The neo1973 will come with a Global Locate GPS chip. In the following I will try to explain the disadvantages of that situation.
First thing to keep in mind is that all the tomtom PDAs do pretty well without any "A-GPS" at all!! So what is that A-GPS good for? ------------------------------- There are two points: * TTFF - time to first fix after cold or warm start * precision of position during the first minutes of navigation How is that achieved? --------------------- This is achieved simply by preloading the GPS-chip with the ephemeris data, meaning that a satellite can immediately be used for getting a fix at the moment it comes in sight instead of waiting 30secs while downloading the data. The ephemeris data contains the precise position of a satellite and outdates within two hours. However it is only 1500 bits long (times 12 satellites over your head) so can be quickly downloaded via i.e. GPRS. The ephemeris data is available here: http://igscb.jpl.nasa.gov/components/prods_cb.html The SiRF chipsets do allow for preloading the data and the protocol specs are published by SiRF, however nobody has even bothered yet to write the few lines of code to extend the gpsd (gpsd.berlios.de). Now what's the problem with Global Locate? ------------------------------------------ The problem is that the protocol specs for communicating with the GPS chip are only available under NDA. Their whole marketing is based on this and they never mention "ephemeris data". This allows them to paraphrase it over and over again and pretend they have something unique. Some examples (taken from http://www.globallocate.com/NETWORK/NET_WWRN_frameset.htm ): Full GPS-constellation data Satellite assistance data provided for 100% of satellites. -> means: they have ephemeris data Strategically located Each GPS satellite is monitored by several RSs at all times to ensure no coverage gaps. -> means: nothing. just marketing blurb. Their 'WWRN' of RSs (worldwide network of reference stations) is what others call CORS (continously operating reference stations) http://www.ngs.noaa.gov/CORS/ No missing satellites Unlike regional RS solutions that leave the handset with a critical shortage of assistance data, WWRN data includes assistance data for rising satellites. -> means: they have ephemeris data (we heard that already, didn't we?) Highest likelihood of E911/E112 location fix Important in the typical obstructed environment, handset is assured of having assistance data for all visible satellites. -> means: they have ephemeris data (we heard that already, didn't we?) Assistance data always current Changes in orbital navigation data or health status broadcast by the satellites is processed in real-time by the WWRN. -> means: they have ephemeris data (oh, really?) Minimizes requests to A-GPS server No additional network assistance required as new satellites come into view. -> means: they have ephemeris data (it starts to get boring) Shared infrastructure Full GPS-constellation data enables single A-GPS server to support handsets in multiple networks worldwide. -> means: they have ephemeris data - yaaawwnnn and on and on and on like this, paraphrasing over and over again that they have ephemeris data. They are selling H20 in bottles. * Conclusion * ============== Global Locate: You should just publish the specs for the binary protocal of your chip. We do the rest for ourselves. If they don't do that, please Sean, follow your Mantra for an open plattform and substitute their chip with a more open one. A word of advice for Global Locate: actually the OSS community likes underdogs and compared to the market leader SiRF you are exactely that. But don't show up as arrogant jerks on mailing lists pretending to be an engineer but talking like a marketing droid. Marcus _______________________________________________ OpenMoko community mailing list community@lists.openmoko.org http://lists.openmoko.org/mailman/listinfo/community