Cell reselection consists of two steps: neighboring cell measurement and reselection evaluation. Accordingly, parameters are optimized in the two steps.
Neighboring Cell Measurement
l Intra-Frequency Measurement
The CellResel.SIntraSearch parameter specifies the intra-frequency measurement triggering threshold. A UE decides whether to perform intra-frequency measurements by comparing the value of this parameter with the Srxlev value of the serving cell. If the Srxlev value is less than or equal to the value of CellResel.SIntraSearch, the UE performs intra-frequency measurements.
l Inter-Frequency or Inter-RAT Measurement
The CellResel.SNonIntraSearch parameter specifies the inter-frequency or inter-RAT measurement triggering threshold. A UE decides whether to perform inter-frequency or inter-RAT measurements by comparing the value of this parameter with the Srxlev value of the serving cell. If the Srxlev value of the serving cell is less than or equal to the value of CellResel.SNonIntraSearch, the UE performs inter-frequency or inter-RAT
measurements on cells whose priorities are lower than or equal to the priority of the serving cell.
NOTE
The value of CellResel.SIntraSearch must be greater than that of CellResel.SNonIntraSearch.
Reselection Evaluation
The eNodeB evaluates only the cells that fulfill the cell selection criteria for reselection.
l Evaluation of Intra-Frequency Cells or Cells on Equal-Priority Frequencies The CellResel.Qhyst parameter specifies the hysteresis for cell reselection. This parameter is used to adjust the border of the serving cell to prevent a ping-pong effect that may occur during cell reselection. A larger value of CellResel.Qhyst leads to larger coverage of the serving cell and therefore a lower probability of reselection to the neighboring cell.
The EutranIntraFreqNCell.CellQoffset parameter specifies the offset between the serving cell and the neighboring cell. It is used to adjust the border of the neighboring cell. A larger value of EutranIntraFreqNCell.CellQoffset leads to smaller coverage of
the neighboring cell and therefore a lower probability of reselection to the neighboring cell.
The CellResel.TReselEutran parameter specifies the time for cell reselection within the E-UTRAN. The UE reselects an E-UTRAN cell if the cell reselection criterion R is fulfilled within the time specified by this parameter.
l Evaluation of Inter-Frequency or Inter-RAT Cells on Different-Priority Frequencies The CellResel.ThrshServLow parameter specifies the threshold for the serving
frequency used in reselections to inter-frequency or inter-RAT cells that work on lower-priority frequencies. The reselections are performed only when the Srxlev value of the serving cell is less than the value of this parameter. A larger value of this parameter leads to a higher probability of reselection to lower-priority cells.
To prevent ping-pong cell reselections, a reselection timer must be set for each RAT. A UE reselects a cell only when the reselection criteria are fulfilled throughout the time specified by the related timer. The parameter IDs of these timers vary based on the RATs.
The parameter IDs are as follows: CellReselGeran.TReselGeran for GERAN, CellResel.TReselEutran for E-UTRAN, CellReselCdma2000.TreselectionHrpd for CDMA2000 HRPD, and CellReselUtran.TReselUtran for UTRAN.
The evaluation of inter-frequency or inter-RAT cells is dependent on the
EUTRANINTERNFREQ.ThreshXHigh and EUTRANINTERNFREQ.ThreshXLow parameters, which specify the thresholds used in reselection to higher-priority and lower-priority cells, respectively. The two parameters are RAT-specific. A larger value of a parameter leads to a lower probability of reselection to related cells.
Paging
l Paging success rate
Decreasing the paging message code rate specified by
CELLDLSCHALGO.RarAndPagingCR help improve the paging success rate.
However, decreasing the paging message code rate increases the PDSCH resources occupied by paging messages, which cause the downlink throughput to decrease.
With UE compatibility problems taken into account, set the paging message code rate to 0.035 or higher (setting CELLDLSCHALGO.RarAndPagingCR to 35). The number of single-paging message RBs less than or equal to 40% of the total number of single-TTI RBs prevents insufficient downlink power. Therefore, when adjusting the
CELLDLSCHALGO.RarAndPagingCR setting, you are advised to limit the the number of paging records contained in a single paging message (specified by
PCCHCFG.MaxPagingRecordsNum) to limit the maximum number of single-paging message RBs.
The following table lists the recommended values for PCCHCFG.MaxPagingRecordsNum in case of different
CELLDLSCHALGO.RarAndPagingCR values (20 MHz bandwidth used as an example).
Number of single-paging message RBs
CELLDLSCHALGO.RarAn
dPagingCR PCCHCFG.MaxPagingR
ecordsNum
≤ 40 ≥ 78 16
≤ 40 ≥ 73 15
Number of single-paging message RBs
CELLDLSCHALGO.RarAn
dPagingCR PCCHCFG.MaxPagingR
ecordsNum
≤ 40 ≥ 69 14
≤ 40 ≥ 64 13
≤ 40 ≥ 60 12
≤ 40 ≥ 55 11
≤ 40 ≥ 50 10
≤ 40 ≥ 45 9
≤ 40 ≥ 41 8
≤ 40 ≥ 36 7
≤ 37 ≥ 35 6
NOTE
In this table, the recommended number of RBs is calculated based on the paging messages containing UE flags "S-TMSI".
l Uu interface paging capacity
The Uu interface paging capacity is related to nB (specified by PCCHCFG.Nb) and the number of paging message records (specified by PCCHCFG.MaxPagingRecordsNum).
The maximum number of paging message sent over the Uu interface within 1s is equal to the result of (nB/T) multiplied by 100 and PCCHCFG.MaxPagingRecordsNum, where T represents the paging period.
NOTE
The above formula calculates the theoretical maximum paging capacity, and the actual paging capacity is also related to the hardware processing capability.
Assume nB equals 1T, and the value of PCCHCFG.MaxPagingRecordsNum is 16, a maximum of 1600 UEs can be paged over the Uu interface within 1s. You can increase nB and PCCHCFG.MaxPagingRecordsNum to increase the Uu interface paging capacity. However, increasing nB may increase the overhead of PDCCHs occupied by paging messages.
When adjusting the PCCHCFG.MaxPagingRecordsNum setting, query the paging message code rate specified by CELLDLSCHALGO.RarAndPagingCR, and ensure that the number of single-paging message RBs is less than or equal to 40% of the total number of single-TTI RBs, in accordance with the description in the preceding table.
l Paging priority
If paging messages are congested over the Uu interface, you are advised to set
PCCHCFG.PagingStrategy to PAGING_STRATEGY_DIFFPRI, to ensure that CS paging messages or high-priority paging messages are preferentially sent over the Uu interface.
System Information Message Update
If the paging occasion (PO) of a UE supporting Single Radio LTE (SRLTE) falls in the paging listening window of a CDMA2000 1X network, the UE cannot receive paging messages from the LTE network, and cannot update LTE system information. As a result, RRC establishment may fail.
You are advised to select the RsvdSwPara3_bit5(ReservedSwitchParameter3_bit5) check box under the eNBCellRsvdPara.RsvdSwPara3 parameter in scenarios with both CDMA and LTE network coverage.
l If this check box is selected, when the paging period of the LTE network is less than that of the CDMA network, RRC establishment failures can be avoided; when the paging period of the LTE network is greater than or equal to that of the CDMA network, the problem persists.
l If this check box is deselected, the problem persists regardless of the paging periods of LTE and CDMA networks.