cellular communications

Topics: Mobile phone, Cellular network, GSM Pages: 10 (2742 words) Published: December 4, 2013


D. Jyothsna
Jyothsna_magical@yahoo.co.in G. Anusha


A cellular mobile communications system uses a large number of low-power wireless transmitters to create cells—the basic geographic service area of a wireless communications system. Variable power levels allow cells to be sized according to the subscriber density and demand within a particular region. As mobile users travel from cell to cell, their conversations are handed off between cells to maintain seamless service. Channels (frequencies) used in one cell can be reused in another cell some distance away. Cells can be added to accommodate growth, creating new cells in unserved areas or overlaying cells in existing areas. Now we are going to discuss about -

1.Mobile communication principles

2.Mobile telephone system using the
cellular concept

3.Cellular system architecture

4.North American analog cellular system

5.Cellular system components

6.Digital systems

1. 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

Figure 1. Basic Mobile Telephone Service Network
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. 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 kilometers. 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 with low-power transmitters using 12 conversations each, system capacity could be increased from 12 conversations or voice channels using one powerful transmitter to 1200 conversations using one hundred low-power transmitter

Figure 2. Early Mobile Telephone System Architectecture

2. 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 percent, service providers could increase the number of potential customers in an area fourfold. Systems based on areas with a one-kilometer radius would have one hundred times more channels than systems with areas 10 kilometers in radius. Speculation led to the conclusion that by reducing the radius of areas to a few hundred meters, millions of calls could be served. The cellular concept employs variable low-power levels, which allow cells to be sized according to the subscriber density and demand of a given area. As the population...
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