With network planning and network design in the can, the small cell deployment’s most critical phase begins: the actual indoor installation and commissioning. Or did you know that more than 50% of subscriber issues originate in the antenna system?
Many of these faults don’t necessarily trigger an alarm at the Operations Support System (OSS), at least not until a critical level is reached. Consequently, these errors could remain undetected by the network for a long time, causing a “silent” degradation of site performance and subscriber services.
For this reason, it is important to have a high-quality indoor installation and detailed tests right from the beginning. Usually, the installation phase involves members from many different teams. Performing measurements after each implementation is thus the only way to ensure that both the network quality and planned and expected capacity increase will be achieved.
Testing the new indoor installation
From a pragmatic point of view, the sooner a problem is identified and addressed, the easier and less expensive it is to solve. In passive and hybrid Distributed Antenna Systems (DAS), for example, technicians should always test the RF cable and antenna to avoid installing damaged goods. Sounds logical, but this step is often skipped, assuming it would save time. Now, just imagine the extra effort needed to change cables that have just been installed! Cable loss and distance-to-fault (DTF) measurements don’t take much time. Problems with a cable can be easily and quickly located with a cable and antenna analyzer, for example with our Cable Rider ZPH.
During the indoor installation, quality workmanship is key. When mating connectors, it pays off to make sure that cables are clean-cut and connector surfaces are spotless so as to prevent passive intermodulation (PIM). Little things, such as cleaning connectors with isopropyl alcohol instead of blowing on them, make a huge difference (our breath is moist and can start corrosion on connectors!)
How to minimize PIM during an indoor installation
The location of the new antenna has already been specified by the planning tools. During the installation, however, it is important to consider all objects in close proximity. Despite an indoor antenna’s low power levels, metal objects, such as mounting structures or air conditioning tubes, that get illuminated by the antenna can generate PIM. Moving the antenna between 50 and 100 cm, however, can considerably reduce PIM effects and keep coverage as planned.
Once the installation has taken place, reflection measurements should be performed to assess the complete antenna system. The return loss indicates how effectively the antenna radiates the energy (high levels of reflected energy can lead to transmitter damages). Cables that might have gotten pinched or broken during the installation have a negative impact on the overall return loss.
DTF measurements can help locate and correct these faults. Actually, these measurements can be carried out by using predefined test sequences, so that even non-technical staff can perform them fast and efficiently, without having to worry about missed measurements or erroneous settings. Static and dynamic PIM measurements help verify that the new cell doesn’t generate undesired intermodulation products, affecting the network.
Over-the-air testing after the indoor installation
After commissioning, spectrum measurements can show that the downlink (DL) signal is present, but they can hardly determine whether MIMO or carrier aggregation settings are correct. These verifications along with signal quality analysis can be achieved when the signal is demodulated, for example, with a handheld spectrum and signal analyzer such as the R&S®FSH. These types of tests are even more important in small cell deployments where no RF measurements can be performed during the installation.
Does the small cell have to coexist with a macro cell? If so, we recommend using a network scanner to get a complete overview of the network, technologies, and bands. Our ROMES test software, in combination with one of our TSMx scanners, can help identify potentially interfering neighbor cells with a high-speed and dynamic range.
This brings us to another common challenge in indoor scenarios: interference. Think of a shopping center with its many electronic and lighting devices. They’re all potential sources of interference. Spectrum measurements are the basis to verify that no interference is present. For a faster and more sensitive tool, some users prefer portable receivers. More on interference hunting in our webinar report.
When we talk about over-the-air (OTA) testing, we refer to spectrum and signal measurements, network scanning, and interference analysis. To guarantee signal quality, OTA-testing allows technicians to have an in-depth view of a signal that just went on air and the RF environment around it. In the end, the better the signal quality, the higher the increase in network capacity.
Test solutions for your indoor installation
From cable and antenna testers, spectrum and PIM analyzers to receivers and network scanners, we offer a wide portfolio of tools to keep testing quick and simple after installation and commissioning.
Are you now wondering about testing subscriber experience? Indoor site acceptance and testing quality of experience will be covered in the next and final post of this series on HetNets and small cells. Keep following us!