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.