11520957-GSM-basic

2

GSM Foundation Course

• Course Content Basic Telephony & Cellular

Principal of Cellular Communication

GSM Features

GSM Network Components

GSM Terrestrial Interfaces

Basic GSM Processes

GSM Air Interface

Radio Interface Optimization, Supplementary services &

Contemporary Networks

3

ESSAR Telecom

• Telecom Service Provisions– GSM – Basic– Internet

• ESSAR– GSM Service Provider in Punjab, Delhi,

Rajasthan, U.P (East) & Haryana– Basic Service Provider in the state of Punjab.

4

Service Industry

• Service Provider is not a Equipment

Manufacturer.

• The Service Provider has a license to operate in a

geographical boundary (state/circle/ country).

• It buys equipment from OEM Suppliers (Vendors).

• Installs & commissions the equipment thus

making it’s own Network.

• Provides the desired service to it’s subscribers.

ESSAR CELLPHONE

Punjab

Haryana

U.P (East)Rajasthan

Delhi

Coverage Area

6

ORGANISATION STRUCTURE

PROMOTERS

TECHNICAL PLANNING

IMPLEMENTATION

OPERATIONS

OPERATIONS SYSTEM SUPPORT

BILLING

IT

ACTIVATIONS

MARKETING

CUSTOMER CARESALES

SUPPORT FUNCTIONS

HR, ADMIN, ACCOUNTS

7

Basic Telephony

•Off Hook

•Dial Tone

•Dialing Digits

•RBT

•Conversation

•Ring

•Off Hook & Conversation

•Signaling•Traffic

SWITCH / EXCHANGE

8

2 Mb E1 (PCM)

Sample Rate 8 kHz8 bits per sample

64 kbps

1

31

16

0

300 - 3400 Hz

E1 b

i t s tream

1st TCH

17th TS

30thTCH

15th TCH

9

Wireless Telephony

BSC

BTS BTS

Mobile Subscriber...

MSC

10

Wireless Communication

• Alternative means of wireless communication

– Walkie - Talkie– Pagers– Trunked private radios

• Mobile Phone - the magic technology that enables everyone to communicate anywhere with anybody.

12

Cellular Communication

• A cellular system links Mobile subscribers to Public

Telephone System or to another Mobile subscribers.

• It removes the fixed wiring used in a traditional

telephone installation.

• Mobile subscriber is able to move around, perhaps

can travel in a vehicle or on foot & still make & receive

call.

13

Advantage of Cellular Communication

• Mobility

• Flexibility

• Convergence

• Greater QOS

• Network Expansion

• Revenue/Profit

WHAT IS CELLULAR TELEPHONY ?

CONSIDERATIONS -

FREQUENCY

SUBSCRIBER DENSITY

COVERAGE

Base Station

Base Station

Base Station

Base StationBase Station

Base Station

15

The Cell

• Cellular Radio involves dividing a large service area

into regions called “cells.”

• Each cell has the equipment to switch, transmit and

receive calls.

• Cells - Reduce the need of High powered transmission

• Cells - Conventionally regarded as being hexagonal,

but in reality they are irregularly shaped.

• Cell shape is determined by the nature of the

surrounding area e.g. Hills , tall building etc.

The CELL

What is a cell ?

A cell is a certain area that can be reached with one transceiver

or A small collection of

transceivers on different channels at a single base site.

The hexagonal-shaped communication cells are artificial & are generated to simplify the planning & design of a cellular network.

BTS

17

Coverage & Capacity

• Coverage

– Percentage of the geographical area covered by cellular service where mobile telephony is available

• Capacity -

– Number of calls that can be handled in a certain area within a certain period of time.

– Capacity can also refer to the probability that users will be denied access to a system due to the simple unavailability of radio channels.

18

Cells

19

Cell Size

• Large Cells

• 35 Km

• Remote Areas

• High Transmission

Power

• Few subscribers

• Small Cells

• Near about 1 KM

• Urban Areas

• Low Transmission

Power

• Many Subscribers

20

MICRO CELL

Below Rooftop~ Railway Platforms, Airports,~ Busy Shopping Bazaar etc.

Low Tx Power~ 1 Watt max.

Limited Coverage~ 200m - 500m

Hotspot Solution

Special Algorithms for HO

21

PICO CELLS

Pico Cell

Inside offices, Buildings

Very Low Tx Power~ Less than 1 Watt

Limited Coverage~ 50 -100m

Capacity Solution

Special Algorithms for HO

22

Analog Mobile Telephony

• End of 1980’s Analog Systems unable to

meet continuing demands

– Severely confined spectrum allocations

– Interference in multipath fading environment

– Incompatibility among various analog systems

– Inability to substantially reduce the cost of

mobile terminals and infrastructure required

23

Digital Mobile Telephony

• Spectrum space - most limited and precious

resource

• Solution - further multiplex traffic (time

domain)

• Can be realized with Digital Techniques only.

24

Different Standards Worldwide

• Till 1982 Cellular Systems were exclusively

Analog Radio Technology.

• Advanced Mobile Phone Service (AMPS)

– U.S. standard on the 800 MHz Band

• Total Access Communication System (TACS)

– U.K. standard on 900 MHz band

• Nordic Mobile Telephone System (NMT)

– Scandinavian standard on the 450 & 900 MHz

band

25

GSM History and Organization

• 1979 Europe wide frequency band reserved for Cellular

• 1982 “Groupe Speciale Mobile” created within CEPT

• 1986 GSM had full time in Paris

• 1988 ETSI takes over GSM Committee

• 1990 The phase 1 GSM Recommendations frozen

• 1991 GSM Committee renamed “Special Mobile Group” and GSM renamed as “ Global System for Mobile Communication”

• 1992 GSM is launched for commercial operations

26

GSM - IN CELLULAR TELEPHONY

• Each Cell in the Cellular Network consists of one or more RF carriers.

• An RF carrier is a pair of radio frequencies– One used in upward direction by MS - Uplink– Other used in downward direction by BTS -

Downlink– The transmit and receive frequencies are

separated by a gap of 45 MHz in GSM of 75 MHz in DCS.

• There are 124 carries in GSM Band. With each carrier carrying 7 timeslots, only 124 x 7 = 868 calls can be made!

• Frequency Reuse is the solution

27

Uplink-Downlink

Downlink = 935 to 960 MHz

Uplink = 890 to 915 MHz

BTS Tx MS Rx

BTS Rx MS Tx

dl

ul

28

Frequency & ARFCNu

l= 8

90 t

o 9

15 M

Hz

dl=

935

to

960

MH

z

Ful(n) = 890.0 + (0.2) *n MHz

Fdl(n) = Ful + 45 MHz

where n =ARFCN ; 1 n 124

29

TDMA F

RAME n

+10 7

3

0

5

01

2

0 7

3

0

5

01

2

4.61

5 m

S

TDMA F

RAME n

T D M

A

TDMA & FDMA

F D M A200KHz

Uplink - MS Tx890MHz to 915MHz

Downlink - BTS Tx935MHz to 960MHz

30

GSM Burst & TDMA Frame

0 1 2 3 4 5 6 7 2 4 5 6 730 1

FRAME 1 FRAME 2

Training sequenceInformation Information

GUARD PERIOD GUARD PERIOD

TAIL BITS TAIL BITS

31

Frequency Reuse Pattern

Three types of frequency reuse patterns

• 7 Cell reuse pattern

• 4 cell reuse pattern

• 3 cell reuse pattern

32

Cell Dia = R

FREQUENCY RE - USE

– Frequency Re-use

7/21 cell cluster

1

2

3

45

6

7

Two re-use distances

D D/R = (3N)1/2

where N is Cluster size

33

Principal Of Sectorization

• Omni Directional Cells• 120 degree Sectors • 60 Degree sectors

– Each Sector in a Site has its own allocation of Radio Carriers.

• Advantage

– By frequent reuse of frequency more capacity can be achieved.

34

a1a2

a3a3

a4a6

a5

Cell Sectorisation

OMNI CELL

1 ANTENNA

b1

b2

b3

120O CELLS

3 ANTENNAS

60O CELLS

6 ANTENNAS

35

3 Site Reuse Pattern

c2

c1

c3

a1

a2

a3

b1

b2

b3

c1c2

c3Cell Re-use

36

Cellular 1Planning Steps

– Cellular Topology • Cell splitting & Cell Repeat Patterns

3 cluster site 3/9 cell cluster 4 cluster site 4/12 cell cluster

Sites in the middle

37

GSM Antennas

• Directional Antennas

• Vertically Polarized.

• Collinear Dipole Array with

8 to 12 elements.

• Beam Width 45o, 60o, 90o.

• High Gain Antennas with

gain of 16 to 18 dbi.

• Mechanically/Electrically

Downtiltable.

39

Features of GSM

• Compatibility

• Noise Robust

• Increased Capacity & Flexibility

• Use of Standard Open Interfaces

• Improved Security & Confidentiality

• Cleaner Handovers

• Subscriber Identification

• ISDN Compatibility

• Enhanced Range of Services

40

Compatibility

• With rapid Developments there was a need for a common Standard for Mobile Communication.

• With GSM, one could drive from Germany to Spain without a Call Drop.

• Due to versatility of GSM, it was adopted by many countries, even outside Europe.

41

Noise Robust

• To combat the problems due to Noise-

Digital Interface is used.

• Digital Interface

– Protect these errors using Error Detection & Correction Techniques.

– Immune to higher levels of noise and interference

– Improvements in Quality as well as Efficiency- Robust Air Interface.

42

Increased Capacity and Flexibility

• Analogue Air Interface

– Every connection requires a

separate RF carrier and thus

RF hardware.

– System Expansion

• Time Consuming

• Costly & Labor Intensive.

• Intricate RF Planning.

• Digital Interface

– 8 simultaneous conversations

on one RF carrier.

43

Standardized Open Interfaces

• Low Price

– Uses standard interfaces like C7, X.25 etc.

Versatility to choose equipment from different

manufacturer thereby reducing the pricing

monopoly.

• Flexibility

– Great flexibility in situating Network

components because of Standard Interfaces.

– Efficient use of terrestrial links.

44

Better Security & Confidentiality

• High Security risk for

Analogue System operators.

• GSM

– No Eavesdropping

– High speech and data

confidentiality.

– Digitized, Encoded and

Encrypted (A8 algorithm)

– Subscriber Authentication

(A3 algorithm)

45

Cleaner Handovers

• The mobile measures up to 32 adjacent cells for

– Signal Strength (RxLevel)

– Signal Quality (RxQual)

– updated every 480 mS and sends to BTS

• Sophisticated Handover based on

– RxLevel

– Interference

– RxQual

– Timing Advance

– Power Budget

46

Base Station 2

Base Station 3

Base Station 1

Handovers

47

ISDN Compatibility

• ISDN (Integrated Services Digital Network)

– Advanced Telecom Network designed to carry

voice and user data over the standard

telephones lines.

• 2B+D Signalling and information on ISDN line.

• The GSM Network is designed to operate within

the ISDN System.

• GSM provides features compatible with ISDN.

50

GSM NETWORK ELEMENTS

PSTNEC

MSC

HLR

AUC

VLR

EIRIWF

TRAU BSC

BTS

Network Switching System

BSS

SIM

ME

MS

51

GSM Network Components

• Mobile Station consists of two parts-

– Mobile Equipment (ME)

– Subscriber Identity Module (SIM)

• ME

– Hardware e.g. Telephone, Fax Machine,

Computer.

• SIM

– Smart Card which plugs into the ME. NETCOMP

52

Mobile Equipment (ME)

• ME are of three types-

– Vehicle Mounted

– Portable Mobile Unit

– Handportable Unit

• ME’s have distinct features-Classmarks sent in

initial message to Network.

NETCOMP

53

ME (Classmark Information)

• Revision Level

– Phase of the GSM specs ME comply with.

• RF Power Capability

– Max power ME is able to Transmit.

• Ciphering Algorithm Used

– Presently A5

– Phase 2 specifies Algorithms A5/0 to A5/7.

• Frequency Capability

• SMS CapabilityNETCOMP

54

Typical Settings

Mobile Equipment

Class Power O/p

1 20 W

2 8 W

3 5 W

4 2 W

5 0.8 W

NETCOMP

55

SIM

Subscriber Interface Identity Module

The SIM stores

– Subscriber Parameters

– Personal Data for identifying

Subscriber to the Network.

– IMSI,, MSISDN, PIN, PUK, Ki,

A3, A8 (for Kc generation)

– Space reserved for TMSI & LAI

--------------

--------------

Small SIM

Full Size SIM Card

--------------

--------------

NETCOMP

56

SIM - Internal Structure

CPU

EEPROM

RAM

ROM

I/O8

User Data 16 kB

Basic Operating System16 to 24 kB

Working Area for CPU256 to 512 bytes

NETCOMP

57

SIM(IMSI)

• IMSI(International Mobile Subscriber Identity)

– Transmitted over Air Interface on initialization

– Permanently stored on SIM card

– 15 digit Decimal

MCC (3) MNC (2) MSIC (10)

NETCOMP

58

• LAI (Location Area Identity)

– MCC 3 digit number (BCD), two Octets ( A & B)

– MNC 2 digit number (BCD), one Octet

– LAC 3 digit number (Binary) , two Octets

0-65535

– CI 5 digit number (Binary) , two Octets

0-65535

SIM (LAI)

LACMCC MNC CI

NETCOMP

59

SIM

• MSISDN – 10 digit number to which a subscriber is being

called.• PIN (Personal Identification Number)

– Four digit PIN– An internal security to Protect the SIM from

illegal use.– Card blocks itself after three wrong entries

• PUK (Personal Unblocking Key)– 8 digit code to unblock the SIM Card

• Ki (Authentication Key), A3 & A8 AlgorithmsNETCOMP

60

SIM (TMSI)

• Temporary Mobile Subscriber Identity

– Periodically changed by the System Management on instances like location update etc.

• Reason for use of TMSI

– To prevent a possible intruder from identifying GSM users, TMSI is used

• Management

– Assignment, Administration & Updating is performed by VLR.

NETCOMP

61

Transcoder

• Converts 64 Kbps PCM circuits from MSC to 16

Kbps BSS circuits.

• Each 30 channel 2 Mbps PCM link can carry 120

GSM - specified voice channels.

NETCOMP

62

Transcoder

MSC BSS

XCDR120 GSM TCH

1 2 3 4

Transcoder Information from FOUR calls (4x16 KBPS put into ONE 64 KBPS timeslot

30 Channel PCM

1234

NETCOMP

64

Base Station System (BSS)

• BSS (Base Station System)– BSC (Base Site Controller)– BTS (Base Transceiver Station)– XCDR (Transcoder)

Network Switching System (NSS)

XCDR

BSC

BTSNETCOMP

BTS

65

Base Station System (BSS)

• BSC– Controls upto 40 BTS– Conveys information to/from BTS– Connects terrestrial circuits & Air Interface

Channels– Controls handovers between BTSs under itself

• BTS– Contains RF Hardware– Limited control functionality– 1 - 6 carriers in a BTS Cabinet– 7 - 48 simultaneous calls per BTS

NETCOMP

BTS

66

A BTS Cabinet

OUTER VIEWINNER VIEWNETCOMP

67

BSS Configuration

• Collocated BTS

• Remote BTS

• Daisy Chain BTS

• Star Configuration

• Loop Configuration

NETCOMP

BTS

68

Daisy Chain Configuration

BSC

BTS

BTS

BTS NETCOMP

All B

TS

on

1 E1

69

Star Configuration

BSC

BTS

BTS BTS

BTS

NETCOMP

70

Loop Configuration

BSC

BTS

BTS BTS

BTS

Loop Configuration

NETCOMP

71

Network Switching System(NSS)

• NSS (Network Switching System)

– MSC (Mobile Switching Centre)

– HLR (Home Location Register)

– VLR (Visitor Location Register)

– EIR (Equipment Identity Register)

– AUC (Authentication Centre)

– IWF (Interworking Function)

– EC (Echo Canceller) NETCOMP

MSC

72

MOBILE SWITCHING CENTRE

NETCOMP

73

GSM Network Component

• MSC

– Call Switching

– Operation & Management Support

– Internetwork Interworking

– Collects call billing data

• Gateway MSC

– MSC which provides interface between PSTN & BSS’s in the GSM Network.

NETCOMP

74

Home Location Register (HLR)

• Reference database for the Subscriber profiles-

– Subscriber ID (IMSI & MSISDN)

– Current VLR Address

– Supplementary Services subscribed

– Supplementary Service Information

– Subscriber Status (Registered/deregistered)

– Authentication Key and AUC functionality

– TMSI

– MSRN NETCOMP

75

Visitor Location Register (VLR)

• Temporary Data, which exists as long as the subscriber is active in a particular Coverage area.

• Contains the following-

– Mobile Status (Busy/ Free/ No Answer/etc.)

– Location Area Identity (LAI)

– TMSI

– MSRN (Mobile Station Roaming Number)

NETCOMP

76

Equipment Identity Register (EIR)

• Contains Database for validating IMEI

– White List (valid ME)

– Black List (Stolen ME)

– Grey List (Faulty ME)

NETCOMP

77

• Provides function to enable the GSM System to interface with Public/Private Data Networks.

• The basic feature of the IWF are – Rate Conversion

– Protocol adaptation

• IWF incorporates Modem Bank.

e.g. GSM DTE PSTN DTE

IWF Analogue Modem

Inter Working Function

NETCOMP

78

Echo Canceller

• Echo is apparent only in Mobile - Land conversation & is generated at the 2 wire to 4 wire interface.

• To avoid it, Echo Canceller (EC) is used.

– Echo is irritating to MS Subscriber

– Total Round Trip delay of 180 ms in the GSM system

– EC is placed on the PSTN side of the Switch

– Cancellation up to 68 ms with ECNETCOMP

79

Operation & Maintenance Centre

• Event & Alarm Management

• Fault Management

• Performance Management

• Configuration Management

• Security Management

o The OMC has access to the (G)MSC, BSC.

o Handles error messages being reported from the Network

o Controls the traffic load of the BSC, and the BTS.

Operation & Maintenance Centre

o NETWORK MANAGEMENT CENTRE (NMC)– Offers Hierarchical Regionalised Network

Management of a complete GSM system.

• Functionality of the NMC

• Monitors Nodes on the Network

• Monitors Network Element Statistics

• Monitors OMC regions & provides

information to OMC staff

• Enables Long Term Planning for

entire Network

NETWORK MANAGEMENT CENTRE

MMI RAM>

MMI RAM>

MMI RAM>

NMC

OMC OMC

OMC

REGION 2 REGION 3

REGION 1

NETWORK

NETWORK MANAGEMENT CENTRE

83

GSM Terrestrial Interfaces

Broadly classified into two types of interfaces-

• Standard Interfaces

– 2 Mbps Trunks (E1)

– Signalling System No. 7 SS7 ( CCS7)

– X.25 (Packet Switched Mode)

• GSM Interfaces

84

GSM Interfaces

• Um MS - BTS

• Abis BTS - BSC

• A BSC - MSC

• B MSC - VLR

• C MSC - HLR

• D VLR - HLR

• E MSC - MSC

• F MSC - EIR

• G VLR - VLR

• H HLR - AUC

87

Basic Processes

• AUTHENTICATION

• CIPHERING

• REGISTRATION

• CALL ESTABLISHMENT

• HANDOVER / HANDOFF

• ROAMING

88

AUTHENTICATION ALGORITHM

NSS

MS

HLR

AUC

AUTH.ALGORITHMS

A3

SIM

MS

AUTH.ALGORITHMS

A3

Ki

RAND

RAND

COMPARE

SRES

SRES

Ki

AIR INTERFACE

89

Ciphering

• Data protection is required on air interface.

• A5 algorithm is used.• A specific key called Ciphering Key (Kc), is

generated from RAND and A8 algorithm. • A8 is on the SIM.

A8

RANDKi

Kc

90

Ciphering

A5Data

Kc

Ciphered

Data A5

Kc

Data

ROAMING

MSC

ME

ME

PSTN

MSC

VLR

HLR

INDIA

UK

o The mobile roams to another country (UK) and requests a

Location Update when switched ‘ON’.

o The VLR (UK) informs the home HLR (India) of the mobile’s

new location (UK).

o The HLR updates its location information and sends the

subscriber information to the VLR (UK).

o The HLR requests the subscriber information be removed

from the VLR (India).

o The VLR (India) acknowledges, and removes the subscriber

information from its database.

o After the mobile’s registration is completed in UK’s MSC/VLR,

the mobile is able to use network services (MOC, MTC etc.)

ROAMING

93

Transmission Media

• Access Network

– Microwave 15 /23 GHz

• Backbone Network

– Microwave 7 GHz

– Optical Fibers

– Leased Line( From Dot or any other

service provider on any media)

94

Access Microwave ( 15 GHz)

• 14.250 to 14.500 MHz and

14.400 to 15.350 MHz

• 4 QAM & 16 QAM Modulation

• Split Mount Version with Hot

Standby Facility

• Bandwidth ranging from 1.25

MHz to 28 MHz depending

upon Data Rate and

Modulation type

• 4 E1 Radio with 3 spot

frequencies in our case

95

Backbone Microwave (7 GHz)

• 7.125 to 7.850 MHz and 7.725

to 8.500 MHz

• 4 QAM & 16 QAM Modulation

• Split Mount Version with hot

standby facility

• Bandwidth ranging from 1.25

MHz to 28 MHz depending

upon Data Rate and

Modulation type

• 16 E1 Radio with 1 spot

frequencies in our case

96

Optical Fiber

• Low Losses 0.5 dB/km & High Data Rates

• Types of Fiber– Step Index– Graded Index

# Graded Index are better.

Modes of Light in fiber

– Mono Mode

– Multi Mode

# Mono Mode has less losses than Multi Mode.

97

Optical Fiber

Different Possible Combinations Mono Mode Step Index 10 / 125 m

Mono Mode Graded index

Multi Mode Step Index 100 / 300 m

Multi Mode Graded Index 75 / 130 m Mono Mode Graded Index would have been

the best but fabrication not possible

140 Mbps OLTE , Mono Mode Step Index in our case

99

Channels On Air Interface

• Physical Channel • Logical Channel

• Physical Channel

– Physical channel is the medium over which the information is carried.

• Logical Channel

– Logical channels consists of the information carried over the Physical Channel.

100

TDMA F

RAME n

+10 7

3

0

5

01

2

0 7

3

0

5

01

2

4.61

5 m

S

TDMA F

RAME n

T D M

A

TDMA & FDMA

F D M A200KHz

Uplink - MS Tx890MHz to 915MHz

Downlink - BTS Tx935MHz to 960MHz

101

LOGICAL CHANNELS

0 1 2 3 4 5 6 7

3

57 encrypted

57 encrypted

26 training

1S

1S

3T

8.25GP

3T

577S

577S x 8 = 4.615mS

TDMA Frame

Normal Burst

26 Frame Multi-frame

102

BURST

• Time is divided into discrete periods

called “Timeslots”

• The Time Slots are arranged in a sequence

, conventionally numbered 0 to 7.

• Each repetition of this sequence is called

a TDMA Frame.

• The information content carried in one

time slot is called a “burst”.

103

BURST

• Information– Main Area where the Speech, Data or Control info

is held • Guard Period

– To enable the burst to hit the time slot (0.031ms)• Stealing Flags

– 2 bits are set when TCH is to stolen by a FACCH• Training Sequence

– For estimation of transfer characteristics of physical media

• Tail Bits– Used to indicate beginning and end of the burst.

104

Five Types of Burst

• Normal BurstTraffic & Control Channels Bi-directional

• Frequency Correction Burst

FCCH Downlink

• Synchronization Burst

SCH Downlink

• Dummy Burst

BCCH Carrier Downlink

• Access Burst

RACH Uplink

105

GSM Logical Channels

• TCH

– SACCH

– FACCH

• Control Channels

– BCCH

– CCCH

– ACCH

– DCCH

106

LOGICAL CHANNELS

TDMA Frame

26 Frame Multi-frame

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

107

Frames & Multiframes

• Several Logical channels share one time slot.

• Individual channels are sequenced, & each

channel gets the time it requires.

• Sequence is carried out using Multiframes.

– Traffic Channel occupy a 26-frame multiframe

(120 ms)

– Control Channel occupy a 51-frame multiframe

(235 ms).

108

Traffic Channels - TCH

TCH

TCH

TCH / FS 9.6

DATA

TCH / HS

4.8

2.4

FACCHSAACH

109

BCCH Channel

CCH

BCCH

BCCHSynchronizing Channels

FCHSCH

Broadcast Control Channel - Downlink only

110


• BCCH

– Transmitted at all times & conveys information about Cell Timing and Configuration

• BCCH, FCCH, SCH

• CCCH

– Used by BSS & MS when trying to initiate a connection over the air

• RACH, PCH, AGCH, CBCH

111


• DCCH

– Used to convey signaling information during call setup

• SDCCH

• ACCH

– Used to transmit signaling information when a call is in progress

• FACCH & SACCH

112


• ACCH

– SAACH

• Conveys Power Control & Timing

Information in the downlink direction.

• RSSI and Quality reports in the uplink

direction.

– FACCH

• To carry out user authentication and handovers. It steals the TCH burst and inserts its own information.

113


• Acronyms

– BCCH Broadcast Control Channel

– CCCH Common Control Channel

– DCCH Dedicated Control Channel

– ACCH Associated Control Channel

– SDCCH Standalone Dedicated Control Channel

– RACH Random Access Channel

– PCH Paging Channel

– AGCH Access Grant Channel

114


• BCCH– Location Area Identity

– List of neighbouring cells, to be monitored

– List of frequencies used in the cell

– Cell Identity

– Power Control Indicator

– DTX permitted

– Access Control (e.g emergency calls, call

barring)

115


– Always transmitted at constant power at all

times

– Dummy burst are sent to ensure continuity

when no traffic information is sent.

• FCCH– Mobile corrects the frequency of its internal

time base by reading this logical channel.

– Easily detected by the mobile.

– After FCCH, mobile is able to detect SCH

which contains timing information.

116


• SCH– Carries the information for mobile to

synchronize to the TDMA frame structure &

know the timing of the individual timeslots.

– Frame Number & BSIC (Base Station Identity

Code)

• CCCH– RACH

• Transmitted by the Mobile when it wishes to

gain access to the system

117


– PCH

• Transmitted by the BTS when it wishes to

contact a specific mobile.

– AGCH

• Transmitted by the BTS to assign dedicated

resources to an MS such as SDCCH

– CBCH

• To transmit messages to all mobiles within

a cell. CBCH will steal some time of an

SDCCH to do this.

118

Channel Combinations

• Full rate Traffic Channel Combination

– TCH8/FACCH + SACCH

• Broadcast Channel Combination

– BCCH + CCCH

• Dedicated Channel Combination

– SDCCH8 + SACCH8

• Combined Channel Combination

– BCCH + CCCH + SDCCH4 + SACCH4

119

Channel Combinations (Timeslots)

– Traffic Channel Combination• TCH8/FACCH +SACCH

• Can be on any Time slot

– Broadcast Channel Combination• BCCH +CCCH

• Can be on Timeslot 0, 2, 4, 6

– Dedicated Channel Combination• SDCCH8 + SACCH8• Any Time slot

– Combined Channel Combination• BCCH + CCCH +SDCCH4 + SACCH4• Can only be on 0 Timeslot

120

TCH Multiframe

0 5 10

SACCH

15 20

IDLE

Downlink & Uplink SACCH

121

BCCH/CCCH Multiframe

• BCCH/CCCH

– In Downlink direction the timeslot (physical

channel) is shared by a different logical

channels.

– In the Uplink direction all timeslots are

allocated to RACH.

122

BCCH/CCCH Multiframe

10 20 30 40 50

Downlink to MS

Uplink from MS

0 10 20 30 40 50

FS FS FS FS S IFCCCH8 TS

CCCH4 TS

BCCH CCCH8 TS

CCCH8 TS

CCCH8 TS

RR RRRRRR RR RR RR RR RR RRRR RR RR RRRRR RRR RR R R RR RR RRRR R RRRR

0

123

Combined Multiframe

– BCCH and SDCCH share a common timeslot

• Less No. of subscribers support (as only 4

SDCCH)

• 102 frame structure

• Superframes And Hyperframes

• 1326 TDMA frames (26*51) make a superframe

• 2048 superframes make one hyperframe, after

which ciphering and frequency hopping

algorithm are restarted.

124

Combined Multiframe

0 10 20 30 40 50

F

F

S

S

BCCH F

F

S

S FS FS

S

S A2

A0 A1

A3

I

I

F

FCCCH8 TS

F S FSCCCH8 TS

CCCH

4 TS

CCCH

4 TS

BCCH D2

D2 D3

D3

D0 D1

D0 D1

0 10 20 30 40

D3 R

R

R

R A2 A3D3

A0 A1 R

R

R

R D2

D2R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

D0 D1

D1D0

50

Downlink to MS

Uplink from MS

125

SDCCH Multiframe

0 10 20 30 40 50

I

I

Downlink to MS

Uplink from MS

I

I

I

I

D0 D1 D2 D3 D4 D5 D6 D7 A0 A1 A2 A3

D0 D1 D2 D3 D4 D5 D6 D7 A4 A5 A6 A7

0 10 20 30 40 50

I

I

I

I

I

I

D0 D1 D2 D3 D4 D5 D6 D7A1 A2 A3 A0

D0 D1 D2 D3 D4 D5 D6 D7A5 A6 A7 A4

126

Block - 1 : 1, 5, 9 ….. Samples

Block - 2 : 2, 6, 10, …… Samples

& so on for Block - 3 & Block - 4.

Voice Coding

LPC

RPE

Divid

ed in

to 4 B

locks

of 40 S

amp

les each

LTP

Class Ia Class Ib Class II

50 bits 132 bits 78 bits

20 mS Sample Rate 8 kHz

13 bits per Sample160 Samples

2080 bits

104 kbps

Reduction in DataSpeech Encoder selects Blockwith Most Energy

127

Channel Coding

• Error Protection And Detection– To protect the logical channel from

transmission errors by the radio path, different coding schemes are used.

• Coding & Interleaving Schemes dependent upon logical channel to be encoded.

• 3 Coding Protection schemes– Speech Channel Encoding– Control Channel Encoding– Data Channel Encoding

128

Speech Channel Coding

• Speech Information of 20 ms block is divided

over 8 GSM burst.

• 260 bits are grouped in three classes depending

upon the intelligible part of speech

• After encoding 456 bits block is interleaved

129

Speech Channel Coding

ParityCheck

456 bits

Class 1b 132 bits

Class 1a 50 bits

Class 2 78 bits

50 1323 4

Convolutional Code

378 78

Tail Bits

378 78

Convolutional Coding

130

Control Channel Encoding

• Control Channel Encoding– Block of 184 bits received by BTS– Bits are protected by Cyclic Codes of Class

Fire Codes– Adds 40 Parity Bits– 4 Tail Bits are added– Convolution Coding is done

• O/p from 184 Signalling bits is 456 bits.

131

Control Channel Coding

184

Coding

184 40 Parity Bits


456

456 bits

4TB

132

Data Channel Coding

240

184


488

4

Punctuate

456

133

Interleaving

• Responsible for Robustness of the GSM air interface

• 10 -20 % burst destroyed or corrupted on the air interface.

• Spreads the content of one information block across several TDMA timeslots.

• Two types of Interleaving -

– Diagonal Interleaving

– Rectangular Interleaving

134

DIAGONAL INTERLEAVINGSPEECH

Speech Blocks

456 bits

EIGHT blocks of 57 bits,Sent on 8 ALTERNATE timeslots

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

456 bits

135

RECTANGULAR INTERLEAVINGCONTROL CHANNEL

Data Blocks

456 bits

114Bits Odd

114Bits Odd

114Bits Even

114Bits Even

FOUR blocks of 114 bits,Sent on 4 timeslots

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

136

Interleaving

• Interleaving Depths– Speech - 8 blocks– Control - 4 blocks– Data - 22 blocks

• Speech & Data blocks are diagonally interleaved• Control block is rectagularly interleaved

137

Interleaving

TRAU Frame Type

Data

Control

Speech

Number of GSM Burst Spread Over

22

4

8

TRAU = Transcoder Rate Adaption Unit

140

MOBILE TO LAND

MSC

BSC

BTS

PSTN

141

Multiple Point of Interconnect

BSS TRAFFIC

POI TRAFFIC

BSS TRAFIC POI TRAFIC

7 GHz BACKBONE

CITY A

CITY B

142

Call Scenarios

• Mobile to Mobile

– Intra-city

– Inter-city

• Mobile to Land

– Intra-city

– Inter-city

• Land to Mobile

– Intra-city

– Inter-city

143

Mobile To Land Sequence

1

3

CHANNEL REQUEST

DCCH ASSIGN

SIGNALLING LINKESTABLISHED

REQUEST FOR SERVICE

SET CIPHER MODE

SET-UP

EQUIPMENT ID REQUEST

AUTHENTICATION

MS BSS MSC VLR HLR PSTN EIR

RACH

AGCH

SDCCH

SDCCH

Call Info7

4

6

5

2CR

CC

144

8 COMPLELTE CALL

CALL PROCEEDING

9 ASSIGNMENT COMMAND

INITIAL & FINAL ADDRESS (IFAM)

ASSIGNMENT COMPLETE (ACM)

10

ANSWER(ANS)

11

CONNECT ACKNOWLEDGE

SDCCH

SDCCH

ASSIGNMENT COMPLELTE

MS HEARS RINGTONEFROM LAND PHONE

ALTERING

RING TONESTOPS

CONNECT

(channel)

(TCH)

FACCH

FACCH

FACCH

TCH

(circuit)

FAACH

BILLING STARTS

Hello!

MS BSS MSC VLR HLR PSTN EIR

145

Land to Mobile Sequence

Initial & Final Address Msg. (IFAM)

Send Routing Information

Routing Information Ack

INITIAL & FINAL ADDRESS (IFAM)

Send Info for I/c Call Setup

Channel Request

Signalling Link Established

MSISDN

Paging Request

PAGE

DCCH Assign

PCH

AGCH

SDCCH

IMSI

MS BSS MSC VLR HLR GMSC PSTN

MSISDN

MSRN

MSRN

MSRN

TMSI

LAI &TMSI

TMSIRACH

Page ResponseSDCCH

TMSITMSI &

status

Status

146

Land to Mobile Sequence

Complete Call

SETUP

CALL Confirmation

ADDRESS COMPLETE

Assignment Command

Ring Tone at MS

Alert

Assignment Complete

Connect

TMSI

MS BSS MSC VLR HLR GMSC PSTN

SDCCH

SDCCH

TCH

FACCH

Connect ACK

<SDCCH>

Channel Circuit

FACCH

Subscriber Picks Up

FACCH

ANSWER TCH

BILLING STARTS

FACCH

Ringing Stops at Land Phone

RingTone at Land Phone

Hello

147

Mobile Initiated Call Clearing

1 DISCONNECT

PSTN RELEASE

MOBILE RELEASE

2 PSTN RELEASECOMPLETE

MS BSS MSC VLR HLR PSTNFACCH

FACCH

MOBILE RELEASE COMPLETE

3 CLEAR COMMAND

CHANNEL RELEASE

5 RLSD

4

UA

CLEAR COMPLETE

DISC

RELEASE COMPLETE

FACCH

FACCH

MS -MSC SignallingReleased

FACCH

FACCH

148

Inter-BSS Handover Sequence

1

3

Periodic MeasurementReports

Handover Required

Handover Request

Handover Req Ack

Information Interchange

Handover Complete

Clear Command

Handover Command

MS BSS BSS MSC HLR PSTN

SAACH

7

4

6

5

2 TMSI Cct. Code

HO ref No.

HO Ref No.

FACCH

FACCH

Periodic Measurements Reports

SAACH

8

9

150

Radio Interface Optimization

• Transmission Timing

• Power Control

• VAD and DTX

• Multipath Fading

• Equalization

• Diversity

• Frequency Hopping

151

THREE TIMESLOT OFFSET

0 1 2 3 4 5 6 7

0 1 2 3 4 5 6 7

Mobile Rx

Mobile Tx3 TS Offset

152

TIMING ADVANCE

6 70 1 2 3 4 5 6 7

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5

BURST arrivesLATE

BURST arrivesIN TIME

BURST sent early

T = 3.69S to 233S

Cell Radius = 35km

153

Power Control

Cell Radius = 35km

•In steps of 2dB

•Enhances Battery Life

•Reduces Interference13 dBm (min)

33 dBm (max)

154

Dis-Continuos Transmission

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

VAD - Voice Activity Detection

•MS identifies presence/ absence of speech

•Generates Comfort noise

DTX - Dis-Continuous Transmission

•MS does not TX during silence period

155

MULTI-PATH PROPAGATION

156

DIVERSITY

Approx. 10 Wavelengths3.3 meters

Diversity Receiver

157

FREQUENCY HOPPING

F0

F2

F3

F4

FN

F1

T I M E

FR

EQ

UE

NC

Y

158

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5

FREQUENCY HOPPINGMobile Activity

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

Mobile Rx

MONITORING Other Cell

6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5

Mobile Tx

Rx1

Rx2

Tx1

Tx2

160

Speech Services

• Telephony (13 kbps full rate)

• Emergency Call (with/without SIM card in the Mobile Station)

• Short Message Services (SMS)

• Point to Point (128 Byte Max.)

• Cell Broadcast(75 bytes Max.)

• Dual Personal and Business Numbers.

– Allows calls to be made and billed, either to business or personal numbers.

161

Data Services (Bearer Services)

• Data rates supported as of today are

– 2.4 Kbps

– 4.8 Kbps

– 9.6 Kbps

162

Supplementary Service - Call Waiting

Call in Progress

PSTN Phone

Another Mobile Calls. Kept Waiting ……...

163

Supplementary Services - Call Hold

1. Call in Progress

2. Put on Hold

3. Calls another Mobile

164

Supplementary Services - Call Forwarding

Incoming Call

Voice MailSystem

PSTNPhone

AnotherMobile

Divert if

•All Calls

•Busy

•Not Reachable

•No Answer

165

Supplementary Services

• Calling Line Identification– Present– Absent

• Connect Line Identification

– Present

– Absent

• Closed User Group - CUG

– Only incoming

– Only outgoing

• Operator Controlled Barring

166

Voice Mail System

ANSWERING MACHINE

167

Voice Mail System

MSC

168

Short Message Service

SMSC

MSC

BTS

169

Short Message Service

SMSC

MSC

BTS

Point to Multipoint

Point to Point

170

PRE - PAID SYSTEM

• SIM BASED– Data on SIM– Decrements with use– Over the air charging !!??

• NETWORK BASED

– Data secure on with the network– Over the air re-charging– Features

• Inquiry• Warnings …..

172

SEPARATE GSM & WLL INFRASTRUCTER

DUAL BAND / MODEHANDEST

MSC GSM BSC

GSM BTS

PSTN FIXED LINE SWITCH CDMA BSC

CDMA BTS

CDMA BTS

GSM BTS

173

SEPARATE GSM & WLL INFRASTRUCTER

GSM + CDMA

GSM GSM

CDMA

Call Drop.Toggle to GSM

Still on GSM.Toggle to WLL

GSM

On WLL


GSMCoverage

CDMACoverage

Every individual is a WLL subscriber under any and only one CDMA BTS and is a regular subscriber for the rest of the GSM network in the whole of Punjab.The subscriber also has the advantage of roaming within & outside the country.

174

COMMON GSM & CDMA INFRASTRUCTER


MSC

GSM BSCGSM BTS

PSTN

CDMA BSC CDMA BTS

A - INTERFACE

A - INTERFACE

175

IRRIDIUM

• BTS in the Sky– LEO ~1400km– Inter Satellite Links - 22.55GHz to 23.55GHz– L-Band (1616MHz to 1626.5 MHz)– Band Width - 10.5MHz– Use TDM/FDMA scheme– World-Wide Coverage

• 60+ Now Operational• Small Hand held terminals• Dual Mobiles under development

11520957-GSM-basic

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