If a wireless phone tower only covers a few square miles, how is it, I can travel for miles and never drop my call with the person I am talking to?
The first thing I will need to explain to you are some basic wireless terms that will be used in this article.
1) BTS: Stands for Base Station Controller. It is a fancy name for a cell site
2) BSC: Base Station Controller. Controls all messaging back and forth to the BTS
3) MSC: Mobile Station Controller. This is the main switching computer that controls the BSC and all call traffic
4) CDMA/GSM or UMTS: These are different Digital Technologies used by wireless carriers
Now let’s start talking a little about how this all works.
First you will need to set up a call on your wireless phone. Once you are on that particular call you begin driving down the road. There is a slight difference in this process between GSM and CDMA. I will attempt to point them out as we go through this. As you are on the phone, your signal is constantly being monitored and evaluated, also each BTS on the BSC has a database that lists all the corresponding sites around it that a customer could possibly drive into the area of.
The next step there is a difference in how it works:
CDMA / UMTS: In CDMA and UMTS, your call is actually being processed but all the surrounding sites at the same time. The BSC monitors the signal quality on the call and as you drive, the levels will get better on one site over another and the BSC just process the call on the best quality site. As you drive on, your noise level changes, and the BSC will just process the call from the new site. This is called Soft Hand Off’s. As you drive on, this process is just repeated over and over with the sites going down the road based on the BSC database listing of the surrounding sites.
GSM: In GSM it works a little different. The calls are not actually processed over multiple sites at one time, because the phone in GSM is forced to retune to a different Freq every time you move from one site to another. So how it works, is it just monitors your signal level on all surrounding sites based on the BSC database. Then once your signal level is stronger on one of the neighbor sites than the one you currently are on, the phone receives a message from the BSC telling it to retune to the channel of the neighbor site and the phone retunes and the call hands off.
Because of these differences, if you listen closely, you may hear a small click or a word of audio may be muted because of the retuning of the phone. In CDMA, all sites actually operate on the same frequency and it performs a Soft Hand Off, so it is seamless to the customer and device.
The signal levels that these processes us to compare and performed at are also set by the carrier in their BSC database.
The number one reason for a consumer to drop their call is usually a neighbor cell site is not loaded properly in the BSC as a hand off candidate or that possibly the signal levels that are set in the database may need to be adjusted slightly. This process is not an exact art for all situations so drop calls will happen that cannot be explained.
Now let me explain quickly how this whole process works when you drive on a road where one area is on one wireless carrier system and the other area is on someone else’s wireless system. Because this requires two different carriers to be involved, many times your calls will just drop because the two carriers have not gone into an agreement among themselves, most of the times this is due to costs associated in putting the process in place.
If both carriers decide they want to put this in place, it is very similar to what already happens above. The difference is, that the BSC database also has to have information on the neighbor BTS’s. However, when it needs to get info of the neighbor’s site it has to communicate over a link that is put in place connecting the two companies. If the call actually reaches levels that it hands off the call, the neighbor has to take the audio for that call also and that requires some sophisticated signaling and trunking to be in place. Also due to the time it takes for all this messaging to take place between carriers, it is not uncommon for the calls to drop if the areas terrain is hilly or the customer drives too quickly through. The costs associated with this, is the main reason carriers do not put this in place. You will usually only see this in place if the area in question is on a major interstate or where there is enough traffic to justify not dropping the calls.
I hope this all made sense to you and if not feel free to drop me a note or comment and I will try to answer your questions for you.
First let me start off by saying that I do not write these articles about the Wireless Phone Business to defend the carriers and the way they operate. I would be the first to tell you that from my experience in the industry for many years running one of them, that it is a business like everything else an it’s all about maximizing rate of return on investment when it comes to customers and charges.
I get asked a lot from people when they learn who I am, as to why when they switch from one carrier to another they usually have to purchase a new phone? This is actually a very simple answer but I will need to explain in more detail how a phone or data device works for you to understand.
First thing you have to understand that until everyone goes to LTE technology, that there are basically two types of Digital systems made in the wireless industry.
1) The first is CDMA which is the technology used by such carriers such as Verizon and Sprint
2) The second is GSM/UMTS which is the technology used by Carriers such as AT&T and T-Mobile
The first reason you can’t move your phone is probably the most obvious to people, that is that if you are moving from one digital technology to another, the phone will not be designed to work on the other carriers technology.
The second reason is actually the most complicated to explain but I will try and list it all for you. This would be the case if you were moving from a CDMA carrier to a CDMA carrier or the same for GSM/UMTS Carriers.
It all comes down to the programming of the phone itself. There are so many parameters that go into the programming of a cellular phone to make it work the way customers are accustomed to. This includes things such as to how to do run applications like SMS, MMS, and WAP. Each one of the applications in the phone requires certain programming to match the carrier’s equipment. This includes things such as DNS server IP addresses, how often the phone scans for a stronger signal, the max size of a picture to be sent via MMS, and things along that line. These are all settings that are installed in the phone in what is called a PRI file.
Many of you may have heard of a PRL file, which is where the phone gets its roaming list from as to who the phone can roam on and who it cannot. But actually the more important file is called a PRI and that is what tells the phone how to operate in general. This has become even more complicated of a file since the introduction of data aps and the internet.
You will see all over the internet in forums about people unlocking or hacking a phone. 90% of the time this is just enough to allow you to change the phone number or the data address of the device, most of the time doesn’t unlock it enough to allow someone to change the entire PRI. Unlocking a phone usually just allows someone to use a tool called QPST or CDMA Toll that can go into the phone and change particular parameters that will allow you to make phone calls or surf but doesn’t actually allow you to change fields used for MMS and WAP and certain other applications.
To truly change the PRI for a particular vendor phone you have to have flashing software and tools. Almost every manufacturer of mobile devices has their own version of the QPST for doing that. To get that software you usually have to be a seller of that manufacturer or a carrier before it is totally shared with you.
As you can imagine a carrier is not going to have this software available at all sales stores you may go into to sign up for service. A company may only have 1 or 2 copies of this software and that is just for testing in there lab the different models of phones and how they operate in different scenarios.
Also not all phones are alike, some of the major carriers will actually put each phone model through extensive testing on their network to make sure it meets certain criteria. There are some models of phones that may drop more calls than others because of the way the antenna is built into the device. They won’t allow these models on their network because it just opens up the opportunity for customers to start calling and complaining about the service, when it’s actually the device they are using not the service. This is very expensive for most carriers to perform so you will find only the major carriers will have test labs..
Even with the emergence of LTE and the fact that all carriers will eventually go to LTE, This technology doesn’t support voice calls as the average consumer thinks of it. Voice calls will actually be made over a data application and in order to perform these functions there are even more detailed requirements that must be put into each phone based on the home carriers system. LTE does solve the problem of different digital technologies on different carriers but the other issues will still prevail.
So as you can see there are some technical reasons why a carrier will not let you bring a phone from one carrier to another carrier. It’s more about the phone itself and the programming of it than it is about the carrier wanting to sell you something new. I agree, it’s very frustrating as a customer to have to purchase a new phone if you are changing carriers. Again, you can hack them and unlock them to allow you to do the basics, but you still can’t expect a carrier to do that for you due to time and effort. Even the IPHONE when it is hacked into the only real data most people can get is via Wi-Fi and not 3G.