Data flow for configured MIMO 4T when UE does not support it

[esoestemp]

Hello,
I have the following question.
When 4T mode is configured, but UE does not support it or the radio conditions do not allow its usage, how are the data streams mapped to the logical ports?
Lets say UEs supports Rank2: is the node going to send to it 2 data flows at 2 logical ports(no TX diversity) and 2 ports DTX?
...or there will be 2 flows mapped to 4 antenna ports, where will still have TX diversity?

Thanks in advance!

[subway]

It depends on the configuration:

If a UE does not support more than 2R, then it will act as transmit diversity. Even if your config is CRS 2, you can still exploit 4-Way receive diversity to improve your uplink with the 4T4R antenna.

If there are UEs that supports 4R, and you turned on CRS 4 (and 4x4 MIMO in general), then you can exploit the extra speed if the UEs are in proper reflective environment. But be careful: if you have a very low number of 4x4 capable UEs and/or you dont have refelctive enough environment, you will just increase the overhead by turning on CRS 4 and 4x4 MIMO in the downlink. In rural areas, you will only get Rank4 for a very small number of UEs, it does not wort it.