power => the device transmits more power. As a result, this signal is stronger and will interfer with the signals which are sent by other devices.
in UL : transmitter = MS, receiver = BTS
in DL : transmitter = BTS, receiver = MS
UL power is power used by the MS to send a signal to the BTS.
DL power is the power used by the BTS to send a signal to the MS.
I one MS sends a strong signal, then it might interfer with other mobiles located in other cells which are using the same frequencies.