Overcoming testing hurdles of 5G

Soma Tah

5G has added a new level of complexity to the devices. For engineers who are developing complex 5G systems, testing poses a set of technical challenges previously unheard-of, and hence, need to be addressed by new test techniques. Over-the-air (OTA) testing is one such technique that is becoming increasingly crucial for testing 5G devices and components.

Alejandro Buritica, Semiconductor Marketing Specialist, National Instruments(NI) takes a deep-dive into the testing challenges in the 5G era and shares more detail on the OTA testing. 

What challenges does 5G pose in terms of Testing?

One of the major alterations that 5G brings is an increase in device complexity because they operate in wider channels and many more bands, including in the millimeter wave (mmWave) mmWave bands above 24 GHz. This complexity demands new test techniques that can adapt quickly to these changes. The move towards mmWave bandwidth frequencies is one of the biggest areas where 5G is affecting test and measurement. 5G components for mmWave applications operate between 24 and 45 GHz, and rely on large antenna arrays to overcome high losses through space. Manufacturers are creating antenna arrays with multiple elements (8, 16, 32, 64 or more) in small spaces, or in many cases, in a single package. This is commonly designated as Antenna-in-Package (AiP), and it’s mostly targeted for mobile devices. The goal of these new 5G devices is to take advantage of antenna array gain by beamforming the signals. The miniaturization of these arrays to the chip level in 5G mobile devices makes it much more difficult, if not impossible, for test engineers to test the device at the antenna ports directly, forcing them to implement Over-the-Air (OTA) test scenarios and test models.

OTA testing relies on beam-steered measurements of the radiation patterns to determine how the antenna array is concentrating its power as the radiation angle changes. 5G test methodologies also include measuring the modulation accuracy of the beamformed signals. However, OTA tests need to happen in properly controlled RF environments, and at specific distances (far-field) from the device under test (DUT). Sweeping the beam in space and measuring in various directions as the results are integrated usually requires isolated RF enclosures (RF chambers) and precise mechanical DUT manipulators. Comprehensive OTA characterization of 5G devices can result in very long test times.

Besides testing large antenna arrays at mmWave frequencies, there are test challenges related to testing devices that must support simultaneous operation of 4G and 5G technologies below 6 GHz. This can be in both non-standalone mode, in which the network and the User Equipment must support concurrent operation and signaling using the existing 4G infrastructure to support 5G connections; and in standalone mode, in which the 5G network and devices don’t need any support from legacy standards.

How can engineers address the fast-evolving 5G test requirements? What are the limitations in the currently available OTA testing techniques?

As 5G defines the way forward for the industry, test engineers must now contend with exponential miniaturization of technology that seeks to deliver greater utility at similar or lower costs. The digitization of all industry processes has also affected the testing ecosystem with traditional techniques that relied on physical connections now giving way to wireless technology. OTA testing is trying to become the industry standard, but there are still some technical test conditions that haven’t been fully specified and studied for maximum test efficiency. OTA testing, in general, eliminates the need to check each antenna element of the array separately, focusing instead on the overall performance of the array. One of the biggest driving forces for mmWave OTA test engineers is reducing test times and test complexity while maintaining product quality. To that effect, there are several active areas of research in terms of Near-Field to Far-field conversion to reduce RF chamber size, antenna radiation pattern matching, speeding up DUT manipulation, and specifying a reduced set of production test steps. Optimizing production throughput by reducing test sequence execution time will play a critical role in cost-effective deployment of new mmWave 5G systems.

Which areas of 5G testing are you currently focusing on?

We’re currently focusing on further optimizations of our successful sub-6 GHz device testing techniques, and on testing new devices for beamforming with antenna arrays, such as digitally controlled PAs, LNAs, phase shifters and mixers. We’re taking advantage of NI’s software-designed test platform to keep pace with the latest 5G NR PHY layer requirements. We benefit from our instruments’ large instantaneous bandwidth to test wider NR component carriers and carrier-aggregated signals. NI’s high-bandwidth instrumentation also allows for linearization of the DUTs using digital pre-distortion techniques. Furthermore, the NI platform provides for phase-coherent and time-aligned expansion into multi-channel measurement systems for comprehensive test coverage of the latest 5G NR semiconductor devices.

Given today’s rapid development cycles, flexible and scalable test methodologies will be critical for OTA testing. NI continues to collaborate very closely with industry leaders on highly modular, software-defined test strategies and solutions to ensure their capital expenses keep pace with the wireless industry’s ever-evolving test needs.

(The article was first published in Voice & Data).