What is Idle Mode?
UE in IDLE MODE has the following properties :
-UE is Powered ON , while it doesn't have connection to the Radio Network
-UE is synchronized with Radio Network and can read broadcast information , Accordingly UE can access the Network request services .
-UE is registered on the network , updating Network with its LAC , Accordingly UE becomes reachable by the network.
Normal Service
When the UE select accepted level cell in its HPLMN
Limited Service
When the UE didn’t find any accepted level cells at its home PLMN it selects any accepted level cell at any other PLMN
Cell selection procedure
PLMN Selection
–What is it ? And When it happens ? What are the types of PLMN
selection
PLMN Selection is the process in which the UE decide which PLMN it
should register
in and this process happens when the Mobile turned on or when the
mobile returned
back from limiting service
–Automatic PLMN selection
–Manual PLMN selection
When the mobile powered on
The mobile uses information about the last registered PLMN (Freq,
the stored neighbors before off)
Mobile search the strongest signal cells and read its system
information to get (MCC and MNC)
If the chosen cell is accepted the mobile try to do the
registration
If the last chosen cell not available or there is no stored info
in the mobile USIM then the mobile might select any accepted PLMN automatically
or manually
In the automatic selection if no last register PLMN exists or available
the Mobile will select the PLMN that is available and allowed as follow
HPLMN if not previously selected due to RAT
Each PLMN in User controlled PLMNs list in the USIM, in order of
priority
Each PLMN in operator controlled PLMN list in the USIM, in order
of priority
Other PLMNs according to the high quality criteria randomly the
minimum CPICH RSCP power is
-95dBm
Other
PLMNs that don’t fulfill high quality criteria
#Manual
PLMN Selection
-UE
displays all the available PLMNS after carriers scanning
-
All the available PLMNs will appear regardless it is allowed or not and
ignoring the forbidden LACs
#Roaming
*It is the services in which the user will be able to obtain
services from another PLMN
-Same country (national roaming)
-Another country (international roaming)
*Every 30 minutes the UE try to reselect its home PLMN
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Cell Search
Cell selection procedure
-Squal = Qqualmeas – Qqualmin(For
WCDMA)
#Qqualmeas is CPICH Ec/No
#Qqualmin is minimum
required Ec/No
-Srxlev = Qrxlevmeas - Qrxlevmin– Pcompensation (For all cells)
#Qrxlevmeas is CPICH
RSCP
#Qrxlevmin is minimum
required RSCP
Pcompensation=
max(UE_TXPWR_MAX_RACH – P_MAX, 0) (dB)
-P_MAX:maximum
O/P power of the UE accoring to its class
-UE_TXPWR_MAX_RACH:maximum
power used in accessing (SIB3)
-Pcompensation
is introduced for UEs that cannot transmit at maximum power on the RACH in the
cell. The cell range decreases for those UEs.
#The
cell consider as accepted if
-Squal
> 0 and
-Srxlev
> 0
*from the Drive test Tems invetigation layer 3 messages we found that :
Cell
selection occurs when
#When
UE is switched on
#When
UE in idle mode has had a number of failed RRC connection request
#UE
returns to idle mode from connected mode (cell-DCH)
#When
a UE returns to idle mode after an emergency call on any PLMN
#When a UE return to Idle mode from connection mode on common channel (cell-Fach) after a number of failed cell updated .
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Cell reselection procedure:
#When cell on which it is camping is no longer suitable
#When there is any neighbor with better quality than the selected one
#When the UE in the limited service state on an acceptable cell
#When the UE is in cell _FACH state
#According to the cell reselection criteria. In order to perform cell ranking, the UE measures the serving cell and neighbor cells listed in SIB11 according to the measurement rules
Measurement Rules fro cell reelection
1. Intra frequency measurements starts when
Squal <= Sintrasearch
SintraSearch : Controls when intra-frequency measurements are performed
(0 dBm-Not sent), Always measuring
2. Inter frequency measurements starts when
Squal <= Sintersearch
Sintersearch : Controls when intra-frequency measurements are performed (0 dBm)
3. GSM
measurements starts when
Squal <= SsearchRAT
OR Srxlev <=
SHCS,RAT
SsearchRAT : Controls quality Threshold at which GSM measurements are
performed (4 dBm)
SHCS,RAT : Controls Signal Strength Threshold at which GSM measurements
are performed (3 dBm)
#When the UE triggers a cell reselections procedure it starts ranking for the cell satisfy S-criteria (Squal > 0 and Srxlev > 0) and the ranking will be according R-criteria
Rs = Qmeas,s + Qhysts
Rn = Qmeas,n - Qoffsets,n
Qmeas: is the quality value of the received signal which is derived from CPICH Ec/No or
CPICH RSCP
Qhysts: hystersis value sent to mobile in system information used to delay the reselection as possible on the LA boarders
Qhyst1s if the ranking based on CPICH RSCP
Qhyst2s if the ranking based on CPICH Ec/No
Qoffsets,n: is the offset between the serving and the neighbor cell also used to shift the cell boarder
Qoffset1s,n : if the ranking based on RSCP, there are 2 Qoffset1s,n one for WCDMA neighbor and the other one for GSM neighbor.
Qoffset2s,n : if the ranking based on Ec/No
#“Cell_selection_and_reselection_quality_measure information element”: is the parameter that determine if we will do the ranking based on RSCP or Ec/No
#The UE reselect the better cell if it stay better for time interval more than Treselection
UMTS to UMTS cell Re-selection
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Engineering-Academy
thanks to the legend Abdelrahman Fady who teach me these information and let me use his material to publish it
thanks to the legend Abdelrahman Fady who teach me these information and let me use his material to publish it