1-Introduction to UMTS and WCDMA

Introduction to UMTS & WCDMA

April 2008

Oussama Akhdari

ROSI / INTPS / NAD / RASQ / International Radio support

2 Groupe France Télécom Introduction to UMTS & WCDMA / April 2008 /confidential/Oussama Akhdari

3G Generation General AspectsIntroduction to UMTSUMTS Radio Access Network QoS ArchitectureWCDMA Principles

Agenda


IMT 2000 Standards

IMT-2000 is a term used by the International Telecommunications Union (ITU) to refer to many third generation (3G) wireless technology, that provide higher data speed between mobile phones & base antennas. ITU activities on IMT-2000 comprise international standardization, including frequency spectrum & technical specifications for radio & network components, tariffs and billing, technical assistance & studies on regulatory and policy aspects.

IMT- DS

WCDMA/UTRA FDD

Direct Spread

IMT- MC

CDMA2000Multi-Carrier

IMT- TC

UTRA TDDTD - SCDMATime - Code

IMT- SC

UWC - 136Single-Carrier

IMT- FT

DECTFrequency Time

IMT2000 Terrestrial radio interfaces

IMT- OFDM

WiMaxOFDMA

CDMA CDMA - TDMA

Paired Spectrum Paired/Unpaired Spectrum

TDMA TDMA - FDMA

Unpaired Spectrum Paired Spectrum

OFDMA


IMT 2000 FrequenciesWorldwide frequency plans for IMT-2000 bands already identified

Assigning a non IMT2000 spectrum would result in higher handset prices for 3G systems complex circuitry to support international roaming across different frequency bands.

Europe

China

Japan Korea

North America

ITU Alloc.


3rd Generation Projects

3GPP “3rd Generation Partnership Project” www.3gpp.org Present about 80% of the users within the World Technical specifications for the 3rd Generation Mobile System based on the evolved GSM core networks and UTRA. Include a Technical Specification Group (TSG) for the GSM EDGE Radio Access Network (GERAN). Responsible of GSM (2G) and UMTS (3G) including its evolution HSDPA/HSUPA (3.5G) Evolution of HSPA / SAE (System Architecture Evolution) / Long Term Evolution (LTE)

3GPP2 “3rd Generation Partnership Project 2” www.3gpp2.org Present about 20% of the Mobile users Working on AIE (Air Interface Evolution) / EV-DO Rev. C

IEEE 802.16 & WiMAX Forum Deployment very shy and limited to fixed WiMax (3.5 GHz)


3GPP Specification Series www.3gpp.org



Agenda


UMTS Terrestrial Radio Access - UTRAW-CDMA (UTRA FDD)

For the paired band Uplink and downlink are separated in frequency Chosen as the technology for UMTS publish, wide -area service

TD-CDMA (UTRA TDD) For the unpaired band Uplink and downlink are separated in time Flexible time duration for uplink & downlink for asymmetrical traffic Chosen for private, indoor services in the unpaired TDD

FDD Mode TDD Mode

1900 1920 1980FDD ULTDD

UL/DLTDD UL/DL

MSSUL

2010 2025MSSDL

2110 2170 2200

FDD DL

FUL

FDL

FUL/DL

FDD Mode TDD Mode

1900 1920 1980FDD ULTDD

UL/DLTDD UL/DL

MSSUL

2010 2025MSSDL

2110 2170 2200

FDD DL

1900 1920 1980FDD ULTDD

UL/DLTDD UL/DL

MSSUL

2010 20251900 1920 1980FDD ULTDD

UL/DLTDD UL/DL

MSSUL

2010 2025MSSDL

2110 2170 2200

FDD DL

FUL

FDL

FUL/DL


UTRA FDD - Characteristics Wide band code division multiple access W-CDMA multiple access Frequency band Region 1 (Europe)

Uplink 1920 - 1980 MHz & Downlink 2110 - 2170 MHz GSM bands: 900 (including E-GSM band) & 1800 bands

ARCEP provided authorization to OFR & SFR to reuse 900 spectrum for UMTS

Mobistar to launch UMTS900 during 2008 New bands attributed to UMTS @ 2.6 GHz (new auctions?)

Carrier Bandwidth 2x5 MHz (theoretical occupied bandwidth = Chip rate 3,84 Mcps)

Services Both circuit and packet data & asymmetric bitrates AMR Multi Rate Wide Band AMR Multi service possible User Rate Up to 384 Kbits/s

FDD foreseen for Macro & Microcellular coverage for all Orange MCos.


3G vs. 2G Network services

A 3G networks has a very flexible air interface that can meet the demands of both packet services and circuit switched voice or data.


Frequency resources within 3G MCo

The standard resources allocation is 3 carriers per MCo The resources allocation is country dependent (Local

Telecommunication authority strategy)

Uplink (MHz) Downlink (MHz) Total (MHz) Third carrier Available MHz Total (MHz)Mobistar 1964.9 - 1979.7 2154.9-2169.7 2 15 MHz Yes (1 carrier is used) 1910-1915 1 5 MHzOrange Spain 1935 - 1950 2125-2140 2 15 MHz Yes 1900-1905 1 5 MHzOrange France 1964.9 - 1979.7 2154.9-2169.7 2 15 MHz Yes (2 carriers are used) 1910.1-1915.1 1 5 MHzOrange Poland 1920.5 - 1935.3 2110.5 - 2125.3 2 15 MHz Yes 1915.1-1920.1 1 5 MHzOrange Romania 1950.1 - 1964.9 2140.1 - 2154.9 2 15 MHz Yes (2 carriers are used) 1904.9 - 1909.9 1 5 MHzOrange Slovekia 1920 - 1940 2110 - 2130 2 20 MHz Yes (2 carriers are used) 1900-1905 1 5 MHzOrange Switzerland 1950 - 1965 2140 - 2155 2 15 MHz Yes 1905-1910 1 5 MHz

Orange UK 1969.7 - 1979.7 2159.7 - 2169.7 2 10 MHz No (OUK granted only 2 carries, both used) 1904.9 - 1909.9 1 5 MHz

Mobinil (Granted) 1930 - 1935 2120 - 2125 2 5 MHzMobinil end 2010 1930 - 1940 2120 - 2130 2 10 MHzOrange Reunion 1940.2 - 1945.2 2130.2 - 2135.2 2 5 MHz 1 carrier is availableOrange Caraïbe 1940.2 - 1945.2 2130.2 - 2135.2 2 5 MHz 1 carrier is available

Not GrantedNot Granted

MCo UMTS FDD UMTS TDD

Not Granted1 carrier is available


FT Group Supplier

Mobistar Huawei ( ALU Swapped)Orange Spain E/// & NSNOrange France ALU & NSNOrange Poland NSN & HuaweiOrange Romania HuaweiOrange Slovekia ALUOrange Switzerland NSNOrange UK NSN Mobinil ( Egypt ) NSN & HuaweiOrange Reunion HuaweiOrange Caraïbe ALUOrange Moldova HuaweiCell Plus (Mauritius) Huawei

MCo Mco Suppliers



Agenda


WCDMA Access structure


UMTS radio access networkNode B

Radio base station like the BTS in GSM RF Processing (Modulation, Coding, Interleaving, Spreading, de-spreading…)

RNC “Radio Network Controller” Controls radio resources of several Node Bs Manage the Radio Access Bearers for user data transport Control user mobility Supports the Iu interface to the core network

RNS “Radio Network Subsystem” Like BSS in GSM

UMTS Radio Access Network

Iu

Iur

UTRAN

Iub

RNS

RNSNodeB

NodeB

RNC

NodeB

NodeBRNC


RNC Roles: Serving, Drift, Controlling

RNC SRNC

Core Network

Node B Node B Node B Node B

Iu Iu

Iur

Iub IubIub Iub

UE

UTRANSRNSRNS

SRNC• Each connected mode UE is controlled by a Serving RNC (SRNC)• The SRNC terminates Iu towards the CN

DRNC SRNC

Core Network


Iu Iu

Iur

Iub IubIub Iub

UE

UTRANSRNSDRNS

Macro DiversityCombining/splittingfunction

DRNC • Inter RNC soft handover requires a second RNC to be involved• Such an RNC lending resources to an SRNC for a specific UE acts as a Drift RNC (DRNC).

CRNC• Each RNC acts as Controlling RNC (CRNC) for the directly connected Node B’s and their cells• The CRNC controls the radio resources of its cells

CRNC CRNC

Core Network


Iu Iu

Iur

Iub IubIub Iub

UTRANRNSRNS


UTRAN interfaces

Iur interface logical interface between RNCs

Iur is a point-to-point interface between two RNCs

allows more independent radio resource management compared to GSM

RNC mobility (soft handover) Data from the serving RNC is transferred

to the drifting RNC through the Iur interface.

Iub interface Interface between RNC and Node B Allows the RNC & BTS to negotiate about radio resources Transports uplink & downlink transport frames & O&M data Manage Data & signaling Traffic 2 E1 required @ least when HSPA is introduced High Traffic Areas may need a higher IuB capacity

UMTS Radio Access Network

Iu

Iur

UTRAN

Iub

RNS

RNSNodeB

NodeB

RNC

NodeB

NodeBRNC


Core network - circuit switched

Iu - CS for circuit switched services

MSC-Mobile Services switching Center

switch for circuit switched (CS) services

VLR-Visitor Location Register register database for visitors of the radio network

GMSC - Gateway MSC switch from mobile network to external networks for circuit switched services

Core NetworkCN

Iu-CS

GGSNSGSN

MSC/VLR GMSC

HLR


Core network - packet switched

HLR - Home Location Register permanent database of subscriber data

Iu - PSfor packet switched services

SGSN - Serving GPRS Support Node

switch for packet switched (PS) services

GGSN - Gateway GPRS Support Node

switch from mobile network to external networks for packet switched services

Core NetworkCNIu-PS

GGSNSGSN

MSC/VLR GMSC

HLR


Iu interface main Function Establishing, maintaining, and releasing radio access bearers Performing intra-system & inter-system handovers as well as SRNC relocations Transferring NAS signaling messages between UE & CN (direct transfer) Location services - transfers requests from CN to RAN, and location information from RAN to CN. Simultaneous access to CS & PS core network domains for single UE Paging the user, provides the CN with the capability to page user equipment Controlling the security by sending the security keys to RAN and by Setting the operation mode for security functions Reporting data volume Controlling the tracing of the user equipment activity



Agenda


UMTS QoS Architecture

UMTS QoS is provided by the UMTS bearer service, which consists of two parts:

Radio access bearer (RAB) service Provides the confidential transport of user data between the UE and

CN with a QoS that is adequate for the negotiated UMTS bearer Consists of a radio bearer (RB) service & a Iu bearer service

“The RB service is realized in the radio link control (RLC) layer between the SRNC & the UE, using UTRA FDD/TDD, while the Iu bearer service provides transport between the UTRAN & CN”

CN bearer service connects the UMTS CN with CN gateway to the external network


CN = Core networkTE = Terminal EquipmentMT = Mobile Termination

UMTS QoS Architecture

TE MT UTRAN CN IuEDGENODE

CNGateway

UMTS

“End-to-End Service”

TE/MT LocalBearer Service

UMTS Bearer Service External BearerServiceUMTS Bearer Service

Radio Access Bearer Service(RAB)

CN BearerService

BackboneBearer Service

Iu BearerService

Radio BearerService (RB)

UTRA FDD/TDD Service

(Radio Physical Bearer Service)

PhysicalBearer Service

TETE MT UTRAN CN IuEDGENODE

CNGateway

UMTS

“End-to-End Service”

TE/MT LocalBearer Service

UMTS Bearer Service External BearerServiceUMTS Bearer Service

Radio Access Bearer Service(RAB)

CN BearerService

BackboneBearer Service

Iu BearerService

Radio BearerService (RB)

UTRA FDD/TDD Service

(Radio Physical Bearer Service)

PhysicalBearer Service

TE


UMTS QoS Architecture The RAB is the service that the access stratum provides through its service access points (SAP) to the non-access stratum (NAS) for transfer of user data between the user equipment (UE) and the core network (CN)

The RAB provides transport of user data with the quality of service (QoS) adequate to the UMTS bearer service negotiated on the non-access stratum. This service is based on the characteristics of the radio interface and is maintained for a moving user equipment

A bearer service includes all aspects to enable the provision of a contracted QoS. These aspects are the control signaling, user plane transport, and QoS management functionality

The UMTS operator offers the UMTS bearer service, which provides the UMTS QoS.


QoS Classes

There are four different QoS classes (or traffic classes) for UMTSbearer service and radio access bearer service:

conversational streaming interactive background

The main distinguishing factor between these classes is how delay sensitive the traffic is.

Conversational class is meant for traffic that is very delay sensitive, while background class is the most delay insensitive traffic class.

RNC manages the QoS requirements.

Data Integrity sensitive

+

Delay sensitive

-

+ -


+


+

Delay sensitive

-

+

Delay sensitive

-

+


+


+

Delay sensitive

-

+

Delay sensitive

-

+ --


+


+

Delay sensitive

-

+

Delay sensitive

-

+


QoS Classes

Traffic classes provide the means for the network to differentiate between end-to-end user applications according to their required traffic characteristics.

The purpose is to offer good quality connections for both real time & non-real time traffic between MS and the background data networks.

The radio interface is the main capacity limiting factor & must be planned & controlled to achieve the required system performance

Error correction and delay is managed and prioritized to ensure goodquality connections.


Application Groups

Traffic class Conversational Class Streaming class Interactive class Background class

Fundamentalcharacteristics

Conversational RT. Preserve timerelation (variation)between informationentities of the stream. Conversational pattern (stringent & low delay)

. Streaming RT

. Preserve timerelation (variation)between informationentities of the stream

. Interactive best effort. Request response pattern. Preserve payload content

. Background best effort. Destination is not expecting the data within a certain time. Preserve payload content

Example of theapplication Voice Streaming video Web browsing Background

download of emails

Service classes and priorities are one of the main differences between 2G and 3G. Priorities are obtained from CN.

WCDMA RAN uses the QoS parameters obtained from CN to optimize the use of radio resources. In GSM BSS, packet-switched traffic is always lower priority traffic, using only whatever resources are available.



Agenda


WCDMA Transmitter The WCDMA transmitter looks similar to the TDMA transmitter, with the synchronization, control/signaling and multiple user data channels. In a WCDMA transmitter, neither time nor frequency is used to separate different users, but codes in an operation known as spreading.


Multiple Access TechniquesFDMA Frequency Division Multiple Access

uses band pass for carrier signal which are non-overlapping in the frequency domain

TDMA Time Division Multiple Accesscarrier signals are non overlapping in the time domain

CDMA Code Division Multiple Accessspreads the signal over the entire available bandwidth by using codes with good correlation properties

FFrreeqquueennccyy

TTiimmee

PPoowweerr

OOnnee UUsseerr

FFrreeqquueennccyy

TTiimmee

PPoowweerr

UUsseerr

Power

Time

FrequencyOne User

Carrier 1 Carrier 2


W-CDMA No Frequency reuse

W-CDMA = Wideband Code Division Multiple Access Users are separated with code sequences: spreading / despreading technique

All users are transmitting simultaneously on the same frequency In FDD mode, different frequencies are used on uplink and downlink

Frequency Planning No Frequency Planning

All cells are assigned the same frequency

All cells within a given cluster are

assigned different set of frequencies


Spread spectrum technique

The user bits are coded with a unique sequence (code). The bits of the code are called chips and the chip rate is higher than the user bit rate

TimeDomain

Bandwidth = 3.84 Mhz for UMTS

Code Ci(t)

Resulting spread signalDi (t) = Si (t) x Ci(t)

Bit1 Bit2

Source signal Si (t)before spreading

Frequency

Domain Narrowband signal

Bit Rate =Rb

Chip Rate =Rc = 3.84 Mcps in UMTS

Chip Rate =RcSpreading Factor

SF =Rc/Rb


Channelization coding


Spreading Example

Spreading with a spreading factor of 4 is shown in the Figure below.


Spreading / Despreading

In the receiving path, despreading is achieved by auto-correlation with the same code Due to low cross-correlation properties with other codes, the received signal energy is increased compared to noise and other signal interference The gain due to despreading is called processing gainExample for PS 128 Kbps:

dBkbpskcps

RateBitUserRateChipPG 77.1430

1283840


Spreading / Despreading

The figure shows the properties of the Channelization (Orthogonal) codes.


Spreading example

De-spreading applied to another user with a different

spreading code

Increase the data rate by 8 corresponds to a widening of the occupied spectrum of the

spread user data signal


Channelization codes

Orthogonal Variable Spreading Factor (OVSF) are used for channelization for spreading

The codes are mutually orthogonal, if they are synchronized in the time domain Codes are taken from the OVSF code tree

The code tree corresponds to different discrete Spreading Factor (SF) levels, SF=1, 2, 4, 8…(n2) SF: 4 - 512 is allowed in the WCDMA DL SF: 4 - 256 is allowed in the WCDMA UL

Following codes are not allowed to be used: Codes between a used code and the code tree root Codes following a used code


Spreading codes: OVSF code tree

1c4,1=

c4,2=

c4,3=

c4,4=

c2,1=

c2,2=

c1,1= 1

1 1

1 -1

11

1 1

1 -1

1 -1

reverse

copy 1 1copy

reverse-1 -1

1 -1

-1 1reverse

SF=4SF=1 SF=2

1 1 1 1 1 1 1

1 1 1 1 -1-1-1

-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

-1-1-1

-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 1-1-1-1

-1-1-11 -1

-1-1

-1-1-1

1 1 -1-1-1

-1-1-1

1

1 -1-1-1

-1-1-1

1 -1-1-1

1 -1-1-1

1

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

Up to SF = 256

…

1c4,1=

c4,2=

c4,3=

c4,4=

c2,1=

c2,2=

c1,1= 1

1 1

1 -1

11

1 1

1 -1

1 -1

reverse

copy 1 1copy

reverse-1 -1

1 -1

-1 1reverse

SF=4SF=1 SF=2

1 1 1 1 1 1 1

1 1 1 1 -1-1-1

-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

-1-1-1

-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 1-1-1-1

-1-1-11 -1

-1-1

-1-1-1

1 1 -1-1-1

-1-1-1

1

1 -1-1-1

-1-1-1

1 -1-1-1

1 -1-1-1

1

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

Up to SF = 256

…


OVSF : Orthogonality property

1c4,1=

c4,2=

c4,3=

c4,4=

c2,1=

c2,2=

c1,1= 1

1 1

1 -1

11

1 1

1 -1

1 -1

1 1

-1 -1

1 -1

-1 1

1 1 1 1 1 1 1

1 1 1 1 -1-1-1

-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

-1-1-1

-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 1-1-1-1

-1-1-11 -1

-1-1

-1-1-1

1 1 -1-1-1

-1-1-1

1

1 -1-1

-1-1

1 -1-1

1 -1-1

1Codes freeCodes used


Uplink and Downlink Channelization Code Usage

Downlink: Channelization Codes used to distinguish data channels coming from each cell

Uplink: Channelization Codes used to distinguish data channels coming from each User Equipment, UE


Spreading and scrambling codes Spreading codes (channelization codes)

used to differentiate mobiles and services different lengths (spreading factor) according to service in UMTS Orthogonal Variable Spreading Factor (OVSF) in UMTS

Scrambling codes To distinguish between User Equipments in uplink To distinguish between cells in downlink

DLUL

Node B

SpreadingOVSF

(Service/ user identifier)

ScramblingPN

(Cell identifier)

DescramblingDespreading

UE

Descrambling Despreading

SpreadingOVSF

(Service identifier)

ScramblingPN

(User identifier)


The CDMA Cocktail Party

What do YOU hear…

A) If you only speak Japanese?

B) If you only speak English?

C) If you only speak Italian?

D) If you only speak Japanese, but the Japanese-speaking person is all the way across the room?

E) If you only speak Japanese, but the Spanish-speaking person is talking very loudly?


Scrambling Coding


SC: Scrambling Code

Downlink Scrambling Code

SC#2

SC#0

SC#1

SC#116

SC#114

SC#115

RNC

SC#2

SC#0

SC#1

SC#2

SC#0

SC#1

SC#2

SC#0

SC#1

SC#116

SC#114

SC#115

SC#116

SC#114

SC#115

SC#116

SC#114

SC#115

RNC

Downlink scrambling code The number of codes used in the downlink is restricted to 8192 in Total to speed up the process for the UE to find the correct scrambling code. 512 of these are primary codes (the rest are secondary codes, 15 codes per primary). The primary codes are divided into 64 code groups each group containing 8 different codes.One code per cell (sector/carrier) : Configurable by operatorOnly the primary scrambling code is used for all Common Channels


Modulation

Graphical representation of an QPSK modulated signal

1 Modulation Symbol represents 2 data bits Modulation efficiency = 2 bits/symbol


Filtering

Filtering allows the transmitted bandwidth to be significantly reduced without losing the content of the digital data improves the spectral efficiency Raised-Cosine Data Filter

occupied bandwidth = symbol rate x (1+ α)


“Near-Far-Problem”

Illustration Example: Up to around 80 dB attenuation between UE1 and UE2

If UE1 and UE2 transmitted with the same power, UE1 would jam UE2 : so-called “near-far” effect

Solution : power control Need for an efficient power control able to fight against slow AND fast fading!

UE 1

UE 2

Before despreading After despreading


Power control

In UMTS FDD, all users are sharing the same frequency band

W-CDMA requires power control to minimize the level of interference (interference-limited system)

Power control is applied on both uplink and downlink

Power control minimizes the transmission power to match the quality target for each radio access bearer service

No one should get more power than necessary to reach the required QoS Avoids near-far problem on uplink Minimizes waste of common power resource on downlink


Interference limiting system

Thanks to spreading / despreading Desired signal is raised Interference signals are kept low

The level of interference must be controlled to allow the decoding of the received signal

spreadingspreading DespreadingDespreading

BB

ChannelChannel

WW

Thermal NoiseThermal Noise

BBProcessing

gainspreadingspreadingspreadingspreading DespreadingDespreadingDespreadingDespreading

BB

ChannelChannel

WW

Thermal NoiseThermal NoiseThermal NoiseThermal Noise

BBProcessing

gain

BBProcessing

gain


Interference limited

0

2

4

6

8

10

12

14

16

18

20

0 10 20 30 40 50 60 70

Number of simultaneous users per sector

Inte

rfere

nce

leve

l rel

ativ

e to

Noi

se le

vel

(dB

)


Cell breathing

Considering the limitation of maximal transmit power, the increase of required received power due to high traffic will lead to decrease the cell range

The cell coverage decreases when the traffic increases : so-called “cell breathing” phenomenon

Coverage and capacity are linked in CDMA systems


Tr affic den s it y

in cr e ase s

Deployed intersite distance

Load control

In order to avoid power control instability and coverage holes due to high traffic level the level of interference received by a base station should be controlled by means of admission and load control algorithms


Other W-CDMA particularities

No frequency reuse pattern

Scrambling code planning required 512 scrambling codes in W-CDMA

Soft-handover capability

RAKE receiver

SC#116

SC#114

SC#115

SC#2

SC#0

SC#1


Mobile connected to more than one base station during handover procedure Called “softer” handover for sector cells of the same site Soft Handover for Dedicated Channels (circuit and packet data) Hard Handover

HS-DSCH Inter-frequency handovers Inter-RAT Handovers

Soft Handover i

Macrodiversity

Received PilotSignal

Node-B 2

3 dB

Node-B 1

Same carrier

RNC


Soft Handover ii

Advantages Avoids link failure during handover, “make before break” handover Reduces the interference level by decreasing the required UE transmit power Increases downlink quality thanks to macro-diversity at the UE receiver level

Drawbacks Increases the required number of traffic channels Can create too much downlink interference : trade-off on the percentage area of soft-handover


RAKE receiver

Reflections, diffractions, attenuations caused by obstacles will lead to multipath

RAKE receiver is a spread-spectrum receiver that is able to track and demodulate resolvable multipath components : takes benefit of multipath diversity

In W-CDMA, with 3.84 Mcps, a RAKE receiver will be able to discriminate multipath having delays higher than one chip duration (0.26 µs)


The RAKE Receiver

CDMA Mobile Station RAKE Receiver ArchitectureEach finger tracks a single multipath reflection

• Also be used to track other base station’s signal during soft handover

One finger used as a “Searcher” to identify other base stations

Finger #1

Finger #2

Finger #N

Searcher Finger

Combiner

Sum ofindividual multipath components

Power measurement of Neighboring Base Stations


0 50 100 150 200 250 300 350 400-2

0

2

4

6

8

10

12

14

16

18

0 50 100 150 200 250 300 350 400-2

0

2

4

6

8

10

12

14

16

18

0 50 100 150 200 250 300 350 400-2

02468

10

121416

18

The RAKE Receiver

1/2-chip delay

To Viterbi Decoder

Composite Received Signal

PN, Walsh Codes

1/2-chip delay

1/2-chip delay

Ai

Ai

Ai

Correlator

Correlator

Correlator

Equal Combining, ML Combining,

or Select Strongest

time

0 50 100 150 200 250 300 350 400-2

0

2

4

6

8

10

12

14

16

18

1

23

1

23

1

23

1

23 1

2

3 + Interference

+ Interference

+ Interference


RAKE receiver ii

It combines the delayed replicas of the transmitted signal to improve reception quality : time-diversity technique

Identify the delay positions on which significant energy arrives and allocate correlation receivers (RAKE fingers) to those peaks

Within each correlation receiver, track the changing phase and amplitude values and correct them (thanks to pilot symbol estimation)

Combine the demodulated and phase-adjusted symbols across all active fingers and present them to the decoder for further processing (maximal ratio combining)


Spreading Spectrum Advantages

The wideband transmission has the advantage of being less sensitive to frequency selective interference and fading.

The power density of the spectrum is decreased several times and the transfer of information is still possible even below background noise.

CDMA is very spectrum efficient due to the possibility of reusing each carrier in each cell.

High Capacity in comparison with GSM

Soft handover is required in WCDMA.


Spreading Spectrum Drawbacks

The power levels of all UE’s transmissions received at the BS must be equal if the bit rates are equal and therefore fast power control is necessary

As UEs in soft handover mode require resources of more than one cell, the system capacity may be reduced.


an exchange!

based on discussions!

… share our experiences

any questions?let’s discuss!


Back UP


Logical channels i

PCCH - Paging control Channel (DL) DL Paging information

BCCH - Broadcast Control Channel (DL) DL System control information e.g. Cell identity, UL interference level

CCCH - Common control Channel (UL/DL) For transmitting control information between the network and UEs The CCCH is commonly used by UEs having no RRC connection and after cell reselection e.g. initial access (RRC connection request, cell update)


Logical channels ii

CTCH - Common Traffic Channel (DL) channel to transfer dedicated user information to all or a group of UEs e.g. SMS Cell broadcast

DCCH - Dedicated Control Channel (UL/DL) transmits dedicated control information between UE and UTRAN e.g. measurement reports, radio bearer setup

DTCH - Dedicated Traffic Channel (UL/DL) The DTCH carries user data e.g. speech, Fax, video, web, ...


DL Transport Channels i

BCH - Broadcast Channel For broadcasting of system information over entire cell no power control, fix bit rate

PCH - Paging Channel association with Page Indicator Channel PICH, to support efficient sleep mode procedures must be broadcast over entire cell

FACH - Forward Access Channel Common DL channel used for transmission of

control information small amount of packet data

open loop power control


DL Transport Channels ii

DCH - Dedicated Channel DCH is the only Dedicated Transport Channel Channel dedicated to one UE Supports

Fast Power Control, variable bit rate, SHO, transmit diversity, beam forming

DSCH - Downlink Shared Channel Similar to the FACH Carries dedicated user data and/or control information Always associated with a downlink DCH (with SF of 256) DSCH supports

sharing between different users no SFH, but Fast PC due to associated DCH


UL Transport Channels

RACH - Random Access Channel carries control information or small amounts of packet data

e.g. for initial access or non-real-time dedicated control or traffic data transmitted over entire cell supported by open loop power control

CPCH - Common Packet Channel

Similar to DSCH in DL, used for transmission of bursty data traffic possibility to

transmit over part of the cell (beam forming) change rate fast fast power control

initial risk of collision, but collision detection (CD/CA-ICH) is shared by the UEs in a cell -> common resource

DCH - Dedicated Channel (same as for UL)


Physical Channels

Channels without connection to transport channels are called Stand-alone channels

All Stand-alone channels exist in DL only

Stand alone channels are CPICH Common Pilot Channel SCH Synchronization Channel (Primary & Secondary) AICH Acquisition Indication Channel PICH Paging Indicator Channel CSICH CPCH Status Indicator Channel CD/CAICH Collision Detection / Channel Assignment

Indicator Channel


DL Physical Channels - CPICH

CPICH - Common Pilot Channel Primary CPICH (PCPICH)

• SF=256, predefined bit/symbol sequence, fixed channelization code• Scrambled with the primary scrambling code• Only one PCPICH per cell• Used for level measurements & channel estimation• The PCPICH is the phase reference for all DL physical channels• Transmitted over the entire cell

Secondary CPICH (SCPICH)• SF=256, arbitrary channelization code• Zero, one or several SCPICH per cell• Not necessarily transmitted over entire cell


DL Physical Channels - SCH

SCH - Synchronization Channel Time multiplexed with PCCPCH

• first 256 chips of slot SCH, rest PCCPCH Primary SCH

• Consists of a a fixed 256 chips code Primary Synchronization Code (PSC)

• The PSC is the same for every cell in the system• The PSC is repeated in each slot

Secondary SCH• Transmitted in parallel to the Primary SCH• In each of the 15 slots a different Secondary Synchronization Code

SSC is transmitted• The SSC sequence indicates the used downlink scrambling code set

(8 codes) out of 64 scrambling code groups


DL Physical Channels - Other Stand-Alone

AICH - Acquisition Indication Channel• SF256, Frame length 20ms 5120 chips/slot• Used to confirm reception of (P)RACH

PICH - Paging Indicator Channel• SF=256, carries the paging indicators• associated with an SCCPCH to which a PCH transport channel is

mapped• Once a PI message has been detected on the PICH, the UE decodes

the next PCH frame transmitted on the SCCPCH whether there is a paging message intended for it.

CSICH - CPCH Status Indication Channel CD/CA-ICH - CPCH Collision Detection/Channel Assignment Indicator Channel

• All CPCH related physical channels support the operation of the UL CPCH transport channel


DL Physical Channels

DL Channels associated with a transport channel PCCPCH - Primary Common Control Physical Channel

Used to carry the BCH Time multiplexed with SCH Fixed transmit power / fixed data rate

SCCPCH - Secondary Common Control Physical Channel Used to carry the FACH or PCH / no fast power control

PDSCH - Physical Downlink Shared Channel Carries DSCH Not yet included in 3GR1.1

DPCCH - Dedicated Physical Control Channel Pilot field, TFCI field, TPC field

DPDCH - Dedicated Physical Data Channel carries “real” user data + Layer 3 signaling on DCCH


UL DPCH

UL Physical Channels

UL Channels associated with a transport channel PRACH - Physical Random Access Channel

• Carries RACH• open loop power control / collision risk

PCPCH - Physical Common Packet Channel• Carries CPCH• Fast power control on the message part / open loop for pre-ample

DPCCH - Dedicated Physical Control Channel• Pilot field, TFCI field, FBI field, TPC field

DPDCH - Dedicated Physical Data Channel• Carries “real” user data + Layer 3 signaling on DCCH


Valid for all Dedicated Physical Channels

Existing in uplink or downlink Possibility to use beam forming Possibility to change rate fast on a frame basis (10 ms) Fast power control (Closed Loop Power Control)


One radio frame, Tf = 10 ms

TPC NTPC bits

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

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

Data2Ndata2 bits

DPDCH

TFCI NTFCI bits

Pilot Npilot bits

Data1Ndata1 bits

DPDCH DPCCH DPCCH

DL Physical Channel Example

Example of physical channel structure: DL - DPDCH

Signaling information (DPCCH) is time multiplexed with DPDCH


Pilot Npilot bits

TPC NTPC bits

DataNdata bits

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

Tslot = 2560 chips, 10 bits

1 radio frame: Tf = 10 ms

DPDCH

DPCCHFBI

NFBI bitsTFCI

NTFCI bits

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

UL Physical Channel Example

Example of physical channel structure: UL - DPDCH/DPCCH

DPCCH and DPDCH are in UL NOT time multiplexed, they are I/Q multiplexed.


Use of DPCCH

On the DPCCH channel the following information is transmitted Pilot field

Bit sequence known in the receiver and and used for radio channel estimation

Optimal adaptation of RAKE receiver TFCI field

Transport Format Combination Indicator FBI field (UL DPCCH only)

Feed Back Information given by the UE to the Node B for optimizing closed loop transmit diversity mode (phase &

amplitude) site selection diversity transmission (SSDT)

TPC field Transmit Power Control This field is used to transmit the power control commands to the

Node B (UL) or the the UE (DL).

1-Introduction to UMTS and WCDMA

Documents

umts wcdmaapril

confidentialoussama

generation mobile system

radio network components

generation partnership

evolution hsdpahsupa

cdma utra fdd

different frequency