LTE Network 

Cell Selection : constitutes the primary step in the establishment of an LTE network connection. It involves the User Equipment (UE) identifying and selecting the most suitable cell within the available PLMNs for communication. During Cell Selection, the UE evaluates various parameters such as signal strength, signal quality, and operational status of neighboring cells to make an informed decision regarding the optimal cell for connection.

Occasions for PLMN and Cell Selection:

As we mentioned before
1️⃣ -New SIM or Initial Mobile Activation: When a user inserts a new SIM card into their device or activates their mobile service for the first time, the UE performs both PLMN selection and cell selection to establish an initial network connection.
2️⃣ -Out-of-Coverage Scenario: If the UE moves into an area where its current PLMN is unavailable or out of coverage, it may need to perform PLMN selection again to identify an alternative network operator. Subsequently, it will perform cell selection within the newly selected PLMN to establish a connection.

Triggers for Cell Selection:
Cell selection occurs in various scenarios, including:

1️⃣ -When the UE is powered on or off (switched on or off).
2️⃣ -After the completion of a call (call end).
3️⃣ -After a call drop occurs due to signal degradation or other reasons.
4️⃣ -Out of Coverage: Firstly select PLMN and secondly, search for cells

Criteria for Cell Selection:

There are specific criteria for selecting the best cell, including :
-checking whether the cell is barred or Not barred CB= No, not part of forbidden TACs,
-satisfies cell selection criteria, Scriteria = (S rxlev > 0 & S qual > 0)

◼ Srxlev = Qrxlevmeas-[Qrxlevmin+Qrxlevminoffset] - Pcomp
Qrxlevmeas = RSRP measured by UE in dBm
Qrxlevmin = min. required RSRP signalled within SIB-1
Qrxlevminoffset = usually included in SIB-1. If not included than value of zero is set.
Pcompensation Defined as MAX(PEMAX - PUMAX, 0)
◼ Squal = Qqualmeas-[Qqualmin+Qqualminoffset]

Let's clarify something important:
🗒 : At the top is the cell selection, and PLMN selection is part of this procedure.