Yes, all the Windows Mobile, Blackberry and Symbian phones with GPS that were running Google Maps Mobile (GMM) starting back in 2006, were secretly being used to collect a cell tower database.
An interesting scenario. In the USA, only CMDA carriers had GPS chips in them due to the FCC E911 requirement, and that for only the last few years or so. GSM, of course, took a network, non-gps approach. So that means Verizon, etc users and Verizon, played a major hand in making up the GPS'd coordinates for Cell ID location service by Google. Assuming they were running Google Maps. Yet today, we are taking about GSM (non gps )carriers using the service, sort of for free. What a coup!
If so, how does the CDMA carriers Cell ID translate to a GSM Cell ID for Google location service? Does that mean that Google's LBS has vastly more data points for Verizon than a GSM carrier? The few GSM phones with gps did play a part, for certain.
Still today, a majority of aGPS chips are in the CDMA phones, except for some high end GSM models,like the new 3g iPhone. But that is changing. But still I would guess that the number of GPS GSM handsets in in the single digit % of total users.
And then in Europe, GSM-land, GPS in a phone has still been rare. Nokia the biggest phone maker, has only today a handful of GPS units, mostly the N series. So do we think that Google Locate Me service in Europe is less accurate or covered than the US? They really have a sparse CDMA offering over there, or the world really.
Well interesting thoughts, but it will get better over time. Over the weekend, Google place me 2 miles off my real location, yet the blue circle said my error was 1000 meters (less than a mile).
As far as changing Cell ID frequently, I doubt an individual carrier would do that today very often. They would place themselves at a disadvantage compared to other carriers, since they would lose the Google Locate Me feature. Assuming of course the whole system is based on user GPS coordinates to help google locate the cell towers, and then you. Customers would not like losing Locate Me, via the cell tower ID changing! Plus, internally, Verizon needs to keep the GPS'd base stations ID's clean and simple to assist the mobile based aGPS chip for 911 calls. What a headache if there was confusion there. But I suppose they could, a computer could keep track of those changes. But would they relay them to Google? Not from what I'm reading in these posts.
Back to the original thread topic, from all the interesting posts and corrections (including mine) in this thread, I think we could summarize how the 3G iPhone’s location service works.
First from the Apple web page it can be concluded that Apple uses 3 ways to locate you, with the aGPS being primary and the best service, if available:
1. The aGPS chip is used first. It turns on when needed to get a location and then turns off.
2. If GPS is not available for some reason, it goes next to
a) WiFi if you are in a dense area like the city and the city is wifi mapped by Skyhook. Or it uses
b) Google’s GSM cell ID location service.
aGPS
Since the aGPS is the primary and the best, for the 3G iphone, the primary location of the phone is performed by 'triangulation'.The correct term may be 3D trilateration or multi lateration, as I stated before, but the terms are used very loosely in practice. As an example, here is a quote from Garmin (the GPS maker) web page on how GPS works:
How it works
‘GPS satellites circle the earth twice a day in a very precise orbit and transmit signal information to earth. GPS receivers take this information and use triangulation to calculate the user's exact location. Essentially, the GPS receiver compares the time a signal was transmitted by a satellite with the time it was received. The time difference tells the GPS receiver how far away the satellite is.’ - (From Garmin, http://www8.garmin.com/aboutGPS/)
From the horse’s mouth, so to speak. I wouldn’t jump on anyone for using this term. I’m calling them interchangeable in common language at this point now. aGPS is not a possible form or board definition of ‘triangulation’, it really is. The ‘a’ in GPS uses the cell tower (and it’s known GPS coordinates, and advance processor power) to port that rough location and other information to the phone, but from there on, the phone is receiving the Sat signals like a regular GPS.
WiFi and Google Celluar Tower location methods
I can understand why people are going to use ‘triangulation’. Now from Apples web page :
So in summary of previous posts the 3G iPhone uses:
1. aGPS which uses triangulation with orbiting satellites (Best)
2. WiFi location (Best in mapped cities).
Poorest with 1 wifi (700feet). Works better with multiple WiFi’s (3 or 4) down to 150 feet. In very dense urban areas, down to 60 feet. GPS is used by provider (Skyhook) to reverse triangulate WiFi locations and a choice of several algorithms (one including but not limited to triangulation, per US patent) to locate the mobile.
3. Google’s Cell Tower ID. (Best if no GPS or dense WiFi is not available). Seems to use only one Cell Tower and previous mobile users GPS location to locate that cell tower. Gives a weighted estimate of where other mobile users have been when using that same cell tower. Could be off miles in non urban areas. No clear documentation that it makes use of more than 1 tower. Much better in cities, but Google promises no better than ~3000 feet.
And last (number 4), the network based E911 location system in use by all GSM providers and phone, is based on triangulation (trilateration) of multiple cell towers to find you. Works in all areas, rural and urban, and indoor, but only available to 911 services.
An interesting side note is that all of these 4 methods use GPS somewhere in the method. That may explain why apple uses the term loosely.
An interesting scenario. In the USA, only CMDA carriers had GPS chips in them due to the FCC E911 requirement, and that for only the last few years or so. GSM, of course, took a network, non-gps approach. So that means Verizon, etc users and Verizon, played a major hand in making up the GPS'd coordinates for Cell ID location service by Google. Assuming they were running Google Maps. Yet today, we are taking about GSM (non gps )carriers using the service, sort of for free. What a coup!
Actually, no! The Google Cell ID location database is built by mobile users reporting both (1) their actual location, and (2) the CGI of the serving sector. A VZW mobile may know it's actual location (via aGPS), but it has no idea about GSM Cell IDs. Therefore, it can't help build the database.
If so, how does the CDMA carriers Cell ID translate to a GSM Cell ID for Google location service?
It doesn't! First of all, each carrier runs its own network, with their own set of base stations, which might be in totally different places for different carriers. A VZW mobile is completely oblivious to the Sprint/AT&T/T-Mobile/etc. networks around it. It only sees the native VZW network, unless it's roaming of course. Second, CDMA2000 base stations don't have a Cell ID. There simply is no equivalent to the CGI in the CDMA world. CDMA base stations are differentiated by their PN, but that's not a globally unique identifier in the sense of the CGI.
Does that mean that Google's LBS has vastly more data points for Verizon than a GSM carrier? The few GSM phones with gps did play a part, for certain.
I don't believe the Google Locate Me feature is available on CDMA at all. Either the mobile has aGPS and will get an exact fix that way, or it won't get a location period. There's no comparable equivalent to the GSM Cell ID location lookup for CDMA.
I am a little confused. My Verizon phone was able to roam on GSM because they used TDMA. Tell it was shutdown. The phone recognizes it as Analog. If PCS has TDMA, It could be technically be used on GSM.
Originally Posted by Tabla
Y'know, I'm used to hysterical 14-year-old ******** on the internet, but this is exceptional. Never before in human history have so many nerds hyperventilated so publicly over so little.
Actually, no! The Google Cell ID location database is built by mobile users reporting both (1) their actual location, and (2) the CGI of the serving sector. A VZW mobile may know it's actual location (via aGPS), but it has no idea about GSM Cell IDs. Therefore, it can't help build the database.
It doesn't! A VZW mobile is completely oblivious to the Sprint/AT&T/T-Mobile/etc. networks around it. It only sees the native VZW network, unless it's roaming of course. Second, CDMA2000 base stations don't have a Cell ID.
I don't believe the Google Locate Me feature is available on CDMA at all. Either the mobile has aGPS and will get an exact fix that way, or it won't get a location period.
XFF, so my post was more of the rehtorical question kind, to make one think a bit. I know that each carrier's phone is oblivious to the other networks around them!
The question is then how good can the My Location cell id mapping be? Locate Me works in over 20 countries, but the number of GSM phones that have aGPS or GPS in them is so tiny today, one has to one wonder how well mapped the Google service really is. I suppose that is why it is in Beat testing.
There is nothing on the Google web page to limit Locate Me to GMS phones, GSM carriers only, but I suppose it is. As you said, all CDMA phones, today, in the US have aGPS chips in them. But then they have little options if they are indoors and need a location fix.
The CDMA towers do need to send information to the aGPS phone to help it locate itself.
The question is then how good can the My Location cell id mapping be? Locate Me works in over 20 countries, but the number of GSM phones that have aGPS or GPS in them is so tiny today, one has to one wonder how well mapped the Google service really is. I suppose that is why it is in Beat testing.
Google Maps for Mobile only runs on smartphones to begin with: Windows Mobile, Palm OS, BlackBerry, and iPhone. Chances that one of those devices has GPS are much better than 1%. We don't know how deep Google's Cell ID database is. They say they got millions of location fixes from the field, evenly distributed over 50,000 - 100,000 base stations, that works out to 10's of reports per sector. As the service becomes more popular, the database will get deeper and their matching and weighting algorithms will be able to better narrow a user's location.
There is nothing on the Google web page to limit Locate Me to GMS phones, GSM carriers only, but I suppose it is. As you said, all CDMA phones, today, in the US have aGPS chips in them. But then they have little options if they are indoors and need a location fix.
gpsOne works fine indoors, in fact better than autonomous GPS.
Can we speculate that with more 3G iPhones on the market, wifi/tower locations database will be populated faster and old iPhone users will be getting more accurate location information?
Can we speculate that with more 3G iPhones on the market, wifi/tower locations database will be populated faster and old iPhone users will be getting more accurate location information?
That's an excellent point. I believe that Google CGI lookup database will greatly benefit from the iPhone 3G deployment. Skyhook doesn't work the same way (as far as we know they don't correlate Wi-Fi MAC addresses with actual locations known to users' handsets the way Google does, they rely on their volunteer contributors to populate the database), so probably not.
-When I first saw the title, I thought... "Who cares?"
-When I saw that it was made a sticky, I really thought... "Who cares, and why is this is a sticky, is it that important?"
-Every time I see the thread has been updated, I think... "really, people are still commenting on this?"
I'm just joking, I know there are many out there who love the technical answers for such, but I still wonder, "why is this is a sticky, is it really information that will make or break my iPhone experience?" I think not, lol.
A-GPS is not cheaper than GPS. It is more expensive. It contains everything an autonomous GPS does, plus more.
Actually, it depends. The term aGPS (or A-GPS) is often misunderstood and misused, because there's different modes and types of implementation, at least 3 of which are significant and need to be carefully differentiated:
MS-assisted
MS-based
enhanced autonomous (LTO)
In MS-assisted mode, the mobile station receives the GPS ranging signal from the orbiting satellites, but simply passes it on to the base station, which then calculates the position fix and sends it back to the mobile. This is the method implemented in most cheap CDMA phones. If this is the only mode supported by the mobile, it is cheaper than autonomous GPS, and it does rely on the location entity server (and hence an active data connection) to obtain a position fix.
In MS-based mode, the mobile receives the ranging data from the satellites and does all the calculations locally, however it uses almanac and ephemeris data supplied via the network in order to speed up time-to-first-fix (TTFF). This mode is a superset of autonomous operation and is neither cheaper nor less accurate than autonomous, it's simply faster.
Enhanced autonomous mode is similar to MS-based, except the almanac and ephemeris data are not pulled via the mobile's data connection, but are side-loaded and locally stored in flash. Those data are then good for several days, whereas regular (real-time) almanac and ephemeris data are only good for a few hours. Enhanced autonomous mode is chiefly used in appliances where a short TTFF is critical, but a live data network connection is usually not available. Such applications include stand-alone cameras or personal navigation devices.
It is important to understand that location accuracy is absolutely identical, regardless which of the 4 methods (the 3 outlined above plus autonomous mode) are used, they only differ in where the position fix locations are done and how the almanac and ephemeris data are supplied. Nothing else!
The iPhone works just fine tracking my position with the SIM card removed.
A-GPS just allows GPS receivers to get their initial lock much faster, by downloading the almanac and ephemeris data over the network, rather than waiting to receive it from the satellites.
I'm going to tell you right now: you're wrong. There's a reason XFF made that sticky.
In MS-assisted mode, the mobile station receives the GPS ranging signal from the orbiting satellites, but simply passes it on to the base station, which then calculates the position fix and sends it back to the mobile. This is the method implemented in most cheap CDMA phones. If this is the only mode supported by the mobile, it is cheaper than autonomous GPS, and it does rely on the location entity server (and hence an active data connection) to obtain a position fix.
BTW, I just learned that the Palm Pre uses MS-assisted mode exclusively, and hence no location fix without an active network connection. So this is not limited to just cheap CDMA phones.
The A-GPS mandatory tie-in with cell towers, apart from charging one for data,(roaming especially) renders the iPhone location apps non-functional in an airplane or at sea.
iPhone switches to autonomous GPS mode when assistance is unavailable due to a lack of network connectivity or any other reason. There is no dependancy on "cell towers" to get a position fix with iPhone.
It actually goes into detail using a more practical rather than just theoretical approach. So there is no guessing what is actually supported on the iPhone. However, it does cover the theoretical stuff as well.
Originally Posted by KDarling
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