Gsm BTS allowed power

How much power BTS are allowed to radiate in 900MHz band?
What type of antennas are used in bts and their gain?
BTS use three directional antennas ,does it means that they are drived from three different amplifies?
in other words if a bts is rated for 15 wats , then it is generating 45 watts of power to cover 360 area.

The transmitter can radiate power up to 100W. But their radiate power is 100W+antenna gain.
yes, each antenna have a transmitter.
If one bts rated 15W, to cover 360 area is not 45W, since each bts can adjust its power by itself.

When you see 3 antennas you actually see 3 sectors, or in other words 3 Cell IDs.
the antenna gains are usually 15-22dBi and the power is usually 40dBm at the antenna port.

Thanks for reply.

How much power is required for a bts, using single omnidirectional antenna, to cover same area or distance?

Normally, sector antenna gain is 18dBi, and omnidirectional antenna gain is 11dBi. So the power is 40dBm+(18-11)dB=47dBm.