CMPE 477

Evolution of GSM in to 2.5G and 3G

New Data Services for GSM

HSCSD

GPRS

3G – UMTS

IMT2000

UMTS Architecture

UTRAN Architecture

CMPE 477 – Wireless and Mobile Networks

Data services in GSM I

Data transmission standardized with only 9.6 kbit/s

advanced coding allows 14,4 kbit/s

not enough for Internet and multimedia applications

HSCSD (High-Speed Circuit Switched Data)

mainly software update

bundling of several time-slots to get higher AIUR (Air Interface User Rate)(e.g., 57.6 kbit/s using 4 slots, 14.4 each)

advantage: ready to use, constant quality, simple

disadvantage: channels blocked for voice transmissionAIUR [kbit/s] TCH/F4.8 TCH/F9.6 TCH/F14.4

4.8 1

9.6 2 1

14.4 3 1

19.2 4 2

28.8 3 2

38.4 4

43.2 3

57.6 4

Data services in GSM II

GPRS (General Packet Radio Service)

Avoids the problems of HSCSD by packet switching

Network providers charge on volume rather than duration

One to 8 slots can be allocated per frame, no fixed assignment but on demand

Maximum rate 171.2kbps but …

Available data rate depends on the current cell load: using free (idle) slots only if data packets ready to send

Transfer rate depends on the capabilities of the MS, also the maximum number of slots per frame is limited

Typical Class 10 device achieves a receiving rate of 53.6kbps and a sending rate of 26.8kbps

All GPRS services can be used in parallel to conventional GSM services

advantage: one step towards UMTS, more flexibledisadvantage: more investment needed (new hardware)

GPRS network elements

GSN (GPRS Support Nodes): GGSN and SGSN (Routers)

GGSN (Gateway GSN)

interworking unit between GPRS and PDN (Packet Data Networks; IP, X25)

Performs address conversion, tunnels data

Connected to IP networks

SGSN (Serving GSN)

supports the MS (location, billing, security-ciphering)

the delivery of data packets from and to the mobile stations within its geographical service area

GR (GPRS Register also called Gateway Location Register)

user addresses, part of HLR, current SGSN, current VLR

GPRS architecture and interfaces

MS BSS GGSNSGSN

MSC

Um

EIR

HLR/GR

VLR

PDN

Gb Gn Gi

SGSN

Gn

Towards 3G: UMTS and IMT-2000

Proposals for IMT-2000 (International Mobile Telecommunications)

UWC-136, cdma2000, WP-CDMA

UMTS (Universal Mobile Telecommunications System) from ETSI (European Proposal)

UMTS

UTRA (was: UMTS, now: Universal Terrestrial Radio Access): the radio interface

requirements

min. 144 kbit/s rural (goal: 384 kbit/s)

min. 384 kbit/s suburban (goal: 512 kbit/s)

up to 2 Mbit/s urban

Should be compatible with GSM, IP and ISDN-based networks

IMT-2000 family

IMT-DS(Direct Spread)

UTRA FDD(W-CDMA)

3GPP

IMT-TC(Time Code)

UTRA TDD(TD-CDMA);TD-SCDMA

3GPP

IMT-MC(Multi Carrier)

cdma2000

3GPP2

IMT-SC(Single Carrier)

UWC-136(EDGE)

UWCC/3GPP

IMT-FT(Freq. Time)

DECT

ETSI

GSM(MAP)

ANSI-41(IS-634)

IP-NetworkIMT-2000Core NetworkITU-T

IMT-2000 (3G)Radio AccessITU-R

Interface for Internetworking

Flexible assignment of Core Network and Radio Access

Initial UMTS(R99 w/ FDD)

As a single standard could not be found, the ITU standardized five groups of 3G Radio Access Technologies

Enhancements of GSM

EDGE (Enhanced Data rates for GSM Evolution) – 2.75G:

GSM up to 384 kbit/s, using the same 200kHz wide carrier and the same frequencies

Uses enhanced modulation techniques, 8PSK instead of GMSK

CAMEL (Customized Application for Mobile Enhanced Logic)

VHE (virtual Home Environment) for visiting subscribers

services to be offered when a subscriber is roaming, like, for instance, no-prefix dialing

QoS Aspects, several migration aspects …

UMTS architecture (Release 99)

UTRANUE CNIuUu

UTRAN (UTRA Network)

Cell level mobility

Radio Network Subsystem (RNS)

Encapsulation of all radio specific tasks (handover, resource management, etc.)

UE (User Equipment)

CN (Core Network)

Inter system handover

Gateways to other networks

UMTS domains and interfaces I

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

USIMDomain

MobileEquipment

Domain

AccessNetworkDomain

ServingNetworkDomain

TransitNetworkDomain

HomeNetworkDomain

Cu Uu Iu

User Equipment Domain

Zu

Yu

Core Network Domain

Infrastructure Domain

UMTS domains and interfaces II

Universal Subscriber Identity Module (USIM)

Functions for encryption and authentication of users

Located on a SIM inserted into a mobile device, stores all user related data

Mobile Equipment Domain

Functions for radio transmission

User interface for establishing/maintaining end-to-end connections

Access Network Domain

Access network dependent functions

UMTS domains and interfaces III

Core Network Domain

Access network independent functions

Serving Network Domain

Network currently responsible for communication

Home Network Domain

Location and access network independent functions

Transit Network Domain

Necessary if the serving network cannot directly contact the home network domain

Spreading and scrambling of user data

UMTS uses DS-CDMA

Constant chipping rate of 3.84 Mchip/s

Different user data rates supported via different spreading factors

higher data rate: less chips per bit and vice versa

User separation via unique, 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

Spreading Data

The first step in a sender is spreading user data using orthogonal spreading codes.

This separates the different data streams of a sender.

These codes are called orthogonal variable spreading factor (OVSF) codes.

Doubles a chipping sequence X with and without flipping the sign of the chips: X and –X

The spreading factor sf=n become sf=2n

OVSF 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,-1,1

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,-1,-1

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

SF=n SF=2n

...

...

...

...

Spreading and Scrambling of user Data

data1 data2 data3

scramblingcode1

spr.code3

spr.code2

spr.code1

data4 data5

scramblingcode2

spr.code4

spr.code1

sender1 sender2

OVSF spreads the data streams but the spreading codes chosen in the senders can be the same

After spreading all chip streams are added and scrambled.

Scrambling does not further spread the chip sequence but XORs chips based on a code

In the FDD mode, this code is unique for each sender and separates all senders

In the TDD mode, the scrambling code is cell specific.

UMTS FDD frame structure

W-CDMA• 1920-1980 MHz uplink• 2110-2170 MHz downlink• chipping rate:

3.840 Mchip/s• spreading: 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 synchronisation for periodic functions!

UTRA-FDD Channels

Dedicated Physical Data Channel (DPDCH):

Conveys user or signaling data.

Spreading factor varies between 4 and 256

Data rates: 960 kbps(spreading factor 4), 480, 240, 120, 60, 30, 15kbps (spreading factor 256)

Dedicated Physical Control Channel (DPCCH):

Conveys control data for the physical channel

Constant spreading factor, 256.

Dedicated Physical Channel (DPCH):

Multiplexes user and control data

Spreading factors between 4 and 512

Data rates 6, 24, 51, 90, 210, 432, 912, and 1872kbps

UTRA-FDD Medium Access

No collisions on the downlink: Only the Basestation sends

Uplink: Nodes use slotted Aloha (15 random access slots)

Access a slot by sending a preamble with the lowest transmission power

If no acknowledgement is received, try another slot with the next transmission power level

UMTS TDD frame structure (burst type 2)

TD-CDMA• 2560 chips per slot• spreading: 1-16• symmetric or asymmetric slot assignment to UL/DL (min. 1 per direction)• tight synchronisation 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 FDD or TDD or both

RNC is responsible for handover decisions requiring signalingto the UE

Cell offers FDD or TDD

RNC: Radio Network Controller

RNS: Radio Network SubsystemNode 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

RNC functions

Admission control

Congestion control

Encryption/Decryption

ATM Switching and Multiplexing

Radio resource control

Code allocation

Handover control

Management

B-node and User Equipment

B-Node

Power control to mitigate near-far effects

Measuring connection qualities and signal strength

Supports softer handover

User equipment

Power control, signal quality measurements, spreading, modulation, encryption and decryption, requesting services from the network

Cooperates with RNC for handover

Core network: architecture

BTS

Node B

BSC

Abis

BTS

BSS

MSC

Node B

Node B

RNC

Iub

Node BRNS

Node BSGSN GGSN

GMSC

HLR

VLR

IuPS

IuCS

Iu

CN

EIR

GnGi

PSTN

AuC

GR

Core network

The Core Network (CN) and thus the Interface Iu, too, are separated into two logical domains:

Circuit Switched Domain (CSD) Circuit switched service incl. signaling

Resource reservation at connection setup

GSM components (MSC, GMSC, VLR), IuCS

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

IuPS

Release 99 uses the GSM/GPRS network and adds a new radio access! Helps to save a lot of money …

Much faster deployment

Handover

Hard Handover: Similar to GSM, switching between different antennas or systems.

Inter-frequency handover: Changing the carrier frequency

Inter-system handover: Handover to and from GSM or to other IMT-2000 systems

Soft handover:

New mechanism in UMTS:

With hard handoff, a definite decision is made on whether to handoff or not

With soft handoff, a conditional decision is made on whether to hand off

Available in the FDD mode

Soft handover

Multicasting of data via several physical channels

UE can receive signals from up to three antennas which may belong to different node B’s

Uplink

simultaneous reception of UE data at several Node Bs by splitting data

Reconstruction of data at RNC

Downlink

Simultaneous transmission of data via different cells

Different spreading codes in different cells

CNNode B RNC

Node BUE

Soft Handover, Intra RNC

RNS controlling the connection is called SRNS (Serving RNS)

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

SRNC forwards data to its not B and to the DRNC

SRNC combines both data streams and forwards to CN

SRNC

UE

DRNC

Iur

CN

Iu

Node BIub

Node BIub

Example handover types 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

Intra Node-B, intra RNC (Softer Handover): Between the antennas of a B-nodeInter Node-B, intra RNC: RNC1 supports soft handover by combining and splitting dataInter RNC: Internal or external inter-RNCInter MSC: Hard handover MSC2 takes overInter system: Hard handover from 3G UMTS network to 2G GSM.

Review Terms

HSCSDGPRSIMT-2000UMTSEDGECAMELUTRAUTRANOVSF codeDS-CDMAUTRA-FDDUTRA-TDDGateway GSNServing GSN

GPRS RegisterB-nodeRNCHard HandoverSoft HandoverSofter Handover