Global Locate Ephemeris Data

Robert Michel openmoko at
Wed Dec 13 19:28:44 CET 2006

Salve Richard!

Ahh, it seems that the idea of distributed lightning detection 
has inspired you for something (maybe) more usefull *g*

On Wed, 13 Dec 2006, Richard Franks wrote:

> Would we be violating the license by redistributing this data, or
> additional data based entirely upon that data source to other Neo1973
> units?
AFAIK no. Otherwise NTRIP casts would illegal as well.

> I'm wondering about the possibility of leveraging off the fact that
> all Neo1973 units should have a very unified idea of the current time
> to increase the fix accuracy.
> For example, if you have three Neo1973s in a rough geographic
> triangle, such that:
> Neo 1 - has LOS to satellites a,b,c,d
> Neo 2 - has LOS to satellites c,d,e,f
> Neo 3 - has LOS to satellites a,c,d,f
> Each unit computes a positional fix with 5m accuracy as normal, but
> all at the same coordinated time.

GPS normaly needs the signal from 4 satellites - what about instead
of making the accuracy higher, helping neo4 that could receive data
from ony 3 satellites?

> Scaling this up to a downtown city environment, where you could have
> 100 Neo1973's with a 5 mile radius... if they all took positional
> fixes at the same time, would it be possible to use all of this
> coordinated data, plus the ephemeris info, to increase the fix
> accuracy?
- Nice idea, but how to feed the GPS chip whith this?
  (Close Chip, close binary in user mode)
- How to avoid that other users could track you?
- and with 100 receivers there would be a need for a smart
  distributed calculating...
- traffic? 4x100x50 bit/s? 20kbit/s realy so few? To
  have exact time stamps and sender id there must be a big overhead?

I'm not so conviced that such a brute force with 100 receivers
would help with errores due e.g. Ionosphere because non of this
recievers is a fixed/stationary one and a fixed public receiver
in the city with receiving a,b,c,d,e,f would help more.

But shure, there should be a way that a local receiver network
would be usefull. At last to have one Neo in the car and getting
the needed assited data inside a building from this directly
(Wi-Fi, PMR). So a little more information about AGPS but also
about the globallocal chip, which data could be acessed would


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