my problem is, that my GE910-GNSS’s GPS needs about 30 minutes to have the first fix after a cold start. I could find, that it is possible to use AGPS to get a fix sooner.
If I’am not mistaken, there are two ways to achive this: with ST-AGPS seed or with an EPO file (our product will have poor GPRS connection, it is not possible to wait, till we download a 3 MB file from an FTP server).
In both of the cases we have to establish a connection with a HTTP server and download a file. Can you please tell me the average size of these files? Can you please name such HTTP server(s)? What will happen, if I do not have an accurate date an time (only from an RTC)?
I would like to clarify a lot of things.
The GE910GNSS is based on ST GNSS chipset so only the ST-AGPS techonology will work as AGPS aiding on the GE910-GNSS, and the EPO is the protocoll and aiding used from Mediatek chipset only. Every manufacturer has their own protocoll and AGPS data.
You mentioned a problem of 30minutes for a cold star condition; this is a typical situation of cold star where the RF level is very poor and also the ST-AGPS cannot mitigate these 30minutes, because what you are missing it’s the live signal coming from the satellites.
The bases of every AGPS is to decrease the TTFF due to the fact that the UTC is valid and the decoding time of the data receive from the satellites will be less because there are parameters like almanac, gps satellite position, already provided into the AGPS file but you cannot remove the live signals.
In order to have more information and help you I would need to ask you a NMEA log file, a picture and more information about your test setup.
Antenna datasheet included.
thank you for your reply.
If I undersant you correctly, the only way for us would be, that we update the alamanc and ephemeris data even in sleep mode. Would it be a solution for us, that in sleep mode we turn off the GE910-GNSS’s GSM module, but we put the GNSS module into one of its power saving modes? Do you have any information about the current consumtion of the GE910-GNSS in the different GNSS power saving modes (Full, Trickel, PTF, Micro)? Do you have any information about the expected TTFFs wakeing from these modes?
We are doing indoor tests with our Telit EVK2 Mother Board with the GE910-GNSS Interface board, with a passive Glonass+GPS antenna (I do not have datasheet for this. We got the antenna from one of your colleagues at Telit (from Mr. Staps). After its sticker it is for 1574-1610 MHz.), and the whole setup is about 2 m from the next window.
Thank you for your answer in advance.
let me clarify some points.
Every test with every GNSS receiver must be performed with a direct sky visibility, the GNSS RF line can’t receive and decode any RF signals in indoor environment. The GNSS antenna must “see” the sky.
The GE910GNSS is equipped with the ST TeseoII gnss that doesn’t have any low power mode. The low power mode you mentioned are for CSR-QCOM chipset only. (push to fix, trickle power etc)
Normally the GE910GNSS TTFF should be: 40sec for a cold star, 25-30sec for a warm start, and 1-3 seconds for an hot start.
The only possibility to keep the GE910GNSS in low power consumption will be switching off the GNSS when it’s not needed by the means of the AT$GPSP command.
Regarding the aiding on TTFF (speed up the fix) there are two item:
1) the antenna do the main job
2) the GE910GNSS must be equipped with the latest firwmare version (108)
Basically I have to send you all the material (NDA +credentials) in order to have the access to our agps file that has a validity of 7days after it has been downloaded and injected on the GE910GNSS.
I just want to underline that, the values of COLD,WARM,HOT start I mentioned above are what could be reached in good RF level as stated on the documentation.
These value could drastically increase if the sky visiblity is poor or the antenna isn’t so good as performances.
thank you for your quick answer and great help.
Ok, I see, we have to do some outdoor tests to get the real TTFFs.
The TTFFs you mentioned would fully fulfil our expectations. How can we reach them? Apart form the actual firmware and the proper antenna do we have to use Telit’s AGPS service? If yes, how many data do we have to download from your server? Which power mode (I mean here the whole setting – state of the power pins, power state of the GSM (GSM module must be able to receive SMS during this sleep mode) and GPS module, etc.) do we have to apply? Do you have any information about the current consumption in this state?
Hot and warm start means, that (at least part of the) GPS data is kept (last position, almanac, ephemeris). How can we trigger the GE910GNSS to store these data before powering it down? Do we have to set the time of the GPS module after wake up to enable the validation of the stored data?
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