Hi All,
If we increase the number of UEs supported per TTI in 5G from 16 or 32 UEs/TTI (to let’s say 64 or 128 UEs/TTI), then how will it impact the L2 or upper layer processing?
What could be the bottleneck?
Basically If I change UEs/TTI from 8 to 64 given a fixed resource allocation.
Per slot in 5G.
It depends on PDCCH and UL Ack/Nack.
As per my knowledge till date there is no parameter to control no of users in 5G per slot.
It’s fixed 1 only.
Others can comment.
Yes there is no parameter.
What my question is If I schedule 8 UE/slot vs 64 UEs/slot or 128 UEs/slot, what becomes the bottleneck for L2 and upper layers.
Is it the storage, processing?
Can anyone with L2/L3 expertise comment?
In my view no of PRB can be bottleneck.
From processing side there is no as such bottleneck seen from hardware side used.
If we have proper ecpri link between Base Band and Radio module.
I think PDCCH capacity is can be bottleneck.
If UEs are in poor radio condition, then due to high AL requirement, we cannot schedule as many user in 1 TTI.
PRB is also possible, but in NR with very high BW less chances.
Yes as of now for NR high capacity site scenario not there, even we don’t have any single live site for NR 
If I have 8 UEs I schedule 32-35 PRBs per UE where if I have 64 UEs.
Then I schedule 4-5 PRBs per UE.
Given the full 100 MHz bandwidth, I can put 64 DCIs with agregation level 1-2, given that the channel is very good.
In LTE we seen limitation of PUCCH resources as well with high users.
Think it’s L2 processing.
Higher UEs per slot is impacted by HARQ feedback processing, etc.
So in my view higher UEs per slot is L2 processing capacity.
Can you please put little more details?
Not an L2 expert, but came across this request in one of my projects.
From development perspective, tracking all HARQ threads in gNB L2 is extensive processing task. Higher UEs need higher buffering, processing, scheduling, etc.
Hi ,
I have same concern on same question.
Can you please explain what do you mean on what you said?
Assume in UL I’m increasing UEs per TTI from 1 to 8, let’s say.
Hi.
This means, due to the aggregation level of the PDCCH components (Control-Channel-Element) the UEs number reduced in the TTI, typically when the user in bad radio condition, and due to the critical nature of the PDCCH (very very critical that the user gets it correct) the coding rate increases, which increases the resources consumed to transfer the PDCCH, that increases the level of aggregation (since each CCE contains a fixed amount of PRB [REG] - Take a look at the table below).
So, to recap, when the user in bad condition that site tends to increase the coding rate (since the modulation is fixed in this channel to QPSK) of the sent information to make it more immune to errors, this typically means the useful data in these PRBs is less, that requires the site to aggregate more CCE to send these data, which means in a fixed format framing nature of the mobile NW, the number of user is reduced (per TTI).
I hope that make sense to you.
You can get more theoretical / practical information from this website:
Thanks dear.
I understand that, but PDCCH the Aggregation level is constant and configured. It is static once configured.
So on that case assume that I configure Aggregation level for PDCCH as 4, now is it still a bottleneck when I increase UE per TTI?
No.
PDCCH Aggregation level is not constant for PDCCH.
It can go from AL1 till AL16 in 5G.
Only modulation is fixed at QPSK for PDCCH.
It s dynamic, and max agg level you can use is restricted per slot by 3gpp.
There are two limitations for UE side as 3GPP 38.213 indicates: PDCCH parameters can be adjusted / optimized based on field traffic as long as not exceeding above two tables.
As per my understanding,
actMaxNumUeDlNonGbr - Activate maximum number of non-GBR UEs per TTI for nokia
Max Value = 20 Steps
Min Value = 1 Step
maxNumUeDl - Maximum amount of users per TTI in DL for nokia
Max Value = 20 Steps
Min Value = 1 Step
