If you are a student, tech hungry, or researching on the World’s most used devices i.e. cell phone its basic principle and working with network, here is complete tutorial for you.
Tring !!! tring !!!
Hello everyone!! Hello!! Hello! Am I audible hello!! Hello! Oops sorry I thought I am talking on phone, no I am writing. Anyways the above greeting style is not coincidental (aka not kaalpanik). Our generation is known as the mobile generation. Cell phones have a great impact on our lives and its true imagining a day without phone is …… don’t ask!!
Starting with types of mobile communication it is of three types
Simplex: – only one channel present. A single person communicates at a particular time or one way communication is there. Example baby monitors, garage door openers, surveillance cameras.
Half-duplex:- two channels are present. A single person communicates at a particular time or one way communication. Example: – walkie-talkie.
Full duplex: – two channels are present. Two persons or simultaneous communication is possible. Example: – cell phones.
The cell-phone carrier receives about 800 frequencies to use across the city. The carrier chops up the city into cells. Each cell is typically sized at about 10 square miles (26 square kilometers). Cells are normally thought of as hexagons on a big hexagonal grid.
A single cell in an analog cell-phone system uses one-seventh of the available duplex voice channels. That is, each cell (of the seven on a hexagonal grid) is using one-seventh of the available channels so it has a unique set of frequencies and there are no collisions. The combination of all cells of a MTSO is known as a cluster. All available channels are divided in the cluster accordingly. These Hexagonal grids are not really present it is just an adaptation for a cell as after circle hexagon is the shape closer to show uniformity of signal 3600around the base station. Circular cells are not considered as they will leave voids.
Every cell has a single base station which looks after all communication happening involving all mobile stations and mobile users in that cell. Four channels are used for communication i.e. forward voice channels responsible for transmission of voice, reverse voice channels responsible for receiving of voice. Two control channels are also present one is forward control channel which are responsible for initiating and setting up of calls.
Well starting from a cellular system. A cellular system provides a wireless connection to the public switched telephone network (PSTN) for any location within the range of the system. A basic cellular system consists of mobile stations, base stations and a mobile switching center (MSC) or mobile telephone switching office (MTSO) which is responsible for all communication with PSTN. A cell phone (mobile station) is like a radio which communicates with the base stations. The base station consists of several transmitters and receivers which serve as a bridge between all mobile users in the cell.
All cell phones have special codes associated with them. When we switch on our phone it looks for control channels or SID. If the phone is not able to find any control channel then it is “OUT OF RANGE” and displays “NO SERVICE”. When it receives the SID or control channel, it compares it with SID programmed in the phone. If it matches the SID of the phone the phone is in its home network.
Calling a mobile user
When a phone call is made to a mobile user, the MSC sends request to all base stations and the mobile identification number (MIN) is broadcasted over the forward control channel. The mobile receives the broadcasted message and identifies it over the reverse control channel. The base station relays the acknowledgment and informs MSC of handshake.
Then the call is moved to an unused voice channel within the cell. At this instant the base station asks the mobile to move to unused voice channels and instruct the phone to ring by sending it an alert message
Calling from a mobile
When a mobile originates a call, a call initiation request is sent on reverse channel. With this the mobile station transmits it MIN, electronic serial number (ESN) and the number of the called party. The mobile also transmits a station class mark (SCM) which indicates that transmitter power level is for particular user. The cell base station receives this data and sends it to MSC which further connects to the PSTN, and instructs the base station and mobile to move to a unused frequency.
Suppose the call is in progress and the mobile user moves towards the edge of the cell (assuming the base station antenna is at the center of the cell) the strength of the signal gets weaken, Meanwhile, the base station in the cell you are moving toward (which is listening and measuring signal strength on all frequencies, not just its own one-seventh) sees your phone’s signal strength increasing. and as the mobile station enters another cell, the MSC then switches the voice channels according to the new base station to maintain the call. This is called hand-off.
Cellular systems provide us a service known as roaming. It is a service which allows users to communicate in areas or regions rather or away from their home network. MSC issues a command asking all mobiles to verify their MIN and ESN. If new phones are reported, then MIN/ESN data is used to request billing status from home location register. Good news is that roaming will be vanished by mid 2013 in INDIA.
FOR MORE DEEP STUDY ON THE CONCEPT OF CELL PHONES
WAIT FOR CELL PHONES PART 2