PPT ON GSM

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GSM  Presentation Transcript

1.GSM

2.Telecom Basics
Communication
Voice and Data
Analog and Digital
Circuit Switched and Packet Switched
Media - Copper Wire, Co-axial cable, Air, Optical Fibre
Networks -PSTN, ISDN, PDN and Mobile Networks

3.Background to GSM
1G :   Advanced Mobile Phone Service (AMPS)
Analog, Circuit Switched, FDMA, FDD
2G :   Digital Advanced Mobile Phone Service (D-AMPS)
Digital, Circuit Switched, FDMA, FDD
2G :   Global System for Mobile (GSM)
Digital, Circuit Switched, FDMA and TDMA, FDD
2G :   Code Division Multiple Access (CDMA)
Digital, Circuit Switched, CDMA, FDD

4.Circuit-Switched or Packet-Switched

5.GSM Concepts - Cellular Structure

6.What are the types in GSM Network?
GSM-900 (Channels 125 operating band 900Mhz carrier spacing 200khz spacing 45Mhz)

GSM -1800 (Channels 374 spacing 95Mhz)

GSM -1900(Used in USA)

7.Multiple Access Technique
Multiple Access – Achieved by dividing the available radio frequency spectrum, so that multiple users can be given access at the same time.
FDMA - Frequency Division Multiple Access
( eg: GSM each Frequency channel is 200KHz)
TDMA - Time Division Multiple Access
( eg: GSM each  frequency channel is divided into 8 timeslots)
CDMA - Code Division Multiple Access
(eg: IS95- Each User data is coded with a unique code)

8.Duplex Technique
Duplex - How the up link and Down link of a user is separated
FDD - Frequency Division Duplex
(eg:In GSM the up link and down link of a user is separated by 45MHz )
TDD - Time Division Duplex
(the up link and down link of a user will be at the same frequency but at different Time )

9.Access Techniques ...
Time Division Multiple Access
Each carrier frequency subdivided in time domain into 8 time slots
Each mobile transmits data in a frequency, in its particular time slot - Burst period = 0.577 milli secs.
8 time slots called a TDMA frame. Period is .577 * 8 = 4.616 milli secs

10.GSM in comparison with other Standards

11.GSM  - Network Structure

12.GSM Network

13.Base Transceiver Station (BTS)
Handles the radio interface to the mobile station.
Consists of one or more radio terminals for transmission and reception
Each Radio terminal represents an RF Channel
TRX and MS communicates over Um interface
Received data transcoding
Voice encryption/decryption
Signal processing functions of the radio interface
Uplink Radio channel power measurements

14.Base Station Controller (BSC)
Provides all the control functions and physical links between the MSC and BTS
External Interfaces
‘Abis’ interface towards the BTS
‘A’ interface towards the MSC
Monitors and controls several BTSs
Management of channels on the radio interface
Alarm Handling from the external interfaces
Performs inter-cell Handover
Switching from ‘Abis’ link to the ‘A’ link
Interface to OMC for BSS Management

15.Mobile Switching Center (MSC)
Performs call switching
Interface of the cellular network to PSTN
Routes calls between PLMN and PSTN
Queries HLR when calls come from PSTN to mobile user
Inter-BSC Handover
Paging
Billing

16.Home Location Register (HLR)
Stores user data of all Subscribers related to the GMSC
International Mobile Subscriber Identity(IMSI)
Users telephone number (MS ISDN)
Subscription information and services
VLR address
Reference to Authentication center for key (Ki)
Referred when call comes from public land network

17.Database that contains Subscriber parameters and location information for all mobile subscribers currently located in the geographical area controlled by that VLR
Identity of Mobile Subscriber
Copy of subscriber data from HLR
Generates and allocates a Temporary Mobile Subscriber Identity(TMSI)
Location Area Code
Provides necessary data when mobile originates call

18.Transmission on the radio channels
A timeslot has a duration of .577 m seconds (148 Bits)
  8 timeslots(8 x 0.577 = 4.62 ms) form a TDMA frame
  If a mobile is assigned one TS it transmits only in this time slot
   and stays idle for the other 7 with its transmitter off, called bursting
  The start on the uplink is delayed from downlink by 3 TS periods
  One TS  = duration of 156.25 bits, and its physical contents is
   called a burst

19.Frequency Hopping
Frequency Hopping permits the dynamic switching of radio links from one carrier frequency to another.
Base Band Hopping
At the BTS each the timeslot is shifted to another transceiver, which is transmitting at the hop frequency. User will be connected to different Transceivers depending on hop sequence.
Synthesis Hopping
At the BTS transceiver changes the frequencies used. The user will be connected to only one transceiver.
Decreases the probability of interference
Suppresses the effect of Rayleigh fading