Prior to this commit, noise power estimation could be zero because of a
call to clearArray() in gNB_I0_measurements(). This is problematic, as
this can lead to a noise power of 0 if all symbols in a RB are used,
which in turn leads to a spike in SNR.
To avoid this, use an intermediate array to store noise power, and only
update n0_subband_power if not all RBs are used (i.e., we can detect
noise power). Further, use an exponential moving average to smoothen
noise estimation.
Fixes: fb4235fd50 ("changes in PUCCH0 SNR measurement, testing for
PUCCH power control")
Robert Schmidt
b533127553