CELL PHONESIt’s not magic, but it’s like magic

CELL PHONES ARE BASICALLY…

RADIOS… CBs Walkie talkies

“Half Duplex” system

Both transmitters use the same frequency

Only one person can talk at a time

Range dependant on transmitter wattage

• A cell phone is a full-duplex device. That means that you use one frequency for talking and a second, separate frequency for listening. Both people on the call can talk at once.

A CONVERGENCE OF TECHNOLOGIES The power

consumption of the cell phone is relatively low

Low power means small batteries,

Small batteries made handheld cellular phones possible

MOBILE PHONES IN THE 80S Installed in cars

Radio Required Powerful

Transmitters (big black box in the car)

Could transmit 40 to 50 miles

One Central Antenna per city

About 25 Channels

NOW, IT’S ABOUT SIGNAL TRANSFERENCE

Cell phones operate within cells, and they can switch cells as they move around.

Cells give cell phones incredible range. Someone using a cell phone can drive hundreds of miles and maintain a conversation the entire time because of the cellular approach.

PHONE HOME AND THE CARRIER All cell phones have special

codes called SID (system identification) programmed into the onboard SIM chip When you first power up

the phone, it listens for a SID on the control channel.

When the SID is received, the phone compares it to the SID on the SIM – if the SIDs match, the phone knows that the cell is communicating on the home system

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.

A SID is a unique, 5-digit identifier assigned by the FCC to each carrier

IF NOT COMMUNICATING WITH THE HOME SYSTEM...

MOBILE TELEPHONE SWITCHING OFFICE (MTSO) Along with the SID,

the phone also transmits a registration request, and the MTSO in range keeps track of your phone's location in a database

In this way, the MTSO knows which cell you are in when it wants to ring your phone.

INCOMING CALL The MTSO gets

the call, and it tries to find you. Searches its

database to determine 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 which frequencies to use, and once your phone and the tower activate those frequencies, the call is connected and talking by two-way radio.

ON THE MOVE As you move toward

the edge of your cell, your cell's base station notes that your signal strength is diminishing.

The base station in the cell you are moving toward (which is listening and measuring signal strength on all channels) sees your phone's signal strength increasing

Control of the signal passes to the next cell

Sprint Coverage Cell Map

EVOLUTION Analog cellular systems

are considered first-generation mobile technology, or 1G.

Digital cellular systems are considered 2G

3G is the current technology built for smartphones carries a much more

complex signal carrying layers of data, voice and multi-media