The CSFB UTRAN EventB1 RSCP Trigger Threshold defines the RSCP value required for UEs to trigger Event B1 during Circuit-Switched Fallback (CSFB) to UTRAN. Proper configuration ensures timely handovers to 3G networks, reducing call drops and improving voice fallback performance.
Parameter Overview
- Parameter ID: CsfbHoUtranB1ThdRscp
- Network Element: eNodeB
- MML Command: MOD CSFALLBACKHO
- Default Value: -106 dBm
- Recommended Value: -106 dBm
- Value Range: -120 to -25 dBm
- Unit: dBm
- Feature Specification: 3GPP TS 36.331
Function and Impact on Handover
This parameter determines when the UE reports a UTRAN cell’s RSCP measurement to the eNodeB. For Event B1 to trigger, the UE must detect a UTRAN cell with RSCP exceeding this threshold alongside other conditions.
- Higher Thresholds (-90 dBm or higher): Reduce handovers to UTRAN by requiring stronger signals, minimizing unnecessary inter-RAT handovers in stable environments.
- Lower Thresholds (-110 dBm or lower): It give faster handovers to UTRAN by accepting weaker signals, which helps ensure voice continuity in weak LTE coverage areas.
Optimization Strategy
- Coverage Analysis:
- Evaluate LTE coverage gaps and UTRAN signal strength to identify handover-triggering zones.
- Threshold Tuning:
- Urban Areas: Use a higher threshold to avoid premature handovers due to fluctuating signals.
- Rural or Weak LTE Coverage Areas: Use a lower threshold to ensure CSFB triggers before LTE drops completely.
- Performance Monitoring:
- Track Call Setup Success Rate (CSSR), Call Drop Rate (CDR), and CSFB Success Rate to validate improvements.
Practical Example
Scenario: High voice call drops during CSFB in a suburban cluster.
- Current Setting: CsfbHoUtranB1ThdRscp = -106 dBm
- RSCP Analysis: Average UTRAN RSCP in the area = -112 dBm
- Optimization: Set CsfbHoUtranB1ThdRscp to -115 dBm to ensure earlier handover triggering.
- Result: CSFB success rate increased by 4%, and voice call drops reduced by 6%.
Conclusion
Fine-tuning CSFB UTRAN EventB1 RSCP Trigger Threshold ensures seamless voice fallback and reduces call drop rates. Regular performance analysis and adjustments based on field data are essential for maintaining optimal CSFB optimization.