How Frequencies Transmit Data

That's the basic story of what frequencies are, but how does the data get from your PC to the frequency and from there to its destination? To begin with, the data is a series of electrical impulses at certain intervals, usually represented with 1s (impulse) and 0s (no impulse) in this instance, let's say mat it's an e-mail message. When you click the Send button (or equivalent thereof), you send the collection of 1s and 0s that make up your e-mail message and addressing information to a transmitter. Depending on what kind of transmitter it is, the transmitter converts the 1s and 0s to a related pattern of electrical signals that can be sent on a particular frequency band. For example, if your PC is equipped with a radio-frequency (RF) transmitter, then it will send the signals via either the HF or VHP bands. A reciever of the same type in the area can then pick up on the signal that you transmitted if it's tuned to the same frequency.

That's the easy part. The complex part comes when you try to limit the number of receivers or when you've got a number of devices that want to use the same bandwidth.

You now know in general terms what frequency is, and how bands with different frequencies respond to environmental conditions and carry data. You might be wondering how, since there are a finite number of bands, wireless services can expect to expand. For that matter, how have they expanded as far as they have without using up all the available bandwidth?

This question is crucial to wireless networking. Like any other resource, radio frequencies are limited but the uses for them are not. When wireless transmissions were only for television signals and CB radios, this was less of a concern. Today, though, wireless communications are increasingly important to many business applications. Where will the bandwidth needed to sustain growth in these services come from?

Part of the answer stems from me fact that RF signals don't extend forever. A particular frequency can be in use in more man one place as a time, as long as the usages are separated enough not to interfere with each other. For example, you can use the frequency 33MHz in Melbourne and Seattle at the same time, attenuation would prevent signals that originate at points so far apart from interfering with each other. By the time the Seattle signal gets to Australia, it is so weak as to be practically nonexistent.

The fact that you can use a frequency in more than one place at a time naturally has led to the creation of frequency "cells" that electrically isolate geographic areas from each other. These cells are hexagonal in shape and have a transmitter located at their center to handle transmissions. The closer a subscriber is to the transmitter, the stronger the signal is, but it won't cut off until the subscriber moves to a different cell. Electronic barriers between the cells keep me signals from extending beyond their cell. Adjoining cells can't use the same frequencies at the same time in cellular communications, they must be separated by at least six cells but the cells allow some level of frequency reuse. The smaller the cells are, the greater the possible frequency reuse.

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