Awesome! And nice job on the pretty pictures! I think this is strong evidence that we should get access to a real satellite simulator, soon.
Though I don't understand why it saw a -14.8kHz Doppler shift. The original file is a zero-IF sample. Did you set the HackRF at a center frequency different than 1575.42MHz, or multiply the file sample by a sine wave, perhaps? That seems outside the range of reasonable clock errors to me. Hey, does your copy of soft-correlator produce the same output mine does for the looped original prn1? It looks like we didn't push the change that sets the IF center frequency to 0 instead of 1.95MHz. Notice the bogus satellites have very low signal/noise ratios (although you should be skeptical of my math for computing those, FYI). Apparently my heuristic is wrong for guessing that a satellite is visible; I based it on my clock error estimate, and all of that is something I made up, not something I've seen documented as the usual way to build a receiver. Jamey On Jun 4, 2015 10:27 AM, "Kenny" <ke...@romhat.net> wrote: > For all you folks following along at home who want to see some pretty > pictures, here you go! > > > https://drive.google.com/open?id=1pnFV5MWkx5YR9ZlutetgDrejNG9SZx6Zp6xbdKl48Ps&authuser=0 > > I sometimes have blissful moments of forgetting that Google wants all of > my data, always. In this particular instance, we may as well let them > help out. So there is a Google Drive folder linked at the bottom of the > doc which contains "gpslog_big-outside.raw" along with various other > files we have been talking about. > > Transmitting the prn1 converted to complex floats through the HackRF and > grabbing a sample with jGPSv3 correlates! Check out that > signal-to-noise ratio for SV 1!. > > $ ./soft-correlator < data/gpslog_prn1_rx.raw > # frequency of 1-bits: i-sign 51.7%, i-mag 33.6%, q-sign 48.8%, q-mag 30.0% > # SV, S/N ratio, doppler shift (Hz), code phase (chips), sample clock > error (chips/s) > * 1 601.457508 -14801.532243 253.000000 9.611385 > * 2 14.721936 -799.801893 330.000000 0.519352 > * 4 15.425549 -6801.062185 669.000000 4.416274 > * 11 14.114000 -10801.489275 302.000000 7.013954 > * 17 15.250208 2199.254809 77.000000 -1.428088 > * 24 14.148221 -7794.920364 335.000000 5.061637 > * 28 13.145979 14199.180477 545.000000 -9.220247 > * 30 13.199176 5798.007429 466.750000 -28.764940 > # 8 satellites in view; average clock error -1.598834 chips/s > > I'm surprised to see that the added noise was enough to correlate the > pseudo-noise sequence from other satellite vehicles. This was done in > the basement, so I know it wasn't accidentally picking up any real > satellites. > > -- > Kenny > > -+---+++-++-++++--+------+-+-++--++--+-+-++--+++-++----+-++-+++---+----+--+----+ > > > > >
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