Hi Palani,
I will like you to know that a combiner combines the various Transmit signals to one output(Antenna) to reduce cost of many antennas for each Transmit signal.As is the case with Ericsson Combiners known as CDUs,this conbiners also distribute the receive signals from the mobiles to the various Tranceivers in the BTS.
Combiners are of different kinds,ones that can support only one two carriers and ones that can suppot 4 or more carrier.
This is just to let you know that each carrier will still maintain its output power though combinedBut at the output of the Antenna,The EIRP will be the sum of the 4 carriers which means 7 x 4 user can now call from that sector or cell site.