gsm&gprs fundamentals
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HUAWEI TECHNOLOGIES CO., LTD. Huawei ConfidentialHUAWEI TECHNOLOGIES CO., LTD.
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Huawei Confidential
Security Level:7/9/11
GSM/GPRSFundamentals
HUAWEI
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Chapter 1 GSM System Overview
Chapter 2 GSM Network Structure
Chapter 3 Channels on the Wireless Interface
Chapter 4 GPRS/EGPRS Fundamentals
Chapter 5 GSM/GPRS Procedure
Contents
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GSM system overview
q The GSM system is a frequency- and time-division cellular system, each physical channel ischaracterized by a carrier frequency and a timeslot number
q Cellular systems are designed to operate withgroups of low-power radios spread out over thegeographical service area. Each group of radiosserve MSs presently located near them. The areaserved by each group of radios is called a CELL
q Uplink and downlink signals for one user areassigned different frequencies, this kind oftechnique is called Frequency Division Duplex(FDD)
q Data for different users is conveyed in timeintervals called slots several slots make u a
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Cell Technique
q A certain radio coverage area formed by a set of
transceivers that connected to a set of antennas is called a
CELL.
q Macro Cell
mIn the beginning , High-Power BTSs are adopted to
provide services. The BTS covers a wider area , but its
frequency utilization is not efficient. So , it can only
provide a few channels for subscribers.
q Micro Cell
mLater the Low-Power BTS joins the system for getting a
better service area with high capacity . At the same
time it adopts the frequency reuse technique to
Macro Cell and Micro Cell
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Multiple Access Technique
q Multiple Access Technique allows many
subscribers to use the same
communication medium.
q There are three kinds of basic Multiple
Access Technique : FDMA , TDMA and
CDMA.
q GSM system adopt FDD-TDMA (FDMA and
TDMA together).
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FDMA
q FDMA uses different frequency
channels to accomplish
communication.
qThe whole frequency spectrumavailable is divided into many
individual channels (for
transmitting and
receiving) every channel can
support the traffic for one
subscriber or some control
information.
Frequency
Time
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TDMA
qTDMA accomplishes the
communication in different
timeslot.
q A carrier is divided into
channels based on time.
Different signals occupy
different timeslots in
certain sequence , that is ,many signals are
transmitted on the same
frequency in different time.
Time
Frequency
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GSM 900
Duplex Separation: 45MHzChannel Bandwidth: 200KHz
The Frequency Spectrum
Uplink
890 915 935 960MHz
Downlink
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Duplex Separation: 95MHzChannel Bandwidth: 200KHz
Base Station Receive
1710 1785 1805 1880MHz
Base Station Transmit
DCS 1800
The Frequency Spectrum
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Frequency Reuse
qThe frequency resource of mobile system is very
limited.
q The different Subscribers can use the same
frequency in different places.
q The quality of communication must be ensured.
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4 site X 3 cells reuse
1
8
9
210
46
5 37
11
12
R
Frequency Reuse
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Chapter 1 GSM System Overview
Chapter 2 GSM Network Structure
Chapter 3 Channels on the Wireless Interface
Chapter 4 GPRS/EGPRS Fundamentals
Chapter 5 GSM/GPRS Procedure
Contents
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OMC
HLR/AUC/EIR
SMC
MSC/VLR
BSC
MSCBT
S
MS
MS
BTS
BTS
MAP
A-bis
A
PSTN
ISDN
GSM Network Structure
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q The Base StationController BSC
q The Base Transceiver
Station BTS
BTS
BSCBSS
MSC
Base Station Subsystem BSS
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q Packet data
switching
qIntegrated intoBSC
q Provide Gb
interface
BTS
BSC/PCU
BSS
MSC
Packet Control Unit-----PCU
Click to edit Master text
Second level Third level Fourth level
Fifth level
GPRSBackbone
SGSN
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Mobile-service Switching Center MSCHome Location Register HLRVisitor Location Register VLREquipment Identity Register
EIRAuthentication Center AUC
AUCHLR
MSC/VLR
PSTN
NSS
EIROMC
BSS
The Network Switching System
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Chapter 1 GSM System Overview
Chapter 2 GSM Network Structure
Chapter 3 Channels on the Wireless Interface
Chapter 4 GPRS/EGPRS Fundamentals
Chapter 5 GSM/GPRS Procedure
Contents
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2 30 16 74 52 3
The physical channel is the medium over whichthe information is carried: 200KHz and 0.577ms
0 1
TDMA FRAME
Timeslot The information carried in one timeslot is called a burst
Physical Channel and Logical Channel
The logical channel consists of the informationcarried over the physical channels
TDMA FRAME
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Two types of Logical Channel
Traffic Channel (TCH) :
Transmits traffic information, includedata and speech.
Control Channel (CCH) :
Or Signaling Channel, transmits all
kinds of control information.
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Traffic Channel (TCH)
TCHTraffic Channels
TCH Traffic ChannelTCH/FS Full rate SpeechChannelTCH/HS Half rate SpeechChannelTCH/9.6 Data Channel9.6kb/s
TCH/4.8 Data Channel4.8kb/s
Speech
TCH/FS TCH/HS
Data
TCH/9.6 TCH/2.4
TCH/4.8
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FCCHSCH
CCH (Control Channels)
DCCH
SDCCH
BCH
BCCH Synch. CH.ACCH
SACCHFACCH CCCH
RACH CBCH
PCH/AGCH
Broadcast Control Channel BCCHCommon Control Channel CCCHDedicated Control Channel
Control Channel (CCH)
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Allocate signaling channel
FCCH
SCH
BCCH
PCH
RACH
AGCH
SDCCH
SDCCH
TCH
FACCH
Power-off
Idle mode
Dedicated mode
Idle mode
How to use these channels?
Search for frequency correction burst
Search for synchronous burst
Extract system information
Monitor paging message
Send access burst
Set up the call
Allocate voice channel
Conversation
Release the call
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GSM Logical Channel Combination
Main BCCH combination FCCH + SCH + BCCH +
CCCH
SDCCH combination SDCCH/8 + SACCH/8
Combined BCCH BCCH + CCCH +SDCCH/4 +
SACCH/4
TCH/FR combination TCH/F + FACCH/F + SACCH/F
TCH/HR combination TCH/H + FACCH/H + SACCH/H
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TDMA Frames
0 1
0 1 2 43 46 47 48 5049
51 Frame Multi-frames
0 1 10
CONTROL CHANNELS
2 3 4 5 6 7 2 3 5 764
GSM Multi-frames
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GSM Multi-frames
TDMA Frames
0 1
0 1 2 43 21 22 23 2524
26 Frame Multi-frames
0 1 10
TRAFFIC CHANNELS
2 3 4 5 6 7 2 3 5 764
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Chapter 1 GSM System Overview
Chapter 2 GSM Network Structure
Chapter 3 Channels on the Wireless Interface
Chapter 4 GPRS/EGPRS Fundamentals
Chapter 5 GSM/GPRS Procedure
Contents
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What is GPRS?
General Packet Radio Service
An end-to-end packet switched service on the basis of GSM
The maximum reuse of the existing GSM network
infrastructure
Providing efficient utilization of radio resources
Interaction with the existing GSM switched circuit system
Based on a standard open interface
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GPRS Structure and Network Interfaces
GPRSbackbone
network
SGSN
SGSNGGSNGn
IP interface
SS7 interface
BSS MSC SMS-GMSC
AUm
PDP network
(IP/X.25)
GiInternet
TE
MT
MS
HLR
Gs
Gr
Gd
Gc
Gb
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Data Transfer Plane
Application Application
IP/X25 IP/X25 IP/X25
SNDCP GTP
LLC LLC UDP/TCP UDP/TCP
RLC RLC (BSSGP) (BSSGP) IP IP
MAC MACFramerelay
Framerelay
L2 L2
L2 (MAC)
Physical
Layer
Physical
Layer
Physical
Layer
Physical
Layer
Physical
Layer
Physical
Layer
Physical
Layer
MS BSS SGSN GGSN
relay
relaySNDCP
GTP
Um Gb Gn Gi
MAC: Media Access Control
RLC: Radio Link Control
LLC: Logical Link Control
l BSSGP: BSS GPRS Protocol
l SNDCP: Sub-Network Dependency
Convergence Protocol
l GTP: GPRS Tunneling Protocol
MS BSS/SGSN Si li Pl
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MS-BSS/SGSN Signaling Plane
BSSGP
GMM/SM
LLC
RLC
MAC
GSM RF
GMM/SM
LLC
BSSGP
L1bisUm G
b
NetworkService
RLC
MAC
GSM RF L1bis
NetworkService
Relayrelay
Physical layer: radio coding and decoding, channelmultiplexing and mapping, radio link control and radiomeasurementRLC/MAC: media access and link control of radiointerface
LLC: Provision of a reliable logical link betweenMS andSGSN for data transfer. LLC protocol supportsacknowledgement and non-acknowledgement modes,and encryption and non-encryption modes.SNDCP: Lay 3 transfer protocol, atransition betweennetwork layer and subnet layer,segmentation/packaging andcompression/decompression of IP/X.25 subscriber dataGMM/SM: Layer 3 Signaling Protocol
L1bis: Physical Transport LayerNS: transmission of upper-layerBSSGPPDU, based on frame relay/IPBSSGP: Provision ofa connectionless link betweenBSS and SGSN for non-acknowledgementdata transfer on the transport platform. Transmission of QoS and routinginformation related to radio on the signalingplatform, paging request processing, andflow control of data transfer
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q Packet Data Channel (PDCH)
q Packet Data Traffic Channel and Packet Data Control Channel
q Packet Data Traffic Channel (PDTCH)
q Unidirectional traffic channel
q Packet Data Control Channel
q Packet Broadcast Control Channel (PBCCH)
q
Common Control Channel: PPCH, PRACH, PAGCH, PNCH
q Dedicated Control Channel: PACCH and PTCCH
Packet Data Logical Channel
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q Packet logic channels (PDCH) can be combined via the
following three modes
qMode 1: PBCCH+PCCCH+PDTCH+PACCH+PTCCH;
qMode 2: PCCCH+PDTCH+PACCH+PTCCH;
qMode 3: PDTCH+PACCH+PTCCH
q In case of small GPRS traffic, GPRS and circuit services use the
same BCCH and CCCH in the cell. In this case, only combination
mode 3 is needed in the cell
q With the increase of traffic, the packet public channel should
be configured in the cell. Channel combination mode 1 and mode
2 should be adopted
Combination of packet logic channel
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Radio-Packet Resource Allocation
q The basic unit of radio resource allocation and radio transmission is data
block.
q One PDCH can be used by multiple MSs; One MS can use multiple PDCHs
simultaneously.
B1 B2 B3 B4 B5 B6 B7 B8 B9 B10 B11B0
B1 B2 B3 B4 B5 B6 B7 B8 B9 B10 B11B0
B1 B2 B3 B4 B5 B6 B7 B8 B9 B10 B11B0
MS3MS2
TS 0
TS 1
TS 2
MS1
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qRouting Area: a subset of location area
qMobility Management Entities: SGSN, HLR, and MS
qGMM Status
qIdle: GMM context is not set up; MS is not reachable.
qStandby: GMM context is set up; MS can receive paging, but
cannot transfer data.
qReady: MS can transfer data.
Concept of Mobility Management
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GMM State Model
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What is EDGE?
EDGE: Enhanced Data Rates For GSM Evolution.
EDGE consists of EGPRS and ECSD.
EGPRS: Enhanced GPRS, applied in more and more GSM
networks. Introduce the 8PSK modulation mode, Adopt
MCS-1~9 encoding modes and Modifies RLC/MAC protocols
ECSD: Enhanced HSCSD, not applied
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qNew modulation method: 8PSK
qBit rate on physical layer is three times higher than GMSK.
qUnder poor radio conditions, likelihood of misinterpretation of
the 8PSK symbols is higher than GMSK.
qNew channel coding methods: MCS1~MCS9
qEach has different amount of error-correcting coding.
qShould be used with different modulation method.
EGPRS Enhancement strategy1
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Increasedcapacityandspectral efficiency
Data21.4Kvoicevoicevoice voice
Data21.4K
Data21.4K
voicevoicevoice voice
Standard GSM/GPRS Radio Interface
EDGE Radio Interface
voice voice
voice
Data59.2K
Data59.2K
Additional!
Higher Spectral Efficiency than GPRS
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8PSK Modulation Mode
Modulating
bits
D3i, d3i+1,
d3i+2
Symbol
parameter
l
(1,1,1) 0
(0,1,1) 1
(0,1,0) 2
(0,0,0) 3
(0,0,1) 4
(1,0,1) 5
(1,0,0) 6
(1,1,1) 7
qEDGE introduces 8PSK(8-phase shift keying)
qModulation mode, which expresses symbols bythe phase of the signal and the symbol has 8
types and each symbol is mapped to 3 bits.
Hence, EDGE data rate can reach 3 times GSM
data rate.
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qLink Adaptation
qLA can select appropriate MCS and modulation method
according to radio link quality.
qIf a packet is received incorrectly, it will be retransmitted.
qIncremental Redundancy
qIR uses higher MCS without consideration for the actual radio
link quality.
qIf a packet is received incorrectly, additional error-correcting
coding will be transmitted.
EGPRS Enhancement strategy 2
Li k Q lit C t l
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Link Quality Control
qLink Adaptation Scheme
Selects appropriate modulation and codingscheme according to link quality
For GPRS, retransmission with another CS isimpossible
For EGPRS, retransmission with another MCSis possible
qIncremental Redundancy Scheme
Information sent with little coding
If decoding succeeds, high bit rate isachieved
If decoding fails, additional coded bits aresent and combined with previous info in thereceiver
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Chapter 1 GSM System Overview
Chapter 2 GSM Network Structure
Chapter 3 Channels on the Wireless Interface
Chapter 4 GPRS/EGPRS Fundamentals
Chapter 5 GSM/GPRS Procedure
Contents
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GPRS GMM Procedure
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GPRS GMM Procedure
GPRS TBF Establishment
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GPRS TBF Establishment
qTBF Temporary Block Flow
qTFI Temporary Flow Identity
qUSF Uplink State Flag
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