Concept of GSM

8/11/2019 Concept of GSM

1/11

A. Steffen / H. Weibel, 30.6.2000, KSy_GSM.ppt 1

Zrcher

Hochschule

Winterthur

Kommunikationssysteme (KSy) - Block 12

Global System for

Mobile Communications

Global System for

Mobile Communications

Dr. Andreas Steffen

Hans Weibel

2000 Zrcher Hochschule Winterthur

R


Zrcher

Hochschule

WinterthurGSM Mobile Communications

Overview

Part I GSM Basics & GSM Circuit-Switched Voice/Data

Properties of Wireless Channels

GSM Network Elements and Topology

GSM Radio Interface

Physical and Logical Channels for Circuit-Switched Voice/Data

Full Rate and Half Rate Traffic Channels

Channel Coding of Voice Connections

Evolution of GSM (HSCSD / GPRS / EDGE)

Part II GSM Packet-Switched Data & UMTS

Physical and Logical Channels for Packet-Switched Data (GPRS)

GPRS Random Access Protocol (Uplink State Flag USF)

3rd Generation Partnership Project (3GPP / IMT-2000)

Universal Mobile Telecommunications System (UMTS)

Frequency Bands / Deployment Schedule

Technology

Services


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Multipath Propagation / Fading

Wavelength @ 900 MHz: 30 cm

direct path

(line-of-sight)

reflections


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Special Properties of Wireless Channels

Multipath propagation due to reflections

Desireable, if line-of-sight between transmitter and receiver is

not available (urban areas / buildings)

Annoying, since it causes fading (local signal cancellation).

Frequency hopping improves the situation for stationary MS

Large delay spreads cause inter-symbol interference (ISI)

Channel estimation by periodic transmissions of a training

sequence is the basis of optimum channel equalization

Bit Errors are not randomly distributed

Errors often occur in bursts of several consecutive bits

The raw uncorrected bit error ratio (BER) is around 10-2... 10-3

Channel coding based on forward error correction (FEC)

Achieves a satisfactory BER after correction in the range

of 10-5... 10-6


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B = 200 kHz

B

B

B

B

Guard Band

f

fN

fk

f2

f1

0

Radio

Frequency

Channels

Guard Band fL

fU

Frequency

Band

...

GSM Mobile Communications

Combined FDMA / CDMA Scheme

t

...0 1 2 ... 7 0 1

...0 1 2 ... 7 0 1

...0 1 2 ... 7 0 1

...0 1 2 ... 7 0 1

Time Slots

Frame

T

T 577 s


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The GSM 900 MHz Frequency Band

860 870 880 890 900 910 920 930 940 950 960 970

25 MHz25 MHz

10 10

4 4

P-GSM

E-GSM

R-GSM

*)

*) several other Systems:- Cordless Telephone CT1, CT1+, CT2

- Telemetry / Telecommand

- Terrestrial Trunked Radio (TETRA)

- Digital Satellite System Receiver (DSSR)

Uplink Downlink

Duplex Distance 45 MHz


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The GSM 1800, DECT and UMTS Bands

1700 1750 1800 1850 1900 1950 200 2050 2100 2150 2200 2250

75 MHz

UMTS

GSM 1800

DECT

1: Time Division Duplex (TDD)

2: Frequency Division Duplex (FDD)

3: Mobile Satellite System (MSS)

Uplink Downlink

Duplex Distance

95 MHz

75 MHz

1 2 3 1 2 3


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Winterthur

f2

f1...0 1 2 ... 7 0 1

...0 1 2 ... 7 0 1

GSM Radio Interface UmBursts

156.25 Bits in 576.923 s(3.6923 s/Bit)

useful part

Power p(t)

t

8.25 Bits Guard Period

26 Training Bits

2 x 58 Encrypted Bits

3 Tail Bits 3 Tail Bits


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WinterthurGSM Radio Interface UmMapping of Traffic Channels (TCH)

T T A IT T T T T T TT T T

TCH / F : one full rate traffic channel

20 ms 20 ms 20 ms 20 ms 20 ms 20 ms

T Traffic Channel (TCH)

A Slow Associated Control Channel (SACCH)

I Idle Frame

T T T T TT T T T T T T

T T A at T t T t T tt T t T T t T tt T t T t T t

t

a

TCH / H : two half rate traffic channels

TCH Multiframe = 26 TDMA frames in 120 ms


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WinterthurGSM Radio Interface UmEnhanced Full Rate Voice Channel Coding

every

20 ms

78 182

78 182

3 bit CRC

4 tail bits

78 189 189

160 Samples

260 bits

267 bits

456 bits

4 blocks

@ 114 Bits

RPE-LPC

Codec

Block

Coding

Convolutional

Coding

Inter-

leaving

sensitive (class I)

insensitive (class II)

1 2 3 8

Encryption

456 bits spread

over 8 bursts


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WinterthurGSM Radio Interface UmTraffic Channels (TCH)

Full Rate Traffic Channel (TCH / F) Speech Codec

Speech @ 13 kbps (TCH / FS) Full Rate Speech @ 12.2 kbps (TCH / EFS) Enhanced Full Rate

Data @ 14.4 kbps (TCH / F14.4)




Half Rate Traffic Channel (TCH / H) Speech Codec

Speech @ 6.5 kbps (TCH / HS) Half Rate

Data @ 4.8 kbps (TCH / H4.8) Data @ 2.4 kbps (TCH / H2.4)

Traffic Channels are used for bidirectional transmission of

circuit switched voice or data.


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WinterthurGSM Radio Interface UmAdaptive Multi Rate Speech Codec (AMR)

Adaptive Multi Rate Speech Channel (TCH / AFS)

Speech @ 12.2 kbps 244 bits (TCH / AFS 12.2)








Adaptive tradeoff between speech quality (compression ratio)

and strength of error protection/correction depending on the

current state of the radio channel. AMR offers a family of eight

codecs with speech rates in the range 4.75 .. 12.2 kbps.


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Winterthur

1993 1996 1998 1999 2000 2002

Evolu

tiono

fmob

ileda

taservice

s

Fax/

Data /SMS 9.6 kbit/s

Fax/

Data /SMS 9.6 kbit/s

GSM Evolution

Data Services

Datacom-

pression(2.5

9.6 kbit/s

Datacom-

pression(2.5

9.6 kbit/s

Mobileinternetaccess

Mobileinternetaccess

HSCSD

28.8 kbit/s(+ data

compression)

GPRS pilot

system

HSCSD

28.8 kbit/s(+ data

compression)

GPRS pilotsystem

GPRS

(8 - 92 kbit/sper

subscriber+

datacompression)

GPRS

(8 - 92 kbit/sper

subscriber+

datacompression)

UMTS

(8 - 2000 kbit/sper

subscriber+

datacompression)

UMTS

(8 - 2000 kbit/sper

subscriber+

datacompression)


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WinterthurGeneral Packet Radio Service (GPRS)

System Architecture and Interfaces

MS

GGSNGGSNBSCBSCBTSBTS

Um

SGSNSGSN

MS-SIM

HLRVLR

EIR

Internet

GiGnGb

SGSN Serving GPRS Support Node

GGSN Gateway GPRS Support Node

Gf Gs Gr

D

Gc

Traffic

Signalling

MSC

GGSNGGSN

GGSNGGSNGp

Other

GPRS

Network


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Protocol Stack

IPv4 or IPv6

Um GbMSGn GiBSS SGSN GGSN

PHY

Data Link

Layer

IP

TCP/UDP

GTP

PPP

IP

PHY

Data Link

Layer

IP

TCP/UDP

PHY

Network

Service

BSSGP

LLC

GTPSNDCP

PHY

Network

Service

BSSGP

PLL

RFL

MAC

RLC

PLL

RFL

MAC

RLC

LLC

SNDCP

PPP

IP


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Protocol Stack

GPRS Tunneling Protocol (GTP)

zur Vernetzung von GSNs (auch zwischen verschiedenen

PLMNs) auf einem herkmmlichen IP-Netz

Subnetwork Dependent Convergence Protocol (SNDCP)

Multiplex of several layer 3 connections onto a LLC link

Compression of header information and payload data

Logical Link Control (LLC)

Highly reliable HDLC-type connection between MS and BSS

Radio Link Control (RLC)

Wireless transmission of data blocks, repetition of faulty blocks

Medium Access Control (MAC)

Slotted Aloha random access to the radio channel Physical Link Layer (PLL) und Physical RF Layer (RFL)

Channel coding (FEC), Interleaving, Modulation


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Logical Channels

Packet

Control

Channels

Packet Data

Traffic Channels

(PDTCH)

Packet

Dedicated

Control

Channels

Packet Timing Advance Control Channel (PTCCH)Packet Associated Control Channel (PACCH)

Packet

Common

Control

Channels

Packet Paging Channel (PPCH)

Packet Random Access Channel (PRACH)

Packet Access Grant Channel (PAGCH)

Packet Notification Channel (PNCH)

Packet Broadcast Control Channels (PBCCH)

Downlink (DL)

Uplink (UL)


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Mapping of Packet Data Channels (PDCH)

B0

60 ms 60 ms 60 ms 60 ms

Radio Block

T Packet Timing Advance Control Channel (PTCCH)

I Idle Frame

T

PDCH Multiframe = 52 TDMA frames in 240 ms

B1 B2 B3 IB4 B5 B6 TB7 B8 B9 IB10 B11

Bx


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Radio BlockCoding Schemes

GPRS Coding Schemes

CS-1 9.05 kbps

CS-2 13.4 kbps

CS-3 15.6 kbps

CS-4 21.4 kbps

EGPRS Coding Schemes (EDGE)

MCS-1 8.8 kbps

MCS-2 11.2 kbps

MCS-3 14.8 kbps

MCS-4 17.6 kbps

The multislot capability of GPRS allows the bundling of 2-3

slots fr simple MS and up to 8 slots for special GPRS MS.

MCS-5 22.4 kbps

MCS-6 29.6 kbps

MCS-7 44.8 kbps

MCS-8 54.4 kbps

MCS-9 59.2 kbps

GMSK 8-PSK


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Quality of Service (QoS)

Reliability Classes

Class

1

2

3

Probability

of lost packet

10-9

10-4

10-2


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Quality of Service (QoS)

Delay Classes

Class

1

2

3

128 Byte Packet

Mean 95%

< 0.5 s

4

10-9< 1.5 s

1024 Byte Packet

Mean 95%

< 2 s 10-9< 7 s

< 5 s 10-9< 25 s < 15 s 10-9< 75 s

< 50 s 10-9< 250 s < 75 s 10-9< 375 s

best

effort

best

effort

best

effort

best

effort


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GPRS Attach

GPRS Detach

General Packet Radio Service (GPRS)

State Diagram of a GPRS Mobile Station

IDLEIDLE

READY timer expiry

or force to STANDBY

PDU transmission

READYREADY STANDBYSTANDBY

PagingRouting Area (RA)

Update Request


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Mobile Originated Packet Transfer

MS Network

Packet Channel RequestPRACH

Packet Uplink AssignmentPAGCH (assignment of TFI)

Packet Resource RequestPACCH (optional)

Packet Uplink AssignmentPACCH (optional)

USF with correct TFIPDTCH (downlink radio block)

Send Data Block

PDTCH (uplink radio block)

USF Uplink State Flag (3 bits)

TFI Temporary Flow Identifier

Documents

Concept of GSM