Wireless Test Faces New Challenges

The advent of 5G and other emerging wireless technologies make test more difficult. Over-the-air testing is one possible solution.

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Your mobile phone is far more complex than it was even five years ago, and it’s about to become even more complex with new wireless technologies. That has set off a scramble among test equipment vendors to come up with solutions, methodologies and equipment that is affordable, effective and reliable enough to make sure all of this technology works as planned—and that it continues to work throughout its expected lifetime.

Testing wireless components and systems is gearing up for the fifth generation of cellular technology, commonly known as 5G. It will take some time for 5G to replace 4G LTE — many parts of the world are just now implementing 4G LTE service — and the rollout promises to present numerous challenges to telecommunications carriers, handset manufacturers, semiconductor suppliers, and those engineers charged with testing the chips, the phones, and the networks supporting 5G.

The 3GPP Release 15 last December defined the 5G New Radio technology that will underpin the new standard, which still needs more international development. There’s also the International Telecommunication Union’s IMT-2020 definition for high-frequency bands.

Making matters more complicated, other forms of new wireless communications are also on the way as 5G gets hammered out. That includes IEEE 802.11ax, the latest Wi-Fi flavor, which will utilize multiple-input and multiple-output (MIMO) and multi-user multiple-input and multiple-out (MU-MIMO) technology, akin to the Massive MIMO tech of 5G.

Jason White, director of wireless test for National Instruments, sees multiple factors affecting the field now and in the future.

“If you look at the challenges that people are facing right now, today, in terms of stuff that we’re deploying in handsets and IoT devices that we’re purchasing today, the biggest challenges that the industry is facing in this space has to do with volume and cost,” White says. “Those things are tied up in the fact that all those devices are far more complex today than they were 10 years ago. If you look at the smartphone you have sitting in front of you, that thing has multiple radios, testing multiple technologies. The cost of that test, in theory, should be higher than it was 10 years ago because I’m actually testing probably 10 times more things than I was back then. I’ve got more antennas, more radios. Besides cellular, I’m now testing Wi-Fi, GPS, NFC, wireless charging — all these things represent air interfaces on the product. The trends that you’re seeing in that space from a test equipment perspective affect the semiconductor value chain that goes into those devices, and they also affect the end devices’ manufacturing test. You’re seeing more and more pieces of test equipment that can test multiple standards.”

So the same kind of convergence that has happened in devices such as smartphones is happening in the test world, as well. “You’re starting to see trends where the cost of test equipment has gone down,” said White. “Or in some cases, the cost of test equipment may not have gone down, but the pressures around being able to utilize that test equipment more and also having much less faster test times than you had in the past—those are all part of the buying decisions that consumers are making, both in semiconductor and on into end device production test.”

Alongside of that convergence, and to some degree because of it, the parts inside those devices are becoming more difficult to test, as well. “Ten years ago, you might just test the power amplifier for cellular,” he says. “Now, nobody buys a single PA by itself. They’re buying consolidated front-end modules, where there are multiple power amplifiers, switches, and filters, all built into a single part. The level of the complexity has gone up with that consolidation and with that technology. Everybody’s talking about 5G, and the reality is that there are pieces of 5G that are here today. We’ve deployed test solutions for 5G below 6 gigahertz. That technology is pretty well understood because it’s not that different from what was LTE, and what was 3G before it. Things are a little faster, the measurement performance has to be a little bit better, but ultimately, it’s a lot of new software.”

5G also will add some interesting twists because its rollout is closely associated with assisted and autonomous driving.

“Lots of testing as we ‘follow the chips’ will be necessary to verify that designs and manufacturing operations produce solutions that are defect-free and safe according to regulatory standards,” said Anil Bhalla, senior manager at Astronics. “Automotive will require the use of much more proven technology than consumer devices, such as smartphones. This testing will happen both at the component and system-level.”


Fig. 1: 5G usage models. Source: 5G Americas Spectrum Recommendations

Staggered introduction
The rollout of 5G will come in two phases. One utilizes the sub-6 GHz band, which offers some improvement over 4G LTE. The other utilizes spectrum above 24 GHz, ultimately heading to millimeter-wave technology. As the frequency goes up, so does the speed and the ability to carry more data more quickly. But as the frequency rises, the distance that signals can travel goes down and the amount of interference and potential interference becomes more critical.

That adds some interesting new twists to test. “Above 6 GHz, there’s a lot of discussion about millimeter wave and what happens with millimeter-wave adoption and 5G. Here you’ve got a whole lot of different perspectives coming together. The first major perspective is the market perspective. And that is, when exactly will millimeter waves be a significant part of the wireless test infrastructure? There are pretty well-defined use cases for they refer to as fixed-wireless access, where I’m using millimeter waves to make high-speed connections from my base station to backhaul or possibly from a base station to a small-cell-type device in-house so I can deliver high-bandwidth connections to the house. And in those fixed-use cases, the business models and even some of the devices are pretty well-understood. But then when you talk about the mobility use case of actually putting that technology into a cell phone and dealing all of the issues that come with millimeter waves – they don’t pass through walls, they don’t even pass through your hand – and so, there are all these challenges when I start trying to put that in a phone.”

One such challenge involves over-the-air testing, which will be required with 5G handsets because the standard cables and probes won’t suffice for the tasks.

New silicon has emerged lately for 802.11ax and for sub-6 GHz 5G, according to White. “One of the things that’s interesting with both of those standards, because of tighter sub-tier spacings and the need for better performance of these chipsets, it’s actually driven a lot of requirements back on the test equipment.”

Jeorge Hurtarte, a product manager at the LitePoint unit of Teradyne, points to four main challenges in wireless testing now:

• Higher frequencies;
• 10X increase in bandwidth;
• Over-the-air testing for millimeter waves;
• The need for faster, nimbler test equipment.

“Very few experts know about millimeter waves,” Hurtarte says, noting the complexity of the technology, which involves “much, much shorter” distances that they can travel. For those and other reasons, test equipment needs to be simpler.

Making things even more confusing, the frequency bands designated by the Federal Communications Commission in the United States are not the same as those being utilized in China and the European Union.

“This is an economical challenge,” he says. And because of the Massive MIMO technology, which can involve 64 to 256 antennas, contact testing doesn’t work. It has to be over-the-air.

With the progress being made in 5G standards, and the accompanying research and development in the private sector, most experts expect to see the first true 5G products emerge early next year, possibly in tablet computers introduced at the Mobile World Congress.

Putting 5G in perspective
5G isn’t the only high-frequency standard out there. WiFi is evolving alongside the cellular 5G standard, basically providing the same kind of relationship for the next generation of technology that exists today with 4G LTE and WiFi. Two new Wi-Fi standards, 802.11ay and 802.11az, will operate in the 60 GHz bands with transfer speeds of up to 20 Gbps.

Hurtarte predicts that 5G technology will become available for vehicle-to-infrastructure, vehicle-to-vehicle, and V2x communications in 2020. That will likely be the sub-6GHz piece of 5G, however. The higher-frequency portion of 5G will require a massive buildout of infrastructure because the signals are subject to interference from trees, people, and even weather. That requires multi-streaming of signals as well as beamforming technologies, and far more antennas and repeaters than exist today.

But that could happen more quickly as autonomous driving enters into the picture due to a massive increase in the amount of data that needs to be moved around.

“The rising adoption of vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2X) means a continued increase in the number of vehicular radar systems,” said Steven Liu, vice president of marketing at UMC Foundry. “Technologies needed for these systems include the car’s anti-collision radars and global positioning systems, as well as sensors that will be needed to interact with stoplights and vehicle dispatchers. These will work in conjunction with existing systems such as passenger comfort and infotainment control and engine monitoring subsystems that regulate temperature, tire pressure, and gas. Trucks for long distance transportation will require systems for load leveling, load shifting, curve and wind shear, all working together to ensure that cargo is not damaged during transport and that the truck container is stable throughout its journey. All of these 5G communication applications will be essential for the system’s ability to perform its respective operations.”

This has a big impact on test, and it points the way to a variety of approaches, including over-the-air testing because these systems will need to meet certain levels of reliability in the field as well as during manufacturing. “You can’t connect 50, 60, 100 cables to antennas,” said Tony Opferman, the wireless business development manager for Rohde & Schwarz. “Testing has become much more complex. People are asking for solutions that are more automated, and for more horsepower in test equipment. The power consumption on these boxes is crazy.”

Customers are looking into 802.11, Bluetooth, LoRa, and Sigfox, in addition to cellular, according to Opferman.

Keith Cobler, the senior marketing manager for the wireless unit at Rohde & Schwarz, sees customers seeking greater flexibility in wireless test. “Our customers are always asking for faster, wider, cheaper-type solutions across the whole design chain,” he says. “They’re testing a lot of different types of technologies. On the fly, they may have to switch from testing a LoRa device to now testing a Sigfox or a Narrowband-IoT device. Being able to have that flexibility and having that performance, being able to reach a figure, is really key. There’s a lot of buzz in the market about 5G. A lot of people imagine 5G as kind of a rip-and-replace technology, which is not the case. 5G is partly evolution—the 3GPP evolution, which really began in 2008, and has moved really forward with LTE in a steady progression.”

Beamforming and carrier aggregation were part of past cellular technologies, and millimeter waves are a key aspect of the new wireless communications, according to Cobler. “5G will leverage a lot of that.”

Millimeter-wave technology will help boost bandwidth capabilities by 10 to 20 times. Still, millimeter-wave cables are very expensive. Today the price runs into the thousands of dollars, although that will likely drop over time.

“It’s very expensive to test this stuff,” says Opferman. “The cost of test is going to dramatically increase. And you need pretty deep RF experience. You have to have a deeper knowledge of RF.”

The greater expense of 5G test equipment could mean that companies will outsource 5G testing to test labs, he notes.

It’s not just the equipment, either. It’s also the amount of testing that needs to be done with that equipment.

“Safety-critical applications will require additional testing as we better understand the defect mechanisms,” said Astronics’ Bhalla. “The industry is assuming this will work based on early trials.  More trials on a broader scale will support the gradual roll-out of this new technology.  The economics of autonomous driving is motivating the entire semiconductor ecosystem to evolve during this transition.”


Fig. 2: Usage scenarios and bands. Source: 5GAmericas.org

Conclusion
Wireless testing is going through many technology changes, especially in response to 5G wireless communications, 802.11ax Wi-Fi, and other communications protocols. As a result, the cost of test equipment won’t be going down anytime soon.

On top of that, customers for wireless test equipment want more flexibility to handle the higher frequencies, faster data transmission, and over-the-air testing that new technologies will require.

As communications technology gets more complex, so does test. And if future roadmaps for protocols and communications within and outside of cars and other mobile devices are any indication, that complexity is going to skyrocket over the next decade.

—Ed Sperling contributed to this report.

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