Let's say you have a cell phone, you turned it on, and someone tries to call you.
Here is what happens to the call:
When you first power up the phone, it listens for an SID (see sidebar) on the control channel. The control channel is a special frequency that the phone and base station use to talk to one another about things like call set-up and channel-changing. If the phone cannot find any control channels to listen to, it knows it is out of range, and displays a "no service" message.
When it receives the SID, the phone compares it to the SID programmed into the phone. If the SIDs match, the phone knows that the cell it is communicating with is part of its home system.
Along with the SID, the phone also transmits a registration request, and the MTSO keeps track of your phone's location in a database -- this way, the MTSO knows which cell you are in when it wants to ring your phone.
The MTSO gets the call, and it tries to find you. It looks in its database to see which cell you are in.
The MTSO picks a frequency pair that your phone will use in that cell to take the call.
The MTSO communicates with your phone over the control channel to tell it what frequencies to use, and once your phone and the tower switch on those frequencies, the call is connected. You are talking by two-way radio to a friend!
As you move toward the edge of your cell, your cell's base station will note that your signal strength is diminishing. Meanwhile, the base station in the cell you are moving toward (which is listening and measuring signal strength on all frequencies, not just its own one-seventh) will be able to see your phone's signal strength increasing. The two base stations coordinate themselves through the MTSO, and at some point, your phone gets a signal on a control channel telling it to change frequencies. This hand off switches your phone to the new cell.
Cool Facts
Most newer digital cellular phones have some sort of entertainment programs on them, ranging from simple dice-throwing games to memory and logic puzzles.
Approximately 20 percent of American teens (more girls than boys) own a cellular phone.
Cellular phones are more popular in European countries than they are in the United States - with nearly 2/3 of Europeans owning a phone, compared to only about � of Americans.
The GSM standard for digital cell phones was established in Europe in the mid-1980's - long before digital cellular phones became commonplace in American culture.
The technology is now possible to locate a person using a cellular phone down to a range of a few meters, anywhere on the globe.
3G (third generation wireless) phones may look more like PDAs, with features such as video-conferencing, advanced personal calendar functions, and multi-player gaming.
Why is a cell phone called a cell phone?
One of the most interesting things about a cell phone is that it is really a radio. Before cell phones, people who needed mobile communications ability installed radio telephones in their cars. In the radio telephone system, there was one central antenna tower per city, and perhaps 25 channels available on that tower. The cellular phone system divides the area of a city into small cells. This allows extensive frequency reuse across a city, so that millions of people can use cell phones simultaneously.
Cell Phones
