PRX / DRX / RX2 / RX3 Physical Meaning

For the RM500Q series / RM502Q-AE each of the RSRP, RSRQ, SINR AT commands have PRX, DRX, RX2 and RX3 paths. Please could explain the meaning of PRX, DRX, RX2 and RX3?

RX2 and RX3 seem to not give valid responses.

I get answers like:
+QRSRP: -98,-96,-140,-140,LTE
+QRSRQ:-12,-13,0,0
+QSINR:16,15,0,0

hi,epwr:
Since RM500/RM502 supports multi-antenna (4T2R) MIMO
PRX: Primary RX
DRX: Diversity RX
RX2: MIMO-RX2
RX3: MIMO-RX3