Draw the block schematic of how GSM works
Abbreviations used in this diagram:
MS= Mobile station= Mobile Phone
BSS=Base Station System. It consists of Base Tranceiver Station(BTS) and BSC(Base Station Controller)
MSC=Mobile Services Switching Centre
GMSC=Gateway MSC
HLR=Home Location Register
VLR=Visitor Location Register
AuC=Authentication Centre
NSS=Network Sub System
EIR=Equipment Identity Register
PSTN=Public Switched Telephone Network
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Which frequency band is used for GSM?
900Mhz and 1800 is used in most of the countries.'
In USA 850Mhz and 1900Mhz are used
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What is the purpose of EIR? Stolen and Malfunctioning mobile phones can be locked as well as located.
Whenever a call is initiated, the EIR registers the IMEI. It maintains 3 lists: GREY LIST=phones to be tracked. BLACK LIST= barred mobile phones, WHITE LIST=valid mobile phones.
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What is the Uplink frequency range for GSM-900?
\890 to 915MHz
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What is the Downlink frequency range for GSM-900?
935 to 960 MHz
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GSM-900 frequency band is divided into how many physical carriers?
124 carriers
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Each 200khz carrier is split into how many timeslots?
8 timeslots.
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What is the bandwidth of each physical carrier?
200KHz
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I am a mobile service provider. I have been allotted with 36 carriers of 200khz each. I am using a K-factor of 12. What will be the total number of traffic channels if a) i use a single cell ie no cell-splitting b) if my jurisdiction is divided into 72 cells c) my jurisdiction is divided into 246 cells.
a) when there no cell-splitting ::: 36 carriers x 8 timeslots =288 traffic channels.
b) when there are 72 cells >>>> 36 carriers x 8 timeslots x 72/12=1728 traffic channels
c) when there are 246 cells >>>> 36 carriers x 8 timeslots x246/12=5904 traffic channels
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Draw the GSM Layer-3 message format
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In GSM-900, how many timeslots form a multiframe?How many frames for a superframe?
Howmany superframes form a hyperframe?
diagram courtesy: Wireless Communications Systems and Networks, By Mullett, Thomson Publisher
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What is a traffic multiframe?
There are two types of multiframes. Traffic multiframe which consists of 26 frames.Control multiframe consists of 51 multiframes.
In case of 26-multiframes, 24 slots are used for carrying voice. 1 slot is used for SACCH of that channel.
FACCH has not any slot allocated. It steals timeslots from this channel whenever required.
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Write short notes on 51-frame multiframe.
51-multiframe is used for Control Channels.
Note: The BCCH (beacon) is a downlink channel.Its uplink counterpart contains RACH channel
What is SCH?
SCH is Synchronization channel. it helps the MS to sync with the base station clock.
What is FCCH?
FCCH is Frequency Correction Channel. The whole data space (142 bits) is used for unmodulated carrier (pure sinusoid) or carrier modulated with all zero bits. This pure carrier is the ‘identity’ of a beacon frequency or BCCH(base frequency). Each BTS has one or more frequency channels ie physical channels. One of these is called as beacon frequency. The first timeslot of this frequency is used as base control channel bcch. the remaining 1 to 7 slots are used for any mix of traffic and control channels.
Write short notes on 51-frame multiframe.
51-multiframe is used for Control Channels.
What is SCH?
SCH is Synchronization channel. it helps the MS to sync with the base station clock.
FCCH is Frequency Correction Channel. The whole data space (142 bits) is used for unmodulated carrier (pure sinusoid) or carrier modulated with all zero bits. This pure carrier is the ‘identity’ of a beacon frequency or BCCH(base frequency). Each BTS has one or more frequency channels ie physical channels. One of these is called as beacon frequency. The first timeslot of this frequency is used as base control channel bcch. the remaining 1 to 7 slots are used for any mix of traffic and control channels.
