Mobile phones use electromagnetic waves of a specific frequency band to communicate with each other. In part, a mobile phone works like a radio, meaning that radio signal emitted by a mobile phone tower nearby.
A cellular network consists essentially of mobile phone base station, a switching center and a telephone. To initiate a call, the mobile phone should communicate with radio stations of mobile network, ie it must be within range of one of the stations.
Each radio station provides coverage for a particular geographic area, called cell. Radio stations are interconnected thereby forming a mobile network. The cells are so set that radio coverage areas to coalesce. When you have no signal you are out of reach of any base stations. Central communications network provides transfer call between cells. The cellular system requires the transfer of a call between cells, to allow the passage of a phone discussion and from one cell to another.
Switching center processes calls and connects the phones and PBX equipment. Also keep data on users who use the network know the status and position of each subscriber, determine how users are interconnected and counted using the network equipment.
The great advantage of a network of cells is the fact that the frequencies used within the cell can be reused in another cell as well. If, for example, the base station number 1, you can manage 100 frequencies in fact can do more, around 830 frequencies is used by 50 speakers simultaneously, each connection established between any two users will use 2 frequencies, one for transmission and one for reception duplex channel, thus depleting all available frequencies. That means that in terms of this cell network is busy. In neighboring cell users can be much smaller and the call can be performed with ease. In the same cell neighboring frequencies used by users can be the same as those used in cell.
That there are a limited number of frequencies for each cell explains why certain days December 31, natural disasters etc. telephone network becomes inaccessible, which does not necessarily mean that the network is blocked, but they are more than willing to use frequencies available network at any given time. In reality, things are a bit more complicated. For instance GSM, used in USA, uses TDMA technology Multiple Access Time pision dividing the frequencies into time slots, so you can use a frequency for more data channels.
Transferring a call from one cell to another
In the hypothetical situation where two speakers are in cells that do not leave during the conversation, how interacting elements are clear: Caller base station, central base station, called. Only things are usually more complicated in reality, people often being in motion when using mobile phones. In order not to interrupt the conversation out of a cell, mobile network must know how to teach / take the call between adjacent cells.
Teaching or call acceptance is a very simple process, sometimes interrupting communication occurring. For this process to occur, the system must decide when to switch the connection, what radio stations they reconnect to the speakers and on what channel without interrupting the discussion. The system must determine the strength of the signal emitted by the base station used by the speaker, to compare the stations neighboring evaluate your channels free of stations neighboring reserve a free channel to a radio station available, then transmit signal shift to mobile. Once connected to the new station, the mobile phone sends a message announcing that the incoming signal, allowing the network to lay the channel using the phone until recently.
GSM phones use a Subscriber Identity Module microchip called (SIM). SIM is used to store configuration data on the phone’s existing subscription etc. Each card is enabled by a unique identification number; once activated, identification number is registered and the card is linked to the network that has been activated this site http://gps-phonetracker.net/ shows you how to locate devices.
As you may know, the mobile network there who need phones have SIM cards. Do not use SIM phones that have data loaded in memory.
IMEI (International Mobile Equipment Identity) is a 15-digit number used to identify the device standard GSM phone. It can be seen under the phone’s battery. This identification number is entered in the phone by the manufacturer and when the phone tries to access a network, IMEI is compared with data from a database, thus being able to determine if the phone is or is not stolen.
HOW THE ROAMING?
Roaming is the ability to use a network other than the subscriber is registered.
Technically, the phone is in roaming when, on the one hand, the verification center switching SID network does not match the SID phone, and on the other hand, after verifying that the switching center of the foreign network makes the switching center of the home network SID caller’s apparent validity.
Mobile phone manufacturers
The major manufacturers of mobile phones, according to the figures available for 2007 are: Nokia, with 40% of the market, Samsung 14%, Motorola 14%, 9% Sony Ericsson, LG 7%. In 2008 a great success it had already famous company Apple iPhone.