How does GPS in a mobile phone work exactly

Question

I assume it doesn t connect to anything  other than the satelite I guess   is this right  Or it does and has some kind of charge

User · Answer

There s 3 satellites at least that you must be able to receive from of the 24-32 out there  and they each broadcast a time from a synchronized atomic clock  The differences in those times that you receive at any one time tell you how long the broadcast took to reach you  and thus where you are in relation to the satellites  So  it sort of reads from something  but it doesn t connect to that thing   Note that this doesn t tell you your orientation  many GPSes fake that  and speed  by interpolating data points   If you don t count the cost of the receiver  it s a free service  Apparently there s higher resolution services out there that are restricted to military use  Those are likely a fixed cost for a license to decrypt the signals along with a confidentiality agreement   Now your device may support GPS tracking  in which case it might communicate  say via GPRS  to a database which will store the location the device has found itself to be at  so that multiple devices may be tracked  That would require some kind of connection   Maps are either stored on the device or received over a connection  Navigation is computed based on those maps  databases  These likely are a licensed item with a cost associated  though if you use a service like Google Maps they have the license with NAVTEQ and others

User · Answer

GPS  the Global Positioning System run by the United States Military  is free for civilian use  though the reality is that we re paying for it with tax dollars   However  GPS on cell phones is a bit more murky   In general  it won t cost you anything to turn on the GPS in your cell phone  but when you get a location it usually involves the cell phone company in order to get it quickly with little signal  as well as get a location when the satellites aren t visible  since the gov t requires a fix even if the satellites aren t visible for emergency 911 purposes    It uses up some cellular bandwidth   This also means that for phones without a regular GPS receiver  you cannot use the GPS at all if you don t have cell phone service   For this reason most cell phone companies have the GPS in the phone turned off except for emergency calls and for services they sell you  such as directions    This particular kind of GPS is called assisted GPS  AGPS   and there are several levels of assistance used   GPS  A normal GPS receiver listens to a particular frequency for radio signals   Satellites send time coded messages at this frequency   Each satellite has an atomic clock  and sends the current exact time as well   The GPS receiver figures out which satellites it can hear  and then starts gathering those messages   The messages include time  current satellite positions  and a few other bits of information   The message stream is slow - this is to save power  and also because all the satellites transmit on the same frequency and they re easier to pick out if they go slow   Because of this  and the amount of information needed to operate well  it can take 30-60 seconds to get a location on a regular GPS   When it knows the position and time code of at least 3 satellites  a GPS receiver can assume it s on the earth s surface and get a good reading   4 satellites are needed if you aren t on the ground and you want altitude as well   AGPS  As you saw above  it can take a long time to get a position fix with a normal GPS   There are ways to speed this up  but unless you re carrying an atomic clock with you all the time  or leave the GPS on all the time  then there s always going to be a delay of between 5-60 seconds before you get a location   In order to save cost  most cell phones share the GPS receiver components with the cellular components  and you can t get a fix and talk at the same time   People don t like that  especially when there s an emergency  so the lowest form of GPS does the following    Get some information from the cell phone company to feed to the GPS receiver - some of this is gross positioning information based on what cellular towers can  hear  your phone  so by this time they already phone your location to within a city block or so  Switch from cellular to GPS receiver for 0 1 second  or some small  practically unoticable period of time  and collect the raw GPS data  no processing on the phone   Switch back to the phone mode  and send the raw data to the phone company The phone company processes that data  acts as an offline GPS receiver  and send the location back to your phone    This saves a lot of money on the phone design  but it has a heavy load on cellular bandwidth  and with a lot of requests coming it requires a lot of fast servers   Still  overall it can be cheaper and faster to implement   They are reluctant  however  to release GPS based features on these phones due to this load - so you won t see turn by turn navigation here   More recent designs include a full GPS chip   They still get data from the phone company - such as current location based on tower positioning  and current satellite locations - this provides sub 1 second fix times   This information is only needed once  and the GPS can keep track of everything after that with very little power   If the cellular network is unavailable  then they can still get a fix after awhile   If the GPS satellites aren t visible to the receiver  then they can still get a rough fix from the cellular towers   But to completely answer your question - it s as free as the phone company lets it be  and so far they do not charge for it at all   I doubt that s going to change in the future   In the higher end phones with a full GPS receiver you may even be able to load your own software and access it  such as with mologogo on a motorola iDen phone - the J2ME development kit is free  and the phone is only  40  prepaid phone with  5 credit    Unlimited internet is about  10 a month  so for  40 to start and  10 a month you can get an internet tracking system   Prices circa August 2008   It s only going to get cheaper and more full featured from here on out     Re  Google maps and such  Yes  Google maps and all other cell phone mapping systems require a data connection of some sort at varying times during usage   When you move far enough in one direction  for instance  it ll request new tiles from its server   Your average phone doesn t have enough storage to hold a map of the US  nor the processor power to render it nicely  iPhone would be able to if you wanted to use the storage space up with maps  but given that most iPhones have a full time unlimited data plan most users would rather use that space for other things

[gps] How does GPS in a mobile phone work exactly?

The answer is

Examples related to gps

Examples related to mobile-phones

Tags