In every post, someone is talking about something different. So I’ll write this “recap”, and please comment on this…
There is 2 types of antenna diversities :
the RX diversity and the TX diversity.
And there are two ways to implement them : with crosspolar antennas (2 branches per antenna) or vertical polar antennas (1 branch per antenna)
The Rx Diversity is a very standard feature of a BTS : two or four branches are used to collect the signal from the MS’s.
It improves the UL sensitivity by 2 to 6dB, depending on environment and MS speed.
In urban areas, crosspolars are recommended.
In rural / open areas, vertical polars are recommended.
Average gain in UL RX for 2-Rx Div = 3dB
Average gain in UL RX for 4-Rx Div = 5dB
The Tx diversity is quite recent, and is used by the BTS as well : two branches are used for emitting the DL signal :
the power is increased by 3dB (double power) and 2 to 3 additional dB’s are gained thanks to diversity. Therefore the DL TX is increased by 5 to 6 dB.