1.0 Introduction to Cellular Communications
Mobile Communications Principles
Each mobile uses a separate, temporary radio channel to talk to the cell site. The cell site talks to many mobiles at once, using one channel per mobile. Channels use a pair of frequencies for communication one frequency (the forward link) for transmitting from the cell site and one frequency (the reverse link) for the cell site to receive calls from the users. Radio energy dissipates over distance, so mobiles must stay near the base station to maintain communications. The basic structure of mobile networks includes telephone systems and radio services. Where mobile radio service operates in a closed network and has no access to the telephone system, mobile telephone service allows interconnection to the telephone network.
Cell phones, also known as mobile phones or wireless phones, are hand-held phones with built-in antennas. Unlike home phones, cell phones can be carried from place to place with a minimum of fuss. This makes them a good choice for people who want to be in touch with other people even when they are away from the house.
How Do Cell Phones Work?
Not many people know it, but cell phones are actually two-way radios, much like the walkie-talkies of the past, albeit much more advanced. When you talk into your cell phone receiver, it registers your voice and converts the sound into radio waves. These waves travel through the air until they reach a receiver, which is usually found at a base station. This station will then send your call through a telephone network until it contacts the person you wish to speak with. Similarly, when someone places a call to your cell phone, the signal travels through the telephone network until it reaches a station near you. The station sends the radio waves out into the neighboring areas. These radio waves are then picked up by your cell phone and converted into the sound of a human voice.
Cell phones are a vast improvement over the telecommunications technology of the past, and are daily becoming a fixture of modern life. As always, communication is vital, and cell phones will help you to better communicate with the key people in your life. Using a cell phone is one of the first steps you must take to participate effectively in the emerging global economy.
Early Mobile Telephone System Architecture
Traditional mobile service was structured in a fashion similar to television broadcasting: One very powerful transmitter located at the highest spot in an area would broadcast in a radius of up to 50 kilometres. The cellular concept structured the mobile telephone network in a different way. Instead of using one powerful transmitter, many low-power transmitters were placed throughout a coverage area. For example, by dividing a metropolitan region into one hundred different areas (cells) with low-power transmitters using 12 conversations (channels) each, the system capacity theoretically could be increased from 12 conversations or voice channels using one powerful transmitter to 1,200 conversations (channels) using one hundred low-power transmitters. Figure 2 shows a metropolitan area configured as a traditional mobile telephone network with one high-power transmitter.
2.0 Mobile Telephone System Using the Cellular Concept
Interference problems caused by mobile units using the same channel in adjacent areas proved that all channels could not be reused in every cell. Areas had to be skipped before the same channel could be reused. Even though this affected the efficiency of the original concept, frequency reuse was still a viable solution to the problems of mobile telephony systems.
Engineers discovered that the interference effects were not due to the distance between areas, but to the ratio of the distance between areas to the transmitter power (radius) of the areas. By reducing the radius of an area by 50 per cent, service providers could increase the number of potential...
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