5G Effects

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GaryRR
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5G Effects

Post by GaryRR »

For you long time pilots.
Could a 5G signal really interfere with a radio altimeter or other avionics?

alan CXA651
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Re: 5G Effects

Post by alan CXA651 »

Hi GaryRR.
As an x aircraft electrical engineer , i dont think it can , but i think they are also concerned about navigation equipment as well if i remember correctly , and i think 5g is already in use in europe , and not heard of any issues over here personally , i think this concern is in the USA going by the news at this time.
regards Alan. 8)
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tbaac
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Re: 5G Effects

Post by tbaac »

According to an article read on the BBC, 5G in Europe uses a lower frequency than in the US, and 'Band C' for 5G is pretty close to the frequency used for radio altimeters.

It seems a bit weird to me that they let it get this far though.
(apparently they're thinking of non-5G areas close to airports at the moment).
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AKar
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Re: 5G Effects

Post by AKar »

The problem is that the requirements (or lack thereof!) for the receiver selectivity in radio altimeters are insufficient to ascertain that somewhat nearby C-band 5G transmissions are not picked up by the radio altimeter, thus this could potentially cause issues. From what I gather, the 5G systems work exactly as certified whereas the radio altimeter systems have generally not been tested to confirm that they stick within their allocated band in what comes to reception. This makes the position of the telecommunications companies rather understandable.

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CAPFlyer
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Re: 5G Effects

Post by CAPFlyer »

There has been a study released that showed 5G signals at the upper end of the US spectra allocation can and do interfere with the operation of Radio Altimeters (RA) on some aircraft. In fact, they interfere in such a way as to be invisible to the crew and not generate any flag or other warning that they are not working properly.

As was pointed out above, the issue is that in the US, the allocation is *much* closer (right at 200MHz spacing) to the allocation for RAs. Also, as RAs operate at much lower power than C-Band 5G (RA's are 40 milliwats to 5 watts, 5G is 1 watt to 10 watts for the towers), there is sensitivity issues for the receivers being overpowered by stray or harmonic signals from the higher powered 5G transmissions.

The RTCA published a report showing that at the spacing the FCC had proposed and auctioned (without consultation with the FAA, against protest from aviation groups who were concerned about the lack of testing, and without actual testing beforehand) did cause interference. This isn't some "we don't like 5G" thing. There are demonstrable changes between the FCC US frequency allocation and the rest of the world. *NOTHING* was done by the telecoms or the FCC to check to ensure there wasn't going to be interference with an essential safety system or ensure there were restrictions (as were implemented in Canada) to limit transmission power in the vicinity of airports. The response from the FCC was basically - we believe this is "necessary" to expand public internet access so it overrides everyone else's concerns. Now the FCC is having to back down because the Telecoms have been hearing not just from US airlines and the FAA that they want them to slow their roll, but from European operators and regulatory agencies who've said the same thing - don't do this, you *will* create a dangerous situation. Emirates Airlines, Lufthansa, and I believe 1 other airline had announced reduction, or removal of planned spring flights into a number of their US destinations when the FCC didn't back down. I don't know if that will change back now that the Telecoms have backed down, but I think that was the trigger that made everyone involved on the 5G side understand that it was really a serious issue, not just the FAA and "aviation" complaining about a perceived issue.

RCTA Report - https://www.rtca.org/wp-content/uploads ... hanges.pdf
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AKar
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Re: 5G Effects

Post by AKar »

A couple of points I think need addressing. Just to disclaim my views on the issue, I'm a telecommunications engineer by education, and I have spent the most of my professional life in aviation-related fields. So, take my gall on the actors for what it's worth!

First, this entire issue is ridiculous and should have been completely avoidable. It is not like FCC is acting renegade here and pushing the 5G frequencies right against the frequency band allocated for radio altimeters. There apparently is a good 200 MHz of gap in between - this is a huge space by modern standards. When a band of frequencies gets allocated for specific uses, some strict limitations are imposed on the maximum power levels within that spectrum, and on the amount of 'stray' interference on the adjacent bands. Due to highly congested RF spectrum of these days, the requirements are very strict indeed.

Technically speaking, testing of the RA units for interference was not, nor should have it been, a problem of the telecom side. Their problem is to remain strictly within their allocated band with their emissions, and I dare to say for a fact that this has been fairly meticulously tested and confirmed as per industry practices.

Instead, it would have been a problem of the avionics industry to ascertain that the radio altimeter equipment is sufficiently immune to emissions well outside their own band allocated to RAs! It would have been a problem of the FAA and other relevant authorities to keep the requirements up to date, and to create and enforce ruling to make sure no problems like this rise. But I think they were caught sleeping at the wheel.

The issue, in my opinion, is not the 5G interfering with the RAs, but that the RA designs have been held to such ridiculously unrobust standards. All this time they have gotten away with such poor receiver selectivity criteria simply due to the fact that no wide-spread use of these frequencies happened to exist. It is "not ok" that the aviation industry keeps other industries liable for their own problems rising due to not keeping up with the world with lax designs. They should have either updated the design criteria - or purchased the offending frequency bands to themselves!

Of happier note is that there are plenty of RAs out there, it turns out, that actually are immune to these issues. I sincerely wish they get appropriately acknowledged via a good increase in their customer base, for doing their job right.

-Esa

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CAPFlyer
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Re: 5G Effects

Post by CAPFlyer »

The FCC *did* operate against practice. They posted the proposal in May 2020. They refused to cooperate in the creation of a testing group with the RTCA (who does many of these types of tests) who was asked by multiple entities, including the FAA, to do the testing. They did the testing and delivered the report in *OCTOBER* of 2020 saying that the RAs weren't going to work well with signals that close. They also noted that deployment in other countries had given more space without problems. The FCC was also asked to delay auctioning of the spectra to give time for new certification efforts to occur (and noted that it typically takes 18-24 months for this to occur) and that this was in progress.

The result? The FCC pretty much said tough, and auctioned the spectra in December 2020 (and announced the winners in Feb. 2021) with an implementation of January 2021. The FAA, aviation groups, and the RTCA meanwhile were continuing to lobby the FCC to delay implementation or move the spectra. The FCC refused.

So yes, you're right that the designs aren't great. They probably shouldn't have ever had a problem. But the fact of the matter is - they do. The FCC was told that if they moved forward that it would cause problems. They were given alternatives - alternatives in use by *OTHER COUNTRIES* to mitigate the problem. The FCC ignored them and moved forward. The FCC TO THIS DAY has not done a thing to respond to the credible problems the allocation creates beyond come out and basically call the RTCA liars. Even the telecoms were calling the RTCA liars until they started getting hit with pressure from foreign airlines and regulators because the FCC wasn't budging.

Aviation regulations mean that getting new designs certified, even with something as simple as a better signal filter, takes time. Time that the FCC didn't give. Time that the Telecoms didn't want to give. Now the hand is being forced, and the FAA and Aviation is winning because the issue is *safety* and safety thankfully is winning over commerce in this case.

BTW, as an engineer - don't you usually fix problems by the easiest and least costly method? Is not the easiest and least costly method in this case to simply move the spectrum allocation to match what is the standard in other countries? Or maybe just to limit the output power as is already being done in Canada? Change the new thing you haven't "frozen" design on instead of trying to fix the old that is going to be more costly in both time and money? It's not like anyone is saying that you can't use the C-band at all. The issue was that the band allocation was not in line with the rest of the world and that there was no mitigation or testing performed before allocating the band to ensure it didn't create a hazard.
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AerialShorts
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Re: 5G Effects

Post by AerialShorts »

For whatever it’s worth, phone manufacturers have already been shipping 5G phones that use the frequencies the FCC approved. They may not be able to accommodate moving down spectrum and if they can’t, that would cause lots of problems and lawsuits. There may not be open spectrum to move to as well.

What would be really handy is if a simple inline filter could be inserted into the RA antenna cables in the aircraft. If narrowing the bandpass of signals the RA sees can fix the issue, that could probably be done pretty cheap and easy but no idea what regulations or testing requirements would apply.

If the 5G signals are just too wide and have power in the RA assigned frequency band, a filter won’t help since it would still let them through. I believe, though, that by FCC rules, the telecoms would be liable then for causing interference.

Just my opinion but I put this on Ajit Pai. He was head of the FCC through the period leading up to this situation and he was all for commercial use of the radio spectrum. There were a lot of bad decisions that leaned hard to big business interests.
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Hook
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Re: 5G Effects

Post by Hook »

Change the new thing you haven't "frozen" design on instead of trying to fix the old that is going to be more costly in both time and money?
Some people break out in hives at the mere mention of "backwards compatibility".

And in this case there are votes to be won and money to be made.

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AKar
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Re: 5G Effects

Post by AKar »

CAPFlyer wrote: 20 Jan 2022, 15:23 The FCC *did* operate against practice. They posted the proposal in May 2020. They refused to cooperate in the creation of a testing group with the RTCA (who does many of these types of tests) who was asked by multiple entities, including the FAA, to do the testing. They did the testing and delivered the report in *OCTOBER* of 2020 saying that the RAs weren't going to work well with signals that close. They also noted that deployment in other countries had given more space without problems. The FCC was also asked to delay auctioning of the spectra to give time for new certification efforts to occur (and noted that it typically takes 18-24 months for this to occur) and that this was in progress.
I don't know the politics of this, nor how the regulatory organizations are exactly structured in US, and how they interact (or don't). Sounds indeed that there is more into this than pure technicalities, as usual. Obviously, I am all support for regulatory agencies acting together on these issues. But on the other hand, all that is way outside of my sphere of competence to comment really.

Regardless, I can imagine if I were working for FCC, and I was told that, hey, they've got these radio altimeters that may not work correctly due to my signals, meeting all the requirements, occupying a band some 200 MHz away from theirs... I would simply tell them to fix their stuff.

In a technical sense, the issue is simple. When I am given a band to operate within, my responsibilities are
a) to make sure I actually stay within it and at or under the power levels allowed, and
b) to make sure I am not affected by what is happening outside my band, as I don't have, nor should I have, anything to say about my neighbors (be the 'properties' occupied or not), as long as they play by the rules and stay within their respective envelopes.

Seeing how all this unfolds, by the time of me writing this 13 radio altimeter models, making up some 78 % of commercial fleet, have been "cleared" of this issue. In these cases it appears that the actual engineering was done at least somewhat properly. Given how quick process this has been, I wouldn't be surprised if the manufacturers simply submitted their interference testing documentation from some tests they've done way back in time (like they should have - kudos on them if that's the case!).

This turns my head towards the actual root of the problem. Quoting the RTCA slide deck [.pdf],
In all cases (TSO-C87, DO-155, and ED-30), there have been no specific requirements regarding interference susceptibility or receiver masks
  • Latest update to requirements was 1980—what did the RF spectrum look like then?

How come, on the equipment considered by the industry critical enough to 'wave the safety card'? It is not much of a stretch to expect safety critical stuff to be held to at least similar standards than pretty much the every single appliance in production is.

Returning to my imaginary seat working for the FCC above, if I didn't have my aviation background to help understanding that quite everything is possible with this stuff, it would be likely that I indeed would not initially believe the existence of such a ridiculous problem, and might dismiss these claims as lies myself!

CAPFlyer wrote: 20 Jan 2022, 15:23 Aviation regulations mean that getting new designs certified, even with something as simple as a better signal filter, takes time. Time that the FCC didn't give. Time that the Telecoms didn't want to give. Now the hand is being forced, and the FAA and Aviation is winning because the issue is *safety* and safety thankfully is winning over commerce in this case.
In short, my (engineering) opinion is that no such time was ever needed, if the aviation industry was held up to the same standards that basically everyone else is. Yes, the issue is safety, but the specific safety issue is the existence of obsolete requirements allowing for substandard designs in safety critical applications. This is a part of a bigger problem plaguing and stagnating the aviation industry, despite some good efforts. I am not going into it now, but in a nutshell, the regulatory framework has created a hideous pretzel of don't touch it to not break it style of engineering culture. Which is okay when the foundations are solid, but extremely detrimental when they are not.

CAPFlyer wrote: 20 Jan 2022, 15:23 BTW, as an engineer - don't you usually fix problems by the easiest and least costly method? Is not the easiest and least costly method in this case to simply move the spectrum allocation to match what is the standard in other countries? Or maybe just to limit the output power as is already being done in Canada? Change the new thing you haven't "frozen" design on instead of trying to fix the old that is going to be more costly in both time and money? It's not like anyone is saying that you can't use the C-band at all. The issue was that the band allocation was not in line with the rest of the world and that there was no mitigation or testing performed before allocating the band to ensure it didn't create a hazard.
Engineering experience suggests that the easiest and least costly method to fix the problems is to avoid them in the first place, preferably via sound designs. I don't know the specifics of rationale (or maybe lack thereof) behind the frequency allocation in the US, but in grand scheme of things the mobile frequencies (among others) tend to differ from those used in Europe and elsewhere. That's why mobile manufacturers have different sub-models for American, European and Asian markets. They usually utilize some bands from outside of their 'regionalization' to support global roaming, but usually not all of them. Within the US, it is not so simple to simply moving the frequency either - not only have the equipment been designed, tested, and certified to utilize these frequencies, the entire spectrum is extremely congested [.pdf from 2016]. Further, the bids on the bands run in such figures that it is likely not the cheapest way out.

-Esa

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CAPFlyer
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Re: 5G Effects

Post by CAPFlyer »

@AKar - Oh, I don't disagree that the design sucks. Don't get me wrong there. But the problem is that "Because Aviation", fixing it takes years (like 3-5 on average). The FAA and the Airlines asked the FCC to delay implementation to give them time to fix it (remember, the report of there being a problem came out in October 2020) or at minimum implement mitigating strategies to make it safe until the final fix could get approved.
AerialShorts wrote: 20 Jan 2022, 16:03 For whatever it’s worth, phone manufacturers have already been shipping 5G phones that use the frequencies the FCC approved. They may not be able to accommodate moving down spectrum and if they can’t, that would cause lots of problems and lawsuits. There may not be open spectrum to move to as well.
The problem isn't the phones. It's the base sites. They operate at a much higher power and this is where the issue is. That's why the telecoms were so easily able to agree to delaying implementation, they really aren't loosing much because the stuff they're working with on the "base" side is much more flexible than the phones.
What would be really handy is if a simple inline filter could be inserted into the RA antenna cables in the aircraft. If narrowing the bandpass of signals the RA sees can fix the issue, that could probably be done pretty cheap and easy but no idea what regulations or testing requirements would apply.
The fix is probably that easy. The problem is getting it approved isn't. You can't just add a filter "Because Aviation" if it was that simple they'd have already done it. Instead, they're having to go through all the regulatory process to get the modification approved, which takes time (see above).
Just my opinion but I put this on Ajit Pai. He was head of the FCC through the period leading up to this situation and he was all for commercial use of the radio spectrum. There were a lot of bad decisions that leaned hard to big business interests.
Ehh, he was only there for a very short period of time and there was a lot of stuff thrown on him because of his public statements, but remember that these agencies are much bigger than one person and so while they might be the final word in a lot of things, these projects were started before he got there and only the last couple of steps occurred under him. The FCC has gained a reputation in the last 15 or so years of not being a team player, especially when it comes to aviation and space. It started with LightSquared, and the 5G C-Band auction is only the latest of several big spectra allocations/auctions that have ruffled feathers at many civilian and military agencies.
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Re: 5G Effects

Post by AerialShorts »

CAPFlyer wrote: 22 Jan 2022, 17:38 The problem isn't the phones. It's the base sites. They operate at a much higher power and this is where the issue is. That's why the telecoms were so easily able to agree to delaying implementation, they really aren't loosing much because the stuff they're working with on the "base" side is much more flexible than the phones.
What I said was that phones have been being manufactured and sold that may or may not be locked into the 5G specification that was being rolled out. I never said phones were the interference problem. A lot of stuff is very firmware/software configurable so maybe phones could be moved down spectrum, but the tower transmitters would also need to be shifted down spectrum and again, no idea if there is any provision for that kind of configurability. I was talking about the frequencies and not the power. It was said early on in the news and elsewhere that phones themselves are low power and not the issue. Plus, I’d guess that the phones wouldn’t be transmitting on the 5G frequencies anyway without a 5G signal from towers. But yeah, it’s not a phone interference problem at least from what has been said.
Ehh, he was only there for a very short period of time and there was a lot of stuff thrown on him because of his public statements, but remember that these agencies are much bigger than one person and so while they might be the final word in a lot of things, these projects were started before he got there and only the last couple of steps occurred under him. The FCC has gained a reputation in the last 15 or so years of not being a team player, especially when it comes to aviation and space. It started with LightSquared, and the 5G C-Band auction is only the latest of several big spectra allocations/auctions that have ruffled feathers at many civilian and military agencies.
Ajit Pai was head of the FCC for four years from 2017 to 2021 and was very active setting policy and direction during that time. Engineering development cycles would tend to say 5G was being worked on long before Pai became head, but as 5G was about to roll out, it was up to Pai to cross the t’s and dot the i’s. Pai was a bad head for the FCC and prioritized selling off spectrum and a hands off approach to spectrum management. It’s hard to give Pai any kind of pass when the final parts of the 5G rollout occured square on his watch. Pai was a hatchet man and over his head. But telecom companies sure were happy. That’s on Pai.
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AKar
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Re: 5G Effects

Post by AKar »

CAPFlyer wrote: 22 Jan 2022, 17:38 @AKar - Oh, I don't disagree that the design sucks. Don't get me wrong there. But the problem is that "Because Aviation", fixing it takes years (like 3-5 on average). The FAA and the Airlines asked the FCC to delay implementation to give them time to fix it (remember, the report of there being a problem came out in October 2020) or at minimum implement mitigating strategies to make it safe until the final fix could get approved.
Luckily, it appears that most of the designs don't suck at least too bad, as so far all major Boeing and Airbus aircraft models, among the others, have been cleared by the FAA for the low-visibility approaches in 5G deployment areas, at least with some P/N radio altimeters. More so, the problem is that there has been no requirements to design up to the standards that could be expected nowadays. Hence, compatibility of the radio altimeters with other systems on the nearby bands was unverified from the certification point-of-view, and there probably was not much documentation available to make assumptions on. In a nutshell, there were no other incentives to create robust off-band rejection characteristics but engineering judgement, and even then the specific characteristics likely were not formally documented.

Now, everything I've written on this topic has been more of an opinion piece. Of course, I do understand perfectly that there are much more details in the weeds of actual EMC testing that would certainly benefit from collaboration between aviation and telecom industries even if the radio altimeters were held up to similar standards that they would be if the certifying specs were written today. Even in that case there could be some unexpected issues coming up, but all these could be handled via more regular means.

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Re: 5G Effects

Post by CAPFlyer »

AerialShorts wrote: 23 Jan 2022, 08:20What I said was that phones have been being manufactured and sold that may or may not be locked into the 5G specification that was being rolled out.
Sorry if I wasn't clear on what I meant by that statement. I doubt the phones were designed in such a way as to be unable to operate in the entire C-Band spectrum for 5G that the ITU designated. While 5G moves within certain parts of it, the entire band available for 5G is pretty well defined and everyone stayed within it, it's just some areas picked higher and lower segments of it.
Ajit Pai was head of the FCC for four years from 2017 to 2021 and was very active setting policy and direction during that time. Engineering development cycles would tend to say 5G was being worked on long before Pai became head, but as 5G was about to roll out, it was up to Pai to cross the t’s and dot the i’s. Pai was a bad head for the FCC and prioritized selling off spectrum and a hands off approach to spectrum management. It’s hard to give Pai any kind of pass when the final parts of the 5G rollout occured square on his watch. Pai was a hatchet man and over his head. But telecom companies sure were happy. That’s on Pai.
I don't disagree fully, but Pai didn't decide what part of the 5G allocation to auction, his people did. And that's where my issue is - why did they choose to go higher than anyone else? I'm sure the telecoms asked in some way for it, but also knowing what the existing Canadian and European allocations were, it makes no sense for the FCC to eliminate half the lower part of the spectra and expand so far up. It also wouldn't have been Pai who drafted the power limitations near airports and such and would have been aware of such restrictions in Canada. That's more my point. Yes he pushed for the auctions to occur, but it was the rank-and-file below him that already had a history in recent years of not really doing their jobs that are mostly to blame.
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Re: 5G Effects

Post by AerialShorts »

CAPFlyer wrote: 23 Jan 2022, 14:16 And that's where my issue is - why did they choose to go higher than anyone else? I'm sure the telecoms asked in some way for it, but also knowing what the existing Canadian and European allocations were, it makes no sense for the FCC to eliminate half the lower part of the spectra and expand so far up. It also wouldn't have been Pai who drafted the power limitations near airports and such and would have been aware of such restrictions in Canada. That's more my point. Yes he pushed for the auctions to occur, but it was the rank-and-file below him that already had a history in recent years of not really doing their jobs that are mostly to blame.
Bandwidth is why. Using the higher frequency part of the band gets more capacity and more speed. It’s cited a lot as why the US went higher in frequency. As to reconfiguration to lower frequency, maybe phones could be reprogrammed to use lower frequencies for 5G - I don’t know. It’s a red flag though. There’s a lot that gets optimized for certain frequencies in transmitter and receiver designs. The way things are being handled now with the FAA clearing hardware, I suspect there’s lots of reasons why moving down frequency might not be a practical option now.

Blaming government workers seems to be the go-to now. If the rank and file weren’t doing their jobs, that’s on the managers and higher-ups. I worked in government and the people I saw were hard-working and cared about their work. Government workers are just like everyone else. Tone and direction gets set from the top. You don’t know who did and didn’t do their jobs at the FCC to make those hand wavy claims. I don’t know what Pai said or did behind closed doors. But he was head during the time 5G was being rolled out and was notorious for taking sections of public airwaves and selling them off to telecoms. He spoke out against monitoring the effects of social media and pushed for telecoms to be able to tie their services to proprietary hardware. Pai also worked to dismantle net neutrality and endorsed ISPs being able to surcharge or block traffic from other services. Pai’s tenure at the FCC was controversial and not in the interests of the public. Again, Pai weighted everything heavily to telecoms and big corporations. He pushed to end rules that limited how much of a television and radio market corporations could own. He was a busy man. Naggy little things like telecoms endangering the lives of air passengers probably weren’t a big concern.
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