Following your question of what is a Bts?,
A BTS is a Base Tranceiver Unit.It consists of the following:
-Combiners coupled with duplexers
Depending on the equipment manufacturers,we have different configurations ranging from 2TRxs to even 24TRxs in one BTS.It should be noted that the higher the TRXs the higher the capacity of the Cell.Combiners are used to combine the Transmit signals to a common Antenna for transmission and Distribute the receive signals to the various Tranceivers.
I am good with Ericsson and Alcatel BTS but the truth is that they all have the same features but different appeltions or terminology.
If you can mention your email then I can sent you useful information on BTS and their functionality.