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Implement GLONASS string error correction

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Signed-off-by: Vladislav P <vladisslav2011@gmail.com>
This commit is contained in:
Vladislav P 2022-08-26 16:27:01 +03:00
parent f09da3ded6
commit e4a3a060ee
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4 changed files with 36 additions and 6 deletions
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1
src/core/system_parameters/GLONASS_L1_L2_CA.h
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@ -238,6 +238,7 @@ const std::vector<int32_t> GLONASS_GNAV_CRC_M_INDEX{20, 21, 22, 23, 24, 25, 26,
const std::vector<int32_t> GLONASS_GNAV_CRC_N_INDEX{35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65};
const std::vector<int32_t> GLONASS_GNAV_CRC_P_INDEX{66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85};
const std::vector<int32_t> GLONASS_GNAV_CRC_Q_INDEX{9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85};
const std::vector<int32_t> GLONASS_GNAV_ECC_LOCATOR{0, 0, 1, 8, 2, 9, 10, 11, 3, 12, 13, 14, 15, 16, 17, 18, 4, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 5, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 6, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84};
// GLONASS GNAV NAVIGATION MESSAGE STRUCTURE
// NAVIGATION MESSAGE FIELDS POSITIONS

27
src/core/system_parameters/glonass_gnav_navigation_message.cc
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@ -36,7 +36,7 @@ Glonass_Gnav_Navigation_Message::Glonass_Gnav_Navigation_Message()
}
bool Glonass_Gnav_Navigation_Message::CRC_test(const std::bitset<GLONASS_GNAV_STRING_BITS>& bits) const
bool Glonass_Gnav_Navigation_Message::CRC_test(std::bitset<GLONASS_GNAV_STRING_BITS>& bits) const
{
uint32_t sum_bits = 0;
int32_t sum_hamming = 0;
@ -128,7 +128,28 @@ bool Glonass_Gnav_Navigation_Message::CRC_test(const std::bitset<GLONASS_GNAV_ST
return true;
}
// All other conditions are assumed errors. TODO: Add correction for case B
if (C_Sigma && (sum_bits & 1))
{
int32_t syndrome = C1;
syndrome |= (C2 ? 2 : 0);
syndrome |= (C3 ? 4 : 0);
syndrome |= (C4 ? 8 : 0);
syndrome |= (C5 ? 16 : 0);
syndrome |= (C6 ? 32 : 0);
syndrome |= (C7 ? 64 : 0);
if (syndrome < 85)
{
const int32_t locator = GLONASS_GNAV_ECC_LOCATOR[syndrome];
bits[locator] = !bits[locator];
return true;
}
else
{
return false;
}
}
// All other conditions are assumed errors.
return false;
}
@ -238,7 +259,7 @@ int32_t Glonass_Gnav_Navigation_Message::string_decoder(const std::string& frame
uint64_t P_1_tmp = 0;
// Unpack bytes to bits
const std::bitset<GLONASS_GNAV_STRING_BITS> string_bits(frame_string);
std::bitset<GLONASS_GNAV_STRING_BITS> string_bits(frame_string);
// Perform data verification and exit code if error in bit sequence
flag_CRC_test = CRC_test(string_bits);

2
src/core/system_parameters/glonass_gnav_navigation_message.h
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@ -55,7 +55,7 @@ public:
* \brief Compute CRC for GLONASS GNAV strings
* \param bits Bits of the string message where to compute CRC
*/
bool CRC_test(const std::bitset<GLONASS_GNAV_STRING_BITS>& bits) const;
bool CRC_test(std::bitset<GLONASS_GNAV_STRING_BITS>& bits) const;
/*!
* \brief Computes the frame number being decoded given the satellite slot number

12
src/tests/unit-tests/system-parameters/glonass_gnav_crc_test.cc
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@ -17,14 +17,14 @@
#include "glonass_gnav_navigation_message.h"
#include <bitset>
#include <string>
#include <iostream>
TEST(GlonassCrcTest, GnssSdrCRCTest)
{
// test data
std::string string1Real_14_18_00("0000100000111001001001000011101010101100010101001000001001011101010101110011110110101");
std::string string1Real_14_18_30("0000100000111001001011000011101010101100010101001000001001011101010101110011100001010");
std::string string1Wrong_14_18_00("0000100000111001001001000011101010101100010101001000001001011101010101110011100001010");
std::string string1Wrong_14_18_00("0000100000111001001001100011101010101100010101001000001001011101010101110011100001010");
auto gnav_msg = Glonass_Gnav_Navigation_Message();
std::bitset<GLONASS_GNAV_STRING_BITS> bits;
@ -34,4 +34,12 @@ TEST(GlonassCrcTest, GnssSdrCRCTest)
ASSERT_TRUE(gnav_msg.CRC_test(bits));
bits = std::bitset<GLONASS_GNAV_STRING_BITS>(string1Wrong_14_18_00);
ASSERT_FALSE(gnav_msg.CRC_test(bits));
bits = std::bitset<GLONASS_GNAV_STRING_BITS>(string1Real_14_18_30);
for (int k = 8; k < 85; k++)
{
std::bitset<GLONASS_GNAV_STRING_BITS> corrupt_bits = bits;
corrupt_bits[k] = corrupt_bits[k] ? false : true;
ASSERT_TRUE(gnav_msg.CRC_test(corrupt_bits));
ASSERT_TRUE(corrupt_bits == bits);
}
}