Comment by bunnie | Hacker News Reader

Comment by bunnie | Hacker News Reader

As a small time hardware maker who spends an inordinate amount of my limited resources trying to meet FCC rules, I find this infuriating.

Whenever I complain about how outdated and ineffective the FCC is, the literal pushback I get is "but what about airplanes and satellites". To which I say, touche', we should all do our part to make sure we have safe airports and open channels for satellites and astronomy.

Reading through a Link posted by @supernova87a (https://www.rtca.org/wp-content/uploads/2020/12/Slides-5G-In...) I have two take-aways:

1. The spectrum involved is valued in excess of $4.6bb

2. Most 5G deployments will create in excess of 100x (20dBm) the allowable interference for radar altimeters

From the report, page 18 (SC-239 study results):

HUGE AMOUNT OF SCENARIOS INVOLVED

Every base station configuration produces harmful interference both from 5G fundamental emissions in the 3.7–3.98 GHz band and 5G spurious emissions* in the 4.2–4.4 GHz band, across virtually all operational scenarios and relative geometries between the aircraft and base station.

5G user equipment (mobile phones) that may be operating onboard aircraft were also found to exceed the safe interference limits for Usage Categories 2 and 3.

I find it increasingly difficult not to be cynical about the role of the FCC with respect to public safety issues with a lapse like this.

If I shipped a product into the US that had a radar altimeter interference profile like this, I'd be fined and sued into the ground a hundred times over, and I'd accept that fine and outrage because I personally couldn't live with being responsible for any planes literally falling out of the sky because they thought the ground was in the wrong place on account of my product's interference.

But apparently, with enough lobbyists and money, it's an acceptable risk. It's hard for me to take the rest of the FCC's rules seriously, when they act as just another rent-collecting agency at the beck and call of lobbyists whose sole mandate is to create market barriers against small startups and imported goods, with little regard to actual safety, science, or modern technology...

edit - formatting

"Don't interfere with defective radar altimeters" is not the way the law works. The law says don't emit more power than you are allowed to within your assigned frequency band, and much less outside it.

The basic problem here is that way too many radar altimeters are fundamentally defective in terms of being sensitive to emissions they should have been designed from the beginning to ignore.

The FCC doesn't make any promises that listening to the wrong frequencies won't produce harmful interference. That is the receiver's job to avoid listening to signals on those frequencies.

And if somehow radar altimeters can't or couldn't be designed to ignore radio emissions outside their assigned frequency range, the FAA should have demanded a far larger frequency band from the beginning instead of implying the one that was assigned was adequate for the purpose and then later attempting to squat all over frequency bands they were never assigned.

The root problem here is that this used to be a satellite downlink band. So virtually no guard bands were required. It is like if someone bought a house in a residential area, knocked it down, and built a steel mill.

The filter mask is reasonable for broadband radar, especially considering that we have to consider equipment older than 5G (I am plagued by FCC rules that protect AM radios, so why should radar altimeters be considered defective and not AM radios?). If you have to make a guess as to which is wrong, the legislation, or the laws of physics, I'd put my bets on the legislation being wrong.

Furthermore, things could be much worse because the filters that are used to prevent leakage into radar altimeter frequencies can fail on a 5G device, but the 5G device would continue to operate just fine without anyone noticing (except for the plane that ended up in pieces on the runway).

In other words, 5G transmitters would normally emit sidebands that jam altimeters, if not for a handful of components that prevent it from happening. But if one of these components were to fail -- say, a user dropped their phone and one of the filter elements cracked or de-tuned -- it'd just straight up jam an airplane's altimeter.

I'd like to think that regulatory bodies exist because they are supposed to consider public safety as part of their mandate. We don't want to lose our children in an airplane crash and have the best answer be "whelp, that radar designed 20 years ago should have anticipated 5G jamming. Therefore that altimeter was defective. Anyways, no actual laws were broken, so those lives lost is just the price of progress".

I think an alternative view would be that the FCC should have spectrum auctions not just "because valuable things should go to the highest bidder", but in part to raise funds to upgrade things like airplane radars so they could tolerate the interference caused by the new equipment that was going to be installed in an adjacent band. Government does this all the time: you want to move your business into the neighborhood? You have to upgrade the infrastructure to support the burdens of your new business. We didn't run megawatt-scale power lines to every suburban block just in case someone wants to setup a datacenter there, and if the power goes out because of the datacenter's loads we don't blame the residents of the town for not having anticipated the Internet.

And with over $80 billion raised in spectrum auctions, you'd think that'd be within the realm of possibility - one could replace 100,000 radar altimeters at $10k a pop for "just" a billion dollars, or about 1% of the auction proceeds.

Verizon, AT&T, and T-Mobile spent nearly $100B for their C-Band spectrum (including relocation costs). I think that creates a lot of pressure for them to be allowed to put them to use. I'm not saying it should, just that it does.

I think the US wants to be a 5G leader and it sees delays as potentially sacrificing that leadership. This might not be a real concern, but people complain anytime the US isn't the #1 in something and blame everything from politicians to capitalism. At the same time, it seems reasonable to believe that companies that have access to new 5G capabilities (speed, capacity, latency) will be able to develop and gain marketshare in new services. If American companies are going to develop the next generation of NewThings, playing around with the capabilities and limits of 5G networks in the real world will be an important part of that.

We've seen different countries with different scenarios. European countries that have nearly twice the guard band; countries that are mandating down-tilts; countries that have strict power limits; countries that don't have as strict power limits and are comfortable with the risk.

Personally, I don't understand why we didn't go with a phased approach. Set low power levels and a downward-tilt mandate. Ease the restrictions month by month and measure the real-world interference. Sure, maybe it means that C-Band networks aren't quite as good as they could be for 6 months, but I think predictable goals and timelines based on real-world data would satisfy cell carriers (who at least state they're confident that there will be no issue).

> 5G user equipment (mobile phones) that may be operating onboard aircraft were also found to exceed the safe interference limits for Usage Categories 2 and 3.

In some ways, this is what I'm more worried about. People have a smug sense that their phone can't interfere with planes and that regulations around cell phone use on planes are just BS. While the FAA/FCC will be able to enforce restrictions on cell carriers, it's going to be impossible to enforce it on users in-flight. You can't effectively make sure that devices are in airplane mode. Flight attendants can't see the indicator on my device (or lack thereof) when quickly walking up and down the aisles.

If C-Band causes interference with radio altimeters, I can see the FAA and FCC adding exclusion areas around airports, mandating antenna down-tilts and lower power levels in certain areas, and other mitigations. I think it's reasonably easy to get AT&T and Verizon to implement those and reasonably easy to check compliance. They might fight it, but it's still reasonably easy.

I think if C-Band phones cause interference, it's going to be a problem since we simply won't be able to police everyone on planes.

One thing mitigating interference from phones inside the plane is that at those frequencies, the metal shell should prevent the signal from going that far, and once you're airborne the phone will stop getting usable signal fast (and thus stop transmitting without beacons from base station, in order to save power).

Problem is that some new popular designs are composite shells...

To be instrument rated (all airline aircraft), composite aircraft must have a metal weave in the outer layer to dissipate static electricity build up from flying through clouds. This preserves the faraday like signal reduction as a side effect. My phone's GPS seems to struggle bus as much in a 787 as any other airline.

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