Multi-GNSS support increases the reliability and signal availability. Commercial chipset will usually add support for all of them and don't just choose one.

Newest phones (like iPhone 8) work with GPS, Galileo, Glonass, and QZSS. Beidou support will come in the future.

Note you can buy off-the-shelf GPS modules today that will work across all four GNSS:

https://www.u-blox.com/en/product/neo-m8-series

One of the reasons for this, about seven years ago Russia put a 30%+ import tariff on any mobile phone that didn't work with GLONASS. Thereby motivating chipset makers like Qualcomm to integrate GLONASS receive features into their existing RF chipsets.

Exactly. At the moment, the consumers benefit from the increased accuracy and coverage provided by multiple GNSS.

Sidenote: the ublox M8 chips are a pleasure to work with, and there are variants that have IMUs (gyros and accelerometers) on board for sensor fusion. All for <10$. What an exciting time we live in!

> Sidenote: the ublox M8 chips are a pleasure to work with, and there are variants that have IMUs (gyros and accelerometers) on board for sensor fusion. All for <10$. What an exciting time we live in!

I wish someone would build a USB data logger using one of these. I still use one to geotag photos and record trips, but all the available models use old GPS-only chips and can be pretty jumpy when reception is poor. Having one that fused multiple GNSS and had an IMU to smooth out some of the random jumpiness would be ideal.

Yep, we use those in (hobby) drones for extra precise location data.

It’s interesting and odd to me that Beidou requires two-way communication, as opposed to other satellite tracking systems where the receivers are purely passive and satellites only transmit, not receive. Is there an explanation for why this was done?

I suspect this is either a misunderstanding or just copy-pasted from descriptions of a different earlier system.

It doesn't make any sense to have the ground station transmit to figure out its location. To give a baseline, that's how the original analogue COSPAS SARSAT worked last century, using doppler measurements to get a location over time - and its accuracy was appalling, a human operator has to use equipment to narrow down where the signal is, it takes significant time to get a 1 nautical mile search area. Which is much better than "I dunno, in the sea?" for a lost ship or plane, but you're still going to need a serious search-and-rescue operation to find anybody.

A modern digital COSPAS SARSAT system you may have seen if you're a serious hiker or outback flyer just does GPS, it uses GPS to figure out where it is, then sends a digital signal that says "I need help, here are my GPS co-ordinates" hence the slogan "Taking the search out of search and rescue".

Appears that two-way comms was required for Beidou-1, not BeiDou-2. See https://space.stackexchange.com/questions/30839/is-two-way-c...

I am highly skeptical of this claim, it's either for higher accuracy of military stuff, or an internet connexion to get a key or the ephemerides or something. But nobody is sending signal to a satellite 21000km from the surface straight from a watch-sized device.

I agree with the thrust of your post, but Um Actually...

The current Breitling Emergency (a bulky men's watch, but it wouldn't look out of place on some big out-of-doors type guy's wrist) is a working PLB transmitter.

So that means signals from it can be received not just 21000km up, but 36000km up where Geostationary birds live.

If you activate it, that watch will transmit the digital signal with its unique ID in it, and assuming you filled all the paperwork out soon after somebody from the relevant local emergency response (maybe a coastguard, mountain rescue, that sort of thing) will be phoning your emergency contacts

"Hi, do you know nraynaud? They went flying today? OK, do you know where they were headed? We have an emergency transmission from their beacon so we're going to send somebody to take a look and check they're OK. We'll let you know, thanks".

A "real" beacon would be better, more robust, better battery life, easier and more obvious for random strangers to operate if you're unconscious, not to mention much cheaper. But the Emergency has the advantage that you'll actually have it when shit goes wrong, because it's your watch.

Unavoidable collection of user location data is the obvious reason. I would absolutely stay away from any device that has support for this positioning technology.

Yes, first generation beidou were mandatory two way, to do crypto handshake. The Party wanted "more control," just as usual.

The idea was realisedly lunatical even back then, but party boffins really though that reality and laws of physics will yield to party's mandate.

It’s not about “more control”. The first beidou was two way mainly because they need some kind of satellite phone functionality.

That what was said to the populace. In reality, first gen beidou sats already had functionality to provide atomic clock signal and advanced station keeping. The accuracy was quite lower than from leo GPS sats, but still.

The explanation that beidou 1 was a glorified, super expensive satellite pager, with navigation functionality as an afterthought does not hold water. This "explanation" came much later than the commencement of beidou 1 project.

Looks like some misunderstanding here. No one ever claimed Beidou I was developed as a satellite pager.

The reason Beidou I needs two way transmission is they wanted add pager functionality to its navigation functionality. The party wants more control has nothing to do with Beidou I's two way transmission mechanism. When Beidou I was developed, it's mostly used by military. The party doesn't need "more control" there.

Military use??? You understand what two way transmission means during a conflict? An enemy tunes an antiradiation missile on your frequency, and voila...

China already had military digital satellite coms working by late nineties. For them, it was of even lesser utility.

Perhaps some background info can help. Beidou I was developed in early 2000s. And at that time Chinese military satellite wasn’t advanced at all. Even though beidou I is vulnerable to anti radiation missles, it’s the best they have and at least it worked well for purposes such as border patrol and terrain survey.

My point is that many things in China may be explained by the party wanting more control, but two way transmission of beidou I is not one of them.

The article talks about how it can be used to send messages but my first thought is that it could allow tracking of receivers. A scary thought if it does achieve widespread adoption.

There are two different and independent beidou systems. One is passive and cannot track receivers, and the other is similar to a simple satellite internet.

"We are likely to see an increased bifurcation of the world into two camps - 'pro-China' and 'pro-US'", says Blaine Curcio, founder of Orbital Gateway Consulting

Why do some people view it as a with-us-or-against-us problem? Combining beidou with GPS gives a better accuracy. Some competition and collaboration in the GPS field can benefit us as a whole.

I wouldn't want to be navigating critical transportation during a dispute between China and the United States with this track record (would you?):

http://fortune.com/2018/08/28/china-has-been-withholding-bir...

https://www.wired.com/story/australias-ban-on-huawei-is-just...

https://nypost.com/2018/09/19/chinas-social-credit-system-is...

http://fortune.com/2016/05/20/chinese-social-manipulation/

It's precisely the fear of having navigation turned off that led to nations launching their own GPS alternatives. More satellites is better for critical transportation if one nation (be it China or US) wants to turn disable their system for civilians.

Eventually most mobile devices will contain a single chip that supports GPS, GLONASS, Galileo, Beidou, and other smaller regional GNSS's. They all rely on somewhat similar technology so it's mainly a software problem.

> "We are likely to see an increased bifurcation of the world into two camps - 'pro-China' and 'pro-US'", says Blaine Curcio, founder of Orbital Gateway Consulting

Why just two? If our stranglehold on the world breaks, the EU and Russia are easily capable of carving out their sphere of influence.

People really underestimate how populous and wealthy and powerful the EU is.

It's strange how the narrative changes in such a short time period. Just 10 years ago, I remember people talking of "chimerica" as if the US and china were going to merge into a single world ruling entity.

The EU is wealthy but has limited power projection. Only France and the UK can realistically be considered great powers, and even then not on the scale of the US, China, or Russia.

France and the UK? What about Germany?

In term of military power mostly I guess. It's the only EU nations with nuclear weapons, aircrafts carrier, nuclear submarines, ...

Correct. Germany is an economic powerhouse, but lacks military might and therefore power projection.

No one doubts the EU's power, but they doubt its stability and unity. With the surge of right wing nationalist governments in Europe it's a fair concern.

I was curious what Beidou meant, apparently it refers to the "Big Dipper": https://en.wikipedia.org/wiki/BeiDou_Navigation_Satellite_Sy...

Yep, Big Dipper as part of Ursa Major translates to something used as a wine vessel about 2 to 3 thousands year ago.

https://en.wiktionary.org/wiki/%E6%96%97

GPS has become so ubiquitous I honestly forgot that it was something that could be owned. It is cool to see some competition in the GPS world.

GPS systems are not so much 'owned' as 'paid for'.

And designed and maintained...

GPS is aging technology, its satellites are dying already and its limits are showing clearly. It won’t be around forever.

That's not true... The U.S. is actually in the process of launching the next generation of GPS satellites.

Why is 'rival' quoted?

Because GPS do not rival each other in any practical sense, instead they complement each other. More GPS systems means more satellites means greater accuracy for users.

Let's hope even more countries get into GPS "rivalry."

Oh, I guess you're right. In my mind it was like "not really a competition" in a negative aspect but it turns out the negativity was in my mind.

>... even precision missiles.

So if GPS were to be jammed, or disabled by a hack into the ground control systems -- PLA missiles would still work just fine. Hmm.

It would be unwise for Chinese missiles to use a positioning system controlled by the US military, to say the least...

GPS is one of the many many component inside modern missile to determine location. An IMU ( https://en.wikipedia.org/wiki/Inertial_measurement_unit ) being usually the main component and GPS being just there for error correction.

GPS is too easy to jam, no serious military application would use GPS exclusively.

Due to COCOM limits, GPS was never an option for China to use on their missiles.

https://en.wikipedia.org/wiki/CoCom#Legacy

Edit: I'm wrong.

COCOM is a non issue when building your own devices from scratch.

GPS satellites are transmit only so they can’t impose such limits directly it’s device manufacturers that implement COCOM.

You are right that COCOM is not the issue, but there are other measures.

The new military M code transmitted from the latest satellites is encrypted with a frequently changing key, so in the event of a war the DOD can disable the civilian signal as the M code will work standalone, hence a third party nation cannot rely on GPS.

The previous P(Y) code was also encrypted, but is theorised to need the civilian C/A code as well to work.

> so in the event of a war the DOD can disable the civilian signal as the M code will work standalone, hence a third party nation cannot rely on GPS.

They also had the option in older satellites of turning on selective availability, which would degrade the civilian location service from 5-meter to 100-meter accuracy without affecting the military service. Purportedly newer GPS satellites don't have the option anymore.

https://en.wikipedia.org/wiki/Error_analysis_for_the_Global_...

> Purportedly newer GPS satellites don't have the option anymore.

That does sound suspiciously like something the military would want you to believe

Selective availability was defeated a very long time ago so no reasons to doubt that the military gave up on it. Pretty sure they're just using an encrypted transport for the military signal so they can do whatever they want to civilian GPS wholesale without impacting the military. However, I'm not sure how that will work since it underpins our entire economy from logistics to air travel. On the other hand, at the point the military is disabling civilian GPS probably the economic impact is less of a concern.

It's worth mentioning here that SA-less Block IIF (and newer) satellites came after "codeless" and "semi-codeless" techniques were publicly-known. Those allow a receiver to use the encrypted P(Y) code to obtain a precise position fix without any knowledge of the encryption key.

There are probably other, newer ways to prevent an adversary to use the GPS signal, but there is little reason to doubt that SA is gone.

No one seems to have mentioned that the US has actually blocked GPS signals before for military reasons (during the Kargil war in 1999): https://timesofindia.indiatimes.com/home/science/How-Kargil-...

There's a good reason and precedent for China (and others; see GLONASS, IRNSS, Galileo) to be afraid of this.

No, the US has never done any blocking in the GPS system. The article refers to a request by India for access to the military GPS signal and military equipment, which was not granted.

The US, as well as virtually all other technological powers, does have the capability to jam GPS signals using ground, sea, or air-based jamming platforms but those are not part of the GPS system.

Yup it did - I was flying aerial surveying at the time. Bad timing. Actually I didn't notice anything in the end so was all good but when I saw the NOTAM I couldn't believe my bad luck.

Edit - link: https://www.theregister.co.uk/2016/06/07/us_military_testing...

Not sure whether you're agreeing or disagreeing, but that refers to jamming done by electronic warfare units, not part of the GPS system, as I indicated above.

The United States actually does have the ability to selectively degrade signals. I don't know enough to comment on this capability in more detail (another comment seems to indicate that it is through jamming). A relevant excerpt (from 2000) is below:

> Additionally, we have demonstrated the capability to selectively deny GPS signals on a regional basis when our national security is threatened.

https://www.faa.gov/about/office_org/headquarters_offices/at...

Selective availability was defeated a long time ago which is one of the motivations for Clinton formally turning it off in 2000. Also while I'm sure that the US military is fully capable of turning off GPS satellites however they want the efficacy of this is probably limited considering the coverage of GLONASS + EGNOS.

The point of that article is that a main justification for turning off selective availability was that the US could still deny access in certain geographic areas. Selective denial != selective availability.

As I indicated above, separate systems on electronic warfare platforms can jam GPS signals. This is not part of the GPS system, and is what the article refers to.

Building your own GNSS system does nothing to protect against electronic warfare platforms.

> The US, as well as virtually all other technological powers, does have the capability to jam GPS signals using ground, sea, or air-based jamming platforms but those are not part of the GPS system.

As well as anyone that has access to basic electronic parts. It's very easy to swamp a 30 watt transmitter that's ten thousand miles away.

India did something similar a few months ago. Each country wants to build it's own GPS for military purposes. At some point we have to stop calling it 'Global' Positioning System.

The "global" refers to the fact that it works globally, not that it exists for the good of humanity.

Navstar (owned by USDoD, what is commonly called "GPS"), GLONASS and soon Galileo all have global coverage.

Yup, GLONASS = GLObal NAvigational Satellite System.

Although one should note that name is the intention; it has not always had global coverage (it does now), and may not always have global coverage in the future (say, if they decide to increase the precision in a strategic area at the cost of loss of coverage in others).

The generic term is Global Navigation Satellite System (GNSS). GPS is one type of GNSS.

I really don't see a problem with describing any and all systems that tell you your position on the globe as "global positioning systems".

Japan has its own positioning satellites (QZSS) that are only visible from the region around Japan. It’s designed so positioning works if you’re in a city with skyscrapers.

So China has the technology to destroy satellites [1], and is developing alternatives to US satellites.

Does this make anyone else nervous?

Maybe Trump has a point when he says we should stop letting China steal our technology.

[1] https://en.wikipedia.org/wiki/2007_Chinese_anti-satellite_mi...

>So China has the technology to destroy satellites [

Any country that can launch a satellite has a technology to destroy one. It's called a missile. You don't even need to go to orbit - just intersect the orbit of the target and dump a bucket of nails in its path.

> Any country that can launch a satellite has a technology to destroy one

It's easier to put something in orbit than to knock something out of orbit.

You can destroy something without taking it out of orbit. The pieces will happily carry on along their orbital trajectories.

It's easier to put something in orbit than to hit something in orbit.

Well I'll disagree with my own unsubstantiated claim. Consider that its easier to manufacture flak shells than make airplanes. The same applies to space.

Not meaningfully. If you can get into a similar orbit, it's easy in comparison to intercept.

You don't even need much of a missile, if you happen to have an air force; back in 1985 the USAF did a test in which the pilot of an F-15 shot down a satellite, from an altitude of 38,000 feet.

Aren't GPS satellites geostationary?

no, they are not.

Any country/company who has launch vehicles can destroy satellites. SpaceX could just as easily destroy satellites.

Don't give Musk any ideas