10 ms·
Homemade GPS Receiver (2013)
- wanderingjew 8y agoshould have [2012] tag.
- grzm 8y agoOr perhaps 2014, as it contains an update from September 2014.
- wanderingjew 8y agowell the important thing is that the title is clickbait. I hope the mods will fix it shortly.
- craftyguy 8y agoHow in the world is not having the year in the title, especially for this article, 'clickbait'? I could understand if the article was "Germany invades Poland" and they left out [1939], but come on...
- paulmd 8y agoHackerNews: threads may contain up to 25% "posts whining about titles" by weight. (it's a seriously endemic problem here and it's worthless white-noise.)
- _emacsomancer_ 8y agoFrance invades England [1066]
- deleted 8y ago[deleted]
- brian-armstrong 8y agoDSSS [1] is really interesting and worth reading up on if you’re already familiar with LFSRs. To summarize, you start by generating a deterministic, pseudorandom, periodic sequence. You then take your message and modulate (bitwise XOR) each bit of the message by the entire sequence e.g. if my sequence is 31 bits long, then my message modulated is now 31x long. The receiver just correlates the received message by the pseudorandom sequence. The correlation gives me what each bit is and a belief/probability for that bit. This works really well because the sequence is orthogonal to just about every other sequence (it’s white noise!). It’s even orthogonal to time shifted versions of itself, meaning that it does well at rejecting multipath distortion. 1: https://en.m.wikipedia.org/wiki/Direct-sequence_spread_spectrum https://en.m.wikipedia.org/wiki/Direct-sequence_spread_spect...
- madengr 8y agoI wonder how many orthogonal codes exist? The Walsh codes in CDMA have a pretty low correlation, as long as they all stay synchronized.
- lpmay 8y agoAnother cool thing, that was counter intuitive to me is that more than just rejecting multipath, spread spectrum can actually make use of multipath to improve the link (although I doubt it is done much in practice). Conceptually, what you do is correlate on the incoming signal like normal, this first lock is the dominant path. You take the component that correlated and subtract it from the incoming signal and correlate again on what remains. This lock is the second multipath. You can do this to recover as many multipaths as you want or have dynamic range for. Finally, the relative offsets in the correlations tell you how to re-align all the multipaths in time. Once they are aligned you can sum them together and get more SNR than if there had been no multipath at all.
- brian-armstrong 8y agoYes, this is really cool! If anyone’s curious, this is called a rake receiver https://en.m.wikipedia.org/wiki/Rake_receiver https://en.m.wikipedia.org/wiki/Rake_receiver
- Maxious 8y agoFurther work in this space: https://gnss-sdr.org/ https://gnss-sdr.org/
- ohazi 8y agoThis is impressive enough, but his other projects are also awesome and totally worth a look: http://www.aholme.co.uk/Projects.htm http://www.aholme.co.uk/Projects.htm
- amaterasu 8y agoThanks for linking this - I didn't even think to look and his work is amazing!
- gh02t 8y agoIndeed, I was impressed just by his PCB layout... it's so neat with that big Spartan-3, while I struggle to make tidy layouts with a simple 32-pin TQFP chip. And that's probably the simplest part of this project.
- TheOtherHobbes 8y agoEven more amazing - these are part-time hobby projects.
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- bunkydoo 8y agosfasdfasd
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- okket 8y agoSee also previous discussion from 3 years ago: https://news.ycombinator.com/item?id=9470376 https://news.ycombinator.com/item?id=9470376 (55 comments)
- Jacq5 8y agoIs this what people are doing in their free time? I might have no friends, but this is another level. Salute, sir.