diff options
| author | Sylvain Munaut <tnt@246tNt.com> | 2012-10-17 23:25:45 +0200 |
|---|---|---|
| committer | Sylvain Munaut <tnt@246tNt.com> | 2013-07-06 13:14:56 +0200 |
| commit | 2b642535b63a1542fee9a9bc114c32432ea31dfb (patch) | |
| tree | 0924dd4ae08dbc9415b56961a4ff83113d95a3b6 | |
| parent | 028f0bd95d36e5b74915cf2fb6e774c26e63c321 (diff) | |
sdr/dkab: Add validation of DKAB to differentiate for nothingness
We compare the energy in the peaks with the energy in the valley,
that should be significantly higher.
Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
| -rw-r--r-- | src/sdr/dkab.c | 34 |
1 files changed, 30 insertions, 4 deletions
diff --git a/src/sdr/dkab.c b/src/sdr/dkab.c index 7e2696e..6ecf155 100644 --- a/src/sdr/dkab.c +++ b/src/sdr/dkab.c @@ -43,19 +43,25 @@ #include <osmocom/gmr1/sdr/dkab.h> +/*! \brief Ratio between peak power and valley power for DKAB detection */ +#define DKAB_PWR_RATIO_THRESHOLD 10.0f + + /*! \brief Finds the precise TOA of a DKAB burts by looking for power spikes * \param[in] burst Complex signal of the burst * \param[in] sps Oversampling used in the input complex signal * \param[in] p DKAB position * \param[out] toa_p Pointer to TOA return variable - * \returns 0 for success. -errno for errors + * \returns 0 for success, 1 if DKAB not found, -errno for fatal errors */ static int _gmr1_dkab_find_toa(struct osmo_cxvec *burst, int sps, int p, float *toa_p) { struct osmo_cxvec *pwr = NULL; - int w, i, ofs[2], d, mi; + int rv, w, i, ofs[2], d, mi; float mp, toa; + float egy_peak, egy_valley; + int l_peak, l_valley, toa_i; /* Window size */ w = burst->len - (GMR1_DKAB_SYMS * sps) + 1; @@ -111,10 +117,30 @@ _gmr1_dkab_find_toa(struct osmo_cxvec *burst, int sps, int p, float *toa_p) *toa_p = toa; + toa_i = (int)roundf(toa); + + /* Check the ratio between the peaks and valley to validate */ + egy_peak = 0.0f; + l_peak = d * 2; + for (i=0; i<d; i++) { + egy_peak += + osmo_normsqf(burst->data[toa_i+ofs[0]+i]) + + osmo_normsqf(burst->data[toa_i+ofs[1]+i]); + } + egy_peak /= l_peak; + + egy_valley = 0.0f; + l_valley = ofs[1] - ofs[0] - d; + for (i=0; i<l_valley; i++) + egy_valley += osmo_normsqf(burst->data[toa_i+ofs[0]+d+i]); + egy_valley /= l_valley; + + rv = ((egy_peak /egy_valley) > DKAB_PWR_RATIO_THRESHOLD) ? 0 : 1; + /* Done */ osmo_cxvec_free(pwr); - return 0; + return rv; } /*! \brief Converts a burst into softbits given proper TOA @@ -152,7 +178,7 @@ _gmr1_dkab_soft_bits(struct osmo_cxvec *burst, int sps, int p, float toa, * \param[in] p DKAB position * \param[out] ebits Encoded soft bits return array * \param[out] toa_p Pointer to TOA return variable - * \returns 0 for success. -errno for errors + * \returns 0 for success, 1 if DKAB not found, -errno for fatal errors * * burst_in is expected to be longer than necessary. Any extra length will be * used as 'search window' to find proper alignement. Good practice is to have |