The Radio Network and basics of WCDMA

ObjectivesUpon completion of this chapter the student will be able to:

Explain the main differences between the multiple access technologies FDMA, TDMA and WCDMA

Explain spread spectrumExplain why power control is necessaryExplain the different handover scenarios in terms of

soft, softer and hard handoverExplain the difference between FDD and TDD modeExplain the Radio Access Products in UTRAN

WCDMAWideband Code Division Multiple Access

High data rates in 5 MHz 384 kbps with wide-area coverage

2 Mbps with local coverage

High service flexibility support for services with variable rate

support for simultaneous services

support of multiple parallel variable-rate services on one connection

packet and circuit switched services

Fast and efficient packet access

Higher capacity

Development Key Features 1WCDMA

Built-in support for future

capacity enhancements

Adaptive antennas

Advanced receiver structures for

multi-user detection

Increased coverage compared to

existing systems

Development Key Features 2WCDMA

Supports Hierarchical

cell structures Inter-frequency

handover

No need for GPS synchronization

USIM

USIM

SIM

BTSBTSBTSBTSBS

BTSBTSBTSBTSBS

BTSBTSBTSBTSBTS

UMTS/GSM Reference ModelUser equipment GSM BSS Core network External

network

Cu Uu

Um

Iu

A

Iu

Gb

Iur

Abis

Iub

ME

ME

MT

SCP SMS-GMSC

RNC

RNC

BSC

UTRAN

SIM MT BTS BSC

MSC

EIR

GGSN

GMSC

SGSNAUCHLR

Figure 1 - 6

WCDMA was chosen as the technology for UMTS public, wide-area service, on the paired FDD bands:

TD/CDMA was chosen for private, indoor services in the unpaired TDD band.

ETSI Decision on UMTS

1920 - 1980 MHz (uplink)2110 - 2170 MHz (downlink)

1900 - 1920 MHz2010 - 2025 MHz

(1) The WCDMA technology can also be deployedin existing frequency bands, e.g. 900, 1800 and 1900 MHzFit into 2*5 MHz spectrum allocations.

(2) The two modes have harmonized parameters.

Frequency Division Multiple Access (FDMA)

Orthogonal in frequency within cell Narrow bandwidth per carrier Continuous transmission and reception No synchronization in time

f

t

Power

MS1 MS 2 MS 3

NMTAMPSTACS

Time Division Multiple Access (TDMA)

Orthogonal in time within cell Increased bandwidth per carrier Discontinuous transmission and reception Synchronization in time

Power

t

f

MS 1MS 2

MS 3

200 kHz

GSM

PDC

D-AMPS

Separate users through different codes Large bandwidth Continuous transmission and reception

f

Code

t

MS 1MS 2MS 3

5 MHz

Direct Sequence Code Division Multiple Access (DS-CDMA)

IS-95 (1.25 MHz) CDMA2000 (3.75 Hz) WCDMA (5 MHz)

WCDMATechnical characteristics

5 MHz carriers Frequency Division Duplex, FDD 3.84 Mcps chip rate Variable spreading codes

f

t10 ms frame

4.4-5.0 MHz

P

Optimised packet access on common ordedicated channel

High spectrum efficiency

Why Spread Spectrum ?Frequency selective fading - Frequency Diversity

Interference Averaging

f

ChannelQuality

f

ChannelQuality

BITS 11001

SPREADING

CHIPS 1101001001Chiprate = Spreading Factor * Symbol Rate = Constant = 3.84 Mchip/s

Direct Sequence Spread Spectrum Signals

TS

TC

t

t

t

d(t)

c(t)

d(t)c(t)

Information signal

Spreading Signal

Transmission Signal

Bit-rate FlexibilityWCDMA variability principle:Power is the commonshared physical resource

Varyinguser bit rate

Translates into Varying power level Varying spreading factor

B

i

t

r

a

t

e

P

o

w

e

r

l

e

v

e

l

S

p

r

e

a

d

i

n

g

f

a

c

t

o

r

Service FlexibilityMultiple Parallel Services

For a single user, multiple services with different variability can be mixed easily on a single physical resource

Bitrate

Power level

Bitrate

WCDMA Resource Allocation The common shared resource in WCDMA is power Varying user bit rate is mapped to variable power and spreading on

a single code Different services can be mixed on a single code for a user Resource allocation is more decentralized

CA

CC

Power levels from MS

Received power levels at BTS

CB

CA

CA

CA

CC

CB CB

SF ChiprateMchips/s

User BitrateUplink

3,84

3,84

3,84

3,84

3,84

3,84

3,84

256

128

64

32

16

8

4

15

30

60

120

240

480

960

3,84

3,84

3,84

3,84

3,84

3,84

3,84

3,84

512

256

128

64

32

16

8

4

15

30

60

120

240

480

960

1920

SF ChiprateMchips/s

User BitrateDownlink

SF ChiprateMchips/s

User BitrateUplink

3,84

3,84

3,84

3,84

3,84

3,84

3,84

256

128

64

32

16

8

4

15

30

60

120

240

480

960

Channelization Codes (CC)

CC1 & CC2 CC3,CC4 & CC5

In the Downlink Orthogonal Codes are used to distinguish betweendata channels from the same Base Station

CC1,CC2,CC3 CC1 & CC2

In the Uplink Orthogonal Codes are used to distinguish between data channels from the same mobile

Channelisation Code tree Adapts user bit-rate to code length

C1 = {1}

C2.1 = {1 1}

C2.2 = {1 -1}

C4.1 = {1 1 1 1}

C4.2 = {1 1 -1 -1}

C4.3 = {1 -1 1 -1}

C4.4 = {1 -1 -1 1}SF = 1 SF = 2 SF = 4

OVSF

Channelization codes of different length, depending of the bit rate

Ensures orthogonality even with different rates and spreading factors

Channelisation Code tree Adapts user bit-rate to code length

C2.1 = {1 1}

C4.2 = {1 1-1-1}

C8.3 = {11-1-111-1-1}

C8.4 = {11-1-1-1-111}

SF = 2 SF = 4 SF = 8

Unusable codesC2.1 = {1 1}Using C4.1

C4.1 = {1111}C8.1 = {11111111}

C8.2 = {1111-1-1-1-1}

Using C8.4

Unusable code

Code Correlation

+1 0 -0.5Divide byCode Length

-1 +1 1 +1 +1 1 +1 -1 -1 +1 1 +1 +1 1 +1 -1 -1 +1 1 +1 +1 1 +1 -1Orthogonal code

in Transmitter

x x x

-1 +1 1 +1 +1 1 +1 -1 -1 +1 -1 +1 -1 -1 +1 -1 -1 +1 1 +1 +1 1 +1 -1TransmittedSequence= = =

+1 +1 +1 +1 +1 +1 +1 +1 -1+1 -1 +1 +1 -1 +1 1 +1 1 1 1 +1 1 1 -1

8 0 -4Integrate

Result

Integrate Integrate Integrate

= = =

-1 +1 1 +1 +1 1 +1 -1 +1 +1 +1 +1 +1 +1 +1 +1 -1 -1 +1 1 +1 +1 1 +1Orthogonal Codeused in Receiver

x x x

Case I: Correlation using Channelisation Codes(a) Same Channelisation Code; (b) Different Channelisation codes; (c) Same code with non-zero time offset

Transmitter

Receiver

Input Data +1 +1 +1(a) (b) (c)

Pseudo Noise (PN) Codes

PN code 1

PN code 3

PN code 1

PN code 4

BS 1 transmits on PN code 1

PN code 2

PN code 5

PN code 2

PN code 6

BS 2 transmits on PN code 2

Uses modulus addition (XOR)1 mod 1 = 00 mod 0 = 01 mod 0 = 10 mod 1 = 1

Generation of Pseudo Noise (PN)Codes

Code Correlation

Input Data +1 -1 +1

+1 -1 +1Divide byCode Length

Case II: Auto-correlation using a PN CodeReceiver and Transmitter use identical code at same time offset

+1 1 +1 +1 1 -1 +1 -1 +1 1 +1 +1 1 -1 +1 -1 +1 1 +1 +1 1 -1 +1 -1PN code usedin Transmitter

x x x

+8 -8 +8Integrate

Result

Integrate Integrate Integrate

TransmittedSequence +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 -1PN CodeUsed in Receiver

x x x

Transmitter

Receiver

Code Correlation

Input Data +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

PN code usedin Transmitter

TransmittedSequence

PN CodeUsed in Receiver

-4 0 2Integrate

Result

-0.5 0 0.25Divide by

Code Length

Case III: Cross-Correlation using PN CodesReceiver and Transmitter use different codes

x x x

Integrate Integrate Integrate

= = =

x x x

= = =

Transmitter

Receiver

PN & Orthogonal Codes

2 Data channelsPN1 + OC1 + OC2

2 Data channelsPN3 + OC1 + OC2

1 Data channelPN1 + OC3

2 Data channelsPN4 + OC1 + OC2

User 1 User 2

3 Data channelsPN5+OC1+OC2+OC3 3 Data channelsPN6+OC1+OC2+OC3

User 3 User 4BS2

BS1

Pilot, BroadcastPN1 + OCp + OCb

Pilot, BroadcastPN2 + OCp + OCb

3 Data channelsPN2+OC1+OC2+OC3

3 Data channelPN2+OC4+OC5+OC6

Channelisation Codes = Short Codes = Walsh Codes :

Code sequence repeated for each new data bitCode sequence length = bit length (in time)

+ Orthogonal codes if perfect synchronization+ Good cross-correlation properties

Scrambling Codes = PN-Codes = Long Codes :

Code sequence length >> bit (in time)Code Planning needed

+ Good auto-correlation properties+ Low cross-correlation

Code Properties, summary

Identifies the transmitter

Separate different data channels & data rates

0 1 0

+1

-1

+1

+1

-1

-1

Bipolardata

sequence

1 Bit

Bits/s

Chips/s

Chip

Code(1-1 1-1)

Signal

Chips/s

10 kb/s

3.84 Megachip/s

DS-CDMA - Principle

BITS

11001BITS

11001CHIPS

1

WBI

WBI

WBI = WideBand InterfererNBI = NarrowBand Interferer

frequency

Power

f

P

f

P

f

P

f

P2

3 4 51 2

3

4

5

5 MHz

NBI

MOD DEM LP DET

WCDMA Transport Channels

Common Control Channels BCCH Broadcast Control Channel (DL) FACH Forward Access Channel (DL) PCH Paging Channel (DL) RACH Random Access Channel (UL)

Dedicated Channels DCH Dedicated Channel (DL & UL)

Transport-to-physical Channel Mapping

Secondary Common Control Physical Channel (Secondary CCPCH)

Secondary Common Control Physical Channel(Secondary CCPCH)

Physical Random Access Channel (PRACH)

Dedicated Physical Data Channel (DPCCH)

Dedicated Physical Control Channel (DPCCH)

Synchronization Channel (SCH)

Primary Common Control Physical Channel(Primary CCPCH)BCCH

FACHBCCH

RACH

DCH

Pilot (TFI)TPC

Uplink Dedicated Physical Channels

DPDCH

DPCCH

Data

Slot 14Slot iSlot 2Slot 0

Frame 1 Frame 2 Frame i Frame 72

10 ms

One super frame = 720 ms

Q Mux

I Mux

2560 Chips, 10x2k bits

Transport Format IndicatorTransmit Power Control

Downlink Dedicated Physical Channels

Slot 14Slot iSlot 2Slot 0

Frame 1 Frame 2 Frame i Frame 72

10 ms

One super frame = 720 ms

IQ MuxData Data(TFI)TPCPilot

DPDCHDPCCH

2560 Chips, 10x2k bits

Transport Format Indicator

Primary Common Control Physical Channel

Slot 14Slot iSlot 2Slot 0

Frame 1 Frame 2 Frame i Frame 72

10 ms

One super frame = 720 ms

Data Pilot 8 bitsTx off

256 chips

Secondary Common Control Channel

Slot 14Slot iSlot 2Slot 0

Frame 1 Frame 2 Frame i Frame 72

10 ms

One super frame = 720 ms

Data Data(TFCI) Pilot

2560 Chips, 20 * 2k bits (k=0..6)

PRACH allocated for RACH access slot

Access slot #1

Access slot #2

Access slot #i

Access slot #8

Random access transmission

Random access transmission

Random access transmission

Random access transmission

1.25 ms

Offset of access slot #i

Frame Boundary

Uplink Spreading and Modulation

DPDCH

DPCCH

CCH,di

CCH,di

Q

I

IQMux

I+jQCscramb

QPSKmodulation

Multi-code transmissionAdditional data channels DPDCHs added to either I or Q

CCH,di:Channelization codes (OVSF codes, 4-256 chips)Cscramb:Scrambling code (long Gold code, 38400 chips, or short VL Kasami code, 256 chips)

Downlink Spreading and Modulation

DPDCH/

DPCCH

S Pbits to

symbols

Cch

QPSKmodulation

OVSF codes ensure DL orthogonality even with different rates and spreading factors for different users

Cch: Channelization codes (OVSF codes, 4-256 chips)Cscramb: Downlink scrambling code (Gold code, 38400 chips)

Cscramb

WCDMA Packet AccessOptimized dual mode scheme with adaptive mode selection based on packet-traffic characteristics

Small infrequent packets appended to Random-Access Request

Large or frequent packets transmitted on dedicated channel

Random-AccessRequest Small packet

Random-AccessRequest Small packet

Arbitrary time

Random-Access Channel

Random-AccessRequest

Packet Packet Packet

Random-Access Channel

Dedicated ChannelRelease of channel

T Time-out

Initial Cell search

Matchedfilter

Slot-wise accumulation

Find Maximum

Tslot

One Ray from Base Station AOne Ray from Base Station B

Timing moduloTslot

Step one: Slot synchronizationStep two: Frame synchronization and code group

identificationStep three: Scrambling code identification

Cell Search, Asynchronous System (WCDMA)

Current cell

New cell

MF output

Synch. codeScrambling code

Synch. codeScrambling code

random

est

256 chip/s

3.84 chip/s

10 ms

Handover

Intra-frequency handover within same carrier

Soft handover between different BSs

Softer handover between sector at same BS

Inter-frequency handover between two carriers

Inter-frequency Handover

Inter-frequency measurements needed in both scenarios ETSI WCDMA has a slotted mode for inter-frequency

measurements, thereby supporting the scenarios above

HCS-scenario

Handover f1 f2 always needed between layers

Handover f1 f2 needed sometimes at Hot Spot

Hot-spot scenario

Support for Inter-frequency Handover

Needed for: Hot-spot cells with

additional carriers Hierarchical Cell

Structures (HCS) Handover to GSM

Two measurement approaches:

Dual-receiver approach for mobile terminals with receiver diversity

Slotted downlink for low-complexity terminals

f = 10 ms Idle time for IF measurements

SF=SF0

SF=SF0/2

SF=SF0 SF=SF0

SF=SF0/2

SF=SF0

WCDMA Downlink Slotted Transmission

Enables measuring on neighboring cells by changing spreading factor

Multipath FadingA B C

Multipath Propagation

10

2

3

Time Dispersion

10 2 3

Radio Environment

The RAKE-receiver principle

COM

B

I

N

E

R Power measurements of neighbouring BS

Sum of individual multipath components

Finger #1

Finger #2

Finger #3

Searcher Finger

Finger #N

Buffer/delayCorrelators

Channel

Implemented in both the UE and Base-stations

Improves signal reception by- Multipath diversity (from a single BS)- Macro diversity (in soft handover mode)

Enables Soft handover by

measuring signal strength (or quality) from neighboringcells

The RAKE-receiver,summary

Power Control

What? The Transmitter adapts the output power according to Path

Loss Why?

Mainly to solve the Near-Far problem Goal is that all users should experience the same SIR

How? Open Loop Power control (Initially, No signaling) Inner Loop Power control (Signaling channel, continuously:

1500 times/s, relative changes: up or down) Outer loop Power control (Between BTS and RNC)

Power controlWith power control

MS Tx Power

BS Rx Power

Without power control

MS Tx Power

BS Rx Power

Outer loop:FER/BER

Ul Eb/No target

Adjust target

QoS target

Uplink Power Control

Initial settingOpen loop:

Random AccessPMS

Closed loopPower Control:

UP/DOWN command

Outer loop:FER/BER

Ul Eb/No target

Adjust target

QoS target

Downlink Power Control

Closed loopPower Control:

UP/DOWN Command

Open loop:Initial setting

PBS

BS1 BS2

Power Control in Soft Handover/Handoff

PMS

BS2BS1

UP/DOWN Command

UP/DOWNCommand

Uplink Power Control in Soft Handover

Outer loop:FER/BER

Ul Eb/No target

Adjust target

QoS target

Down + DownDown + Up

Up + Up

Decrease power

Increase power

Closed loop Power Control:UP/DOWN

UP/DOWNCommand

UP/DOWNCommand

BS2BS1

Downlink Power Control in Soft Handoff

Node BNode B

RNC

UTRAN Architecture

IurIub

Core Network

Node BNode B

RNC

Iu Iu

Iub

RNS RNS SRNSDRNS

Serving and Drift RNS

Max planned interference

Max planned

load

Noise floor

Uplink interference

Load

Radio Resource Management (Admission Control AC)

The AC function will guarantee the overall system Qos by admitting (or blocking) new users

Monitors cell load by received interference

in uplink output power in downlink

New users blocked above this point

User added

UTRA/Time Division Duplex

Harmonized parametersto UTRA/TDD

Primarily for private, uncoordinated systems

Deployed in unpairedUMTS bands:

1900-1920 MHz and2010-2025 MHz

The proposal is still evolving

UTRA/TDD Parameters

Identical parameters as FDD

3.84 Mcps 10 ms frame/15 slots per frame QPSK modulation, Re-use factor of 1 Multi-code and variable

spreading factor to handle different source rates

Uplink/downlink Allocation

Each 0.625 ms slot allocated to either uplink or downlink transmission

One slot for downlink (BCCH) one for uplink (RACH) Uplink/downlink asymmetry possible Same asymmetry and frame synch needed within

continuous area in coordinated systems

One frame (10 ms)

One slot (0.625 ms) 15

Examples of Uplink/Downlink Allocations

Symmetric allocation

One frame (10 ms)

Symmetric allocation

Multiple uplink/downlink switching-points

Single uplink/downlink switching-point

Asymmetric allocation

Asymmetric allocation

The TDD CDMA Component

In each slot up to 8 codes are used Multi-code transmission Different users can share the same time slot Since only few codes used in each time slot, joint

detection is supported

One frame (10 ms)

One time slot and code

Traffic and Common Control Burst Structure Two different bursts, different length of mid-amble,

in different environments (delay spreads) Mid-amble used for channel estimation

One slot (2560 chips)

Data Mid-amble Data Guard

Data Mid-amble Data Guard

Physical Channel Format

Frame 71Frame iFrame 1Frame 0

Time-slot 0 Time-slot 2 Time-slot i Time-slot 14

10 ms

One super frame = 720 ms

Super Frame

2560 chips

Multi-rate with variable-rates schemes

Single code transmission withvariable spreading

a mobile uses single code transmission by adapting spreading factor as a function of data rate

a base station should broadcast a single burst per mobile station by adapting spreading as a function of the data rate

Multi code transmission with fixed spreading

within one timeslot more than one burst can be transmitted

different spreading codes are used to allow distinction of multiple bursts

these multiple bursts can be allocated to one, partly to one or to different users.

Up to 8 bursts can be transmitted

Spectrum Requirements for WCDMA The minimum spectrum allocation is a single carrier 5 MHz Available spectrum 2 x 60 MHz

UMTS

4.4 MHzCo-ordinated

5.0 MHz Uncoordinated

3.0 MHz Uncoordinated

GSM

Bandwidth Capabilities

WCDMA

TodayHSCSD

&GPRS

EvolvedEDGE

up to115 kbpswide areacoverage

up to2 Mbps

local areacoverage

up to384 kbpslocal areacoverage

at least 384 kbpswide areacoverage

200 kHz 5 MHz

UMTSGSM

WCDMA ProductsRadio Network Overview

Radio NetworkController

Core Network

Radio BaseStation

Mobile terminals

Radio Access Network

Network Management system

TRAMRANOS

RadioAccessNetworkOperationSupport

Tools forRadioAccessManagement

CN/other management appl.