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 handoverConclusion
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.