Cell Phones!

1. Cell Phones! SL – Option C.4 HL – Option F.6

2. Mobile Phones • The mobile phone is truly a combination of two types of technology • Radio • Telephone • Both technologies have been around for a long time (1880’s) • Progress has made modern cell phones possible

3. Land Lines • Even though the land line system has grown significantly more complex, the principles behind it are the same • When you make a call, a series of electronic switches and a lot of wiring connects you to the other persons phone • The complete system is called the public switched telephone network (PSTN)

4. Radio Communication • Instead of using current in a wire, radio uses low frequency EM waves to transmit signals • This has been around for a long time • Each city has a radio antenna and 25 different frequency channels • This meant that only 25 different people could use the system at a time and they needed to be near the antenna

5. Progress

6. Cell Phones • Our modern cell phones use radio transmission in the same way as the older radio phones but operate using cells. • These cells range from 2km-20km in diameter and at the center of each is a low power transmitter and receiver • The frequencies of neighboring cells is different (<1GHz) to avoid interference • Because they are low power the physical dimensions can be much smaller

7. Cell Phones • Each cell overlaps its neighbors and each cell is connected to the cellular telephone exchange • This acts as the switches directing calls to other phones and areas • It is also connected to the PSTN so that cell phones can call land lines

8. Cell Phones • As users move from one cell to another, the CTE switches the signal to the next receiver with a stronger signal • The signal frequency also switches when this happens • There are 400 possible frequencies (channels) available • To avoid overlap, the 7 closest split these channels up (56 per cell)

9. Making a Call • When you turn on your cell it sends out a signal (not one of the 400 conversation bands) • All the antennas in range receive the signal but only the one that gets the strongest signal responds • The antenna response is also dependant upon your network

10. Implications of the Cell Phone

11. Tracking • You can be tracked with your cell phone • Signal strength is based on distance from a cell tower so using triangulation your exact position can be found • This is why you destroy your cell phone if you are being hunted by the government • Can still send a signal if it is off.

12. Digital Communication • Much easier to communicate while on the move • Downfall of the payphone • Cheaper and easier to send pictures, videos, photos, etc.

13. What about. . . • Etiquette – are you always happy people have cell phones? • Social alienation – why talk when you can text? • Health – CANCER!!!!! AAAAHHHHH! • Also texting/talking and driving • Environmental Impact – Antennas for everyone, everywhere