Testing mmWave equipment for 5G applications
By David Hall, NI
Cellular operators are already working to win over consumers through marketing the capabilities 5G technology brings to society. Through this, operators look to keep customers within their networks, as the ability to sell upgraded network speeds is crucial to compensate for the time, money and research spent on these new networks. While switching to 5G may seem like a relatively simple task, in reality, it comes down to the years of hard work from infrastructure manufacturers, standards committees and engineering teams.
With the rise of 5G, RF engineering, an occupation that already involves working with technology that can be inherently unpredictable, has become even more complex. Due to data rate mandates set by 3GPP standards committees, new and innovative solutions have been developed to integrate with current infrastructure.
5G brings mmWave frequencies between 24 and 40 GHz, along with the need to deal with spectral coexistence with multi-radio access technology systems in the sub 6 GHz frequency range. With these challenges, it is vital to have an all-encompassing test regime throughout the development of 5G systems, from smartphones to infrastructure equipment.
A crucial factor, from a technical standpoint, is maintaining continuity with operator and 3GPP committee specifications. These include a variety of parameters, such as modulation quality, receiver signal-to-noise ratios, transmitter efficiency and RF amplifier linearity. Further, using mmWave functions has created semiconductor design obstacles. Adding onto this, these new propagation and signal path factors have not been experienced with sub-6 GHz cellular technology that is currently utilized.
Figure 1. Potential test insertion points of new 5G architecture components (source NI).
Figure 1 outlines a possible test regime and points for 5G hardware. Engineers must be able to utilize test hardware, test sets and 5G waveform generation that can be used in tandem with high-bandwidth IQ waveforms. Additionally, RF transceivers must also undergo extensive testing.
Much of the above has similarities to the signal chain that is associated with 4G equipment, but it is important to note that 5G capabilities need to leverage beamformers and front-end modules (FEMs). 5G operation at mmWave frequencies relies on beamforming technology through antenna arrays with many elements.
As the industry strives to reduce the size and cost of producing these 5G beamforming devices operating at mmWave, many lack conventional external RF connectors, becoming integrated Antenna-in-Package (AiP) and Antenna-in-Module (AiM) devices. This industry shift presents a tough challenge for engineers in charge of characterization and validation of integrated beamforming designs, prompting them to look for accurate, over-the-air (OTA), radiated test solutions.
Working with wide signals below 6 GHz and at mmWave frequencies requires characterizing and validating greater performance out of RF communications components. Engineers must not only test innovative designs for multiband power amplifiers, low-noise amplifiers, duplexers, mixers and filters but also ensure that new and improved RF signal chains support simultaneous operation of 4G and 5G technologies. Additionally, to overcome significant propagation losses, mmWave 5G requires beamforming subsystems and antenna arrays, which demand fast and reliable multiport test solutions.
Transmit and receive path reciprocity must also be evaluated. Compression is created when power amplifiers produce phase shifts and amplitude. In turn, tolerance of RF components like variable gain amplifiers and variable phase shifters can create phase shift changes and have an impact on the clarity of FEMs.
For 5G, beamforming test systems must encompass a wide spectrum, while also testing the compression behavior and maximum linear output of multiple paths. A test solution that is quick and has bi-directional multi-port switching is pivotal in a 5G test environment.
To get the most accurate measurements of performance, as well as the best characterization of the beamformer and FEMs, OTA testing is ideal. OTA test needs may vary greatly among different applications and DUT types. To help engineers adapt to different test situations, the mmWave OTA Validation Test Software offers a modular approach, extensible to various user needs, like customized DUT control, specific sweep configurations and signal routing.
Figure 2. NI mmWave OTA reference solution diagram (source NI).
Figure 2 showcases the NI mmWave OTA reference solution. This solution consists of high-gain antennas, a RF anechoic chamber with real-time motion-controlled positioner and a NI high-bandwidth mmWave vector signal transceiver (VST).
Engineers can leverage a test sequencer, which allows them to configure a characterization to validate beamforming capabilities of the DUT. Additionally, in-depth software displays multiple visualization options for data. This can be seen below in Figure 3.
Figure 3. Beamforming measurement visualization (source NI).
The advent of 5G will change cellular wireless networks forever, bringing about a range of new network services, while also providing high speeds and low latency in diverse deployments. To achieve these benefits and ensure successful deployments, it is vital that extensive test measurements be applied during the entire development and production processes.