core values. */
38 //@{
39 static const unsigned mIRate = 2; ///< reciprocal of rate
40 static const unsigned mOrder = 4; ///< memory length of generators
41 //@}
42 /**@name Derived values. */
43 //@{
44 static const unsigned mIStates = 0x01 << mOrder; ///< (16) number of states, number of survivors
45 static const uint32_t mSMask = mIStates-1; ///< survivor mask
46 static const uint32_t mCMask = (mSMask<<1) | 0x01; ///< candidate mask
47 static const uint32_t mOMask = (0x01<<mIRate)-1; ///< ouput mask, all iRate low bits set
48 static const unsigned mNumCands = mIStates*2; ///< number of candidates to generate during branching
49 static const unsigned mDeferral = 6*mOrder; ///< deferral to be used
50 //@}
51 //@}
52
53 /** Precomputed tables. */
54 //@{
55 uint32_t mCoeffs[mIRate]; ///< polynomial for each generator
56 // (pat) There are 16 states, each of which has two possible output states.
57 // These are stored in these two tables in consecutive locations.
58 uint32_t mStateTable[mIRate][2*mIStates]; ///< precomputed generator output tables
59 // mGeneratorTable is the encoder output state for a given input state and encoder input bit.
60 uint32_t mGeneratorTable[2*mIStates]; ///< precomputed coder output table
61 //@}
62 int mBitErrorCnt;
63
64 public:
65
66 /**
67 A candidate sequence in a Viterbi decoder.
68 The 32-bit state register can support a deferral of 6 with a 4th-order coder.
69 */
70 typedef struct candStruct {
71 uint32_t iState; ///< encoder input associated with this candidate
72 uint32_t oState; ///< encoder output associated with this candidate
73 float cost; ///< cost (metric value), float to support soft inputs
74 int bitErrorCnt; ///< number of bit errors in the encoded vector being decoded.
75 } vCand;
76
77 /** Clear a structure. */
78 void vitClear(vCand& v)
79 {
80 v.iState=0;
81 v.oState=0;
82 v.cost=0;
83 v.bitErrorCnt = 0;
84 }
85
86
87 private:
88
89 /**@name Survivors and candidates. */
90 //@{
91 vCand mSurvivors[mIStates]; ///< current survivor pool
92 vCand mCandidates[2*mIStates]; ///< current candidate pool
93 //@}
94
95 public:
96
97 unsigned iRate() const { return mIRate; }
98 uint32_t cMask() const { return mCMask; }
99 uint32_t stateTable(unsigned g, unsigned i) const { return mStateTable[g][i]; }
100 unsigned deferral() const { return mDeferral; }
101
102
103 ViterbiR2O4();
104
105 /** Set all cost metrics to zero. */
106 void initializeStates();
107
108 /**
109 Full cycle of the Viterbi algorithm: branch, metrics, prune, select.
110 @return reference to minimum-cost candidate.
111 */
112 const vCand* vstep(uint32_t inSample, const float *probs, const float *iprobs, bool isNotTailBits);
113
114 private:
115
116 /** Branch survivors into new candidates. */
117 void branchCandidates();
118
119 /** Compute cost metrics for soft-inputs. */
120 void getSoftCostMetrics(uint32_t inSample, const float *probs, const float *iprobs);
121
122 /** Select survivors from the candidate set. */
123 void pruneCandidates();
124
125 /** Find the minimum cost survivor. */
126 const vCand& minCost() const;
127
128 /**
129 Precompute the state tables.
130 @param g Generator index 0..((1/rate)-1)
131 */
132 void computeStateTables(unsigned g);
133
134 /**
135 Precompute the generator outputs.
136 mCoeffs must be defined first.
137 */
138 void computeGeneratorTable();
139
140 public:
141 void encode(const BitVector &in, BitVector& target) const;
142 void decode(const SoftVector &in, BitVector& target);
143 int getBEC() { return mBitErrorCnt; }
144 };
145 #endif
ViterbiR2O4::candStruct::oState
uint32_t oState
encoder output associated with this candidate
Definition: ViterbiR204.h:72
ViterbiR2O4::vCand
struct ViterbiR2O4::candStruct vCand
Viterbi.h
ViterbiR2O4::candStruct::iState
uint32_t iState
encoder input associated with this candidate
Definition: ViterbiR204.h:71
ViterbiR2O4::cMask
uint32_t cMask() const
Definition: ViterbiR204.h:98
BitVector
Definition: BitVector.h:115
ViterbiR2O4::ViterbiR2O4
ViterbiR2O4()
ViterbiR2O4::vitClear
void vitClear(vCand &v)
Definition: ViterbiR204.h:78
ViterbiR2O4::encode
void encode(const BitVector &in, BitVector &target) const
SoftVector
Definition: BitVector.h:328
ViterbiR2O4::candStruct::cost
float cost
cost (metric value), float to support soft inputs
Definition: ViterbiR204.h:73
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::deferral
unsigned deferral() const
Definition: ViterbiR204.h:100
ViterbiR2O4
Definition: ViterbiR204.h:32
ViterbiR2O4::candStruct::bitErrorCnt
int bitErrorCnt
number of bit errors in the encoded vector being decoded.
Definition: ViterbiR204.h:74
ViterbiBase
Definition: Viterbi.h:26
ViterbiR2O4::stateTable
uint32_t stateTable(unsigned g, unsigned i) const
Definition: ViterbiR204.h:99
ViterbiR2O4::candStruct
Definition: ViterbiR204.h:70
ViterbiR2O4::getBEC
int getBEC()
Definition: ViterbiR204.h:143
ViterbiR2O4::initializeStates
void initializeStates()
ViterbiR2O4::decode
void decode(const SoftVector &in, BitVector &target)