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Businesses and just plain folks enjoy the convenience that cell phones, PDAs, Amazon Kindles, BlackBerries, and small laptop computers offer.
 
  
 
 
 
 
 
 
 
 
 
PDAs

Bluetooth, Wi-Fi HotSpots, and growing cellular coverage mean that we don't need to be tethered by cables.







Do you have a smartphone and need a reliable Exchange server so that you can synchronize email, contacts, tasks, and calendar?
 
 

Make money with iPhone apps


Inside a cell phone
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 photos: Ray go 
  

 

 

How do cellular phone networks work?

 

The key idea behind cellular networks is the reuse of frequencies, which allows many simultaneous users over a wide area. In traditional mobile radiotelephone systems, powerful base station transmitters covered many square miles. This precluded use of each frequency within the large coverage area. In a cellular system, relatively low-power base transmitters cover much smaller areas, or cells.

 

As a user moves from cell A to cell B, he's "handed off" to cell B, which is operating on a different frequency. Not only the frequency, but the output power of each user's transmitter is controlled by the base station; this minimizes spillover of user signal into other cells and conserves the user's battery power.

Illustration: Andrew pmk

This image shows an example of frequency reuse in cellular networks (in this case 4 frequencies are used). The image is an idealized representation with perfectly hexagonal cells. Eight separate cells are shown packed one next to the other. The first cell on the top left uses frequency 1. The cells which are next to it then use frequency 2 and 3. Beyond those cells, another cell again uses frequency 1. This pattern with the same frequency never being reused by direct neighbors repeats across the diagram. The frequency reuse pattern shown is a typical example for a digital cellular system (i.e. GSM). For earlier analog systems a higher reuse pattern (7 or greater) is more usual.