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©2002 Rohde & Schwarz GmbH & Co. KG - Training Center - 1 ©2002 / Dipl. Ing. (TU) Heinz Mellein / 1 Principles of UMTS according to 3GPP UMTS - Introduction to 3GPP WCDMA 2002 ROHDE & SCHWARZ GmbH & Co. KG Test & Measurement Division - Training Center - This folder may be taken outside ROHDE & SCHWARZ facilities. All rights reserved. To reproduce or translate sections or parts thereof, permission must first be obtained in writing from Training Center Muehldorfstr. 20 81671 Munich More information on R&S training available at www.rohde-schwarz.com/events/seminars.

Introduction to 3gpp Wcdma by Rohde & Schwarz

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Page 1: Introduction to 3gpp Wcdma by Rohde & Schwarz

©2002 Rohde & Schwarz GmbH & Co. KG - Training Center - 1

©2002 / Dipl. Ing. (TU) Heinz Mellein / 1

Principles of UMTS according to 3GPP

UMTS - Introduction to 3GPP WCDMA

2002 ROHDE & SCHWARZ GmbH & Co. KG Test & Measurement Division

- Training Center -

This folder may be taken outside ROHDE & SCHWARZ facilities.

All rights reserved.To reproduce or translate sections or parts thereof, permission must first be obtainedin writing from

Training CenterMuehldorfstr. 2081671 Munich

More information on R&S training available at www.rohde-schwarz.com/events/seminars.

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©2002 Rohde & Schwarz GmbH & Co. KG - Training Center - 2

© Rohde & Schwarz GmbH & Co. KG - Training Center - UMTS - Introduction to 3GPP WCDMA ©2002 / Dipl. Ing. (TU) Heinz Mellein / 2

Introduction to 3GPP WCDMA

l Chapter 1UMTS - Targets and Concepts

l Chapter 2Basics of mobile communication channels

l Chapter 3Signal spreading with orthogonal codes

l Chapter 4Signal scrambling with pseudo noise sequences

l Chapter 5Code scenarios and FDD air interface channel structure

l Chapter 6Cell search and selection

l Chapter 7Basic procedures- Transmit power control- Handover- Radio connection establishment

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UMTS

Introduction to 3GPP WCDMATargets and Concepts

Dipl.-Ing. (Univ) Reinhold KruegerDipl. Ing. (TU) Heinz Mellein

R&S - TRAINING CENTER© 2002

www.rohde-schwarz.com

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© Rohde & Schwarz GmbH & Co. KG - Training Center - UMTS - Introduction to 3GPP WCDMA - 1 ©2002 / Dipl. Ing. (TU) Heinz Mellein / 2

ITU IMT-2000 Program

l ITU call for proposals of radio transmissiontechnologies (RTTs) for future public land mobiletelecommunication systems (FPLMNs)

l ITU Rec. M.817- Guidelines for core network design

l ITU Rec. M.1034- Guidelines for radio interface design

l ITU Rec. M.816- Guidelines for services and applications

l ITU Rec. M.1036- IMT-2000 frequency allocation (WARC-92)

Facing the globalisation process, in particular in internationaltelecomms, the ITU (International Telecommunication Union)considered a third generation global mobile communicationstandard. A set of guidelines have been issued on different aspects ofmobile communication. The international mobile communicationcommunity has been asked to support ITU's IMT-2000 (InternationalMobile Telephony at 2000 MHz) program with appropriate proposalson all these issues.

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Targets of ITU/IMT-2000 Program

IMT-2000 The ITU vision of global wireless access

in the 21st century

Satellite

MacrocellMicrocell

UrbanIn-Building

Picocell

Global

Suburban

Basic TerminalPDA Terminal

Audio/Visual Terminal

l Flexible and global- Full coverage and mobility at 144 kbps .. 384 kbps- Hot spot coverage with limited mobility at 2 Mbps- Terrestrial based and satellite based radio systems

Flexibility and global coverage are the major requirements asspecified by the IMT-2000 program.The system shall not be designed to support a single application or alimited set of applications, like GSM has been initially designed tosupport high quality speech services only. It rather shall provide abearer platform which is independent from the mobile applications.This requires in particular full flexibility with respect to systemparameters, like transmission reliability and speed.

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Requirementsof IMT-2000/UMTS

l High flexibility to introduce new (and yet unknown) services- Provision of a multiservice platform for the future which

provides a range of quality levels (QoS) to match thedifferent needs of the various data and multimedia services(e.g. wireless internet)

- Rather than offering standardised digital bearers for specificservices

l High spectrum efficiencyl High quality of service

- (particularly speech quality) similar to that provided by fixednetworks

l Provision of small, easy to use, low cost terminals with longtalk time and long standby operation

One major target of the IMT-2000 program is the establishment of abearer platform that is independent from the services, however, thatallows any kind of mobile communication applications. As forinstance GSM (Global System for Mobile Communication) has beendesigned for speech services originally, the systems of the thirdgeneration shall allow any kind of service (e.g. telephony, e-mail,downloads etc.), thus provide suitable bearer services on demand. Inaddition multimedia services shall be supported.Thus, the 3G infrastructure shall be responsible for the provision ofthe required bearer parameters to ensure the required quality ofservice.Of course the default requirements, such as high spectral efficiency,low cost and simple, small terminals, are also on the list of theprogram.

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Multiservice platform

SINGLEphysical

link

Audio/Video

Data

Internet

The problem mobile multimedia or multiservice platforms arefacing, is the simultanous transmission of different kinds of data, i.e.sources with different requirements with respect to the transmissionparameters, on a single physical radio link. Whilst a telephone callrequires realtime connections with minimum transmissin delays, afile download of e-mail service doesn't allow transmission errors.

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3G Timescales19

86

1988

1990

1992

1994

1996

1998

2000

2002

ITU Task Group 8/1

EU Research Programmes RACE I, RACE II, ACTS (FRAMES)

"ITU Letter"

5 modesapproved

Launch UMTSWARC'92

ETSI SMG Activites

US PCS Activities

Japan Activities

The IMT-2000 family of radio access technologies (RAT) covering 5different approaches is a result of global research and specificationactivities since the late 80's of the last century. Based on requirementsset by ITU all over the world various institutions and manufacturershave been working on proposals for suitable RATs.

Major Milestones

- WARC92 (World Administrative Radio Conference) defined spectrum for 3G systems in 1992- Letter from ITU sent to administrations in 1998 with request for proposals based on ITU M.1225 specification "Guidlines for Evaluation of Radio Technologies for IMT-2000"- November 1999 out of 11 proposals for terrestrial systems and 6 proposals for satellite systems 5 IMT-2000 flexible modes have been approved- 2001 first commercial prototype UMTS network launched on Isle of Man- 2002 first commercial launches of UMTS networks expected

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Global Frequency Allocation(WARC'92)

IMT-2000 frequency allocations (WARC-92) UMTS_INT_INT_01.VSD

1800 1900 2000 2100 2200

IMT-2000MSS

S-PCN(DL)

IMT-2000Sat.IMT-2000

UMTS FDD

MSSS-PCN

(UL)

IMT-2000Sat.IMT-2000

IMT-200

0

MSSS-PCN(UL)

MSSS-PCN(UL)

MSSS-PCN

(DL)

MSSS-PCN

(DL)

GSM 1800 (DL) DECT UMTS FDDTDD

TDD

IMT-2000TDD

PCS (UL) PCS (DL)PCSUn.Lic.

MSS: Mobile Satellite System/Service S-PCN: Satellite Personal Communication NetworkDL: Downlink UL: UplinkUn.Lic: Unlicensed band WARC92: World Administrative Radio Conference in 1992

TDD

TDD/FDD TDD/FDDTDD

ITU

Japan(Region 1)

Europa(Region 1)

USA(Region 2)

f [MHz]

WARC'92 conference allocated frequency spectrum for the 3Gsystems. However, a harmonised allocation across the entire globewas not possible due to regional restrictions. Thus, two regions havebeen identified with different allocations.

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ITU FPLMN Vision

IMT-DS(Direct Spread)

UTRA FDD(WCDMA)

3GPP

IMT-TC(Time Code)

UTRA TDD(TD-CDMA)

3GPP

IMT-MC(Multi Carrier)

cdma2000

3GPP2

IMT-SC(Single Carrier)

UWC-136(EDGE)

UWCC/3GPP

IMT-FT(Freq. + Time)

DECT

ETSI

IMT-2000 RAT (ITU-R)

GSM

(MAP)

ANSI-41

(IS-634)

IP-Net

v4, v6IMT-2000 CN

(ITU-T)

UMTS

CN ⇔ RAT Mapping

Gateways and Interworking Functions

The ITU vision for Future Public Land Mobile Networks (FPLMN)covers the radio network domain (Radio Access Technology, RAT) andthe core network domain (Core Network, CN). Several inputs on bothdomains have been approved to become a member of the 3G family.Five radio access technologies have been approved, two of thembelonging to the european approach UMTS (Universal MobileTelecommunication System). Those are the UTRA (UMTS TerrestrialRadio Access) FDD mode (Frequency Division Duplex) and theappropriate TDD mode (Time Division Duplex). In addition twoamerican proposals (cdma2000 und UWC-136) and the DECT (engl.Digital European Cordless Telephone ) standard have been selected.Also different approaches of core network technologies have beenapproved. GSM-MAP (Mobile Application Part) and the americanANSI-41 concept completed by IP are valid IMT2000 members.

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3GPP Partners

TTC (Japan)Telecommunication Technology Committee

CWTS (China)China Wireless Telecommunication Standard Group

ARIB (Japan)Association for Radio Industry and Business

ETSI (Europe)European Telecommunications Standards Institute

TTA (S. Korea)Telecommunications Technology Association

T1 (USA)Standards Committee T1 Telecommunication

TIA (USA)Telecommunication Industry Association

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3GPP AgreementThe Partners have agreed to co-operate in the production of globallyapplicable Technical Specifications and Technical Reports for a 3rdGeneration Mobile System based on evolved GSM core networks andthe radio access technologies that they support (i.e., UniversalTerrestrial Radio Access (UTRA) both Frequency Division Duplex(FDD) and Time Division Duplex (TDD) modes).

The Partners have further agreed to co-operate in the maintenanceand development of the Global System for Mobile communication(GSM) Technical Specifications and Technical Reports includingevolved radio access technologies (e.g. General Packet RadioService (GPRS) and Enhanced Data rates for GSM Evolution (EDGE)).

The Project is called the "Third Generation Partnership Project"and may be known by the acronym "3GPP".

Source : www.3gpp.org

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WCDMA vs. cdma2000 (IS-2000)

l chip rate- WCDMA 3.84 Mcps- cdma2000 3.6864 Mcps

l synchronisation- WCDMA a-synchronous- cdma2000 synchronous using GPS (global

positioning system) signall core network

- WCDMA GSM-MAP- cdma2000 ANSI-41

The two CDMA based radio access technologies (WCDMA andcdma2000) have basic differences in key parameters. Different chiprates and different synchronisation methods are the most obviousones.

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UMTS Services

l 144 .. 384 kbps up to max. speed of 500 km/hl 384 kbps in urban areas up to speed of 120 km/hl 2 Mbps inhouse service in business areas and city

centers with very low mobility ( < 10 km/h )l (Realtime) Bearer servicesl Circuit and packet switched servicesl Asymmetric servicesl Interworking with other radio access networks (e.g.

GSM)l Maintain compatibility to GSM, ATM, IP und ISDN

Initial concept considerations for UMTS services have been launchedin the 80ies alrady. UMTS became a part of the global IMT-2000family which has been specified by the ITU. 1992 the WARC'92conference has allocated the IMT-2000 frequencies. 230 MHz havebeen allocated: 1885-2025 MHz and 2110-2200 MHz. UMTSrepresents the european approach for third generation mobilecommunication.With respect to supported data rates a range of minimum 144 kbpsup to maximum 384 kbps is specified for full mobility and coverage.Up to 2 Mbps are specified for inhouse, i.e. stationary servicesrespectively very low mobility. Bearer services for realtime servicesshall be provided. From the switching point of view, circuit andpacket switched services shall be supported as well as assymmetricand symmetric services. Interworking with other radio access andcore networkss shall be achieved by maintaining minimumcompatibility with those.

Note: Latest considerations (HSPDA - High Speed Packet Data Access) within the3GPP community is planning data rates up to 10 Mbps downlink using e.g.adaptive modulation schemes. However, specifications on that issues are ongoingand will be covered by release 5.

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UMTS QoS

l (RT) Conversational class (eg. Voice)- preserve time relation- conversational pattern

l (RT) Streaming class (eg. Streaming video)- preserve time relation

l Interactive class - best effort (eg. Web browsing)- request - response pattern- preserve payload content

l Background class - best effort (eg. Email)- destination is not expecting data within a certain

time- preserve payload content

UMTS follows the idea of providing a generic mobile communicationplatform. Thus, the quality of service requirements for allconsiderable applications must be supported.Four quality of service (QoS) classes have been defined. Regardingtheir individual technical requirements the following parameters areof interest:Transmission speed (bit rate), transmission reliability (bit error rate,BER), and transmission delay (e.g. realtime requirement).The transmission speed is limited by the available transmissionbandwidth at the air interface, the transmission reliability dependson the available signal to noise ratio only. Transmission delay is notonly given by propagation and processing delay, it also dependsstrongly on the switching technologies. Realtime transmissionbasically requires circuit switched lines, however, packet switchedtechnologies also can maintain realtime transmissions (e.g. voice overIP).

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TSG CNCore Networks

TSG GERANGSM EDGE

Radio Access Network

TSG RANRadio Access

Network

TSG SAServices & System

Aspects

TSG TTerminals

CN WG 1MC/CC/CS (lu)

CN WG 3Interworking withExternal Networks

CN WG 2CAMEL

CN WG 5OSA

(Open Service Architecture)

CN WG 4 MAP/GTP/BCH/SS

GERAN WG 1Radio Aspects

GERAN WG 2Protocol Aspects

GERAN WG 3Base Station Testing

and O & M

GERAN WG 4Mobile Station

Testing

RAN WG1Radio Layer 1specification

RAN WG2Radio Layer 2 spec. & Radio

Layer 3 RR spec.

RAN WG3lub spec, lur speclu spec & UTRAN

O&M requirements

RAN WG4Radio performance & Protocol aspects

SA WG 1Services

SA WG 2Architecture

SA WG 3Security

SA WG 4Codec

SA WG 5Telecom

Management

T WG 1Mobile Terminal

Conformance testing

T WG 2Mobile Terminal

Services & capabilities

T WG 3Universal Subscriber

Identity Module (USIM)

3GPP -Technical Specification Groups

The 3GPP specification work is organised in 5 technical specificationgroups (TSG). Each TSG takes care of a specific area and is divided infurther sub working groups (WG).TSG CN (core network) is looking after network aspects. TSGGERAN is the successor of the former ETSI SMG group andmaintains the GSM phase 2+ issues (e.g. GPRS and EDGE). TSG RAN(radio access network) specifies the WCDMA air interface incl. thelower protocol layers. TSG SA (service aspects) takes care ofapplications and services. TSG T (terminal) specifies all terminalrelated items.For the UMTS air interface in particular the outcome of the TSG RANworking groups WG1 (physical layer) and WG4 (radio parameters) isof interest.

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SMG and 3GPP specifications

ETSISMG Release

3GPPRelease 4

3GPPRelease 99

Requirements 01.xx 41.xxx 21.xxxService Aspects 02.xx 42.xxx 22.xxxTechnical Realisation 03.xx 43.xxx 23.xxxSignalling US – RSS 04.xx 44.xxx 24.xxxRadio Aspects 05.xx 45.xxx 25.xxxCodecs 06.xx 46.xxx 26.xxxData Services 07.xx 47.xxx 27.xxxSignalling RSS – CN 08.xx 48.xxx 28.xxxSIM, USIM 11.xx 51.xxx 31.xxxUE Test Specifications 34.xxx

The ETSI specifications of SMG (special mobile group), which definethe current and future GSM enhancements (e.g. GPRS, EDGE), hasbeen included into the 3GPP specification process. In particular thisis reflected in a re-numbering of the specifications according to the3GPP scheme. Above table illustrates the fusion of ETSI and 3GPPrelease 99 specifications into 3GPP release 4.

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UMTS reference architecture

CNCore Network (PS or CS)

UTRANUMTS Terrestrial Radio

Access Network

UEUser Equipment

Iu

Uu

Three major elements are to be considered:Core network (CN), offering e.g. switching services and gateways toother communication networks. There are circuit switched (CS) andpacket switched (PS) approaches which shall be supported.The radio access network UTRAN (UMTS Terrestrial Radio AccessNetwork) offers radio access to mobile communication network. Allradio subsystem specific functions (e.g. handover and radioressource administration) are covered by the UTRAN.The user equipment (UE) represents the mobile subscriber. It offersapplication interfaces towards the user and provides the radio linktowards the network.

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UMTS network concepts

Circuit Switched

Packet Switched

The evolution from the second (GSM) generation towards the third(UMTS) generation with respect to the core network and the radionetwork is illustrated above.Due to the enhancements with GPRS packet services, the CN of theGSM networks already include the required CS elements (MSC,Mobile Switching Center, GMSC, Gateway MSC, VLR, Visitors LocationRegister, HLR, Home Location Register, EIR, Equipment Identity Register)and the PS elements (GSN, GPRS Service Node).The GSM radio subsystem (BSS, engl. Base Station Subsystem) incl. BSC(Base Station Controller) and BTS (Base Transceiver Station) will becompleted by the UMTS radio subsystem (RNS, Radio NetworkSystem) incl. RNC (Radio Network Controller) and Node B.

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UTRAN architecture

Node B

Node B

Node B

Node B

RNC

RNC

Node B

Iub

Iur

IuUSIM

ME

UE

Uu

Cu

UTRAN

Tasks of the RNC - Radio Network Controller- Allocation of radio ressources (e.g. code channels).- control of one or several node B's- traffic monitoring- admission control- OSI layer 2 of the air interface- Management of QoS radio aspects (e.g. management of channel coder)

Tasks of Node B - Base Station- OSI layer 1 of the air interface (e.g. channel coding, CDMA and FDMA multiplexing, spreading, scrambling etc.)- Management radio links (e.g. transmit power control)

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UTRAN network elements

RNS

RNC

RNS

RNC

Core Network

Node B Node B Node B Node B

Iu Iu

Iur

Iub IubIub Iub

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UMTS

Introduction to 3GPP WCDMABasics of mobile communication

channelsDipl.-Ing. (Univ) Reinhold Krueger

Dipl. Ing. (TU) Heinz MelleinR&S - TRAINING CENTER

© 2002www.rohde-schwarz.com

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Transmission principles

Transmitter ReceiverChannel

source codingchannel codingmodulationRF...

demodulationdetection

estimationdecoding

...

delayattenuation

multipath propagationfading

interference...

Above illustration shows the basic components of a transmissionline: transmitter, channel and receiver. The channel specifies theavailable transmission ressources, such as time, bandwidth andsignal-to-interference-ratio. Transmitter and receiver are trying tooptimise the useage of the availble channel capacities withappropriate technologies for coding and modulation. Thosetechnologies are in general selected according to the type ofconsidered application (e.g. speech transmission) or to optimisesingle transmission parameters (e.g. data rate, bit error rate etc.).

The receiver, in particular in a mobile communication system, facesfast changing channel quality due to fading which needs to becompensated by fast adaptive technologies.In digital systems the source data - after source coding - is a finite setof specified symbols, e.g. binary digits or binary sequences (e.g.ASCII binary representation for textual transmission). The receiverneeds to detect those symbols, however, due to the statisticaldegradation of the signal on the mobile communication channel dueto the superposition of noise and interference, the detection becomesan estimation of the most probable symbol.

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General requirements

l Max data rate ( Bitrate R [bps] )

l Min error rate ( Bit error rate BER )

l Min transmission power ( Ebit/N0 )

l Min bandwidth

l Max availability

l Min complexity, effort and costs

Above listed are the most common requirements to a communicationsystem. Unfortunately, they contradict themselves, as usual. Inaddition some basic laws of communications (e.g. Nyquist criteriaand Shannon laws) restrict the transmission capabilities as well aslegal circumstances (e.g. emission laws, frequency regulations).Thus, the challenge of the standardisation of a communicationsystem is to optimise the useage of available ressources under givencircumstances.

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Signal analysis

Fourier Analysis / Transformation

Periodic signals can be transformed into the frequency domain byFourier analysis. Thus, they can be represented as a finite number ofcosine signals with different amplitudes, phases and periods. Due tothat, signals can be analysed in both domains, the time and thefrequency domain, depending on the information required. Thefrequency domain analysis in particular is of interest to evaluate thefrequency response of transmission components, such as transmittersand receivers as well as the transmission channel itself.

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Signal representation

Time domain Frequency domain Constellation

The representation of a signal in the complex plane, as the sum of aninphase and quadrature component, leads to a suitable format toevaluate the transmission reliability of a given signal shape. Inaddition it easily allows the design of digital modulation schemes,such as QPSK for WCDMA.The magnitude of the vector represents the instant signal amplitude,the angle the instant signal phase.

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Modulation & Demodulation

In radio transmission technologies the data is carried by RF carriers.The carrier frequency in particular defines the range the transmissioncan achieve, and thus, it has a great impact on the required signalpower. The data is manipulating the RF carrier by appropriatemodulation schemes. Basically three RF carrier parameters can bemodulated: Amplitude, frequency and phase. Those physicalparameters can be detected by a receiver circuit and thus the data canbe regenerated there. This leads to the basic modulation techologies,such as amplitude modulation, frequency modulation and phasemodulation. Depending on the type of data, analog or digitalmodulation schemes are to be considered.Starting with the mobile communication systems of the 2nd

generation, all user and control data to be transmitted are digitalsequences. Thus, digital modulation schemes are requried, calledamplitude shif keying ASK, frequency shift keying FSK or phase shiftkeying PSK, accordingly. The latter in particular is very robustagainst amplitude variations, as we face them in mobile radiochannels due to multipath propagation. Thus, the quadrature phaseshift keying QPSK has been selected for the UMTS air interface.

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Signal-to-Noise ratio S/N

⊕ Ideal LP s(t) + n(t)

noise

Signal

f [Hz]

power density[W/Hz]

B/2-B/2

N0

N = N0 · B

Signal power S

Tim

e do

mai

nF

requ

ency

dom

ain

Assuming the wanted signal s(t) and the superposing interferencesignal n(t) are ergodic processes, the signal to interference ratio SIR isdefined as the quotient of the mean signal power and the meaninterference power. In case of additive white gaussian noise (AWGN)superposition, the signal to noise ratio SNR is to be considered as thequotient of the mean signal power S and the noise power N. Whitegaussian noise is evaluated in real, band limited systems modelledby an ideal low pass. Thus, the following relations are of interest:SNR = S/N = Ebit· R/N 0 Bwith R = Bit rate and Ebit = Energy per Bit. N0 = noise power density(which is equal to the variance of the gaussian noise amplitudedistribution) and B = available channel bandwidth, with B ≥ wantedsignal bandwidth.With R = 1 s-1 and B = 1 Hz the SNR is standardised with respect toone single bit per Hertz, and thus the following parameters areachieved:SNRbit = Ebit/N0

orSNRbit[dB] = 10· log10(Ebit/N0).SNRbit is an important value to evaluate the quality of a transmissionsystem. The smaller the required SNRbit , the better, i.e. more efficientthe system.

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Bit Error Ratio (BER)

-12

-11

-10

-9

-8

-7

-6

-5

-4

-3

-2

-1

0

-10 -5 0 5 10 15

Ebit/N0 [dB]B

ER

10

x

3 dB

bipolar

unipolar

The bit error probability BEP, or the resulting bit error rate BER dueto signal distortion by AWGN on the transmission chain isdepending on the available SNR only, thus it is a function of theavailable Ebit/N0.

Consequently the modulation schemes have direct impact on theBEP.For instance, a digital, unipolar signal ("0" = +A Volts and "1" = 0) is3 dB worse with respect to the BEP compared to a bipolarmodulation scheme ( "0" = +A Volts und "1" = -A Volts). The sameapplies when comparing a BPSK signal with a QPSK signal, wherethe QPSK is more sensitive, however it allows the double data rate asthe BPSK modulation at a given bandwidth.

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Multipath propagation

Direct line of sight

Reflection

The mobile radio communicaton channel does suffer of variousimpacts due to the nature of mobility and radio propagation, whichare not of interest in line based communication systems. Due toreflection and dispersion effects on the different possible signal pathsfrom the transmitting antenna to the receiving antenna, the receiverhas to deal with the superposition of multiple signal "copies", ratherthan with a clean "line of sight" signal (which even could be notavailable at all for some time).The fading characteristics can be modelled by a multiple path modelwith an average channel impulse response, reflecting the statisticalnature of the fading process. However, due to the complexity of themathematical fading models, still empirical models are of interest, inparticular when focussing on particular mobile communicationsystems.Based on that, various fading profiles have been specified by the ITUin order to allow the definition of unambiguous conformance testingscenarios. These are basically described by a sample impulseresponse reflecting the mean values of their statistical parameters (eg.path loss, delay spread) and by their dynamic performance (eg.Doppler shift, statistics like Rayleigh or Rice distributions etc.).

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Channel impulse response

Scattering

Reflections

Origin impulse

Due to different path propagation delays caused by echo reflection anddispersive reflections, the origin signal arrives scattered and delayed atthe mobile receiver. The impulse response of such a fading channelrepresents all different multi-path-propagations with their specificparameters delay and loss, however, it does not represent the dynamicbehaviour of these parameters. However, for realistic description andthus simulation of fading performance, that must be taken into accountalso (Rayleigh, Rice Fading). The impulse response leads to a veryimportant fading parameter, when evaluating the delay spread caused bythe fading channel. This parameter describes the average widening of achannel input pulse (Dirac Pulse) over time. The calculation of the delayspread is equal to the calculation of the standard deviation, regarding thepropagation delay t as the stochastic variable, and the normalised signalpower P refers to the probability densitiy function of t. The reciprocal ofthe delay spread is also known as coherent fading bandwidth. The widerthe fading channel impulse response is in time, the greater the delayspread and thus the smaller the coherent fading bandwidth. When thedelay spread exceeds the symbol period of the transmitted signal, it willcause intersymbol interference (ISI). Since significant ISI obviously limitsthe maximum symbol rate on the radio channel it causes low passbehaviour with cut-off frequency ≈ the reciprocal of the maximumpropagation delay. This kind of fading is classified as frequency selective.This matter is important for wideband systems as WCDMA in particular.For small delay spreads with respect to the symbol period the frequencyselectivity can be neglected.

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Doppler effect

The doppler effect is well known in acoustics. However, it must beconsidered in the world of electromagnetic wave propagation aswell. Due to the mobility of the receiver in mobile communicationsystems, frequency shifts due to the doppler effect need to becompensated.With α = 0 or 180 the receiver moves directly towards or away fromthe transmitter. In those cases a maximum frequency shift isachieved.Example:f = 2 GHz (UMTS frequency)c = 3· 108 m/s (velocity of light)v = 60 m/s ( 216 km/h, velocity of the receiver with respect to thetransmitter )gains a frequency drift of +/- 400 Hz.

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Channel capacity(Shannon-Hartley law)

Capacity in [bps] per [Hz]

-2

0

2

4

6

8

10

12

14

-10 0 10 20 30 40

SNR [dB]

+⋅=NS

BC 1log 2

SNRBC ⋅⋅≈31

1>>NS

[ ]NSdBSNR log10=

The channel capacity of a frequency band limited channel, suffering ofadditional white gaussian noise (AWGN), assuming an equallydistributed binary set of symbols, without any channel coding, isgiven by the Shannon-Hartley equation:

C = B · log2(1 + S/N)C = channel capacity in bits per secondS/N = Signal to Noise power ratioB = bandwidth in Hertz

In most cases S/N >> 1 can be assumed. Thus, defining SNR = 10 log(S/N), the following simple approximation can be used:

C = 1/3 · B· SNRThis fundamental relation is the basis of transmission technologies. Itoutlines in particular, that with wide frequency bandwidth even verynoisy channels still can transport data with specified reliability, whichin fact is the basic principle for WCDMA.It is important to note, that this relation also is the basis for channelcoding schemes, where the target is to reduce bit errors at a given SNR,and thus increasing the channel capacity for a give transmissionreliability.Typical values:Classic telephony B = 3.1 kHz S/N = 40 dB C = 40 kbpsTV broadcast channel B = 5 MHz S/N = 45 dB C = 75 MbpsGSM B = 200 kHz S/N = 15 dB C = 1 MbpsWCDMA B = 5 MHz S/N = 10 dB C = 16 Mbps

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Multiple access schemes

Using the Shannon-Hartley equation, the maximum data volume thatfits into a given channel can be represented by a simple block. Thedimensions of that block are given by the physical channelparameters bandwidth, time frame and signal amplitude respectivelythe signal to noise ratio.To allow multiple access to that channel means in that model, todistribute the available block to multiple subscribers. In FDMA(frequency division multiple access) schemes the different users getdistinct portions of the frequency domain. In case of TDMA (timedivision multiple access) the time domain is split into distinct slots.Those are allocated to different users then. To divide the block alongthe signal to noise domain, different users are coding their signalwith suitable algorithms which is known as CDMA (code divisionmultiple access).To achieve even more complex distributions, combinations of thementioned multiple access schemes are possible. For instance GSMapplies a combination of FDMA (200 kHz frequency channels areassigned to individual users) and TDMA (one out of 8 possibletimeslots are assigned to individual users). UMTS FDD appliesFDMA (5 MHz frequency channels) and CDMA. UMTS TDD appliesall three of them.

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Cellular networks: SDMA

Due to the natural attenuation of a radio signals depending on thereceivers distance to the transmitter (~ 1/d2, d = distance), thecoverage of a base station is limited. This allows in cellular FDMAsystems for instance the re-use of frequencies in other cells, in CDMAthe re-use of scrambling codes is possible. Thus, the cellualrestructure allows multiple access to a mobile network called SDMA(space division multiple access), however, the users can't be withinthe same cell coverage area.

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Comparison access schemes

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UMTS

Introduction to 3GPP WCDMASignal spreading with orthogonal

codes

Dipl.-Ing. (Univ) Reinhold KruegerDipl. Ing. (TU) Heinz Mellein

R&S - TRAINING CENTER© 2002

www.rohde-schwarz.com

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Spreading of two signals

Example of a transmitter CDMA_PRI_03.VSD

t

+1

-1

01

0 0

t

+1

-1T 2T

t

+1

-1T 2T

t

+1

-1T 2T

d1(t)

c1(t)

d2(t)

c2(t)

t

+1

-1T 2T

x1(t) = d1(t ) * c 1(t)

t

+1

-1T 2T

x(t) = x1(t) + x2(t)

t

+1

-1T 2T

+2

-2

x2(t) = d2(t ) * c 2(t)Multiplication

Sum

Multiplication

0 -> +11 -> -1

The multiplication of binary data d - similar to exclusive OR resp.modulo2 operation to logical representation of data - with a higherrate binary code word c results in a binary sequence x that requiresobviously more bandwidth than the original data d. This operation isknown as signal spreading, due to the signal spreading over thebandwidth.In the illustrated example the upper transmitter multiplies the datad1 = {01} with the code word c1 = {0101}, which corresponds to anexclusive OR operation of the logical symbols. Another transmittermultiplies its data d2 = {00} with another code word c2 = {0110}. Then,the sum x1 + x2 is transmitted.This illustrates the principle situation on a mobile radio channel,where for instance a single base station needs to provide multiplemobile station with data at the same time on the same frequencychannel, or a mobile station wants to send two different types of data(e.g. video and speech) simultaneously to its serving base station.

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Despreading of two signals

Example of a receiver

t

+1

-1T 2T

t

+1

-1T 2T

c1(t)

c2(t)

y(t)

t

+1

-1T 2T

+2

-2

y(t) * c1(t)

t

+1

-1T 2T

+2

-2

t

+1

-1T 2T

(2+2+0+0)/4 > 0 => 0

(0+0-2-2)/4 < 0 => 1

y(t)

t

+1

-1T 2T

+2

-2

y(t) * c2(t)

t

+1

-1T 2T

+2

-2

t

+1

-1T 2T

Integration

Multiplication

MultiplicationAverage

Average

CDMA_PRI_04.VSD

0 -> +11 -> -1

(2+2+0+0)/4 > 0 => 0 (0+0+2+2)/4 > 0 => 0

The receiver gets the total signal, however, is looking for one of thetwo data streams only. The multiplication of the received total signalr = x1+x2 with the code word c1 again, results obviously in theoriginal data d1. The same applies to d2 when multiplying r with thecode word c2. This simple operation is known as de-spreading.However, to allow that technique of spreading and despreading, thecodes need to fullfill a special requirement: They need to beorthogonal to each other.To explain orthogonality of codes, it makes sense to compare a codeword of length n with a n-dimensional vector. When the vectorscorresponding to the regarded code words are orthogonal to eachother in a geometric sense, also the code words are orthogonal toeach other in an abstract mathematical sense. This correspondancealso leads to the method of verifying the orthogonality of two codewords. The corresponding vectors are orthogonal when their scalarproduct is zero. The same applies to the code words by building anappropriate product to verify if this is zero or not.Thus, the multiplication of data with orthogonal spreading codesprior to transmission together with other spreaded data allows thesimultaneous multiple access of receivers to the same frequencychannel. Each receiver - providing the spreading code is known - candespread its own data.

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Example with three signals

Example of spreading and despreading CDMA_PRI_01.VSD

User DataCode 0 1 0 1 0 1 0 1

Tx Data 0 1 0 1 0 1 0 1

+1

-1

+1

-1

+1

-1

Code

Tx Data

Sum

+1

-1

(-1+3+1+1)/4= 1;

+3

-3

(1+1-1+3)/4= 1;

=> 0 => 0

0 0

USER 1

User DataCode 0 0 1 1 0 0 1 1

Tx Data 1 1 0 0 0 0 1 1

+1

-1

+1

-1

+1

-1

Code

Tx Data

Sum

+1

-1

(-1-3-1+1)/4= -1;

+3

-3

(1-1+1+3)/4= 1;

=> 1 => 0

1 0

USER 2

User DataCode 0 0 0 0 0 0 0 0

Tx Data 1 1 1 1 1 1 1 1

+1

-1

+1

-1

+1

-1

Code

Tx Data

Sum

+1

-1

(-1-3+1-1)/4= -1;

-3

(1-1-1-3)/4= -1;

=> 1 => 1

1 1

USER 3

Product Product Product

User Data User Data User Data

-3 -3

0 -> +11 -> -1

Above illustration proves, that the CDMA principle is valid for anynumber of users. The only restriction is given by the number ofavailable orthogonal codes.The binary symbols of spreading codes are called chips, in order toallow simple separation between spreaded data and original data.

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CDMA Principles

l All users use the same frequency for uplink and thesame frequency for downlink (reuse factor = 1)

l Each user is assigned a unique code sequence(spreading code)

l This code is used to encode the information to betransmitted

l The spread signals of all users are summed andtransmitted together

l The receiver knows the code sequence of the user inadvance, decodes the received signal after receptionand recovers the original data of the user

l This is possible since if the cross correlation betweenthe code of the desired user and the codes of allother users are very small

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Spreading and Bandwith

30 kbps

15 kbps

3.84 McpsSpreading

3.84 Mcps

Spreading

3.84 Mcps

Regarding the spreading operation by multiplication of data with aspreading code in the time domain, the spectrum of the signal ismodified in the following way:The origin, narrow band data signal will be spreaded over thebandwidth due to the spreading operation. Thus, after spreadingoperation, the required bandwidth is increased by the spreadingfactor which corresponds to the number of chips of the used codeword. Since the spreading operation has no impact at all to the totalsignal energy, the spectral power densitiy after the spreadingoperation is reduced accordingly.When two spreaded signals are superposing over the samebandwidth, the total power density is increased. However, in thefrequency domain there is no way to seperate the two origins again.The only way is the de-spreading operation.This is the way WCDMA in UMTS works. All user or control data arespreaded to a fixed bandwidth of 3.84 MHz. This is achieved byusing a fixed chip rate of 3.84 MChip/s.

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Processing gain

Despreading

3.84 Mcps

Channel 15 ksps

Processing gain

Processing gain increases with the spreading factor

The despreading operation recovers the part of the total receivedsignal which has been spreaded by the used code word. In thefrequency domain the origin narrow band signal arises again. Theresidual spreaded signals within the total wideband signal remain asthey are, since they are not touched by the de-spreading operation atall due to the orthogonality of the spreading codes. However, theirenergy remains, and might be regarded as a wideband interference.They reduce the available SIR for the wanted signal. It is obvious,that the more spreaded signals are included, the worse the availableSIR for the wanted signal becomes. This explains the theory ofCDMA, which distributes the total SIR of a given channel to multipleusers.It is obvious that the processing gain in the receiver due to thedespreading operation is directly related to the used spreadingfactor.Finally the spreading factor SF can be definied in different ways:- Number of chips per code word- Relation between chip rate and user data rate- Relation between spreaded signal bandwidth and origin signalbandwidthThe processing gain is specified by 10log(SF).

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Properties ofSpread Spectrum Signals

l Multiple access capabilities- Receiver is able to distinguish between users provided

each user has a unique code

l Protection against multipath interference- Many pathes between a transmitter and a receiver

- Received signals are copies of the transmitted signal butwith different amplitudes, phases, delays, ...

- Spread spectrum modulation can combat and usemultipath interference

l Privacy- The receiver can only recover the data if the code is

known to the receiver

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CDMA security aspects

l Anti-jamming capability, especially narrowbandjamming- See interference rejection

l Low probability of interception- Due to the low power density, it is not easy to

detect and intercept the spread spectrum signal byhostile listeners

l è Attractive for military applications

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CDMA interference rejection

l Narrow band interferencel A CDMA receiver rejects that interference due to spreading

Despreading

Interferer

Processing gain

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DS - CDMA - Spectrum

l The energy of a narrow band signal is spread over a widebandwidth by multiplication of the low rate data with symbolperiod Ts and a code word with chip period Tc, while Tc >> Ts.

l Spreading factor SF = chip rate 1/Tc : symbol rate 1/Ts

l SF corresponds to the length of the code word

1/Tcf

1/Ts

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DS- CDMATransmitter and Receiver design

Spreading

Direct sequence CDMA transmitter & receiver CDMA_PRI_10.VSD

CodeGene-rator

Up

converter

CarrierGenerator

Datasignal

Codesynchroni-

sation& tracking

DataDemodulator

Ts

Tc

1/Ts = Data Rate Bt = Transmission bandwidth1/Tc = Chip Rate Bi = Information bandwidth

Tc << TsBt >> Bi

Constant Powerspectral density

Down

converter

CarrierGenerator

Despreading

CodeGene-rator

Datasignal

The similar spreading and despreading operations allow very similartransmitter and receiver designs for CDMA. The most importantissue for the receiver is the knowledge of the spreading code used inthe transmitter.

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Principle of signal spreading (Direct sequence) CDMA_PRI_06.VSD

1

-1

t

1

-1

t

t

1

-1

Data signal

Code signal

Spreaded signal

Tc

1/Ts=Data rate Ts/Tc=Spreading factor Chip Rate >> Data rate1/Tc=Chip rate

Ts

Principle of Direct sequenceCDMA (DS-CDMA)

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Generation of orthogonal,variable spreading codes (OVSF)

1

1

-1

1

1

Generation of OVSF codes UMTS_CDS_SPC_06.VSD

1

1 1

1 1

-1 -1

1

1

1 -1

-1 1

-1 1

-1

Repeat

Invert

Repeat

Repeat

Invert

Invert

According to the definition of the UMTS WCDMA signal, theresulting chiprate of any spreading operation shall be 3.84 MChips/salways. Thus, regarding different data rates of the data sources,variable spreading factors are required. A very simple method togenerate orthogonal spreading codes with varibale length is given byHadamard functions, as illustrated above. By this method,orthogonal spreading codes of length 2k can be generated.

Note: Another method found by Walsh, which is almost similar tothe above illustrated, is used in IS-95 or cmda2000. Those codes areknown as Walsh Codes accordingly. The Walsh method results inexactly the same spreading code sequences, however, their order inthe code tree columns is different.

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Code tree of OVSF codes

Code-tree for generation of OVSF codes UMTS_CDS_SPC_02.VSD

Cch,1,0 = 1

Cch,4,0 = (1,1,1,1)

Cch,4,1 = (1,1,-1,-1)

Cch,4,2 = (1,-1,1,-1)

Cch,4,3 = (1,-1,-1,1)

Cch,2,0 = (1,1)

Cch,2,1 = (1,-1)

Cch,8,0 = (1,1,1,1,1,1,1,1)

Cch,8,1 = (1,1,1,1,-1,-1,-1,-1)

Cch,8,2 = (1,1,-1,-1,1,1,-1,-1)

Cch,8,3 = (1,1,-1,-1,-1,-1,1,1)

Cch,8,4 = (1,-1,1,-1,1,-1,1,-1)

Cch,8,5 = (1,-1,1,-1,-1,1,-1,1)

Cch,8,6 = (1,-1,-1,1,1,-1,-1,1)

Cch,8,7 = (1,-1,-1,1,-1,1,1,-1)

The code tree allows a simple view of available orthogonal variablespreading codes at a glance.

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Numbering of spreading codes

SF=1

Spreading code numbering UMTS_CDS_SPC_01.VSD

SF=2

SF=4

SF=8

SF=16

SF=32

SF=64

SF=128

SF=256

2,0

2,1

4,0

8,016,0

32,0

64,0128,0

256,1

256,3

256,4256,5

256,6

256,7

256,8

256,9

256,10256,11

256,12

256,13

256,14

256,15

16,15

16,1

16,216,3

16,4

16,5

16,6

16,7

16,8

16,916,10

16,11

16,12

16,13

16,14

8,1

8,2

8,3

8,4

8,5

8,6

8,7

4,1

4,2

4,3 256,249

256,250

256,251

256,252

256,253

256,254256,255

256,248

1,032,1

32,31

64,1

64,2

64,3

64,62

64,63

128,126

128,127

256,2

128,125

128,124

128,1

128,2

128,3

128,4

128,5

128,6

128,7

32,30

::

256,0

According to the code tree representation a spreading codenumbering scheme has been introduced for WCDMA. Thus, a singlespreading code is identified by its spreading factor SF and a floatingnumber 0 .. SF-1 to distinguish spreading codes of the samespreading factor.

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Blocking

Blocking of codes UMTS_CDS_SPC_07.VSD

SF 4DataCch,4,2 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

0 0 0 0

0 1 0 1 0 1 0 1 1 0 1 0

0 1 0 1Cch,8,4

Cch,8,5

0 0SF 8

0 1 0 1 0 1 0 1 1 0 1 0

0 1 0 1

SF 16

Cch,16,8

Cch,16,9

Cch,16,10

Cch,16,11

0 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 1 0 1 0 1 0 1 0 0 1 0 1 1 0 1 0 0 1 0 1 1 0 1 0 0 1 0 1 1 0 1 0 1 0 1 0 0 1 0 1

2,0

2,1

16,4

16,5

16,6

16,7

16,8

16,9

16,10

16,11

8,2

8,3

8,4

8,5

4,1

4,2

1,0

2,0

2,1

16,4

16,5

16,6

16,7

16,8

16,9

16,10

16,11

8,2

8,3

8,4

8,5

4,1

4,2

1,0

Data

Data

SF 4DataCch,4,2 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

0 0 0 0

0 1 0 1 0 1 0 1 1 0 1 0

0 1 0 1Cch,8,4

Cch,8,5

0 0SF 8

0 1 0 1 0 1 0 1 1 0 1 0

0 1 0 1

SF 16

Cch,16,8

Cch,16,9

Cch,16,10

Cch,16,11

0 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 1 0 1 0 1 0 1 0 0 1 0 1 1 0 1 0 0 1 0 1 1 0 1 0 0 1 0 1 1 0 1 0 1 0 1 0 0 1 0 1

Data

Data

Basically all spreading codes of the same spreading factor areorthogonal to each other. Also codes with different spreading factorscan be orthogonal to each other, however, not all of them. Aspreading code is neither orthogonal to its own child codes nor to itsparent code. Thus, a single code is blocking defined branches of thecode tree which must be considered during radio resource allocation.

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Blocking

16,132,2

32,3

256,8256,9256,10256,11256,12256,13256,14256,15

32,1

64,2

64,3

128,4

128,5

128,6

128,7

2,0

4,0

8,0

16,0

32,0

64,0128,0

1,0

256,0

Blocking of codes UMTS_CDS_SPC_09.VSD

256,1

256,3256,4256,5256,6256,7

16,2

16,38,1

64,1

256,2128,1

128,2

128,3

256,0 Used code

Blocked code

Free code

Legend

This example shows the blocking of the complete upper branch of thecode tree when using the 256,0 code (red branch). However, still theother codes (green) are available out of this subtree.

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Correlation of binary sequences

l CorrelationBit sequences get compared with each other. Thecorrelation value is the amount of matching bitsminus the amount of unmatched bits

l Auto CorrelationA bit sequence is compared with itself and with allshifted versions of itself

l Cross CorrelationDifferent bit sequences and the shifted versions ofthis sequences are compared with each other

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Auto correlation

Auto-correlation BASICS_ACC_07.VSD

Sequence length (T)

Bit length (t)

Bit sequence (S) Bit sequence (S)

Bit sequence (S)

Bit sequence (S)

Bit sequence (S)

Bit sequence (S)

Bit sequence (S)

With respect to the synchronisation aspect the auto correlationproperties of orthogonal codes are of interest.The auto correlation of a binary sequence is a measure of thesimilarity of a sequence with its own shifted versions. Of course, thesimilarity of a sequence with itself, i.e. with a non-shifted copy ofitself, will gain the maximum. However, strong similarities withshifted versions have unpleasant impact on the synchronisationcapabilities of such a signal regarding the multipath progpagation.

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Auto correlation of orthogonalcodes

Auto-correlation of orthogonal codes CODES_OCD_06.VSD

0 0 1 1 1 1 0 0 1 1 0 0 0 0 1 1

0 0 1 1 1 1 0 0 1 1 0 0 0 0 1 1 0

0 0 1 1 1 1 0 0 1 1 0 0 0 0 1 1

0 0 1 1 1 1 0 0 1 1 0 0 0 0 1 1

0 0 1 1 1 1 0 0 1 1 0 0 0 0 1 1 0 0 1 1 1 1 0 0 1 1 0 0 0 0 1 1

1 1

8

1 11 1 1 1

0 0 1 1 1 1 0 0 1 1 0 0 0 0 1 1 0 0 1 1 1 1 0 0 1 1 0 0 0 0 1 1

1 1 1 1 1 1 1 1 1 1 1 11 1 1 11 1 1 1-1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1

32

0 0 1 1 1 1 0 0 1 1 0 0 0 0 1 1 00 0 1 1 1 1 0 0 1 1 0 0 0 0 1 1

-24

0 0 1 1 1 1 0 0 1 1 0 0 0 0 1 1 0 0 1 1 1 1 0 0 1 1 0 0 0 0 1 1

0

-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

Above illustration explains the calculation of the auto correlation of aselected code, presented by its logical representation 001100110011...

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-1,2

-1

-0,8

-0,6

-0,4

-0,2

0

0,2

0,4

0,6

0,8

1

1,20 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60 62

Bit shifts

Sequence length N = 64

Auto correlation function (ACF)of orthogonal codes

Above illustration shows the auto correlation function of a ortogonalcode sequence. The auto correlation value is drawn with respect tothe relative shift of the sequence and its copy in chip durations. Asexpected, at the relative shift of zero a maximum of correlation isachieved, which then is normalised to 1. However, also non-zerorelative shifts outline significant correlation which doesn't allowsimple correlation reception.

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Cross correlation

Cross-correlation BASICS_ACC_08.VSD

Sequence length (T)

Bit length (t)

Bit sequence (S) Bit sequence (S)

Bit sequence (T)

Bit sequence (T)

Bit sequence (T)

Bit sequence (T)

Bit sequence (T)

Cross correlation describes the similarity of two different sequences.In case of orthogonal spreaded sequences the cross correlation is zerowhen they are not shifted in time to each other, due to theirorthogonality - in fact orthogonality means no correlation. However,the question is what happens to the required orthogonality when thespreaded sequences are not synchronised in time. Thus, it is ofinterest to evaluate the cross correlation properties of orthogonalcode sequences.

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Cross correlation of orthogonalcodes

Cross-correlation of orthogonal codes CODES_OCD_09.VSD

0 1 1 0 1 0 0 1 1 0 0 1 0 1 1 0

0 0 1 1 1 1 0 0 1 1 0 0 0 0 1 1

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0

0 1 1 0 1 0 0 1 1 0 0 1 0 1 1 0

0 0 1 1 1 1 0 0 1 1 0 0 0 0 1 1

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

0

24

-1-1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1

-1 -1

0 0 1 1 1 1 0 0 1 1 0 0 0 0 1 1

0 1 1 0 1 0 0 1 1 0 0 1 0 1 1 0

0 0 1 1 1 1 0 0 1 1 0 0 0 0 1 1

0 1 1 0 1 0 0 1 1 0 0 1 0 1 1 0

1 1 -1 1 -11 1 1

0 1 1 0 1 0 0 1 1 0 0 1 0 1 1 0

0 0 1 1 1 1 0 0 1 1 0 0 0 0 1 1 00 0 1 1 1 1 0 0 1 1 0 0 0 0 1 1

0 1 1 0 1 0 0 1 1 0 0 1 0 1 1 0

0

11 1 1 11 11 1 1 111 1 1 1-1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 0

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-1,2

-1

-0,8

-0,6

-0,4

-0,2

0

0,2

0,4

0,6

0,8

1

1,2

0 2 4 6 8

10

12

14

16

18

20

22

24

26

28

30

32

34

36

38

40

42

44

46

48

50

52

54

56

58

60

62

Bit shiftsSequence length N = 64

Cross correlation function (CCF)of orthogonal codes

The above illustration shows the cross correlation between twodifferent orthogonal spreading codes. Per definition it is zero due totheir orthogonality when the sequences are synchronised, i.e. zerorelative shift. However, obviously the orthogonality is lost when thetwo different sequences appear shifted in time.Thus, the CDMA system using orthogonal codes as desribed up tonow only works when the multiple spreaded signals aresynchronuous. However, the consideration of the auto correlationproperties does not offer sufficient synchronisation capability of suchsignals. Another signal processing stage is required in order to allowsufficient synchronsiation for the despreading operation: Scrambling

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Summary Orthogonal Codes

l CorrelationOrthogonal codes have zero correlation if they arenot shifted against each other

l Cross-correlationShifted versions of different orthogonal codes havehigh correlation=> Time alignment necessary

l Auto-correlationShifted versions of the same orthogonal code havehigh correlation=> Cannot be used for synchronisation in time

l Orthogonal Codes are ideal for channel separation ifthe codes are time aligned

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UMTS

Introduction to 3GPP WCDMASignal scrambling with PN sequences

Dipl.-Ing. (Univ) Reinhold KruegerDipl. Ing. (TU) Heinz Mellein

R&S - TRAINING CENTER© 2002

www.rohde-schwarz.com

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Block Scrambling

Channel ⊕⊕

PN Sequence PN Sequence

a(k)x(k)

c(k)

a(k)x(k)

c(k)

c(k) = a(k) ⊕ x(k) a(k) = c(k) ⊕ x(k)

⊕ = modulo 2 (XOR)

ReceiverTransmitter

The statistics of a data sequence a(k) depends on the statistics of theorigin source data. For instance appears the probability of a singleletter with different probabilities in different languages, i.e. they havedifferent a-priori probabilities. For instance the ASCII standardspecifies a source coding scheme which represents individual letterswith a specific 8 bit sequence. Thus, the probability of the binarydigits is directly depending on the a-priori probabily of theindividual ASCII coded letters.To achieve a reliable transmission of data in digital systems the bitclock is required at any time. The clock signal could be retrievedfrom a separate clock line, however, this is not very simple in radiosystems. Thus, the clock must be retrieved from the received signal,i.e. altering bit sequences would be appreciated. However, thisdepends again on the a-priori probability of the source symbols. Toavoid long constant bit sequences the data are scrambled prior totransmission using pseudo noise sequences. The statistics of such PNsequences is such that the probability of binary "0" and binary "1" isequal to 50% for a sufficient period of time.The receiver can descramble the received signal when the used PNsequence is known, however, synchronisation of the PN generators isrequired. This can be achieved by adding pilot sequences to thesignal.In fact UMTS applies block scrambling by using special PNsequences introduced by Gold, so-called Gold codes.

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Pseudo Noise Sequences

l Pseudo Noise (PN) Sequenzesl Simple, reproduceable generationl Properties of random sequences

l Other names- PRBS - Pseudo Random Bit Sequences- PN sequences- Maximal-length (shift-register) sequences- m-sequences

Pseudo Noise sequences are random with respect to their statisticsand correlation properties, however, they can be easily reproducedand thus can be exactly predicted.

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PN sequence generation withfeedback shift register

Feedback shift register for generation PN sequences CODES_PCD_01.VSD

1 2 3 i mr

xm-mxm-1xm

m-2 m-1

xm-2 xm-3 xm-i xm-r xm-(m-2) xm-(m-1)

xm+xm-i+xm-r+1

ir = {i,r,m)

l Polynomial representation of the register: xm+xm-i+xm-r+1

l Feedback points: ir = {i, r, m}

The generation of PN sequences is quiet simple using feedback shiftregisters.The feedback of shift register content at certain feedback points irresults in a PN sequence. In case of m cells the shift register can have2m-1 states which represents the maximum length the PN sequence,since the state all "0" is excluded.

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PN sequence with max length(m-sequence)

Maximum-length sequences CODES_PCD_02.VSD

1

0 0 0 1

Ir = {1,4}y=x4+x3+1

0 0 011 0 0

1 1 1 01 1 1 10 1 1 11 0 1 10 1 0 11 0 1 01 1 0 10 1 1 00 0 1 11 0 0 10 1 0 00 0 1 0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

Length of sequence

0 0 0 1

Ir = {3,4}y=x4+x+1

0 0 01

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

Length of sequence

0 0 0 1

I r = {2,4}y=x4+x2+1

0 0 01

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

Length of sequence

1 0 000 1 000 0 111 0 011 1 000 1 111 0 100 1 011 0 111 1 011 1 111 1 100 1 10

1 0 000 1 011 0 100 1 000 0 100 0 011 0 000 1 011 0 100 1 000 0 100 0 011 0 00

The maximum length of 2m-1 is not achieved with all possiblefeedback circuits. Only a few configurations produce sequences ofthe maximal length called m-sequences.Above illustrations show two m-sequence circuits producingmaximum length sequences with L = 15 = 24 - 1.The third feedback proposal does not achieve maximum length.

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Auto correlation PN sequence

Auto-correlation BASICS_ACC_02.VSD

31

1 0 0 0 0 1 0 1 0 1 1 1 0 1 1 0 0 0 1 1 1 1 1 0 0 1 1 0 1 0 01 0 0 0 0 1 0 1 0 1 1 1 0 1 1 0 0 0 1 1 1 1 1 0 0 1 1 0 1 0 0

1 0 0 0 0 1 0 1 0 1 1 1 0 1 1 0 0 0 1 1 1 1 1 0 0 1 1 0 1 0 01 0 0 0 0 1 0 1 0 1 1 1 0 1 1 0 0 0 1 1 1 1 1 0 0 1 1 0 1 0 0 1

-1

1 0 0 0 0 1 0 1 0 1 1 1 0 1 1 0 0 0 1 1 1 1 1 0 0 1 1 0 1 001 0 0 0 0 1 0 1 0 1 1 1 0 1 1 0 0 0 1 1 1 1 1 0 0 1 1 0 1 0 0 10

1 0 0 0 0 1 0 1 0 1 1 1 0 1 1 0 0 0 1 1 1 1 1 0 0 1 1 0 1 001 0 0 0 0 1 0 1 0 1 1 1 0 1 1 0 0 0 1 1 1 1 1 0 0 1 1 0 1 0 0 1

00

x5 + x2 + 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 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

The auto correlation of m-sequences is almost ideal. There ismaximum correlation for exact copies of the signal, and almostneglectable correlation - provided long sequences - in case of shiftedcopies.

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-0,4

-0,2

0

0,2

0,4

0,6

0,8

1

1,2

t/T

sequence length L

-1/L

Auto correlation of m-sequences

The auto correlation of m-sequences have very strong periodicalmaxima with the distance of L. In between the correlation is equal to- 1/L. Thus, for large L this is neglectable. This is very muchappreciated for synchronisation purposes.

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Auto correlation of a sequencewhich is not a m-sequence

Auto-correlation CODES_PCD_05.VSD

Auto-correlation ofx5+x+1

-0,6

-0,4

-0,2

0

0,2

0,4

0,6

0,8

1

1,2

-1 0 1

The auto correlation of a PN sequence which is not a m-sequence is no more thatinteresting for synchronisation purposes as real m-sequences.

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Cross-correlation BASICS_ACC_06.VSD

3

1 0 0 0 0 1 0 1 0 1 1 1 0 1 1 0 0 0 1 1 1 1 1 0 0 1 1 0 1 0 0

1 0 0 0 0 1 0 1 0 1 1 1 0 1 1 0 0 0 1 1 1 1 1 0 0 1 1 0 1 0 0

5

1 0 0 0 0 1 0 1 0 1 1 1 0 1 1 0 0 0 1 1 1 1 1 0 0 1 1 0 1 0 0

1 0 0 0 0 1 0 1 0 1 1 1 0 1 1 0 0 0 1 1 1 1 1 0 0 1 1 0 1 0 0

x5 + x2 + 1 / x5 + x3 + 1

1 1 1 1 1 1 1 1 1 1 1 1

-9

-7

1 0 0 0 0 1 0 0 1 0 1 1 0 0 1 1 1 1 1 0 0 0 1 1 0 1 1 1 0 1 01 1 1 1 1

1 0 0 0 0 1 0 0 1 0 1 1 0 0 1 1 1 1 1 0 0 0 1 1 0 1 1 1 0 1 0

1 0 0 0 0 1 0 0 1 0 1 1 0 0 1 1 1 1 1 0 0 0 1 1 0 1 1 1 0 1 0

1 0 0 0 0 1 0 0 1 0 1 1 0 0 1 1 1 1 1 0 0 0 1 1 0 1 1 1 0 1 0

1 1 1 1 1 1 1 1 1 1 1 1 11 1 1 1 1

1 1 1 1 1 1 11 1 1 1

1 1 1 1 1 1 1 1 1 1 1 11 1 1 1 1 1 1

1

1 0

1 0 0

-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

Cross correlation m-sequences

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-0,4

-0,2

0

0,2

0,4

0,6

0,8

1

1,2

-1

t/T

Cross correlation of twom-sequences

The cross correlation of m-sequences is a measure of mutualinteference. The mutual degradation is no neglectable, however asignificant improvement compared to orthogonal codes sequences.Further studies of m-sequences (Gold codes) gained someimprovements of the cross correlation which are applied by UMTSscrambling techniques.

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Generation of downlinkscrambling codes

Downlink scrambling code UMTS_CDS_SCC_03.VSD

7 6 01617

7 5 01617

x18 + x7 + 1

Initial condition:00000...00001

x18 + x10 + x7 + x5 + 1

Initial condition:11111...11111

0 218-2 = 262 141

I

131 072

38400 38400

218-1 downlink scrambling codes0 ... 262 142

910 z-n68

5

Q

910 8

::

GOLD found that an Exclusive OR combination of two distint m-sequences, called mother codes, result in a new PN sequence withimproved cross correlation properties. By simple relative shifting ofthe mother codes more distinct PN sequences can be achieved. Thus,a very simple method has been found to produce scrambling codeswith sufficient cross correlation properties. The GOLD codes areused for UMTS scrambling.

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Grouping of downlinkscrambling codes

Scrambling Code GroupsScrambling Code Sets

0: Primary Scrambling Code1: Primary Scrambling Code

7: Primary Scrambling Code0: Primary Scrambling Code1: Primary Scrambling Code

7: Primary Scrambling Code

Scrambling Code Group #6380648080

8176Scrambling Code Group #1144160

256

0: Primary Scrambling Code1: Secondary Scrambling Code

15: Secondary Scrambling Code

Scrambling Code Set #51181768177

8191 0: Primary Scrambling Code1: Secondary Scrambling Code

15: Secondary Scrambling Code

Scrambling Code Set #11617

31

Grouping of the downlink scrambling codes UMTS_CDS_SCC_02.VSD

218-1Scrambling Codes

(0 .. 262 142)

0: Primary Scrambling Code1: Secondary Scrambling Code

15: Secondary Scrambling Code

Scrambling Code Set #001

15

0: Primary Scrambling Code1: Primary Scrambling Code

7: Primary Scrambling Code

Scrambling Code Group #00

16

128

Left alternative scramblingcodes

for compressed mode(k+8192)

Right alternativescrambling codes

for compressed mode(k+16384)

A set of 218-1 scrambling codes are available for the downlink inUMTS. A subset of 213 codes are taken to build 64 code groups eachcontaining 8 primary scrambling codes. The residual codes are usedas secondary scarmbling codes.Thus, 8192 codes are divided into 512 code sets, each containing 16scrambling codes, the first of them used as primary scrambling code.The residual 2 x 8192 codes are reserved for future applications.The allocation of scrambling codes to the base stations is a matter ofnetwork planning.

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Generation of uplink scramblingcodes

Uplink long scrambling code UMTS_CDS_SCC_01.VSD

3 2 1 042324

3 2 1 042324

x25 + x3 + 1

Initial condition:1 + Scrambling sequence number

x25 + x3 + x2 + x + 1

Initial condition:11111 ...11111

0 225-2 = 33 554 430

Clong,1,n Clong,2,n

16 777 232

38400 38400

224 uplink longscrambling codes0 ... 16 777 216

For uplink scrambling the GOLD codes are produced as illustratedabove. A single GOLD code is used and portions of 38400 chips aretaken for scrambling. Two different portions Clong,1,n and Clong,2,n areused to scramble the I and Q branch separately.

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Uplink scrambling

l UEs are using distinct scrambling codes, temporarilyassigned by the node B

l Node B identifies UEs according to their scramblingcode

l 224-1 Uplink scrambling codes availablel Scrambling process

- I and Q branch are scrambled with complex GOLDsequences

- Scrambling codes are selected such that thenumber of origin crossing due to modulation isminimised. (HPSK - Hybrid PSK)

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UMTS

Introduction to 3GPP WCDMACode scenarios and FDD channel

structure

Dipl.-Ing. (Univ) Reinhold KruegerDipl. Ing. (TU) Heinz Mellein

R&S - TRAINING CENTER© 2002

www.rohde-schwarz.com

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Downlink Code Scenario

Code scenario for the downlink

BS separation:Primary scrambling code

MS separation:Spreading code

Primaryscrambling

code 1

MS2Ch3 , Code x

Ch4 , Code o

MS1Ch1, C

ode l

Ch2, Code n

Base station 1

MS2

Ch3 , Code xCh4 , Code o

MS1

Ch1 , Code lCh2 , Code n

Primaryscrambling

code 2

Base station 2

The combination of orthogonal spreading and block scramblingallows the following downlink scenario:Using orthogonal spreading codes, data for different mobile stationsare channelized prior to transmission. The total signal of the node Bthen is scrambled and modulated. The scrambling allowssynchronisation at the mobile station receiver due to sufficientcorrelation properties of the used GOLD codes.Each node B uses a unique scrambling code, selected from theavailable set of 512 primary scrambling codes. The cross correlation issufficient to allow the mobile station receiver to identify the node Baccording to its primary scrambling code.The scrambling codes are assigned to the base stations as part of thenetwork planning process.

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Uplink Code Scenario

Code scenario for the uplink

BS separation:Uplink scrambling code

MS separation:Uplink

scrambling code

MS1Ch1 , Code l

Ch2 , Code n

Base station 1

MS2 Ch1, Code lCh2 , Code n

Base station 2

On the uplink the node B selects individual mobile stations accordingto their unique scrambling code. The uplink scrambling code hasbeen assigned temporarily by the node B to the mobile station duringlink establishment procedure.

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UTRA Transmitter

⊗G2

Σ

P-SCH

S-SCH

GP

GS

⊗G1

S

P

⊗⊕

⊗ ⊗⊗Cch,SF,m

Sdl,n

I+jQ

I

Qj

Channelisation and Scramblingof all DL channels (except SCH)

Σ

Spreading of downlink signals is based on OVSF channelisationcodes according to Hadamard functions. Allowed spreading factorsare 4, 8, .. 512. The spreading or channelisation process gets analogvalues +1, -1 and 0 ("0" indicates DTX - Discontinuous Transmission)as input. At the downlink all physical channels are scrambledseperate or altogether, except the synchronisation channels P-SCHund S-SCH, which are neither spreaded nor scrambled.Typically all physical channels are scrambled with the same primaryscrambling code. However, along with the introduction of smartantennas secondary scrambling codes may apply in the future.

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Downlink spreading code tree

16,48,2

4,1

4,2

4,3

256,0

Codes used by the UTRAN UMTS_CDS_SPC_10.VSD

2,0

2,1

4,0

8,016,0

32,0

64,0128,0

256,1

256,3256,4

256,5

256,6256,7

256,8256,9

256,10256,11

256,12256,13

256,14256,15

16,15

16,116,2

16,3

16,516,6

16,7

16,816,9

16,1016,11

16,1216,13

16,14

8,1

8,3

8,4

8,5

8,6

8,7

256,249

256,250256,251

256,252256,253

256,254256,255

256,248

1,032,1

32,31

64,1

64,2

64,3

64,62

64,63128,126

128,127

256,2

128,125

128,124

128,1

128,2

128,3

128,4

128,5

128,6

128,7

32,30

::

Legend

CPICH

P-CCPCH

256,0

256,1

256,8 DPDCH

512,25

512,24

512,17512,16

blocked

512,24 DPDCH

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QPSK Modulation Downlink

Serial /Parallel

scrambled sequence withuser and signalling data

RRCFilter

..11010100..

odd Bits..1000..

cos(ω·t)

RRCFilter

even Bits..1110.. ⊗

-sin(ω· t)

+s(t)

QPSK Modulation groups a binary sequence into two parallel bitsequences by serial/parallel transformation. The resulting symbolsare called di-bits and are mapped onto a RF symbol in the modulator.Di-bits can have 4 different states {00,01,10,11}, thus 4 different RFsymbols are required which leads to QPSK as the suitablemodulation scheme.Appropriate base band filtering reduces the intersymbol interferenceduring transmission. For that purpose root raised cosine filters withroll-off factor 0.22 are used in both, the modulator and thedemodulator.

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UE Transmitter

j

cd,1 βd

Sdpch

I+jQ

DPDCH1

Q

cd,3 βd

DPDCH3

cd,5 βd

DPDCH5

cd,2 βd

DPDCH2

cd,4 βd

DPDCH4

cd,6 βd

DPDCH6

cc βc

DPCCH

Σ

S

SCRAMBLING

CHANNELISATION

IQ multiplexing is applied in the uplink. Thus, code channels arefully mapped either on the I branch or the Q branch. In particular thefirst data channel DPCCH1 is mapped onto the I branch, and theuplink DPCCH is mapped on the Q branch.Further data channels are mapped alternately onto the I and Qbranch.The IQ multiplexing of user and control data avoids pulsed uplinksignals which could cause troublesome interference with otherelectronic equipment.

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UE spreading code tree

16,48,2

4,1

4,2

4,3

256,0

Codes used by the UE on DPCH UMTS_CDS_SPC_08.VSD

2561286432168444

Spreadingfactor

Spreadingcode

6432168421

1,21,2,3

DPDCH

2,0

2,1

4,0

8,016,0

32,0

64,0

128,0256,1

256,3256,4

256,5256,6

256,7

256,8256,9

256,10

256,11256,12

256,13

256,14256,15

16,15

16,116,2

16,3

16,5

16,616,7

16,8

16,916,10

16,11

16,1216,13

16,14

8,1

8,3

8,4

8,5

8,6

8,7

256,249

256,250256,251

256,252256,253

256,254

256,255

256,248

1,032,1

32,31

64,1

64,2

64,3

64,62

64,63128,126

128,127

256,2

128,125

128,124

128,1

128,2

128,3

128,4

128,5

128,6

128,7

32,30

::Legend

DPDCH

DPCCH256,0

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2xBPSK Modulation Uplink

Scrambling

Data: BPSK Modulation of I branch

RRCFilter

..1000..⊗

cos(ω·t)

RRCFilter ⊗

-sin(ω· t)

+s(t)

..1110..

Signalling: BPSK Modulation of Q branch

Due to the IQ multiplexing of uplink data also the modulator isdifferent from the downlink. Basically both branches are BPSKmodulated seperately. Finally, when there are data on both branches,i.e. user and control data, the modulator output is similar to a QPSKmodulation.

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3GPP FDD air interfacechannel structure

l Frequency channels and radio framesl Logical channelsl Transport channelsl Physical channelsl Selection of important channels

Standardised mobile communication (wie z.B. GSM, UMTS,CDMAone, D-AMPS) consist of several components. Along with thedefinition of the radio transmission technologies comes also thedefinition of source coding schemes for instance for speech (speechcodec), capacity parameters, core netowork design etc. However, themost difficult part is the definition of the air interface architecture,since this is obviously the bottleneck of the system with respect tocapacity and data rates.The most important parameters are:- available bit rate (bandwidth)- capacity (number of subscribers)- requried cell density- costs for network implementationExcept the latter one, all these parameters are restricted by the airinterface in particular. The air interface not only needs to transportthe data, however, a minimum of transmission quality, e.g.reliability, or simultaneous up- and downlink transmission (fullduplex) must be provided.

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FDD Frequency allocationRegion 1 (e.g. Europa)

l Frequency channel 5 MHz

l Channel raster 200 kHz

l Numbering scheme (UARFCN1):

Nuplink = 5 * Fu ; 1920 MHz ≤ Fu ≤ 1980 MHz

ie. 9612 ≤ Nuplink ≤ 9888

Ndownlink = 5 * Fd ; 2110 MHz ≤ Fd ≤ 2170 MHz

ie. 10562 ≤ Ndownlink ≤ 10838

l Duplex distance190 MHz1) UARFCN = UMTS Absolute Radio Frequency Channel Number

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FDD Frequency allocationRegion 2

l Frequency channel 5 MHz

l Channel raster 200 kHz

l Numbering (UARFCN1):

Nuplink = 5 * Fu ; 1850 MHz ≤ Fu ≤ 1910 MHz

ie. 9262 ≤ Nuplink ≤ 9538

Ndownlink = 5 * Fd ; 1930 MHz ≤ Fd ≤ 1990 MHz

ie. 9662 ≤ Ndownlink ≤ 9938

l Duplex distance 80 MHz1) UARFCN = UMTS Absolute Radio Frequency Channel Number

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Radio frames and time slots

Radio frame (FDD) UMTS_PHL_PHC_43.VSD

Radio Frame

10 ms38400 chips

at a chip rate of 3.84 MChips/s

Slot #0 Slot #1 Slot #n Slot #13 Slot #14

....

....

666,6 µs2560 chips

at chip rate of 3.84 MChips/s

....

....

Time on the UMTS WCDMA air interface is organised by means of10 ms radio frames. Each radio frame is divided into 15 time slots of2/3 ms duration each.Regarding the fixed chip rate of 3.84 MChip/s , each time slotcontains 2560 chips, which cover - depending on the currentspreading factor - more or less data bits.While time slots are numbered from 0 to 14, radio frames areidentified by their system frame number (SFN = 0 .. 4095). This SFNis continuously broadcasted by the network on the P-CCPCH.

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Lower layers

PHYSICAL LAYER

Medium Access ControlMAC

Transport channels„How to transmit“

Logical channels„What to be transmitted“

Physical channelsCode, Frequency, etc.

Radio Ressource ControlRRC

Con

trol &

Mea

sure

men

ts

Service Access PointSAP

According to the OSI layer model for communication, for WCDMAin particular the lower layers are of interest. Layer 1, the physicallayer, is responsible for spreading, scrambling etc. Layer 2, themedium access control layer, controls the required transmissionformats (data rates, channel coding etc.) and provides all datatowards the physical layer by means of transport channels. Inaddition, layer 2 already performs data multiplexing, i.e. layer 1 hasno knowledge at all about the data content. The lower end of layer 3,the radio ressource control layer, does provide the user andsignalling data by means of logical layers towards layer 2. A directlink between layer 3 and layer 1 allows fast reactions of the networkwith respect to changes of the radio link quality, for instance.

The lower layers according to the OSI mode are responsible for theunambiguous addressing and save transmission of user andsignalling data. Therefore, radio interface protocols are specified,which control the communication in vertical direction (ie. from onelayer to the upper or lower adjacent layer within one entity) and inhorizontal direction (e.g. between node B and UE).

The transmission of signalling data must be error free by default,whilst for instance speech data transmission allows bit errors up to acertain extend. Thus, signalling data need other channel codingschemes than user data.

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Logical channels

Control ChannelCCH(Signalling data)

Broadcast Control ChannelBCCH

Paging Control ChannelPCCH

Dedicated Control ChannelDCCH

Common Control ChannelCCCH

Shared Channel Control ChannelSHCCH (TDD mode only)

Traffic ChannelTCH(user data)

Dedicated Traffic ChannelDTCH

Common Traffic ChannelCTCH

Basically it is distinguished between signalling channels and traficchannels.

Traffic channels of the user plane are divided into two logicalchannel types, DTCH (dedicated traffic channel) and CTCH (commontraffic channel). DTCH is used for mutual, dedicated communicationbetween the node B and one UE: point-to-point connection. CTCHmight be used for point-to-multipoint connections (e.g. advertisingchannel).

Signalling channels of the control plane are also mapped ontodifferent logical channels depending on their useage. BCCH(Broadcast Control Channel) is used for downlink broadcasting ofcommon system information, PCCH (Paging Control Channel) coverspaging messages only (e.g. for initiation of mobile terminated calls).

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Mapping of logical channel totransport channels in the UE

BCH PCH DSCHFACHRACH DCH

BCCH DCCH CCCHPCCH DTCH

CPCH

CTCH

Service Access PointSAP

All UEs have to read system information on the BCCH (broadcastcontrol channel) and paging messages on the PCCH (paging controlchannel) on a regular basis.

CCCH (common control channel) is a bi-directional channel whichallows radio access. DCCH (dedicated contro channel) is a bi-directional channel which operates in association with a DTCH tomaintain a point-to-point connection. SHCCH (shared common controlchannel) is for TDD mode only, to deal with traffic peaks.

All logical channels are mapped onto transport channels, whichdefine the transmission characteristics, like data rates and channelcoding. Transport channels are a service of the physical layertowards the upper layers for transportation of any data structures.The upper layers deliver the data at service access points (SAPs)representing a certain transport channel. Regarding the uplink, thephysical layer delivers received data to the transport channel SAPsfor higher layers for further processing. Transport channels offerflexible data rates and channel coding schemes, thus, they offeradaptation of higher layer data streams onto the available radioressources. This includes for instance a suitable data multiplexing ofvarious upper layer data streams onto an available transport datastream.

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Mapping of logical channels totransport channels in the node B

BCH PCH DSCHFACHRACH DCH

BCCH DCCH CCCHPCCH DTCH

CPCH

CTCH

Service Access PointSAP

A transport channel specifies the way "how" data is to betransmitted via the air interface. Since that transport format isvariable, an identifier called TFI (Transport Format Indicator) indicatesthe current configuration. While mapping data from transportchannels onto physical channels, all TFIs are converted onto a singleTFCI (Transport Format Combination Indicator), which is transmittedpermanently on the DPCCH. However, in case of fixed datastructures throughout a communication session, the transmission ofTFCI might be skipped.

Types of Transport Channels

DCH (Dedicated channel)

This bi-directional channel is used to transport dedicated user andsignalling data. It covers the data of the logical channels DTCH andDCCH. For physical transmission the data are mapped onto theDPCH including the DPDCH and DPCCH. Broadcast

BCH (Broadcast channel)

This downlink only channel conveys the data of the logical BCCHusing the physical channel P-CCPCH. It uses always the sameformat.

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Transport channels

DEDICATED TRANSPORT CHANNELl DCH - Dedicated CHannel

COMMON TRANSPORT CHANNELl BCH - Broadcast CHannell FACH - Forward Access CHannell PCH - Paging CHannell RACH - Random Access CHannell CPCH - Common Packet CHannell DSCH - Downlink Shared CHannel

Forward Access Channel FACH

This downlink only channel can be used to convey data of the logicalchannels BCCH, CCCH, DCCH and CTCH.

Paging Channel PCH

This downlink only channel conveys paging messages towards theUE.

Random Access Channel RACH

This uplink only channel is used for inital radio access by the UE.

Common Packet Channel CPCHThis is a pure packet channel to exchange packet data between nodeB and UE.

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Mapping of transport channels tophysical channels

Overview of the channels of the physical layer UMTS_PHL_PHC_39.VSD

BCH PCH CPCH(FDD only)

FAUSCH USCH(TDD only)

DSCH DCHRACH FACH

PhysicalChannels(FDD)

PHY

P-CCPCH S-CCPCHDPDCHDPCCHPCPCH PRACH PDSCH

CPICHPICHP/S-SCH

AICHAP-AICHCSICHCD/CA-ICH

TransportChannels

DPCH

There are dedicated physical channels and common physicalchannels.A dedicated physical channel (DPCH) consists of two parts, theDPDCH (Dedicated Physical Data Channel), which conveys the userdata and the associated signalling data, and a DPCCH (DedicatedPhysical Control Channel), which transmits pilot symbols for coherentdetection, the transmit power control (TPC) command and thetransport format identifier.Downlink common physical channels are P-CCPCH (primaryCommon Control Physical Channel), which is broadcasting systeminformation with a fixed rate continuously, and the S-CCPCH(secondary Common Control Physical Channel), which conveys e.g.paging information.For initial access by the UE the uplink only PRACH (Physical RandomAccess Channel), shall be used.

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Timing of physical channels

Frame timing of the downlink physical channels UMTS_PHL_PHC_34.VSD

PrimarySCH

SecondarySCH

Any CPICH (Primary/Secondary)

P-CCPCH, (SFN modulo 2) = 0 P-CCPCH, (SFN modulo 2) = 1

k:th S-CCPCH

PICH for k:th S-CCPCH

AICHaccess

slots

#0 #1 #2 #3 #4 #5 #6 #7 #8

Any PDSCH

n:th DPCH

One Frame = 10 ms

Slots#0 #1 #2 #3 #4 #5 #6 #7 #8 #9 #10 #11 #12 #13 #14 #1

τ DPCH,n

τ S-CCPCH,k

τ PICH

With respect to radio frame and time slot borders, the physicalchannels may have different and variable offsets.The CPICH and the P-CCPCH are the reference channels in thatrespect, since they are perfectly synchronised into the frame and slotscheme.All other physical channels may have a variable offset in time withrespect to the radio frame borders. That offset can be selectedbetween 0 and 10 ms in steps of 256 chips periods (i.e. 0 .. 38144Chips in steps of 256 Chips). This is of interest to compensated forinstance propagation delay offsets between different node B's duringsoft handover.P-SCH and S-SCH are no spreaded code channels at all. Theytransmit well known synchronisation information to support the UEduring cell search procedures. In addition, they are active only for 10% of the time, however, always starting at the time slot borders.

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Synchronisation Channel (SCH)

The primary and secondary synchronisation channels are used forthe cell search procedure.Both synchronisation channels are no code channels. They are neitherspreaded nor scrambled. They transmit periodically at the beginningof each and every time slot a known synchronisation code of length256 chips.

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Common Pilot Channel (CPICH)

Frame structure for common pilot channel

Tslot = 2560 chips, 20 bits = 10 symbols

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

Tf = 10 ms

Pre-defined symbol sequence

l Fixed rate (30kbit/s, SF=256,0)l Transparent transmission of scrambling sequence of 38400

Chips (synchronuous to radio frame boundaries)

Properties of primary CPICH•Spreading code (256,0)•Primary scrambling code•One per radio cell•Covers complete radio cell•Always phase reference for the following channels

SCH, CCPCH, AICH, PICH•Phase reference for all other channels by default•Transmit code channel power -10 .. + 50 dBm

Properties of (optional) secondary CPICH•Fixed spreading factor - SF=256•Primary or secondary scrambling code•No S-CPICH, one or multiple S-CPICH per radio cell•Optional Phase reference channel for S-CCPCH and downlink DPCHs

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Primary Common ControlPhysical Channel (P-CCPCH)

Frame structure for primary common control physical channel

Tx OFF

Tslot = 2560 chips, 20 bits

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

Tf = 10 ms

256 chips

Data18 bits

Primary &Secondary SCH

instead

Properties P-CCPCH

•Always the same spreading code 256,1•Broadcast channel to distribute system information•Scrambled with primary scrambling code•Covers complete radio cell

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Downlink DPCH

Frame structure for downlink DPCH

PilotNpilot bits

TFCINTFCI bits

TPCNTPC bits

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

One radio frame, Tf = 10 ms

DPCCH

Data1Ndata1 bits

Data2Ndata2 bits

DPCCH DPCCHDPDCHDPDCH

Tslot = 2560 chips, 10*2k bits (k=0..7)

•DPCCH are DPDCH time multiplexed•DPDCH transmits signalling from higher layers and user data•DPCCH transmits layer 1 signalling (e.g. for transmit powercontrol)

•Pilot bits•Channel estimation, frequency and time synchronisation•Changing pilot sequences in successive slots for frame synchronisation•variable number of pilot bits depending on the channel quality

•TFCI bits (Transport Format Combination Identifier)•Identification of current transport format•Allows variable data rates•Allows multi service•Optional

•TPC bits (Transmit Power Control)•Closed loop transmit power control

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DPDCH and DPCCH data fields

DPDCH and DPCCH fields UMTS_PHL_PHC_23.VSD

13 240 120 32 160 28 112 4 8* 8 15 13A 240 120 32 160 28 104 4 16* 8 8-14 13B 480 240 16 320 56 224 8 16* 16 8-14 14 480 240 16 320 56 232 8 8* 16 15 14A 480 240 16 320 56 224 8 16* 16 8-14 14B 960 480 8 640 112 464 16 16* 32 8-14 15 960 480 8 640 120 488 8 8* 16 15 15A 960 480 8 640 120 480 8 16* 16 8-14 15B 1920 960 4 1280 240 976 16 16* 32 8-14 16 1920 960 4 1280 248 1000 8 8* 16 15 16A 1920 960 4 1280 248 992 8 16* 16 8-14

DPDCH Bits/Slot

DPCCH Bits/Slot

Slot Format

#i

Channel Bit Rate

(kbps)

Channel Symbol

Rate (ksps)

SF Bits/ Slot

NData1 NData2 NTPC NTFCI NPilot

Transmitted slots per

radio frame NTr

0 15 7.5 512 10 0 4 2 0 4 15 0A 15 7.5 512 10 0 4 2 0 4 8-14 0B 30 15 256 20 0 8 4 0 8 8-14 1 15 7.5 512 10 0 2 2 2 4 15

1B 30 15 256 20 0 4 4 4 8 8-14 2 30 15 256 20 2 14 2 0 2 15

2A 30 15 256 20 2 14 2 0 2 8-14 2B 60 30 128 40 4 28 4 0 4 8-14 3 30 15 256 20 2 12 2 2 2 15

3A 30 15 256 20 2 10 2 4 2 8-14 3B 60 30 128 40 4 24 4 4 4 8-14 4 30 15 256 20 2 12 2 0 4 15

4A 30 15 256 20 2 12 2 0 4 8-14 4B 60 30 128 40 4 24 4 0 8 8-14 5 30 15 256 20 2 10 2 2 4 15

5A 30 15 256 20 2 8 2 4 4 8-14 5B 60 30 128 40 4 20 4 4 8 8-14

: : :

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Downlink multicodetransmission

Downlink slot format in case of multi-code transmission UMTS_PHL_PHC_09.VSD

TFCIDPDCH

TPC

DPDCH

Pilot

One Slot (2560 chips)

DPCCH

DPCH 1

DPDCH DPDCH DPCH 2

DPDCH DPDCH DPCH NTransmissionPower

TransmissionPower

TransmissionPower

In case of multiple DPCH channels belonging to a single link, eg. incase of soft handover, only one DPCCH is used, however, withstrong code channel power to ensure save reception.

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Uplink DPDCH/DPCCH frame

Frame structure for uplink DPDCH/DPCCH UMTS_PHL_PHC_03.VSD

DataNdata bits

PilotNpilot bits

TFCINTFCI bits

FBINFBI bits

TPCNTPC bits

Tslot = 2560 chips, NData = 10*2k bits (k=0..6)

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

DPDCH

DPCCH

1 radio frame: Tf = 10 ms

Tslot = 2560 chips, 10 bits

•DPCCH and DPDCH are IQ multiplexed•Dedicated Physical Data Channel DPDCH

•transmits DCH Transport channel•0 .. 6 uplink DPDCHs possible

•Dedicated Physical Control Channel DPCCH•transmits layer 1 Signalling info•Pilot bits for channel estimation, frequency and time synchronisation

•TPC bits for transmit power control•FBI bits for diversity control•TFCI bits (optional)•1 uplink DPCCH per radio link

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Uplink DPDCH data

Ndata bits

Tslot = 2560 chips (2/3 ms)

Ndata = 2560 / SF bits per Tslot

SF = 4 8 16 32 64 128 256

Ndata = 640 320 160 80 40 20 10

Rate[ksps] 960 480 240 120 60 30 15

slot format 6 5 4 3 2 1 0

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Uplink DPCCH time slot forms

Pilot TFCI TPC

SF = 256 ie. 10 bits per slot

0

slot

form

1

2

3

4

5

FBI

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12.2 kbit/s UL reference channel

CRC+16 bits

R=1/3coding

22 %Repetition

Interleaving

DTCH12.2kbps

244 bits perTTI = 20 ms

260+ 8 tail bits per TTI

804 bits per TTI

490 bits per radioframe

49 kbps

DCCH2.4 kbps

100 bits perTTI = 40 ms

DPDCH

60 kbps

SF = 64MU

X

CRC+12 bits

R=1/3coding

22 %Repetition

Interleaving

112+ 8 tail bits per TTI

360 bits per TTI

110 bits per radioframe

11 kbps

ChannelCoding

RateMatching

Radio framealignment

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64 kbit/s UL reference channel

CRC+16 bits

R=1/3coding

17 %Repetition

Interleaving

DTCH64kbps

1280 bits perTTI = 20 ms

1296per TTI

3888+12 bits per TTI

2294 bits per radioframe

229,4 kbps

DCCH2.4 kbps

100 bits perTTI = 40 ms

240 kbps

SF = 16MU

X

CRC+12 bits

R=1/3coding

17 %Repetition

Interleaving

112+ 8 tail bits per TTI

360 bits per TTI

106 bits per radioframe

10,6 kbps

ChannelCoding

RateMatching

Radio framealignment

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UMTS

Introduction to 3GPP WCDMACell search and Synchronisation

Dipl.-Ing. (Univ) Reinhold KruegerDipl. Ing. (TU) Heinz Mellein

R&S - TRAINING CENTER© 2002

www.rohde-schwarz.com

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Introduction

?

Base Station

Base Station

Base Station

Introduction to synchronisation UMTS_PRC_SYN_04.VSD

Base Station

Base Station

What does the mobile need to know?

1) Strongest base station 4) Primary scrambling code2) Slot border 5) BCCH information3) Frame border

After switching on the mobile station a suitable base station of thewanted operator must be found. Therefore, the mobile station first islooking for WCDMA signals. After synchronisation on that, it readsthe broadcasted system information to identify the network operator.Four steps cover that cell search procedure.

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Physical channels required forSynchronisation

Physical channels used for synchronisation UMTS_PHL_PHC_37.VSD

P-SCH

S-SCH

P-CCPCH

CPICH

One Frame = 10 ms (38400 chips)

Slot # 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

DPCH3

DPCH2

DPCH1

InformationScrambling

Code

User InfoPrimary

Secondary

User Info

User Info

PrimarySecondary

PrimarySecondary

Predefined pattern

PrimaryBCH Info

Primary

Predefined code word(256 chips)

---

Sequence of predefinedcode words (256 chips)

---

Data TPC TFCI Data Pilot

2560 chips

SpreadingCode

CC H,x,y

CCH ,a,b

CC H,n,m

CC H

,256,0

CC H

,256,1

---

---

Base Station

..........

256 chips

For identification of WCDMA signals some known synchronisationchannels are required. The downlink WCDMA signal includestherefore a primary (P-SCH) and a secondary synchronisationchannel (S-SCH), which are neither spreaded nor scrambled, sincethe scrambling code of the base station is not known yet to the mobilestation.The synchronisation channels allow synchronisation in time onto theWCDMA signal, i.e. on radio frame and time slot boundaries.Another, spreaded and scrambled common pilot channel (CPICH)allows the detection of the primary scrambling code. Thus, thebroadcast information, transmitted by the primary common controlphysical channel (P-CCPCH) can be decoded and analysed.

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P-SCH - Primary Sync Channel

Base Station

Physical channels used for synchronisation UMTS_PHL_PHC_38.VSD

P-SCH

S-SCH

P-CCPCH

CPICH

15 Slots = 1 Frame = 10 ms (38400 chips)

256 chips

l Conveys primarySynchronisation code (CPSC) forbase station selection and timeslot synchronisation

l CPSC

- Known code word (256chips)

- Identical for all Basestations

- Identical in all time slots

The time domain in UTRAN FDD mode is organised in 10 ms radioframes and 15 time slots of 2/3 ms duration each, which arenumbered from 0 to 14. For time synchronisation the first informationrequired are the time slot borders. Therefore the base stationtransmits continuously the primary synchronsiation code PSC on theprimary synchronisation channel P-SCH at the beginning of each andevery time slot. The PSC is 256 chips long, ie. it lasts 1/10 of a time slotduration. The PSC content is identical for each and every base station.

The PSC is a so-called generalised hierarchical Golay Sequence withvery good a-periodical auto correlation properties. It is built by a 16times repetition of a 16 chip sequence. By multiplication of each chipwith the complex value (1+j) the signal vector is turned by π/4 whichgains an almost constant signal envelope of the QPSK modulatedsignal.

For detection of the PSC matched filters are useful which cangenerate exactly the time slot clock.

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Selection of base station andtime synchronisation

Sync step 1: BS selection and slot synchronisation UMTS_PRC_SYN_01.VSD

Matched Filterr(t)

- Slot timing- Gross frequency error- BS presence

tSlot x Slot x+1 Slot x+2

BS1 BS2

BS2

BS 1

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Matched filter

1 1 1

-1⊗ ∫

T

dt0

Max SNRfor sampling

instant

Integrateand

Reset

copy ofsignal

An optimum receiver for AWGN channels gains maximum SNR atits output by definition. This can be achieved by matched filtercircuits, which simply "wait" for the arrival of known datasequences.

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Reception of spreaded signals

1 1 1

-1⊗ ∫

T

dt0

Max SNRat sampling

instant

Integrateand

Resetcopy ofsequence

1 1 1

-1

T T

1/T1/Tc

Tc

correlator

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Reception of spreaded, multipathsignals

⊗ ∫T

dt0

Max SNRat sampling

instant

Integrateand

Resetcopy ofsequence

1 1 1

-1

T T

1/T

1/Tc

1 1 1

-1

Tc

correlator

1 1 1-1

∆t

Pat

h 2

Pat

h 1

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Reception of spreaded signals

Path 1

Path 2

Despreadedenergy of

Path 1

Still spreaded energy of path 2out of the wanted signal bandwidth

Still spreaded energy of path 2within the wanted signal bandwidth

Despreaded energy of path 2due to loss of orthogonality

Bandwidth of wanted signal

1/Tc

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RAKE Receiver

l „Collecting“ of all signal energy of different pathsl Each correlator builds a „Finger“ of the RAKE

receiverl For synchronisation on single paths very good

correlation properties and supporting pilot channelsare required

l A common searcher detects pilots and regeneratessymbol clocks

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RAKE Receiver Principle

Searcher

Finger 1

Finger 2

Finger n

Com

bine

ror

Sel

ecto

r Sum

or

Selection

Clock regeneration

Individual Path compensation(e.g. delay, attenuation)

The RAKE receiver collects signal energy like a garden rake collectsthe leaves after a windy autumn day. On a multipath channel eachfinger of the RAKE receiver does take the portion of the signal energythat comes along on a single path. It is obvious, the more fingers aRAKE receiver does include, the more signal energy can be collected,however, each additional finger does obviously increase thecomplexity of the receiver implementation.Each finger might be designed as a correlation receiver, which getsthe required clock from the searcher unit. The searcher unit, e.g.designed as a matched filter circuit does retrieve the symbol clockfrom the available synchronisation channels P-SCH and S-SCHwithin the downlink WCDMA signal.The following combiner or selector network might compensate theknown timing offsets between the individual fingers and add up thesignal energy portions delivered by the finger outputs, or just selectthe strongest finger output.

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S-SCHSecondary Sync Channel

l Transmits secondarysynchronisation Codes (CSSC)for frame synchronisation andIdentification of currentScrambling Code Group

l CSSC

- 16 defined code words of256 chips

- 16 code words buildidentifiers for scramblingcode groups

Base Station

Physical channels used for synchronisation UMTS_PHL_PHC_38.VSD

P-SCH

S-SCH

P-CCPCH

CPICH

15 Slots = 1 Frame = 10 ms (38400 chips)

256 chips

For frame synchronisation the secondary synchronisation channel isused. This channel does transmit a pre-defined sequence ofsecondary code words, which can be selected out of a set of 16secondary synchronisation codes SSC resp. CSSC

These are orthogonal code words which are Hadamard functions. All16 possible SSCs are known to the receiver in the mobile station, andthus can be easily detected by correlation reception. Across acomplete radio frame a pre-defined sequence of 15 SSCs istransmitted, which is then repeated radio frame by radio frame.

There are in total 64 code groups defined, each containing 8 primaryscrambling codes. Each code group does transmit its uniquesequence of SSCs per radio frame, which in fact is used to identify thescrambling code group. Thus, the secondary synchronisation channelis used to identify the scrambling code group of the monitored nodeB, which reduces the number of possible primary scrambling codesto 8. Since the SSC sequences of each code group are synchronised tothe radio frame, the radio frame borders are known to the receiverafter detection of the scrambling code group.

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Grouping of DownlinkScrambling codes

Scrambling Code GroupsScrambling Code Sets

0: Primary Scrambling Code1: Primary Scrambling Code

7: Primary Scrambling Code0: Primary Scrambling Code1: Primary Scrambling Code

7: Primary Scrambling Code

Scrambling Code Group #6380648080

8176Scrambling Code Group #1144160

256

0: Primary Scrambling Code1: Secondary Scrambling Code

15: Secondary Scrambling Code

Scrambling Code Set #51181768177

8191 0: Primary Scrambling Code1: Secondary Scrambling Code

15: Secondary Scrambling Code

Scrambling Code Set #11617

31

Grouping of the downlink scrambling codes UMTS_CDS_SCC_02.VSD

218-1Scrambling Codes

(0 .. 262 142)

0: Primary Scrambling Code1: Secondary Scrambling Code

15: Secondary Scrambling Code

Scrambling Code Set #001

15

0: Primary Scrambling Code1: Primary Scrambling Code

7: Primary Scrambling Code

Scrambling Code Group #00

16

128

Left alternative scramblingcodes

for compressed mode(k+8192)

Right alternativescrambling codes

for compressed mode(k+16384)

218-1 downlink SCs (scrambling codes) are available.

213 = 8192, numbered by 0 .. 8191 are used for primary and secondaryscrambling purposes.

Those 213 codes are divided into 29 = 512 groups, each containing a 24

= 16 SCs. The first of that set of 16 SCs is always used as the primaryscrambling code SC ( n = 16⋅i with i = 0..511) for that group and theresidual 15 SCs are available as secondary scrambling codes.

The number of 512 primary scrambling codes are organised again in64 scrambling code groups, each containing 8 scrambling codes, ofcourse.

The following relation with respect to the code numbering applies:

SC number = 16 ⋅ 8 ⋅ j + 16 ⋅ k

with

j = 0..63 (code group number) and

k = 0..7 (primary SC number within the code group j).

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Frame synchronisation andScrambling Code Groups

Sync step 2: Frame sync and identifying scrambling code group UMTS_PRC_SYN_05.VSD

P-SCH

S-SCH

P-CCPCH

CPICH

15 Slots = 1 Frame = 10 ms (38400 chips)

256 chips

Cssc,1

256 chips

Cssc,2

Cssc,3

Cssc,4

Cssc,13

Cssc,14

Cssc,16

Cssc,15

::

Table of secondarysynchronisation codes

slot number Scrambling Code Group #0 #1 #2 #3 #4 #5 #6 #7 #8 #9 #10 #11 #12 #13 #14

Group 0 1 1 2 8 9 10 15 8 10 16 2 7 15 7 16

Group 1 1 1 5 16 7 3 14 16 3 10 5 12 14 12 10 Group 2 1 2 1 15 5 5 12 16 6 11 2 16 11 15 12

Group 3 1 2 3 1 8 6 5 2 5 8 4 4 6 3 7

Group 4 1 2 16 6 6 11 15 5 12 1 15 12 16 11 2

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CPICH - Common Pilot Channel

l Conveys well defined pilotsequence

l SF 256 (Cch,256,0)

l Scrambled, using primary

scrambling code according toscrambling code group

l UE attempts possiblescrambling codes (one out ofeight) according to knownscrambling code group

Base Station

Physical channels used for synchronisation UMTS_PHL_PHC_38.VSD

P-SCH

S-SCH

P-CCPCH

CPICH

15 Slots = 1 Frame = 10 ms (38400 chips)

256 chips

The primary scrambling code sequence, when transmitted on the airinterface, is cut down to 38400 chips, which obviously corresponds tothe duration of a single radio frame of 10 ms. In fact, the primaryCPICH channel, which is exactly synchronised to the downlink radioframe borders, does contain the plain scrambling code.

The data on the CPICH, before spreading with (256,0) consists of thesequence "1111". After spreading with (256,0), which is a sequence of256 "1" the CPICH data contains simply 38400 "1" per frame beforescrambling. The scrambling operation then does multiply the datachip by chip with the 38400 chips of the scrambling code word.Obviously, then the plain primary scrambling code is sent radioframe by radio frame of the P-CPICH.

Since the receiver, after detection of the scrambling code group doesknow out of which set of 8 possible primary scrambling codes thescrambled data on the P-CPICH comes from, it can detect the usedSC on the P-CPICH.

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Primary Common ControlPhysical Channel (P-CCPCH)

l Includes system information andcurrent SFN (System FrameNumber)

l SF 256 (Cch,256,1)

l Scrambled by primaryscrambling code

l UE can descramble anddespread BCH systeminformation

Base Station

Physical channels used for synchronisation UMTS_PHL_PHC_38.VSD

P-SCH

S-SCH

P-CCPCH

CPICH

15 Slots = 1 Frame = 10 ms (38400 chips)

256 chips

After all, the physical cell search process is completed after threesteps:

1. Time slot synchronisation by P-SCH

2. Frame synchronisation and code group detection by S-SCH

3. Detection of primary scrambling code by P-CPICH

Now the receiver can descramble the downlink signal and look forfurther code channels. Since it is known, that the P-CCPCH,containing the BCCH broadcast system information, is spreaded by(256,1) by default, the receiver can finally despread and read therequired system information to complete the cell selection process.

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Summary cell search procedure

The four synchronisation steps UMTS_PRC_SYN_03.VSD

Primary synchronisation code(CPSC)

Secondary synchronisationcode sequence (CSSC,n)

(64 unique sequences of secondarysynchronisation codes)

P-SCH

S-SCH

Scrambling Code GroupsScrambling Code Sets

0 : Primary Scrambling Code1 : Primary Scrambling Code

7 : Primary Scrambling Code0: Primary Scrambling Code1: Primary Scrambling Code

7: Primary Scrambling Code

Scrambling Code Group #6380648080

8176Scrambling Code Group #1144160

256

0: Primary Scrambling Code1: Secondary Scrambling Code

15: Secondary Scrambling Code

Scrambling Code Set #51181768177

8191 0: Primary Scrambling Code1: Secondary Scrambling Code

15: Secondary Scrambling Code

Scrambling Code Set #11617

31

Grouping of the downlink scrambling codes UMTS_CDS_SCC_02.VSD

218-1Scrambling Codes

(0 .. 262 142)

0: Primary Scrambling Code1: Secondary Scrambling Code

15: Secondary Scrambling Code

Scrambling Code Set #001

15

0 : Primary Scrambling Code1 : Primary Scrambling Code

7 : Primary Scrambling Code

Scrambling Code Group #0016

128

Left alternative scramblingcodes

for compressed mode(k+8192)

Right alternativescrambling codes

for compressed mode(k+16384)

P-CCPCH

CPICH

2

Cellsand

Slot boarder1

3

4BCH

informationFrameborder

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System information broadcast

l Elements of system information are grouped inSystem Information Blocks 1..18 (SIB) with variableorder

l SIB order info available in master information block(MIB)

UE UTRAN

SYSTEM INFORMATION PCCPCH ← BCH SCCPCH ← FACH

BCCH

The logical channel BCCH transmits via the transport channel BCHand the physical channel P-CCPCH continuously system informationblocks to all mobile stations. The System information is distributedwithin max. 18 blocks - called system information blocks SIB - overthe entire radio cell, scrambled with the primary scrambling code.The order of SIB transmission is written in a master informationblock MIB, which is sent out every 8 radio frames.

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System Information Elements

l Core Network (CN) information elements (IE)l UTRAN mobility information elementsl User Equipment (UE) information elementsl Radio Bearer information elementsl Transport Channel information elementsl Physical Channel information elementsl Measurement information elementsl Other information elementsl ANSI-41 specific information elements

l Specified in 3GPP TS25.331

The SIBs provide the UEs with all necessary technical andadministrative information regarding the mobile radio network.Along with core network parameters also network operatorinformation (e.g. mobile country and network codes) and locationinformation are distributed.In particular very important technical parameters to control forinstance the transmit power control algorithms or the cell selectionand reselection process are sent within dedicated SIBs.For future applications the transmission of SIBs is very flexible andmight include for instance network operator proprietary information.

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Idle mode Processes

cell selectionand Reselection

PLMN Selektionund Reselektion

display available PLMNs

select PLMN

LocationRegistration

Changing locationarea

LocationRegistration

Info

Automaticor manual

After analysis of the system information of various node B's, a list ofavailable network operators is produced an offered to the subscriber.The PLMN selection then is done manually or automatically,depending on the terminal settings. After PLMN selection theregistration process is initiated by the UE on the selected (orreselected) cell. The cell selection / reselection is a continuousprocess of the UE in idle mode, thus, a continuous monitoring of thenode B neighbourhood is required.

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Measurements for cell selection

l Different measurements in different RATs - RadioAccess Technologies

l GSM- RXLEV (range 0 .. 63)- RXQUAL (range 0 .. 7)

l UTRA / FDD- CPICH Ec/N0

- CPICH RSCPl UTRA / TDD

- P-CCPCH RSCP

For selection of a node B some basic physical measurements arerequired, which differ from RAT to RAT. For instance in GSM thedownlink level, expressed in RXLEV parameter is measured andcompared against a given cell selection threshold. In connectedmode, the UE still estimates the current quality and reports thisRXQUAL measure to the network.UMTS in FDD mode requries measurements on the downlinkreference channel P-CPICH. The evaluated SNR on that channel,expressed by Echip/N0 , and the received code channel power on theCPICH (RSCP, Received Signal Code Power).Those measurements again are compared agains given thresholds forcell selection purposes.

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Cell selection criterion

0 < Squal = Qqualmeas - Qqualmin (FDD only)

0 < Srxlev = Qrxlevmeas - Qrxlevmin - Pcompensation

cell selectionquality value

[dB]

Minimum requiredcell quality valuerange -20 .. 0 dB

Note: Cell selection and reselection Info provided by SIB11/12

cell selectionRX level value

[dB]

Measured RX level valueFDD: CPICH RSCP [dBm]

Minimum required RX level valuerange -115 .. -25 dBm (2 dB step)

max(UE_TXPWR_MAX_RACH - P_MAX, 0)

max allowedUE TX power

range: -50 .. +33 [dBm]

Note:Default value is P_MAX

max UE TX power [dBm]

∈ { 33, 27, 24, 21 }

Measured cell quality valueFDD: CPICH Ec/No [dB]

Example:

P_MAX = 24 dBmUE_TXPWR_MAX_RACH = P_MAXi.e. path compensation = 0Level selection criterion: Qrxlevmeas > Qrxlevmin

Quality selection criterion: Qqualmeas > Qqualmin

If UE_TXPWR_MAX_RACH > P_MAX, i.e. a UE shall tranmist morepower than possible, Qrxlevmin is reduced by the that difference.

With Ebit/N0 = SF · Echip/N0 the criterion Squal with respect to Ebit/N0and SF = 256 ≅ 24 dB for CPICH becomes0 < Squal = Qqualmeas - Qqualmin , with Qqualmin = 4 .. 24 dBif looking at CPICH Ebit/N0

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Cell ranking for reselection

Rs = Qmap,s - Qhyst,s

Rn = Qmap,n - Qoffset,n

Quality of cell

Quality of neighbour cells

Once a cell is selected, the UE continuously does monitor theneighbouring cells for possibly better service conditions. The UE,according to the given reselection criterions, does maintain a cellranking, which, whenever a neighbour cell gets on top of the list,triggers a reselection process.The reselection of the UE must be reported to the UTRAN in case ofchanging the location area. Thus, the UTRAN always knows therough location of the UE and can forward mobile terminated calls.

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UMTS

Introduction to 3GPP WCDMABasic WCDMA Procedures

Dipl.-Ing. (Univ) Reinhold KruegerDipl. Ing. (TU) Heinz Mellein

R&S - TRAINING CENTER© 2002

www.rohde-schwarz.com

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UMTS

Introduction to 3GPP WCDMATransmit Power Control

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Transmit Power Control

Power Control CDMA_TPC_09.VSD

Base Station

The need for fast and highly accurate transmit power control (TPC)may be regarded as the most serious (negative) issue of CDMAsystems in total.

There is a need for TPC on the downlink and the uplink, however,facing different requirements.

The implementation of TPC is a great challenge for all parts, softwareand hardware, and must be realised with highest priority.

The simple fact, that a single mobile transmitting too much powerwill block the complete radio cell, outlines the great importance ofTPC in a very obvious way.

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Transmit Power Control

DPCCH 15 ksps

3.84 Mcps

Spreading

3.84 Mcps

Spreading

DPCCH 15 ksps

3.84 Mcps

Looking at the spreading operation of CDMA systems in thefrequency domain, a weak subscriber with respect to its transmitpower, does contribute a very small portion of spectral powerdensity to the total WCDMA signal at the air interface.Different contributions of spectral power density is simply caused bydifferent distances of the mobiles to the node B receiver.

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Transmit Power Control

Despreading

3.84 Mcps negative SNR

It may happen, that the processing gain in the node B receiver is notsufficient to achieve a positive SNR for the selected code channel. Inthat case, decoding and processing of those data is no more possible,the radio link for that code channel is cut.

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Power Control

l Most serious negative pointl Every mobile is an interferer for every other mobilel Every base station is an interferer for every other base stationl A single overpowered mobile/base station could block a whole

cell since every mobile/base station is an interferer for everyother mobile/base station

l Power control is directly related to the capacity of the systeml Uplink

- The output power of all mobiles must be controlled in a waythat all signals arrive at the base station with the same meanpower level

l Downlink- The output power of the base stations should be minimised to

minimise the interference to other cells

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Uplink Power Control

Power control in uplink direction CDMA_TPC_01.VSD

Base Station

Power control commands

TPC in uplink is responsible to maintain the full radio cell capacity. Asingle dB of SNR unnecessarily used by a mobile does reduce theresidual cell capacity. Thus, a very "loud" user may block the entirecell. This is known as the "near-far" problem.

On the other hand, when taking SNR away from a single mobile, thequality of serve (QoS) does suffer with respect to the transmissionreliability.

Thus, it is vital to meet exactly the required SNR for each individualsubscriber. Due to the fast changing quality of a mobile channel, theSNR assignment must be controlled as fast as possible. The requiredfast power control is provided by the closed loop TPC algorithm.

The target SNR for the individual mobiles must be provided by theradio network controller towards the node. This process is calledouter loop TPC.

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Uplink Power Control

Power control in uplink direction CDMA_TPC_02.VSD

Base Station

Power control commands

Keep receivedpower levels

equal

The TPC process is performed by exchanging continuously TPCsymbols on the DPCCH. A number of bits, depending on the usedtime slot format, is reserved to indicate the required power controlsteps. Since the DPCCH is sent regularly each and every time slot, thetransmit power can be modified 1500 times per second (compared toGSM this is 750 times faster). With that speed, even fast fading effectsmay be compensated.

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Uplink Power Control

Power control in uplink direction CDMA_TPC_03.VSD

Base Station

Power control commands

However, for the first UTRAN access by the mobile station on thePRACH, no closed TPC control is available yet. Thus, an open loopalgorithm applies. To avoid any problems, the mobile startstransmitting PRACH preambles with the lowest power possible andincreases the power in predefined steps until the UTRAN doesacknowledge the reception of the access attempt and establishes theclosed loop TPC.

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Downlink Power Control

Power control in downlink direction CDMA_TPC_04.VSD

Base Station

Power control commands

Base Station

On downlink there is no "near-far" problem as in the uplink.However, in might be necessary to increase individual code channelpower for individual mobile stations. However, it is important tomonitor the total downlink signal power, since it determines the intercell interference.

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Downlink Power Control

Power control in downlink direction CDMA_TPC_05.VSD

Base Station

Power control commands

Base Station

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Types of transmit power control

open loop Power Control closed loop Power Control

inner loop Power Control outer loop Power Control

For random access procedure

Fast power control tocompensate fading

Slow power control to maintainrequired SNR

TPC

(Transmit Power Control)

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FDD Open loop power control

CPICH → RSCPSystem Info → BCCH → P-CCPCH

UE- Primary CPICH DL TX power- UL interference- Constant Value- Power Ramp Step- Preamble Retrans Max

P = Primary CPICH DL TX power – CPICH_RSCP + UL interference + Constant Value (+ Power Ramp Step)

Parameters for open loop power control:•Primary CPICH DL TX power = { -10 .. 50 } dBm•UL interference = { -110 .. -70 } dBm•PRACH Constant value = { -35 .. -10 } dBm

Calculation of the inital PRACH Preamble power:Preamble_Initial_Power =Primary CPICH DL TX power - CPICH_RSCP + UL interference +Constant Value

The following preambles - i.e. as long there is no receptionacknowledgement by the UTRAN on the AICH - shall be transmittedwith the power increased by the PowerRampStep = {1..8} dB. Thenumber of PRACH preamble attempts is limited byPreambleRetransMax = { 1..64 }.

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FDD closed loop power control

TPC Bit PatternNTPC = 1 NTPC = 2

Transmitter powercontrol command

10

1100

10

Data DataTFCI PilotTPC

Downlink DPCH = DPCCH/DPDCH

As soon as a DPCCH link is established the closed loop algorithmusing the TPC symbols applies.

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Parameters for Uplink TPC

l UTRAN parameters of higher layers- SIRtarget

- PCA PowerControlAlgorithm: {Algorithm1, Algorithm2}

- TPC step size {1dB,2dB}l OSI Layer 1 Parameter

- ∆TPC (derived from TPC step size)l Operational parameters

- SIRest (current SIR estimation)

- TPC Symbol( 0 if SIRest > SIRtarget ; 1 otherwise )

- TPC_cmd { -1 if TPC = 0 ; 1 otherwise }

- ∆DPCCH (Absolute step size for DPCCH transmit power in [dB], derived from ∆ TPC and TPC_cmd)

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Uplink TPC :Algorithm 1

TPC_cmd

{ 0, 1 }

∆DPCCH [dB] = ∆TPC ⊗ TPC_cmd

{ -1, +1 }

Data DataTFCI PilotTPC

Downlink DPCH = DPCCH/DPDCH

given by higher layersTPC_stepsize

In case of TPC algorithm 1, the mobile station does decode thereceived TPC symbol into a TCP_cmd. The TPC_cmd does eitherrequest to increase or to decrease the transmit power by one TPC stepsize.

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TPC_cmd (slot 1..4) = 0TPC_cmd (slot 5) = 1 if TPC (slot 1..5) = 1TPC_cmd (slot 5) = -1 if TPC (slot 1..5) = 0TPC_cmd (slot 5 ) = 0 otherwise

∆DPCCH [dB] = ∆TPC ⊗ TPC_cmd

{ -1, 0, +1 }

{5 time slots} alternating TPC Symbol switches off

TPC

TPC TPC TPC TPC TPC

Uplink TPC :Algorithm 2

TPC algorithm 2 allows slower transmit power changes or evenswitching off the TPC to maintain constant transmit power.

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UMTS

Introduction to 3GPP WCDMAHandover

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Handover Definition

Hard handover UMTS_PRC_HOV_02.VSD

BS1 (f1) BS2 (f2)

MS

BS1 (f1) BS2 (f2)

MSStep 1 Step 2

l Forwarding of a mobile station from one radio cell to another,without interruption of the service.

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Handover Types

Soft handover UMTS_PRC_HOV_01.VSD

BS1 (f1) BS2 (f1)

MS

BS1 (f1) BS2 (f1)

MS

BS1 (f1) BS2 (f1)

MS

Step 1 Step 2

Step 3

Hard handover UMTS_PRC_HOV_02.VSD

BS1 (f1) BS2 (f2)

MS

BS1 (f1) BS2 (f2)

MSStep 1 Step 2

l Soft Handover- UE connected to several

BS’s at the same time- All BS’s transmit on the

same frequencyl Hard Handover

- UE at any timeconnected to a single BS

- BS’s use differentfrequencies or belong todifferent RTT’s

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Soft Handover

Soft handover UMTS_PRC_HOV_01.VSD

BS1 (f1) BS2 (f1)

MS

BS1 (f1) BS2 (f1)

MS

BS1 (f1) BS2 (f1)

MS

Step 1 Step 2

Step 3

Softer handover UMTS_PRC_HOV_03.VSD

BS1 (f1) BS2 (f1)

MS

BS1 (f1) BS2 (f1)

MS

BS1 (f1) BS2 (f1)

MS

Step 1 Step 2

Step 3

l Soft Handover- Handover to a cell with

the same frequencyl Softer handover

- Soft Handover within asingle node B

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Hard Handover

l Frequency-Handover- Cell A and cell B with different frequencies

l System-Handover- Handover to other RTTs- e.g. WDCMA <> GSM

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Handover Parameter

Handover parameters UMTS_PRC_HOV_04.VSD

Add threshold

Drop threshold

Pilot 1

Pilot 2

Add pilot 2 to theactive set

Add timer Drop timer

Remove pilot 1 fromthe active set

Active set total signal

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UMTS

Introduction to 3GPP WCDMARadio link establishment

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random access procedure

UELayer 1

RACH PreamblePRACH

AICH positive aquisition indication

Node BLayer 1

Repetition with alternatingSignatures and increasingtransmit power

RACH message part

UEMACRRC

RACH

PHY-Data-REQ

RACH transmittedincl. „establishment cause“

It is the higher layers which initiate the random access, since theyknow resp. decide what kind of connection is required for therequested service. The lower layers are asked then to establish first ofall a physical connection, ie. to "ask" for physical ressources. Whenthe physical ressource for communication via the radio interface isestablished, the higher layers will continue the communication on theassigned channel, until they ask the lower layers again to release theradio link.Initiated by the upper layer request, the physical layer initiates therandom access procedure to ask for the establishment of a physicalradio link. It transmits a PRACH preamble, starting with minimumpower according to the opern loop power control mechanism, untilthere is an acknowledgement on the downlink, represented by theAICH. After AICH reception the physical layer transmits the RACHmessage part including higher layer information. The transmission ofthe message part is acknowledged to the higher layers.

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L1 PRACH Preamble

1. Random selection of a Signature Ps out of s = 0..15 possible Hadamard codes of length 16

2. 256 times repetition of Ps builds preamble signature code Csig,s of length 4096 chips

3. Preamble scrambling code Sr-pre, n = C long, 1, n

n = 0..8191 (213 - 1) provided by system information

4. Build complex-valued random access preamble codes: Cpre,n,s = S r-pre,n ⋅ Csig,s ⋅ exp( j(π/4+ k⋅π/2)

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Random access

RACH messageRACH Preamble withchanging signatures

AICH Preamble∆ Po

open loopPreamblewith initial

transmit power

PRA

CH

AIC

H

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Paging

UE UTRAN

PAGING TYPE 1

TYPE 1: PCCH → PCH → S-CCPCH

TYPE 2: DCCH → FACH → S-CCPCH

PAGING TYPE 1 or 2

The paging message for mobile terminated call establishment isprovided by the logical channel PCCH. Via the transport channelPCH and the physical channel S-CCPCH it is transmitted towards allmobiles within the related location area.

Two types of paging are specified

PAGING TYPE 1This RRC message is transmitted to mobile stations in idle mode. Themessage may include a paging message or an indication of changesin the system information (BCCH modification information)

PAGING TYPE 2This paging message is used to page mobile stations which alreadyare in allocated mode, ie. already maintain a radio link.

Identification of called mobile station

GSM-MAP: IMSI, TMSI, P-TMSI (Packet-TMSI)ANSI-41: IMSI, TMSI

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RRC link establishment

UE UTRAN

RRC CONNECTION REQUEST

RRC CONNECTION SETUP

RRC CONNECTION SETUP COMPLETE

CCCH → RACH → PRACH

CCCH → FACH → S-CCPCH

DCCH

The radio link establishment is initiated by the random accessprocedure via the PRACH of the mobile station, e.g. as a response ofa paging type 1 message. Important information, such as theestablishment cause, the UE identity and a first measurement reportare already known then to the UTRAN.

With RRC CONNECTION SETUP message, provided by the logicalCCCH via the transport channel FACH and the physical channel S-CCPCH a dedicated control channel is assigned by the UTRAN.Therefore this L3 message transmits the necessary radio link data(spreading code, uplink scrambling code etc.)

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ref . 3GPP TS34.108

Call setup steps

RRC or AS connection setupEstablishment of a Dedicated Common Control Channel

NAS call setupAuthentication and Security Procedures

RAB call setupAssignment and enabling of target radio bearer

A call establishment may be regarded in three phases. First of all theradio link on the air interface between UE and UTRA is established.When a dedicated channel (DCCH) is available the next phase canstart, which includes authentication and security procedures (i.e.establishment of ciphering algorithms). This already includes corenetwork elements like HLR (home locatio register) which providesrequired subsriber data. When that phase is passed by the mobile, thefinal phase provides the final connection towards the called party.

AS = Access StratumNAS = Non-Access StratumRAB = Radio Access Bearer

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ref . 3GPP TS34.108

MT Call setup / CS

Paging (PCCH)

RRC connection request (CCCH)

RRC connection setup (CCCH)

RRC connection setup complete (DCCH)

Paging response (DCCH)

Authentication request

Authentication response

Security mode command

Security mode complete

Setup

Call confirmed

Radio bearer setup

Radio bearer setup complete

Alerting

Connect

Connect Acknowledge

Nod

e B

UE

Mobile terminated calls are initiated by the UTRAN by the pagingprocedure. The paging message is indicated by the physical pagingindicator channel, which is monitored continuously by all mobilestations.

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ref . 3GPP TS34.108

MO Call setup / CS

RRC connection request (CCCH)

RRC connection setup (CCCH)

RRC connection setup complete (DCCH)

CM service request (DCCH)

Authentication request

Authentication response

Security mode command

Security mode complete

Setup

Call proceeding

Radio bearer setup

Radio bearer setup complete

Alerting

Connect

Connect Acknowledge

Nod

e B

UE

A mobile originated call is directly initiated by the mobile stationusing the random access procedure.

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ref . 3GPP TS34.108

Registration

RRC connection request (CCCH)

RRC connection setup (CCCH)

RRC connection setup complete (DCCH)

Location Updating request (DCCH)

Authentication request

Authentication response

Security mode command

Security mode complete

Location updating accept

TMSI reallocation complete

RRC connection Release

RRC connection Relese Complete

Nod

e B

UE

Registration is required whenever the mobile is switched on or ischanging its location. Like for a mobile originated call, first of all aradio link is establihed initiated by the random access procedure. Thecalling party for registration purposes in fact is the serving mobilenetwork, thus, no "phase 3" for through connection towards thecalled party is required.