Cisco Phone System

Why do cellular telephone systems need only seven sets of frequencies in a metropolitan area?

Public Comments

1. Okay... now I understand your question... your not talking about frequencies your talking about clusters and the common 7 cluster of channels that is used... well.. the answer is that the hexagon shape fits pretty well... however a 4 or 12 cluster system is also possible...
2. Frequency reuse, time division, and code division. I like CDMA the best. Many phones transmit and receive power at the same frequencies at the same time. Each phone receives ALL of the energy in a given band, selects only the channel it wants with a SAW filter, and separates what it wants to hear from all others with a software decoding process. Analogy: 1) One hundred people speak at once in one hundred different languages. All speak at roughly the same frequency (about 10 to 3000 Hz for humans) and all of the sounds get to your ears at about the same volume. 2) You close some doors and windows (filter) and most of the voices get quiter. Now thirty voices are audible at your ears. 3) You understand English, but not the other thirty languages. It is difficult but if you concentrate, your baseband processor (brain) is capable of picking up the English language words (corect code) against the noises like German, French and Swahili (incorrect codes). 4) The person you are listening to understands the noise problem, so they add some redundant information (forward error correction). It is like talking at a friend at a rock concert.