Thanks for writing such a good definition and why people's use of the term "triangulation" with Google Maps is wrong. I already knew most of the info but never bothered to write a post about it. Great writeup....thanks !!
I just noticed this post. That article has a lot of misinformation. They say:
A-GPS means that there are many ways to obtain your location besides reading the multiple GPS geosynchronous satellites signals
Which is totally incorrect. A-GPS is about using GPS satellite signals. Not cell. Not WiFi.
In the iPhone's case, the GPS is a standalone receiver, but the host CPU can request Assistance in the form of quickly getting status and orbit information from a master server on the Internet, instead of slowly from the satellites, to speed up a fix.
Hmm... If you re-read what you wrote, you are not contradicting what you are trying to contradict. In other words, you are actually supporting what the article in the webpage said in your quote.
But if you want to get into technicalities, I suggest you re-read the whole article. The cell towers do have a fixed position that never moves, and this is provided as a quick way to allow you to get your positioning. If the cell towers could move, you would not be able to get your positioning in seconds because of A-GPS, as the cell towers would need to get a GPS signal live. If the cell towers's location is never involved with A-GPS, how do you know how close you are to a location?
Wi-Fi is part of WPS, another method of location services in addition to A-GPS provided by the iPhone. It was never mentioned as being part of A-GPS. But now that you brought it up, you have a point. So a Location Services header is now above A-GPS, and WPS is still where it is.
But if you want to get into technicalities, I suggest you re-read the whole article. The cell towers do have a fixed position that never moves, and this is provided as a quick way to allow you to get your positioning.
No, it's not. The cellular system does not broadcast or relay the location of the BS to the MS. The cellular data network is used merely as a conduit to access an assistance server from which the mobile can download the almanac and ephemeris data near instantaneously versus observing the GPS constellation for up to 12.5 minutes in order to obtain the same data. The geographic location of the BS transmitters is completely irrelevant to A-GPS, at least the MS-based variety as implemented in iPhone. MS-assisted technologies as often deployed by CDMA carriers do take the BS location into consideration, but that has nothing to do with how iPhone works.
If the cell towers could move, you would not be able to get your positioning in seconds because of A-GPS, as the cell towers would need to get a GPS signal live. If the cell towers's location is never involved with A-GPS, how do you know how close you are to a location?
Complete nonsense. Read the entire thread (especially post #42) to gain a better understanding of how A-GPS really works.
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.
Well, if you insist. I think what you are trying to say is that the Cell tower location is irrelevant to A-GPS. But it IS! It is the only way to determine your location. Where the DATA of the location of the cell tower is (be it in a server separate from the cell tower base station, or separately on an internet server out on the internet somewhere in another country), is not relevant. Also, never was it mentioned the cell tower always broadcasts the location data from the cell tower directly. I think you are reading too much into things that are not there. Again, if you don't have the location of a cell tower, how do you determine your location without the satellites? Answer this question. You CAN say the DATA of the location of the cell tower may be located outside the cell tower, but the actual location data of the cell tower IS STILL relevant to A-GPS. And you have no guarantee that the assistant server the iPhone is using is never on the same premise as a cell tower. And even before you get to the assistent server, you still have to tell it where you are, and that is determined by the last communication of your iphone with the cell tower (well, at least the cell tower you are using so you can look up the location data of cell towers), so again, the cell tower location is relevant to A-GPS.
Lastly, in #42 are you implying the location data can be stored in flash of the iPhone. Or are you implying it is stored on an assistant server in this case? In either case, the cell tower location is stored somewhere either in flash or on the assistant server (as you are implying).
There are three totally separate locating methods in the iPhone, with varying speed and accuracy.
1) Cell id. Fast, but low accuracy of possibly thousands of feet.
Originally referenced an estimated cell location database at Google that was generated by GPS-equipped smartphones using Google Maps before the iPhone even showed up. (Yes, the iPhone owes WinMo users bigtime.) Since 3.2, uses an Apple database instead. Originally used only one cell site for locating ... NO triangulation involved.
2) WiFi. Fast, with accuracy from 30-100 feet in an urban setting.
Originally referenced a MAC id database at Skyhook that was generated by previous public domain projects and later by paid wardriving. Since 3.2, uses an Apple database instead. Can use triangulation to increase accuracy.
3) GPS. Fast once locked, with accuracy from 3-30 feet. Can operate in fully standalone mode, although this can take twelve or more minutes to get a first lock without assistance, as orbits change every few hours due to solar winds, gravity, drag, etc.
On the iPhone, the host can request GPS Assistance in the form of satellite status/orbit info, downloaded from an Apple server that itself apparently simply caches the chipmaker's assistance server information. In such A-GPS requests, the current cell id is often passed as a parameter to also get back a rough position estimate, but neither the parameter nor rough estimate is required.
Repeat: all three methods are separate, and A-GPS does NOT require nor involve (1) or (2). The OS itself can combine the information, which is called using a "hybrid locating system"... but is NOT called "A-GPS".
Google's (and no doubt Apple's) cell id method does NOT use a database of towers with exact GPS coordinates, but rather rough data that they collect from phone users.
Wireless phones can make and receive calls because they are connected over the air to a nearby cell tower. The phone knows the ID of the cell tower that it's currently using. If the phone has GPS, the Maps application on the phone sends the GPS coordinates along with the cell ID to the Google location server. Over millions of such updates, across multiple phones, carriers, and times, the server clusters the GPS updates corresponding to a particular cell ID to find their rough center.
There is no need for exactness, simply because the location method isn't that accurate to begin with. Its purpose is only to get a rough estimate of the area you're in for search purposes... not to guide a car or anything like that.
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I think also people get confused because of other forms of A-GPS.
For example, for the past decade almost every Verizon dumbphone has had A-GPS, mostly for E911 call locating. In their case, the GPS assistance consisted not only of what satellites to listen to, but with calculations due to limited handset CPUs.
When you call 911, Verizon's internal network asks the phone to give it the GPS signals it's picking up, and then uses those (along with local building signal echo cancellation and on-tower GPS signal comparison) to calculate the caller's position. This position ONLY goes to the E911 call center, and not back to the phone.
For commerical LBS apps, the same A-GPS chip is used, but a data connection and other servers are used instead of the internal control network, and the result IS returned to the phone. (This is why Verizon didn't allow any old GPS-based app... the A-GPS could not operate in standalone mode.) The fact that nearly every phone had A-GPS, also allowed Verizon to offer VZNavigator on many phones.
Well, thanks for your input. And it supports what I was saying and what is stated in http://www.edepot.com/iphone.html
Again, that is a PRACTICAL guide, not theoretical. Just follow the instructions on that webpage and you can see what the iPhone ACTUALLY supports. Yes, some people get confused because they are basing it on terms (theoretical) and never actually doing it on the device. Also, you are wrong about the iPhone GPS lock time. Look up the actual timing data on the webpage.
Google's location service approximation (and now Apple) is mostly based on cell tower locations (database lookup of rough estimate cell tower triangulation). The fact that the iPhone uses three types of location service (WPS for wifi, GPS satellites, and cell tower id triangulation) was never in doubt.
I think it's great what you're trying to do on your website. However, incorrect information tends to propagate all over the web, and needs to be avoided. I see that you corrected a lot of the A-GPS info, so let's continue polishing. Here are the biggest items I saw about locating:
All the iPhones and the iPad 3G have assisted GPS (A-GPS).
The first iPhone did not have a GPS chip, which means it could not have A-GPS.
A-GPS allows obtaining your location via reading the multiple GPS geosynchronous satellites signals broadcasted in 1.57542 GHz.
Common mistake. The GPS satellites are not geosynchronous. They orbit the earth twice a day.
The iPhone also supports Cell tower triangulation assisted positioning. All cell tower locations are known precisely,
One point of this whole thread is that the tower locations are NOT known precisely. Nor need they be, since cell id locating is not meant to be precise. Instead (see previous posts) they have simply collected rough estimates of cell sector centers. (There are three sectors per tower.)
Most assisted GPS use data from cell tower locations.
No. See previous posts.
Note that starting with iOS 3.2 and above, Apple uses its own database (Apple bought PlaceBase) rather than depend on Skyhook or Google.
Placebase specialized in aggregating data (schools, business info, etc) to put on maps.
Apple created their own WPS database. When you request a location via GPS, the iPhone scans for nearby WiFi hotspots to add to Apple's database.
Note that the mapping software was switched from Google to Poly9 (bought by Apple) in later iOS firmwares to move more features in-house.
The Maps app still uses Google. Poly9 developed map APIs and 3D globe software.
A lot of the things that are confusing are because of the terms. The webpage was modified by putting a "Location" title at the top because people were confusing WPS as A-GPS, as it was placed below it in another section. But if you think about it, WPS be considered assisting satellite GPS. It is assisting a global positioning system (the satellites), but not actually using the satellites. For example. Does the iPhone "2G" support assisted GPS? You say no. And I put it does not have A-GPS in the top chart. But if you look at the term "assisted", are you saying the original iPhone does not have assisted GPS? From what I understand it can take different Cell Tower locations and get a triangulation without the GPS satellites. So is this considered assisted GPS? If you can confirm one way or another, I would gladly change it to state that the original iPhone does not have any assisted GPS. I think you are sticking with A-GPS, as opposed to "assisted GPS". Perhaps A-GPS was an old technology that only worked one way, and with newer technology via software approximation, you are saying all "assisted" is not "assisted" GPS, because it has to be only hardware A-GPS to be considered assisted GPS.
As for three sectors for tower, what are you trying to get at? Are you saying the the cell towers do not in any way have a location? I think this is getting out of hand. If they don't have a location, you can't get a location. If you are implying that the location is never precise because they purposely only take three "sectors" and use that to approximate the center, then that means you are probably talking "more than one" cell tower id in the process. If you are stating only "one cell tower id", and that location is always based on three other locations (not three other cell tower id, but three "sectors" related to the current cell tower id), then you have some explaining to do because what you are implying is that the cell tower purposely puts three "sectors" near it just so it can have a location. I hope you know what I am asking here. If the three sectors are actually other cell tower ID, then well, we are back to square one. Perhaps the terms you are using needs to be clarified.
I did change the geosynchronous to semisynchronous though. As for the rest of the entires, you are getting too picky. You have no guarantee that Apple won't move everything in house because of the purchases. Looking long term I think that is their strategy, and how one purchase won't ever have an effect on certain features is not that precise.
A lot of the things that are confusing are because of the terms.
True, so let's start with the definition of "GPS". It does not mean just any locating method. For example, if a camper found himself using the stars and a compass, is that "GPS"? No. Likewise, WiFi and Cell Id are not "GPS" methods. They are called other types of "locating" methods.
If a locating method contains the word "GPS", it absolutely means that we are using a GPS chip in the device itself and it absolutely means using GPS satellites.
But if you think about it, WPS be considered assisting satellite GPS. It is assisting a global positioning system (the satellites), but not actually using the satellites.
WPS is neither assisting the GPS nor the Cell Id for that matter. Each method is separately assisting in an overall app requirement to locate the phone. Think of it as three separate people holding up their result on cards to see, and the app chooses which one it needs by speed and accuracy.
When a device uses a combination of WPS, Cell Id and GPS, that is called a "hybrid" system. It is not called A-GPS, just as it is not called A-WPS or A-CID.
Interestingly, Skyhook sells a hybrid system they call "X-GPS", in which they do merge all the results to come up with a more accurate location.
But if you look at the term "assisted", are you saying the original iPhone does not have assisted GPS? From what I understand it can take different Cell Tower locations and get a triangulation without the GPS satellites. So is this considered assisted GPS?
No sir. See above. Assisted GPS requires a GPS chip and the use of satellites. Always!
Again, "A-GPS" or "assisted GPS" are not generic terms.
Kevin - senior device engineer with 30 years' experience
As for three sectors for tower, what are you trying to get at? Are you saying the the cell towers do not in any way have a location?
Actually, often towers don't for Cell Id. Their sectors do. Here, I'll explain again how Cell Id databases are generated:
First, you must understand that almost all cells have three sectors. In the picture below, you can see Sectors 1,2,3.
The red dots I put in represent where people with GPS-equipped phones were connected to sector 1. That information is what goes into the database. Over time, you can use many such entries to determine the rough center of that sector.
Let's say the star represents where you are with a non-GPS phone, wondering what your location is. Your phone sees that you are in sector 1, and sends that info as part of a request to Apple's Cell Id database, which then sends back the estimated center of that sector. Note that you even know which side of the tower you're on, which is far better than just using the tower center.
3 ways to Apple user locate you:
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.
3 ways to Apple user locate you:
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.
It's the opposite sequence. It goes from least accurate to most. That's why you often see a large circle on the map first, then it gets smaller down to a pinpoint.
Cell Id is nearly instantaneous.
WiFi is a bit slower, as it uses triangulation.
GPS is fast if already locked in, otherwise it's the slowest.
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Originally Posted by edepot
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