Mastering 5G test complexity: a growing concern

Article By : Joel Conover

As complex as 4G was, 5G is even more so; assuring they’re interoperable increases the complexity, which makes testing a major challenge.

As cellular technology has evolved, at roughly 10-year intervals, from 3G to 4G to 5G 10 years apart, wireless networks have experienced a 10-fold performance increase. That’s been accompanied by an even larger increase in test complexity.

But as we race into 2019, it is good to pause and reflect on the milestones the industry has achieved with 3G, 4G, and 5G technology. Engineers should rejoice! On December 12, 2018, a dedicated group of technical experts meeting in Sorrento, Italy, celebrated the 20th anniversary of 3GPP and a monumental year of 5G accomplishments. The industry delivered two major 5th generation spec milestones in 2018: the 5G non-standalone (NSA) specification (Release 15) released in March 2018 and the 5G Release 15 with standalone access (SA) in September 2018.

A decade earlier, on December 9th, 2008, a similar celebration was held in Athens, Greece. There, two generations of engineering leaders gathered to celebrate the delivery of the 4th generation LTE standard, which would ultimately become the foundation of the vast majority of the world’s mobile networks.

10 years of progress, 20× the complexity
Given that 4G has been in the market for over a decade, the general public seems desensitized to the 4G-to-5G evolution. For the casual user, it may feel that 5G is inevitable with predictable, evolutionary features, and that test methodologies are mainly about faster speeds and more access. There is a lot more. The added complexity of new capabilities on top of 4G-5G coexistence and handoff has profound implications on the design and test complexity. One seemingly simple yet complex key use case to be considered is cellular handoff of calls during mobile roaming events crossing mixed 4G and 5G networks.

The obvious implication of this is expanded test requirements. When you test a 5G device, testing scope is not limited to only the new 5G functionality. Release 15 builds on previous 4G releases, namely 4G LTE (Release 13 and Release 14), so we know the total test suite expands accordingly. But the challenge doesn’t end there.

The 5G standard expands capabilities in many new directions. Release 15 includes a broad set of new capabilities and requirements that require additional test functionality and validation before a product can ship. Here are just a few of the new Release 15 SA and NSA highlights that require additional focus:

  • Support for expanded frequency ranges – FR1 and FR2
  • Wider bandwidth channels
  • Carrier aggregation: up to 16 component carriers in intra-band contiguous, intra-band, non-contiguous, and inter-band, non-contiguous configurations, crossing both FR1 and FR2
  • Over 1 GHz of aggregated spectrum
  • Support for different numerologies on each carrier
  • Variable transport block maps per carrier
  • Support for licensed and unlicensed spectrum with aggregation
  • 4G and 5G coexistence
  • 4G/5G coexistence in the presence of other wireless communications standards: Bluetooth, NFC, GPS, FM Radio, and Wi-Fi (2.4GHz and 5GHz variants)

In addition, millimeter wave spectrum support forces an expansion in the test methodology, driving a shift to over-the-air (OTA) testing for a large portion of the test suite. OTA testing isn’t just a simple shift from cabled test, but also a new style of testing to measure and validate capabilities unique to 5G millimeter wave signal acquisition and management. These include:

  • Signal acquisition and tracking
  • Beamforming performance and accuracy
  • mmWave MIMO signal reception and decoding

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.

None of these concepts are new to device manufacturers, but the methodologies are completely different when executed in millimeter wave (mmWave). Adding to this, 5G devices can operate in sub-6 GHz, mmWave, or both, and may use wider channel bandwidths and channel aggregation in hundreds of different combinations. This is all before we consider different 5G use cases that may each contribute additional constraints or requirements for power usage, latency, or both. In aggregate, new methods and more tests are required to validate the same behavior for mobile devices, and many tests will expand from well-understood and optimized cabled test methods to more complex and time consuming over-the-air test methods.

Predicting the future
The combination of seamless 4G-5G handoff, new frequencies, new use cases, and of course, the combinations and permutations of them, all add up to a lot more testing. Every device manufacturer will start integrating new tests for standards compliance, EMI/EMC requirements, and OTA behavior understanding. Manufacturers will need to add more test cases as well to cover the new functionality.

We have seen the costly impacts over the past decade of cutting corners on testing for functions like carrier acquisition at the edge of the network, antenna placements, RF interference between competing Wi-Fi, BT, RFID, and cellular emitters, and battery performance. No manufacturer wants to suffer the consequences of those defects, yet that trade-off of test time vs. time-to-market is ever present.

The key question design and test teams are asking is, “How much testing is enough?” We can draw on history and current knowledge to pinpoint the near-term test volumes, and even project future test volumes based on past growth.

In looking at some of the earliest GSM (third generation) standards, there were several hundred use cases in their test matrix. The latest Release 14 conformance test suites have approximately 15,000 tests that are required to completely validate LTE UE conformance. That is a large increase.

As we look forward to Release 15, there are over 900 band combinations, each with more than 100 unique test cases that must be implemented. When you execute these tests across both SA (standalone) and NSA (non-standalone) versions of the standard and include device behavior testing across both 4G and 5G networks, the test matrix jumps to over 300,000. That represents a 20-fold increase in tests versus the latest 4G standards. And this doesn’t consider coexistence testing in the presence of five or more wireless signals typically found in a handset.

Here is the summary of how your test matrix can suddenly grow 20-fold:

  1. The number of conformance tests between 4G and 5G is increasing by a factor of 20 so far, and each new release of the 3GPP specification adds more use cases.
  2. With Release 16 on the horizon, we can already anticipate additional test cases related to unlicensed spectrum, as well as future test cases to support additional expanded spectrum available in future releases.
  3. Assuming no other efficiencies, trending the current growth rate would result in as many 6 million test cases by 2030.

As anyone in the business will tell you, not all tests are required to meet the standards. But, each test omitted adds risk to the performance or reliability of a device. Find a partner who understands the test environment and work with them to figure out the right level of test necessary for your specific device. You don’t need to test everything, but you do need to know which tests are the most critical to your device, and your business.

Joel Conover is senior director of Industry Solutions & Digital Marketing at Keysight Technologies.

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