Even a seven year old knows how to make and receive calls using a cell phone, but not too many of us know how a phone processes voice and then sends and receives it digitally over the cellular network.Being an electronics student and that to into the branch of telecommunications I felt it important to learn how this happens…here it goes…
In fact, the question is this: whenever you make or receive a call or text message, what exactly happens in the body of a cell phone? Well a lot of things: there are several components – and therefore several functions – that work together to deliver what has become very routine. So here’s what happens
1.When we enter numbers via the keypad, a circuit behind it records the key-press sequence as commands in a certain order. These commands are sent to the CPU via the firmware located on the ROM.
2.Once the call button is hit , the CPU sends the sequence of commands to the sim reader(which reads information from the sim card).The CPU checks if there is any information about the number on the sim. The command code is also communicated to other components like the ROM, RAM, and display.
3.Once the process of checking the entered information with the sim and phone memory is entered, the commands are passed to the DSP(Digital signal Processor).Along with the voice processing done at the DSP,a highly sophisticated compression of the audio takes place. After that, the processed voice signals are instantly transferred to the Transceiver chip in the RF unit for transmission via the antenna.
4.When the cellular base station receives the request for a call, the request is passed through switches. It is then routed to the destination to check if the destination cell phone is active. Upon this confirmation, the base station routes back the call request to the callers antenna in the form of modulated signals(radio waves).
5.The cell phone antenna transfers the modulated signals to the transceiver chip(in the RF unit).RF amplifiers convert the modulated signals to digital instructions, which ride to the CPU.
6.The CPU gives out multiple instructions upon receiving the request. On one side, it gives instructions to the screen to display the relevant information(call being connected, in progress,etc.).On the other side, the OS records the call entry in the “Outgoing Calls” list.
7.Once the call is being connected , the CPU sends the modulated signals to the analogue-to digital convertors, and the digital voice signals that will be sent to the speaker.Once the destination cell phone user presses the call button, the call request is active and the communication between both the phone begins.
8.When the call is in progress, voice signals in analogue form are sent to the DSP unit according to the instructions of CPU. Those voice signals are processed and converted into digital form by the DSP with an audio codec.Then they are instantly transferred to the RF unit. The RF unit amplifiers then process those to transmit via the antenna through the transceiver chip.
The antenna finally transmits the modulated signals on the network in the form of radio waves. This process sounds lengthy , but it takes just a couple of milli seconds!
