do drive tests, and check what is the actual rxlev measured indoor. if you see -110dBm, then you must install an indoor site (no amount of optimization can provide coverage in such a “hole”…)
if it’s about -95dBm, then you can do some optimization.
– install high power TRX (that will enhance only DL) + a TMA (to balance the UL signal too)
– install a signal booster at the bottom of the antenna (it enhances UL and DL signals)
– install a repeater with donor antenna located outdoor, and serving antenna located indoor (antenna or radiating cable).
with parameters, you could try to set rxlev access min = -110dBm, and slow down handovers and power control. Problem is, it will affect the whole coverage of the cell, not only the indoor subscribers.
you can also implement lower frequencies and frequency hopping (SFH ?) in order to provide better wall penetration.
the general rule is : you CANNOT increase coverage with parameters. Coverage is physical, parameters are logical. It’s just not working this way at all.