Presentation Transcript
Cellular Phones : Cellular Phones SIT Conference 2005
Heartland Community College
Items of Interest: Items of Interest How Do Cell Phones Work
Why Is It Called Cellular
Cell Phone Identity Systems
Digital Verse Analog Cell Phones What Happens When Your Cell Phone Places A Call
How Does Roaming Work
How A Telephone System Works
How Cell Phones Work: How Cell Phones Work A cell phone is a radio like a walkie-talkie
Walkie Talkie is simplex
Only 40 channels to choose from
5 Watts can go about 4 miles
Cell phone is Duplex
There are around 1664 channels
Has few milliWatts only limited range
Block Diagram of Cell Phone: Block Diagram of Cell Phone From Texas Instruments Web Site
http://focus.ti.com/vf/docs/blockdiagram.tsp?family=vf&blockDiagramId=2007
Why is it called Cellular?: Why is it called Cellular? An antenna tower handles calls from a short distance from it (Base Station)
More antenna towers means more users can talk on cell phones
Lower power the cell phone emits
Repeat the frequencies used
The antennas form small cells of coverage around the city
Cell Sites Around A City: Cell Sites Around A City
Cell Phone Identity Systems: Cell Phone Identity Systems Every cell phone has 2 unique identifications
MIN – Mobile Identification Number
A 10 digit telephone number
309-555-1212
ESN – Electronic Serial Number
32 bit binary number
Built into the cell phone
Slide8: Inside of a Phone A Cell Tower
Digital Verse Analog Systems: Digital Verse Analog Systems Older cell phones were analog
Analog – AMPS, NMT
Digital – GSM, PCS, CDMA
The difference is between how your voice is transmitted between the phone and base station
Cassette tape as analog
CDs as Digital
What Happens When Your Cell Phone Places a Call: What Happens When Your Cell Phone Places a Call Enter Phone #
Scan Control Channels – finds closest base (determines which control signal is strongest)
Sends Signal ¼ second
MIN and ESN
Number you want to call
Base sends a Channel Assignment
What frequency pair conversation will be on
Connection
The person you are calling is connected
How Does Roaming Work: How Does Roaming Work Phone is on sends data message to cell site (MIN and ESN)
Computer switches at phone company compare MIN of your phone to all of their customers MIN
If you are a customer it gives you HLR (Home Location Register)
If your are from another system, telephone system sends messages that you are on the system and creates a VLR (Visitor Location Register)
How a Telephone System Works: How a Telephone System Works http://electronics.howstuffworks.com/telephone-image.htm