GSM Network - from an Operators View SWINOG Meeting 10th of April 2003, Bern [email protected] Swisscom Mobile AG, Engineering&Operations

GSM Network - from an Operators View

SWINOG Meeting 10th of April 2003, Bern

[email protected] Mobile AG, Engineering&Operations

Thema: Menü Ansicht, Master, Folien-Master

2Vorname, Name, Dateiname (Menü Ansicht, Kopf-und Fusszeile)tt. MMMM jjjj

Agenda

History

Network Architecture

Traffic Cases

Transmission Process and Air Interface

Cell Planning

The Operators Challenge

Network Evolution



History

Early 1800: Theory of Inductance (Faraday, Henry)

1906: Transmission of human voice over radio (Reginald Fessenden)

1935: Invention of frequency modulation (FM)

1947: Cellular Concept (D.H. Ring, Bell Labs)

1969: Standardization of the Nordic Mobile Telephone system

1981: First cellular system launched (NMT450; Ericsson)

1991: GSM standard launched

1993: Start of GSM rollout in Switzerland (Natel D)

2003: GSM networks have similar importance as fixed PSTN’s



Fessenden’s Radio Tower (1906) vs. GSM Base Station (2003)



Network Architecture



GSM / GPRS Network

GMSCGMSC

GGSNGGSN

HLRHLR

EIREIR

AUCAUC

SCFSCF

SMS-IWMSC

SMS-IWMSC

CN ExternalNetworks

D

Gd,Gp,Gn+

SGSNSGSN

MSCMSC

E,G

SMS-GMSC

SMS-GMSC

SGSNSGSN

MSCMSC

Gb

SMS-SC

ISDNPSTNPSPDNCSPDNPDN:-Intranet-Extranet-Internet

Iu

ANUE

BSCBTSUmSIMSIM MTMT Abis A

BSS

Note:Not all interfaces are shown and named

F

Gf

Gr

Gn+

H



HLR / AUC: Subscribers

HLRHLR AUCAUC



GMSCGMSC

HLRHLR

EIREIR

AUCAUC

SCFSCF

SMS-IWMSC

SMS-IWMSC

CN ExternalNetworks

MSCMSC

SMS-GMSC

SMS-GMSC

MSCMSC

SMS-SC

ISDNPSTN

MSC/VLR, Core Network



Base Station SystemANUE

BSCBTSUmSIMSIM MTMT Abis

BSS GMSCGMSC

HLRHLR

EIREIR

AUCAUC

SCFSCF

SMS-IWMSC

SMS-IWMSC

CN ExternalNetworks

MSCMSC

SMS-GMSC

SMS-GMSC

MSCMSC

SMS-SC

ISDNPSTN



GPRS in addition

GMSCGMSC

GGSNGGSN

HLRHLR

EIREIR

AUCAUC

SCFSCF

SMS-IWMSC

SMS-IWMSC

CN ExternalNetworks

D

Gd,Gp,Gn+

SGSNSGSN

MSCMSC

E,G

SMS-GMSC

SMS-GMSC

SGSNSGSN

MSCMSC

Gb

SMS-SC


Iu

ANUE


BSS


F

Gf

Gr

Gn+

H



Good Coverage requires high number of Sites and Cells

Area Coverage 83%Population Coverage 99,5%Area Coverage 83%Population Coverage 99,5%



Train Coverage (Intrain Repeater)

Following coaches are or will beequipped: ICN 2000, IC2000, EW 4



MS - Hardware (User Equipment)

Mandatory Display of called

number DTMF tones Indication of call

progress PLMN indication /

selection IMSI / IMEI Algorithms SMS handling Emergency calls

Optional Keypad Key + Datacom

interface ...

Additional Last numbers list Voice dialling ...



Security Features (Authentication, Ciphering)

Forbidden PLMN BCCH Information (Neighbor Frequencies)

IMSI (International Mobile Subscriber Identity)

LAI (Location Area Identity)

PIN (Personal Identification Number)

PUK Personal Phonebook SIM Service Table (Optional Services)

SIM CARD

SIM Card - The Subscriber



Traffic Cases



Key Terms

Idle Mode

Active Mode

Detached

Roaming

Handover

Registration (Location Update)

Paging

Idle Mode

Active Mode

Detached

Roaming

Handover

Registration (Location Update)

Paging



Location Updating

9805057

BSC/TRC MSC

4.

3.

2.

1.2.

3.

4.

HLR

VLR

1-new LAI detected by MS 2-Authentication 3-LA update request to VLR4-VLR stores LAI & sends LA update acknowledge to MS

“Keep the network informed on the actual location of each MS”



9600877

Evaluationand decision

about handover

Measurements from RBS and MS

RBS measures:Signal strength andtransmission qualityon TCH, uplink

MS measures:Signal strength andtransmission qualityon TCH, downlink

Signal strengthfrom neighboringBTS

Measurementreports from MSare sent to RBS

BSC/TRC

MSC/TRC

Measurements sent to BSC

“Keep in touch with the network”



9600878

old

new

BSC

2.

6.

1.

5.

3.

4.

5.

2.

Handover: Cells controlled by the same BSC

1-BSC activates call channel in new BTS

2-BSC informs MS on new freq via old BTS

3-MS sends handshake on new frequency

4-New BTS answers

5-MS sends HO complete via new BTS

6-Old BTS is released

“Do not drop the call when moving”



PSTN/PSTN/ISDNISDN

BTSBTS

BTSBTS

BTSBTS

MSCMSC

HLHLRR

VLVLRRBSCBSC

BSCBSC

PSTN/PSTN/ISDNISDN

BTSBTS

BTSBTS

BTSBTS

MSCMSC

HLHLRR

VLVLRRBSCBSC

BSCBSC

1. Status of the mobile is stored in the HLR of the home network 2. If switched on in a foreign country it searches for an allowed GSM network3. The foreign VLR asks for a copy of the subscription info in the HLR of the home network4. The VLR registers the CH mobile as a visitor and updates the status of the mobile to idle The data is stored temporarely in the foreign VLR 5. In case of a PSTN call (CH) the foreign VLR checks the status of the CH mobile6. If the mobile is switched on, the PSTN call is routed to the foreign GSM network

International Call



Transmission Process and Air Interface



Transmission ProcessBSC SPP RRX

ReceiverDemodulator

ReceiverDemodulator

270 kBit/s, for 8TS

ViterbiEqualizer

ViterbiEqualizer

DeCiphering

DeCiphering

De interleaving

De interleaving

ViterbiDecoder

ViterbiDecoder

SpeechDecoder

SpeechDecoder

A/D SpeechCoding

SpeechCoding

Segmentation

Segmentation

160 Sample20 ms

8 kHz,13 Bit104 kbit/s

ChannelCoding

ChannelCoding

50 Hz, 260 Bits 13 kBit/s

Interleaving

Interleaving

50 Hz, 456 Bits22,8 kBit/s

CipheringCiphering BurstFormatting

BurstFormatting

ModulatorTransmitter

ModulatorTransmitter

33,8 kBit/s, for 1TS

Mobile Station



GSM FrequenciesExample: 900MHz Band

• Separate bands for transmit and receive direction (duplex spacing)• 124 carriers with 8 TDMA channels each• Neighbor channel spacing is 200 kHz• Time separation of transmission and reception signal allows for

simpler RF front end in the mobile station (TDMA)• Frequency resources must be shared between the national

operators

Duplex spacing



Multiple Access Methods

FDMA TDMA W-CDMA

Frequency

Time

Power

Frequency

Time

Power

Frequency

Time

Power

GSM is a combination of FDMA and TDMA

1 user per freq several users per freq all users per freq



Packing Voice Calls into Time Slots

Frequency

Time

Power

Cal

l 1 Cal

l 3 Cal

l 1

Cal

l 2

Cal

l 1

Frequency

Time

Power

Cal

l 1 Cal

l 3 Cal

l 1

Cal

l 2

Frequency

Time

Power

Cal

l 1 Cal

l 3 Cal

l 1

Cal

l 2

Carrier 1 Carrier 2 Carrier 3



Time Slot and Bit Rate

•Timeslot = window in time in which a portion of bits are transported over the air interface from the transmitter to the receiver

•The length of the time slot (577s) allows to send approximately 160 bits, this is called a „Burst“

•1 bit length is 3.7s

•During a connection the burst is repeated 217x per second

•Based on the modulation type of GSM a gross bit rate of 271 kbps per carrier is achieved



TDMA Frame

Carrier with 8 Time Slots,8 Physical Channels

0 1 2 3 4 5 6 7

0 1 2 3 4 5 6 7Uplink

Downlink

915 MHz

960 MHz

4.615 mS0.577 mS



Close to BTS

BTS

TDMA-frame

Far away from BTS

The Time Alignment Problem

TS6

TS7

TS7TS6TS5

•1 bit travels 1 km within 1 bit period (radio wave propagation)

•Far away user must send earlier to compensate for the higher time delay



Shadowing



Rayleigh Fading



Frequency selective Quality Degradation due toRayleigh Fading



The Antenna: A crucial Element for Radio Coverage and Performance



Example: Repeater Intrain Air Interface

Radiating Cable



Example: Intrain Repeater Air Interface

Antenna to/from intrain repeater



Cell Planning



The Cellular Principle

Why do we use cells?

•Traffic capacity

•Limited frequency resources (re-use)

•NIS electromagnetic radiation limitations

•User location



Cell Planning; Theoretical Cell PatternExample: 4/12 = 4 three-sector sites supporting 12 cellsB2B3

C1

C2C3

B1

B2B3

C1

C2C3

B1

B2B3

C1

C2C3

A1

A2A3

D3

D2D1

A1

A2A3

D3

D2D1

A1

A2A3

D3

C2C3

B1

B2B3

C1

C2C3

B1

B2B3

C1

C2C3

B1

B2B3

D3

D2D1

A1

A2A3

D3

D2D1

A1

A2A3

D3

D2D1

A1

B2B3

C1

C2C3

B1

B2B3

C1

C2C3

B1

B2B3

C1

C2C3

A1

A2A3

D3

D2D1

A1

A2A3

D3

D2D1

A1

A2A3

D3



Cell Planning: Real Cell Boarders



The Operators Challenge



The Operators Challenge; some Issues

•Customer Needs

•Service Creation

•Billing

•Interoperability (e.g. International Roaming)

•Public Relations (e.g. NIS)

•Technical Operations



Traffic: Week- and Daytime, but also Event dependant



Hot Spots Load/Overload according to Workday

Workday Sunday



Verify where the Traffic takes place



Managing the Mobility: Neighbor Relations



Operator Benchmarking: Focus on the relevant Issues



Example: Inbound Roaming



Building Permissions



Network Environment

Radiation Measurements

Calculation and preparation of NIS data for local authorities

Negotiations with all involved parties



Network Evolution



Evolution towards 3G

GMSCGMSC

GGSNGGSN

HLRHLR

EIREIR

AUCAUC

SCFSCF

SMS-IWMSC

SMS-IWMSC

CN ExternalNetworks

D

Iu

Gd,Gp,Gn+

SGSNSGSN

MSCMSC

E,G

SMS-GMSC

SMS-GMSC

SGSNSGSN

MSCMSC

Gb

SMS-SC


Iu

ANUE


BSS

RNCBSUu

Iur

USIMUSIM MEME

RNCBSUuUSIMUSIM MEME

Iub

Iub

Cu

Cu

RNS

RNS

UTRAN


F

Gf

Gr

Gn+

H



10 50 100 384 500 1’000 2’000 5’000

GSM CS9.6

UMTS local

Data rate (kbps)

Voice

HSCSD

GPRS

EDGE / EHSCSD

EDGE / EGPRS

UMTS wide area

E-Maildata base access, info services

telebanking, financial services

electronis newspaper, images, sound

teleshopping

video telephony

video conferencing

Mobile Services and Data Rates



Thank you for your attention!

Documents

GSM Network - from an Operators View SWINOG Meeting 10th of April 2003, Bern [email protected] Swisscom Mobile AG, Engineering&Operations