data services in gsm - · pdf filelehrstuhl für informatik 4 kommunikation und verteilte...

Lehrstuhl für Informatik 4

Kommunikation und verteilte Systeme

38Chapter 3.4: Mobile Networks

Data Services in GSM

Data transmission in GSM with only 9.6 kBit/s• Advanced channel coding allows 14.4 kBit/s

• Still not enough for Internet access or even multimedia applications

Thus: UMTS as “3G network”: Integration of data and voice in one network• But: new network infrastructure, new software, new devices, …

• Development of other enhancements of GSM as interim solutions

“2.5G networks” as interim solution• HSCSD as software solution

• GPRS as hardware solution• EDGE as 3G solution in a 2G network




HSCSD

HSCSD (High-Speed Circuit Switched Data)• Put together several time slots for one AIUR (Air Interface User Rate, up to 57.6

kBit/s with 4 Slots of 14.4 kBit/s)• Symmetrical (2 time channels each for up- and downlink) and asymmetrical (3 + 1

channels) communication are supported

• Mainly software update for the realization of the putting together• Advantage: fast availability, continuous quality, simple

• Disadvantage: connection-oriented, 4 channels are blocked the whole time, signaling for several channels necessary

AIUR [kbit/s] TCH/F4.8 TCH/F9.6 TCH/F14.44.8 19.6 2 1

14.4 3 119.2 4 228.8 3 238.4 443.2 357.6 4




GPRS

� Needed infrastructure: GSN (GPRS Support Nodes) - GGSN and SGSN- GGSN (Gateway GSN): translation between GPRS und PDN (Packet Data

Network)- SGSN (Serving GSN): support of the MS (location, accounting, security)- GR (GPRS Register): Management of user addresses

GPRS (General Packet Radio Service)

• Packet-oriented transmission, usable also for multicast• Usage of up to 8 time slots of a TDMA frame on demand

• Usage of time slots only when data are available for sending (e.g. 50 kBit/s with short usage of 4 slots)

• Advantage: step towards UMTS, flexible

• Disadvantage: expensive because some new infrastructure is needed to handle the new transmission mechanism, wireless transmission becomes a bottleneck for high traffic amount




GPRS – Infrastructure Components

HLRGR VLR

PSTNISDNMSC GMSC

4

4

4 NSS

RSS

GPRS

EIRAUC

OSS

BSC

PCU

SGSNPDNGGSN

AUC: Authentication CenterBSC: Base Station ControllerEIR: Equipment Identity RegisterGMSC: Gateway Mobile Switching CenterHLR: Home Location RegisterMSC: Mobile Switching CenterVLR: Visitor Location Register

GGSN: Gateway GPRS Support NodeGR: GPRS RegisterPCU: Packet Control UnitSGSN: Serving GPRS Support Node




GPRS Data Rates [kBit/s]

171,2149,8128,410785,664,242,821,4CS-4

124,8109,293,67862,446,831,215,6CS-3

107,293,880,46753,640,226,813,4CS-2

72,463,3554,345,2536,227,1518,29,05CS-1

8 time slots

7 time slots

6 time slots

5 time slots

4 time slots

3 time slots

2 time slots

1 time slot

(error-)coding

CS-1 to CS-4: decreasing error protection

• Dynamic choice of coding

• Basing on measurements of signal quality (and the needed QoS)

• The user is assigned the highest possible data rate

Position

Data rate

CS-4

CS

-3

CS

-2

CS-1




Advantages of GPRS

“Always connected”• Long duration for connection establishment are eliminated

• Transmission of data on demand• Accounting by data volume, not by

connection duration

• Robust connection� Coding of data bases

on current signal quality

� Even the BSS checks the data correctness and initiates – if necessary – a transmission repeat




EDGE

EDGE (Enhanced Data Rates for GSM Evolution)

• Up to 384 kBit/s by enhanced modulation (8PSK instead of GMSK)• Transmission repeat:

Change of coding to adapt to the current channel quality

• Is build upon the existing GSM/GPRS system:

� New transceiver are needed (hardware upgrade in the BSS)

� Software-Upgrade BSS und BSC� New devices (8PSK)

� No changes in the core network!� Cheap alternative to UMTS?




UMTS und IMT-2000

Proposals for IMT-2000 (International Mobile Telecommunications) as world-wide standardized 3G communication system:

• UWC-136, cdma2000, WP-CDMA• UMTS (Universal Mobile Telecommunications System, ETSI)

UMTS• … bases on UTRA: Universal Terrestrial Radio Access

• Integration of different mobile, cordless and pager systems into only one radio access network supporting world-wide roaming

• Integration von voice, data, and multimedia data services

• Enhancement of GSM: higher data rates, enhanced service concept, global roaming• Data rates: 144 kBit/s up to 2 MBit/s

– min. 144 kBit/s rural (target: 384 kBit/s)– min. 384 kBit/s suburban (target: 512 kBit/s)– up to 2 MBit/s urban

• Compatibility to GSM, ATM, ISDN and IP




Frequencies for IMT-2000

IMT-2000

1850 1900 1950 2000 2050 2100 2150 2200 MHz

MSS↑ITU allocation IMT-2000

MSS↓

Europe

China

Japan

NorthAmerica

UTRAFDD ↑

UTRAFDD ↓

TDD

TDD

MSS↑

MSS↓

DECT

GSM1800

1850 1900 1950 2000 2050 2100 2150 2200 MHz

IMT-2000 MSS↑ IMT-2000

MSS↓

GSM1800

cdma2000W-CDMA

MSS↓

MSS↓

MSS↑

MSS↑

cdma2000W-CDMA

PHS

PCS rsv.

MSS: Mobile satellite servicesDECT: Digital Enhanced Cordless TelecommunicationsPHS: Personal Handyphone System PCS: Personal Communications Service (GSM1900)




IMT-2000 Family

IMT-DS(Direct Spread)

UTRA FDD(W-CDMA)

IMT-TC(Time Code)UTRA TDD(TD-CDMA);TD-SCDMA

IMT-MC(Multi Carrier)

cdma2000

IMT-SC(Single Carrier)

UWC-136(EDGE)

IMT-FT(Freq. Time)

DECT

GSMANSI-41(IS-634)

IP networkIMT-2000core networkITU-T

IMT-2000radio accessITU-R

Interface for networking

Flexible assignment of core network and radio access

Initial UMTS(Release99 with FDD)

UMTS ≠ UMTS …




Licensing of UMTS in Germany, 18.8.2000

Sum: 50,81 billion €

• UTRA-FDD: �Uplink 1920-1980 MHz�Downlink 2110-2170 MHz

�Duplex spacing 190 MHz � 12 channels, 5 MHz each

• UTRA-TDD:

� 1900-1920 MHz � 2010-2025 MHz

� 5 MHz channels

• Planned coverage: 25% of the population till 12/2003, 50% till 12/2005




UMTS Architektur (Release 99)

UTRANUE CN

IuUu

• UTRAN (UTRA Network)

� Cell level mobility� Comprises several Radio Network Subsystems (RNS)� Encapsulation of all radio specific tasks

• UE (User Equipment)

• CN (Core Network)� Handover between systems� Gateways to other systems

� Location management, if there is no dedicated connection between UE and UTRAN

� Usage of existing GSM/GPRS infrastructure, change to an IP-based core network?




UMTS Domains and Interfaces

USIMDomain

MobileEquipment

Domain

AccessNetworkDomain

ServingNetworkDomain

TransitNetworkDomain

HomeNetworkDomain

Cu Uu Iu

User Equipment Domain

Zu

Yu

Core Network Domain

Infrastructure Domain

• User Equipment Domain� Assigned to a single user in order to access UMTS services

• Infrastructure Domain� Shared among all users

� Offers UMTS services to all accepted users




UMTS Domains and Interfaces

• Universal Subscriber Identity Module (USIM)� Functions for encryption and authentication of users� Located on the SIM

• Mobile Equipment Domain� Functions for radio transmission � User interface for establishing/maintaining end-to-end connections

• Access Network Domain� Access network dependent functions

• Core Network Domain� Access network independent functions� Serving Network Domain

• Network currently responsible for communication� Home Network Domain

• Location and access network independent functions




Spreading and Scrambling of User Data

• Constant chipping rate of 3.84 million chip/s

• Different user data rates supported via different spreading factors� Higher data rate: less chips per bit and vice versa

• User separation via unique, quasi orthogonal scrambling codes

� Users are not separated via orthogonal spreading codes� Much simpler management of codes: each station can use the same

orthogonal spreading codes� Precise synchronization not necessary as the scrambling codes stay quasi-

orthogonaldata1 data2 data3

scramblingcode1

spr.code3

spr.code2

spr.code1

data4 data5

scramblingcode2

spr.code4

spr.code1

sender1 sender2




OSVF Coding

1

1,1

1,-1

1,1,1,1

1,1,-1,-1

X

X,X

X,-X 1,-1,1,-1

1,-1,-1,11,-1,-1,1,1,-1,-1,1

1,-1,-1,1,-1,1,1,-1

1,-1,1,-1,1,-1,1,-1

1,-1,1,-1,-1,1,-1,1

1,1,-1,-1,1,1,-1,-1

1,1,-1,-1,-1,-1,1,1

1,1,1,1,1,1,1,1

1,1,1,1,-1,-1,-1,-1

SF=1 SF=2 SF=4 SF=8

SF=n SF=2n

...

...

...

...

OSVF: Orthogonal Variable Spreading Factors• Simple generation of orthogonal chip sequences

• Thus: simple user management• Further simplification: codes are

only used within one station, no coordination between stations




UMTS FDD Frame Structure

W (Wideband)-CDMA• 1920-1980 MHz Uplink• 2110-2170 MHz Downlink• Chipping rate: 3,840 MChip/s

• Soft handover• QPSK

• Complex power control (1500 power control cycles/s)

• Spreading factor: UL: 4-256; DL: 4-512

0 1 2 12 13 14...

Radio frame

Pilot FBI TPC

Time slot

666,7 µs

10 ms

Data

Data1

Uplink DPDCH

Uplink DPCCH

Downlink DPCHTPC TFCI Pilot

666,7 µs

666,7 µs

DPCCH DPDCH

2560 Chips, 10 Bits

2560 Chips, 10*2k Bits (k = 0...6)

TFCI

2560 Chips, 10*2k Bits (k = 0...7)

Data2

DPDCH DPCCH FBI: Feedback InformationTPC: Transmit Power ControlTFCI: Transport Format Combination IndicatorDPCCH: Dedicated Physical Control ChannelDPDCH: Dedicated Physical Data ChannelDPCH: Dedicated Physical Channel

Slot structure not for user separation but synchronization for periodic functions!




UMTS TDD Frame Structure

TD-CDMA• 2560 Chips per slot

• Spreading factor: 1-16• Symmetric or asymmetric slot assignment to UL/DL (min. 1 per direction)

• Tight synchronization needed• Simpler power control (100-800 power control cycles/s)

0 1 2 12 13 14...

Radio Frame

Data1104 Chips

Midample256 Chips

Data1104 Chips

Time slot

666,7 µs

10 ms

Traffic burstGP

GP: guard period96 Chips2560 Chips




UTRAN Architecture

• UTRAN comprises several RNSs

• Node B can support both, FDD or TDD

• RNC is responsible for handover decisions requiring signaling to the UE

• Cell offers FDD or TDD

RNC: Radio Network ControllerRNS: Radio Network Subsystem

Node B

Node B

RNC

Iub

Node B

UE1

RNS

CN

Node B

Node B

RNC

Iub

Node B

RNS

Iur

Node B

UE2

UE3

Iu




UTRAN Functions

• Admission Control

• Congestion Control• System Information Broadcasting

• Radio Channel Encryption• Handover

• Radio Network Configuration• Channel Quality Measurements• Macro Diversity

• Radio Carrier Control• Radio Resource Control

• Data Transmission over the Radio Interface• Power Control

• Channel Coding• Access Control




Core Network: Protocols

MSC

RNS

SGSN GGSN

GMSC

HLR

VLR

RNS

Layer 1: PDH, SDH, SONET

Layer 2: ATM

Layer 3: IPGPRS Backbone (IP)

SS 7

GSM-CSBackbone

PSTN/ISDN

PDN (X.25),Internet (IP)

UTRAN CN RNS can be UMTS RNS or GSM BSS




Core Network

The Core Network and thus also the interface Iu are separated into two logical domains:

• Circuit Switched Domain (CSD)� Circuit switched service inclusive signaling

� Resource reservation at connection setup� GSM components (MSC, GMSC, VLR)

• Packet Switched Domain (PSD)� GPRS components (SGSN, GGSN)

Release 99 uses the GSM/GPRS network and just adds a new radio access

• Lower costs, faster deployment• Not as flexible as newer releases 4, 5, 6 (change to IP based functions, …)




Support of Mobility: Macro Diversity

• A device can receive signals over 3 antennas in parallel

• Multicast of data via several physical channels

� Enables soft handover� only in FDD mode

• Uplink� Simultaneous reception of UE

data at several Node Bs

� Reconstruction of data at Node B, SRNC or DRNC

• Downlink

� Simultaneous transmission of data via different cells

� Different spreading codes in different cells

CNNode B RNC

Node BUE




Support of Mobility: Handover

• From and to other systems (e.g. UMTS to GSM)

� A must for the beginning when UMTS coverage is poor• RNS controlling the connection is called SRNS (Serving RNS)

• RNS offering additional resources (e.g.. for soft handover) is called DRNS (Drift RNS)

• End-to-end connections between UE and CN only via Iu at the SRNS

� Change of SRNS requires change of Iu� Initiated by SRNS

� Controlled by the RNC and CN

SRNC

UE

DRNC

Iur

CN

Iu

Node BIub

Node BIub




Example Handover Types in in UMTS/GSM

RNC1

UE1

RNC2

Iur

3G MSC1

Iu

Node B1

IubNode B2

Node B3 3G MSC2

BSCBTS 2G MSC3

AAbis

UE2

UE3

UE4




Cell Breathing

GSM• Device gets full power from the base station

• Number of connected devices has no influence on the cell size

UMTS• Cell size and capacity are tightly correlated• Capacity is determined at the Signal-to-Noise-Ratio

• Noise is increased by interference…� with other cells� with other participants

• Devices at the cell border are not able to increase their signal strength (power limitation) � for too high noise no communication is possible

• Restriction of simultaneous number of users necessary• Cell breathing makes cell planning complicated




Cell Breathing: Example




UMTS Services

Virtual Home Environment (VHE)• Enables access to personalized data independent of location, access

network, and device• Network operators may offer new services without changing the network• Service providers may offer services based on components which allow the

automatic adaptation to new networks and devices• Integration of existing IN services

circuit switched16 kBit/sSprache

SMS successor, E-Mailpacket switched14,4 kBit/sSimple Messaging

circuit switched14,4 kBit/sSwitched Data

asymmetrical, MM, downloadscircuit switched384 kBit/sMedium MM

low coverage, max. 6 km/hpacket switched2 Mbit/sHigh MM

bidirectional, video telephonecircuit switched128 kBit/sHigh Interactive MM

TransportmodusBandbreiteService Profile

Data Transmission Service Profiles




What is Next?

Cellular phones Satellites Wireless LANs

Cordlessphones

1992:GSM

1994:DCS 1800

2001:IMT-2000

1987:CT1+

1982:Inmarsat-A

1992:Inmarsat-BInmarsat-M

1998:Iridium

1989:CT 2

1991:DECT 199x:

proprietary

1997:IEEE 802.11

1999:802.11b, Bluetooth

1988:Inmarsat-C

analog

digital

1991:D-AMPS

1991:CDMA

1981:NMT 450

1986:NMT 900

1980:CT0

1984:CT1

1983:AMPS

1993:PDC

4G – Fourth Generation – when and where?

2000:GPRS

2000:IEEE 802.11a

200?:Fourth Generation(Internet-based?)




Overlay Networks – the global Goal

region

urban area

company

car,house,

personal range

verticalhandover

horizontalhandover

Integration of heterogeneous fixed and mobile networks with differenttransmission characteristics




Characteristics of Future Networks (?)

• Improved radio techniques and antennas� Intelligent antennas, direction, MIMO (multiple-input-multiple-output) antennas

• Space multiplex for higher capacity, usage of multipath signal propagation� Software defined radios (SDR)

• Usage of different radio interfaces, download of new modulation and coding technologies

• Needs high computing power (UMTS RF: 10000 GIPS)

� Dynamic frequency allocation• Dynamic assignment of frequencies improves capacity

• Convergence of core networks� IP-based, Quality of Service, Mobile IP

• Ad-hoc techniques� Spontaneous communication, power management, redundancies

• Simple and open service platform

� Intelligence a network borders, not in the network (as in IN)� Thus: more service providers, not only the network providers




IP-basedcore network

SS7-Signaling

Internet

Exemplarily IP-based 4G/Next G/… Network

GSM

UMTS

publicWLAN or WMAN

RNC

BSC

Firewall, GGSN,Gateway

Gateways

Server-Farm,Gateways, Proxies

PSTN, CS-Core

MSC

SGSN

Router

Radio/TV broadcast

accesspoints private

WLANprivateWPAN




Possible Problems

• Quality of Service� The Internet provides best effort data transfer

� Integrated Services has bad scalability, Differentiated Services have still to be proofed

� Simplicity of the Internets? DoS attacks auf QoS?• Internet Protocols are well-known…

� …also for attackers, hackers, …

• Reliability, maintenance� Still an open question if Internet technology is cheaper, when a high reliability is

needed (99.9999%) and all demanded services are integrated

• Missing accounting technology� Accounting based of technical parameters (data volume, time) makes no sense

� A content- or application-based accounting is much better• Killer Application! There is no single killer application:

� The selection of provided services and the seamless access to the services using different access technologies is important

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