All About Passive Intermodulation - Common PIM Sources And Problems

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The telecommunication industry is one of the foremost sectors to adopt digital transformations. The transition to 5G is happening so rapidly due to the innovative and highly-advanced technological prowess of telecommunication experts. Their business objectives and scalability are constantly evolving year after year as people are finding smartphones and high-speed network services to be an inevitable part of their daily life. But are telecommunication companies capable of dealing with challenges that future developments in the industry might bring? Especially, the threats to their network service reliability and capacity must be addressed. Passive Intermodulation (PIM) is one such significant barrier to the seamless operations of cellular network operators.


What is PIM?

Passive Intermodulation (PIM) is caused due to the intermodulation products generated when the passive nonlinear devices take on two or more signals. As the LTE, 5G, and Wi-Fi networks are booming in number, the modulated carrier frequency prone to nonlinear passive devices of different source metals generates more self-interference signal distortion. Such unwanted additional frequencies generated will interfere with the uplink or downlink frequencies reducing the receiving cell sensitivity and disrupting the communication. While most cellular operators address the issues caused by active devices, distortions caused due to aging and dirty cables, connectors, or antennas are often ignored. But the growing spectrum usage and antenna-sharing activities have made PIM testing, location, and rectification unavoidable.

Sources of PIM

As high-speed digital communications and data transfers are augmenting, the PIM issue which was traditionally avoided by frequency planning, has become more serious. Recent occurrences show that the following causes elevate the generation of PIM in cellular network systems:


Faulty electrical connections where the surfaces are not smooth cause the high current density in the areas of contact leading to the heating up of the conducting path. If the connections are not tightened with the right amount of torque, a resistance change may occur leading to the generation of intermodulation products that cause signal distortion


Ferromagnetic materials like Iron used in cellular systems may cause high PIM distortion as they may be exposed to high levels of RF energy. Aging of antennas or cable connections can induce rust formation in such ferromagnetic elements leading to reduced conduction area


Metal surfaces of connectors, cables, duplexers, or antennas may have a small layer of oxide, and rusting is inevitable. Also, oxide layers cause a reduced area of conduction and even lead to the Schottky effect. This is a major source of PIM distortion


In general, aging equipment, installing new equipment, overlaying new carriers on old antenna runs, or co-locating new carriers can directly lead to PIM

Impacts of PIM

PIM can have considerable impacts on the performance of cellular network systems. When the receiver cells become less sensitive to weak signals the network coverage is reduced. Such an error leads to dropped calls and disrupted communication with too many interferences. In the case of data transfers, PIM resends more error protection bits leading to a lowering of data rates. Some cellular operators have even faced a complete shutdown of the receiver sector due to PIM. If you are a cellular network operator, watch out for the common signs of PIM including high noise floors, receive-noise-floor-diversity-imbalance, reduction of average call duration, low data rates, more dropped calls, and reduced call volume.

To Sum Up

Do you want to have a high-quality, wide-coverage, reliable, and stable network? Then start working on your PIM testing and detection process. It may seem trivial but may cause serious effects on your network services with time. Utilize advanced PIM cancellation algorithms in your cellular system building. Ensure proper maintenance of active and passive elements of the system and conduct periodic inspections and cleaning. Maintain adequate torque for the connectors. Team up with MobileComm to have advanced and automated PIM testing, detection, and rectification services and support to enhance your service reliability and network capacity.