The top testing challenges in 6 GHz Wi-Fi operation: Part 2

Wi-Fi 7 brings a host of new flexibility features; they all have to be tested

A previous article discussed the challenges associated with breaking the 6 GHz barrier and with testing higher modulation in Wi-Fi 7 devices. In part 2, we will take a look at how two of the next standard’s most exciting features delivering on the promise of more frequency agility — Multi-Link Operation and preamble puncturing — are also impacting the test and measurement space.

Multi-Link Operation

Multi-Link Operation lowers latency by allowing rapid switching between two
different Wi-Fi bands, is considered to be Wi-Fi 7’s headlining feature. But, according to LitePoint’s Director of Product Marketing Adam Smith, this feature is also “driving the frontend module companies nuts.”

This is because the ability to use the 5 and 6 GHz bands simultaneously means that there isn’t much space between them, a fact that puts particular pressure on filter companies. “How do you notch out your 5 GHz transmitter from swamping your 6 GHz receiver, for example?” Smith posited. To answer this question, Smith said there is tremendous work being done in the frontend modular component space that LitePoint is supporting.

Further, Keysight’s Senior Application Engineer Bill Koerner explained that
MLO is one leg of a three-legged stool of features. This stool also includes orthogonal frequency-division multiple access (OFDMA) and Multiple Resource Unit (MRU). OFDMA, first introduced in Wi-Fi 6, establishes independently modulating subcarriers within frequencies, allowing for simultaneous transmissions to and from multiple clients. And MRU provides enhanced interference mitigation and OFDMA efficiency, which results in reduced latency.

“Each requires the other to work well — but come up short on any and the stool will fall,” he said. “To that end, exhaustive and predictive testing must be made available to cover the many test cases these three features introduce.”

Preamble puncturing

And then there is preamble puncturing, a powerful capability that makes it possible for regions that did not open up the full 6 GHz band for Wi-Fi to still achieve wider channels. This feature improves spectral efficiency by allowing a Wi-Fi AP to transmit a “punctured” portion of the spectrum channel if some of the channel is being used by legacy users. By avoiding a channel that is already in use by incumbents, a wide swath of spectrum can still be obtained, even for those without the full 6 GHz band available.

But according to Koerner, this capability represents some “unusual changes” to existing tests, most notably in the interference-type tests. Further, Smith indicated that preamble puncturing will stress the frontend of Wi-Fi 7 devices and that power amplifier modules and filtering components will all have to characterized for this feature.

Joerg Koepp, the IoT market segment manager for IoT at Rohde & Schwarz, shared that the company’s customers are struggling somewhat with the new level of flexibility
that Wi-Fi 7 features provide. This agility, he said, is great from an end user’s perspective, but is proving challenging for device makers, especially those looking to enter the global market.

“They ask, “Do I really have to test all of this stuff?’” he said. “Yes, if you want to support it. This flexibility is always good in terms of what you can do but it does not makes the lives of those who have test all these things easier.”