5G: Plunging into open-ended test requirements

Mobile broadband technology is beginning to crawl from commonly known 4th Generation Wireless (4G) transmission standards to fifth generation wireless IMT2020 standardization, also known as 5G. This 5G network technology will influence semiconductor test in two directions, an evolutionary track and a revolutionary paradigm shift. The revolutionary aspect of 5G targets massive amounts of bandwidth not previously thought of as accessible. Many technological challenges have blocked the reasonable implementation of 5G cellular technology. Consumer demand for rapidly growing amounts of bandwidth, has created the need to solve these challenges.

Recent millimeter wave (mmWave) band spectrum studies have put the solution for 5G in reach with large amounts of spectrum available in mmWave. Frequency bands under consideration include 28, 37, 39, 64-71, 71-76, and 81-86GHz, which are far removed from the less than 6GHz technology offered today. Shifting from 6GHz to 28GHz and beyond creates challenges up and down the value chain. This fundamental shift is why many data compression techniques currently in development will become the next evolutionary step towards 5G, also referred to as 4.5G. The techniques for 4.5G focus on better access within currently defined licensed spectrum.

R&D activities in studies beyond 6GHz frequency bands have been restrained because of the mmWave characteristics of limited transmission and wavelength. Studies on standards beyond 6GHz have lived in academia and the military but had limited consumer application. With limited consumer application there was not a great wave of interest in 5G as an acceptable standard. So, what has changed? Consumer demand for more bandwidth which is faster, smarter and less power hungry at a low cost!

Research from NYU Wireless, Ericsson, and many others has driven proof-of-concepts for mmWave applications to acceptable levels of reasonable realization. Areas of research interest include enhancements to the physical layer, interference mitigation, multiple-input-multiple-output (MIMO) antennas, network security, network management and many others. Bridging the gap and creating a learning environment is automotive radar and wireless LAN 802.11ad (also known as WiGig) specification standards. Both standards exist with promising levels of acceptance which drive the need to test semiconductors in the K-Band, and the V & W bands of mmWave cellular channels. Is there one key research breathrough which will put realization in hyperspace?

Since we are discussing a standard that is not yet ratified and the test requirements are not fully known, we must extrapolate to hypotheses based on Xcerra’s years of experience in RF test. This future technology has driven all of the semiconductor test equipment suppliers to rethink the world of RF test. Using our proven experiences in automotive radar and 60GHz WiFi we are applying what we have learned in this area to bring solutions to market. But creating the technology to test these devices is only half of the battle. These products have to fit within a model of production quality test while answering the requirements of mass production and aligning the costs associated with consumer expectations. How will the 5G revolution affect your business and testing operations?

Moving RF test from standard cable and pogo technology, which has been well understood for many years, to waveguides and Over The Air (OTA) connectivity is challenging. Waveguides create a new complexity where mechanical considerations are equal to RF signaling and measurement parameters. We have suddenly had to become plumbers to create and execute multisite test capabilities. For OTA testing, we are now required to speak the language of horn antennas and linear arrays rather than screwing down a Sub-Miniature version A (SMA) connector to a device under test (DUT) board. The benefit of OTA testing is that it allows us to move quickly to multisite test capability without the complexities of creating expensive multisite waveguide connection schemes. Where this becomes a challenge is the mathematical models required to beam-form a signal to the appropriate site for measurement or capture.  As we move forward, test requirements will have to allow for the inconsistencies of sending and measuring signals through the air or accept the costs associated with mmWave. We all know where this is going to go! What role do you see OTA testing playing?

Over The Air test has changed transmission properties versus well known cable models. With the use of cables we have had the benefit of working with known properties regarding RF transmission, and when needed, can adjust for any inconsistencies along the signal path. One obstacle which is commonly taken for granted is the calibration of the Test system. Many systems today calibrate all inconsistencies without the user having to pay great lengths of attention. System calibration, user calibration, and de-embedding are commonly used today to ensure reliable, accurate measurements. Calibration and system to system stability at mmWave frequencies has all of us engineering new solutions for high-volume semiconductor production.

Lastly, we are all devoting time on the subject of Multi-GHz bandwidth requirements for the IF and RF for mmWave technologies. For starters, a 2.16 GHz bandwidth requirement for 802.11ad is driving semiconductor manufacturers, and back-end test suppliers towards a new horizon. Test instrument vendors, whether benchtop or production test, are making strides with up/down conversions to the 60 GHz mmWave band. Creating the 802.11ad modulation in IF is pushing sample rates beyond 1 Gbps, which is 4 times today’s 802.11ac standard. The issue with multi-gigabit sample rates is the heat created by the multichannel high speed ADC’s and DAC’s to achieve the 802.11ad modulation requirements.

In summary, paradigm shifts in our industry has created an opportunity that we are capitalizing on with our deep understanding of RF and mmWave. Our research in automotive radar test has given us the tools to move quickly towards broadband cellular 5G testing in the future. Expectations of production test in this arena will be realized in the near future. Therefore agreements to acceptable standards must be approached with a collaborative mindset between end customer, semiconductor supplier and test vendor, to achieve best practices for mmWave production test.

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