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Investigating the Galileo Satellite Navigation System Outage with a LimeSDR
- Proven 7y agoNice. The EU couldn't properly run a lemonade stand. Before they sunk countless billions into this nonsense the promise was EU's tech independence on the US. Well, it turns out that the worst thing you can depend on in the EU is EU itself.
- jcims 7y agoAnyone in here have a LimeSDR? They look great on paper but I get a sense from what I’ve read that they can be a bit finicky to run. Also I’m curious about the 1-bit recording. Is that a thing?
- debatem1 7y agoI have had access to a limesdr, bladerf, etc. They are finicky. They're great tools, but it took me a long time to go from toy examples to doing useful things with them.
- bpye 7y agoAny suggestions for where to get started? I've had one sitting for a long while as I had some ideas but I've never done anything
- colechristensen 7y agoPutting together a gnuradio pipeline to play radio stations or whatever signals you can find is rewarding. Especially when you can get the waterfall spectrogram working
- debatem1 7y agoI didn't do anything useful before I had to for work, and it took 10x as long as it should have. I'd suggest just taking some known working examples for fm radio, garage door openers, etc and working through them. It'll be painful, but with enough time and effort it'll happen. And it's sort of like makefile debugging-- the first ten times you have to do it it's excruciating, but after that it turns into just another task you know how to do.
- rasz 7y agohttps://greatscottgadgets.com/sdr/ https://greatscottgadgets.com/sdr/
- edejong 7y agoI really second that set of articles. Great introduction.
- jcims 7y agoFWIW there are frontend plugins for LimeSDR that will let it work with SDR# and other standard listening applications. Gnuradio can be extremely frustrating for just basic tinkering.
- patrickyeon 7y ago1-bit recording is in fact a common thing for very noisy signals. You're actually aggressively over-sampling and using correlations over many samples (in time) to get the signal out from under the noise. I've only glanced over it, but this looks like a fun related article, but driving the opposite way (oversampling to get more effective bits) https://thecavepearlproject.org/2017/02/27/enhancing-arduinos-adc-resolution-by-dithering-oversampling/ https://thecavepearlproject.org/2017/02/27/enhancing-arduino...
- jcims 7y agoFantastic article! I think i might be able to put this to use with a load cell project to ge a little more precision out if it.
- deleted 7y ago[deleted]
- acqq 7y agoThanks! There is a lot on the site, I really liked: https://thecavepearlproject.org/2015/01/29/a-simple-diy-underwater-connector-system/ https://thecavepearlproject.org/2015/01/29/a-simple-diy-unde...
- magicalhippo 7y ago> Also I’m curious about the 1-bit recording. Is that a thing? I'm no expert, but sounds like what you'd do with sigma delta modulation[1]. Basically you use a 1-bit ADC (a simple threshold comparator), but sample at a rate much above the Nyquist rate. The idea is that for a given value of the source signal, the noise inherit in the recorded signal will make some samples register as 0 while others 1. You then basically average samples to extract the signal you're after. [1]: https://en.wikipedia.org/wiki/Delta-sigma_modulation#Oversampling https://en.wikipedia.org/wiki/Delta-sigma_modulation#Oversam...
- limsup 7y agoI've got a LimeSDR-mini (which is more economical). If you're only interested in RX, you should definitely consider the cheaper RTL-SDR. I'm just starting to learn about SDR, and am far from sending anything. I wish I had gone with an entry-level device first.
- jcims 7y agoI’ve got at least a dozen RTL’s strewn around the place lol. They are easy to use but once you hit some of their limitations you wind up wanting something more
- tibbon 7y agoThe software documentation for people new to it is awful. The hardware is probably great, but I've had such a hard time with mine. It's not newbie friendly at all, and the people in HAM and SDRs don't know how to teach. It's all jargon that they never define or things just like "Oh do XYZ in this software" and that's an entirely non-obvious thing that's entirely undocumented with no tutorials.
- rachelbythebay 7y agoA lot of SDR stuff is like you're a person wanting to drive to the store to get some ice cream so you can eat the ice cream. So they give you the blueprints.. to an auto factory. So you can build an auto factory. Which will then build a car. Which you can THEN drive to the store. Hope there's still ice cream left by the time you get there.
- jcims 7y agoIf there's a silver lining, you do learn a lot whether you planned to or not (mostly about how much more other people know than you do). I first dipped my toes into it with the RTL SDRs back when they were first 'discovered'. I got into listening to local police scanners but got tired of chasing peaks in the spectrum. So I learned a little bit about DSP, wrote a couple of little auto-tuner plugins for one of the more popular SDR applications, built a crude audio pipeline to demodulate the p25, but ultimately had a $1200 PC doing a bad job at being a $200 scanner. I started to pick it apart more when some genius masochist builds an SDR scanner that does all of the above (including multi-vcos), but then snips out the audio files, tags them with the origin and makes them available for the world to listen via a nice clean web ui. Demoralized and defeated I just moved on to tinker with ADS-B. Geesh, the nerve of some people. :D
- cnvogel 7y ago> Also I’m curious about the 1-bit recording. Is that a thing? Yes. This homemade GPS receiver uses a simple comparator (1 bit) to sample the signal (after amplification to get the noise floor over the decision threshold). http://www.aholme.co.uk/GPS/Main.htm http://www.aholme.co.uk/GPS/Main.htm
- tick_tock_tick 7y agoHow often has GPS, excluding intentional military operations, been unavailable? Edit: Went looking around and it seem GPS has never suffered an outage. They have had issues with some satellites, even two days ago it seem, but never a true outage. http://navigationservices.agi.com/SatelliteOutageCalendar/GPSHistoricalOutages.aspx http://navigationservices.agi.com/SatelliteOutageCalendar/GP...
- makomk 7y agoYeah. Glonass (the Russian system) had an 11-hour outage back in 2014 because they uploaded an incorrect ephemeris to all their satellites and could only correct them when they flew over Russia. I think that was the worst GNSS outage of the modern era until this one.
- superkuh 7y agoIt was just a few weeks ago that there was a US midwest and eastern GPS timing precision error that prevented commercial jet's ADS-B from accepting it and causing them to give up throwing errors. ref: https://hackaday.com/2019/06/09/gps-and-ads-b-problems-cause-cancelled-flights/ https://hackaday.com/2019/06/09/gps-and-ads-b-problems-cause...
- greglindahl 7y agoThat doesn't appear to be an outage. It appears to be equipment that requires GPS to have a particular level of precision, which may or may not have been chosen cleverly enough for times when GPS isn't working perfectly.
- elfchief 7y agoThis ended up not being a problem with the GPS system at all -- it was actually a certain brand of receivers not dealing correctly with leap seconds[1] -- or, specifically, that it's been a while since the last leap second, which caused one of the GPS parameters (basically 'how long since/until a leap second' to roll over, which is not normally a problem, but thanks to a receiver bug, it was, on these specific receivers. This was covered in some detail on the LEAPSECS mailing list.[2] [1] https://www.flyingmag.com/collins-receivers-struck-by-failure-modes/ https://www.flyingmag.com/collins-receivers-struck-by-failur... [2] https://pairlist6.pair.net/pipermail/leapsecs/2019-June/007150.html https://pairlist6.pair.net/pipermail/leapsecs/2019-June/0071...
- Animats 7y agoThey designed a new system and made the time fields too short? Again? The ephemeris only has day of the week? No long timestamp? That's embarrassing.
- patrickyeon 7y agoYou clearly haven't read the rest of the article. It's not even especially far down that it's mentioned that the accumulated error for the orbital calculations has resulted in errors for satellite positions into hundreds or thousands of meters after a few days. They made the time fields short because the information would have no value on timescales larger than that.
- Animats 7y agoThe problem is that the time field apparently wraps in a week. Can receivers then tell the data is totally wrong?
- MrBuddyCasino 7y agoThats what the status bits are for. That they didn't set them to 1 on the full constellation suggests there may have been some trouble they didn't publicize.
- makomk 7y agoThe status bit that was set is supposed to mean "working without guarantee" - that is, the satellite may not meet the normal minimum performance level but is still in service. This specific combination of status bits corresponds to a status of "marginal", between full health and actually out of service. In order to actually mark the satellites as fully out of service they'd need to either replace the navigation data with dummy values or upload new navigation data with some additional status bits set. The whole thing seems a little odd. Even the original 80s GPS satellites could automatically update their ephemeris data with stored predictions for 14 to 60 days after the last contact from the ground segment (with a gradual decrease in the signalled accuracy over time), after which time I believe they would switch to invalid dummy data. The current generation can compute their own ephemeris updates at almost full accuracy for months if the ground segment fails. I have to wonder how Galileo ended up transmitting such stale data that ground-based recievers ended up mistaking it for next week's data and still marked it as basically valid. That seems like quite an oversight.
- wrkronmiller 7y agoI'm no expert but according to this site, linked in the article, it appears the system has started to come back online and that the issue was limited to the ephemerides: http://www.navsas.eu/node/611 http://www.navsas.eu/node/611
- lorenzhs 7y agoService was restored yesterday shortly before 9pm UTC: https://www.gsc-europa.eu/notice-advisory-to-galileo-users-nagu-2019027 https://www.gsc-europa.eu/notice-advisory-to-galileo-users-n...
- Lowkeyloki 7y agoThe author mentions how they're not going to talk about rumors several times over the course of the article. I'd love to hear what the rumor mill is saying about the possible causes of the outage.
- londons_explore 7y agoIt is a massive oversight that the satellites don't mark their own data as bad if not commanded to from earth. There are lots of reasons ground stations could go offline, and having the satellites broadcast no data is far far better than broadcasting incorrect data.