Cellular Phones

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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