If you are speaking of RXlevel requirement, the -70db should refer to the outdoor coverage requirement for dense urban areas where buildings are typically high rise and present an average penetration loss of about 30db. Therefore, the RXlevel inside the building will on the average be about -95db, ensuring acceptable signal quality. The same explanation goes for the -80db (urban area: where penetration loss is approx 20 db)
These RX levels, together with coverage probability assumptions are the basic parameters used in BTS network design, specifically in predicting the cell coverage sizes for various geographical conditions.
i hope the above explanation proves useful.
b.r.