Question about MU-MIMO in uplink: how are beams separated in uplink?
I mean for DL MU-MIMO is very clear as users are separated in different locations/beams but for Uplink is not easy to understand how receiving antenna of gNodeB is separated in different beams for different UEs paired for UL MU-MIMO.
For UL MU-MIMO node consider ul-sinr, orthogonality, number of layers, prb difference to bring UE in pairing.
Generally pairing ratio seen upto 2 UEs with 8 layers in Uplink.
But the signal from 3-4 different UEs reach the gNodeB antenna in same location.
How orthogonality can be maintained in this case?
There is no beamforming for Uplink in the UE as far as I know.
It’s internal calculation by eNodeB.
As of now I’m considering single layer in Uplink for LTE.
For NR we have 2x2 in Uplink.
I mean for DL is easy as there are weights for transmission and so signal in different locations can be sent with orthogonality.
But for Uplink how can be weights used by gNodeB for reception?
For example Huawei has up to PUSCH layers for MU-MIMO in Uplink. How can those be layers sent in uplink using same frequency, same time and same space without interfering each other?
I am not able to understand how it is possible.
8 PUSCH layers for MU-MIMO in Uplink.
For UL per UE single layer in case of MU-MIMO let me check does same concept of weight applied on AE used or not for uplink.
Even for UL, UE can use beams, right?
There is a concept called beam correspondence.
If that is supported by UE, UE will use the same DL beam direction for Tx in UL.
If I am not sure, but beam correspondence is only for only SSB and RACH?
If beam correspondence is supported by UE, UE will use Rx beam direction to transmit the Tx beam. While the first beam correspondence is established during RACH with SSB beam, UE can align the beam with CSIRS beams too. In any case, this beam pair link info is maintained in UE & is not known to network.
If beam correspondence is not supported, there are other procedures where UE will do Rx beam sweep to determine the best beam direction.
Network too can assist with UL SRS.
But UEs do not support beamforming now. There is no massive MIMO in UE.
UE cannot adjust their radiation pattern and even if they can will reach the gNodeB in same location.
The whole principle of massive mimo spatial multiplexing in DL is that UEs are in different locations, one in each DL beam.
This does not apply to Uplink at all since all UL beams will reach gNodeB in same location.
Yes, UL beams from multiple UEs reach the gNB at the same time.
But, the antenna elements tuning to each UE at gNB to receive the UL beams can be different, right?
Though there is no massive MIMO as compared to gNB in UE, UE can still form beams.
Otherwise, it is hard to do UL transmission in mmw freqs.
UEs can change the beam direction too.
Never heard of UE forming beams for UL transmission.
And still this does not clarify how UL mu-mimo works.
Beamforming is linked with DL, Uplink works on layer concept.
In DL is easy: signal of one UE is in a DL beam that is very little interfered by other DL beams due to orthogonality.
In Uplink all signals reach the UE in same location. So even if we have 3 UEs separated at 2 km one from another (just an example) in Uplink will reach the gNodeB in same location.
Yes but we still have MU-MIMO concept for UL.
Huawei has 8 pusch layers for MU-MIMO in Uplink.
Because of higher number of rx antennas and distance between AE helps eNB to de-corelate the signal received from different UEs.
FR1 midband. My understanding is MaMIMO antenna creates “Rx” beams just like it does in DL. Those are calculated from UE’s SRS. gNB knows in which resources there will be incoming signal from UE, so it has precoding weights ready. So UL MU-MIMO transmissions received at gNB are separated by precoding weights just like they are created(multiplexed) in DL.
It’s like TM1 mode in Uplink single TX.
So there is no beamforming in Uplink, right?
Somebody just mentioned that there are beams in Uplink.
How about mmWave UE?
I think in mmWave maximum is 2x2 MIMO for UL per UE that means a single beam with +45 and -45 polarisation.
Please read this:
It says 2 TX in Uplink.