Addressing the Challenge of Over the Air Interference


One of the top reasons end-users switch carriers is dissatisfaction with network performance, which could be spotty coverage, dropped calls, or slow data speed. Knowing this, many mobile operators focus on minimizing any signals that impede the over-the-air connection between their end-users’ devices and their radio towers– a killer of network performance. For mobile operators, testing and mitigating uplink interference can generate significant business value by delivering a better customer experience and consequently reducing churn.

First, let’s look at what causes signal interference and why is it so critical to address. It’s also important to distinguish between downlink (DL) and uplink (UL) interference and how to identify and test for them. For UL interference, there are three main types:

  • PIM (Passive intermodulation)
  • Interference in time division duplex (TDD) signals
  • External sources

Historically, carriers or their contractors had to carry multiple tools to be able to detect these different interference sources – at increased expense, time and even safety concerns for the technicians who might be required to climb the towers. Add to that the expertise needed to effectively use a spectrum analyser and RF testing began to be perceived as an onerous task, even one to avoid. Today, it doesn’t have to be that way. VIAVI has consolidated multiple test tools into one platform – the OneAdvisor 800 Wireless – which simplifies the job. But first, here are three of the top challenges that impact network performance.

The first is Passive Intermodulation (PIM). PIM occurs when two or more signals mix at a passive (unpowered) component, such as an antenna or cable, which creates both harmonics and products of varying orders. Unwanted modulation can create interference and negatively impact signal transmission. If the site was not installed properly or maintenance is inconsistent, PIM can become very problematic. It’s also important to note that not all PIM sources are on the feedline or tower. Sources can be nearby, making detection more complicated.

Another challenge is keeping network timing tight, which directly impacts tower/antenna synchronization. To address timing and synchronization, operators used a technique called Frequency Division Duplexing (FDD) for years with very few issues. Unfortunately, a 5G network has a very tight timing budget and FDD alone is no longer sufficient to support it. Mobile operators are now turning to Time Division Duplex (TDD) to address these new challenges. TDD brings many advantages over FDD – especially far greater spectral efficiency to support high data rates. However, its advantages are partially offset by the precise timing and synchronization required to prevent inter- and intra-cell interference. Just identifying the right TDD uplink slot configuration alone is a challenge.

In addition to PIM and timing and synchronization issues is the prospect of identifying and eradicating external RF interference within the coverage area of a cell tower. Adding to the difficulty is that RF interference sources can come from anywhere, from a streetlight with an electrical short to a signal booster on top of a business. Interference management is a critical yet often difficult aspect of maintenance, requiring both the right tools and expertise.

Luckily, testing technology has advanced in lockstep with the network technology. With the VIAVI OneAdvisor 800 Wireless, you can now address all three categories of interference – PIM, timing and sync, and external RF interference – with a single, compact device. Not only is OneAdvisor 800 Wireless a complete solution that enables the consolidation of multiple test tools, but it also packs value-added features into each test category making the user’s job much simpler.

TestEquity are an approved UK partner for VIAVI
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