5G test gears up

Article By : Martin Rowe

As products emerge and networks assemble, the test-equipment industry must keep up with standards, production, and deployment.

EDN and other AspenCore publications have been covering 5G R&D for several years and we’ve watched it grow from academic research to where the first products and networks that are now coming online. 5G is surely moving out of R&D and is becoming a reality. While widespread 5G use is still a few years away, engineers are beginning to move parts and subsystems into characterization, validation, production, and deployment. As part of this AspenCore Special Project, we look at how the test industry is responding. Six other articles will look at topics covering deployment (technical and policy) and supply chain as 5G moves out of the lab and onto the street.

Editor’s Note: After perhaps a decade in research labs and drawing boards, 5G is on the verge of deployment. Indeed, early deployments of the technology are coming online now. You can tell because the marketers have sunk their teeth in and started promoting it. With 5G moving out of the lab, the team at AspenCore looks at what it will take to reach full deployment — from technical, supply chain, carrier, and policy perspectives.

5G deployments have begun, and thus much of the work is still focused on infrastructure: the radios and networks that will carry all that data. Indeed, there’s still plenty of R&D activity going on, and these early products—modems, antenna arrays, amplifiers, data converters, etc.—will surely improve over time. Test equipment is showing signs of use outside the engineering lab. Even ATE manufacturers are gearing up for forthcoming high-volume production of parts; network installation testing gear for 5G has emerged.

5G is also bringing changes at the higher network layers. Because 5G is expected to reduce latency and increase reliability over LTE, core networks will evolve into software-defined networks (SDNs) that will treat data differently depending on use case.

The radio’s the thing
Much of the 5G development has focused on 5G new radio (5G NR) with emphasis on millimeter wave (mmWave) frequencies starting at 24.25 GHz. Such high frequencies offer much wider bandwidths (up to 400 MHz) than are possible in the sub-6 GHz range where wireless communication takes place today. Indeed, early demonstrations such as Verizon’s November 13 announcement of using an early 5G handset to transport data at 28 GHz are still very much tied to LTE, which for now will handle control signals while some data will use mmWave. These systems are called “non-standalone” because they rely on the dual connectivity of LTE and 5G. Some sub-6 GHz bands will be used for data as well, especially in areas where mmWave signals aren’t available. That’s why specifications such as TS 138 101-3 V15.2.0 (2018-07) specify use of and tests for dual connectivity. Eventually, we will see “standalone” 5G that includes radio-access networks (RANs) and core networks that incorporate SDNs without the need for LTE (Figure 1).

5G standalone non-standalone
Figure 1. 5G will begin life using non-standalone radios, eventually moving to standalone. Courtesy of Anritsu.

The need for using both LTE and 5G radios creates a power-consumption problem in handsets, which is why the first 5G phone’s attachment comes with its own battery. Line-powered base stations and industrial internet of things (IIoT) devices that will use 5G won’t have that issue. Furthermore, 5G handsets that communicate over mmWave channels will likely have beam-steering capabilities, explained in Beam steering: one of 5G’s many technologies. Base stations and small cells will likely have multiple sets of power amplifiers, data converters, mixers, and other RF components, to go along with phased-array antennas that contain 256 elements. Handsets will likely have just one set of such components to drive a four-element phased-array antenna.

Andreas Roessler
Rohde & Schwarz

According to Andreas Roessler at Rohde & Schwarz, much of the validation, characterization, and conformance testing, particularly in the frequency range 1 (FR1, 450 MHz to 6 GHz) uses many of the same RF measurements used for LTE. Measurements such as error-vector magnitude (EVM), RF signal power, and adjacent channel power are still valid for 5G signals. Roessler told EDN that the exact specification for measurements, particularly in FR2 (24.25 GHz to 52.6 GHz), are still being defined but should be published early in 2019.

Power amplifiers (PAs) can add to the power-consumption issues facing handset designers. Analog Devices’ Thomas Cameron explained that handset manufacturers are pushing back on having both LTE and 5G signals on adjacent subcarriers. because a single PA needs to drive both LTE and 5G NR signals.

The problem is particularly acute with Sprint, which uses band n41 (2.502 GHz to 2.690 GHz) and has to place its LTE and 5G NR signals on adjacent channels within that band. “That’s an unfavorable condition,” noted Roessler, who said that Sprint will use three 20 MHz LTE downlink subcarriers alongside two LTE uplink subcarriers and two 5G NR subcarriers of 60 MHz, 80 MHz, or 100 MHz, depending on the market. That causes a PA to amplify both LTE and 5G NR signals, which result in intermodulation distortion that reduces PA efficiency. Roessler said that Sprint must solve the problem by preventing the handset from transmitting both LTE and 5G NR signals at the same time.

Test equipment
Test equipment, both benchtop and PXI, can generate and analyze LTE and 5G NR signals. Figure 2 shows one such PXI-based system from National Instruments. It consists of a Vector Signal Transceiver and Vector Signal Analyzer. Other instruments are an oscilloscope for envelope tracking, source-measure units (SMUs) for providing power and measuring power consumption, and digital instrument for DUT control.

National Instruments PXI 5G test system
Figure 2. A 5G NR test system generates and analyzes both LTE and 5G signals. Courtesy of National Instruments.

Alejandro Buritica
National Instruments

“Testing of 5G NR is moving into a preproduction state of validation and characterization,” said Alejandro Buritica of National Instruments. Buritica has seen engineers using systems such as that in Fig. 1 as well as developing their own to test early ICs and subsystems for base stations, with handsets just starting.

“The ecosystem is in early production,” said Keysight’s Roger Nichols. “We’re seeing engineers testing devices for 5G radios and for the high-speed digital links. Early conformance testing to standards has begun.” Nichols noted that engineers are not only testing at the physical layer, they’re making bit-error measurements and testing protocols up to the application layer.

Roger Nichols
Keysight Technologies

Over the air

While you can test 5G NR components using wired connections. Testing integrated phased-array antenna systems requires testing the whole system over the air. OTA testing is taking off and will only increase in importance as more 5G NR products are developed.

OTA tests require chambers to reduce the amplitude of ambient signals and minimize reflections. Figure 3 shows a system that engineers can use to perform initial testing on integrated beam-steering antennas that combine amplifiers, data converters, mixers, and beam-steering ICs.

Keysight 5G test validation system mmWave
Figure 3. An over-the-air test of an integrated phased-array antenna (white box on right) needs receiving antennas (left) plus a signal source and a signal analyzer. Courtesy of Keysight Technologies.

Test systems such as the ATS1000 from Rohde & Schwarz (Figure 4) include chambers that minimize interference from ambient signals and minimize reflections so you can measure signals directly from the antenna.

Rohde & Schwarz ATS1000 antenna test system for 5G
Figure 4. The ATS1000 Antenna Test System from Rohde & Schwarz includes a chamber to isolate the antenna under test from ambient signals. Courtesy of Rohde & Schwarz.

Figure 5 shows a some of the measurements needed for in-band and out-of-band output power for a channel centered at 3.5 GHz. Constellation diagrams show mean RMS EMV for four component carriers.

National Instrument 5G signal power
Figure 5. Automated test systems and traditional box instruments measure in-band (blue) and out-of-band signal power. Courtesy of National Instruments.

[Continue reading on EDN US: Production and network testing]

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