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ELEC6040, Mobile Radio Communications, Dept. of E.E.E., HKUp. 1
Part 6. 3G Mobile Communication Systems―WCDMA and cdma2000
ELEC6040, Mobile Radio Communications, Dept. of E.E.E., HKUp. 2
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
ELEC6040, Mobile Radio Communications, Dept. of E.E.E., HKUp. 3
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.
ELEC6040, Mobile Radio Communications, Dept. of E.E.E., HKUp. 4
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
ELEC6040, Mobile Radio Communications, Dept. of E.E.E., HKUp. 5
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
ELEC6040, Mobile Radio Communications, Dept. of E.E.E., HKUp. 6
Introduction ― Spectrum allocation of 3G (2)
WRC-2000 IMT-2000 Frequencies source: http://www.umtsworld.com/technology/frequencies.htm
ELEC6040, Mobile Radio Communications, Dept. of E.E.E., HKUp. 7
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
ELEC6040, Mobile Radio Communications, Dept. of E.E.E., HKUp. 8
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
ELEC6040, Mobile Radio Communications, Dept. of E.E.E., HKUp. 9
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.
ELEC6040, Mobile Radio Communications, Dept. of E.E.E., HKUp. 10
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
ELEC6040, Mobile Radio Communications, Dept. of E.E.E., HKUp. 12
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"
ELEC6040, Mobile Radio Communications, Dept. of E.E.E., HKUp. 13
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
ELEC6040, Mobile Radio Communications, Dept. of E.E.E., HKUp. 14
Introduction ― Commercial 3G Services (2)
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
ELEC6040, Mobile Radio Communications, Dept. of E.E.E., HKUp. 15
Introduction ― Commercial 3G Services (3)
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
ELEC6040, Mobile Radio Communications, Dept. of E.E.E., HKUp. 16
Introduction ― Commercial 3G Services (4)
ELEC6040, Mobile Radio Communications, Dept. of E.E.E., HKUp. 17
Introduction ― Commercial 3G Services (5)
CDMA20001x
WCDMA
CDMA20001xEV-DO
ELEC6040, Mobile Radio Communications, Dept. of E.E.E., HKUp. 18
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
ELEC6040, Mobile Radio Communications, Dept. of E.E.E., HKUp. 19
WCDMA
ELEC6040, Mobile Radio Communications, Dept. of E.E.E., HKUp. 20
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
ELEC6040, Mobile Radio Communications, Dept. of E.E.E., HKUp. 21
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
ELEC6040, Mobile Radio Communications, Dept. of E.E.E., HKUp. 22
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
ELEC6040, Mobile Radio Communications, Dept. of E.E.E., HKUp. 23
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
ELEC6040, Mobile Radio Communications, Dept. of E.E.E., HKUp. 24
System Architecture (1)
source: http://www.mobileguru.co.uk/Mobile_Technology_globe.html
New protocols for WCDMA
UMTS R99 Architecture
ELEC6040, Mobile Radio Communications, Dept. of E.E.E., HKUp. 25
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
ELEC6040, Mobile Radio Communications, Dept. of E.E.E., HKUp. 26
System Architecture (3)
Note: the functionality of each pair is not necessary the same
Compare GSM and UMTS Terminologies
ELEC6040, Mobile Radio Communications, Dept. of E.E.E., HKUp. 27
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
ELEC6040, Mobile Radio Communications, Dept. of E.E.E., HKUp. 28
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
ELEC6040, Mobile Radio Communications, Dept. of E.E.E., HKUp. 29
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
ELEC6040, Mobile Radio Communications, Dept. of E.E.E., HKUp. 30
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
ELEC6040, Mobile Radio Communications, Dept. of E.E.E., HKUp. 31
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
ELEC6040, Mobile Radio Communications, Dept. of E.E.E., HKUp. 32
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
ELEC6040, Mobile Radio Communications, Dept. of E.E.E., HKUp. 33
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
ELEC6040, Mobile Radio Communications, Dept. of E.E.E., HKUp. 34
Uplink - Frame Structure
Source: Jiangzhou Wang, Broadband Wireless Communications, 3G, 4G and Wireless LAN
Frame structure for uplink DPDCH/DPCCH
ELEC6040, Mobile Radio Communications, Dept. of E.E.E., HKUp. 35
Uplink - Spreading
Spreading for uplink DPCCH and DPDCHs
Source: Jiangzhou Wang, Broadband Wireless Communications, 3G, 4G and Wireless LAN
Complex Scrambling
ELEC6040, Mobile Radio Communications, Dept. of E.E.E., HKUp. 36
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
ELEC6040, Mobile Radio Communications, Dept. of E.E.E., HKUp. 37
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
ELEC6040, Mobile Radio Communications, Dept. of E.E.E., HKUp. 38
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
ELEC6040, Mobile Radio Communications, Dept. of E.E.E., HKUp. 39
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
ELEC6040, Mobile Radio Communications, Dept. of E.E.E., HKUp. 40
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
ELEC6040, Mobile Radio Communications, Dept. of E.E.E., HKUp. 41
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
ELEC6040, Mobile Radio Communications, Dept. of E.E.E., HKUp. 42
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
ELEC6040, Mobile Radio Communications, Dept. of E.E.E., HKUp. 43
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
ELEC6040, Mobile Radio Communications, Dept. of E.E.E., HKUp. 44
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
ELEC6040, Mobile Radio Communications, Dept. of E.E.E., HKUp. 45
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)
ELEC6040, Mobile Radio Communications, Dept. of E.E.E., HKUp. 46
Two types of scrambling codes: long and short scrambling codesScrambling Codes (2)
ELEC6040, Mobile Radio Communications, Dept. of E.E.E., HKUp. 47
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
ELEC6040, Mobile Radio Communications, Dept. of E.E.E., HKUp. 48
Signal detection at BS
Scrambling Codes (4)
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)
Terminal #1(Scrambling code #1)
Terminal #2(Scrambling code #2)
ELEC6040, Mobile Radio Communications, Dept. of E.E.E., HKUp. 49
Descrambling usingscrambling code #0
Descrambling usingscrambling code #1
Descrambling usingscrambling code #2
Signal detectionfor user #0
Signal detectionfor user #1
Signal detectionfor user #2
Receivedsignal at BS
Recovered datasymbols for user #0
Recovered datasymbols for user #1
Recovered datasymbols for user #2
InterferenceRegenerator for user #0
Delay
Descrambling usingscrambling code #0
Signal detectionfor user #0
Recovered datasymbols for user #0
Multiuser detectors or interference cancellation receivers
Scrambling Codes (5)
Advantage of short scrambling codes: reduce of processing delay
ELEC6040, Mobile Radio Communications, Dept. of E.E.E., HKUp. 50
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)