Evolution of GSM in to 2.5G and 3G

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}

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 transmission

AIUR [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 flexible

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)}

GPRS architecture and interfaces

MS BSS SGSN GGSN MSC U_m EIR HLR/ GR VLR PDN G_b G_n G_i SGSN G_n

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}

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-Network IMT-2000 Core Network ITU-T IMT-2000 (3G) Radio Access ITU-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

UMTS architecture (Release 99)

UTRAN

UE _{Uu Iu} CN

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}

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}

USIM Domain Mobile Equipment Domain Access Network Domain Serving Network Domain Transit Network Domain Home Network Domain C_u U_u I_u

User Equipment Domain

Z_u

Y_u

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

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}

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

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

scrambling code₁ spr. code₃ spr. code₂ spr. code₁ data₄ data₅ scrambling code₂ 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

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 DPCH TPC 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 Information TPC: Transmit Power Control

TFCI: Transport Format Combination Indicator DPCCH: Dedicated Physical Control Channel DPDCH: Dedicated Physical Data Channel DPCH: 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

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 Data 1104 chips Midample 256 chips Data 1104 chips Time slot 666.7 µs 10 ms Traffic burst GP GP: guard period 96 chips 2560 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 Subsystem Node B Node B RNC I_ub Node B UE₁ RNS CN Node B Node B RNC I_ub Node B RNS I_ur Node B UE₂ UE₃ I_u

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

Core network: architecture

BTS Node B BSC A_bis BTS BSS MSC Node B Node B RNC I_ub Node B RNS Node B SGSN GGSN GMSC HLR VLR I_uPS I_uCS I_u CN EIR G_n Gi PSTN AuC GR

Core network

The Core Network (CN) and thus the Interface I_u, 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

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

CN

Node B RNC

Node B UE

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 I_ur CN I_u Node B I_ub Node B I_ub

Example handover types in UMTS/GSM

RNC₁ UE₁ RNC₂ I_ur 3G MSC₁ I_u Node B₁ I_ub Node B₂ Node B₃ 3G MSC₂ BSC BTS 2G MSC₃ A A_bis UE₂ UE₃ UE₄

Intra Node-B, intra RNC (Softer Handover): Between the antennas of a B-node

Inter Node-B, intra RNC: RNC1 supports soft handover by combining and splitting data Inter RNC: Internal or external inter-RNC

Inter MSC: Hard handover MSC2 takes over

Review Terms

HSCSD GPRS IMT-2000 UMTS EDGE CAMEL UTRA UTRAN OVSF code DS-CDMA UTRA-FDD UTRA-TDD Gateway GSN Serving GSN GPRS Register B-node RNC Hard Handover Soft Handover Softer Handover