Military scrambling to understand aviation crash risk from new 5G sale | Hacker News Reader

Military scrambling to understand aviation crash risk from new 5G sale

defensenews.com

120 pointsbookofjoe104 comments

Not a single interview with someone who actually understands how the systems work, nor any reference to any studies that show any results, positive or negative. Not one single "hey, so we set up a terrain avoidance radar and blasted it with variations of 5G communication and guess what?" (my suspicion is the answer would be "no effect", but let's at least do the study, huh?)

Radar altimeters use vastly more power than anyone would waste on mere communication. They also don't depend on subtle variations in the signal to communicate. It's basically just listening for a return and measuring time-of-flight. Timing measure is more complicated, but doesn't depend on subtleties of the signal that could be easily interfered with. (Full disclosure: I've worked on Herc terrain-avoidance radar, but that was forty years ago.)

Note also that commercial aviation pilots don't use terrain avoidance radar in normal flight operations. It's an emergency system. If you're low enough to need it, you're supposed to have an airport in sight. If you start getting the "Terrain. Pull Up" warning, several things have already been going wrong for a while. If you blocked the TAWS system of a commercial airline in normal flight, it's unlikely they'd even know it. You'd have to wait around for a lost or damaged aircraft that was already about to crash, which is a pretty unrewarding hobby.

To be honest, I'd be surprised if the military didn't already have a pretty good idea how to spoof terrain avoidance radar, it would be the kind of thing that might be nice to have in a special operations toolkit. But I doubt it looks like sitting on the end of a runway with a cell phone. More like humping several car batteries, a dish antenna and a Halliburton case full of electronics to the top of a ridge. (Which, another thing: terrain avoidance radar is the opposite of stealthy, you wouldn't use it for special operations, especially when you have access to GPS, satellite maps and inertial navigation systems).

Even a 5G transmission from ground to geosynchronous orbit would be columnated by a dish, so would only interfere with a moving altimeter for a fraction of a second, and those systems are designed to handle transients. I'm not saying there isn't a potential issue, I'm saying you're not going to find out if you limit yourself to interviewing bureaucrats.

Anything big (like an airliner) isn't allowed to rely on radio altimeter alone for terrain avoidance for many years now. They're GPS augmented. Whenever it is confident where it is (which will be always or almost always) the plane is deciding whether it could hit something by continuing to move apparently forward and alerting the pilots about that.

When you hear "Obstacle Obstacle" announced in Sully, that's not a radio altimeter detecting the bridge, the computer has concluded that the plane's motion is uncomfortably close to the bridge tower based on GPS and a database of tall things you might fly a plane into (and thus it knows this is an "Obstacle" whereas a mountain is "Terrain").

In that movie there's not a damn thing they can do beyond avoiding the bridge itself, because they don't have any thrust - but ordinarily pilots should near instinctively try to ascend immediately for any of this group of warnings. The training is specific that this is not the time for diagnostics, if you aren't already absolutely sure why the computer thinks you're about to hit something you must assume the computer is correct and climb at best rate. This routinely saves lives when pilots become confused about where they are.

Except in something like AirFrance 447 I guess?

There was no obstacle alert there. They just stalled.

Why do you even bother? I thought it was obvious by now this is propaganda to delay the adoption of 5G, allowing US competitors to catch up on Chinese equipment. The "concerns" are coming from bureaucratic positions no technically-savvy ones.

Indeed, if there is not a credible explanation from first principles it should be assumed that the article was written primarily for reasons other than illuminating knowledge.

Is there some evidence to support this idea that this is "obvious" propaganda? A plausible link, like what dog does the "Aerospace Industries Association" have in the 5G network hardware market?

From my not-very-informed perspective US competitors don't need to catch up to Chinese equipment, the Chinese equipment makers are locked out. If anything the US equipment makers would have the OPPOSITE motivation, get the spectrum sold and get their sub-standard equipment into the networks before the position of the US government could possibly change and they face real competition. And that is kind of what is happening, right? The actual story here is the FCC (lead by carrier and equipment friendly folks) are seemingly pushing ahead despite concerns from other industries, no?

The Chinese equipment might be locked out from the US market, but not from the world market. Unless the US could leverage the trust the world has on them to keep China from gaining market share. Remember they asked candidly the British to not buy China's 5G.

Also, not so long ago there were "reports" claiming Huawei devices were compromised and no evidence was provided. The negative marketing against China has been candid and in the open. The US is just trying to win in the court of public opinion on several fronts.

So yeah, "The military is scrambling to understand the aviation crash risk from a new 5G sale" and don't provide a technical basis for the concern: it reads propaganda all over.

I think China is effectively locked out of Western countries or at least US allies. The UK has banned Huawei and any purchased 5G equipment has to be decommissioned by 2027. Australia and NZ have also banned Huawei.

In this case the concern is with interference in the 4.0-4.2Ghz spectrum, nothing specific to 5G technology.

Is this frequency congested anywhere in the world with or without 5G technology to test?

But again, this doesn't really explain why US military hardware makers are concerned about this, unless the theory is that the US 5G equipment makers are pressuring the private industry groups that make military aviation equipment to pressure the US military and the FCC.. pretty far down a rabbit hole at this point with zero evidence.

And around the world 5G is not being deployed at the same frequencies! They are concerned about a particular spectrum. Lots of the purchased spectrum as I understand it is 30Gz+, they are raising zero concerns about that.

These are all good points, however just because this is a system that's only used in emergencies does not mean that this should be overlooked.

Just this year Kobe Bryant died because his helicopter impacted the terrain.

If this happened after the sale, you'd have to do just as difficult of an analysis to prove that 5G frequencies did not play a role in the impact, so why not do the analysis before hand?

I don't recall advocating not investigating this because the affected systems are emergency ones. I'm advocating against claiming there is danger without investigating ('abundance of caution' is usually shorthand for 'we could check this, but we're not going to bother and just make decisions without information because, hey, no one ever got fired for saying no, right?') My point is that even if there is potential issue that is highly unlikely, it will still have to line up with several other highly unlikely things for it to be a problem, which is a fairly good definition of 'safe' in modern complex systems engineering.

As to Kobe Bryant, yes his helicopter flew into terrain (unsurprisingly, 'flew into terrain' is incredibly common in aircraft accidents. Sadly, most of them are perfectly serviceable when they do so). There is no indication that the issue was a radar altimeter (if one was even installed, I don't believe they're required in that class), much less one that was being interfered with. I don't think the NTSB report is out yet, but I expect the cause will be what it commonly is: a pilot (with a famous and rich client who wanted to get somewhere quickly) taking their vehicle into marginal weather conditions beyond what they and their aircraft are competent to handle. Working on that problem will save a hell of a lot more lives than investigating 'may be a problem' that no one can even describe a mechanism for.

The Kobe crash could have been prevented by many things.

Existing synthetic vision systems would have easily prevented this. They're not even that expensive - built in systems can be had for a few tens of thousands of dollars, or non-certified iPad based systems for a few hundred.

That crash was likely due to disorientation in dense fog with an experienced, IFR rated pilot but who didn't experience much fog in LA. A radar altimeter would have been unlikely to help.

The Kobe crash could have been avoided by him driving his daughter to school rather than wasting resources on a helicopter every day.

And the potential car crash could be avoided by flying a helicopter. What kind of argument is this? I don't even think it's one.

I'm not really sure the 2020 Calabasa crash is a relevant example. That helicopter had a radio altimeter, and it surely wasn't being jammed. And before hitting the ground, the helicopter was descending at 20 m/s. The last known intent of the pilot was to climb, not descend. Some witnesses on the ground report that the helicopter sounded like it was malfunctioning before the crash. I do not particularly credit eye witnesses, but their story seems to fit with the rapid descent of the helicopter more than an altimeter issue.

Another point I should make about the Bryant crash (now that i've looked it up): while the pilot was IFR rated and the helicopter theoretically had the required instruments, the owning company was not certified for IFR passenger service. That means he the flight was filed as VFR. One of the things they teach you when you get an IFR rating is that you don't fly into IFR weather (IFC for the pedants) during a VFR flight without a pre-filed plan. His IFR training didn't teach him to fly in those conditions---it taught him to avoid them. They didn't have an IFR flight plan or clearance, so flying into a fog bank and persisting in that flight was forbidden and if unavoidable would constitute an emergency. Which is why I tend to look pretty hard at the pilot in this case, not the instruments.

What I don't understand here - if the US need their aircraft to work in combat operations spheres, surely it needs to be robust against this anyway? Nothing to stop an enemy nation state using this to confuse

Effective signal range, maybe? If an operational base is large enough, 5G sources outside of this perimeter will not be effective. It also sounds like it is trivial to create artificial barriers to absorb the emitted energy.

"5G wavelengths have a range of about 1,000 feet, not even 2% of 4G's range. So to ensure a reliable 5G signal, there needs to be a lot of 5G cell towers and antennas everywhere. We're talking on every lamppost, traffic light, etc. because even trees can block 5G signals."

[p.s. hmm. Counter point: Disposable loitering EM-drone swarms. I guess this boils down to battery tech again.]

Which is why, when people tell me how "awesome" 5G will be, I have to remind them of the massive infrastructure cost. DC power in Europe also has a similar issue. It's a "short haul" technology. 5G repeaters may be possible, but I'd want to understand the roadmap for what comes next... could they be reusable for whatever "6G" might be? Otherwise we're going to spend a TON of money littering up the landscape for a short term gain.

What are you referring to by 'DC power'?

Differences between AC and DC power distribution and why you might chose one over the other. TLDR, AC is the most common choice for good reason, but there are also conditions where DC would be the better choice:

You may have heard something like "AC is better for power distribution than DC." I would not go so far as to call this a lie, AC is in fact "better" than DC in lots of common cases, probably the big two being that at some (but not all) voltages, AC transmission is more efficient than DC and the second being that AC can be stepped up and down in voltage very efficiently without electronics or anything else more complicated than several loops of varnished copper wire.

Of course this is not true in 100% of cases. For example, at very high voltages (think 100s of thousands of volts) something called the skin effect can become so pronounced that DC becomes more efficient than AC. There's a high voltage DC power transfer backbone in Europe for this very reason. When you're dealing with multiple countries and potentially different standards for AC power distribution, this has the nice side effect of eliminating the need convert between frequencies and phases of AC.

The other, and probably the biggest reason you would choose a DC power distribution system is because your power source is DC. Pretty much all power is generated the same way, from fossil fuels to hydroelectric and even nuclear power - you use energy to spin a turbine, and that circular motion is used to induce an alternating current. There's really only one way to get efficient DC power and that's solar panels. Depending on the use case, the losses of converting DC to AC (and often, rectified back to DC again for the end-use application) may not be worth it.

Pacific Intertie is borderline-famous application of DC in the US (with Swedish tech) and the Wikipedia article [1] looks like a good description.

[1] https://en.wikipedia.org/wiki/Pacific_DC_Intertie

Recommend the film “The Current War” for those interested in an entertaining look at the history of AC vs DC and the characters involved. I found it balanced, and not really picking sides between Edison and Tesla, in terms of hagiographic treatment.

https://www.imdb.com/title/tt2140507/?ref_=fn_al_tt_1

>massive infrastructure cost........It's a "short haul" technology.

Again, only in US, and only mmWave.

It seems US is the only part of the world where they use mmWave and 5G interchangeably. ( I guess I could blame the Media for it. ) Most part of the world aren't even thinking of implementing mmWave.

5g already is awesome, and the vast majority of it uses the same exact spectrum bands as 4g. mmWave, which is a portion not shared with 4g which has high infrastructure costs, only tends to get deployed in super high density places that need the extra bandwidth. You can buy a 5g phone today and get the advantages of 5g without ever connecting to a cell site that your 4g phone couldn't connect to.

Also, you aren't spending that money, some cartel telco is spending that money. You don't have any reason to be concerned about the amount of money they're spending. Those costs they're incurring has almost no relationship to the price you are paying...this is cartel economics 101.

When you say cartel telco, are you talking about the telco's the cartels have set up?

https://www.reuters.com/article/us-mexico-telecoms-cartels-s...

Or just AT&T, Verizon and T-Mobile? Is there anything that shows they have been working to limit access to the market?

Are people trying to bring back DC for distribution? I love the idea but the short range and larger conductors seem to be barriers.

I've been working on a 24VDC network for my workshop, but even across the room I'm accounting for voltage drop.

The whole point of the high frequency portion of 5G is providing more bandwidth in dense urban areas with a lot of devices.

5G works on a variety of frequencies. The limits quoted are mmWave frequencies, which are very high 25 - 52GHz, and meant for short-range density.

The frequencies in this article are in the 3GHz range.

At that point why can't we just use WiFi? Or develop WiFi until it's as useful as 5G? Why all these special exemptions for large organizations building networks?

IMO, 5G is about automation and command/control of roving robots, “Smart Cities”, and finally Augmented Reality (AR) in industrial and urban contexts. Applications range from benign factory automation to Boston Dynamics police dogs patrolling your neighborhood, to your walking in downtown Tokyo and being (virtually) greeted by AR entities.

What is it that WiFi can not do but 5G can? 5G’s much lower latencies allow for R/T CnC (which enables all of the above).

So, for example, your factory floor bot’s camera sees something that it’s local AI can’t categorize, so a central node with greater computational power and storage capacity can (in R/T) make decisions and send operative commands:

Do the roundtrip latency calc for below for 4G and 5G:

    node -> base station -> fast network —> central control

Is WiFi really the slow part there? How does 5G improve on it? No retransmits?

This what the search engine pulled up when asked about 5G latency:

"5G technology offers an extremely low latency rate,the delay between the sending and receiving of information. From 200 milliseconds for 4G, we go down to 1 millisecond(1ms) with 5G. Just think about it. A millisecond is 1/1000 of a second."

National Security Implications of Fifth Generation (5G) Mobile Technologies

5G technologies could have a number of potential military applications, particularly for autonomous vehicles, C2, logistics, maintenance, augmented and virtual reality, and ISR systems—all of which would benefit from improved data rates and lower latency (time delay).

https://fas.org/sgp/crs/natsec/IF11251.pdf

Interesting enough, a simple 'r/national security/civil liberty' and 'r/military/police' highlights a peculiarly undiscussed aspect of the enthusiasm of goverments worldwide to implement 5g, so that "gamers can have a better gaming experience!".

That's about what you get with WiFi. It still doesn't matter because the internet will add 30ms in the best of cases.

I don't remember the source that discussed the specific applications. But rtt from edge to basestation is 400ms wifi and 2ms for 5g, which is almost like something vs nothing. So we're talking applications that are OK with the hardwire network latencies (here lets say 100ms rtt including the time for computing). That 400ms rtt for wifi must get the total rtt over some viability threshold, would be my guess.

I'm pretty sure I get closer to 2ms on my local 2.4ghz WiFi network without doing anything special. If those numbers where real then no one could play games over WiFi.

Without considering the merits of the issue, given the scarcity of spectrum: militaries accept that safety margins are much lower during combat operations; however that doesn't seem like a strong argument for reducing safety margins during peacetime operations.

The military has its own effective means of silencing interfering sources permanently it can't use in peacetime.

Also these altimetes are most useful when landing which is generally done on your side of the lines.

Those interfering sources cost on the order of $10, the, uh, "mechanisms of silencing them" probably cost a couple orders of magnitude more, and the aircraft that could be brought down (such as the C130 in the article) cost on the order of $100M.

It's a highly asymmetric problem.

Also, bombing every cell phone within a few miles of your airport is likely to have some undesired side effects...

Edit: A commenter further down mentioned the AGM-88 HARM, which is a $280k missile. That's significantly more expensive than my estimate of a couple orders of magnitude for a 'dumb' missile from a helicopter.

Tube artillery also works to silence sources. HARM is for things like air defense radars in enemy territory.

The combination of battery tech advances, cheap wireless comms and cheap processors has created a huge range of asymmetric risks like this. I suspect terrorists/freedom-fighters (depending on which side of which conflict you're on) will be exploring them for a long time to come - bomb-drones and remote IEDs are just the start of the development curve.

Everyone keeps calling these risks asymmetric, but we haven't seen the price of a birdshot flak cannon because there hasn't been that much of a need yet.

The cannon, targeting system, radar, and so on, is likely to be more expensive than the number of suicide drones to destroy it.

Well as the famous game theorist Voltaire said, you shoot one to encourage the others. That brings down the cost pretty quickly.

10$ of parts, manufactured in some basement with soldering iron... Or similar level stuff... Add batteries(for this regular ones work too) add basic timer software and spread around...

Yep, pretty funny if it really would work.

A lot of the old justification for not having LEO satellite internet in the past, was that doing so would cross over marine GPS spectrum for older GPS devices. I'm surprised they okayed anything that interferes with their spectrum.

Radio altimeters are mainly used during landing. Presumably, you'd always be landing in friendly territory, so the threat of malicious interference would need to be very close to a base to be effective.

For many types of flight, planes are robust against radio altimeter failure. The RA is really only used as a non-essential part of instrument approaches (e.g. landing in heavy fog, as opposed to a visual approach where a pilot can see the terrain) and as part of the ground proximity warning system (which should never be triggered if a pilot is flying correctly).

For military applications, they reduce the risk to pilots and civilians from military aircraft which fly in ways civilian aircraft would never be allowed to. Military pilots are often ordered to hug the ground when deployed in order to avoid RADAR, but this raises the risk of controlled flight in to terrain. RAs are one tool which can help avoid CFIT when flying irresponsibly close to the ground.

Military aircraft would still be able to fly at higher altitudes without RAs.

I think a better counterexample is to ask how those same planes with the same altimeters would fly (safely?) to Europe or Australia that are rolling out 5G in C-band. I seriously doubt EASA would authorise anything remotely unsafe.

Surely if your cutting edge fighter jets can be crashed by a stray not-even-malicious signal from some random 3W radio transmitter, there's something very very wrong with your design?

> 3W radio transmitter

I agree with your point, but most outdoor radio antennas have an output power of like 20-80W btw (which is still significantly lower than many television transmitters).

Ah, good point. I was thinking of the power of most phone radios, not the base stations.

Also, why in the world would a cell phone tower waste any energy at all radiating up? You know, the general direction of airplanes vs out and down where cell phones are actually located

I work in mobile spectrum, and one of the tasks my systems do is account for and maintain compliance with special conditions placed on licenses. There are tons of these...for example, you cant use your 600mhz A block license within a certain distance of a medical facility that uses any WMTS device. C band already has a ridiculous amount of special conditions, and this is actually the first time I've heard of this one in particular, which is pretty insane considering the risks relative to other special conditions IMO.

I do have some capacity to advise stakeholders on upcoming auctions, and my advice so far has been to stay away from C Band, but it's pretty ridiculous how little importance they place on technical aspects of certain bands...they just see spectrum and they want it. Hey, don't listen to me, I'm just the guy who is saving you from 8 digit noncompliance fines. :::rant over::

In case folks are initially confused as I was, the 5G being referred to here is the 5G used for next generation cellular networks – I.e., 5th generation, not 5GHz like used for WiFi in standards such as 802.11a/n/ac.

Also, as another comment points out, this 5G can use more than one broad range in the frequency spectrum, this only affects one of those, and not the street corner/short range one, which is at a much higher frequency.

To make things even more confusing (and harder to Google), 5GHz WiFi has its own history of contention with U.S. military spectrum use [0]:

>In 2007, the FCC (United States) began requiring that devices operating in the bands of 5.250–5.350 GHz and 5.470–5.725 GHz must employ dynamic frequency selection (DFS) and transmit power control (TPC) capabilities. This is to avoid interference with weather-radar and military applications

[0] https://en.wikipedia.org/wiki/List_of_WLAN_channels#United_S...

It's astonishing how much radio spectrum the military sits on but barely uses.

I fly with a radar altimeter safety device and I am not in the military.

Same here... though it appears to be getting flaky and I can't decide if it's worth putting any money into fixing that old instrument... sigh.

As someone who doesn't know much about telecommunication tech, I have a hard time understanding how this happens. From what I've read, the frequency of 5G doesn't interfere with the C-band, as the C-band is 4-8 GHz. This is between the ranges used by the mid and high band spec of 5G.

So why do they auction off "parts of the C-band", and how is it connected to 5G? I'm sure I got something wrong, just curious what it is.

There is a letter here that does a better job than the linked article: https://transportation.house.gov/news/press-releases/chair-d...

Basically, it sounds like they agreed to auction 3.7 - 3.98 GHz & 4.0 GHz - 4.2 GHz. This leaves a gap in the region of 3.98 - 4.0 GHz for radar altimeters. The letter states "recent research confirms that even this spectrum gap is insufficient to ensure radio altimeters are protected from harmful RF interference by 5G networks".

I don't know enough about a radar altimeter's operation to speculate as to why it could be an issue.

No, it's not the 3.98-4.0 GHz gap.

> Given the neighboring aviation band (from 4.2 to 4.4 GHz) allocated exclusively for vital aeronautical radionavigation equipment

They are afraid of (a) heavy use in the 3.7 - 3.98 GHz band (fundamental emissions) and (b) "accidental" broadcasts in 4.2 to 4.4 GHz range (spurious emissions). The study [1] on p. 12 in §6.1.1 basically assumes the 5G equipment will blast an interfering signal on altimeter band at full power. I think any frequency allocation request can be shut down this way.

And I don't think 5G network will work properly if even a fraction of the assumptions in that report are true. If you look at https://en.wikipedia.org/wiki/5G_NR_frequency_bands, you will see that bandwidths are in 10s of MHz and the sub-carrier spacing [2] is as low as 15kHz. If 5G radios will be off by 15kHz (as opposed to 202000 kHz from 3.98 to 4.2 GHz as the aviation industry is implying), 5G network transmissions will not work properly.

[1] https://www.rtca.org/wp-content/uploads/2020/10/SC-239-5G-In...

[2] https://info-nrlte.com/tag/subcarrier-spacings/

>If 5G radios will be off by 15kHz (as opposed to 202000 kHz from 3.98 to 4.2 GHz as the aviation industry is implying), 5G network transmissions will not work properly.

But that's not really how RFI tends to work - you can be perfectly aligned to your target frequency and generating the signals you expect there, but still be generating mixing or LO spurs, image response, third-order intermodulation products and so on which can be at totally different frequencies.

Thank you for the correction.

> mixing or LO spurs, image response, third-order intermodulation products

Do I understand it correctly that it will only be a fraction of the output power and equation (6-1) in https://www.rtca.org/wp-content/uploads/2020/10/SC-239-5G-In... must have a coefficient so that P_source would become P_source*k_spurious where k_spurious < 1 or even k_spurious << 1?

Edit: by not working properly I did not mean that the signal on the target frequency will have severe interference but that just 15kHz apart there could be another target frequency that must be free of interference or otherwise multiple operators will not be able to use the 5G spectrum (12f, ie 180kHz seems to be an accepted guard band as per [1] and FCC seems to have mandated 23MHz guard band [2] which is 127x the norm) or even a single operator will not be able to use OFDM effectively. Am I still wrong in my understanding?

Edit 2: with the interfence evaluation from [1], almost all evaluated guard bands result in -20dBm interference which would make proper k_spurious=0.01. My understanding remains that the aviation industry report used overzealous assumptions and overestimated the interference emission power by at least 100x.

[1] E. Memisoglu, A. B. Kihero, E. Basar and H. Arslan, "Guard Band Reduction for 5G and Beyond Multiple Numerologies," in IEEE Communications Letters, vol. 24, no. 3, pp. 644-647, March 2020, doi: 10.1109/LCOMM.2019.2963311.

[2] https://arstechnica.com/tech-policy/2020/05/millions-of-gps-...

As far as I can see, based on a very quick skim reading, the study is essentially divided into a consideration of impacts from fundamental and spurious emissions from 5G transmissions.

For the fundamental emissions, the study considers primarily the impact of receiver front-end overload on the operational margins for the radar altimeters. The referenced ITU document suggests that radar altimeters are specified with "modest selectivity", e.g. 24dB/octave below 4.2GHz up to a maximum of 40dB. I believe that a power spectral density envelope derived from the ITU specifications is the basis of the fundamental emission calculation, not assuming the entire power will be dissipated spuriously.

This is nowhere near my area of expertise, but it seems like those selectivity assumptions (I have no basis for opinion about them) in conjunction with large gains from beamforming are what creates the perception of risk.

Alright, thanks. But what is the use case for the 4 - 4.2 range? If it's outside of the spec, what would operators use it for?

Remember BUDs (Big Ugly Dishes) used for satellite reception? The band they operate on is 3.7 to 4.2 GHz. The FCC has repurposed 3.7 to 4.0 GHz (3.98 to 4 GHz is a guard band) for 5G. Satellite downlinks will continue to operate at 4.0 to 4.2 GHz.

I am not familiar with this specific situation in the US but there are also similar topics in other parts of the world (with civil airborne radio-altimeters as a victim). It might seem odd to talk about interferences while 5G is in its dedicated band far away from radio-altimeters spectrum (> 4.2 GHz), however you have to understand there are 2 phenomenons to take into account :

1°/ transmitter unwanted emissions of 5G (i.e. how much out-of-band/spurious emissions "leak" outside of the 5G band i.e. above 3.8 GHz). This is most likely a negligible issue here even though there are still uncertainties whether the antenna pattern of AAS remains the same in-band and in spurious emissions

2°/ receiver blocking of the radio-altimeter (i.e. even if 5G emissions were perfect, the victim receiver can catch energy from other bands if it doesn't include a proper filter) : this is most likely the main issue here -> from my understanding, those airborne equipments have poor filters (the antenna limited passband probably helps a little bit which is why this blocking phenomenon did not happen previously with 4G in lower bands, but apart from that there is probably a low selectivity with regards to adjacent bands)

Yeah, your second point didn't occur to me. It makes sense that filtering might be lacking if you have a relatively calm frequency neighborhood. Thank you!

This C-band frequencies sale has been in discussion for a few years, it should not have been a surprise to the aviation industry

Precociously, and already utilised in other regions already.

However, when 5g wifi first came about, many weather radars had issues and DFS was born, compulsory in some countries and is designed to make sharing bandwidth less impacting. So historically, there may be some jitter in some regions and more so for regions like the USA that would of utilised that spectrum differently and with that, the impact may well be deeper and like most change - people will always have concerns, however long they are given before that change.

It's odd, I remember the Department of Defense complaining about the L-band auction back in April[0] but I don't see anything about them opposing C-band auction.

[0]: https://arstechnica.com/tech-policy/2020/04/fcc-to-approve-5...

Obviously they don't rely on just one type of system for low altitude altimeter measurements, because they just basically told you how someone could go out and broadcast interference in that spectrum and crash a bunch of planes. Common altimeter system types found on aircraft include barometric, laser, ultrasonic, and GPS. Plus the only time they would be below 2000 feet is near an airport. 5G is limited in distance, thus you could easily establish a no 5G zone around airports and that would mitigate the risk.

...airports and ski resorts: https://en.m.wikipedia.org/wiki/Cavalese_cable_car_disaster_...

Good point, except that was pilot error not outside interference. Plus planes aren't supposed to be flying near ski resorts or mountains in general.

Isn't 5G highly directional? Even if there is some crosstalk isn't it mitigated by the directionality of 5G antennas?

There are two “kinds” of 5G, since 5G is a broad marketing term:

- Regular deployments anywhere between 600MHz and 3500MHz (or so), as an iteration on 4G. Actual band depends on the country, licensing and spectrum needs.

- 5G ultra wide band (UWB), which is often deployed around 30-38GHz, and is thus highly attenuated and needs to be extremely directional. This is the “street corner only” type of 5G.

I'd pay more attention to this if I wasn't told (for 2 decades) that I had to turn my cell phone off for take and landing or people would die.

I came to the conclusion a looooong ago that mobile phones cause either 1) very, very little or 2) absolutely no problems whatsoever to an aircraft.

(If they did, you wouldn't be allowed anywhere near an airplane -- let alone inside one in flight -- with such a "dangerous" device.)

5G Auction Shatters Record as Bidding Tops $69 Billion

https://www.wsj.com/articles/5g-auction-shatters-record-as-b...

https://archive.vn/Yh7Rf

> “It’s so important to have an accurate reading, because if it’s a bad reading it could lead to the airplane doing something you don’t want it to do.” explained Terry McVenes, the RTCA president and chief executive. McVenes is a former Boeing safety executive with 30 years’ experience in the commercial aviation industry.

That doesn't address OP's question, which is "what happens if the enemy is using this?"

If our war machines crash because of spectrum allocation, there may be a problem with the military’s threat modeling.

ikr, is it really that easy to mess with a radar altimeter? (hides signal generator and RF amp behind my back)

From this comment I deduce you have been working out.

You must have at least a 19" wide back then, I suspect that a good ramp generator and an amp for that kind of frequency range with sufficient power and bandwidth is going to be a rackmounted device if not multiple of those. This baby from Rohde & Schwarz https://cdn.rohde-schwarz.com/pws/application/cards/3607_446... should do nicely.

So 5G rollout is going to put one of those on every street corner?

Those little boxes at the bases of antennae for cell phone towers are quite full of gear. Nothing that massive but a single rack with various bits and pieces (and batteries!) is the norm.

https://www.extremetech.com/wp-content/uploads/2013/06/sprin...

Look at all those Samsung goodies.

Pic is from 2013. Image appears to have a sprint watermark. Looks like a base station controller (or whatever the cdma equivalent is).

I don’t see the Samsung branding. Not aware of them as a major appliance vendor for cell sites.

Yes, so what? This is typical of what a base station looks like inside, whether or not it is current isn't really all that important, the gear gets a bit smaller every generation but it's not as though it suddenly becomes pocket size.

As for you not seeing the Samsung branding, you can take my word for it or you can look up some of type numbers visible. Your lack of knowledge about what Samsung offers doesn't really matter.

Sorry- not attacking, just observing.

Google says 120W for the largest 5G MIMO arrays.

50 dBm is nothing crazy for a benchtop unit.

Presumably the military assumes that radar altimeters can be jammed. The potential problem here is that they might be jammed when there is not an actual war in progress. It's a generic aviation thing and is not specific to any one group.

In a war situation, blasting out high power RF would also be painting a huge target on your antennae for an AGM-88 HARM.

It's still a game of cat and mouse, because the operators either will have enough sources not to care or be clever enough to only paint a target at the last moment.

Anti-radiation missiles seem fun to work on, for example the (now retired) ALARM missile will loiter at 13 km with a parachute then use a secondary rocket motor to attack a target it finds. The signal processing these things do is probably unbelievable.

Thinking about it some more, a radar altimeter is only effective to ~2000 feet so it’s probably going to be a relatively close range highly-directional beam which would make it harder for a seeker head to find but also means you’d need a truck close to the airfield perimeter, painting aircraft on final approach.

WRT last minute painting, I guess the E model would help a bit with that:

> the AGM-88E Advanced Antiradiation Guided Missile (AARGM), features the latest software, enhanced capabilities intended to counter enemy radar shutdown

At 870k USD a pop you wouldn’t want to be lobbing a lot of them, though - as you say, it’s going to cheaper to build jammers than countermeasures to destroy them.

I certainly hope that there's some sort of channel-hopping strategy in place to prevent accidental jamming. In fact, I would hope that "can't be accidentally jammed by a bunch of 14 year olds on their cell phones," is a lower-bounds for measuring the efficacy of the system.

Even if interference is accounted for, it seems unnecessary to apply it knowingly, no? It might only increase the probability of failure by a tiny amount, but if applied constantly, I'd be concerned too.

Wasn't DFS created to mitigate this: https://en.wikipedia.org/wiki/Dynamic_frequency_selection

Been used in a few countries fine from what I know of and I live near Heathrow airport and use it to no ill effect. Though don't have the details of what bands they just opened up and how they compare with other countries and any impact.

[EDIT ADD] Whilst looking this document had a nice insight into the middle band usage globaly https://mma.prnewswire.com/media/1136543/5G_Mid_Band_Spectru...

Page 5 has current regions bandwidth assignment in that block and does seem that from that the USA is slow compared to other countries in assigning that band for consumer usage.

Page 6 has a nice visual showing the use/proposed use comparing regions - most insightful.

DFS is usually disabled and you have options to enable it via "I am outdoors" flag.

Guess how many people enable it.

In some regions it is compulsory. USA being one.

DFS is only for wifi, and only with regards to co-channel interferences with radars.

Here (as far as I understand) the main issue is the airborne receiver blocking (i.e. catching energy from other bands) because of poor filtering on the receiver side.

> property’s going to be destroyed and people are going to die

It always strikes me how some people list financial loss before loss of life.

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