[HN Gopher] Why Is GPS Free?
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Why Is GPS Free?
Author : tooltower
Score : 73 points
Date : 2023-06-03 18:52 UTC (4 hours ago)
(HTM) web link (old.reddit.com)
(TXT) w3m dump (old.reddit.com)
| vlovich123 wrote:
| Wasn't SA killed because the algorithms defeating it became
| widely known and thus there wasn't really any point to it?
| jrockway wrote:
| Near the end of SA people did figure out how to minimize its
| influence. Not because they could decrypt the military code,
| but because of differential GPS (compare the raw signals you
| receive with the raw signals at a known location called a
| continuously operating reference station; the reference station
| didn't move, so if the signals said it did, that's how wrong
| they are in that particular corner of the earth) and the
| ability to solve the navigation equation based on the actual
| carrier phase/doppler shift instead of only the transmitted
| messages.
|
| Both of these techniques are still good for removing much of
| GPS's error, which mostly involve the uncertainty about the
| "speed of light". It changes locally as the total electron
| content of the ionosphere changes. Measure against a reference
| station or between two different radio frequencies (L1/L2C),
| and that error can be minimized. You don't need a reference
| station anymore, as things like WAAS try to transmit these
| corrections from a satellite.
|
| If you want to play with high-precisions GPS, you can easily
| buy fancy u-blox modules from Sparkfun, connect them to a
| Windows computer running uCenter (from ublox), and get access
| to reference stations through your state to do full DGPS. With
| good sky conditions, you should be able to move your receiver a
| few centimeters and watch the lat/lon change accordingly. (New
| York State's service is here: https://cors.dot.ny.gov/. It's
| free! They use a software suite that's designed to charge
| customers money for using the data, but the prices are all set
| to $0.)
|
| People say that the achievement of the 20th century was the
| Internet, but I think GPS was a lot harder. The Internet is
| just computers connected to each other with cables! This is
| atomic clocks in space sending you messages indistinguishable
| from noise that let you find your position in space within a
| centimeter. When the aliens invade, I think they'll be
| impressed! I am, anyway.
| vlovich123 wrote:
| Yup I was talking about differential GPS.
|
| As for difficulty, both are achievements and don't undersell
| the difficulty of networking. At the 500ft level it's all
| just wires but the actual details of doing it are incredibly
| difficult. It's just that we've had so much experience
| pushing it forward that there's a lot we can just take for
| granted which removes the magic from it.
|
| https://www.allaboutcircuits.com/news/ethernet-
| turns-50-look...
|
| And that's just local area networking. Networking broad area
| networks is even more complicated.
|
| As for people calling it the achievement of the 20th century,
| it's more because of how it made the world smaller and the
| network effects of the changes it's wrought to society (and
| from that perspective it is bigger than GPS and the computer
| itself).
| moffkalast wrote:
| Fundamentally because supporting one receiver costs the same as
| supporting an infinite amount of them, the rest is politics.
| lucb1e wrote:
| Nobody indeed buys a satellite, but they could have put a tax
| on receivers to fund the system. In my country they even tax
| data carriers (CD, HDD, laptop/phone with internal storage,
| etc.) for the music industry because we may store songs on
| it... clearly this is achievable, and funding satellites is a
| much more direct benefit than the bullshit that the music
| labels keep coming up with so the general public could actually
| be in favor of it.
| aaomidi wrote:
| Either way we can't really charge people for seeing
| electromagnetic radiation.
| jeroenhd wrote:
| I'm pretty sure the British TV license says otherwise,
| although in practice it's an often abused extortion
| mechanism. It's quite possible to detect dedicated tuned
| receivers as well.
|
| In fact, in many countries pointing your SDR at 2G/3G/4G/5G
| frequencies is basically an instant felony, even without
| attempts to decrypt the traffic. If you get caught watching
| such traffic, you'll pay much more than just a small tax.
| arp242 wrote:
| You pay for the programmes, not the broadcast, obviously.
| You can just say "I don't need a TV license" online and
| usually that's the end of it.
| https://tvlicensing.co.uk/noTV
|
| And in many other countries the "TV license" is just
| included in general tax; in e.g. when the TV license was
| abolished in the Netherlands taxes went up by 1.1% to
| compensate. In Germany it's EUR220/year/person (not
| household) regardless of whether you have a TV or not.
| This way you don't pay for a product I don't use.
| lucb1e wrote:
| You mean listening to those frequencies, not
| broadcasting? I didn't know that was illegal anywhere,
| besides maybe military or other government bands.
| lucb1e wrote:
| As if there's no way to codify that a device determining a
| spacetime location from GPS signals is a taxed good.
|
| To give another example, you used not to have to pay public
| broadcasting tax in Germany if you didn't have a TV or
| radio in your household. I would be highly amused to see
| you try to argue "it's just an electromagnetic radiation
| plotter, what do you mean tele, eh, vision?" to an unamused
| government official.
| ThunderSizzle wrote:
| If there's a tax for that, then all digital music should be
| free after that tax.
| Someone wrote:
| I don't see how that would necessarily follow.
|
| I would think the fairest tax rate would be such that
| giving people the ability to easily copy music would be
| profit-neutral for music owners/producers.
|
| If so, tax revenues would only have to cover whatever that
| decreases the profits of music sales by, and that isn't
| necessarily 100%.
|
| (Of course, determining lost profits basically is
| impossible, even ignoring that the ideal solution would
| determine that for each rights owner in isolation, but that
| is a different issue. Certainly, requiring all digital
| music to be free doesn't avoid that)
| jeroenhd wrote:
| I'm Dutch and many people considered this to be a "piracy
| tax" of sorts. The government and police also weren't in a
| particular hurry to take care of piracy.
|
| The tax is based on a quirk of copyright law designed by
| the media industry all the way back in the age of cassette
| recorders. Music companies realized that people were making
| copies of their songs from the radio for free (you could
| put together entire albums if you timed it correctly!) and
| from the cassettes they bought, and after some mess the
| "thuiskopie" (home copy) system was born.
|
| Basically, you can make legal copies of any media you have
| legal access to as long as you pay the fee. This fee goes
| directly to on organisation (think MPAA but for all
| artists) which then redistributes the money according to
| Some Kind Of Model[1]. The fee is part of the sale of any
| digital or analogue container that can contain copyrighted
| works; it's a fixed price fee
| (https://www.thuiskopie.nl/nl/opgave/tarieven).
| Professionals who won't use their devices to store other
| people's work can get their money back if they fill in a
| form and send over the right paperwork, but let's be
| honest, nobody does this.
|
| For a long time, the de facto interpretation of the
| thuiskopie law was that a copy you make for yourself (or
| your direct family/friends) at home is legal. That implied
| downloading MP3s and other files from the web was also
| legal [2]. Torrents involve sharing, so they were always
| off the table, but copies of torrented files given to
| family was treated like a legal copy. You could still be
| caught for piracy, but as long as someone else got you all
| of your pirated disks you were pretty much Technically
| Okay.
|
| This interpretation was killed off when the media industry
| won a lawsuit against the government. It was always too
| good to be true, but it seemed to be one of the ways many
| pirates were appeased about this law. I'm pretty sure
| everyone considers this system to be stupid now that it's
| no longer a de facto piracy license. The copyright lobby is
| incredibly strong, though, so I doubt we'll see a change
| any time soon.
|
| The copyright industry gets to charge you twice for the
| media you listen to. As long as this stupid system remains
| part of the law, I'm personally opposed to any subsidies
| for commercial media. If only a politician worth voting for
| actually cared about this crap...
|
| [1]: Yes, this is legal, though I still don't know why.
|
| [2]: Software has always been excluded from this, though;
| downloading software and games was never part of the deal,
| and software companies can't claim their take from the
| Thuiskopie system
| lucb1e wrote:
| I'll say. There's been a lot of public debate around this
| but in the end, nothing changed and people got tired of the
| topic so here we are
|
| Anyway the point was that taxing receivers would be an
| option if they had wanted to finance the system, but for
| some reason they didn't, not so much to discuss this data
| storage tax to be paid out to the music industry
| amelius wrote:
| If the fundamental part of your argument played any role in
| medicine, then all the >$1M cancer treatments would be
| practically free too.
| SnowHill9902 wrote:
| Pharmaceutical companies are not charging for the cost it
| took to develop that drug, but for the rolling cost it'll
| take to develop future ones.
| schwartzworld wrote:
| Also CEO bonuses
| jeroenhd wrote:
| Not necessarily, incredibly large amounts of money
| pharmaceutical companies spend is actually spent on
| advertising their products to maintain their cash flow.
| Examples can be found online but this source [1], which
| is obviously biased, shows the statistics for the biggest
| companies in a nice list.
|
| The (hundreds of) millions spent on bonuses are nothing
| compared to the billions spent on making sure your doctor
| recommends UmbrellaCorp PainAWay(tm) over a generic brand
| that will cost you a tenth of the price [2]. That
| includes not just TV ads, but also buying conference
| tickets and free lunches for doctors; anything to make
| sure they get the upper hand.
|
| [1]: https://www.csrxp.org/icymi-new-study-finds-big-
| pharma-spent...
|
| [2]: It should be noted that some generics can work less
| effectively or cause additional side effects in some
| people, but for many types of medication the difference
| is minimal and sometimes the big-brand products even come
| with more side effects than their competitors' product
| [deleted]
| HWR_14 wrote:
| In non-US major economies, aren't they?
| avalys wrote:
| Thought one: wow, the fact that this was asked on a subreddit
| called "Ask Historians" really makes me feel old.
|
| Thought two: I've never considered how bizarre it is that GPS is
| an enormously expensive satellite constellation launched and
| maintained by the United States military that we make available
| for free to the entire world. As a US citizen I take it for
| granted - but it must be strange for someone to grow up in (for
| instance) Lebanon and use a GPS device.
| bojan wrote:
| I'd dare guess that a vast majority of people in Lebanon (or
| any other country for that matter) have no idea that GPS is
| basically a US military service. It's just something that
| works.
|
| I still remember my fascination with it when I got to use it
| for the first time, using a Garmin app on my Nokia 5800.
| AstralStorm wrote:
| It was a very calculated decision - it made the others rely on
| US tech dominance, with the moment someone gets too uppity the
| P(Y) and M code encryption, and Selective Availability noisy
| mess on normal code gets turned on and only USA plus some
| advanced multiband tracking receivers get accurate location...
|
| For good 30 years the strategy generally worked so much that
| satnav got synonymous with GPS.
|
| Big players launched their own constellations anyway. GLONASS,
| Beidou and fledgling but accurate Galileo. And there are still
| more systems. So if GPS wasn't free manufacturers would use
| something else.
| aynyc wrote:
| I tho it's paid for by American general tax. Is it not?
| djaouen wrote:
| I dunno. Why is fire free?
| smrq wrote:
| Because fire doesn't require a substantial amount of
| infrastructure in orbit?
| vidanay wrote:
| And GPS isn't spontaneously created by lightning striking a
| tree.
| K0balt wrote:
| Not with that attitude it's not, anyway.
| Simulacra wrote:
| I'm surprised no one has mentioned that the a reason it's free is
| that people will use it. If people had to pay for it then they
| might not leave it on, or use it as much, and as a result a lot
| of the mobile apps that harvest location data would be affected.
| acchow wrote:
| Full-precision GPS has been open for public use long before
| location-tracking apps were invented.
| caminante wrote:
| I'd trust the wiki entry [0] over Reddit comments.
|
| [0] https://en.wikipedia.org/wiki/Global_Positioning_System
| Animats wrote:
| Because it's one-way and predates the era of DRM. To charge for
| it (which the EU's Galileo system originally planned to do), you
| need a crypto system, secure modules in receivers, a key
| distribution and billing system, and customer service. That could
| end up costing more than providing the service.
| Laremere wrote:
| GPS had this capability, and it was turned off:
| https://en.m.wikipedia.org/wiki/Error_analysis_for_the_Globa...
| toomuchtodo wrote:
| Soft power from a public good > picking up pennies
| ApolloFortyNine wrote:
| Very misleading comment, none of that section implies the
| government was selling access. They were limiting it so other
| militaries couldn't use it.
| fsh wrote:
| The high-precision P(Y)-signal and the new M-signal are still
| encrypted. This is essential for military applications since
| otherwise GPS would be trivial to spoof.
| EscapeFromNY wrote:
| And it would probably be reverse engineered anyway the same
| week the public got their hands on the receiver hardware.
| nimish wrote:
| If the M-code has been reverse engineered, then it's not
| public.
| jrockway wrote:
| From reading the thread, I have a question that maybe HN knows
| the answer to. I feel like I haven't had to do a cold start on
| new GPS chips in a really long time. Even in terrible sky
| conditions, I've never had to wait 12 minutes to download the
| almanac. Do chips just ship from the factory with this data, or
| is it not needed anymore. (I know about AGPS, but that's not
| involved. This happens on receivers with no possible way of
| communicating to the outside world other than the serial port I'm
| reading navigation messages from.)
|
| Even if I do a reset + cold start in u-center or similar, I still
| don't have to wait 12 minutes. I wonder why.
| fh973 wrote:
| It may have flash. Parts of the AGPS data are valid for weeks
| and may help the cold start.
| [deleted]
| robinduckett wrote:
| Drone GPS chips on FPV quad copters still need significant time
| to acquire satellites (several minutes)
| throw0101b wrote:
| > _Do chips just ship from the factory with this data, or is it
| not needed anymore._
|
| While the general orbits of the satellites (each is uniquely
| identifiable) can be pre-shipped, orbits do fluctuate, so the
| data would still need to be updated / fine tuned.
|
| > _The receiver is missing or has inaccurate estimates of its
| position, velocity, the time, or the visibility of any of the
| GPS satellites. As such, the receiver must systematically
| search for all possible satellites. After acquiring a satellite
| signal, the receiver can begin to obtain approximate
| information on all the other satellites, called the almanac.
| This almanac is transmitted repeatedly over 12.5 minutes.
| Almanac data can be received from any of the GPS satellites and
| is considered valid for up to 180 days._
|
| * https://en.wikipedia.org/wiki/Time_to_first_fix
|
| But a general fix can do done without any initial data, and is
| sped up by being near the previous last fix and caching some
| data.
| pithon wrote:
| Discarding assisted GPS where GPS data messages are obtained
| through about channel such as cellular or Wifi...
|
| Almanac gives coarse satellite position information (and some
| other stuff), good enough to know which ones are probably
| visible and therefore prioritize signal acquisition attempts
| which used to be very very costly in terms of signal
| processing. That's the message that takes up 12.5 minutes to
| piece together. Nowadays you can just brute force all possible
| satellite signals and there's no need to wait around for the
| almanac information. Each satellite signal broadcasts precise
| satellite location information (ephemeris), which takes maybe
| 30 seconds to get a few frames I believe. So that's basically
| the bottleneck for a modern chipset which starts with zero
| information and relies solely on the GPS signals to navigate.
| fsh wrote:
| I believe this might be the correct answer. The signal from a
| GPS satellite is incredibly weak (way below the thermal noise
| of a typical amplifier) and can only be detected by
| correlating it with the satellite's unique gold code. In
| addition, the satellites move pretty fast which leads to
| sizeable Doppler shifts of their carrier frequencies (tens of
| kHz). This has to be taken into account in the signal
| demodulation.
|
| Classical GPS receivers use the almanac (and a reasonably
| accurate local clock) to determine which satellites are
| probably in view, and with which Doppler shifts. I would not
| be surprised if modern GPS chips had enough compute power to
| simply correlate the received signal with all gold codes and
| at all reasonable Doppler shifts. The almanac is then no
| longer necessary.
| AstralStorm wrote:
| Once the initial code is had, you can just store the
| almanac and reuse it most of the time with reasonable
| accuracy to make the computation faster.
|
| Usually that approach cuts the sync time by factor of ten,
| even if the real ephemeris diverges from the general
| almanac.
| 29083011397778 wrote:
| The third and fourth requests even de-Googled (Qualcomm) phones
| make is to download the GPS almanac. You don't have to wait
| because it downloads over wifi or cellular, which have gotten
| pretty quick. There was a recent kerfuffle about this [0].
|
| [0] https://blog.brixit.nl/nitrokey-dissapoints-me/
| mensetmanusman wrote:
| History: America puts it up to help target ICBMs, etc. US
| taxpayers/military give it away for free as a gesture of good
| will which also has political benefits.
| JumpCrisscross wrote:
| > _America puts it up to help target ICBMs_
|
| Modern ICBMs use GNSS. Historically, they didn't. Certainly not
| when the GPS constellation was deployed.
| philipkglass wrote:
| _Modern ICBMs use GNSS._
|
| Do they? The US hasn't deployed a new generation of ICBMs
| since the GPS constellation became operational. I would also
| expect that plans for nuclear war wouldn't rely on vulnerable
| satellites remaining operational.
|
| I thought that US weapons used GPS guidance as a low-cost
| alternative to other guidance methods in forgiving
| environments that don't have electronic warfare
| countermeasures (e.g. fighting the Taliban or armed forces
| equipped with old gear).
| fsh wrote:
| ICBMs are probably the only part of the military that doesn't
| need GPS. Star trackers are more than accurate enough for that.
| whartung wrote:
| GPS is important to the military, but many modern combat
| systems can get along without it. Most systems that use it have
| some manner of backup.
|
| GPS in combat debuted during the Gulf War, but mostly as a
| backup for navigation rather than targeting. We did not have
| 100% coverage back then, all of the satellites were not up yet.
| AstralStorm wrote:
| You did have 100% coverage back then, but not high quality
| all of the time. In some rare cases only a single satellite
| pseudofix would have been available. That can still be
| accurate if the location device carries a decent synchronized
| clock.
|
| IOC was defined as always being in sight of 3 or more
| satellites, plus maintenance capability. That was achieved in
| 1993.
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