1

Introduction to WCDMA and

WCDMA Dimensioning for UMTS

2

Third generation services2M

384K

64K

32K

16K

9.6K

2.4K

1.2K

point to point multipoint

bidirectional unidirectional multicast

video

conference

video

conference

remote

medical

service video

catalogue

shopping

video

on

demand

mobile

TV

inte

rn

et

telephone

conference

telephone

voice

mail

electronic

newspaper ISDN

electronic

publishing

FAX

distribution

services

(data)

mobile

radio

distribution

services (voice)

pager

4

UTRAN (UMTS Terrestrial Radio Access

Net) Architecture

Core Network

RNC RNC

Site Contr

BTS BTS BTS

Site Contr

BTS BTS BTS

Site Contr

BTS BTS BTS

Site Contr

BTS BTS BTS

RNS

UTRAN

RNS

Iub IubIub Iub

Iur

IuIu

B-node B-node B-node B-node

5

Access techniques for mobilecommunications

P - Power

T - Time

F - Frequency

P

T

P

T

F

P

T

F

FDMA (TACS)

TDMA,FDMA (GSM)

CDMA (UMTS)

F

6

W-CDMA (Wide Band CDMA)

Key features

• Improved capacity and coverage (over second generation); thus, backward compatible

• High degree of service flexibility: multiple, parallel services per connection; efficient pkt access

7

Basics of Spread Spectrum

and CDMA

8

Overview

• Why consider Spread Spectrum ?

• What is Spread Spectrum & CDMA ?

• Frequency Hopping Spread Spectrum

– Impact of channel

– Current systems

• Direct Sequence Spread Spectrum

– Spreading Codes

– Analytical Performance Model

– Rake Processing

– Near Far Effect (Power Control)

– Handover

9

Why Consider Spread Spectrum ?

• Spread Spectrum has been adopted as the air

interface standard for 3rd Generation Mobile

Systems (IMT2000):

– Europe (ETSI): UMTS (W- CDMA )

– Japan (ARIB): Wideband CDMA

– USA (TIA TR45. 5) CDMA 2000

• 2nd Generation standard deployed in US and Korea

– IS95 (Qualcomm CDMA)

10

What is spread spectrum?

Narrow Band

Message

Narrow Band

Message

Wideband

Message

11

Frequency Hopping Spread

Spectrum

12

• Classification of Spread Spectrum

Systems

• Frequency Hopping (FH)

• Narrow band message signal is

modulated with a carrier frequency which

is rapidly shifted . The hop frequency is

indicated by a spreading function.

• This spreading function is also available

at the receiver and enables it to retune to

the correct channel for each ‘hop’.

13

Hop rates in an FH system

• Fast frequency hopping

• – Data symbol spread over several hop frequencies

• –Symbol diversity

• – Very resistant to jamming and interference, often used in military systems

• Slow frequency hopping

• – Several data symbols on each hop frequency

• –Codeword diversity with interleaving

– Less complex

14

Direct Sequence Spread

Spectrum

15

Classification of Spread Spectrum

Systems

• Direct Sequence (DS)

– Secondary modulation in the form of pseudo-

noise is applied to an already modulated

narrowband message, thereby spreading the

spectrum.

– At the receiver, the incoming waveform is

multiplied by an identical synchronized

spreading waveform in order to recover the

message.

16

Direct sequence spread spectrum

D(t)

C(t)fc fc C(t)

S(t)

Narrow Band

Message Narrow Band

Message

Wide Band

Pseudo Random

Noise

Up conversion

To fixed carrier

frequency

Down

conversionWide Band

Pseudo Random

Noise

17

Data

Signal

Code

Signal

Multiplication

18

Spreading codes

• Maximal length sequences

– good auto- and cross- correlation

Gold codes and Kasami sequences are

derived from M- sequences with similar

• correlation properties, and a larger code

set.

19

Orthogonal spreading Codes

• Walsh and Hadamard sequences

– zero correlation between codes when aligned

– cross- correlation non- zero when time shifted

– fixed spreading factor (codes of different length are not orthogonal)

• Orthogonal Variable Spreading Factor (OVSF) codes

– permit orthogonal codes for different rate services

• Both types of code lose orthogonality when shifted due to channel dispersion

– e. g. 40% loss of orthogonality in a large macrocell

Orthogonal Variable Spreading Factor

c4,1

= (1,1,1,1)

c2,1 = (1,1)

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

c4,3 = (1,-1,1,-1)c2,2 = (1,-1)

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

21

22

23

24

DS-SS Application for CDMA

Mod.

g1(t)

S1(t)

Coswt

S1(t)g1(t)

S2(t)g2(t)

g1(t)

SN(t)gN(t)

X1(t)

25

Theoretical CDMA capacity

• DS- CDMA capacity is inversely proportional to the energy per bit per noise power density which is tolerated

• A standard DS- CDMA system is interference limited by

- intra- cell interference

- Therefore increase capacity by:

- voice activity detection

- antenna sectorisation

- adaptive antennas

- interference cancellation

26

The Multipath Environment

• The received signal

is made up of a sum

of attenuated, phase-

shifted and time

delayed versions of

the transmitted signal.

• Propagation modes

include diffraction,

transmission and

reflection.

27

Path diversity in the multipath Path

diversity

• Path diversity can be exploited by

separating out the multipath components,

co- phasing and summing them.

• Number of paths resolved (Lm) depends

on the total multipath delay (Tm) and the

chip period (Tc) Lm< Tm/Tc +1

28

RAKE Receiver

• One method of realising path diversity is with a RAKE and a bank of correlators

tc tc tc

Int. Int Int

Diversity Combiner

Out

Put

C(t) C(t-tc) C(t-LTc)

29

Diversity and diversity combinig

• Diversity: providing multiple versions of the transmitted signal. Commonly:

– multiple antennas

– multiple paths

• Diversity combining

–selection: best branch is chosen

–equal gain: equal combining: all branch summed

–maximal ratio: branches summed and weighted

depending on their quality

30

The near-far effect in CDMA

• Everyone on same

• frequency at the same

• time.

• A MS close to the BS will “drown out” other MSs unless it reduces it’s power.

• Power control is required.

31

CDMA Power Control

• Power control required on uplink, desired on

• downlink.

• Open loop control can be used to remove shadowing (as the channel is reciprocal).

• Closed loop control is required to remove the

• fast fading

– BS receives MS signal and calculates the SIR

– BS sends MS a transmit power control (TPC)

• signal to increase or decrease its power

• TPC issues include rate and step size

32

Uplink closed loop power

control algorithms

• Sigma- delta scheme used

• Command rate must be sufficient to track

channel changes

• Trade- off in step size between tracking

and accuracy

33

Handover and Mobility

BS1 BS2

34

W-CDMA in UMTS

• W- CDMA is used in FDD mode in UMTS

• On the downlink it is possible to use orthogonal

reading codes to reduce interference. A

scrambling code is used to separate the cells

• On the uplink, low cross correlation codes are

used to separate the mobiles. A single mobile

can use multi-code transmission: each service is

mapped onto several bearers, each of which is

spread by an orthogonal code.

35

WCDMA Air Interface

36

RLCRLC

LACLAC

Radio Interface - protocol

architecture

RLC

RRC

LAC

MAC

Physical Layer

L3

L2/LAC

L2/MAC

L1

C-plane U-plane

Logicalchannels

Transportchannels

RLC

37

Layer 1 - up link physical

channels

(W-CDMA example)Data

Pilot

Dedicated PhysicalData Channel

Dedicated PhysicalControl Channel

Transmitpower control

Transportformat ind.

Slot#1Slot#2 Slot#i Slot#15

Frame#1Frame#2 Frame#i Frame#72

0.667 ms

10 ms

Feedbackindicator

38

Layer 1 - down link physical

channels

(W-CDMA example)

Data

Slot#1Slot#2 Slot#i Slot#15

Frame#1Frame#2 Frame#i Frame#72

Pilot TPC TFI

DPCCH DPDCH

frame

superframe

0.667 ms

10 ms

39

Transport channels (example)

• Dedicated Channel (DCH): fast change of bit rate (10ms)fast power controlinherent MS addressing

• Random Access Channel (RACH) - up link: collisionopen loop power controlexplicit MS addressing

• Broadcast Control Channel (BCH) - down link

• Forward Access Channel (FACH) - down link: slow power controlexplicit MS addressing

• Paging Channel (PCH) - down link: use of sleep modes

40

Multiplexing transport channels onto

physical channels

DCH

DCH

DCH

DCH

cod

ing

inte

rle

avin

g

cod

ing

inte

rle

av

ing

rate

m

atc

hin

gra

te

matc

hin

g

inte

rle

avin

gin

terle

av

ing

ra

te

ma

tch

ing

inte

rle

av

ing

mu

ltip

lexin

g

inter frameinterleaving

intra frameinterleaving

static

dynamic(up link)

trasport channelsmultiplexing

41

MAC Services and Functions

mapping

phy ch phy ch

DCHDCHDCH

Coding and

multiplexing

mapping

phy ch

DCH DCH

Coding and

multiplexing

• set-up, release of logical channels• data transfer service on logical channels• allocation/re-allocation of radio resources• measurement report

• Selection of the transport format

• Handling of priority within one user/between users

• Scheduling of control messages (broadcast, paging,

notification)

• Multiplexing/de-multiplexing of higher layers PDUs

on/from common or dedicated transport channels

• Contention control on the random access channel

Functions

42

Radio Network planning And

Dimensioning Procedures

• Preparation

• Estimation No. of Cells

• Detailed Planning

43

Preparation

• 1-Targets of Capacity and Coverage

• 2-Strategy of Network Planning

44

Estimation No. of Cells

Population of Region

Influence

percentage

No of UsersTraffic/User

Offered Traffic Capacity/Cell Cell Rangr

No of Cells

45

Estimation Capacity of Cell

• Principle Factors :

1. Data Rate

2. Traffic characteristics (variation Rates,..)

3. Requirements (delays, BER)

4. Disconnect Probability

5. Sectorized Effect

6. Load Effect

46

Cell RangeLink Budget

A Chip Rate 3.84 Mchip/s

B Information Rate 12.2 Kbit/s

C Processing Gain

(10log(A/B))

24.98 dB

47

D Mobile transmit power 21.0 dBm

E Mobile antenna gain 2.0 dBi

F Body Loss 3.0 dB

G Mobile EIRP (D+E-F) 20.0 dBm

48

H Base Station antenna Gain 14.0 dBi

I Thermal noise density -174.0 dBm/Hz

J Base Station Noise density -108.2 dBm

K Base Station Noise Figure 5.0 dB

L Target Eb/N0 5.5 dB

M Base Station Sensivity -122.68 dBm

49

N Cable Loss 3.0 dB

O Lognormal shadowing margin 9.0 dB

P Noise Rise (intracell) 3.0 dB

Q Noise Rise (intercell) 2.0 dB

R Soft handoff gain 4.0 dB

Maximum path loss=G+H-M-N-O-P-Q+R= 143.68 dB

50

UMTS Dimensioning

Operators required

(QOS,Capacity,

Coverage)

Condition of

Radio

Propagaiton

Estimation The

Number of

users

Available

Techniques

Dimensioning Process

Estimation of required equipments and arrangment of network array

Optimization

51

UMTS RAN Dimensioning Process

Node B Dimensioning

RNC Dimensioning

Interface Dimensioning

Offering prepare topology for RAN

52

• Required Data for each phase of

Network development

1. Radio coverage (regions, subregions,

region classifications)

2. Traffic ( Frequency spectrum, customers

Density in each region, customers

profile)

3. QOS (coverage probability, Blocking

prob. , service level in each region)

53

Node B Dimensioning

• Up Link

1. Considering a radius for cell r1

2. Estimation average traffic inside cell

3. Estimation no. of channels for peak traffic

service

4. Considering a Statistical method for calculating

accumulated noise

54

Up Link

5. Calculating Maximum path loss then cell

range r2

6. Continuing till r1 = r2

7. Cell bar test

55

Down Link

1. Considering a cell range r1

2. From input traffic, estimate average cell traffic

3. Estimation no. of channels for peak traffic service

4. Calculation of One user required power for each service

5. Calculating transmit accumulated power in Node B

56

Down Link

• Calculating Cell range r2

• Continue till r1=r2

57

RNC Dimensioning Process Steps

1. Knowing No. of Node Bs then By Considering

Management Limitations ,Estimate minimum

RNC, RNC1

2. By considering input average traffic and traffic

limitations , Estimate minimum RNC that

needs for traffic handling , RNC2

3. Average traffic for each RNC is known, then

peak traffic for each RNC must be calculated

4. Max(RNC1,RNC2)=No. of RNC

58

RNC Dimensioning Process

Efficient factors for RNC Dimensioning

Process are:

1. Traffic Limitations

2. Management Limitations

3. Communications Limitations