Reselection parameters in LTE networks help determine when a UE should switch from one cell to another. Following is list of LTE reselection parameters with explanations:
Start Reselection.
SIntraSearch:
- It is a Signal threshold for starting intra-frequency reselection.
- Its Range is 29×2=−58dBm to 31.
- A higher value encourages the UE to start reselection earlier when the signal is weak.
sNonIntraSearch:
- It is a Signal threshold for starting inter-frequency or inter-RAT reselection.
- Its Range is 2 to 5.
- Higher values discourage reselection to other RATs (Radio Access Technologies) like GSM or WCDMA.
- Example Calculation is −114+5×2 = −104dBm.
TcrMaxConnMode:
- It is a Maximum time for mobility calculations in connected mode.
- Its Range is T_CRMAX_30S to T_CRMAX_60S.
- Longer times discourage reselection but improve precision in mobility calculations (celResTiF, sIntrasearch, sNonIntrsearch).
High Mobility Scaling:
- Scaling factor for high mobility scenarios.
- Its Range is QHystSfHigh DB0_Q_HYST_SF_HIGH(0dB) to DB_2_Q_HYST_SF_HIGH.
- Higher values discourage reselection during high mobility.
- Offset (qRxLevMinOffset): 0 to 2.
TreselectionRAT:
- It is a time to trigger reselection to another RAT.
- Increasing this time decreases the likelihood of reselection.
- Example Value is TreselectionRAT = 7sec.
Reselection Decision.
IdleQhyst1s:
- It is a hysteresis for staying with the current cell in idle mode.
- If we make range 4 to 2. Lower values discourage sticking to the current cell.
Cell Offset (qOffsetCellEUtran, qOffsetCell, qOffCell):
- Offset applied to the cell’s signal strength.
CellReselPriority:
- It is simple Priority for cell reselection.
- It’s Range is 0 to 2 for high priority.
- Function: Lower values discourage reselection.
- Priority Values: cellReselectionPriority 5 to 3.
- Related: threshXHighHrpd, tReselectionEutra 2 to 4, tReselectionEutraSfHigh 3 to 2.
NcellReselectionHigh:
- It is a threshold for entering high mobility state.
- Range: 16 to 10.
- Function: Lower values make the UE enter high mobility state earlier.
- Related Parameters: threshXHigh, threshXLow, tReselectionEutraSfHigh, threshServingLow 62, sPrioritySearch1, , interFrqThrH, tResEutSF, eutResTiFHM, celResTiFHM, cellReSelPrio 3 to 0 will discourage, mobStateParamNCelChgHgh mobStateParamTEval, qRxLevMinOffset 0 to 2dB, q-RxLevMin, spStResPars, qHystSfHigh, tReselEutr, timeToTriggerSfMedium, tResUtra, tResUtraSF, utrResTiFHM.
Qrxlevmeas.
- Tevaluation:
- It is time period for evaluating reselection.
- Its Range is 30 to 60s.
- T320:
- Definition: Timer for UE attach procedure.
- Related Timers:
- T3410 (UE): Timer for UE attach.
- T3450 (eNodeB): Timer for eNodeB attach.
System Information Messages (SIB)
- SIB1: Contains information about access and message scheduling, and reselection criteria.
- SIB2: Provides UE timers, common/shared channel configurations, and uplink resource blocks (RBs).
- SIB3: Contains intra-frequency reselection information.
- SIB4: Provides information about intra-frequency neighbors.
- SIB5: Contains inter-frequency neighbor information.
- SIB6: Provides reselection information to WCDMA.
- SIB7: Contains reselection information to GSM.
- SIB8: Provides reselection information to CDMA.
- Sib3Period: RF16 to RF32 – Less resource usage but might cause access delays.
Related Parameters:
- maxCrSibDl: Maximum cell radius for SIB.
- si4Periodicity: Periodicity for System Information 4.
These parameters are crucial for managing the cell reselection process, ensuring that UEs maintain optimal connections while balancing network load and performance.