If BSC makes decision for performing Power Control on uplink (MS PC) and it should send some message through Um interface to MS for starting power control.
What is the name of this message? Is it coming on the System Information messages, if yes on which
SI message is it?
There is no message to signal the start of PC.
It is all up to the BSC, the MS doesn’t have to know anything.
As soon as PC is enabled, the BSC will start sending power control orders to MS and BTS.
The power control orders is not really an order : it is just that instead of telling the MS to transmit at 33dBm (for ex.) it will say “30dB” or “28dB”, etc.
By default, with PC disabled, the BSC always transmit the value 33dBm.
To the BTS, for the DL PC, it says “0dB”, which means the BTS should attenuate its tx power by 0dB.
On the downlink SACCH, the BTS sends the MS a power order, which informs the MS as to which power to transmit on. When MS power control is activated in the cell, the power order can ‘instruct’ the MS to transmit on a lower or higher power.
In TEMs, you can’t see the SACCH message, but you can see the current ‘MS Power Control Level’ the GSM Radio Parameters window. The values given there are in multiples of 2, so eg, if the power control level is 3, the MS should transmit 6dB below the maximum power.