GSM Mobile Technology

Cell Info Display

This is a feature in the mobile receiver which shows the location on which we are on the display. The mobile always get under into the nearest BTS (Base Transreceiver Station). The BTS is always in the link with MSSC (Mobile Switching Service Center). The MSSC is the main mobile station, it has 2 main controls viz. HLR (Home Location Registration) and Call Authentication.

HLR is a main server which has all the data of the BTS in encoded format. Each BTS has a code number and it is stored in the form of data in HLR.

Call Authentication server looks for accounts, availability and non-availability of the subscriber. If HLR found the subscriber, it gives to the Call Authentication to link the call. If call is out of the link we get the message from the operator. This process is only for local call.

Services Description:Airtel Operational on 1800 MHZ, distance between 2 towers is 3 km. Orange and Dolphin works on 900 MHZ, distance between 2 towers is 1 km.

Transmitter

When we want to make a call, we say we are transmitting a call. The 10 digit number is dialed and given to the CPU. The CPU converts these digits into Tx signals. Further these signals are given to the RF processor where 2 carrier frequencies are stored. Hence the call is made for the Airtel subscriber so it get mixed with the carrier frequency of 1800 mhz. On the same time the link of the MIC gets opened and the COBBA IC converts the signal into Tx signal which is then further given to the RF processor. Now the process of Frequency Modulation (Mixing of 2 frequencies) takes place and both the signals are combined into one as a carrier frequency of 1800 mhz. This signal is to be amplified (Strong Signal) which is done by PFO (Power Amplifier). PFO is a dual band amplifier. This signal is further given to a antenna switch which only selects the frequency with respect to the PFO. This signal is then given to the antenna and hence the call is transmitted.

VCO is Voltage Control Oscillator which generates the frequency of 900 mhz and 1800 mhz call as a Carrier Frequency.

The CPU collects all information all the mobile IC’s and then stores software into the FLASH IC. If there is any fault in any of the IC’s we get an error on the computer by which we follow to repair the fault.

Receiving

The antenna receives the signal i.e. in the form of Radio Frequencies (RF). It is given to the antenna switch. The antenna switch will select the band with respect to the SIM and this signal is then given to the Amplifiers (GSM 900 MHZ, DCS 1800 MHZ).

The GSM (Global System for Mobile) and DCS (Dual Channel system) are the amplifiers for the receiving stage. This signal is then given to the IF IC which is also called Dual Signal Processor (DSP). Now the frequency demodulation process takes place (Separation of 2 Frequency). One frequency is given to the COBBA IC and another is given to the CPU.

When the CPU gets the signal, it gives voltage to UI module IC and Ringer, Vibrator and LED gets activated.

The UI IC has two supplies, one it gets at the time of incoming call and another from the battery.

When we press the OK button from the Mobile’s keypad, the signal which was on the Audio IC goes into the COBBA and hence we can receive call.

Data Information Technology

The CPU connects the information from all the IC and matches the file in the flash IC and if it finds both H/W and S/W information balancing then it gives information to the display. If the file inside the Flash IC for ex. If the Charging IC is corrupted, so on the display we will get an error such as Not Charging or reconnect charger. The rest of stages also work on the same process.