RF interference is one of the largest contributors to poor network performance. It manifests itself in dropped calls and low data throughput rates. When you invest in new bands to improve network performance and then get less than 50% of the expected performance improvement, it is time to tackle the problem head on. In LTE, for every 10 dB less signal-to-interference-plus-noise ratio (SINR), you lose 50% of your network capacity.
The objective is to prepare new frequency bands for the deployment and switch-on of LTE or 5G NR networks by characterizing the radio environment and conducting spectrum clearance. The principal task ahead is to identify and eliminate external interference sources, which are most troublesome in the uplink.
Traditional RF Interference Hunting
Traditionally, RF interference hunting means that you get a list of sites with bad performance, according to the operations support system (OSS). The sites on the list define the areas for interference hunting. Next, you send a dedicated interference hunting team to the specific site sectors to start hunting.
One of the main factors delaying the interference hunting process includes overlapping signals. The trouble is, once you switch your new network on, external interference signals overlap with your network’s signals. This situation leads to the idea of clearing the spectrum before the network is being rolled out to prevent masking by your network’s signals.
However, this idea creates a new challenge: until you have deployed a network, there is no OSS and, of course, no list of sites with bad performance. Therefore, interference hunting has to be done in the entire network area. The area, however, could include cities or even countries. An error-prone task when using traditional spectrum analyzers and portable receivers, not to mention the significant amount of time, budget and resources this would entail.
5G NR Interference Hunting Challenges
5G NR will initiate a worldwide deployment of time division duplex (TDD) networks in an unknown radio environment where unwanted transmitters will create uplink interference that is masked by the network’s own downlink signals. A TDD network downlink (DL) and uplink (UL) use the same frequency band in different time slots. When viewing such TDD signals on a conventional spectrum display, it is impossible to differentiate between the two and any other unwanted signals present in the same spectrum. This makes interference hunting extremely difficult. In such a scenario, interference hunting becomes a particularly demanding task. It uses traditional manual techniques and can be greatly assisted by the automated detection of interference signals before the network is switched on. If this task can be automated, it will vastly reduce the time and difficulty of the process.
R&S Automated Spectrum Clearance Solution
The R&S®TSMA autonomous network scanner, which is battery powered, fits neatly into a shoulder bag for comfortable drive or walk tests. The R&S®ROMES4 drive/walk test software runs on the “Next Unit of Computing” PC integrated into the R&S®TSMA. The software is supported by a GPS receiver and a mapping capability. The R&S measurements are controlled by a tablet that displays the results to the user in real-time.
The Rohde & Schwarz automated spectrum clearance solution for LTE and 5G mobile networks offers:
- Central measurement control: predefined measurement setups can be distributed, ensuring good quality of measurement results
- Extremely sensitive scanner (able to scan the complete uplink 30 MHz bandwidth with –130 dBm DANL) enables quick and precise separation between clear spectrum and interference sources
- Very fast scanner allows more data to be collected per test time (or shorter measurement time for the same amount of data)
- Proven drive test platform able to handle large volume of data
- Fast automated and integrated postprocessing tool
How to Clear the Spectrum
To effectively clear the spectrum in LTE or 5G mobile network, three steps must be completed before the network is switched on:
Step One – Identify/map interference sources: collect spectrum data by driving a scanner, like the R&S®ROMES4, around the site. Use the RF power scan to measure the spectrum on a given frequency range. You can use any number of cars, depending on how fast you want to be, and the size of the area identified for interference hunting.
Step Two – Post-processing spectrum data: Once collected, hand over the location, frequency and spectral shape to interference hunting teams for post-processing. Use the network problem analyzer (NPA) with the R&S®ROMES4N18 spectrum analysis module to automatically detect interference in the bands that should be empty; since the network has not been rolled out yet. After you have configured the settings (bandwidth, duration, power, etc.), the analysis algorithm finds potential narrowband and wideband interferers and lists them with geolocation, level and frequency.
Step 3 – Find the interference source and eliminate it: start interference hunting with a receiver and a directional antenna to find the source quickly. With the list of interfering signals at hand, the interference hunting team’s task is set. They can start closing in on the source of inference and identify the device causing the problem.
Compared with the “traditional way” of directly deploying interference hunting teams equipped with spectrum analyzers or handheld receivers to the relevant area and manually searching for interference, the above method has three main benefits. First, the identification of potential interference signals and their characteristics is far faster than when using manual techniques. Second, since the collection of data and analysis of data are done separately, data collection, which is the most time-consuming part, can be achieved far more quickly using less skilled personnel. Third, the experts in the interference hunting teams are more effective because they concentrate only on the predefined interference spots.
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