How to do optimization of PS CSSR in LTE?

To optimize PS CSSR (Packet Switched Call Setup Success Rate) in LTE, focus on improving RRC (Radio Resource Control) and E-RAB (Evolved Radio Access Bearer) setup success rates. Below is a structured approach based on technical principles.

1. Root Cause Analysis

Weak Coverage: High TA (Timing Advance) values and cell-edge users cause RRC NoReply failures.

Congestion: UL/DL power, channel element, or lub bandwidth limitations during admission.

Formula Mismatch: Vendor-specific behaviors (e.g., Nokia’s PS 0/0K access) may skew KPI calculations.

Parameter Misconfiguration: Suboptimal timers (T300/T301) or thresholds (RrcConn PunishThd).

2. Optimization Strategies

A. Coverage Optimization

RF Adjustments:

Physical Tilt: Lower antenna tilt to reduce overshooting and improve cell-edge coverage.

RET (Radio Equipment Tilt): Adjust RET values (e.g., from 20 to 50) to control coverage range.

Interference Mitigation: Optimize hopping offset and filter timers to reduce interference.

B. Parameter Tuning

RRC Timers:

Increase T300 (RRC connection setup timer) from 1000ms to 1500ms to allow more time for UE response. Adjust T301 (RRC reestablishment timer) to 600ms for better reestablishment success.

Penalty Mechanisms:

Set RrcConnPunish hd to 10s to penalize repeated failed UEs. Enable FilterReptRrcConnReqTimer (5s) to filter repeated requests.

C. Congestion Management

Admission Control:

Monitor UL/DL power and channel element usage. Increase resources if congestion is due to UL Channel Element or Uplink Power. Optimize lub bandwidth allocation for service-based prioritization.

Load-Based Reconfiguration:

Enable P2D (Power-to-Data) adjustments based on load to increase channel reconfiguration attempts.

D. Formula Alignment

Vendor-Specific Adjustments:

For Nokia networks, update PS CSSR formula to include reconfiguration success rate:

PS CSSR = (RRC Success/RRC Attempt) X (RAB Success+Reconfig Success/RAB Attempt+Reconfig Attempt)

3. Feature Enablement

Blind Handover Optimization:

Enable HO_LTE_PSHO_OUT_DELAY_OPT_SWITCH to reduce UMTS-to-LTE handover latency by using RSCP-based blind handovers. Set U2LNCovRscpThd (RSCP threshold) based on UMTS pilot power (e.g., -87 dBm for 36 dBm pilot)

4. Monitoring & Validation

KPI Tracking:

Monitor L.RRC.StupFail.NoReply and L.RRC.SetupFail. Reject counters post-optimization.

DT/CQT Campaigns:

Conduct drive tests to validate coverage improvements and reduce cell-edge failures.

5. Example Configuration Commands

# Adjust RRC timers and penalty thresholds

SET T300 = 1500; # Increase RRC setup timer

SET T301 = 600; # Optimize reestablishment timer

SET RrcConnPunishThd = 10; # Enable penalty for failed UES

SET FilterReptRrcConnReq Timer = 5; # Filter repeated requests

# Enable blind handover optimization

ADD UCELLU2LTEHONCOV: HO_LTE_PSHO_OUT_DELAY_OPT_SWITCH=ON;

SET UU2LTEHONCOV: U2LNCovRscpThd=-87; # RSCP threshold for blind handover

Conclusion

Optimizing PS CSSR requires a holistic approach combining coverage adjustments, parameter tuning, and vendor-specific formula alignment. Prioritize RRC success rate improvements through timers and coverage, while addressing E-RAB congestion via resource allocation and admission control. Regularly validate changes with KPIs and field tests to ensure sustained performance.