Interference Concerns Still Top of Mind

Ray Butler--thumbnail Ray Butler December 20, 2010

RCR Wireless hosted a Local Speaker Series on November 9 in Dallas under the title “Mobile Broadband: Innovation and Opportunity.” I was one of three Andrew Solutions folks on a panel that fielded a variety of questions about the status of 3.5G and 4G network roll-outs, the role and requirements of in-building systems, and the need for more green, energy-efficient network solutions. But one of my main takeaways was the continued concern about PIM interference in next generation networks.

If you’re not familiar, PIM is passive intermodulation distortion, which is a type of wireless interference that can degrade signal quality at a cell site. PIM usually results from wireless signals mixing together; if they are in the same frequency as the desired wireless signal, PIM interference causes disruption. PIM is especially of concern in next generation networks because it is easier to disrupt data signals to a point where subscribers experience poor quality. That’s why PIM continues to be a main issue when it comes to quality of service and network optimization.

So how do you prevent PIM?

Well, there’s no one trick, since all sources of PIM in the entire cell site combine to yield the total PIM distortion for the system. Some keys to limiting PIM’s impact, though, include:

• Start with quality products ideally envisioned as a complete system, where connections will be clean, properly torqued, properly attached, and resistant to material degradation.

• Make sure products are installed correctly. Probably the most significant causes of PIM are due to improperly installed equipment. Putting together a clear RF Path requires definite know-how and experience. Make sure you are using qualified, well-trained installers.

• Remember that testing PIM levels is challenging because readings are sensitive to test equipment and other surroundings that can increase PIM, resulting in false failures. If you aren’t familiar with PIM testing requirements, you might want to check out the Andrew Institute’s new PIM class.

Obviously this is a pretty cursory overview of a complicated and reasonably concerning topic. PIM has been on Andrew Solutions’ radar for awhile, but there’s always more to be learned. As my experience at the recent RCR event attests, PIM is still on a lot of people’s minds.

What’s on your mind regarding PIM and the networks of today and tomorrow?

About the Author

Ray Butler--thumbnail

Ray Butler

Ray Butler is vice president of Mobility Network Engineering at CommScope, responsible for wireless technical sales leadership in outdoor RF products. Before, Ray led the R&D team responsible for base station antennas, filters, combiners, remote radio heads and RF power amplifiers. He previously worked for Andrew Corporation as vice president of Base Station Antennas Engineering as well as Systems Engineering and Solutions Marketing. He has served as director of National RF Engineering with AT&T Wireless and vice president of Engineering, Research and Development, and International Operations at Metawave Communications, a smart antenna company. Ray was technical manager of Systems Engineering for Lucent Technologies Bell Laboratories, having also held other management positions responsible for the design of RF circuits, filters and amplifiers. Ray holds a Bachelor of Science degree in electrical engineering from Brigham Young University and a Master of Science in electrical engineering from Polytechnic University, and is a member of national engineering honor societies Eta Kappa Nu and Tau Beta Pi.