Analysis of Passive Intermodulation (PIM) Challenges in Massive MIMO and Ultra-Dense 5G Indoor Networks

As 5G networks transition toward Ultra-Dense Networks (UDN) to meet the demand for multi-Gbps data rates, especially in indoor environments, they face significant physical-layer impairments. One of the most critical challenges is Passive Intermodulation (PIM), which is defined as unwanted emissions resulting from non-linearities in RF circuitry, connectors, and adjacent metallic structures. In Massive MIMO systems, the high density of antenna elements and the use of complex beamforming architectures significantly increase the likelihood of intermodulation products falling within the device's receiver band, leading to receiver sensitivity degradation. This research analyzes PIM challenges in the context of LTE/NR Dual Connectivity, where simultaneous transmissions in "difficult band combinations" generate self-interference that complicates the link budget. Furthermore, the study explores how the dense deployment of small cells in indoor scenarios amplifies these effects due to signal proximity and shared spectrum resources. Potential mitigation strategies, including advanced RF filtering, improved power amplifier linearization, and spatial coordination between access nodes, are evaluated to ensure the required network reliability and capacity.