How much intelligence is in the GPS aerial?

deep_south · Occasional Visitor Joined: May 26, 2004 Posts: 22

Just wondering - does the aerial provide simply a "raw" data stream to the PPC which then works out all the "stuff" it needs, or does it decode all the information and send simple "postioning and status" info to the PPC?

The reason I am asking is that I recently started to switch the PPC GPS between TTN3 and MS PocketStreets, and when I switch between them the "new" application seems to know the GPS location almost instantly.

Or is there a "standard GPS working it out module" that is always active that both applications hook into? I need to "stop" the GPS when I exit from PocketStreets, and "End" TTN3 when I leave it to release the GPS COM port (It's a wired aerial with a Dell Axim X5)

Any thoughts - or better still, knowledge?

Cheers, Peter

Dave · Posted: Tue Nov 23, 2004 6:54 pm Post subject:

The GPS Receiver is constantly configured to receive satellite signals, and when it has enough information it will turn into a 3D fix. The Pocket PC just receives the data via the COM port which the GPS sends on, so you can for testing purposes plug in the GPS for 5 mins, then power on the PPC and go into any GPS Application and you will have an instant fix.

Therefore the GPS does all the work in acquiring the data and just passes this data onto the PPC when it has all the data.

DavidW · Posted: Tue Nov 23, 2004 9:37 pm Post subject:

As Dave's reply says, all the GPS's intelligence is in what you term an aerial. There's an aerial, GPS chipset and any necessary serial line drivers and power circuitry in that little device.

Power goes up the wire to the GPS, and the connected device like a Pocket PC talks to the GPS chipset using serial communication.

David

carl_w · Lifetime Member Joined: Mar 13, 2004 Posts: 242

So, logically, assuming that the GPS receiver does NMEA-type output, all the calculation of position from pseudoranges, iono/tropo corrections, etc. are done by the GPS receiver and the positional information, FOMs, DOPs, etc. sent down the serial interface to the PDA.

I must have been out of this game for too long -- my TT BT GPS receiver doesn't look big enough to do all of that! :D

DavidW · Posted: Wed Nov 24, 2004 12:17 am Post subject:

You're right - unless the application has set the GPS to a binary mode and asked for raw data.

There's an ARM processor core in most GPSes (certainly SiRF use ARM cores) together with some flash memory and some RAM. There's some pictures of the innards of a TomTom wired GPS here. A SiRFstar II chipset consists of just two chips, as you can see in those pictures.

David

deep_south · Occasional Visitor Joined: May 26, 2004 Posts: 22

Thanks for the interesting replies.

it's amazing what they can do with electronics nowadays - makes you wonder what it will be like in (say) 10 years time, when everyone will have a 4G or 5G phone with GPS and PDA with "always on" internet access...

Peter.

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