RAN optimization: 10 essential KPIs to optimize your LTE/5G network
The 10 essential KPIs for RAN (Radio Access Network) optimization in LTE and 5G NR. How to measure, interpret, and act. A guide for telecom network engineers.
RAN (Radio Access Network) optimization relies on a rigorous selection of KPIs to monitor. With dozens of metrics available in equipment PM (Performance Management) counters and field measurement tools, the risk is drowning in data. This guide identifies the 10 fundamental KPIs that cover 90% of LTE/5G network performance issues and explains how to link them to optimization actions.
Why limit the KPIs you monitor?
The temptation is to monitor everything. In practice, effective optimization teams work with a reduced set of βsentinelβ metrics that alert on degradations and point toward the root cause. Other metrics then serve to confirm the diagnosis.
The 10 KPIs presented here cover: coverage, radio quality, throughput performance, voice quality of service, accessibility, and retention.
KPI 1: Median RSRP (coverage)
Definition: median reference signal power across the coverage area.
Target: median RSRP > -90 dBm in populated areas
What it reveals: the overall network coverage level. A degraded median RSRP indicates under-covered areas, antenna height issues, or transmit power problems.
Action if degraded: drive test to locate areas < -105 dBm, audit antenna heights, verify configured vs. measured transmit power.
KPI 2: Median SINR (radio quality)
Definition: median signal-to-interference-plus-noise ratio across the coverage area.
Target: median SINR > 10 dB
What it reveals: the effective quality of the radio link. A low SINR with good RSRP indicates pilot pollution or inter-cell interference.
Action if degraded: analyze neighbor cells, adjust tilt/azimuth, revise frequency reuse plan.
KPI 3: CSSR β Call Setup Success Rate (accessibility)
Definition: percentage of VoLTE calls or data sessions established successfully out of total attempts.
Target: CSSR > 99.5%
What it reveals: the networkβs ability to establish connections. A degraded CSSR may indicate a load issue (no resource available), a faulty RRC configuration, or transport problems toward the core.
Useful breakdown:
- CSSR RRC (radio link establishment)
- CSSR NAS (network registration)
- CSSR Session (data session / voice bearer establishment)
KPI 4: CDR β Call Drop Rate (retention)
Definition: percentage of VoLTE calls dropped before the subscriber ends the call.
Target: CDR < 0.5%
What it reveals: cell-edge coverage issues, failed handovers, radio retention problems (RLF without successful re-establishment).
Diagnostic approach: correlate each dropped call with GPS location, RSRP/SINR at the moment of the drop, and L3 messages (RLF trigger, T310 expiration, handover failure).
KPI 5: DCR β Data Connection Drop Rate (data retention)
Definition: rate of involuntary data session disconnections (RLF followed by failed re-establishment, or forced inactivity by the network).
Target: DCR < 0.3%
What it reveals: similar to CDR but for data sessions. Particularly critical for real-time applications (OTT VoIP, streaming, gaming) where a 2+ second interruption is noticeable.
KPI 6: Handover Success Rate (mobility)
Definition: percentage of successful handovers (intra-frequency, inter-frequency, inter-RAT) out of total attempted handovers.
Target: Handover Success Rate > 99%
What it reveals: the quality of the neighbor list and mobility parameters. A low rate indicates either an incomplete neighbor list (cells not declared in the neighborList) or poorly calibrated A3/A5 thresholds (trigger too late = RLF before handover).
Complementary KPI: Ping-Pong Rate (handovers that reverse within < 30 seconds). A ping-pong rate > 5% indicates overly aggressive neighbor parameters.
KPI 7: PRB Utilization (capacity)
Definition: Resource Block utilization rate (DL + UL) during peak load periods.
Target: PRB Utilization < 70% (DL), < 60% (UL) during busy hour
What it reveals: radio capacity saturation. PRB Utilization > 80% during peak hours leads to throughput degradation for all simultaneously active users, even those with excellent SINR.
Action if saturated: densification (adding a carrier or site), activation of additional carriers via carrier aggregation (CA), activation of adaptive beamforming.
KPI 8: Median DL throughput (performance)
Definition: median download throughput measured on active data sessions, in Mbps.
Target: > 10 Mbps on LTE, > 50 Mbps on 5G NR mid-band (busy hour)
What it reveals: the overall performance delivered to subscribers. This KPI is directly correlated with customer satisfaction.
Do not confuse: median throughput is not peak throughput. Peak throughput (iperf3 under optimal conditions) is a theoretical capacity measurement. Median throughput is what the typical subscriber experiences.
KPI 9: Median voice MOS (voice QoE)
Definition: median voice MOS score measured on active VoLTE calls (via automated ViSQOL or POLQA measurements).
Target: median MOS > 4.0 (WB), > 3.8 (NB)
What it reveals: the quality perceived by subscribers on their voice calls. This is the most direct QoE KPI and the most correlated with subscriber complaints.
Correlation with radio KPIs: a degraded MOS with good RSRP/SINR points to a latency, jitter, or QCI priority issue in the core network.
KPI 10: NAS Reject Rate (core accessibility)
Definition: rate of registration or session rejections by the core network (NAS Reject messages with cause code).
Target: NAS Reject Rate < 0.1%
What it reveals: configuration issues in the core network (MME/AMF), roaming problems, subscriber provisioning issues (SIM not provisioned, expired data plan, core congestion).
NAS Reject codes to monitor:
- Cause 7 (EPS Services not allowed): subscriber not authorized
- Cause 11 (PLMN not allowed): roaming issue
- Cause 22 (Congestion): core network overload
- Cause 15 (No suitable cells): incorrect network configuration
How to integrate these 10 KPIs into your optimization workflow
Daily monitoring dashboard
Configure automatic alerts on these 10 KPIs with warning (orange) and alarm (red) thresholds. KPIs in alarm trigger a field investigation the same day.
Recommended prioritization:
- Critical priority (action < 4h): CDR, CSSR, NAS Reject Rate
- High priority (investigation < 24h): Handover Success Rate, DCR
- Normal priority (weekly planning): RSRP, SINR, PRB Utilization, DL Throughput, MOS
Field optimization cycle
For each degraded cell or area:
- Identification: alert on one or more of the KPIs above
- Field diagnosis: targeted drive test with L3 capture + RF KPIs
- Analysis: correlate field KPIs with possible countermeasures
- Action: parameter modification or physical intervention
- Validation: field re-measurement after action, compare the 10 KPIs before/after
Management reporting
These 10 KPIs form a concise report understandable by non-technical teams:
- 3 coverage/quality KPIs (RSRP, SINR, PRB)
- 3 accessibility/retention KPIs (CSSR, CDR, NAS Reject)
- 2 mobility KPIs (Handover SR, Ping-Pong)
- 2 subscriber experience KPIs (DL Throughput, MOS)
This format allows you to communicate the network status to a management committee in 5 minutes.
Conclusion
Effective network optimization does not require monitoring hundreds of KPIs. These 10 metrics cover the essential dimensions of LTE/5G mobile network performance and provide an actionable framework for optimization teams. Their field measurement β via drive test with L3 capture and MOS calculation β provides the evidence needed to prioritize actions and validate results.
Further Reading
Founder of HiCellTek. 15+ years in telecom, operator side, vendor side, field side. Building the field tool RF engineers deserve.
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