5G Channel Sounding
The need for higher data rates and thus higher bandwidth for 5G makes it necessary to adopt significantly higher carrier frequencies compared with today’s cellular network implementations below 6 GHz.
Various research projects initially discussed a frequency spectrum in the range of 6 GHz to 100 GHz. The first 5G deployments above 6 GHz are expected to be in the 28 GHz and 39 GHz spectrum range. The entire industry needs to learn how signals in emerging high-frequency bands with very wide bandwidths propagate through the radio channel. Channel sounding is the required process that allows a radio channel to be characterized by decomposing the radio propagation path into its individual multipath components. This information is essential for developing robust modulation schemes to transmit data over the 5G radio channel.
Initially, mobile network operators, research institutes, universities and other industry players conducted extensive channel measurement campaigns in order to define 5G channel models for standardization bodies such as 3GPP. Though some channel models have recently been defined, 5G channel sounding campaigns are still ongoing since channel characteristics at higher frequencies clearly differentiate from the characteristics at traditional frequencies below 6 GHz:
- Since path loss is significantly higher, highly directional beamforming will be required in the mmWave domain.
- Oxygen and water absorption (e.g. rain or humidity loss) has to be taken into account for specific bands.
- The coherence time of a radio channel is much shorter.
- The attenuation of most obstacles is stronger (e.g. even high foliage loss is present).
- Specular reflections are more common in mmWave.
5G NR test solutions for channel sounding
The Rohde & Schwarz test solution for 5G channel sounding is based on the pulse compression method. The R&S®SMW200A vector signal generator transmits a band-limited channel sounding signal at the frequency of interest. The radio channel alters this signal depending on the surrounding environment, which can include obstacles, reflections, scattering, oxygen absorption and movement. The R&S®FSW signal and spectrum analyzer receives and processes the signal from the channel and forwards the resulting I/Q data to the data analysis software. The software correlates the received I/Q data with the originally transmitted signal in order to estimate the channel impulse response that describes the radio channel.
The applied 5G channel sounding signals exhibit very good autocorrelation properties, which provide an additional processing gain. Nevertheless, this method can only be used when both the signal generator (transmitter) and the signal analyzer (receiver) provide the needed bandwidth capability. The R&S®SMW200A and the R&S®FSW both offer up to 2 GHz internal bandwidth, allowing an excellent echo time resolution of up to 0.5 ns.
The channel sounding test solution from Rohde & Schwarz enables direct measurement of the channel impulse response (CIR) in the time domain. Using a signal generator and a signal analyzer allows fast CIR measurements over the full bandwidth. This approach is much faster and more flexible than a test setup based on a network analyzer. Since the R&S®SMW200A and the R&S®FSW offer very high reference frequency stability, relative power delay profile measurements can be performed without the need for synchronization, making this test solution ideal for 5G outdoor channel measurements over longer ranges.
The channel sounding measurement setup from Rohde & Schwarz provides a unique dynamic range due to the R&S®FSW analyzer’s high receiver sensitivity and built-in low-noise power amplifier. A further increase in dynamic range is possible by the use of special channel sounding signals that enhance the achievable processing gain.
Products for 5G channel sounding
-
R&S®SMW200A Vector Signal Generator
Generation of a frequency band limited signal based on a special pseudo-noise (PN)
-
R&S®FSW Signal and Spectrum Analyzer
Unique dynamic range due to high receiver sensitivity and built-in low-noise power amplifier
More About 5G
- 5G channel sounding – flexible and ready for use cm- and mm-wave test solution
- Webinar: Internet of Things (IoT) and over-the-top (OTT) applications
- Webinar: Unleashing 5G mm-Waves - a Test & Measurement Perspective
- Video: Unleashing 5G mm-wave frequencies presented at GSMA MWC 2015
- More Information
- Rohde & Schwarz and Fraunhofer HHI realize 5G millimeter-wave channel sounding test solution
- The R&S SMW200A creates digitally modulated signals up to 40 GHz for complex A&D and 5G applications
- Rohde & Schwarz implements unique 2 GHz analysis bandwidth in R&S FSW high end signal analyzer