54 lines
1.8 KiB
C
54 lines
1.8 KiB
C
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#include <stdint.h>
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// Define FT8 symbol counts
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constexpr int FT8_ND = 58; // Data symbols
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constexpr int FT8_NS = 21; // Sync symbols (3 @ Costas 7x7)
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constexpr int FT8_NN = FT8_NS + FT8_ND; // Total channel symbols (79)
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// Define the LDPC sizes
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constexpr int FT8_N = 174; // Number of bits in the encoded message
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constexpr int FT8_K = 91; // Number of payload bits
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constexpr int FT8_M = FT8_N - FT8_K; // Number of checksum bits
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constexpr int FT8_K_BYTES = (FT8_K + 7) / 8; // Number of whole bytes needed to store K bits
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// Define CRC parameters
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constexpr uint16_t CRC_POLYNOMIAL = 0x2757; // CRC-14 polynomial without the leading (MSB) 1
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constexpr int CRC_WIDTH = 14;
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// Costas 7x7 tone pattern
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extern const uint8_t kCostas_map[7];
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// Gray code map
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extern const uint8_t kGray_map[8];
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// Parity generator matrix for (174,91) LDPC code, stored in bitpacked format (MSB first)
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extern const uint8_t kGenerator[FT8_M][FT8_K_BYTES];
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// Column order (permutation) in which the bits in codeword are stored
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// (Not really used in FT8 v2 - instead the Nm, Mn and generator matrices are already permuted)
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extern const uint8_t kColumn_order[FT8_N];
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// this is the LDPC(174,91) parity check matrix.
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// 83 rows.
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// each row describes one parity check.
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// each number is an index into the codeword (1-origin).
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// the codeword bits mentioned in each row must xor to zero.
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// From WSJT-X's ldpc_174_91_c_reordered_parity.f90.
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extern const uint8_t kNm[FT8_M][7];
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// Mn from WSJT-X's bpdecode174.f90.
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// each row corresponds to a codeword bit.
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// the numbers indicate which three parity
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// checks (rows in Nm) refer to the codeword bit.
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// 1-origin.
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extern const uint8_t kMn[FT8_N][3];
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// Number of rows (columns in C/C++) in the array Nm.
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extern const uint8_t kNrw[FT8_M];
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