Feature: Test & Measurement
causing propagation delays to vary depending on the position of the satellite. Te satellite only becomes visible on the horizon when it reaches the minimum elevation angle (sunup) and disappears again when it falls below this angle (sundown). Te propagation delay is longest at both of these times and shortest when the satellite is positioned directly above the transmitter or receiver (Fig. 3). Tis has consequences for the higher
protocol layers. On the one hand, they have to tolerate a longer propagation delay, while on the other, they have to synchronise the signal received by the satellite. Te timing advance (TA) method can be used to overcome these challenges, but it is important to bear in mind that synchronisation with 5G NTN is much more difficult than it is in a purely terrestrial network.
Doppler effect Compared to a network of fixed base stations, a constellation of satellites that can quickly change their relative position to the end-user device represent a paradigm shiſt. Te high relative speed of satellites to ground stations causes the frequency to shiſt, a phenomenon known as the Doppler effect. How much the frequency shiſts depend on the frequency used, the height of the satellite’s orbit and its relative speed. In Figure 3, Te Doppler shiſt is plotted against the elevation angle and follows an S-curve. To compensate for this, the satellite sends
trajectory data (ephemeris) to the device with system information. Te mobile device uses navigation services (GNSS) to determine its own terrestrial position and pre-compensate for the Doppler shiſt.
The role of test and measurement equipment in 5G NTN and IoT NTN Te measurement methods used in non- terrestrial networks need to be adjusted, both in terms of infrastructure and end-user devices. To verify device reliability, a system simulator must simulate not only high latency and the Doppler effect but also signalling parameters and handover scenarios. In some scenarios, positioning also requires a GNSS signal.
Test solution for end-user devices Combining the R&SCMW500 wideband radio communication tester with the R&SSMBV
Figure. 4: Various test solutions for 5G NTN devices: Combining the R&S SMBV100B signal generator and the R&SCMW500 radio communication tester (left) emulates IoT NTN use cases. Users can test NR NTN applications by combining the signal generator with the R&SCMX500 radio communication tester (right).
vector signal generator creates the perfect test solution for IoT NTN applications. Tis setup emulates a GNSS navigation signal that allows the end-user device to determine its position Te R&SCMW500 lets users test physical parameters, signalling processes and end-to- end connections (E2E). Tey can also expand this setup by adding the R&SCMX500 radio communication tester to test NR NTN- capable devices.
Test solution for infrastructure Signal generators and signal analysers can be used to test the functions of infrastructure components like satellites. Rohde & Schwarz has expanded the capabilities of the R&SSMW200A signal generator to emulate
radio channels, which allows receivers to measure infrastructure components. Te R&SFSW can be used to test the transmission properties of infrastructure components, including spectral measurements for interference emissions and coexistence testing.
Re-looking test metrics 5G NTN also affects test metrics such as over-the-air (OTA). For example, if a moving satellite and end-user device are 1000 kilometres (621 miles) apart and both are using beamforming antennas, then a beam-peak deviation of 1° in the direction of the transmitting antenna will cause it to shiſt by 30 kilometres (19 miles) on the receiving side. Tis yields useful new test metrics such as directional beam accuracy, long-term stability of antenna characteristics and the speed and accuracy of readjustment. Rohde & Schwarz offers customers additional test and measurement equipment to monitor satellites, design satellite links and even aid the production of highly integrated parts and components for satellite technology.
Future prospects Tree-dimensional, uniform and organic network structures are the long-term goal of 5G NTN. Although 5G NR Release 17 laid the foundations for 5G NTN, it should only be viewed as a springboard. Two ecosystems that were previously separate, satellite and mobile communications, are now growing together. Rohde & Schwarz is one of only a
Figure 5: The R&SSMW200A signal generator and the R&SFSW signal analyser. Satellite manufacturer Thales Alenia Space in Madrid uses these devices to test infrastructure components for 5G NTN.
handful of companies that can be called a global technology leader in both mobile communications test and measurement technology and satellite communications. Te company helps further develop this technology with proven expertise and extensive experience.
www.electronicsworld.co.uk Dec 2024/Jan 2025 35
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