Top GSM Interview Questions & Answers:

1. Does Extended Cell have any impact on the system? If yes, what?

★ The cell radius could be double or even more, based on the antenna, type of terrain and timing advance.
★ Indoor coverage is supported by GSM and could be achieved with the usage of picocell base station or an indoor repeater along with distributed indoor antennas.

2. What do you mean by extended cell?

★ Extended cell feature enables the operators for extending the coverage without installing new cell cites.
★ Extended cell feature is designed specifically for providing covering in rural areas, where density of population is low and installation of additional cell sites.
★ New features can be deployed in coastal areas for providing GSM coverage in offshore waters.

3. Explain TDD in GSM Technology?

★ Time Division Duplexing, a 3GPP standardized version of Universal Mobile Telecommunications System networks.
★ The designated mobile sends the data in a stipulated time and receives data from the BTS in another time.
★ The time is divided into various time slots and user sends data in few time slots and receives the data in the rest of the time slots.
★ Alternative downlink and uplink directions are used.

4. Explain FDD in GSM Technology?

★ Frequency Division Duplex is one of the techniques, in which one frequency band is utilized for transmitting and another used for receiving.
★ To up-link the carrying data from mobile phones to the base station, one electromagnetic block spectrum is allocated.
★ Various blocks of spectrum is allocated to down-link carrying data from the base station to the mobile telephone hand sets.

5. What is the mean of power control in GSM Technology?

★ Power control is the intelligent selection of transmit power in a communication system for achieving best performance within the system.
★ The performance is depend on context and there are chances to include optimizing metrics like link data rate, network capacity, geographic coverage and range.
★ A higher transmit power translates into a higher signal power at the receiver.
★ The bit error rate will be reduces at the receiver of a digital communication link, by having higher signal-to-noise ratio.
★ Higher transmit power provides more protection against a signal fade in a wireless fading channel.

6. What do you mean by ARFCN in GSM Technology?

★ Absolute Radio Frequency Channel Number, a code to specify a pair of physical radio carriers and channels within the spectrum that is allocated for cellular mobile communications.
★ ARFCN is used for transmitting and receiving on the UM Interface, one to uplink signal and one to downlink signal.
★ ARFCN's bandwidth is 270.833 kHz; channel spacing is 200 kHz in a given GSM band.
★ The uplink-downlink spacing is generally 45 / 50 MHz.
★ If Frequency Division Duplex is operated in the system, then the channel number is associated with both uplink and downlink radio channels.
★ ARFCN is 1-124 within GSM900 spectrum, 512-885 within GSM1800, 512-810 within GSM1900, are used.

7. Explain MS-IDN in GSM Technology?

★ Mobile Subscriber Integrated services Digital Network Number, a unique number identifying a subscription in a GSM / UMTS mobile network.
★ It is the telephone number of the SIM card in a mobile phone.
★ MSIDN and IMSI are important numbers used to identify a mobile subscriber
★ MSIDN is used for routing the calls to the subscriber, where as IMSI identifies the SIM.
★ In the HLR, the IMSI is the key, and MSIDN is the number that is dialed for connecting a call to the mobile phone.

8. What is IMEI in GSM Technology?

★ International Mobile Equipment Identity is a number usually unique for identifying GSM,WCDMA and iDEN mobile phones.
★ It is generally printed inside the battery compartment of the phone.
★ The number can be displayed on the screen by entering *#06# into the keypad on most of the phones.
★ A stolen phone can be stopped from accessing the network within the country, by using IMEI number for valid devices.
★ Unlike CDMA/MEID's electronic serial number, the IMEI is only used for identifying the device and has no permanent relation to the subscriber
★ The subscriber is identified by IMSI number, stored on the SIM card, which then can be transferred to any other handset.

9. What is TMSI in GSM Technology?

★ Temporary Mobile Subscriber Identity for most commonly sent between the mobile and the network.
★ TMSI is assigned randomly by VLR to each mobile in the area.
★ The TMSI number is local for a specific local area, and need to be updated every time when the mobile moves to a new geographical area.
★ Paging a mobile is the key use of the TMSI.
★ The communication between the mobile and the base station is known as paging.
★ The emphasis of broadcast information is top set up channels for paging.
★ Broadcast mechanism is available in every cellular system for distributing broadcast information to a plurality of mobiles.

10. Explain IMSI in GSM Technology?

★ International Mobile Subscriber Identity - a unique identification that is associated with all GSM and UMTS network mobile phones.
★ The SIM inside the phone contains it as a 64 bit field.
★ Used for acquiring certain details in Home Location Register or Visitor Location Register.
★ IMSI is rarely sent for preventing eavesdroppers to identify and track the subscriber on the radio interface.
★ It is presented as 15 digit long number, where first 3 digits represent the Mobile Country Code and followed by the Mobile Network Code.
★ Remaining digits are mobile station identification number within the customer base network.