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Tweak correlator weighings to be right, and scale up some more to avoid losing precision.

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Further tweaking to which phase offsets we look for.
This commit is contained in:
Oliver Jowett 2014-09-27 13:35:41 +01:00
parent 69a30535d4
commit 309f79c488
1 changed files with 15 additions and 8 deletions
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23
mode_s.c
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@ -1953,19 +1953,19 @@ void detectModeS(uint16_t *m, uint32_t mlen) {
// (adding any constant value to all of m[0..3] does not change the result)
static inline int correlate_phase0(uint16_t *m) {
return (5 * m[0] - 3 * m[1] - 2 * m[2]) * 10 / 19;
return (5 * m[0] - 3 * m[1] - 2 * m[2]) * 30 / 19;
}
static inline int correlate_phase1(uint16_t *m) {
return (4 * m[0] - 1 * m[1] - 3 * m[2]) * 10 / 13;
return (4 * m[0] - 1 * m[1] - 3 * m[2]) * 30 / 13;
}
static inline int correlate_phase2(uint16_t *m) {
return (3 * m[0] + 1 * m[1] - 4 * m[2]) * 10 / 13;
return (3 * m[0] + 1 * m[1] - 4 * m[2]) * 30 / 13;
}
static inline int correlate_phase3(uint16_t *m) {
return (2 * m[0] + 3 * m[1] - 5 * m[2]) * 10 / 14;
return (2 * m[0] + 3 * m[1] - 5 * m[2]) * 30 / 19;
}
static inline int correlate_phase4(uint16_t *m) {
return (1 * m[0] + 5 * m[1] - 5 * m[2] - 1 * m[3]) * 10 / 28;
return (1 * m[0] + 5 * m[1] - 5 * m[2] - 1 * m[3]) * 30 / 26;
}
//
@ -2024,13 +2024,18 @@ static int best_phase(uint16_t *m) {
int best = -1;
int bestval = 50; // minimum correlation quality we will accept
// empirical testing suggests that 3..8 is the best range to test for here
// empirical testing suggests that 4..8 is the best range to test for here
// (testing a wider range runs the danger of picking the wrong phase for
// a message that would otherwise be successfully decoded - the correlation
// functions can match well with a one symbol / half bit offset)
test = correlate_check_3(&m[0]);
if (test > bestval) { bestval = test; best = 3; }
// this is consistent with the peak detection which should produce
// the first data symbol with phase offset 4..8
//test = correlate_check_2(&m[0]);
//if (test > bestval) { bestval = test; best = 2; }
//test = correlate_check_3(&m[0]);
//if (test > bestval) { bestval = test; best = 3; }
test = correlate_check_4(&m[0]);
if (test > bestval) { bestval = test; best = 4; }
test = correlate_check_0(&m[1]);
@ -2041,6 +2046,8 @@ static int best_phase(uint16_t *m) {
if (test > bestval) { bestval = test; best = 7; }
test = correlate_check_3(&m[1]);
if (test > bestval) { bestval = test; best = 8; }
//test = correlate_check_4(&m[1]);
//if (test > bestval) { bestval = test; best = 9; }
return best;
}