Interference management in 5G with drones
How can drones help us to protect the radio airwaves? In our latest Research blog post, we explore how radio-scanner drones can be used to protect network performance by measuring and evaluating outdoor radio signal interference from private indoor 5G networks. Could this be the future of interference management in 5G? Read more below.
5G is designed with demanding industrial applications in mind and is a central part of the industry 4.0 vision. For these use cases, such as in factories, consistent high performance can be critical. One attractive solution for business owners is purpose-built private 5G networks.
Enabling wireless spectrum for private 5G networks
Wireless spectrum for industrial 5G networks can be accessed in several ways. The network can be deployed on mobile network operator spectrum, directly by the network operator or by another party leasing the spectrum from the operator. Another option, that has been discussed in several countries such as Germany, Japan, United Kingdom, France and Sweden, is to issue local spectrum licenses directly to property owners, for example.
Regardless of how the spectrum is accessed, radio signal interference to surrounding networks needs to be controlled and kept below certain limits, because interference is a key factor affecting network performance. Without efficient methods to manage interference, dedicated industrial networks can end up disturbing other surrounding industrial networks or the macro networks used by other subscribers and applications.
Typically, this has been ensured either through calculating the interference with propagation prediction tools or by doing signal measurements with walk tests or drive tests.
Using drones to measure radio signal interference
Drones, or unmanned aerial vehicles (UAVs) as they are technically referred to, offer new opportunities. When it comes to evaluating interference from indoor systems, measurements using UAVs has several benefits compared to the traditional methods. Propagation prediction tools require significant work in order to model the building accurately and does not take environmental changes, such as installation of new industrial machines, into account. Traditional interference measurement methods, such as walk- and drive tests, are time consuming and can present difficulties to ensure consistency in the measurements.
Figure 1. A bird’s perspective of the industrial site where the measurements were performed. The main measurement path is shown with a blue line. Shown in yellow is the approximate position of the indoor 5G base station (X) and its main antenna lobe.
UAVs, equipped with a radio scanner that can detect 4G and 5G signals, can be programmed to perform the measurements along a predefined 3D flight path which can be repeated several times for increased accuracy. It is also possible to take the measurements at several heights. This offers a significant advantage as radio signal interference is strongly height dependent.
In order to verify the feasibility of using UAVs for this purpose, our research teams made a series of flight tests in collaboration with Centria University of Applied Sciences and Tampere University in Finland. The tests were performed outside the Ericsson R&D site in Jorvas, a former factory currently repurposed as office space. An indoor 5G new radio system operating on the 3.5 GHz (band n78) was deployed in the middle of the building and had a directional antenna pointing towards the outer wall (see Figure 1). The transmission power was set to 2 watts.
The UAV was equipped with a radio scanner from test equipment vendor Rohde & Schwarz that can detect 5G NR signals and measure key parameters such as the “synchronization signal reference signal received power” (SS-RSRP).
Figure 2. An example of the measurement results showing the measured signal strength (RSRP) outside the building wall and above the building.
An example of our results can be seen in Figure 2 where the outdoor signal strength along one of the walls at five different heights and along three paths above the building is shown. A more detailed analysis of the results shows a large variation in the signal strength at different heights which would have been difficult to detect with traditional measurement methods. Larger structures in the building such as windows is clearly visible in the signal.
UAVs can also be used for many other measurements in cellular networks. Today, 4G networks solutions are already commercially available, for example, the Ericsson connected drone testing solution.
Why interference management is important
To emphasize the importance of efficient interference management, let’s take a look at an example – the ongoing discussions for local spectrum licenses in Germany.
Under the German proposal for local licensing within the 3.4-3.8 GHz band, neighboring license holders will need to agree on appropriate network configurations to avoid interfering each other. If no agreement can be made, an emission limit of 32 dBμV/m/5MHz should be used in 3 meters height at the border of the license area. If we put the measurement results from our tests into this context, we find that the interference limit would not be met. In Figure 2 the limit corresponds to an RSRP of -138.8 dBm, and as can be seen this value is exceeded for the majority of the measurement points. Thus, the indoor network could not be operated on the used transmitter power without violating the interference limit and appropriate actions need to be taken, e.g. by reducing the transmitter power.
After the reconfigurations are complete, the measurements can easily and quickly be repeated along the same measurement paths to verify that the changes have had the desired effect. This clearly illustrates the value of using UAVs for interference management in 5G cellular networks.
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