Merge remote-tracking branch 'origin/fix-ema-init' into integration_2026_w16 (!4051)

Fix EMA cold-start for noise and SNR/RSSI measurements

Initialize n0_subband_power and power control avg_snr/avg_rssi directly
from the first measurement instead of starting from zero.

Starting from zero causes the EMA to converge slowly, leading to
underestimated noise power at gNB startup. This results in inflated SNR
estimates, which triggers UE uplink power ramp-up, antenna saturation,
and a positive feedback loop of increasing noise.

openair1/PHY/NR_ESTIMATION/nr_measurements_gNB.c

@@ -162,6 +162,7 @@ void gNB_I0_measurements(PHY_VARS_gNB *gNB, int slot, int first_symb, int num_sy
   int32_t n0_subband_tot_perANT[frame_parms->nb_antennas_rx];
   memset(n0_subband_tot_perANT, 0, sizeof(n0_subband_tot_perANT));
 
+  bool init_meas = measurements->n0_subband_power == NULL;
   allocCast2D(n0_subband_power,
               unsigned int,
               measurements->n0_subband_power,
@@ -174,6 +175,9 @@ void gNB_I0_measurements(PHY_VARS_gNB *gNB, int slot, int first_symb, int num_sy
     if (nb_symb[rb] > 0) {
       for (int aarx = 0; aarx < frame_parms->nb_antennas_rx; aarx++) {
         tmp_n0_subband[aarx][rb] /= nb_symb[rb];
+        // Initialize n0_subband_power from the first measurement before EMA
+        if (init_meas)
+          n0_subband_power[aarx][rb] = tmp_n0_subband[aarx][rb];
         // apply exponential moving average to smooth noise measurements
         n0_subband_power[aarx][rb] = 0.9 * n0_subband_power[aarx][rb] + 0.1 * tmp_n0_subband[aarx][rb];
         n0_subband_tot_perPRB += n0_subband_power[aarx][rb];