When does the UE share its an NR UE info?

5G NR
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1

Hello everyone. My understanding of initial access call flow is the following.

  1. gNb sends the SSBs
  2. UE detects ssb and MIB from PBCH
  3. UE can decode SIB
  4. UE can then perform initial access.

Does the ue at any point need to tell the base station that it is an NR UE 100 MHz capable?
My understanding is that after RRC connected mode UE exchanges its capabilitites?
But I’m confused whether gNB knows before then what type of UE ands it bandwidth capability it’s dealing with and if it does, then how?

2

There is no way that gNB can know the bandwidth capability of UE before UE cap exchange. After UE cap exchange, once the gNB comes to know that UE is BW limited, it can configure the bwp for that UE accordingly.

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3

Thank you @pradeep.
One question: when does gNB know this is 4G LTE vs 5G NR UE?

4

Again, through UE cap exchange.
gNB will include both NR and LTE band filters in the UE cap enquiry.
If UE supports LTE, UE will report LTE cap too along with NR cap.

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5

@new_moon UE first share this info. during attach request by using IE dcnr (dual connectivity with NR supported), Thanks.

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6

DCNR request is sent in LTE attach request. But to answer how gNB can know if UE suppports LTE or not - it has to be through UE cap exchange (I am not sure if there is a similar IE to let AMF know about the NE-DC capability in registration request). Please correct me if I am wrong.

7

Hi @pradeep ,
Every 5G UE should be supporting LTE by default? May I have more clear thoughts over your post?

Thanks.

8

Commercially, yes. 5G UEs support 4G too. But @new_moon asked how gNB can know UE’s capability of LTE support - with this question, I am assuming that he asked this in SA mode. In SA mode, there is no DCNR flag to let gNB know about the LTE capability. DCNR is to let MME know that UE supports DC mode with NR so that if policy charging allows, the UE can be activated with ENDC. That is my understanding.