What is the role of BTS in mobile communication? Is there an alternative to BTS in mobile communication?

Base Transceiver Station (BTS) is the equipment which facilitates the wireless communication between Mobile Stations (handsets) and the network. The network can be that of any of the wireless communication technologies like GSM, CDMA, WLL etc...

Alternative can be Private Mobile Networks (PMN) ,PMN can be implemented either by replacement of the PBX or by integration with the existing PBX infrastructure.