MOD-GPS power saving mode

[DUR_OMX]

Hi,
this is my first topic on this forum and I hope someone could help me. I'm working for the first time on Olimex GPS module (MOD-GPS) based on Mediatek 3329 chipset; I read on "Global Top PMTK command packet" document that for the 3329 chipset all commands for energy saving are disabled so I'm wondering what is the meaning about cold, warm and hot start commands if it's impossible to use stand-by mode or any other power saving modality. Is there any mode to save energy with this GPS module ? Please, could anyone help me ?
Regards
DUR_OMX

[MBR]

I'm not sure about powersaving modes of Mediatek chips, but the term cold, warm and hot start are a part of the standard GPS glossary. The cold start means that the GPS has been powered off (without backup battery), so all data are lost and the GPS has to scan all channels to gets visible satelittes. On modern mutichannel GPSs, this may take up to minute (cca. 45s on average). The warm start is when the GPS has valid time and almanach data (long-term predictions of satelitte orbits and such) and aproximate position (up to cca. 100km), but has to wait for ephemeris data (exact posititon and other parameters of the corresponding satelitte) or the ephemeris data are expitred (they are valid only up to four hours), the average time is little more than half of minute. The hot star is when the GPS has valid time, almanach and ephemeris data, so it can get valid position almost instantly (cca. one second on most GPSs).

Note that the times are valid only when the signal reception is good (e.g. clear view on the sky), with a poor reception, the cold and warm start may take many minustes (this is why the cell phones use assisted GPS, which can get approx. postion, time, almanach and ephemeris data from the internet).

[DUR_OMX]

Ok, but when the module start-up and I don't send any command, which starting method it uses ? Hot, cold or warm ?

[MBR]

The module has backup battery for RTC, so it depens on the interval when the modules was powered last and in what state was powered down. If the interval was shorter than two hours, you will probably get the hot start (assuming that the GPS had full reception on the last time). More than two hours, it will be either warm or cold start.

There is an easy way to tell the "starts" apart - run a program like cgps/xgps/anything that can display satelittes and if they used. If you got satelittes and they are used almost immediately, it was hot start. If you got correct time and some satelittes with good signal, but they are not used for some time (cca. 30s), it was warm start. If you don't see any satelittes (or only very few) upon the start, or you have incorrect time, it was definitely cold start.