Mobile telephone system
A system designed to exchange data and information between two mobile devices or one mobile and one fixed device is called a mobile telephone system. The mobile device is called Mobile Station (Mobile Station or MS) or Mobile Unit or Mobile Set and the fixed device is called Land Unit. A mobile service provider divides its coverage area into smaller segments. Each division is called a cell. From this cell another name of mobile phone has been given as cellular phone. A cell consists of an antenna and a small office, the small office with the antenna is called a base station. Each base station is controlled by a mobile switching center from where call connection, call information recording, billing system are controlled in a computerized manner.
Cell size usually depends on population density. Cell sizes can typically range from 1 mile to 12 miles. Cellular phones are now also known as mobile phones. Nowadays, data such as audio, video, image, text etc. can be exchanged by cellphone or mobile phone. One can even stay connected with the whole world through internet. Mobile phones with advanced computing capabilities are called smartphones. America Cooper, co-founder of a mobile company called Silicon Valley and former vice president of Motorola Company, invented the modern mobile phone. He is also called the father of mobile phones.
In 1973, he first demonstrated a hand-held mobile phone weighing about 1 kg. In 1983 the Motorola Dyna TAC BOOOX modem was used commercially. There were about 12.4 million mobile subscribers worldwide in 1990, which rose to about 5.6 billion in 2011. According to the report of BTRC (Bangladesh Telecommunication Regulatory Commission - BTRS) in March 2011, the total number of mobile phone users in Bangladesh is 7,41,90,000 which is about 48.6% of the country's population.
Basic concept on cellular network: Radio frequency is used in cellular network. In cellular radio systems, the signal or signal is delivered over a land area with radio service, which is divided into regularly sized cells. Cells can be hexagonal, square, circular, or any other irregular shape, although hexagonal is the most common. Each cell is assigned a number of frequencies, with corresponding radio base stations. A class of these frequencies can be reused. Care must be taken in this regard. So that the same frequency is not recycled in neighboring or adjacent cells.
The same radio frequency can be reused in different areas for completely different transmissions. If there is only one common transmitter, only one transmission may be used on any given frequency. A standard FDMA system must have at least one cell break between different cells when reusing the same frequency.
Cell signal encoding: The process of separating signals sent from different transmitters with the help of encoding method is called cell signal encoding. FDMA (Frequency Division Multiple Access) CDMA (Code Division Multiple Access) technology was developed to separate signals from different transmitter signals.
* In FDMA the transmitting and receiving frequencies used by each cell are different from the frequencies used by each neighboring cell. In a typical taxi system, the taxi driver manually tunes to a selected frequency for the cell to achieve a strong signal and avoid interference from signals from other cells.
*The basic theory of CDMA is more complicated, but achieves the same result. The distributed transceiver can select a cell and listen to it
Other methods of multiplexing such as PDMA (Polarization Division Multiple Access) and TDMA (Time Division Multiple Access) do not separate signals from one cell to another. This is because the results of both vary with location and it is practically impossible to separate the signal in this process. However, TDMA has to be used in combination with FDMA or CDMA in various systems to provide multiple channels within the coverage area of a single cell.
Basic mobile or cellular system: A basic mobile or cellular system consists of four parts, they are-
(i) Mobile Unit, (i) Cell Site, (iii) Mobile Telephone Switching Office and (iv) Connection.
(i) Mobile Set: A mobile telephone unit consists of three main parts, namely- (1) a control unit, (2) a transceiver and (3) an antenna system.
(ii) Cell Site : Cell site facilitates communication between mobile units. It has a control unit, radio cabinet, antenna, a power plant and a data terminal.
(iii) Mobile Telephone Switching Office or MTSO : The MTSO is the central coordinating element of all cell sites which contains processors and cellular switches. It performs the following functions --
1. Contact the Zonal Office of the Mobile Telephone Company.
2. Controls call processing.
3. Manages billing activities.
(iv) Connectivity : Radio and high speed data links connect the three sub-systems. Each mobile unit uses only one channel at a time for communication. However, the channel is not fixed, it can be any one in the entire band. It has multi-channel capability at each site, which can connect to many mobile units simultaneously. MTSO is called the heart of the cellular mobile system. Its processor helps in central coordination and cellular administration. Cellular switches can be analog or digital. Switching calls to connect mobile subscribers to other mobile subscribers and to the nationwide telephone network. It uses voice tasks similar to telephone company interoffice voice tasks. It also contains data links, which provide supervision links between processors and switching and cell sites and processors. Radio links carry voice and signaling between mobile units and cell sites. High-speed data links cannot be converted through standard telephone trunks. So of course the microwave link or T-Carius carries both voice and data between Cellsite and MTSO.
Roaming:
Mobile service providers have limited coverage areas. It can be a specific area or a country. Adjacent areas are covered by other service providers. Service providers interconnect with each other to provide convenience to customers, a process called roaming. As a result, the customer of one service provider can use the mobile even in the area of another service provider. For example, if a Grameenphone customer activates the roaming service while traveling in India, he can use the same mobile even when he is in India.
Introduction of mobile unit or set (Mobile unit of set)
A mobile or cellular telephone unit consists of three main parts, namely—
(i) a control unit,
(ii) a transceiver and
(iil) An antenna system.
Apart from these three basic components, mobile phones have the following features—
(a) A battery, which provides the power required to run the overall function of the phone properly.
(b) an input mechanism, which enables users to interact or communicate with the phone system; The most common input mechanism is the key pad. However, some smart phones have touch screens.
(c) A SIM (Subscriber Identity Module) card is provided by the GSM mobile phone service provider to the user. CDMA devices have a similar card, called R-UIM.
(d) Independent GSM, WCDMA, IDEN and some satellite phone device IMEI numbers are uniquely identified.
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