The CSFB UTRAN EventB1 ECN0 Trigger Threshold parameter defines the Ec/No threshold that determines when a UE reports a UTRAN cell for Circuit Switched Fallback (CSFB) under Event B1 conditions. Proper tuning of this parameter helps balance between timely handovers and avoiding unnecessary ones, ensuring reliable voice call fallback to UMTS networks.
Parameter Overview
- Parameter ID: CsfbHoUtranB1ThdEcn0
- Network Element: eNodeB
- MML Command: MOD CSFALLBACKHO
- Default Value: -13 dB
- Recommended Value: -13 dB
- GUI Value Range: -48 to 0 (0.5 dB steps)
- Actual Value Range: -24 to 0
- Feature Specification: 3GPP TS 36.331
Function and Impact on Handover
This parameter controls the Ec/No requirement for UTRAN cells to qualify for inclusion in a measurement report when CSFB is needed. The UE sends the report only if at least one UTRAN cell exceeds this threshold alongside other event B1 triggering conditions.
A higher threshold (e.g., closer to 0 dB) reduces the likelihood of handovers by requiring better signal quality, minimizing unnecessary handovers in areas with high signal fluctuation. A lower threshold (e.g., closer to -24 dB) increases handover probability, ensuring faster fallback in weak coverage areas.
Optimization Strategy
- Network Environment Analysis:
- Evaluate areas with high signal variance or coverage gaps.
- Threshold Adjustment:
- For cells with large signal fluctuations, increase the threshold to avoid unnecessary handovers.
- For stable cells or weak coverage zones, lower the threshold to ensure timely CSFB handovers.
- Performance Validation:
- Monitor KPIs such as Call Setup Success Rate (CSSR), Call Drop Rate (CDR), and CSFB Success Rate.
Practical Example
Scenario: A site experiences delayed CSFB handovers causing voice call setup failures.
- Current Setting: CsfbHoUtranB1ThdEcn0 = -13 dB
- Ec/No Analysis: Average UTRAN cell Ec/No = -18 dB
- Optimization: Lower the threshold to -19 dB for faster handover triggering.
- Result: Improved CSFB handover success rate by 6% and reduced call setup delay.
Conclusion
The CSFB UTRAN EventB1 ECN0 Trigger Threshold is essential for optimizing CS fallback performance. Adjusting it according to network conditions enhances call setup success and minimizes unnecessary handovers. Regular monitoring ensures KPIs performance improvements.