Hacker News Reader

Comment by onepremise | Hacker News Reader

I worked for a firm, which studied satellite navigation and implementation for air traffic control, guidance, safety, and ILS. I don't think that will ever happen. There are huge gaping issues with GPS, both WAAS and GBAS. It's very unreliable, especially in bad weather. The old-school RF tower and ILS, which used Carrier frequency pairings by the runway, are way more reliable and propagate bad weather while guiding the plane into a runway. There's also been ongoing issues with truckers, with GPS jammers, which drive by airports impacting the quality of signal for planes coming into runway. Even the GPS signal itself has latency and lag, which prevents the plane from making quick adjustments for avoiding traffic and ILS guidance.

View on HN

The ATC scenario has significantly more relaxed requirements than ILS, and this change is intended primarily to provide coverage in situations where there is no, or limited, coverage from conventional methods (primary/secondary radar), and likely ultimately to replace the outdated secondary radar system with a space-based one.

ADS-B is not a guidance tool and will not lead to any more usage of GPS for guidance than is currently common - and certainly won't impact ILS. They're just totally different use-cases.

> Even the GPS signal itself has latency and lag

What do you mean by this? You sound pretty knowledgeable, so you must know that it's simply not possible for the GPS signal to have latency or lag.

Not the poster, but while the GPS signal doesn't have lag, many receivers run the output through a Kalman filter for higher precision.

It's actually impossible for GPS to show your current position.

The signals have to be received from each satellite, then processed to yield a position valid at the time of transmission.

Every GPS fix you get is delayed by AT LEAST that processing time. Any filtering adds more lag.

Most navigation systems look at the T(fix) -> T(now) difference and project your now position from the prior fixes. Especially if you're following driving directions as opposed to free movement, then programs like Maps etc project how much further you've moved on the route, not just along your velocity vector.

After a few seconds, though, that projection will stop moving, too, when the gap between last fix and now gets too large.

The position output by a GPS receiver certainly can (will) have lag. That's probably what the poster I replied to was referring to, and I hadn't thought about it.

This change allows every pilot to have essentially a 'radar view' of their surroundings, cheaply. A receiver and an iPad app give them a picture much like the aircraft control tower would have.

Lots of issues I'm sure. It'll be interesting to see how this sorts out.

Why do truckers have GPS jammers?

You either didn't see the comma or you're joking

I'm pretty sure I parsed it correctly. It's "Truckers (with GPS jammers) who drive my airports...". Parsing it as a list means it no longer makes sense.

Don’t think they’re wrong in their interpretation. Why would a trucker without a GPS jammer driving by an airport cause an issue?

https://gizmodo.com/jamming-gps-signals-is-illegal-dangerous...

> he’s seen truckers trying to avoid paying highway tolls, employees blocking their bosses from tracking their cars, high school kids using them to fly drones in a restricted area, and even, he believes, undercover police officers using them to avoid tails

Don't forget the Kremlin spoofing the local airport to try to keep drones from flying near their government buildings!

To defeat "the Qualcomm", which records hours. This may let them drive longer than the DOT allows.

Beating DOT legalities, hiding things like side trips to casinos/mistresses/bars from the boss, general dislike for big brother, etc.

It should be straightforward to have GPS jammer detectors along the road. Throw in a giant federally enforced fine and people will stop using them.

In fact these do exist. I saw a demo a few years back from a company that tracked bogus GPS signals and how they could watch jammers drive around the streets of London all day long.

These guys were doing it because they were tasked with keeping LTE towers synchronized and they did it with GPS time so they were building in resilience to their time sources by measuring the signal level and rejecting anything that came in too strong. Spotting jammers was a side benefit.

The GPS antenna on the LTE tower should only be picking up signals from the sky. Transmitters on trucks would need to reflect off of aircraft in order to cause trouble, which would greatly weaken the signal.

Yes the antenna pattern will attenuate the signal coming from the ground somewhat, but it also doesn't suffer from 182 dB of freespace attenuation like the real signal. It doesn't have to bounce off of an airplane either, the Earth has a layer of atmosphere around it that gets ionized by the sun and is also full of water vapor. We also don't have the ability to build perfect antennas, especially since it has to cover the entire sky (GPS antennas do not physically track the individual satellites).

So their corporate telemetry system doesn't document their long lunch at the strip club which, for other reasons, happens to be located just around the corner from the airport.

Reply on news.ycombinator.com