Inter-RAT Cell Reselection Trial
Objective
• To find a good balance between coverage and
performance for LTE by adjusting UMTS
reselection to LTE
Background Information
• Idle mode reselection parameters from LTE to UMTS and vice versa was set
to -110 dBm for the market
– 30% RRC MO-Signaling: UE ping pong from LTE to UMTS with high RRC
failures
• Reselection from UMTS to LTE was set to AT&T GSV of -104 dBm while LTE
to UMTS was retained at -110 dBm
– 12% RRC MO-Signaling, reduced RRC failures due to signaling
– 20% ERAB attempts lost
– 6 dB reselection hysteresis may be too high
Summary of UMTS SIB19
Impact
• Negligible impact seen on Accessibility and Retainability
– Increased RRC, ERAB and S1 Signaling Attempts
– RRC Distribution shows a 6% (abs) increase in RRC MO signaling
• Threshhigh at 16 – RRC signaling at 12%
• Threshhigh at 14 – RRC signaling at 18%
– Traffic increase
• Small Increase in IRAT Session Continuity to WCDMA
• Throughput is unchanged
Parameterization
• UMTS
– Threshhigh – 16 (Gold Standard Value, initial value)
– Threshhigh – 14 (Current Setting)
• LTE (idle mode)
– EUtranCellFDD: qRxLevMin: -120 (GSV)
– EUtranCellFDD: sNonIntraSearch:10 (GSV)
– EUtranCellFDD: threshServingLow:10 (GSV)
• LTE (dedicated mode)
– ReportConfigEUtraBadCovPrim: a2ThresholdRsrpPrim: -115 (Current Setting)
Idle Mode Behaviour
UE reselects to UMTS when RSRP falls below -110 dBm and UE reselects to
LTE when LTE measured RSRP is -106 dBm
Dedicated Mode Behaviour
UE will IRAT to UMTS when RSRP is -116 dBm (-115 dBm + 1 dB hysteresis).
UE will remain in LTE longer when in dedicated mode.
SiB19 Performance Impact
SiB19 Performance Impact
SiB19 Performance Impact
SiB19 Performance Impact
SiB19 Performance Impact
SiB19 Performance Impact
SiB19 Performance Impact
SiB19 Performance Impact
THANK YOU