5G Requires a New Approach to Testing
When the industry first had the concept of 5G, the International Telecommunications Union (ITU) proposed a framework of three main use cases that 5G is expected to solve.
First is the EMBB or enhanced mobile broadband, according to David Hall, chief solution marketer at National Instruments. "That's the idea that we can get higher throughput, higher data through mobile communications. Another one is EMTC or enhanced machine-type communications, which is more about being able to have time-critical communication with many devices. The third use case was more of the IoT, where we had this notion of needing to support large numbers of wireless devices on the network. We need a network that could handle that type of capability," he explains.
Out of those three use cases, the one that is by far the most difficult for engineers designing and testing products is the EMBB use case. The reason for this is that the industry will be deploying 5G at millimeter wave frequencies between 28 and 40GHz, with significantly wider bandwidths than the current instrumentation.
"The rules about how you design a test fixture, or conduct testing of those products is changing," says Hall. "As an example, in the past, you might connect a device under test (DUT) to a test instrument over a long cable, because at 1 GHz or 2 GHz, you don’t worry about insertion loss. But now, when you are looking at a 28GHz or a 40GHz center frequency, you can’t have a long connection between the device under test and the instrument because it is subject to significant attenuation."
Therefore, manufacturers should re-architect their test systems to get the instrument closer to the DUT. Hall adds that they are also seeing the move for radios at 28GHz to have much more integrated antennas into the actual package itself.
"What that means is it increases the likelihood of needing to do over-the-air testing, which is once taboo—a no-no in the wireless community for many years," Hall says. "But now, it’s actually essential when you have antennas that are tightly integrated with the radio itself. By far, 5G is one of the biggest test challenges of mobile communications today, even as other standards are coming out—such as IEEE 802.11ax and Bluetooth Low Energy. But for the other standards, they sort of follow all the same rules. But 5G, and the use of new bands, creates a lot of challenges."
One of the biggest challenges that their customers are facing right now is the accelerating rate of technology changes. The time it took for the industry to go from 2G to 3G was longer than what it is when going from 4G to 4.5, to 5G.
"What that means is that customers have less time to react to handling new test challenges and new technical challenges. Our goal to provide a platform-based approach is to allow our customers to develop a test system—the main IP for the customers is their software—and allow them to continue to reuse that software for long periods of time and be able to insert new hardware as the needs arise," explains Hall. "An example of that is the vector signal transceiver, which we announced in 2012. If you wrote a piece of test software that uses the vector signal transceiver back in 2012, you can still use that software today with the newest vector signal transceiver. But now, the new vector signal transceiver has better error vector magnitude (EVM) performance, better noise floor performance, and over 10x the bandwidth. That’s a good example of helping customers preserve their investment—by giving them access to the latest and greatest hardware, without having to do significant rework."
Developing 5G Test Systems
National Instruments provides automated test equipment and virtual instrumentation solutions. To help customers going into 5G, the company is working with several lead users of the 5G test front, "because many of these customers are looking at millimeter-wave testing systems for the very first time, and it is something they have never dealt with before," says Hall.
NI is working closely with them in lead-user engagements where it gives them the first prototype of some of the company's test technologies, and the users give feedback on what’s working and what’s not, and some of the challenges that they are uncovering in test. In this way, the company—with the help of their customer manufacturers—are defining some of the 5G test products together.
According to Hall, the company recently collaborated with AT&T is to help them build a channel sounder, a system used to measure some of the real-world electromagnetic propagation effects in the 28GHz spectrum. In that collaboration, NI provided the software-defined radio hardware as well as engineering resources to help AT&T develop the system.
"With this system, AT&T is already taking real measurements and being able to characterize the channel in a way that was impossible before," notes Hall.
5G Use Cases
According to Hall, the 3GPP—the standards body responsible for 5G—is simultaneously working on additional wireless technologies to support more of the IoT use case.
"This is a little bit of a shift from years past, where we start with GSM, then we did 3G, then we did LTE, and we saw people attempt to use the cellular technology to support the non-cellular use case. An example of that is in automobiles, there's a technology called OnStar, which uses CDMA network—2G mobile communications—to radio a base station if there’s a problem with the vehicle. Obviously, CDMA wasn’t designed for that use case, but it’s a good enough technology to solve that problem," says Hall.
Hall says 3GPP is shifting towards designing one flavor of standards for mobile broadband, a different flavor for the IoT, and even a different flavor for automotive. Two of the technologies that are actively being developed—one of them is called NB-IoT (Narrowband IoT), is an implementation effectively like LTE, that’s designed for low-power, long-range transmissions and to support many devices on the network. Another one that’s happening in parallel is LTE V-to-X and 5G V-to-X, which is a vehicle-to-vehicle communications standard based on some of the 5G and LTE technologies, but designed for high-doppler situations, such as moving vehicles communicating with each other.
To read the full version of this article, which appeared in the May 2018 issue of SMT007 Magazine, click here.