May 18, 2021
5G New Radio (NR) continues to be rolled out at an exponential rate. According to GSA, there were 756 announced 5G devices as of April 30, 2021. This is a 28.6% rise compared to the number of announced devices at the end of January.
Device availability is growing at an equally impressive rate. As of April 30, 468 5G devices were commercially available. This represents an increase of 28.2% since the end of last quarter. Slightly more than half (51.2%) of those devices are mobile phones.
Ensuring 5G NR UE operability as it is commercialized requires a greater emphasis on over-the-air (OTA) testing. OTA testing has been a verification method of 4G cellular technology since its deployment and standards adoption. It has gained more emphasis in 5G UE design due to the integrated nature of transmitters and the expanded use of millimeter wave (mmWave) spectrum.
5G Use Cases
To better understand the importance of OTA testing, it’s helpful to consider the advanced use cases associated with 5G:
- eMBB (enhanced Mobile Broadband) is focused on high throughput and supports high speeds from 5-20 Gbps. It is geared towards data-driven use cases in need of high data rates across a wide coverage area.
- mMTC (massive Machine Type Communications) addresses the explosion of devices in a variety of use cases and associated connectivity challenges. It can support up to 1 million devices per square km, including those that only send data sporadically. mMTC is particularly well suited for IoT environments.
- uRLLC (Ultra Reliable Low Latency Communications), with its 1 ms latency, is for mission critical use cases that demand extremely high reliability. Think remote surgery and autonomous vehicles.
OTA Measurement Fundamentals
As mentioned earlier, OTA measurements have been a conventional technique for 4G cellular device verification. Performance evaluations, antenna measurements, and MIMO verification are done via OTA.
For 5G NR, there are three main OTA tests to measure key UE characteristics:
EIRP (Effective Isotropic Radiated Power) is the total power radiated by a hypothetical isotropic antenna to give the same signal strength as the actual source in a single direction. Positive dBi values indicate gain; conversely negative dBi values represent loss.
EIRP CDF (Cumulative Distribution Function) is a combination of transmitted power and array gain. It measures power distribution at every angle. This evaluation is conducted to determine spherical coverage.
TRP (Transmission/Reception Point) is a measurement of radiated power at all possible angles. It is done to evaluate emissions, such as error vector magnitude (EVM). It is noteworthy that TRP can be calculated from EIRP.
A three-step test procedure is used to conduct these measurements:
- Lock the UE transmission beam
- Adjust the azimuth and evaluation angle
- Conduct the respective power measurement
Determining Measurement Distance
To ensure accurate measurements, the appropriate distance between the device-under-test (DUT) and measurement point must be established. Typically, OTA tests are conducted in either the near-field or far-field regions of the antenna array (figure 3). With far-field regions, the distance between UE to the measurement antenna is sufficiently far enough that there is no influence on the directional characteristics. The waves are approximated as plane waves at the measurement point. If the distance between the two is not far enough, it is considered to be in the near-field region, also known as radiative near field. In this scenario, the measurement result may be distorted by the measurement antenna.
Far-field conditions are typically achieved in one of two ways – Direct Far Field (DFF) or Indirect Far Field (IFF), which are outlined in figure 4. To create a DFF condition, the measurement distance must be greater than the far field distance. The only drawback to this approach is that as devices become larger, the test chamber needs to be bigger. This can increase cost and become tenable in a confined lab space. An example of an RF chamber for DFF is the MA8171A. It can be for conformance and protocol tests, such as 5G NR beam management.
IFF, also referred to as Compact Antenna Test Range (CATR), utilizes reflecting mirrors to generate plane waves at shorter distances inside the test chamber. As a result, a much smaller chamber, such as the MA8172A, is used to conduct RF conformance and compliance tests and spurious emissions measurements.
As mentioned, the near-field region uses no plane waves and the measurement antenna distorts the measurement results. The small and economical MA8161A shield box is used in this environment to conduct protocol and functional tests.
Creating a Test Environment
The Radio Communication Test Station MT8000A and Radio Communication Analyzer MT8821C are used in OTA test environments to provide core signaling, emulate the RF environment, and implement the protocol stack. Flexible solutions, they support 4G and 5G – both Standalone (SA) and Non-Standalone (NSA). They replicate a live network to create a real-world testing environment in the lab. Furthermore, the instruments meet all the OTA performance and compliance requirements set by various working groups and test plans of the Cellular Telecommunications and Internet Association (CTIA) and major global cellular operators.
Both instruments are part of an integrated 5G NR OTA test system at the Cetecom laboratories in Milpitas, CA. In this configuration (figure 5), the MT8000A and MT8821C are used with the ETS-Lindgren AMS-8600 Antenna Measurement System and EMQuest software to create a comprehensive testing environment.
You can learn more about OTA fundamentals and their importance on 5G NR UE verification by watching this webinar featuring Anritsu and Cetecom.
About the Author:
Keyvan Yasami is a Market Development Manager for Anritsu with 10+ years in the wireless industry. Keyvan holds a Master’s degree in Electrical Engineering from the University of Maine, and a Business Management degree from Harvard University
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