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gr-gmr1/rach_demod: Improve initial frequency estimation 

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
This commit is contained in:
Sylvain Munaut 2015-03-29 20:59:06 +02:00
parent 8712e570ce
commit 1fefd8f2be
1 changed files with 47 additions and 8 deletions
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55
gr-gmr1/lib/rach_demod_impl.cc
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@ -85,7 +85,7 @@ rach_demod_impl::etoa() const
float
rach_demod_impl::estimate(struct osmo_cxvec *burst, int etoa, float *cw_freq)
{
const int guard = 2 * this->d_sps;
const int guard = 8 * this->d_sps;
struct osmo_cxvec _cw1, *cw1 = &_cw1;
struct osmo_cxvec _cw2, *cw2 = &_cw2;
float complex c1, c2;
@ -103,16 +103,55 @@ rach_demod_impl::estimate(struct osmo_cxvec *burst, int etoa, float *cw_freq)
this->d_sps * 32
);
/* Compute the average rotation speed per sample of cw1 & cw2 */
r = 0.0f;
for (i=guard; i<(cw1->len-1-guard); i++)
/* Coarse (average phase change during the CW1 & CW2) */
{
r += cargf(cw1->data[i+1] * conjf(cw1->data[i]));
r += cargf(cw2->data[i+1] * conjf(cw2->data[i]));
float complex a[2] = { 0.0f, 0.0f };
float complex b[2];
r = 0.0f;
for (i=guard; i<guard+5; i++)
{
float complex e = cexpf(I * i * -M_PIf / (4*this->d_sps));
a[0] += cw1->data[i] * e;
a[1] += cw2->data[i] * e;
}
for (i=guard; i<cw1->len-guard-5; i++)
{
float complex e = cexpf(I * i * -M_PIf / (4*this->d_sps));
float complex f = cexpf(I * (i+5) * -M_PIf / (4*this->d_sps));
b[0] = a[0] + cw1->data[i+5] * f - cw1->data[i] * e;
b[1] = a[1] + cw2->data[i+5] * f - cw2->data[i] * e;
r += cargf(b[0] * conjf(a[0]));
r += cargf(b[1] * conjf(a[1]));
a[0] = b[0];
a[1] = b[1];
}
r /= 2.0f * (cw1->len-2*guard-5);
r += M_PIf / (4*this->d_sps);
}
r /= 2.0f * (cw1->len-1-2*guard);
/* Fine (looking at phase different between CW1 and CW2) */
{
float complex a[2] = { 0.0f, 0.0f };
float complex eo = cexpf(I * 64.0f * this->d_sps * -r);
for (i=guard; i<(cw1->len-guard); i++)
{
float complex e = cexpf(I * i * -r);
a[0] += cw1->data[i] * e;
a[1] += cw2->data[i] * e * eo;
}
r += cargf(a[1] * conjf(a[0])) / (64.0f * this->d_sps);
}
/* Compute the correlation value using that speed to revert rotation */
c1 = c2 = 0.0f;