GCC = 10× log(NTx)
Where NTx is the number of transmit antennas.
Thus, a BS that has 2 transmit antennas and transmit diversity will have 3 dB of improvement in its EIRP versus a BS without transmit diversity.
Typically, only the BS uses multiple transmit antennas and will benefit from the transmit diversity. The subscriber device using a single transmit antenna would not have this benefit.