Hello Experts.
What is a UE downlink receive beam?
How it is different from gnb transmit beam?
I am little confused with this concept of transmit and receive beam pair.
1 Like
UE receive beam will define the beam selected by UE side based on L1 measurement (the UE measure the active RX beam and select the best one) and there is no need for UE to communicate RX beam to gNB.
gNB beam will be the beam activated by gNB on the result periodic L1 RSRP measurement report from UE to gNB.
2 Likes
So UE receive beam is same as gNB transmit beam?
1 Like
Ideal case yes, but not mandatory as beam switching procedure is different for both cases, so usually UE beam switching procedure is faster as it does not involve L1 measurement report.
2 Likes
In a basic sense can I call UE receive beam as tuning UE antenna parameters to receive the gNB transmit beam?
Because I am confused with the beam terminology for reception… Beam is always used for transmission, right?
1 Like
Not antenna parameter but may be reporting parameter.
And yes, always for DL or UL transmission, but you can see it on a differentiation terminology on how both side of the transmission are aligned within the same beam or no.
Let’s say, somehow on the Downlink side that the gNBb will not be aware about selected beam by UE side unless UE report it, so that is what cause a difference between UE and gNB on both side.
2 Likes
If gNB is not aware about the RX beam of UE then how gNB is supposed to schedule downlink transmission?
Isn’t it same?
I am also confuse how these two beams can be different?
1 Like
Actually it is not about scheduling when we say UE is camping in one beam it is only to measure it PDSCH will still follow the activated TCI id which is activated by gNB post measurement.
So as long as UE is still under the coverage of the activated TCI id it can still decode data scheduled for it as long as it remains under that beam coverage.
1 Like
Yes that’s understood as further gNB can further change TCI state with help of MAC CE as per feedback shared by UE in Uplink.
Isn’t this transmitted beam from gNB will be same which UE is going to receive in this case also?
1 Like
Yes and UE need to send harq ack post the mac CE and acknowledge the TCI state then it can received PDSCH from that same beam.
So from UE side does not matter which beam UE is measuring or in the gNB maintain the active beam based on the previous MAC CE ack received by UE, and will reconfigure the CRI based on that as well.
2 Likes
Ok, thanks! 
1 Like