Longitudinal Assessment of LTE/5G Network Performance and Stability Under Staged Indoor Coverage Infrastructure Deployment

Indoor coverage infrastructure plays an important role in maintaining reliable LTE/5G services in shielded and structurally complex environments where outdoor macro-cell signals are strongly affected by penetration loss and internal attenuation. However, indoor coverage solutions are commonly evaluated using spatial measurements or short-duration before/after comparisons, while considerably less attention is given to their temporal interaction with the surrounding operational mobile network. This study presents a longitudinal operator-side assessment of LTE/5G network performance and stability during the successive activation of indoor coverage infrastructure. The experimental campaign was organized into three consecutive operational stages: a baseline state with both coverage-enhancement components inactive, a first intervention state following activation of the distributed indoor coverage component, and a final combined state after activation of the second localized coverage component. Temporally resolved operator OSS records were retained in chronological order and evaluated using a common staged framework. The analysis combined stage-wise descriptive statistics with segmented interrupted time-series regression, accounting for temporal trends, network-load variations, and serial dependence. The analysis focused on complementary network-side indicators representing the uplink radio environment, user-plane traffic dynamics, and 5G connectivity, including LTE and NR uplink interference, downlink and uplink PDCP volume, and the SgNB Add Success Rate. Across Stages 1–3, mean LTE uplink-interference levels were −108.20, −109.22, and −108.85 dBm, respectively, while the corresponding NR values were −110.35, −111.59, and −111.05 dBm. Although intervention-associated changes were identified in the statistical models, the baseline-derived persistence assessment detected no continuous adverse threshold exceedances lasting 24 h or longer during the post-baseline stages. PDCP traffic showed pronounced short-term fluctuations and progressively different stage-wise averages, demonstrating that network utilization changed during the observation period and providing essential temporal context for interpretation of the other KPIs. The mean SgNB Add Success Rate remained above 99.8% in all three stages and reached 99.92% in the final combined state, where its variability was also the lowest. Although transient KPI deviations occurred during the monitoring period, they did not develop into a consistent pattern of persistent deterioration across the monitored radio and connectivity indicators. The findings demonstrate the value of combining longitudinal operator-side KPI monitoring with segmented time-series analysis and explicit stability criteria. The study provides a structured assessment of staged indoor infrastructure deployment while recognizing the limitations of causal inference from single-site observational data.