FCC Engineers Said to Be Taking Conservative Stance in Evaluating 6 GHz Interference
The FCC Office of Engineering and Technology appears to be taking a relatively conservative approach to interference mitigation in the 6 GHz band as it works through issues raised in an April 2020 Further NPRM (see 2004230059), industry officials told us. Apple and Apple/Qualcomm met with OET in recent days on the Monte Carlo simulations the tech companies are relying on to justify very-low power (VLP) operations in 6 GHz at the 14 dBm power levels proposed in the FNPRM.
OET reportedly has questions on how assumptions in models introduced in the proceeding may differ from those the European Union relied on to authorize VLP at that same power level, officials said. The dynamic seems to be that OET is taking a conservative approach on interference. OET apparently prefers not to rely only on mitigating factors emphasized to date, for example body loss, because many VLP devices are wearables, and total power control. The FCC didn’t comment.
“OET is close to drafting a second order, but it is being very careful about to nail the engineering analysis,” said a lawyer active in the proceeding.
Wi-Fi advocates have been hoping for next steps on the 6 GHz band since the U.S. Court of Appeals for the D.C. Circuit upheld the broader order (see 2112280047) in what was considered a major win for the FCC, with a remand asking the commission to address one narrow aspect. Utilities and other 6 GHz incumbents continue to raise concerns (see 2211030066).
“This is an unfortunate step backward for OET,” said Public Knowledge Senior Vice President Harold Feld: “Prudence is one thing. But to reject methods used in the past or approved by other regulators is foolishness, not prudence. The United States has consistently led the world in innovation when the FCC has led world regulatory bodies in innovative regulatory approaches. By contrast, when the commission is too timid, innovations have died in the cradle and we as a country lose our edge.”
Monte Carlo Simulation
Some spectrum experts say they’re not surprised OET is asking questions, especially due to some skepticism about over-reliance on Monte Carlo simulations. “Monte Carlo models are only as good as their assumptions,” said Richard Bennett, High Tech Forum founder. “OET needs to ensure that their models accurately reflect the current state of Wi-Fi deployment as well as reasonable projections for the next five years,” he said.
Monte Carlo simulations “are kind of random” and “done to see is there a likelihood of harmful interference occurring,” said a spectrum expert active in the broader 6 GHz proceeding: “There’s some credence that says this should be done in a field test to determine whether or not there’s spurious interference or some form of directional interference, which could cause a problem.”
“Monte Carlo simulations used to be the coin of the realm in predicting interference, but I think industry has over-relied on them in recent years, and has introduced some pretty flawed studies,” said TechFreedom General Counsel Jim Dunstan. “OET is right in no longer taking these predictive studies at face value, but [is] instead taking a deeper look at them and challenging some of these assumptions,” he said. “The FCC is becoming more skeptical of engineers these days, and possibly rightly so,” he said.
“I think tech and the FCC are at loggerheads,” said Digital Progress Institute President Joel Thayer. “It’s clear Apple and Qualcomm certainly have their preferences,” he said: “But in reality, OET is going to have to balance a lot of interests, and I’m not entirely convinced EU’s situation is entirely comparable to ours in this band, which may also be causing OET some pause.”
“Interference is highly dependent on context,” emailed Joe Kane, Information Technology and Innovation Foundation director-broadband and spectrum policy. “OET uses its best technical judgment between competing studies, but the studies often make different initial assumptions about, for example, whether the device will always be close to the user's body,” he said: “That's really more of a behavioral or policy question rather than an overly conservative approach to interference as a technical matter. The competition of studies with different initial assumptions is a recurring issue that OET and the commission as a whole will have to develop a way to work through systematically.”
That the rules are for unlicensed use is significant, Kane said. “It generally makes sense to have tighter limits on unlicensed bands since device makers and users don't internalize the costs of in-band interference to the same extent that licensees do,” Kane said.
"Generally speaking, the commission should use probabilistic assessments as a key input for evaluating harmful interference because they can provide a more realistic look at how systems will be affected by the introduction of additional radios into a given environment,” emailed Jeffrey Westling, American Action Forum director-technology and innovation policy: “The commission needs to determine the likelihood and consequences of harmful interference, and probabilistic models do a good job answering those questions. The commission may still determine that the potential harmful interference is too great, but understanding the full picture of potential interference is critical to making an informed decision."