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You Are Here: Home > Essay Topics > Science Essays and Research Papers > Communications Research Paper Topics  > Research Paper on Mobile (Cell) Telephones

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Research Paper on Mobile (Cell) Telephones

In the last two decades of the twentieth century, mobile or cell phones developed from a minority communication tool, characterized by its prevalence in the 1980s among young professionals, to a pervasive cultural object. In many developed countries, more than three quarters of the population owned a cell phone by the end of the century.

Cell phone technology is a highly evolved form of the personal radio systems used by truck drivers (citizens band, or CB, radio) and police forces in which receiver/transmitter units communicate with one another or a base antenna. Such systems work adequately over short distances with a low volume of traffic but cannot be expanded to cope with mass communication due to the limited space (bandwidth) available in the electromagnetic spectrum. Transmitting and receiving on one frequency, they allow for talking or listening but not both simultaneously.

For mobile radio systems to make the step up to effective telephony, a large number of two-way conversations needed to be accommodated, requiring a duplex channel (two separate frequencies, taking up double the bandwidth). In order to establish national mobile phone networks without limiting capacity or the range of travel of handsets, a number of technological improvements had to occur.

The major problem with radio-based communications is the limited bandwidth available to transmit all the data of the calls that people wish to make. The high-frequency region of the electromagnetic spectrum has little space left in which to transmit and receive calls. To efficiently use the allocated bandwidth, mobile phone operators began by splitting it up into smaller segments (channels). Before networks were established, a single, high-power base antenna would cover a large area, but within the radius of the transmitter (normally greater than 32 kilometers), the number of users was strictly limited by the small number of channels available within the bandwidth.

An early step toward establishing a network was introduced in St. Louis, Missouri, in 1946, with a further 25 American cities adopting similar services in the next year. These were the first ''zoned'' systems, with multiple receiving stations, allowing users to travel around the city transmitting calls from car-based units to the nearest available receiver (this was controlled automatically in a mobile telephone switching office (MTSO) based on the relative signal/noise ratios detected). However, all transmissions from the mobile radiotelephones were picked up by a central station, making the systems again limited by the small number of channels available. This lack of space also required calls to be ''half-duplex'' only, without simultaneous talking and listening.

Research by Bell labs in the 1940s and 1950s showed that channels could be reused across the network if the areas using the same channels could be separated sufficiently to remove cochannel interference. This was a huge breakthrough, but it would still be three decades before mass-communication systems were up and running. During this time, transmitters and receivers became more efficient, so channels required less bandwidth and more could be squeezed into the same space. In the 1980s, governments began to allocate bands of the electromagnetic spectrum exclusively for nationwide mobile communication. These developments allowed for the implementation of modern cellular networks, which removed the long waiting lists caused by years of excess demand.

Cellular networks require small base stations to communicate on a duplex channel with the mobile phones within their cell (area of coverage). The system is modeled around a hexagonal honeycomb, with a base station at the center of each hexagon (see Figure 9). Each cell has a limited number of channels assigned to it, which can be reused without interference in nonadjacent cells. Crucially, as more users are added to each network, the number of channels can stay the same and the cells can be split into smaller cells by reducing the power and range of base stations. This allows for almost unlimited increases in capacity. As a phone travels from cell to cell, the MTSO allocates the phone to the antenna with the strongest signal, switching the frequency channel to continue the call without interruption. This is known as a ''handoff.'' The phone can travel across the whole network by being regularly reassigned channels (i.e., frequencies).

The network system obviously demands a large number of base stations in busy areas, but these allow clear communication at low power, which in turn allows for smaller batteries, reducing the size and cost of the phones. In the 1980s, improved network coverage along with advances in battery efficiency, computer hardware (microchips and integrated circuits), and software allowed mobile phones to become truly mobile. What was once exclusively a business tool, requiring a cumbersome separate battery unit, could be easily slipped into a pocket and used relatively cheaply, often completely replacing a traditional phone line.

Mobile phone networks cover most urban areas of the world and continue to expand. With increased coverage and greatly reduced cost, the number of users increased more than ten-fold in the 1990s. In 2000 alone, around 400 million handsets were sold. It is estimated that by 2005, there will be more than 1 billion mobile phone subscribers worldwide.

In the early 1990s, there was a worldwide move to a digital standard for mobile phones. Digital compression techniques allow for a greater volume of information to be transmitted within the same frequency band, increasing the capacity of each cell. In Europe, GSM (global standard for mobile communications) operating on the 900 megahertz band, became the digital standard (although many countries, including the U.K., now have a separate 1800 megahertz band used by newer networks). In the U.S., mobile phone systems operate at 800 and 1900 megahertz on the PCS (personal communication system) standard. Although the systems are incompatible, both use a technique called time division multiple access (TDMA). This works by splitting the available transmission time on each channel into a number of time slots (typically eight), allowing more users to simultaneously use each channel.

Digital mobile telephony also allows for the reliable transmission of data. One development is the addition of WAP (wireless application protocol) facilities to handsets, which permits rudimentary Internet access. However, slow downloads and a paucity of available information have prevented WAP from being adopted as quickly as other less advanced features such as SMS (short message service) text-messaging, which has revolutionized the way many users interact with their phones. A third generation of mobile phone technology (the analog standard is the first and digital the second) promises to further change the way we use our handsets, offering multimedia and respectable Internet access, but this will involve the construction of new networks in the twenty-first century.

 

Jack Stilgoe

 

Bibliography:

Akaiwa, Y. Introduction to Digital Mobile Communication. Wiley, New York, 1997.

Lee, W.C.Y., Mobile Cellular Telecommunications: Analog and Digital Systems, 2nd edn. McGraw-Hill, New York, 1995.

Lee, William C.Y. Lee's Essentials of Wireless Communications. McGraw-Hill, New York, 2000.

Lewis, W.D. Bell Telephone Laboratories, coordinated broadband mobile telephone system. IRE Transactions, May 1960, p. 43.

Garg, V. and Wilkes, J. Wireless and Personal Communications Systems. Prentice-Hall, Englewood Cliffs, NJ, 1996.

Rahnema, M. Overview of the GSM system and protocol architecture. IEEE Communications Magazine, April 1993.

Schulte, H.J. Jr. and Cornell, W.A. Bell Telephone Laboratories, multi-area mobile telephone system. IRE Transactions, May 1960, p. 49.

Schwartz,   M.   Telecommunication  Networks. Addison-Wesley, Reading, MA, 1987.

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