I'm done with RRLP!

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Alexander Chemeris alexander.chemeris at gmail.com
Tue Apr 9 10:37:48 UTC 2013


Hi Craig,

On Tue, Apr 9, 2013 at 12:44 AM, Craig Reading <craig.reading1 at gmail.com> wrote:
> PHew! - finally finished my experiments with RRLP. Full details at
> www.genesysguru.com

Your blog seems down - gives me 500/503 errors.

> In summary:
>
> range error=ephemURA of xx.0 (xx) doesn't fit in (0,15)
>
> The problem seems to be that SV accuracy in metres is being used as the URA
> index. The confusion arises due to differences between the Receiver
> Independent Exchange Format (RINEX) 2.10 format and Interface Specification
> IS-GPS-200 (http://www.gps.gov/technical/icwg/). IS-GPS-200 section
> 20.3.3.3.1.3 states: ”SV Accuracy - Bits 13 through 16 of word three shall
> give the URA index of the SV. The URA index (N) is an integer in the range
> of 0 through 15.”
>
> RRLP server needs to be  modified to support RINEX and specifically to add a
> mapping from SV accuracy to URA index. For now I changed line 1084 in
> rrlpserver.erl to assume a URA index of 6 e.g. SV accuracy in the range
> 13.65 – 24 metres:
>
> stuff("ephemURA", nmth(7,1,Tokens), AdjustTable),
>
> Change to:
>
> stuff("ephemURA", “6” , AdjustTable),
>
> With Control.Call.QueryRRLP.Early OpenBTS option configured a crash occurs.
>
> OpenBTS: ../CommonLibs/Vector.h:189: void
> Vector<T>::copyToSegment(Vector<T>&, size_t, size_t) const [with T = char,
> size_t= unsigned int]: Assertion `base+span<=other.mEnd' failed.
>
> Hence the solution for now is to unconfigure this option:
>
> unconfig Control.Call.QueryRRLP.Early
>
> It looks at though the Almanac file downloaded from
> http://www.navcen.uscg.gov/?pageName=currentAlmanac&format=yuma is saved
> into /tmp/almanac as HTML rather than plain text:
>
> As a quick fix I changed my Almanac URL:
>
> config GSM.RRLP.ALMANAC.URL
> http://celestrak.com/GPS/almanac/Yuma/almanac.yuma.txt
>
> My final configuration options are:
>
> config GSM.RRLP.ACCURACY 40
> config GSM.RRLP.ALMANAC.ASSIST.PRESENT 1
> config GSM.RRLP.ALMANAC.URL
> http://celestrak.com/GPS/almanac/Yuma/almanac.yuma.txt
> config GSM.RRLP.EPHEMERIS.ASSIST.COUNT 3
> config GSM.RRLP.EPHEMERIS.REFRESH.TIME 0.5
> config GSM.RRLP.RESPONSETIME 6
>
> Hope this helps!

Sounds great. Could you document this at the OpenBTS wiki?

> I'm moving on to experiments with Uplink-Time Difference of Arrival (U-TDOA)
> methods for locating mobile devices with a bit of GSM burst data analysis ,
> Complex Event Processing (CEP) and data correlation thrown in …. I call this
> Mobile Fingerprinting … lets see!

Looking forward to hear more about your results here - this sounds
like an interesting area to explore. I see many applications where
this would be useful. E.g. we're working with volunteering
organization which search people in woods in Northern Russia - every
year hundreds of people get lost. :(

--
Regards,
Alexander Chemeris.
CEO, Fairwaves LLC / ООО УмРадио
http://fairwaves.ru




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