MOBILE COMMUNICATION

• From the beginning of 21st century the mobile telephone or cellular telephone (communally mobile phone or cell phone) has become so popular that about 80% of the world's population enjoy mobile phone coverage  upto 2014. This figure is expected to increase to 90% by the year end 2016. India expects to reach 500 million subscribers by the end of 2016.Thus mobile phone now is no more a status symbols but it has become necessity of human being.
• Mobile phone is a long range portable electronic device used form mobile communication. In addition to the standard voice function of a telephone,current mobile phones support many other services such as transmission of data,video,internet and other value added services.

THE CONCEPT OF A CELL

• In cellular mobile telephone system the large service area is divided into smaller geographical areas called as 'cell' .The diameter of a cell varies from 2 to 50 km. 

     

                                 (a) hexagonal pattern

                             

                                                            

                                    (b)circular pattern        

• The shape of the cell may be hexagonal fig(a) or circular fig(b) or other geometrical . The typical cell covers only several square km and contains its own receiver and low power transmitter. The size of the cell and number of cell per system is the choice of the service provider depending on the anticipated traffic pattern and geographical area to be convered.     
• communication channel of cellular systems: The cellular system operates in the 800 to 900 MHz range. Originally there were 30 kHz wide full duplex channels available for mobile communication. Today 832 channels are available for mobile phones. Each cell is allocated different frequency channels.                                 

                  

 (c)TYPICAL CELLULAR NETWORK CONFIGURATION

• THE MOBILE unit and base station consists of a trans-receivers antenna (transmitting and receiving ) and control units.the MTSO co-ordinates the activities of all the base station and connects the entire and cellular system through communication protocols and system interconnects.
• ELEMENTS OF CELLULAR SYSTEM:A basic cellular system of the following component as shown in fig(c)

(a) Mobile phone or cell phone :

The mobile hand set consists of a trans-receiver along with antenna for two way telephonic conversation and subscriber identity module(SIM)  .This SIM card has all the subscriber related information like cellphone number,call details,messages and other functions to perform.it has wireless connectivity to the base station.when subscriber applies power to the mobile unit,it turns on the transmitter and receiver. 
                              
                                       

• Cell site antenna (base station):
• Base station has control unit,power unit,data terminals,transmission tower with directional trans-receiver antennas and wireless or optical fiber connectivity with MTSO on one side using wide band media and on the other side with mobile unit.when the subscriber reaches a particular cell zone,his mobile unit seeks an open control channel.twenty one control channels are used to establish initial contact of base station to the mobile unit and the MTSO. when contact is made,the cell site reads the number assignment module (NAM) of mobile phone and the MTSO computer verifies that it is a valid number. 
• MTSO (mobile Telephone switching office):
• MTSO is main head office of cellular system.it controls all the cells and provides interface between each cell and main telephone office.In MTSO,there is an exchange just like telephone exchange which controls witching between land line telephone to mobile handset via cell site for land line subscriber,to mobile subscriber connectivity and vice-versa.it also controls witching between one cell site to another cell site for mobile to mobile connectivity.
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• When the subscriber sends the mobile or telephone number to be called via keyboard and then by pressing a send or call button ,the cell base station and MTSO search for an open channel and send the frequency data to a cellular trans-receiver MTSO send signal called receive signal strength indicator(RSSI) signal back to the cell site so that MTSO can monitor received signal from the cell  and make decisions about switching to another cell. Now handshake signals are exchanged signifying the contact has been established. The MTSO call  the designated number and conversation takes place.

system Inteconnect

• Different types of links ie.wired line or voice trunk or optical fibre can be used to connect mobile unit- base stations. MTSO-PSTN (Public switched telephone networ or land line telephone exchange)network. 

Communication protocols

• The  Protocols govern the   process of call connection and disconnection at the end of conversation. Several layers of protocols are used and each company can have different protocols for its cellular network. Some examples of protocols are IS-54 and IS-95, GSM e.t.c.