All about passive intermodulation distortion in cellular telecommunication networks

By Rajeev Gandhi, Head of Technology, Telco Network Engineering

5G uses similar, and even higher, frequency bands compared to CDMA, HSPA, and LTE.

By Rajeev Gandhi, Head of Technology, Telco Network Engineering

The telecommunications industry is typically an early adopter of new technologies and digital transformation. A case in point is with 5G cellular networks. The industry is transitioning to 5G rapidly because of the many highly skilled technology innovators in the telecommunications industry. Consumers are another reason for the rapid migration to 5G. Whether for work or personal reasons, most people now have an insatiable demand for connectivity, and they find that smartphones and high-speed network services are a critical part of their daily lives.


The potential threat of PIM distortion

As telecom companies strive to grow their customer base and scale network infrastructure, and in parallel, consumers want faster transmission speeds, wireless providers must do their best to anticipate what future developments in the industry might bring and how this evolution will positively or negatively impact their businesses. In particular, telecom companies must pay particular attention to potential threats to service reliability and network traffic capacity.

Wireless network operators should be aware of passive intermodulation (PIM) distortion as a possible obstacle to seamless cellular network functionality. According to this article on, “PIM is an issue for almost every wireless system, but it is most noticeable in cellular applications (CDMA, HSPA, and LTE). This is because the frequency bands used by these technologies are very close to each other.”

5G uses similar, and even higher, frequency bands compared to CDMA, HSPA, and LTE. This makes it even more susceptible to PIM issues due to intermodulation between its own carriers or with other nearby signals.


Understanding PIM

With that brief explanation above, let’s dig a bit deeper to understand PIM better. It is a type of distortion caused by intermodulation, which are currents in an electrical device at two different frequencies. PIM occurs when passive, nonlinear devices take on two or more signals. As LTE, 5G, and Wi-Fi networks become ubiquitous, the modulated carrier frequency prone to nonlinear passive devices using different source metals can generate more self-interference signal distortion.

These unwanted additional frequencies can interfere with the uplink or downlink frequencies, which reduce the receiving cell sensitivity and disrupt communications. The article also says, “PIM lowers the reliability, capacity, and data rate of wireless systems by limiting the receive sensitivity. End results may include dropped calls, decreased system capacity, and decreased data rates.”

Most cellular operators address distortion issues caused by active devices. However, many wireless providers ignore distortions caused by passive network components, such as aging or dirty cables, connectors, and antennas. With spectrum use and antenna-sharing activities growing exponentially, network operators must understand the causes of PIM and add testing, identification, and resolution processes to their network maintenance strategy.


Sources of PIM distortion

Wireless providers have traditionally used frequency planning to avoid most PIM issues. However, PIM has become a much more serious issue for telecom carriers. In general, aging equipment, installing new equipment that overlays old antenna runs, or co-locating two or more carrier’s antennas in a cell tower can lead to significant PIM distortion. With that said, here are some of the most common technical causes of PIM in cellular network systems:


Impacts of PIM

PIM can have considerable negative impacts on the performance of a cellular system. Network coverage decreases when receiver cells become less sensitive to weak signals. This weak signal issue leads to dropped calls, significant interference, and disrupted communications services. In the case of data transfers, PIM tries to resend more error-protection bits, leading to even lower data transfer rates. PIM disruptions have even caused some cellular operators to experience a complete shutdown of their receiver sector.

Wireless network operators need to pay close attention to common indicators of PIM, such as:


Reducing the effects of PIM distortion

If your network isn’t as stable, reliable, or high-quality with as wide of a coverage area as you’d like to provide to your customers, or you want to avoid PIM distortion proactively, we recommend these strategies:


Proactively avoid PIM

While you may think PIM distortion is a trivial matter or something you can manage down the road, it could have a very serious negative impact on your network services over time. Our telecommunications experts are here to help you analyze your potential for PIM distortion and deploy strategies to reduce or avoid PIM with advanced, automated testing, detection, and resolution services to ensure your wireless network is as reliable as possible. Please visit us at