kopia lustrzana https://github.com/OpenRTX/OpenRTX
Added implementation of soft-decision Viterbi decoder for M17 protocol, updated version number in meson.build
Silvano Seva
rodzic
ae8bba88b6
commit
49c6cbd7c0
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@ -2,7 +2,7 @@
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## OpenRTX - Modular Open Source Radio Firmware
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##
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project('OpenRTX', ['c', 'cpp'],
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version : '0.3.3',
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version : '0.3.5',
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default_options : ['warning_level=3', 'b_staticpic=false'])
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##
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@ -140,7 +140,7 @@ private:
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M17LinkSetupFrame lsf; ///< Latest LSF received.
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M17LinkSetupFrame lsfFromLich; ///< LSF assembled from LICH segments.
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M17StreamFrame streamFrame; ///< Latest stream dat frame received.
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M17Viterbi viterbi; ///< Viterbi decoder.
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M17HardViterbi viterbi; ///< Viterbi decoder.
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///< Maximum allowed hamming distance when determining the frame type.
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static constexpr uint8_t MAX_SYNC_HAMM_DISTANCE = 4;
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@ -3,6 +3,7 @@
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* Niccolò Izzo IU2KIN *
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* Frederik Saraci IU2NRO *
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* Silvano Seva IU2KWO *
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* Wojciech Kaczmarski SP5WWP *
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* *
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* Adapted from original code written by Phil Karn KA9Q *
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* *
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@ -43,20 +44,20 @@ namespace M17
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* G2 = 0x17.
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*/
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class M17Viterbi
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class M17HardViterbi
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{
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public:
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/**
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* Constructor.
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*/
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M17Viterbi() : prevMetrics(&prevMetricsData), currMetrics(&currMetricsData)
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M17HardViterbi() : prevMetrics(&prevMetricsData), currMetrics(&currMetricsData)
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{ }
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/**
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* Destructor.
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*/
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~M17Viterbi() { }
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~M17HardViterbi() { }
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/**
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* Decode unpunctured convolutionally encoded data.
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@ -237,6 +238,225 @@ private:
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std::array< std::bitset< NumStates >, 244 > history;
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};
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/**
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* Soft decision Viterbi decoder tailored on M17 protocol specifications,
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* that is for decoding of data encoded with a convolutional encoder with a
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* coder rate R = 1/2, a constraint length K = 5 and polynomials G1 = 0x19 and
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* G2 = 0x17.
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*/
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class M17SoftViterbi
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{
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public:
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/**
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* Constructor.
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*/
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M17SoftViterbi() : prevMetrics(&prevMetricsData), currMetrics(&currMetricsData)
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{ }
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/**
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* Destructor.
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*/
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~M17SoftViterbi() { }
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/**
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* Decode unpunctured convolutionally encoded data.
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*
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* @param in: input data.
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* @param out: destination array where decoded data are written.
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* @return number of bit errors corrected.
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*/
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template < size_t IN, size_t OUT >
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uint32_t decode(const std::array< uint16_t, IN >& in,
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std::array< uint8_t, OUT >& out)
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{
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static_assert(IN < 244*2, "Input size exceeds max history");
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currMetricsData.fill(0);
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prevMetricsData.fill(0);
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size_t pos = 0;
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for (size_t i = 0; i < IN; i += 2)
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{
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uint16_t s0 = in[i];
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uint16_t s1 = in[i + 1];
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decodeBit(s0, s1, pos);
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pos++;
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}
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return chainback(out, pos);
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}
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/**
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* Decode punctured convolutionally encoded data.
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*
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* @param in: input data.
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* @param out: destination array where decoded data are written.
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* @param punctureMatrix: puncturing matrix.
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* @return number of bit errors corrected.
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*/
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template < size_t IN, size_t OUT, size_t P >
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uint16_t decodePunctured(const std::array< uint16_t, IN >& in,
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std::array< uint8_t, OUT >& out,
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const std::array< uint8_t, P >& punctureMatrix)
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{
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static_assert(IN < 244*2, "Input size exceeds max history");
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currMetricsData.fill(0);
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prevMetricsData.fill(0);
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size_t histPos = 0;
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size_t punctIndex = 0;
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size_t bitPos = 0;
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uint16_t punctBitCnt = 0;
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while(bitPos < IN)
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{
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uint16_t sym[2] = {0xFFFF, 0xFFFF};
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for(uint8_t i = 0; i < 2; i++)
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{
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if(punctureMatrix[punctIndex++])
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{
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sym[i] = in[bitPos];
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bitPos++;
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}
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else
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{
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sym[i] = 0x7FFF; //half range for punctured out bit
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punctBitCnt++;
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}
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if(punctIndex >= P) punctIndex = 0;
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}
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decodeBit(sym[0], sym[1], histPos);
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histPos++;
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}
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return chainback(out, histPos) - punctBitCnt;
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}
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private:
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/**
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* Decode one bit and update trellis.
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*
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* @param s0: cost of the first symbol.
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* @param s1: cost of the second symbol.
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* @param pos: bit position in history.
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*/
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void decodeBit(uint16_t s0, uint16_t s1, size_t pos)
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{
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static constexpr uint16_t COST_TABLE_0[] = {0, 0, 0, 0, 0xFFFF,
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0xFFFF, 0xFFFF, 0xFFFF};
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static constexpr uint16_t COST_TABLE_1[] = {0, 0xFFFF, 0xFFFF, 0,
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0, 0xFFFF, 0xFFFF, 0};
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for(uint8_t i = 0; i < NumStates/2; i++)
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{
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uint32_t metric = q_AbsDiff(COST_TABLE_0[i], s0)
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+ q_AbsDiff(COST_TABLE_1[i], s1);
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uint32_t m0 = (*prevMetrics)[i] + metric;
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uint32_t m1 = (*prevMetrics)[i + NumStates/2] + (0x1FFFE - metric);
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uint32_t m2 = (*prevMetrics)[i] + (0x1FFFE - metric);
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uint32_t m3 = (*prevMetrics)[i + NumStates/2] + metric;
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uint8_t i0 = 2 * i;
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uint8_t i1 = i0 + 1;
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if(m0 >= m1)
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{
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history[pos].set(i0, true);
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(*currMetrics)[i0] = m1;
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}
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else
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{
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history[pos].set(i0, false);
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(*currMetrics)[i0] = m0;
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}
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if(m2 >= m3)
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{
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history[pos].set(i1, true);
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(*currMetrics)[i1] = m3;
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}
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else
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{
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history[pos].set(i1, false);
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(*currMetrics)[i1] = m2;
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}
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}
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std::swap(currMetrics, prevMetrics);
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}
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/**
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* History chainback to obtain final byte array.
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*
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* @param out: destination byte array for decoded data.
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* @param pos: starting position for the chainback.
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* @return minimum Viterbi cost at the end of the decode sequence.
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*/
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template < size_t OUT >
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uint32_t chainback(std::array< uint8_t, OUT >& out, size_t pos)
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{
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uint8_t state = 0;
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size_t bitPos = OUT*8;
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while(bitPos > 0)
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{
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bitPos--;
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pos--;
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bool bit = history[pos].test(state >> 4);
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state >>= 1;
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if(bit) state |= 0x80;
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setBit(out, bitPos, bit);
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}
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uint32_t cost = (*prevMetrics)[0];
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for(size_t i = 0; i < NumStates; i++)
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{
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uint32_t m = (*prevMetrics)[i];
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if(m < cost) cost = m;
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}
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return cost;
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}
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/**
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* Utility function to compute the absolute value of a difference between
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* two fixed-point values.
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*
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* @param v1: first value
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* @param v2: second value
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* @return abs(v1-v2)
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*/
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inline uint16_t q_AbsDiff(const uint16_t v1, const uint16_t v2)
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{
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if(v2 > v1) return v2 - v1;
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return v1 - v2;
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}
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static constexpr size_t K = 5;
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static constexpr size_t NumStates = (1 << (K - 1));
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std::array< uint32_t, NumStates > *prevMetrics;
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std::array< uint32_t, NumStates > *currMetrics;
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std::array< uint32_t, NumStates > prevMetricsData;
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std::array< uint32_t, NumStates > currMetricsData;
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std::array< std::bitset< NumStates >, 244 > history;
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};
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} // namespace M17
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#endif // M17_VITERBI_H
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@ -23,10 +23,10 @@
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#include <cstdint>
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#include <random>
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#include <array>
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#include "M17/M17ConvolutionalEncoder.h"
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#include "M17/M17CodePuncturing.h"
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#include "M17/M17Viterbi.h"
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#include "M17/M17Utils.h"
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#include "M17/M17ConvolutionalEncoder.hpp"
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#include "M17/M17CodePuncturing.hpp"
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#include "M17/M17Viterbi.hpp"
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#include "M17/M17Utils.hpp"
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using namespace std;
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@ -72,7 +72,7 @@ int main()
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generateErrors(punctured);
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array< uint8_t, 18 > result;
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M17Viterbi decoder;
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M17HardViterbi decoder;
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decoder.decodePunctured(punctured, result, DATA_PUNCTURE);
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for(size_t i = 0; i < result.size(); i++)
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