cell selection part-2

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In this section, we will learn about cell selection criteria for SA and LTE.

How is cell selection criteria defined?

The cell selection criterion which is abbreviated as S in normal coverage is fulfilled when: Srxlev > 0 AND Squal > 0

Where: Srxlev = Qrxlevmeas – (Qrxlevmin + Qrxlevminoffset) – Pcompensation - Qoffsettemp

Squal = Qqualmeas – (Qqualmin + Qqualminoffset) - Qoffsettemp

Where:

Srxlev	Cell selection RX level value (dB)
Squal	Cell selection quality value (dB)
Qoffsettemp	Offset temporarily applied to a cell (dB)
Qrxlevmeas	Measured cell RX level value (RSRP)
Qqualmeas	Measured cell quality value (RSRQ)
Qrxlevmin	Minimum required RX level in the cell (dBm). If the UE supports SUL frequency for this cell, Qrxlevmin is obtained from q-Qrxlevmin-sul, if present, in SIB1, else Qrxlevmin is obtained from q-Qrxlevmin in SIB1.
Qqualmin	Minimum required quality level in the cell (dB)
Qrxlevminoffset	Offset to the signaled Qrxlevmin taken into account in the Srxlev evaluation as a result of a periodic search for a higher priority PLMN while camped normally in a VPLMN.
Qqualminoffset	Offset to the signaled Qqualmin taken into account in the Squal evaluation as a result of a periodic search for a higher priority PLMN while camped normally in a VPLMN.
Pcompensation	If the UE supports the additionalPmax in the NS-PmaxList, if present, in SIB1: max(PEMAX1 –PPowerClass, 0) – (min(PEMAX2, PPowerClass) – min(PEMAX1, PPowerClass)) (dB); else: max(PEMAX1 –PPowerClass, 0) (dB)

Reference: 38.304

The signaled values Qrxlevminoffset and Qqualminoffset are applied only when a cell is evaluated for cell selection as a result of a periodic search for a higher priority PLMN while camped normally in a VPLMN [23.122]. During this periodic search for higher priority PLMN, the device may check the S criteria of a cell using parameter values stored from a different cell of this higher priority PLMN.

Please Play Video on Cell Selection:

QUS: where you can find Qrxlevmin, Qrxlevminoffset, Pcompensation, Qoffsettemp information in the case of SA?

In SIB1

QUS: where you can find Qrxlevmin, Qrxlevminoffset, Pcompensation, Qoffsettemp information in the case of NSA?

In the case of ENDC, UE initially connect with MCG (LTE cell) so from SIB1 UE will find this information but for SCG addition Qrxlevmin, Qrxlevminoffset, Pcompensation, Qoffsettemp information is not required.

QUS:  where you can find Qrxlevmin, Qrxlevminoffset, Pcompensation, Qoffsettemp information in the case of LTE?In SIB1

QUS: How is RRC_IDLE state is further divided?

The RRC_IDLE state tasks can be subdivided into following three processes:

PLMN-selection, cell-reselection-procedures, and location-registration

QUS: How is RRC_INACTIVE state is further divided?

The RRC_INACTIVE state tasks can be subdivided into following   three processes:

PLMN selection, cell reselection procedures, and location registration and RNA Update.

QUS: IS RNA update applicable for RRC_IDLE mode?

No, RNA update is only applicable for RRC_INACTIVE state.

QUS: How PLMN is selected?

When a device is switched on, a PLMN is selected by NAS. For the selected PLMN, associated RAT(s) may be set base on priority in SIM card. The NAS shall provide a list of equivalent PLMNs, if available (If UE previously camp on any PLMN it is called as a  EPLMN), that the Access Stratum shall use for cell selection and cell reselection.

QUS: What does camping on the cell means?

With cell selection, the device searches for a suitable cell of the selected PLMN, chooses that cell to provide available services, and monitors its control channel. This procedure is defined as "camping on the cell".

QUS: When does RNA update procedure is performed?

In RRC_INACTIVE state, if the new cell do not belong to the configured RNA, then an RNA update procedure is performed.

QUS: When is location registration performed?

If the device finds a more suitable cell, according to the cell reselection criteria, it reselects onto that cell and camps on it. If the new cell does not belong to at least one tracking area to which the device is registered, location registration is performed.

In the next section, we will learn more about Cell selection and its basic. So keep reading……. And Stay tune……………

Pinal Dobariya………..

Reference:

36.304

36.331

38.304

38.331