This was prompted by a text message from AT&T saying that they would no longer support my 2G phone in 2017. Here are some of the issues I’d like to understand.
I understand the concept of cells and switching cells as I move about, but where is the nitty-gritty of their logic. I remember how the old “1G” analog system worked with only two providers, each having their own 20(?) mHz band witdth.
When I get a 3G phone, will it work if I happen to go somewhere where the cell towers are 2G only?
As I understand it, there are really only four providers in the USA (Sprint/Verizon/AT&T/T-Mobile). Do they each have their own cell towers? Do they each have their own assigned frequencies? Do CDMA and GSM share the same frequencies?
If I’m a Verizon user, does my phone automatically switch to a Sprint tower if I become out of range of a Verizon tower?
I live in Atlanta. When I step off a plane in NYC at the same time my wife steps off a plane in Chicago, how does the network know where we are? Does every cell tower know the location of every cell phone? My hunch is that every cell phone has a “home office” (as I call it), Depending on the first few (6?) digits of my phone number. My phone tells my home office where I am. When my wife tries to call me, her phone checks with my home office in Atlanta to see what cell tower has control of my phone.
How often do cell phones broadcast “here I am” to the local cell tower. I would think that each cell tower is monitoring thousands of cell phones at any time. How do they keep track of it if two phones start talking at the same time. Yes, I realize that each message may only be a few microseconds long, but with all that chatter, surely there must be some overtalk.
Do 2G/3G/4G use different frequencies? Is their band width different (e.g. 2mHz v 3mHz wide) or are the all the same width but a different method of transmission?
The answers to these questions can get very complicated very quickly. I’ll try to keep things relatively simple, but if you want to get into detail, I suggest these links:
[ul]
[li]Cell antenna ownership[/li][li]Frequency division multiple access[/li][li]MIMO - multiple input, multiple output[/li][li]Cell network[/li][li]Cell traffic[/li][/ul]
For reference: I’m not an expert, but I used to work in a start-up that made mobile devices, and I wrote some of the technical documentation for internal and external users.
All 3G phones can “downgrade” to a 2G signal. Most will indicate that they’ve done so by showing a different connectivity symbol on the screen.
Each provider builds their own towers for their own network. This can get prohibitively expensive, so they make agreements with the other providers to share some of the towers. Depending on the nature of the agreement, the tower will count as “in-network” or “out-of-network,” which just means you might get charged roaming fees if your phone sends or receives calls while connected to that tower.
Yes. The largest difference between the two is how the phone is built to work with the network, and how the cell tower communicates with the phone. There’s little cross-talk because of a technology called MIMO (multiple input, multiple output).
As stated previously, probably. If Verizon has negotiated a deal with Sprint about that particular tower, then yes. Depending on the deal, your cell phone will be considered either in-network or roaming.
Close. In actuality, the cell tower is just a relay point. Your phone sends out a ping every once in a while to find a tower. That tower then relays that ping to a central switching center, which keeps track of where your phone is.
When a call comes in, it goes to one of the central switching centers and looks up the nearest tower to your phone.
Depends on the manufacturer of the phone, the network it’s on, and what you do with it. Most of the networks just require a ping when the cell phone turns on or attempts to do something on the network (make a call, check email, etc). If the phone hasn’t sent out or received a signal in a while, the central switching center might send out a ping to verify the phone is still turned on and where they last thought it was. This can vary depending on network load, but probably not more than once every half hour.
This is where the MIMO technology comes in. Basically (and this is oversimplifying), when a call is connected, that connecting frequency is reserved for just that call. So there’s no overtalk because there’s a huge difference between, say, 813.25 MHz and 813.27 MHz. Commercial radio stations are a good example of this: there isn’t much overlap between various FM stations, either.
This is only reserved for that tower, though. So there’s a lot of things happening in the background if you’re in transit and moving between towers (or several towers). And there are probably two or more towers covering any given location in an urban setting.
And that’s just for phone calls. If you’re talking about SMS text messages or web services, those include headers (kind of like email messages) that include routing information: which phone to send the message to, which phone it’s from, date, etc. So the tower doesn’t have to know any of that; it just has to be able to receive and send it to the central switching station for processing.
For instance, a 2G phone/network can only do voice calls and some text messaging. A 3G phone can do a whole lot more: connect to wi-fi, send/receive email, but speeds are limited. A 4G phone/network can transmit and receive at faster speeds, making video streaming a real option.
Hope all that helped, and that I didn’t get anything wrong by oversimplifying too much. Where my links and I differ, believe the text in the links.
Related question: I have a 4G phone with Straight Talk. It’s a GSM phone, running on AT&T’s LTE network. I get 5 Gb of high speed data per month. Over that cap, I get throttled to 2G speed. What is likely to happen in 2017 when 2G service ends? Would I get bumped down from 4G to 3G?
Yes. The phone company expects the phone to work on the 2G protocols AND frequencies. But the company is also saying they are turning off most if not all the 2g towers all at once aren’t they ?
The phone company wants to turn of 2G because it can use the frequency better, or sell them, rather than having the frequency assigned to 2g voice, for the dwindling population of 2g only phones.
So its a bit of a tick tock system… The new protocol goes on a new frequency, the old protocol is turned off and its old frequency is available for some other use…
Most likely, yes. Anything over the cap will probably go to 3G.
Phone service is repeating the history of internet connectivity. 2G speeds are approximately 28.8Kbps, or about the speed of a bog-standard modem back in the early 90’s. 3G speeds are a little better: about 144Kbps, comparable to some hardware compression techniques some “high-speed” dial-up modems were using in the late 90’s.
4G averages about 5Mbps, or roughly 35 times the speed as 3G, and ~170 times the speed of 2G. And that’s still about half the speed of what most techies recognize as “broadband” (though broadband in the 90’s was maybe half that).
Basically, think of it this way: your service provider doesn’t want you to use broadband the entire time, so they ask you to use your dial-up modem after a certain limit (or at peak times). What kind of dial-up doesn’t matter; either one takes the stress off the network. And users aren’t likely to care; compared to 5Mbps, either 28Kbps or 144Kbps is going to be painfully slow.
Pretty soon now™, we’ll be seeing 5G networks. Those have been clocked at about 3.6Gbps. As soon as the network can regularly handle that kind of traffic, they’ll phase out 3G, and 4G will be considered “slow.”
That’ll work for me. My 3G phone was plenty fast for me, good enough to play YouTube videos without buffering. Still better than 2G, which is worse than dial-up.
Part of the problem is that marketing has completely mucked around with technical terms and confused them all up.
EDGE is considered part of 2G. back when it first came out it was touted as being as fast as ISDN, so 128K or so.
3G includes HSPA. It also includes HSPA+, which T-Mobile called “4G” because it was as fast or faster than competitor’s LTE networks at the time. I recall seeing statements that some hardware iterations of HSPA+ could hit a theoretical 600Meg, but nobody every actually deployed that–but 5Meg? Sure.
4G LTE can currently hit 40Meg on speedtests.
Of course, what you get in a speedtest and what you actually see downlading things from the internet will vary greatly.
I’ve not really looked into 5G much, from what I do know it sounds like it’s less about raw speed increases and more about better utilization of the spectrum–getting more devices per frequency and whatnot–which still ends up as a benefit to the user, but possibly not as technically obvious.
And it is increasingly unlikely that “downgrades” of your connection is done via an actual technology change–that can all be done in software by the provider simply limiting your bandwidth.
This isn’t oversimplified, it’s just obsolete. The ancient analog AMPS standard (fully shut down in the US by early 2008) did work that way. Anything in use today (GSM, CDMA2000, LTE, etc.) uses techniques such as TDMA or CDMA to enable multiple handsets to use the same frequency channel at the same time. TDMA (“Time Division Multiple Access”), for example, splits the channel into time slices - e.g. device A is allowed to transmit for, say, 20 milliseconds on the second, device B is allowed to transmit at 30 milliseconds after the second, device C is allowed to transmit at 60 milliseconds after the second, etc.
MIMO is none of these things. It’s a technique for expanding the capacity of a radio link by making use of multipath propagation (instead of ignoring it). TDMA and CDMA protocols can and have implemented the sharing of frequencies without using any MIMO.
I’m not positive, but I strongly suspect that the throttling applied when a customer exceeds a data cap does not mean (as posters here have implied) the device actually gets switched to an older-generation radio protocol (e.g. 4G LTE to 2G EDGE), but rather implemented by software rate-limiting (either by the IP network throttling the channel, or the tower assigning less bandwidth to the device). Actually switching radio protocols would solve only one of the carrier’s problems (tower-to-internet-backbone bandwidth usage) without fixing the other (handset-to-tower radio link time use) because the handset would end up using just as much radio time by virtue of speaking more slowly.
Again I suspect (but don’t have proof offhand) that the radio time use is the bigger concern. Internet backbone connectivity is relatively cheap and easy to expand; building more towers (if the carrier even can, within the limits of their license and the nature of the radio protocol) is expensive.
Thus, users could still be throttled to “2G” speeds long after physical 2G equipment is gone.
My 3G can do 14 megabits per second on a good day and 4G 65.
Every company has its own network, and you can generally not use another company’s network. (There are exceptions to this.) Each company owns their own frequencies, which aren’t cheap.
There’s very many frequencies and most of them can be used for different stuff: GSM 2G, CDMA 2G, UTMS 3G, CDMA 3G or LTE 4G. The logical progression is GSM -> UMTS -> LTE. The CDMA folks switched to the more standard LTE for 4G, too.
With some GSM the frequencies get reused by towers in a way that they don’t overlap too much, with CDMA, UMTS and LTE all the towers use the same frequencies and they do actually overlap.
When you turn on your cell phone it will start searching for the network run by the company that you’ve signed up with and when it finds the network it connects to it. The phone periodically (every few hours or so) informs the network that it’s still alive. Towers are grouped together in areas. When you have an incoming call, all the towers in the area where you are present will send a signal so your phone can ring. When you leave the area your phone needs to talk to the network to update its location. These areas used to be quite large (more than one medium-sized city) but they’ve shrunk over time as networks got busier.
