yes, the power commands are sent at the SACCH interval, every 480ms.
the variable or fix step size refer to the amount of power that cn be increased or reduced.
If UL RXLEV is very high, then the BSC will tell the MS to reduce its TX Power:
– if fixed step : power is reduced at a rate of “n” dB every 480ms. Usually, n = 2dB. so it takes 5 seconds to decrease power by 10 dB.
– if variable step : power is reduced by “k” * (rxlev_target – rxlev_measured)
k is usually between 0.6 and 1.
So it takes usually 1 or 2 SACCH to reach the desired power.