How Mobile phone communicates? Fact File 34

Definitely Mobile phone is an excellent communicating device. But it is not a new invention but the improvisation of the crude wireless device invented by Perry Long in 1940.The first fully Automatic mobile phone system, called MTA (Mobile Telephone system A), was developed by Ericsson and commercially released in Sweden in 1956.

In April 1973, Dr Martin Cooper, former general manager for the systems division at Motorola, invented the mobile phone prototype and he made the first call to Joel Engel, his research rival, head of research at Bell Labs. This is the first Mobile phone call.

Mobile phone is primarily designed for Voice communication. In addition to the standard voice function, new generation mobile phones support many additional services, and accessories, such as SMS ( Short Messaging Service) for text messaging, email, packet switching for access to the Internet, gaming, Bluetooth, camera with video recorder and MMS ( Multi Media Messaging Service) for sending and receiving images, video ,songs etc.

The mobile phone system is referred to as cellular telephone system because the coverage area is divided into “cells “each of which has a base station antenna.The mobile phone tower can communicate to 8 mobile phones in 1 second through time sharing method. The signals are in the form of packets to give two way transmission.

The secret of the mobile phone is its SIM (Subscriber Identification Module).The SIM is a form of digital Smart Card containing the user’s subscription information and a phone book. SIM Securely stores the service subscriber key having 15 digits. First 3 digits indicates Mobile country code, Second 2 digits indicate Mobile network code and the Third 10 digits indicates the Mobile station identification number ( Local station that is connecting).

When you first activates the SIM card, every details like, mobile phone make, pin number, area code, area of activation, server code etc will be recorded automatically in the SIM as well as in the server data base. So it is easy to trace the mobile communication and location if there is a complaint regarding misuse. Let us see what is happening when we use the Cell phone...

When the Mobile phone is used for the first time, it sends a number called International Mobile Subscriber Identity – IMSI present in the SIM card to the network, which looks it up in a database to ensure the card is registered. If the IMSI is recognized, the network creates another number called a Temporary Mobile Subscriber Identity (TMSI), which is encrypted and sent back to the phone. In all subsequent calls, the phone identifies itself by broadcasting the TMSI.

Inside the SIM Card. 

A cell phone offers full Duplex Communication and transfer the link when the user moves from one cell to another. As the phone user moves from one cell area to another, the system automatically commands the mobile phone and a cell site with a stronger signal, to switch on to a new frequency in order to keep the link.

Mobile phones have special codes associated with them. These include

1. Electronic Serial Number (ESN) -Unique 32-bit number programmed in the phone

2. Mobile Identification Number (MIN) – 10 digit number derived from the phone’s number.

3. System Identification Code (SID) – unique 5 digit number that is assigned to each carrier by the FCC.
ESN is a permanent part of the phone while MIN and SID codes are programmed in the phone when a service plan is selected and activated.

What happens when we make a call?

1. When we switch on the mobile phone, it tries for an SID on the Control channel. The Control channel is a special frequency that the phone and base station use to talk to one another. If the Mobile phone finds difficulty to get link with the control channel, it displays a “no service” message.

2. If the Mobile phone gets the SID, it compares the SID with the SID programmed in the phone. If both SID match, the phone identifies that the cell it is communicating is the part of its home system.

3. The phone also transmits a registration request along with the SID and the MTSO keeps track of your phone’s location in a database. MTSO knows in which cell you are when it wants to ring the phone.

4. The MTSO then gets the signal, it tries to find the phone. The MTSO looks in its database to find the cell in which the phone is present. The MTSO then picks a frequency pair to take the call.

5. The MTSO communicates with the Mobile phone over the control channel to tell it what frequencies to use. Once the Mobile phone and the tower switch on those frequencies, the call is connected.

6. When the Mobile phone move toward the edge of the cell, the cell’s base station will note that the signal strength is diminishing. At the same time, the base station in the cell in which the phone is moving will be able to see the phone’s signal strength increasing.

7. The two base stations coordinate themselves through the MTSO. At some point, the Mobile phone gets a signal on a control channel and directs it to change frequencies. This will switch the phone to the new cell.