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FT8: add encoding support to library and added more tests

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This commit is contained in:
f4exb
2024-03-28 15:15:48 +01:00
parent c833432675
commit 2e9fc9db64
21 changed files with 1330 additions and 493 deletions
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ft8/ft8.cpp
+37 -7
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@@ -44,6 +44,7 @@
#include "ft8.h"
#include "libldpc.h"
#include "osd.h"
#include "arrays.h"
namespace FT8 {
@@ -2478,13 +2479,11 @@ void FT8::soft_decode_triples(
// given log likelyhood for each bit, try LDPC and OSD decoders.
// on success, puts corrected 174 bits into a174[].
//
int FT8::decode(const float ll174[], int a174[], int use_osd, std::string &comment)
int FT8::decode(const float ll174[], int a174[], FT8Params& _params, int use_osd, std::string &comment)
{
void ldpc_decode(float llcodeword[], int iters, int plain[], int *ok);
void ldpc_decode_log(float codeword[], int iters, int plain[], int *ok);
int plain[174]; // will be 0/1 bits.
int ldpc_ok = 0; // 83 will mean success.
ldpc_decode((float *)ll174, params.ldpc_iters, plain, &ldpc_ok);
LDPC::ldpc_decode((float *)ll174, _params.ldpc_iters, plain, &ldpc_ok);
int ok_thresh = 83; // 83 is perfect
if (ldpc_ok >= ok_thresh)
@@ -2500,11 +2499,11 @@ int FT8::decode(const float ll174[], int a174[], int use_osd, std::string &comme
}
}
if (use_osd && params.osd_depth >= 0 && ldpc_ok >= params.osd_ldpc_thresh)
if (use_osd && _params.osd_depth >= 0 && ldpc_ok >= _params.osd_ldpc_thresh)
{
int oplain[91];
int got_depth = -1;
int osd_ok = OSD::osd_decode((float *)ll174, params.osd_depth, oplain, &got_depth);
int osd_ok = OSD::osd_decode((float *)ll174, _params.osd_depth, oplain, &got_depth);
if (osd_ok)
{
@@ -2518,6 +2517,37 @@ int FT8::decode(const float ll174[], int a174[], int use_osd, std::string &comme
return 0;
}
//
// encode a 77 bit message into a 174 bit payload
// adds the 14 bit CRC to obtain 91 bits
// apply (174, 91) generator mastrix to obtain the 83 parity bits
// append the 83 bits to the 91 bits message + crc to obbain the 174 bit payload
//
void FT8::encode(int a174[], int s77[])
{
int a91[91]; // msg + CRC
std::fill(a91, a91 + 91, 0);
std::copy(s77, s77+77, a91); // copy msg
LDPC::ft8_crc(a91, 82, &a91[77]); // append CRC - to match OSD::check_crc
std::copy(a91, a91+91, a174); // copy msg + CRC
int sum, n, ni, b;
for (int i=0; i<83; i++)
{
sum = 0;
for (int j=0; j<91; j++)
{
n = j/8; // byte index in the generator matrix
ni = j%8; // bit index in the generator matrix byte LSB first
b = (Arrays::Gm[i][n] >> (7-ni)) & 1; // bit in the generator matrix
sum += a91[j] * b;
}
a174[91+i] = sum % 2; // sum modulo 2
}
}
//
// bandpass filter some FFT bins.
// smooth transition from stop-band to pass-band,
@@ -3418,7 +3448,7 @@ int FT8::try_decode(
int a174[174];
std::string comment(comment1);
if (decode(ll174, a174, use_osd, comment))
if (decode(ll174, a174, params, use_osd, comment))
{
// a174 is corrected 91 bits of plain message plus 83 bits of LDPC parity.
// how many of the corrected 174 bits match the received signal in ll174?