The rusty bolt effect: Why telcos should invest in PIM analyzers

With the push for wireless connections in full swing, it can be easy to overlook the importance of the physical components underlying telecom networks. However, the makeup and attributes of that hardware can have a substantial effect on the overall performance and functionality of advanced carrier environments. The “rusty bolt effect” has long been a concern for telcos as a seemingly insignificant piece of structural hardware can prevent signals from being transmitted along a clear path. Something as minor as the aforementioned rusty bolt with its corroded material can cause interference that directly impacts network performance. As carriers expand their infrastructure and develop more advanced services, the overlapping environments take this concept even further with passive intermodulation distortion.
Telecom growth breeds interference
As the telecom world migrates to the next generation of mobile networks, existing structures and new technologies can clash, causing interference across both environments. Adrian Nash, the previous team leader for Aeroflex Wireless Test Solutions’ digital signal processing division, explained that when the signals from 2G and 3G networks intersect, for instance, additional signals are created which can then clog up frequencies. Corroded fixtures often exacerbate these issues by acting as a semiconductor, increasing the likelihood that problematic signals will be picked up by receivers.
Nash warned that if carriers ignore the threat of PIM, they could see their network sensitivity and functionality drop drastically, reducing the coverage of a mobile network.
“The PIM interference in the receive channel adds directly to the thermal noise, thus degrading the signal to noise ratio of a user’s signal,” Nash wrote. He added, “As a result, the basestation cannot receive signals from user terminals distant from it and can only guarantee a Quality of Service over a reduced range.”
Even a slight drop in sensitivity can significantly impact a network’s coverage area. According to Nash, even a 1dB decrease in uplink sensitivity can result in a carrier’s coverage contracting 11 percent. Furthermore, these conditions can place greater strain on certain network components used to maintain standard functionality even in the midst of PIM interference. Network administrators may push the output of nearby terminals by transmitting at a higher power, resulting in even more interference within the network and further impacting cell tower coverage.
Test and measure for PIM
To avoid such issues and enable wireless networks to reach their optimal output, carriers should employ PIM analyzing equipment to measure frequency activity and identify potential problems. In particular, a communication system’s bit error rate can offer a great deal of insight regarding the effect that PIM is having on overall functionality. This measurement will accurately indicate how service delivery will be affected on the user end. According to an Anritsu white paper, a high BER can indicate that there is a greater likelihood of calls being dropped on the network. An analysis of an environment suffering from PIM may also demonstrate lower data rate speeds and call volumes as well as distinctly shorter durations for the average call. Furthermore, PIM can become so disruptive that it can completely block the receiver, resulting in a total shutdown of services in a localized area.
Running PIM tests will help network administrators identify dead zones and begin taking steps to address interference issues. As carriers expand their coverage area or build upon existing infrastructure, they will need to consider how their physical components may affect the quality of their services. This is especially true now that so many telecoms are simultaneously supporting 3G, 4G and 4G LTE networks, creating complicated environments that may prove to be fertile ground for PIM interference.
​Looking to the future
Anritsu noted that although PIM testing has historically been conducted at the installation stage by equipment manufacturers, more telecom members are analyzing their hardware on site these days. Diligently measuring associated performance metrics and staying on top of maintenance duties will help carriers avoid PIM-related issues and keep their networks functioning at a high level. Technicians should inspect equipment for damage and corroded material at regular intervals and be sure to clean all connections.
Purchasing PIM analyzers is a sound investment as carrier networks are only going to get more complex in the future, dramatically increasing the likelihood that signal interference will occur. In the long run, preventive measures such as PIM testing will enable telecoms to provide better services to end users, reducing customer attrition and bolstering revenue streams.
“PIM testing is becoming more critical as cellular systems age and the carrier count is increased,” the Anritsu white paper stated. “A test that was not as important when cellular systems were lightly loaded is becoming a critical part of modern cellular maintenance.”