Thread

1. guenthert · 1789545640 · focus · HN ↗

   "real-time GPS-driven moving map display"

   Not the IMHO more interesting analog tech which lifts signals out of thermal noise.

   1. JPLeRouzic · 1789558778 · focus · HN ↗

      That looks interesting, what technology "lifts signals out of thermal noise"?

      1. FrankPetrilli · 1789561090 · focus · HN ↗

         GPS - look into Gold Codes [1] and auto-correlation. GPS arrives on your device at -128dBm, give or take, while thermal noise is -111dBm at the ~2MHz sampling bandwidth used. We use the processing gain from correlating against the ~1Mchip/s gold code to extract the lower bitrate signal, so you're pulling signals from approximately 20dB below the relevant thermal noise floor.

         [1] <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Gold_code" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Gold_code

      2. y04nn · 1789564028 · focus · HN ↗

         DSSS, direct sequence spread spectrum, used for encoding GPS signal
      3. peaseagee · 1789564797 · focus · HN ↗

         Spread spectrum, it&#x27;s pretty magical.
      4. JPLeRouzic · 1789570315 · focus · HN ↗

         Thanks @FrankPetrilli.
      5. squantor · 1789586390 · focus · HN ↗

         I found this an interesting writeup on the technologies needed to receive GPS signals:

         <a href="http:&#x2F;&#x2F;www.aholme.co.uk&#x2F;GPS&#x2F;Main.htm" rel="nofollow">http:&#x2F;&#x2F;www.aholme.co.uk&#x2F;GPS&#x2F;Main.htm

         The combination of RF electronics and then doing the signal processing in an FPGA for the timing critical stuff and the actual DSP with a raspberry pi, very interesting.

         1. JPLeRouzic · 1789743930 · focus · HN ↗

            Thank you @squantor

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