Testing 5G New Radio Devices

5G NR will require much faster data rates in order to support enhanced mobile broadband (eMBB) use cases like UHD video streaming, virtual reality (VR), and augmented reality (AR). As mobile operators accelerate their 5G NR deployment plans, chipset and device manufacturers must also accelerate their development activities, including determining how to test 5G NR data throughput most effectively.

The 5G eMBB (enhanced mobile broadband) use case targets data rates of up to 20 Gbps in the downlink (DL) and 10 Gbps in the uplink (UL). 5G NR accomplishes this by utilizing higher-frequency mmWave spectrum, in addition to using sub-6 GHz frequencies. LTE operates at frequencies up to 6 GHz, whereas mmWave operating bands up to 52.6 GHz are already approved in 5G NR Release-15. 5G NR introduces new frame structures and beamforming access procedures that increase design complexity, increasing design difficulty and functional prototype test procedures.

Top challenges testing 5G NR device throughput include:

• Configuring 5G NR frame structures for higher throughput
• Configuring 5G NR devices to make and report measurements for optimal link adaptation

Optimizing 5G NR beamforming performance at mmWave frequencies

5G NR frame structures. 5G NR introduces flexible numerology that scales the subcarrier spacing. The scalable slot duration allows the subcarrier to be optimized for different types of service levels, balancing throughput, latency, and reliability. Subcarrier spacing is governed by 2μ x 15 kHz subcarrier spacings. 15, 30, and 60 kHz subcarrier spacings are used for the lower frequency bands, and 60, 120, and 240 kHz subcarrier spacings are used for the higher frequency bands. Figure 1 shows that as the frequency increases, slot duration is shorter in time, decreasing the TTI (transmit time interval) and optimizing the subcarrier spacing for the operating frequency band and channel characteristics.

In TDD (time division duplex) bands, 5G NR also allows dynamic TDD operation where the network can dynamically assign each slot to be DL or UL. This allows more efficient use of the spectrum. By using dynamic TDD, the network can allocate more or fewer resources for DL or UL, depending on the specific traffic requirement of the network, device, and service being provided.

While testing 5G NR device throughput, it is critical to have access into the lower-layer frame structure to configure and test for maximum throughput.

Beamforming performance at mmWave frequencies. Beamforming can be used to overcome propagation and penetration losses at higher frequencies. Beamforming achieves a stronger signal-to-noise ratio (SNR) by using high directive radiation beams that provide additional antenna gain. The following new procedures for beamforming have been defined in the 5G NR specifications:

• Beam acquisition and tracking
• Beam refinement
• Beam feedback
• Beam switching

5G Throughput Test Solution

Using a network emulator, layer 1 (PHY), layer 2 (MAC/RLC/PDCP), and layer 3 (RRC/ NAS) can be simulated to create data throughput tests.1

A sample test configuration (figure 3) uses the Keysight 5G Protocol R&D Toolset to create the test and configuration script elements. Power levels for synchronization and reference signals, beamforming, and resource blocks used for transmitting and receiving control information and data are specified.

A script is used to evaluate data throughput, and an integrated real-time trace displays the progress of the test including layer 3 protocol messages being sent and received. With the dynamic control points enabled, a test engineer can modify parameters in real time.

The Log Viewer includes a KPI viewer that captures key performance indicators at different layers. This includes throughput graphs at different layers (PHY/MAC/ RLC/PDCP and application layer), CQI (channel quality information), MCS (mobile switch center), BLER (block error rate) and ACK/NACKs (acknowledgement/negative acknowledgement) versus time, providing insight into possible bottlenecks in the design. From a signal quality perspective, KPIs like BSI (beam state information) and BRI (beam refinement information) can be verified to ensure that the UE (user equipment) has selected the strongest beam.

Since 5G NR implements new frame structures and beamforming techniques at mmWave frequencies, having a test platform that enables evaluation and tuning at different layers of the protocol stack can be very valuable. Keysight’s 5G Protocol R&D Toolset provides an easy-to-use solution with the ability to monitor and make changes at different layers of the protocol stack, providing insights for rapid optimization of device throughput.

3GPP 5G NR Release-15 specifies mobile operation up to 52.6 GHz. To overcome higher path loss and multi-path propagation issues at these higher frequencies, beam steering or beamforming will be used. Beam steering is not new and can provide high directivity signals to a desired direction. However, beam steering for mobile communications at mmWave frequencies requires new access techniques that need to be tested and validated. Devices and base stations need to find each other and maintain a quality communication link while the device moves through the network.

5G NR devices operating in the new frequency range 2 (FR2) mmWave operating bands are likely to have their antennas integrated into the chipset and handsets making it difficult to probe for conducted tests. Therefore, over-the-air (OTA) testing is expected to replace traditional conducted test methods that were used in sub-

6 GHz designs. OTA testing can also provide a more realistic assessment of beam performance in real-world scenarios.

Top challenges testing mmWave beamforming include:

• Validating mmWave initial access
• Optimizing mmWave beam tracking and switching
• Testing beamforming over-the-air (OTA)

Conclusion

New 5G technologies and performance improvements are driving the need for new test methodologies. As flexible numerology, more complex waveforms and channel coding techniques, frequencies that extend into mmWave, wider channel bandwidths, and advanced multi-antenna access schemes are implemented in 5G devices, designers need to access multiple levels of the protocol stack to sufficiently test throughput and beamforming performance. In addition, the need for OTA test solutions complicates the situation even further.

Keysight partnered early with industry leaders to understand the complexities of 5G and to develop test solutions that span the entire workflow, from simulation and development, to design verification, conformance and acceptance test, and ultimately to manufacturing and deployment.

Our solutions leverage the same measurement techniques throughout the workflow to ensure consistent results, guiding you to the appropriate test solutions specified by chipset vendors and operators, enabling you to leverage measurements and get to market faster.