Part 6. 3G Mobile Communication Systems ―WCDMA and cdma2000

ELEC6040, Mobile Radio Communications, Dept. of E.E.E., HKUp. 1

Part 6. 3G Mobile Communication Systems―WCDMA and cdma2000


Introduction ― Objectives to develop 3G

Achieving significantly higher transmission speed capability, encompassing circuit- and packet-switched networks as well as support of multimedia services.

Higher spectral efficiency and overall cost improvement by utilizing advanced technologies.Maximizing the commonality by radio interfaces for multiple operating environments.Compatibility of services within IMT-2000 and fixed networks.

2G: voice

3G: voice, image, video

Data Networks2G: low rate 2G: low rate

3G: high rate3G: high rate


Introduction ― Key Properties Emphasized in 3GImproved performance over 2G, including:– Improved capacity;– Improved coverage, enabling migration from a 2G deployment.

A high degree of service flexibility, including:– Support of a wide range of services with maximum bit rates above 2 Mb/s and the

possibility for multiple parallel services on one connection;– A fast and efficient packet-access scheme.

A high degree of operator flexibility, including:– Support of asynchronous inter-base-station operation;– Efficient support of different deployment scenarios, including hierarchical cell

structure and hot-spot scenarios;– Support of evolutionary technologies such as adaptive antenna arrays and multi-user

detection.


Introduction ― Differences Between 2G and 3G SystemsFlexible offer of mobile multimedia services– Voice/fax/data– Wideband data services (high speed Internet/high quality images)

Slow bit pipe provided by 2G

Faster bit pipe by 3G

<64kbps(25-64kHz)

VoiceLow rate data

2Mbps(5MHz)Internet

Voice

ImagesMulti-media


Introduction ― Spectrum allocation of 3G (1)

1992, ITU, World Administrative Radio Conference– the frequencies around 2GHz were available for use by 3G mobile systems– called International Mobile Telephony 2000 (IMT-2000)– defined several different air interfaces based on CDMA or TDMA– target: a single common global IMT-2000 air interface for 3G

Target: a single common global IMT-2000 air interface for 3G– Europe and Asia: same air interface WCDMA, frequencies around 2GHz– North America: spectrum around 2GHz has been auctioned for 2G and no new

spectrum is available for IMT-2000, 3G must be implemented within the existing bands by replacing part of the spectrum with 2G


Introduction ― Spectrum allocation of 3G (2)

WRC-2000 IMT-2000 Frequencies source: http://www.umtsworld.com/technology/frequencies.htm


The nature of communications has been changing …– People to People → People to Things → Things to Things

Family of ITU standards consisting of two main systems– Direct Spread Option (Wideband CDMA) with chip rate of 3.84

Mcps and BW of 5 MHz. – Multi-Carrier Option (Cdma2000).

Key 3G Requirements:– High Speed Packet Data: 144 kbps -- Vehicular; 384 kbps --

Pedestrian, 2 Mbps -- Indoor – Global Roaming

Introduction ― 3G Standards


Introduction ― Standardization Efforts (1)

SDO working for radio interfaces standardization

source: Willie W. Lu, "Broadband wireless mobile"

Universal Wireless Consortium (UWC)

Standard Development Organization

PartnershipProject

RadioInterfaces

Japan

China

North America

Korea

Japan

Europe


Introduction ― Standardization Efforts (2)3GPP (3G Partnership Project)– Spearheaded by ETSI (European Telecommunication Standards Institute)– Memberships as in December 1998: ARIB (Japan), ETSI (Europe), T1 (USA), TTA

(Korea) and TTC (Japan); May 1999: CWTS (China)– Aim: to prepare, approve, and maintain globally applicable technical specifications

and technical reports for a 3G mobile system (called Universal Mobile Telecommunication System UMTS) based on the evolved GSM core network and Universal Terrestrial Radio Access (UTRA) (UTRA TDD+FDD=> WCDMA)

3GPP2– Spearheaded by ANSI (American National Standards Institute)– Memberships as in January 1999: ARIB, TIA (USA), TTA and TTC.– Aim: to cooperate in the preparation of globally applicable technical specifications

for a 3G mobile system based on the evolved ANSI/TIA/EIA-41 core networks and cdma2000.

OHG (Operators’ Harmonization Group)– To prevent a multiple standard problem.


Introduction ― Standardization Efforts (3)

Radio interfaces defined for IMT-2000

source: Willie W. Lu, "Broadband wireless mobile"

IMT-Direct SpreadIMT-Multi CarrierIMT-Time CodeIMT-Single CarrierIMT-Frequency Time

IMT Radio Technologies

AccessTechnologies

11ELEC6040, Mobile Radio Communications, Dept. of E.E.E., HKUp. 11

Introduction ─ IMT2000 Capability (1)

Indoor2MbpsIndoor2Mbps Pedestrian

384kbpsPedestrian384kbps

Vehicular144kbps

Vehicular144kbps

IMT2000Network

Planned to deploy in May 2001Frequency band:2GHz bandInformation rates: up to 2Mbps


Introduction ― IMT2000 Capacity (2)

Variable bit rates to offer bandwidth on demandMultiplexing of services with different quality requirements on a single connection, e.g., speech video and packet dataDelay requirements from delay-sensitive real-time traffic to flexible best-effort packet dataQuality requirements from 10% frame error rate to 10-6 bit error rateCoexistence of second and third generation systems and inter-system handovers for coverage enhancements and load balancingSupport of asymmetric uplink and downlink traffic, e.g., web browsing causes more loading to downlink than to uplinkHigh spectrum efficiencyCoexistence of FDD and TDD modes

source: H. Holma and A. Toskala, "WCDMA for UMTS"


Introduction ― Commercial 3G Services (1)

Start with crazy spectrum auctions in Europe– Huge success of 2G– Telecommunication companies in Europe spent more than 120 billion$ on

3G licenses– Great Britain: 34 billion$– Germany: 46 billion$– Vodafone: 9.4 billion$ for one license in Great Britain

“We spent €10 billion too much”

Sir Peter Bonfield, CEO, BTSunday Times, London,

18th February 2001



Voice

E-m

ailing

Web

browsing

TransactionsBankingReservations for flights and accommodationsStock trading, etc

Daily informationWeatherNewsStock prices, etc.

Data baseRestaurant guide Town pageDictionaryTrain transfer info.Cooking recipes, etc.

EntertainmentKaraokeNetwork gameMovie listingsFortune-telling etc.

A successful example of 3G– The world first 3G network was launched by NTT DoCoMo, Japan, in 2001– Big success of its 3G services “i-mode”: internet services are added to voice communications– Creation of mobile multimedia era



Jan. 2004Hutchison

Dec. 2004SmartoneH.K. CSL

Jun. 2005Sunday

Jul. 2006

3G subscribers:

1million

3G in Hong Kong– Mainland China: no 3G services– Hong Kong: only WCDMA is employed

Jun. 2008

3G subscribers: 2.38million

all mobile subscribers: 10.98million

Oct. 2001Spectrum Auction

four 3G licenses; valid for 15 years; each with a spectrum of 2x14.8MHz+1x5MHz



CDMA20001x

WCDMA

CDMA20001xEV-DO


Summary: What Is 3G?

Why necessary?– Explosive expansion of markets– Mobile multimedia communications– Global standard terminals

– Big business chances– Lower cost due to mass markets

Which services?– Unknown, but services indicated by the success of “i-mode”– Point-to-point, point-multi points, broadcasting services


WCDMA


Introduction (1)Wideband CDMA– a predominant wireless access technology for the 3G systems– designed to offer wideband services

wireless internet services: download information from the Web, video transmission,...– data rate: indoor: 2Mbps, pedestrian: 384kbps, vehicular: 144kbps– wide bandwidth (5MHz) is needed for high data rate

physical limitations and impairments on radio channels presents a fundamental technical challenge to reliable high data rate communications

Two Modes: FDD and TDD– Frequency division duplex: optimized for wide-

area coverage, i.e., public macro and micro cells – Time division duplex: optimized for public micro

and pico cells and unlicensed cordless applications

uplink

downlinkBS

BS

MS

MS


Introduction (2)

Freq.Uplink Downlink190MHz

5MHz 5MHzFDD: paired spectrum; ideal for symmetric services (voice); inefficient for asymmetric services (e.g. mp3 downloading)

Freq.Uplink

Downlink

5MHz

TDD: no need for paired spectrum; flexible, efficient for asymmetric services

TimeUplink Downlink

TimeUplink

Downlink

Downlink Downlink


Introduction (3)Main features of WCDMAAsynchronous inter-base-station operation– no requirement on any external system such as GPS – new challenges like cell acquisition and soft handoff


Introduction (4)Main features of WCDMAVariable rate transmission– to provide multimedia services– multi-code transmission is employed in downlink to achieve higher bit rates

Adaptive antenna array– null out interference and maximize the signal to interference ratio– particularly useful for multimedia communications

a small number of high rate users give significant interference to low rate users. Without adaptive antenna array, the link capacity would be significantly reduced.

– dedicated pilot symbols in both up- and down-link facilitate user-unique antenna patterns

Turbo coding– large coding gain

Desired user with

low rate services with high

rate services

like online game


System Architecture (1)

source: http://www.mobileguru.co.uk/Mobile_Technology_globe.html

New protocols for WCDMA

UMTS R99 Architecture


System Architecture (2)UTRA TerminologiesUE: User Equipment– interfaces the user and the radio interface– consists of Mobile Equipment (ME) and UMTS Subscriber Identity Module (USIM)

UTRAN: UMTS Terrestrial Radio Access Network– handles all radio related functionality– consists of Node B (Base Station) and Radio Network Controller (RNC)

Core Network– evolved GSM core network– switching and touting calls and data connection to external networks– consists of Home Location Register (HLR), Mobile Services Switching Center

(MSC), Visitor Location Register (VLR), Gateway MSC, Service GPRS Support Node (SGSN), Gateway GPRS Support Node (GGSN)

External Network– consists of Circuit Switching (CS) network and Packet Switching (PS) network


System Architecture (3)

Note: the functionality of each pair is not necessary the same

Compare GSM and UMTS Terminologies


Radio Interface - Channel ConceptsThree separate channel concepts in UTRA: logical channel, transport channel and physical channelLogical channels define what type of data is transferredTransport channels define how and with which type of characteristics the data is transferred by the physical layerPhysical channels define the exact physical characteristics of the radio channel


Radio Interface - Transport Channels (1)Transport Channels: Data generated at higher layers is carried over the air with transport channels, which are mapped in the physical layer to different physical channels

Higher Layers

Physical Layer


Radio Interface - Transport Channels (2)CCTrCh (Coded Composite Transport Channel): a technology in the UMTS physical layer, is the connection between Transport Channel and Physical Channel which results a data stream from encoding and multiplexing of one or several transport channels

One physical control channel + one or more physical data channel => one CCTrCh

Two types of Transport Channels– dedicated channel (DCH): identified by a certain code on a certain frequency,

reserved for a single user only; carries all the information intended for the given user from layers above the physical layer, including data for the actual services and higher layer control informationFeatures: fast power control, fast data rate change on a frame-by-frame basis, support adaptive antenna, support soft handover (illustrated in later sections)

– common channel: a resource divided between all or a group of users in a cell


Radio Interface - Transport Channels (3)Six types of Common Transport Channels– Broadcast Channel (BCH): downlink, transmit network information, e.g., available

random access codes and access slots, important for register– Forward Access Channel (FACH): downlink, carry control information or packet

data– Paging Channel (PCH): downlink, carry data relevant to the paging process when the

network wants to initiate communication with the terminal– Random Access Channel (RACH): uplink, carry control information from the

terminal, e.g., requests to set up a connection, or packet data– Uplink Common Packet Channel (CPCH): uplink, carry packet-based user data – Downlink Shared Channel (DSCH): downlink, carry dedicated user data and/or

control information, shared by several users, associated with a downlink DCHBasic network operation needs BCH, RACH, FACH and PCH; DSCH and CPCH is optional


Radio Interface - Transport Channels (4)Mapping of Transport Channels onto the physical channels

Transport Channels Physical Channels

DCH

BCHFACH

DSCHRACHPCH

CPCH

Dedicated Physical Data Channel (DPDCH)Dedicated Physical Control Channel (DPCCH)Primary Common Control Physical Channel (PCCPCH)Secondary Common Control Physical Channel (SCCPCH)

Physical Random Access Channel (PRACH)Physical Downlink Shared Channel (PDSCH)Physical Common Packet Channel (PCPCH)Synchronization Channel (SCH)Common Pilot Channel (CPICH)Acquisition Indication Channel (AICH)Paging Indication Channel (PICH)CPCH Status Indication Channel (CSICH)Collision Detection/ Channel Assignment Indicator Channel (CD/CA-ICH)

Not directly visible to higher layers, carry only information relevant to physical layer procedures


Physical Layer (FDD)Multiple access method: DS-CDMASystem bandwidth 5M– allocated spectrum: 1920-1980MHz and 2110-2170MHz– chip rate: 3.84Mcps

Radio frame structure– 10ms/frame, 15slots, 2560chips/slot

Slot #0 Slot #1 Slot #i Slot #14

One radio frame: Tf=10ms

Tslot=2560 chips


Uplink - Introduction

Spreading factors: 4- 256modulation scheme: BPSKTwo type of uplink dedicated physical channels– uplink dedicated physical data channel (uplink DPDCH)

carry the DCH transport channelcan be zero, one, or several DPDCH on each radio link

– uplink dedicated physical control (or pilot) channel (uplink DPCCH)carry control information: known pilot bits to support channel estimation for coherent detection, transmit power control (TPC) commands, feedback information (FBI), and an optional transport-format combination indicator (TFCI)one and only one uplink DPCCH on each radio link

– DPDCH and DPCCH are I/Q code multiplexed within each radio frameVariable data rate: change the spreading factor on DPDCH on a frame-by-frame basis


Uplink - Frame Structure

Source: Jiangzhou Wang, Broadband Wireless Communications, 3G, 4G and Wireless LAN

Frame structure for uplink DPDCH/DPCCH


Uplink - Spreading

Spreading for uplink DPCCH and DPDCHs

Source: Jiangzhou Wang, Broadband Wireless Communications, 3G, 4G and Wireless LAN

Complex Scrambling


Uplink - Design Criteria (1)Two terminal oriented design criteria – maximize the terminal amplifier efficiency – minimize the audible interference from the terminal transmission

Uplink DPDCH and DPCCH: Why I/Q code multiplexed (Dual channel QPSK modulation)?– Time multiplexed: audible interference due to discontinuous transmission


Uplink - Design Criteria (2)uplink DPDCH and DPCCH: Why I/Q code multiplexed? (Con't)– Pure code multiplexed: multicode transmission, increases transmitted signal

envelope variations => Higher PAPR (Peak-to-Average Power Ratio)

– I/Q code multiplexed: DPCCH is maintained on a separate continuous channel, no pulse transmission, minimize audible interference


Uplink - Design Criteria (3)uplink DPDCH and DPCCH: Why complex scrambled?– power levels of the DPDCH and DPCCH are typically different; lead to extreme

cases to BPSK-type transmission if transmitting the branches independently – the I and Q branches are mixed using complex scrambling


Uplink MultiplexingCRC attachment

Transport block concatenation/Code block segmentation

Channel coding

Radio frame equalization

First Interleaving (20, 40, or 80ms)

Radio frame segmentation Rate MatchingTransport Channel

Multiplexing

Other Transport Channels

Physical channel segmentation

Second interleaving (10ms)

Physical channel mapping

DPDCH #1 DPDCH #2 DPDCH #N

Source: Harri Homa and Antti Toskala, WCDMA for UMTS


Downlink (1)Spreading factors: 4-512modulation scheme: QPSKOne type of downlink dedicated physical channel– downlink dedicated physical channel (downlink DPCH)– dedicated data (downlink DPDCH) and control information (downlink DPCCH)

(pilot bits, TPC, TFCI) are transmitted on DPCH in time multiplex mode


Downlink (2)Common downlink pilot channels (CPICH)– fixed rate, SF=256, 30kbps– carry predefined symbol/bit sequence– Primary Common Pilot Channel (P-CPICH): a phase reference for the downlink

channels– Secondly Common Pilot Channel (S-CPICH): a phase reference for a secondary

CCPCH carrying downlink access channels only and /or a downlink DPCH


Downlink (3)downlink DPDCH and DPCCH: Why time-multiplexed?– Time multiplexed: the common channels have continuous transmission, no audible

interference– I/Q code multiplexed: downlink multicode transmission: no need for optimization of

PAPR as with single code (pair) transmission– Code multiplexed: reserving a code for DPCCH results in worse code resource

utilization


Downlink (4)downlink spreading: one scrambling code (one code tree) per sector in the base station– Variable data rate: rate matching operation or discontinuous transmission– Why cannot the spreading factor on DPDCH vary on a frame-by-frame basis?

downlink scrambling: long codes– number of scrambling codes: limited to 512 codes, otherwise the cell search

procedure would become too excessive

scramble code #0

scramble code #1scramble

code #0

scramblecode #1

scramblecode #2

scramblecode #3

scramblecode #4

scramblecode #5

scramblecode #6

scramblecode #7

scramblecode #8


Downlink Multiplexing

CRC attachment

Transport block concatenation/Code block segmentation

Channel coding

Rate matching

Insertion of DTX indication (with fixed bit positions only)

First Interleaving (20,40 or 80ms)

Radio frame segmentation

Transport Channel Multiplexing

Other Transport Channels

Physical channel segmentation

Second interleaving (10ms)

Physical channel mapping

DPDCH #1 DPDCH #2 DPDCH #N

Insertion of DTX indication (with flexible positions only)

Source: Harri Homa and Antti Toskala, WCDMA for UMTS


Scrambling Codes (1)Scrambling in WCDMA is used on top of spreading– does not change the signal bandwidth and symbol rate– to separate terminals or base stations from each other; use pseudo-noise (PN) codes

Spreading in WCDMA– increase signal bandwidth– to separate channels from each other (channelisation); use orthogonal codes

(channelisation codes)


Two types of scrambling codes: long and short scrambling codesScrambling Codes (2)


Uplink physical channels: complex-valued scrambling code, either long or short– Long scrambling codes: used if the base station uses a Rake receiver– Short scrambling codes: used if the base station uses advanced multiuser detectors or

interference cancellation receivers

Scrambling Codes (3)

long scramblingcode, shift #1

long scramblingcode, shift #0

longscrambling

code #1

longscrambling

code #0

long: BS has a Rakereceivershort: BS uses multiuserdetection

GPS

IS-95 or CDMA2000WCDMA


Signal detection at BS


Slot #0Time

Slot #15Slot #1

long scrambling code: one frame: 10ms, 38400 chips

Slot #0 Slot #15Slot #1

Time

Slot #0 Slot #15Slot #1

Time

Received signal at BS

Terminal #0(Scrambling code #0)




Descrambling usingscrambling code #0



Signal detectionfor user #0



Receivedsignal at BS

Recovered datasymbols for user #0



InterferenceRegenerator for user #0

Delay




Multiuser detectors or interference cancellation receivers


Advantage of short scrambling codes: reduce of processing delay


Channelisation Codes (1)Transmissions from a single source are separated by channelisation codes– downlink connection within one sector– dedicated channels in the uplink from one terminal

WCDMA uses Orthogonal Variable Spreading Factor (OVSF) codes

OVSF allows the spreading factor to be changed and orthogonality between different spreading codes of different lengths to be maintained

c1,1=(1)

c2,1=(1,1)

c2,2=(1,-1)

c4,1=(1,1,1,1)

c4,2=(1,1,-1,-1)

c4,3=(1,-1,1,-1)

c4,4=(1,-1,-1,1)

c(c,c)

(c,-c)

Part 6. 3G Mobile Communication Systems ―WCDMA and cdma2000

Technology

Transcript of Part 6. 3G Mobile Communication Systems ―WCDMA and cdma2000