level ii introduction to gsm essentials day 1.pptx
TRANSCRIPT
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Level II
Introduction toGSM Essentialsand Basic
AnalysisQoS Department
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Overview
Introduction to GSM Architecture
Introduction to GSM Channels
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What is GSM ?
Global System for Mobile (GSM) is a
second generation cellular standarddeveloped to cater voice services and data
delivery using digital modulation .
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GSM in WorldFigures: March, 2005
37%
1%4%43%
4%
3%
3%
3% (INDIA)
3%
Arab World
Asia Pacific
AfricaEast Central Asia
Europe
Russia
India
North America
South America
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GSM Services
Tele-services Bearer or Data
Services
Supplementary
services
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Tele Services
Telecommunication services that enable voice communication via
mobile phones
Offered services
- Mobile telephony
- Emergency calling
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Bearer Services
Include various data services for informationtransfer between GSM and other networks like
PSTN, ISDN etc at rates from 300 to 9600 bps Short Message Service (SMS)
- up to 160 character alphanumeric datatransmission to/from the mobile terminal
Voice mailbox
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Supplementary Services
Call related services :
Call Waiting- Notification of an incoming call while on thehandset
Call Hold- Put a caller on hold to take another call
Call Barring- All calls, outgoing calls, or incoming calls Call Forwarding- Calls can be sent to various numbers definedby the user
Multi Party Call Conferencing - Link multiple calls together
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GSM System Architecture
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GSM System Architecture-I
Mobile Station (MS)
Mobile Equipment (ME)
Subscriber Identity Module (SIM)
Base Station Subsystem (BSS)
Base Transceiver Station (BTS)
Base Station Controller (BSC)
Network Switching Subsystem(NSS)
Mobile Switching Center (MSC)
Home Location Register (HLR)Visitor Location Register (VLR)
Authentication Center (AUC)
Equipment Identity Register (EIR)
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System Architecture
Mobile Station (MS)
The Mobile Station is made up of two entities:
1. Mobile Equipment (ME)
2. Subscriber Identity Module (SIM)
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Mobile Equipment
Portable, vehicle mounted, hand held device
Uniquely identified by an IMEI (International MobileEquipment Identity)
Voice and data transmission Monitoring power and signal quality of surrounding cells
for optimum handover
Power level : 0.8W20 W
160 character long SMS.
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Subscriber Identity Module(SIM)
Smart card contains the International Mobile SubscriberIdentity (IMSI)
Allows user to send and receive calls and receive othersubscribed services
Protected by a password or PIN
Can be moved from phone to phonecontains keyinformation to activate the phone
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System Architecture
Base Station Subsystem (BSS)
Base Station Subsystem is composed of two parts that
communicate across the standardized Abis interface
allowing operation between components made by different
suppliers
1. Base Transceiver Station (BTS)
2. Base Station Controller (BSC)
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Base Transceiver Station (BTS):
Encodes, encrypts, multiplexes, modulates and
feeds the RF signals to the antenna.
Communicates with Mobile station and BSC
Consists of Transceivers (TRX) units
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Base Station Controller (BSC)
Manages Radio resources for BTS
Assigns Frequency and time slots for all MSs in its area
Handles call set up Handover for each MS
It communicates with MSC and BTS
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Mobile Switching Center (MSC)
Heart of the network
Manages communication between GSM and other networks
Billing information and collection
Mobility management- Registration
- Location Updating
- Inter BSS and inter MSC call handoff
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Home Location Registers (HLR)
Stores information about each subscriber that belongs to
it MSC in permanent and temporary fashion. As soon as mobile subscriber leaves its current local area,
the information in the HLR is updated.
database contains IMSI, MSISDN, prepaid/ postpaid,
roaming restrictions, supplementary services.
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Visitor Location Registers (VLR)
Temporary database which updates whenever new MSenters its area, by HLR database
Assigns a TMSI to each MS entering the VLR area whichkeeps on changing.
Controls those mobiles roaming in its area
Database contains IMSI, MSISDN, Location Area,authentication key
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Authentication Center (AUC)
Contains the algorithms for authentication as well asthe keys for encryption.
Protects network operators from fraud.
Situated in special protected part of the HLR.
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Equipment Identity Register (EIR)
Stores all devices identifications registered for this network.
Database that is used to track handsets using the IMEI(International Mobile Equipment Identity)
Prevents calls from stolen, unauthorised or defective mobile
devices
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Operation and maintenance centre
(OMC) The centralized operation of the various units in the system
and functions needed to maintain the subsystems.
Dynamic monitoring and controlling of the network.
Functions :
- configuration management
- fault report and alarm handling
- performance supervision/management- storage of system software and data
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Characteristics of GSM Standard
Fully digital system using 900,1800 MHz frequency band.
User/terminal authentication for fraud control.
Full international roaming capability.
Low speed data services (upto 9.6 Kb/s).
Compatibility with ISDN.
Support of Short Message Service (SMS).
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Future Of GSM 2nd Generation
GSM -9.6 Kbps (data rate)
2.5 Generation ( Future of GSM)
HSCSD (High Speed ckt Switched data) Data rate : 76.8 Kbps (9.6 x 8 kbps)
GPRS (General Packet Radio service)
Data rate: 14.4 - 115.2 Kbps
EDGE (Enhanced data rate for GSM Evolution)
Data rate: 547.2 Kbps (max)
3 Generation
WCDMA(Wide band CDMA)
Data rate : 0.3482.0 Mbps
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High level network architecture
(1/2)
SIM
ME:Mobile equipment
Services / Applications
Core Network(CN)
Ext.network
UE: User equipment
Access Network(AN)
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High level network
architecture (2/2) The network contains functionally of: User Equipment (UE),
Access Network (AN), and Core Network (CN)
User equipment: Interfaces the user, handles radio functionality
Access network: Communication to and from the user
equipment, handles all radio related functionality in the network
Core network: Communication between access network andexternal networks, handles all switching and routing
Services and applications lie above the network
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GSM radio interfaceMain
characteristics Frequency bands: GSM 900:
890915 MHz: Uplink (MS transmit)
935 - 960 MHz: Downlink (MS receive)
GSM 1800:
1710 - 1885 MHz: Uplink 1805 - 1880 MHz: Downlink
Carrier bandwidth: 200 kHz Channels / carrier: 8 Multiple access: TDMA / FDMA Duplex: FDD Gross bit rate pr carrier: 270,833 kbit/s Modulation: GMSK Spectrum efficiency: 1.35 bps/Hz
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Radio parameters:
MS:
Sensitivity: -104 (-102) dBm
Typical106 dBm
Max. output power: 33(30) dBm
Numbers in parenthesis for GSM-1800
BTS:
Sensitivity: -104 (-104) dBm
Typical:107 dBm
Max. output power: 43dBm
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Channels in GSM900
890 MHz
45 MHz
960 MHz935 MHz
200 kHz
MS transmit MS receive
41 2 3 4 1241231
8
234567
1
8
234567
1231241 2 3 4
915 MHz
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TDMA - principle
GSM uses TDMA within each carrier Each user occupies the entire carrier one time slot pr. time frame
8 slots per frame
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GSM Channel structure
Logical channels builtup of physical channels Control channels
Traffic channels
Logical channelsdivided between: Dedicated channels
Common channels
25 MHz
124 carriers
577 sBurst period Time slot 1
Time slot 2
..
Time slot 8
= 4.615 ms
=Physical
channel
TDMA frame
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GSM traffic channels
Traffic channels (TCH) are used to carry voice or data
Typically uses one time slot per frame
Gross data rate per TCH: 22 kbps
Effective data rate lower because of forward error correction
Training
sequence
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
BP0 BP1 BP2 BP3 BP4 BP5 BP6 BP7
3 57 1 26 1 57 3 8.25
26 frame length: 120 ms
TDMA frame length: 4.6 ms
Data bitData bit
Normal burst
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Some GSM control channels
BCCH Broadcast Control CHannel Continuously transmitted from the BTS. Containsinformation about cell identity, frequency etc.
FCCH
SCH
Frequency Correction CHannel / Synchronisation CHannel Used to
correct/synchronise the frequency (FCCH) + time synchronise to the frame
structure. Each cell has a FCCH and a SCH
RACH Random Access CHannel Used by the mobile to send a request to thenetwork for access. This is a slotted Aloha channel, no pre-allocation possible
AGCH Access Grant CHannel Used by the network to inform the mobile that accesshas been granted and information about which channel to use
PCH Paging CHannel Used by the network to notify users about incoming calls.
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GSM Channels
Traffic Channels (TCH)
Control Channels (CCH)
Common Control Channels (CCCH)
Paging Channel (PCH): Used by the BTS to inform the MS
about an incoming call. Broadcast channel. Random Access Channel (RACH): Used by the MS for call
establishment. Shared by all MS in cell. Slotted-ALOHArandom access.
Access Grant Channel (AGCH): Used to indicate the slot
assignment.
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GSM Channels
Control Channels (CCH)
Dedicated Control Channels (DCCH): Used to controlindividual MS
Standalone Dedicated Control Channel (SDCCH) :Two-way channel assigned to each MS for keeping
track of movement and call establishment. Certainslots periodically. About 2Kbps per MS.
Slow Associated Control Channel (SACCH): Two-waychannel assigned to a TCH or SDCCH. Used to reportparameters, such as signal power, to maintain the link.
Fast Associated Control Channel (FACCH) : Two-waychannel used to support fast transitions when SACCHis not adequate. FACCH steals the TCH.
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GSM Channels
Control Channels (CCH)
Broadcast Channels (BCH). Used to broadcastinformation to the MSs in the cell
Frequency Correction Channel (FCCH) and
Synchronization Channel (SCH): Keep the MSsynchronized
Broadcast Control Channel (BCCH): providesinformation such as cell ID, available services, Can also be used to keep track of signal
strength for handoff
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GSM Call Flow (Simplified) When the MS wishes to make a phone call
1. User enters the phone number and presses the send button.
2. To set up the phone call, the MS needs to send information to the MSC. TheMS sends Radio Resource Channel Request to the associated BSS on theRandom Access Channel (RACH) according to ALOHA The phone then waitsto hear from the BSS at the Access Grant Channel (AGCH).
3. The BSS allocates a Traffic Channel (TCH), including the frequency and time
slot, and broadcast it in the AGCH. It also contains information about timeand frequency corrections.
4. The MS applies the corrections and tune to the assigned TCH.
5. MSC checks whether the MS is authenticated.
6. The BSS enables ciphering with the phone. At this step the connection hasbeen set up between the MS and MSC. The BSS just forwards the message.
7. The MS sends a connection set up request to the MSC with the called phone
number. The MSC connects to the PSTN and allocates the voicecommunication channel between the BSS.
8. Make the conversation.
9. User presses the end button. The MSC releases the voice channel with theBSS. The MSC informs the PTSN about the call release and the PTSN will informthe call has been released on its end. MSC informs the MS then releases theTCH.
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39
Public switched
telephone
network
mobile
user
home
Mobile
Switching
Center
HLR homenetwork
visited
network
correspondent
Mobile
Switching
Center
VLR
GSM: indirect routing to mobile
1 call routed
to home network
2
home MSC consults HLR,
gets roaming number of
mobile in visited network
3
home MSC sets up 2nd leg of call
to MSC in visited network
4
MSC in visited network completes
call through base station to mobile
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Handoff goal: route call vianew base station (withoutinterruption)
reasons for handoff:
stronger signal to/from newBSS (continuing connectivity,less battery drain)
load balance: free upchannel in current BSS
GSM doesnt mandate why to
perform handoff (policy), onlyhow (mechanism)
handoff initiated by old BSS
Mobile
Switching
Center
VLR
old BSSnew BSS
old
routing
new
routing
GSM: handoff with common MSC
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41
Mobile
Switching
Center
VLR
old BSS
1
3
24
5 6
78
GSM: handoff with common MSC
new BSS
1. old BSS informs MSC of impending handoff,provides list of 1+ new BSSs
2. MSC sets up path (allocates resources) to
new BSS
3. new BSS allocates radio channel for use by
mobile4. new BSS signals MSC, old BSS: ready
5. old BSS tells mobile: perform handoff to
new BSS
6. mobile, new BSS signal to activate new
channel
7. mobile signals via new BSS to MSC: handoff
complete. MSC reroutes call
8 MSC-old-BSS resources released
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General Packet Radio Service
(GPRS) General Packet Radio Service
Supports data service.
Use the same physical link between the network and the MS
An MS maybe assigned with 1 or multiple time slots in achannel
The number of time slot in uplink and downlink may bedifferent
Special network infrastructure added to support data traffic
Serving GRPS Supporting Node (SGSN): a router serves agroup of BSCs. Send and receive packets from the MS.
Gateway GRPS Supporting Node (GGSN): interface tothe Internet. Maintains routing information related to theMS, such that given an IP packet, it knows which SGSN toforward to.
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GRPSMultiple Access
Users are assigned frequency channels and
time slots. Packets are constant length, determined
by the GSM slot.
Downlink: first come first served
Uplink: Slotted ALOHA for reserving,dynamic TDMA for data transmission
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Thank You