LTE UE Initial Access

For LTE once UE powered on below steps mentioned on Sharetech Note:

i) Power-Up Test
ii) Frequency & Time and Frame Synchronization
iii) Decode System Information Message
iv) Select Prefered Network
v) Perform RACH Process
vi) RRC Connection Setup

In my view after step2 PLMN scan step to be included ie before decoding SI as well what views of group experts or it after step 3.

Any view on above query highly appreciated.

This should help:

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PLMN info is included in SIB 1.
So PLMN selection always happened after SIB1.

I have same view but I read UE will go for PLMN scan before reading SIB i.e. intial PLMN scan and then cell selection happen on that PLMN.
Need more clarity.

PLMN scan request from higher layer only triggers cell search.
Then all these MIB, SIB, etc.

Below is correct flow as per 36.304

i) Power-Up Device

  • Try to search cell belong to “Last registered PLMN”
  • Other wise search “all available PLMN”

ii) Frequency & Time and Frame Synchronization

iii) Decode System Information Message

iv) Decode the PLMN broadcasted by cell to NAS layer, if this is desired PLMN the start registration process
Otherwise try searching new cells/PLMN

v) Perform RACH Process

vi) RRC Connection Setup

New additions/queries are welcome.

During i) PLMN search follows sequence from 23.122, i.e. RPLMN-EHPLMN>UPLMN>OPLMN>Others

Yes right. To avoid complexity I avoided that.

Are you sure that in step iv, UE will send PLMN to NAS layer and if rejected by NAS Layer then it will try searching new cells?
it will search all cells and create a list of PLMN from all broadcasted cells and then send that list to NAS layer and NAS layer pick one of desired PLMN and starts registration process.

No, I am not sure. May be you are right.

After powered up, system scan & Deviated band scan occurs right where it performs rssi scan, is it correct?

Yes it is correct.

UE only checks the energy it received from its surroundings, that time ue was not sure of RSSI since RS decoding will be done only after pss&sss serving
Where ever UE find the energy level greater than the threshold defined inside UE (non 3gpp) it creates a list of all energies detected above that threshold and starts scanning one by one.

Good one. So PLMN scan happen after power on.
Sharetech Note (@Jaeku_Ryu) we can suggest to add same in flow…

So between step 1 and 2 we can add PLMN scan.

Again if there is stored stored PLMN only then its valid.
Otherwise it’s like above only.

Yes it always stored PLMN by UE first.

So, If we move from one place1 to another place2 inside country by flight then there is a possibility area1 had some bands which are not present on area2, then from beginning deviated band scan will be started, ue system scan won’t be fruitful here.

For new device for example, it wont be there.

Ya :+1:
In LTE can UE go for re-establishment on target cell if its PLMN different from source cell like between 2 operators?

Re-establishment on new PLMN?
There is no mechanism or logic for this. :confused: