To start with, one of the most interesting things about a mobile phone is that it is a “radio” – an extremely sophisticated radio. An oversimplification would be to say that mobile phones are nothing more than a radio transmitter and receiver operating at the same time without a physical wired connection.
When one talks on a mobile phone, sound waves are converted into radio waves, as in the case of a radio. These waves are sent to a special tower that picks up the signal. This tower is also called as a base station. These cells have extensive frequencies that allow thousands of people to use mobile phones at the same time. In this process, cellular calls are transferred from one base station to other base station.
To simplify more, the major component of mobile phone system is the cell. This system divides an area of service into a set of cells on what looks like a hexagonal grid. A phone tower or a base station in the center of the cell covers an area of 2-3 square miles around the tower. Mobile phone transmits to tower, which then connects the waves to the normal land based telephone system or another mobile phone (if it is within the range of another base station) to route the call. In other words, a hand over has to happen when one moves from one cell to another. A typical large city has hundreds of towers and each carrier in each city runs what is called a central office, known as mobile telephone switching office (MTSO). For example, as one moves from one city to another, every couple of miles, the system hands over to another cell (i.e. tower). It happens automatically and one does not always realize this. But, sometimes, in bigger cities, as one enters the range of one tower in the city, one does get a message like, ‘Welcome to Kolkata. Your charges are xyz per call”. But for this to happen, one must take ‘Roaming’ services.
Let us look at what happens when someone calls you, step by step:
1. When you power up phone, it listens for specific frequencies ( control channel) that the phone and the tower use to talk to one another. If there are no control channels, the phone displays a ‘no service’ message, because it knows it is out of range.
2. The phone transmits a registration request, so that MTSO keeps track of your phone location in the data base. It is important for the MTSO to know which cell you are in, when it wants to ring your phone.
3. MTSO gets the call, and it tries to find you by looking into the database to see which cell you are in.
4. The MTSO chooses a frequency pair that your phone will use in that cell to take a call.
5. The MTSO communicates with your phone over the control channel to tell it what frequency to use and when your phone and the tower switch on those frequencies, you are connected and talking.
6. If you move towards the edge of the cell , the tower notes a diminishing signal. The diminishing signal indicates that it is time for the control channel to hands off you to the next cell.
Mobile phones use a short- wave analog or digital telecommunication in which a subscriber has a wireless connection from a mobile phone to a relatively nearby transmitter and receiver in the base station.
An analog signal has a base carrier’s radio frequency signal, which is modified in some way to amplify the strength of the signal or vary frequency to add information to signal. This represents sine waves because these waves are analogous to the fluctuations of the human voice or other sound that is being transmitted.
Using digital form of communication a small radio time-slice is allotted to each conversation in the same cellular area. Your slice is repeated quickly and often and your mobile selects it alone, giving rise to a slower digital audio voice stream similar to that from a CD player.
Microphone and speaker give you the conversation whereas buttons and other information forms data component.
This is how a mobile phone works.
You can send messages, pictures and even surf the internet using mobile phone. New technologies let mobiles talk to each other, or to computer, without using radio wave. This means you can swap information without even making call.
Mobile Phone Networks use three common technologies:
1. Frequency –Division Multiple Access (FDMA)
2. Time-Division Multiple Access (TDMA)
3. Code-Division Multiple Access (CDMA)
The diagram below will help you understand it: