Key Challenges in 5G Indoor Coverage: Interference and Channel Imbalance

2025-08-20

As 5G adoption accelerates, indoor environments such as smart homes, factories, and AR/VR applications have become major traffic sources, accounting for over 70% of 5G usage. This shift makes high-quality indoor coverage a strategic priority for mobile operators. However, two significant technical challenges have emerged: co-frequency interference from outdoor macro cells and imbalanced power in dual-channel indoor systems.

Outdoor macro cells using 64T64R massive MIMO enhance coverage, but operation in the 2.6 GHz band introduces interference. Tests in scenarios with 4T4R distributed pico cells show that under 50% outdoor macro cell load, the average indoor downlink speed drops from 609 Mbps to 438 Mbps—a 28.1% capacity loss. Performance degradation exceeds 44% when the outdoor signal is stronger than the indoor signal by 5 dB or more. To limit indoor user performance loss to under 20%, the indoor signal must exceed the outdoor signal by at least 6 dB.

For existing LTE-based distributed antenna systems (DAS) upgraded to 5G NR, dual-channel imbalance also poses a critical issue. A power difference of 5 dB between channels results in approximately 20% speed loss, while a 10 dB gap causes nearly 30% degradation, with worse performance at cell edges. The LTE Rank2 ratio serves as an effective metric for evaluating balance: at 0 dB difference, Rank2 ratio is 76%; at 5 dB, it drops to around 60%. A Rank2 ratio below 60% indicates that dual-path imbalance will cause over 20% performance degradation in 5G NR. Thus, pre-upgrade balance correction is essential.

These findings highlight the need for careful network planning, signal optimization, and system calibration to maintain 5G service quality indoors. Operators must address both interference management and hardware consistency to meet growing indoor capacity demands.
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