MCL : i forgot the details about this, I’m sorry.. so here is what I recall :
it is the minimum distance between MS and BTS antenna, converting in to “dB”.
3GPP assumed the minimum distance BTS-MS is 2 meters, in indoor scenario. That equals to 45dB (when using okumura, i believe)
Now the main idea is to avoid the MS to send a signal too STRONG into the BTS Rx antenna, because otherwise it might feedback to the Tx side.
This can easily be avoided by applying UL Power Control.