mirrors/gnss-sdr
1
0
Fork 0
mirror of https://github.com/gnss-sdr/gnss-sdr synced 2024-12-14 12:10:34 +00:00
Code Issues Releases Wiki Activity

Improve design of the Viterbi Decoder API

Browse Source 
Easier to use, it does not require external memory for internal states anymore
This commit is contained in:
Carles Fernandez 2021-09-26 13:23:28 +02:00
parent 43df43ff9d
commit 715987e749
No known key found for this signature in database
GPG Key ID: 4C583C52B0C3877D
5 changed files with 62 additions and 80 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

25
src/algorithms/telemetry_decoder/gnuradio_blocks/galileo_telemetry_decoder_gs.cc
View File

@ -236,17 +236,8 @@ galileo_telemetry_decoder_gs::galileo_telemetry_decoder_gs(
d_inav_nav.init_PRN(d_satellite.get_PRN());
d_first_eph_sent = false;
// vars for Viterbi decoder
const int32_t max_states = 1U << static_cast<uint32_t>(d_mm); // 2^d_mm
d_out0 = std::vector<int32_t>(max_states);
d_out1 = std::vector<int32_t>(max_states);
d_state0 = std::vector<int32_t>(max_states);
d_state1 = std::vector<int32_t>(max_states);
// create Vitrebi decoder and appropriate transition vectors
// Instantiate the Viterbi decoder
d_viterbi = std::make_unique<Viterbi_Decoder>(KK, nn, d_datalength, g_encoder);
d_viterbi->nsc_transit(d_out0, d_state0, 0);
d_viterbi->nsc_transit(d_out1, d_state1, 1);
}
@ -317,7 +308,7 @@ void galileo_telemetry_decoder_gs::decode_INAV_word(float *page_part_symbols, in
}
const int32_t decoded_length = frame_length / 2;
std::vector<int32_t> page_part_bits(decoded_length);
d_viterbi->decode(page_part_bits, d_out0, d_state0, d_out1, d_state1, page_part_symbols_soft_value);
d_viterbi->decode(page_part_bits, page_part_symbols_soft_value);
// 3. Call the Galileo page decoder
std::string page_String;
@ -470,7 +461,7 @@ void galileo_telemetry_decoder_gs::decode_FNAV_word(float *page_symbols, int32_t
const int32_t decoded_length = frame_length / 2;
std::vector<int32_t> page_bits(decoded_length);
d_viterbi->decode(page_bits, d_out0, d_state0, d_out1, d_state1, page_symbols_soft_value);
d_viterbi->decode(page_bits, page_symbols_soft_value);
// 3. Call the Galileo page decoder
std::string page_String;
@ -543,7 +534,7 @@ void galileo_telemetry_decoder_gs::decode_CNAV_word(float *page_symbols, int32_t
}
const int32_t decoded_length = page_length / 2;
std::vector<int32_t> page_bits(decoded_length);
d_viterbi->decode(page_bits, d_out0, d_state0, d_out1, d_state1, page_symbols_soft_value);
d_viterbi->decode(page_bits, page_symbols_soft_value);
// 3. Call the Galileo page decoder
std::string page_String;
@ -617,13 +608,7 @@ void galileo_telemetry_decoder_gs::reset()
d_last_valid_preamble = d_sample_counter;
d_sent_tlm_failed_msg = false;
d_stat = 0;
const int32_t max_states = 1U << static_cast<uint32_t>(d_mm); // 2^d_mm
d_out0 = std::vector<int32_t>(max_states);
d_out1 = std::vector<int32_t>(max_states);
d_state0 = std::vector<int32_t>(max_states);
d_state1 = std::vector<int32_t>(max_states);
d_viterbi->nsc_transit(d_out0, d_state0, 0);
d_viterbi->nsc_transit(d_out1, d_state1, 1);
d_viterbi->reset();
DLOG(INFO) << "Telemetry decoder reset for satellite " << d_satellite;
}

5
src/algorithms/telemetry_decoder/gnuradio_blocks/galileo_telemetry_decoder_gs.h
View File

@ -85,14 +85,9 @@ private:
void decode_FNAV_word(float *page_symbols, int32_t frame_length);
void decode_CNAV_word(float *page_symbols, int32_t page_length);
// data members for Viterbi decoder
std::unique_ptr<Viterbi_Decoder> d_viterbi;
std::vector<int32_t> d_preamble_samples;
std::vector<float> d_page_part_symbols;
std::vector<int32_t> d_out0;
std::vector<int32_t> d_out1;
std::vector<int32_t> d_state0;
std::vector<int32_t> d_state1;
std::string d_dump_filename;
std::ofstream d_dump_file;

44
src/algorithms/telemetry_decoder/libs/viterbi_decoder.cc
View File

@ -33,15 +33,16 @@ Viterbi_Decoder::Viterbi_Decoder(int32_t KK, int32_t nn, int32_t LL, const std::
d_prev_bit = std::vector<int32_t>(d_states * (d_LL + d_mm));
d_prev_state = std::vector<int32_t>(d_states * (d_LL + d_mm));
d_g = g;
d_out0 = std::vector<int32_t>(d_states);
d_out1 = std::vector<int32_t>(d_states);
d_state0 = std::vector<int32_t>(d_states);
d_state1 = std::vector<int32_t>(d_states);
nsc_transit(d_out0, d_state0, 0);
nsc_transit(d_out1, d_state1, 1);
}
void Viterbi_Decoder::decode(std::vector<int32_t>& output_u_int,
const std::vector<int32_t>& out0,
const std::vector<int32_t>& state0,
const std::vector<int32_t>& out1,
const std::vector<int32_t>& state1,
const std::vector<float>& input_c)
void Viterbi_Decoder::decode(std::vector<int32_t>& output_u_int, const std::vector<float>& input_c)
{
int32_t i;
int32_t t;
@ -67,25 +68,25 @@ void Viterbi_Decoder::decode(std::vector<int32_t>& output_u_int,
for (state = 0; state < d_states; state++)
{
// hypothesis: info bit is a zero
metric = d_prev_section[state] + d_metric_c[out0[state]];
metric = d_prev_section[state] + d_metric_c[d_out0[state]];
// store new metric if more than metric in storage
if (metric > d_next_section[state0[state]])
if (metric > d_next_section[d_state0[state]])
{
d_next_section[state0[state]] = metric;
d_prev_state[t * d_states + state0[state]] = state;
d_prev_bit[t * d_states + state0[state]] = 0;
d_next_section[d_state0[state]] = metric;
d_prev_state[t * d_states + d_state0[state]] = state;
d_prev_bit[t * d_states + d_state0[state]] = 0;
}
// hypothesis: info bit is a one
metric = d_prev_section[state] + d_metric_c[out1[state]];
metric = d_prev_section[state] + d_metric_c[d_out1[state]];
// store new metric if more than metric in storage
if (metric > d_next_section[state1[state]])
if (metric > d_next_section[d_state1[state]])
{
d_next_section[state1[state]] = metric;
d_prev_state[t * d_states + state1[state]] = state;
d_prev_bit[t * d_states + state1[state]] = 1;
d_next_section[d_state1[state]] = metric;
d_prev_state[t * d_states + d_state1[state]] = state;
d_prev_bit[t * d_states + d_state1[state]] = 1;
}
}
@ -117,6 +118,17 @@ void Viterbi_Decoder::decode(std::vector<int32_t>& output_u_int,
}
void Viterbi_Decoder::reset()
{
d_out0 = std::vector<int32_t>(d_states);
d_out1 = std::vector<int32_t>(d_states);
d_state0 = std::vector<int32_t>(d_states);
d_state1 = std::vector<int32_t>(d_states);
nsc_transit(d_out0, d_state0, 0);
nsc_transit(d_out1, d_state1, 1);
}
void Viterbi_Decoder::nsc_transit(std::vector<int32_t>& output_p,
std::vector<int32_t>& trans_p,
int32_t input) const

36
src/algorithms/telemetry_decoder/libs/viterbi_decoder.h
View File

@ -28,12 +28,15 @@
* \{ */
/*!
* \brief Class that implements a Viterbi decoder
*/
class Viterbi_Decoder
{
public:
/*!
* \brief Constructor of a Viterbi decoder
* \param[in] KK Constraint Length
* \param[in] KK Constraint length
* \param[in] nn Coding rate 1/n
* \param[in] LL Data length
* \param[in] g Polynomial G1 and G2
@ -43,28 +46,24 @@ public:
/*!
* \brief Uses the Viterbi algorithm to perform hard-decision decoding of a convolutional code.
* \param[out] output_u_int Hard decisions on the data bits
* \param[in] out0 The output bits for each state if input is a 0.
* \param[in] state0 The next state if input is a 0.
* \param[in] out1 The output bits for each state if input is a 1.
* \param[in] state1 The next state if input is a 1.
* \param[in] input_c The received signal in LLR-form. For BPSK, must be in form r = 2*a*y/(sigma^2).
*
*/
void decode(std::vector<int32_t>& output_u_int,
const std::vector<int32_t>& out0,
const std::vector<int32_t>& state0,
const std::vector<int32_t>& out1,
const std::vector<int32_t>& state1,
const std::vector<float>& input_c);
void decode(std::vector<int32_t>& output_u_int, const std::vector<float>& input_c);
/*!
* \brief Function that creates the transit and output vectors
* \brief Reset internal status
*/
void reset();
private:
/*
* Function that creates the transit and output vectors
*/
void nsc_transit(std::vector<int32_t>& output_p,
std::vector<int32_t>& trans_p,
int32_t input) const;
private:
/*
* Computes the branch metric used for decoding.
* \return (returned float) The metric between the hypothetical symbol and the received vector
@ -81,7 +80,7 @@ private:
* \param[in] symbol The integer-valued symbol
* \param[in] length The highest bit position in the symbol
*
* This function is used by nsc_enc_bit(), rsc_enc_bit(), and rsc_tail()
* This function is used by nsc_enc_bit()
*/
int32_t parity_counter(int32_t symbol, int32_t length) const;
@ -89,10 +88,10 @@ private:
* Convolutionally encodes a single bit using a rate 1/n encoder.
* Takes in one input bit at a time, and produces a n-bit output.
*
* \return (returned int): Computed output
*
* \param[in] input The input data bit (i.e. a 0 or 1).
* \param[in] state_in The starting state of the encoder (an int from 0 to 2^m-1).
* \param[in] g An n-element vector containing the code generators in binary form.
* \param[out] output_p[] An n-element vector containing the encoded bits.
* \param[out] state_out_p[] An integer containing the final state of the encoder
* (i.e. the state after encoding this bit)
*
@ -111,6 +110,11 @@ private:
std::vector<int32_t> d_prev_state{};
std::array<int32_t, 2> d_g{};
std::vector<int32_t> d_out0;
std::vector<int32_t> d_out1;
std::vector<int32_t> d_state0;
std::vector<int32_t> d_state1;
float d_MAXLOG = 1e7; // Define infinity
int32_t d_KK{};
int32_t d_nn{};

32
src/tests/unit-tests/signal-processing-blocks/telemetry_decoder/galileo_fnav_inav_decoder_test.cc
View File

@ -18,6 +18,7 @@
#include "galileo_fnav_message.h"
#include "galileo_inav_message.h"
#include "gnss_sdr_make_unique.h" // for std::make_unique in C++11
#include "viterbi_decoder.h"
#include <gtest/gtest.h>
#include <algorithm> // for copy
@ -34,11 +35,8 @@ class Galileo_FNAV_INAV_test : public ::testing::Test
public:
Galileo_FNAV_INAV_test()
{
// vars for Viterbi decoder
viterbi_inav->nsc_transit(i_out0, i_state0, 0);
viterbi_inav->nsc_transit(i_out1, i_state1, 1);
viterbi_fnav->nsc_transit(f_out0, f_state0, 0);
viterbi_fnav->nsc_transit(f_out1, f_state1, 1);
viterbi_fnav = std::make_unique<Viterbi_Decoder>(KK, nn, ((488 / nn) - mm), g_encoder);
viterbi_inav = std::make_unique<Viterbi_Decoder>(KK, nn, ((240 / nn) - mm), g_encoder);
flag_even_word_arrived = 0;
}
@ -48,23 +46,11 @@ public:
Galileo_Fnav_Message FNAV_decoder;
const int32_t nn = 2; // Coding rate 1/n
const int32_t KK = 7; // Constraint Length
int32_t mm = KK - 1;
int32_t flag_even_word_arrived;
const int32_t mm = KK - 1;
const std::array<int32_t, 2> g_encoder{{121, 91}};
std::shared_ptr<Viterbi_Decoder> viterbi_fnav = std::make_shared<Viterbi_Decoder>(KK, nn, ((488 / nn) - mm), g_encoder);
std::shared_ptr<Viterbi_Decoder> viterbi_inav = std::make_shared<Viterbi_Decoder>(KK, nn, ((240 / nn) - mm), g_encoder);
int32_t max_states = 1 << mm; // 2^mm
std::vector<int32_t> i_out0 = std::vector<int32_t>(max_states);
std::vector<int32_t> i_out1 = std::vector<int32_t>(max_states);
std::vector<int32_t> i_state0 = std::vector<int32_t>(max_states);
std::vector<int32_t> i_state1 = std::vector<int32_t>(max_states);
std::vector<int32_t> f_out0 = std::vector<int32_t>(max_states);
std::vector<int32_t> f_out1 = std::vector<int32_t>(max_states);
std::vector<int32_t> f_state0 = std::vector<int32_t>(max_states);
std::vector<int32_t> f_state1 = std::vector<int32_t>(max_states);
std::unique_ptr<Viterbi_Decoder> viterbi_fnav;
std::unique_ptr<Viterbi_Decoder> viterbi_inav;
int32_t flag_even_word_arrived;
void deinterleaver(int32_t rows, int32_t cols, const float *in, float *out)
{
@ -96,7 +82,7 @@ public:
}
std::vector<int32_t> page_part_bits = std::vector<int32_t>(frame_length / 2);
viterbi_inav->decode(page_part_bits, i_out0, i_state0, i_out1, i_state1, page_part_symbols_deint);
viterbi_inav->decode(page_part_bits, page_part_symbols_deint);
// 3. Call the Galileo page decoder
std::string page_String;
@ -151,7 +137,7 @@ public:
}
std::vector<int32_t> page_bits = std::vector<int32_t>(frame_length);
viterbi_fnav->decode(page_bits, f_out0, f_state0, f_out1, f_state1, page_symbols_deint);
viterbi_fnav->decode(page_bits, page_symbols_deint);
// 3. Call the Galileo page decoder
std::string page_String;