Important questions on GSM
Ques1. What is t maximum data rate support by a GSM?
Ans. The maximum data rate supported by a GSM system is 9.6 kbps. However there are extensions to GSM standard to improve throughput. GPRS is one of the extended GSM service. The extended standards of GSM allows theoretical data rates on the order of 114 Kbit/s, but with throughput closer to 40Kbit/s in practice.
Ques 2 Explain sectorization of a cell.
Ans. Sectorization is a process to cut down equipment costs in a cellular network. It influences in traffic load and cell size. Sectorization reduces co-channel interference, when applied to clusters of cells. The maximum traffic capacity of sectored antennas is more than omnidirectional antennas.
Ques 3 Whuch uplink or downlink is allocated the following?
a. GSM 900?
b. DCS 1800?
a.) GSM – 900: Uplink spectrum is 890.2–914.8 and downlink spectrum is 935.2–959.8
b.) DCS – 1800: Uplink spectrum is 1710.2–1784.8, and downlink spectrum is 1805.2–1879.8
Ques 4. Name the algorithm used in following: a. Ciphering b. Authentication
The algorithm 129-EEA3 and 128-EIA3, 3GPP Confidentiality and Integrity Algorithm is used for ciphering in GSM
The algorithm by name A3 is used for authentication in the GSM systems
This algorithm is used in implementing Subscriber Identity Module .
Ques 5. What do you mean by ARFCN?
Ans. 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.
Ques 6. What is power control?
Ans. 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.
Ques 7. What do you mean by extended cell? Does it have any impact on the system?
Ans. 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
It’s impact is :
- 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.
Ques.8 How does GPRS architecture differ from GSM?
Ans. The following table depicts the architectural differences between GPRS and GSM
|Mobile Station||New mobile station is needed for accessing GPRS services. They are backward compatible with GSM for voice calls|
|Base Transceiver Station||Software upgrade is needed in the existing BTS|
|Base Station Controller||Software upgrade and new hardware, Packet Control Unit are needed for GPRS.|
|GPRS Support Nodes||Installation of new core network elements, known as serving GPRS support node, and gateway GPRS support node are needed to deploy GPRS|
|Databases||Requires software upgrade to handle new models and functions to handle databases involved in the network|
Ques9 . What do you mean by following? a. Erlang b. GoS.
- Total traffic volume per hour / 3600 seconds is described by erlang
- For example, 60 calls in one hour and each lasting 5 minutes results the following:
Minutes of traffic in an hour = Number of calls x Duration
Minutes of traffic in an hour = 60 x 5 = 300 minutes
Hours of traffic in the hour = 300 / 60 = 5 hrs
The traffic figure = 5 erlangs
- Grade of Service is a probability of a cell in a circuit group which is blocked / delayed for more than a specified interval
- GoS is expressed as a vulgar fraction / decimal fraction
- It is with reference to the busy hour at the time of greatest intensity of the traffic
- GoS may be viewed independently from the perspective of incoming vs outgoing calls
- The GoS is not essentially equal between source to destination pairs.
Ques 10. Explain: a.) HSN b.) DTX c.) DRX – TRX
- Hopping sequence number is utilized, to spread the interference between all cells that uses the same hopping TCHs
- The correlation between closely located cells can be avoided by using HSN
- HSN of zero corresponds to the cyclic hopping sequence, and 1 through 63 corresponds to various pseudo random patterns.
- Discontinuous Transmission is one of the methods which is based on the advantage of the fact that a person speak less
- Nearly 40% of time in general conversation, the transmitter is turned off during silence periods
- Mobile phone power conservation is an added benefit of DTX
- Voice Activity Detection is the most important component of DTX
- DT X distinguishes between voice and noise inputs.
- The transmitter is turned off when a voice signal is misinterpreted as noise. This causes annoying effect known as clipping is heard at the receiver’s end
- Comfort noise is created at the receiving end, in order to ensure the non-connection.
c.) DRX – TRX
- DRX is referred as driver receiver.
- DRX performs the transmission and reception of signals
- Sends and receives the signals to or from higher network entities, as in base station controller in mobile telephony
- The transceivers allows to serve several frequencies and different sectors of the cell
- Sends and receives signals from / to higher network entities.