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5G Test Challenges Brought on by 5G Physical Layer Changes

By Khushboo Kalyani

March 3, 2021
5G Test Challenges

LitePoint’s Khushboo Kalyani is the author of this two-part blog series on 5G sub-6GHz and mmWave test considerations. Throughout this series of blog posts, you’ll learn about the promise of 5G and some of the physical layer changes that drove crucial RF hardware and antenna changes and important test challenges and considerations.

5G Test Challenges

In my previous blog post, I explored the physical layer changes introduced in 5G, particularly in devices supporting millimeter wave (mmWave) frequencies, and some of the exciting use cases enabled by these changes. The improved physical layer has made it extremely important, and challenging, to validate end user device performance to ensure success in all of the use cases.

Let’s explore some of the test challenges associated with device operation at mmWave frequencies.

Complex Test Assembly – More antennas and more frequency bands have resulted in a dramatic increase in the complexity of test setup when scaled from R&D to production, especially when moving from a single device under test (DUT) to multi-DUT testing. In a multi-DUT setup, apart from the mmWave test equipment, DUT and over-the-air (OTA) chambers, the test setup requires use of multiple RF switches, control box, measurement antennas, RF cables and adapters, making it important to ensure the components are compatible with each other and the overall system is well calibrated.

Beamforming Characterization and Verification – Beamforming characterization aims to find the proper phase angle and gain for each antenna element in order to steer radio energy in a desired direction for the specific DUT design. In the case of beamforming verification, primarily performed at the device verification stage, the DUT itself sets the specific phase and gain for each antenna element required to generate a beam in a certain direction. Both beam characterization and verification across multiple antenna arrays and polarizations is crucial, as the beam pattern at mmWave frequencies is sensitive to antenna packaging, final product casing and multiple channel variations.

Signal Susceptibility to RF Impairments – A typical mmWave transceiver circuit consists of several components including mixers, local oscillator, phase shifters, power amplifiers, low noise amplifiers, integrated antennas, etc. The characteristics of these components can dramatically affect the performance of the communication system.Any imperfections resulting from either a manufacturing defect or mutating frequency response can notably degrade signal quality resulting in poor error vector magnitude (EVM). These effects intensify even further at higher mmWave frequencies, denser modulation schemes and larger antenna array sizes, making test and measurement highly sensitive to RF impairments.

Exhaustive Test Execution – 5G offers a wide range of physical layer features supporting multiple bands, bandwidths, sub carrier spacings, modulation schemes, etc., enabling implementation across a variety of use models. However, this gives rise to a broad range of test cases that must be executed to ensure holistic device quality check and comprehensive verification, increasing the overall test time.

Higher Cost of Test and Increased Time to Market – From a manufacturing or production point of view, all of the above challenges could increase the cost of test and really slow down the time to market, significantly curtailing production throughput and overall cost economics.

Test and Measurement Considerations

Having outlined some of the key test challenges, let’s take a look at some of the test and measurement considerations that can help overcome these challenges.

Choosing the Right OTA Test Chamber – There are two types of OTA test methods: direct far field (DFF) and compact antenna test range (CATR). The choice between the two is largely dictated by the size of the antenna module and its location inside the hardware. Care must be taken to position the device in the far field region to ensure E & H fields are orthogonal to each other and the beam pattern is stable.

Measurement System Linearity – One of the most important factors when setting up a test station is the choice of the test system. Measurement equipment must be well integrated to support both signal generation and analysis at the desired frequency range, modulation bandwidth and must offer a more linear performance reflected in terms of amplitude and phase flatness, repeatability, input/output power accuracy and EVM.  This helps ensure the measurement results are a true reflection of the device performance and are unadulterated by any non-linearities within the test equipment.

Path Loss Calibration – Is a process of determining the composite loss/gain of the entire RF transmission and receiver chain to ensure measurement accuracy and repeatability. As we already discussed, several elements make up a mmWave OTA test setup – with each component either adding a certain level of loss or gain either static or dependent on frequency to the overall measurements. Considering mmWave frequencies are heavily prone to OTA path loss, the calibration procedure helps ensure the radiated power and sensitivity results are related and uninfluenced by the overall system performance.

Simplified Test Assembly – A few of the key goals when choosing test equipment is to enable measurement correlation, to minimize engineering effort, and to reduce time to market. One way to achieve this is by having the flexibility to easily scale the solution from R&D to production so as to be able to correlate results, debug faster and shorten the learning curve. LitePoint’s sub-6GHz tester IQxstream-5G and mmWave test system IQgig-5G together with the turnkey automation test tool IQfact5G facilitate solution simplicity and scalability to support multi-DUT testing, increasing the overall production throughput.

Optimized Test Execution – Cost of test and time to market are two important factors in the production phase, but running thousands of test cases and feature combinations can increase the execution time and prove ineffective. Hence, it is wise to design the test suite based on the SKU under test, based on the bands available in the region of product sale, and understanding that the device has already gone through extensive testing in R&D and device verification. From a manufacturing point of view, optimizing the test suite is critical and can really help reduce the time to market and increase the overall efficiency of production.

Choice of automation software – At the R&D and design verification stages, devices go through extensive antenna performance testing with antenna pattern measurements for a specific DUT design to ensure reliable and accurate functioning of the devices in real world applications. Use of a well-integrated holistic software tool can significantly minimize the engineering effort and development time. LitePoint’s IQfact5G is a high-volume manufacturing automation test tool that facilitates easy test flow customization.

Success with LitePoint

LitePoint offers a variety of 5G test and measurement solutions. Please visit our 5G page to learn more about LitePoint’s 5G solutions and view the full replay of my webinar on this topic.

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