Thanks for the info Zik. Some of the newest chip sets (SiRF III) can warm start in under 2 seconds. Quite amazing to have valid NMEA sentences popping out 2 seconds after a power up. Some GPS's allow the user to input date/time/location to shorten the cold start time. My question was specific to cold starts where all of the above are unknown and a full almanac needs to be downloaded. Robert Zik Saleeba wrote: > Current generation GPS systems take a little over 30s to cold start. > They do this by acquiring a set of satellites during the first few > seconds, then downloading ephemeris and almanac over the next 15-30s. > > This isn't usually necessary though - in nearly every case a warm > start can be done instead. The almanac is already available in > battery-backed RAM so the unit guesses which satellites are in view > based on the time and its last known location. This means that unless > it's moved a long distance it can usually start up in about around 25s > rather than 35s. > > Some GPSs can also hot start, meaning that if they have a sufficiently > accurate time mark and recent ephemeris information available they can > use the ephemeris information straight away, allowing them to fire up > in 5-15s. If the ephemeris is out of date or the time mark isn't > accurate enough the unit has to fall back to warm or cold start. > > Cheers, > Zik > > On 12/6/06, Robert Rolf wrote: > >>Brooke Clarke wrote: >> >>>out of a garage or tunnel), not cold start. That data rate coming from >>>the satellites means that it will take about 12 minutes to download an >>>ephemeris and that can not be speeded up by receiver horsepower. >> >>Is the ephemeris data transmitted by all satellites 'in phase' or is it >>"store and forward" with staggered phases? >> >>Seems that if one can find one satellite in 'search' mode, one could find >>more than one, and so download different pieces of the almanac and ephemera in parallel >>to shorten the cold start time. >> >>And with software correlaters, having more horsepower would mean more correlaters >>so more satellites found sooner (only if the data transmissions are NOT synchronized >>so parallel loading of the data was feasible). >> >>And if this ISN'T the case, wouldn't changing the system to staggered data >>transmission allow for this to happen? Patent anyone? >> >>Expert comment anyone? >> >>Robert >> >>-- >>http://www.piclist.com PIC/SX FAQ & list archive >>View/change your membership options at >>http://mailman.mit.edu/mailman/listinfo/piclist >> -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist