deepak,
that is one of the most common question.. BTS site of what? CDMA? GSM? WCDMA? let’s try one of the most common, GSM.. or 2G.. a BTS is usually installed either 900 or 1800 or 1900 or some 800 i think in the US? its powered up by a rectifier or a battery backup system plus 220VAC and feeder cables connected to combiners of the BTS going to the antenna.. either directional or omni depending on the design by RF engineers depending also on thedemand in the area. like if a motorway, usually back to back panel antenna.. in country sites omni will do.. in in-building solutions or IBS they are using DAS or distributed antenna system.. the traffic is transported via E1 (PCM) from PDH transmission system.. sometimes groomed from ericsson’s DXX.. i dunno about other vendor… then from PDH to SDH hub.. then to the BSC.. others please add