wcdma fundamentals

1 © Nokia Siemens Networks Presentation / Author / Date

WCDMA Fundamentals

MODULE 1


Module 1 – WCDMA Fundamentals

Objectives

After this module the participant shall be able to:-

• Understand the main cellular standards and allocated

frequency bands

• Understand the main properties of WCDMA air interface

• Recognize the main Nokia RRM functions and their main

tasks


Module Contents

• Standardisation and frequency bands

• Main properties of UMTS Air Interface

• Overview of Nokia Radio Resource Management (RRM)


Module Contents


• Standardisation of 3G cellular networks

• IMT-2000 frequency allocations

• UMTS – FDD Frequency band evolution




Standardisation of 3G cellular networks

• ITU (Global guidelines and recommendations)

• IMT-2000: Global standard for third generation (3G) wireless communications

• 3GPP is a co-operation between standardisation bodies ETSI (Europe), ARIB/TTC (Japan), CCSA (China), ATIS (North America) and TTA (South Korea)

• GSM

• EDGE

• UMTS

• WCDMA - FDD

• WCDMA - TDD

• TD-SCDMA

• 3GPP2 is a co-operation between standardisation bodies ARIB/TTC (Japan), CCSA (China), TIA (North America) and TTA (South Korea)

• CDMA2000

• CDMA2000 1x

• CDMA2000 1xEV-DO


IMT-2000 frequency allocations 2200 MHz 2000 1900 1950 2050 2100 2150 1850

Japan IMT-2000

PH

S

IMT-2000

ITU

Mo

bile

Sate

llit

e

IMT-2000 IMT-2000

Europe UMTS

(FDD) DE

CT

UM

TS

(T

DD

)

GSM

1800

UM

TS

(T

DD

) UMTS

(FDD)

USA

PC

S

un

lic

en

se

d

PCS PCS

UM

TS

(T

DD

) IM

T-2

00

0 (

TD

D)

Mo

bile

Sate

llit

e

Mo

bile

Sate

llit

e

Mo

bile

Sate

llit

e

Mo

bile

Sate

llit

e

Mo

bile

Sate

llit

e

Mo

bile

Sate

llit

e

Mo

bile

Sate

llit

e


UMTS – FDD Frequency band evolution

• Release 99

• I 1920 – 1980 MHz 2110 –2170 MHz UMTS only in Europe, Japan

• II 1850 –1910 MHz 1930 –1990 MHz US PCS, GSM1900

• New in Release 5

• III 1710-1785 MHz 1805-1880 MHz GSM1800


• IV 1710-1755 MHz 2110-2155 MHz US 2.1 GHz band

• V 824-849MHz 869-894MHz US cellular, GSM850

• VI 830-840 MHz 875-885 MHz Japan


• VII 2500-2570 MHz 2620-2690 MHz

• VIII 880-915 MHz 925-960 MHz GSM900

• IX 1749.9-1784.9 MHz 1844.9-1879.9 MHz Japan


Module Contents



• UMTS Air interface technologies

• WCDMA – FDD

• WCDMA vs. GSM

• CDMA principle

• Processing gain

• WCDMA codes and bit rates



UMTS Air Interface technologies

• UMTS Air interface is built based on two technological solutions

• WCDMA – FDD

• WCDMA – TDD

• WCDMA – FDD is the more widely used solution

• FDD: Separate UL and DL frequency band

• WCDMA – TDD technology is currently used in limited number of networks

• TDD: UL and DL separated by time, utilizing same frequency

• Both technologies have own dedicated frequency bands

• This course concentrates on design principles of WCDMA – FDD solution, basic

planning principles apply to both technologies


WCDMA – FDD technology

• Multiple access technology is wideband CDMA (WCDMA)

• All cells at same carrier frequency

• Spreading codes used to separate cells and users

• Signal bandwidth 3.84 MHz

• Multiple carriers can be used to increase capacity

• Inter-Frequency functionality to support mobility between frequencies

• Compatibility with GSM technology

• Inter-System functionality to support mobility between GSM and UMTS


WCDMA Technology

5 MHz

3.84 MHz

f

5+5 MHz in FDD mode 5 MHz in TDD mode

Fre

qu

ency

Time Direct Sequence (DS) CDMA

WCDMA Carrier

WCDMA

5 MHz, 1 carrier

TDMA (GSM)

5 MHz, 25 carriers

Users share same time and frequency


UMTS & GSM Network Planning

GSM900/1800: 3G (WCDMA):


Differences between WCDMA & GSM

WCDMA GSM

Carrier spacing 5 MHz 200 kHz

Frequency reuse factor 1 1–18

Power control frequency

1500 Hz 2 Hz or lower

Quality control Radio resource management algorithms

Network planning (frequency planning)

Frequency diversity 5 MHz bandwidth gives multipath diversity with

Rake receiver

Frequency hopping

Packet data Load-based packet scheduling

Timeslot based scheduling with GPRS

Downlink transmit diversity

Supported for improving downlink

capacity

Not supported by the standard, but can be

applied

High bit rates

Services with

Different quality

requirements

Efficient packet data


Multiple WCDMA carriers – Layered network

F 1

F 2

F 2

F 3

F 3

F 3

Micro BTS

Macro BTS

Pico BTSs

1 - 10 km

50 - 100 m 200 - 500 m


Spreading Code

Spread Signal

Data

Air Interface

CDMA principle - Chips & Bits & Symbols Bits (In this drawing, 1 bit = 8 Chips SF=8)

Baseband Data

-1

+1

+1

+1

+1

+1

-1

-1

-1

-1

Chip Chip


Energy Box

Duration (t = 1/Rb)

Originating Bit Received Bit

Energy per bit = Eb = const

Higher spreading factor Wider frequency band Lower power spectral density

BUT

Same Energy per Bit


Frequency Po

we

r d

en

sity (

Wa

tts/H

z)

Unspread narrowband signal Spread wideband signal

Bandwidth W (3.84 Mchip/sec)

User bit rate

R

sec84.3

MchipconstW

R

WdBGp Processing gain:

Spreading & Processing Gain


Frequency (Hz)

Voice user (R=12,2 kbit/s)

Packet data user (R=384 kbit/s)

Po

we

r d

en

sity (

W/H

z)

R

Frequency (Hz)

Gp=W/R=24.98 dB

Po

we

r d

en

sity (

W/H

z)

R

Gp=W/R=10 dB

• Spreading sequences have a different length • Processing gain depends on the user data rate

Processing Gain Examples


Transmission Power

Frequency

5MHz

Power density

Time

High bit rate user

Low bit rate user


WCDMA Codes

• In WCDMA two separate codes are used in the spreading operation

• Channelisation code

• Scrambling code

• Channelisation code

• DL: separates physical channels of different users and common channels, defines

physical channel bit rate

• UL: separates physical channels of one user, defines physical channel bit rate

• Scrambling code

• DL: separates cells in same carrier frequency

• UL: separates users


DL Spreading and Multiplexing in WCDMA

User 3

User 2

User 1

BCCH

Pilot X

CODE 1

X

CODE 2

X

CODE 3

X

CODE 4

X

CODE 5

+

X

SCRAMBLING

CODE

RF

SUM

User 2

User 1

BCCH

Pilot

Radio frame = 15 time slots

Time

User 3

3.84 MHz

RF carrier

3.84 MHz bandwidth

CHANNELISATION codes:

P-CPICH

P-CCPCH

DPCH1

DPCH2

DPCH3


DL & UL Channelisation Codes

• Walsh-Hadamard codes: orthogonal variable spreading factor codes (OVSF codes)

• SF for the DL transmission in FDD mode = {4, 8, 16, 32, 64, 128, 256, 512}

• SF for the UL transmission in FDD mode = {4, 8, 16, 32, 64, 128, 256}

• Good orthogonality properties: cross correlation value for each code pair in the code set

equals 0

• In theoretical environment users of one cell do not interfere each other in DL

• In practical multipath environment orthogonality is partly lost Interference between users of

same cell

• Orthogonal codes are suited for channel separation, where synchronisation between

different channels can be guaranteed

• Downlink channels under one cell

• Uplink channels from a single user

• Orthogonal codes have bad auto correlation properties and thus not suited in an

asynchronous environment

• Scrambling code required to separate signals between cells in DL and users in UL


Channelisation Code Tree

C0(0)=[1]

C2(1)=[1-1]

C2(0)=[11]

C4(0)=[1111]

C4(1)=[11-1-1]

C4(2)=[1-11-1]

C4(3)=[1-1-11]

C8(0)=[11111111]

C8(1)=[1111-1-1-1-1]

C8(2)=[11-1-111-1-1]

C8(3)=[11-1-1-1-111]

C8(0)=[1-11-11-11-1]

C8(5)=[1-11-1-11-11]

C8(6)=[1-1-111-1-11]

C8(7)=[1-1-11-111-1]

C16(0)=[............] C16(1)=[............]

C16(15)=[...........]

C16(14)=[...........]

C16(13=[...........]

C16(12)=[...........]

C16(11)=[...........]

C16(10)=[...........]

C16(9)=[............]

C16(8)=[............]

C16(7)=[............]

C16(6)=[............]

C16(5)=[............]

C16(4)=[............]

C16(3)=[............]

C16(2)=[............]

SF=1

SF=2

SF=4

SF=8

SF=16

SF=256

SF=512

...


Spreading factor

Channel symbol

rate

(ksps)

Channel bit rate

(kbps)

DPDCH channel bit rate range

(kbps)

Maximum user data rate with ½-

rate coding

(approx.)

512 7.5 15 3–6 1–3 kbps

256 15 30 12–24 6–12 kbps

128 30 60 42–51 20–24 kbps

64 60 120 90 45 kbps

32 120 240 210 105 kbps

16 240 480 432 215 kbps

8 480 960 912 456 kbps

4 960 1920 1872 936 kbps

4, with 3 parallel codes

2880 5760 5616 2.3 Mbps

Half rate speech

Full rate speech

128 kbps

384 kbps

2 Mbps

Symbolphyb RR 2_SF

WRSymbol

(QPSK modulation)

Physical Layer Bit Rates (DL)


Physical Layer Bit Rates (DL) - HSDPA

• 3GPP Release 5 standards introduced enhanced DL bit rates with High Speed

Downlink Packet Access (HSDPA) technology

• Shared high bit rate channel between users – High peak bit rates

• Simultaneous usage of up to 15 DL channelisation codes (In HSDPA SF=16)

• Higher order modulation scheme (16-QAM) Higher bit rate in same band

• 16-QAM provides 4 bits per symbol 960 kbit/s / code physical channel peak rate

Coding rate

QPSK

Coding rate

1/4

2/4

3/4

5 codes 10 codes 15 codes

600 kbps 1.2 Mbps 1.8 Mbps

1.2 Mbps 2.4 Mbps 3.6 Mbps


16QAM

2/4

3/4

4/4




HSDPA


Physical Layer Bit Rates (UL) - HSUPA

• 3GPP Release 6 standards introduced enhanced UL bit rates with High Speed

Downlink Packet Access (HSUPA) technology

• Fast allocation of available UL capacity for users – High peak bit rates

• Simultaneous usage of up to 2+2 UL channelisation codes (In HSUPA SF=2 – 4)

• Initial expected capability 1.46 Mbps

Coding rate

1/2

3/4

4/4

1 x SF4 2 x SF4 2 x SF2 2 x SF2 + 2 x SF4

480 kbps 960 kbps 1.92 Mbps 2.88 Mbps

720 kbps 1.46 Mbps 2.88 Mbps 4.32 Mbps

960 kbps 1.92 Mbps 3.84 Mbps 5.76 Mbps


DL & UL Scrambling Codes

DL Scrambling Codes

• Pseudo noise codes used for cell separation

• 512 Primary Scrambling Codes

UL Scrambling Codes

• Two different types of UL scrambling codes are generated

• Long scrambling codes of length of 38 400 chips = 10 ms radio frame

• Short scrambling codes of length of 256 chips are periodically repeated to get the

scrambling code of the frame length

• Short codes enable advanced receiver structures in future


Scrambling Codes & Multipath Propagation

Scrambling code C1

Scrambling code C2

C1+2

UE has simultaneous connection to two cells (soft

handover)


RAKE Receiver

• Combination or multipath components and signal from different cells

Dela

y

1

Code used for the

connection

Rx

Output

Finger

t

Cell-1

Cell-1

Cell-1

Cell-2

Rx

Rx

Rx

Finger

Finger

Finger

Dela

y

2

Dela

y

3


Channelisation code Scrambling code

Usage Uplink: Separation of physical data

(DPDCH) and control channels

(DPCCH) from same terminal

Downlink: Separation of downlink

connections to different users within one

cell

Uplink: Separation of mobile

Downlink: Separation of sectors (cells)

Length 4–256 chips (1.0–66.7 s)

Downlink also 512 chips

Different bit rates by changing the length

of the code

Uplink: (1) 10 ms = 38400 chips or (2)

66.7 s = 256 chips

Option (2) can be used with advanced

base station receivers

Downlink: 10 ms = 38400 chips

Number of codes Number of codes under one scrambling

code = spreading factor

Uplink: 16.8 million

Downlink: 512

Code family Orthogonal Variable Spreading Factor Long 10 ms code: Gold code

Short code: Extended S(2) code family

Spreading Yes, increases transmission bandwidth No, does not affect transmission

bandwidth

Channelisation and Scrambling Codes


Module Contents




• Load control

• Admission Control

• Packet Scheduler

• Resource Manager

• Power Control

• Handover Control


Radio Resource Management

• RRM is responsible for optimal utilisation of the radio resources:

• Transmission power and interference

• Logical codes

• The trade-off between capacity, coverage and quality is done all the time

• Minimum required quality for each user (nothing less and nothing more)

Maximum number of users

• The radio resources are continuously monitored and optimised by several RRM

functionalities service quality

cell coverage cell capacity

Optimization and Tailoring


RRM Functionalities

• LC Load Control

• AC Admission Control

• PS Packet Scheduler

• RM Resource Manager

• PC Power Control

• HC HO Control

PC

HC For each connection/user

LC

AC

For each cell

PS

RM


Load Control (LC)

• LC performs the function of load control in association with AC & PS

• LC updates load status using measurements & estimations provided by AC and PS

• Continuously feeds cell load information to PS and AC;

• Interference levels (UL)

• BTS power level (DL)

LC

AC

PS NRT load

Load change info

Load status


Load Control – Load Status

• Load thresholds set by radio network planning parameters

Overload threshold x

Load Target threshold y

Po

we

r

Time

Load Margin

Overload

Normal load

Measured load Free capacity


Admission Control (AC)

• Checks that admitting a new user will not sacrifice planned coverage or quality of

existing connections

• Admission control handles three main tasks

• Admission decision of new connections

• Take into account current load conditions (from LC) and load increase by the new

connection

• Real-time higher priority than non-real time

• In overload conditions no new connections admitted

• Connection QoS definition

• Bit rate, BER target etc.

• Connection specific power allocation (Initial, maximum and minimum power)


Packet Scheduler (PS)

• PS allocates available capacity after real-time (RT) connections to non-real time

(NRT) connections

• Each cell separately

• In overload conditions bit rates of NRT connections decreased

• PS selects allocated channel type (common or dedicated)

• PS relies on up-to-date information from AC and LC

• Capacity allocated on a needs basis using ‘best effort’ approach

• RT higher priority


Resource Manager (RM)

• Responsible for managing the logical radio resources of the RNC in co-operation

with AC and PS

• On request for resources, from either AC(RT) or PS(NRT), RM allocates:

• DL spreading code

• UL srambling code

Code Type Uplink Downlink

Scrambling codes

Spreading codes

User separation Cell separation

Data & control channels from same UE Users within one cell


Power control (PC) in WCDMA

• Fast, accurate power control is of utmost importance – particularly in UL;

• UEs transmit continuously on same frequency Always interference between users

• Poor PC leads to increased interference reduced capacity

• Every UE accessing network increase interference

• PC target to minimise the interference Minimize transmit power of each link while

still maintaining the link quality (BER)

• Mitigates 'near far effect‘ in UL by providing minimum required power for each

connection

• Power control has to be fast enough to follow changes in propagation conditions

(fading)

• Step up/down 1500 times/second


Uplink power control target

• Minimise required UL received power

minimised UL transmit power and interference

UE1 UE2

min(Prx1)

min(Prx2)

≈

About equal when

Rb1 = Rb2

Target:

Ptx1

Ptx1


Power Control types

• Power control functionality can be divided to three main types

• Open loop power control

• Initial power calculation based on DL pilot level/pathloss measurement by UE

• Outer (closed) loop power control

• Connection quality measurement (BER, BLER) and comparison to QoS target

• RF quality target (SIR target) setting for fast closed loop PC based on connection

quality

• Fast closed loop power control

• Radio link RF quality (SIR) measurement and comparison to RF quality target (SIR

target)

• Power control command transmission based on RF quality evaluation

• Change of transmit power according to received power control command


UL Outer Loop Power Control

Open Loop Power Control (Initial Access)

Closed Loop Power Control

RNC

BS

MS

DL Outer Loop Power Control

Power Control types

BLER target


Power control in HSPA

• In HSDPA (DL) the transmit power from base station is kept constant and the

signal modulation and coding is adapted according to the channel conditions

• 2 ms interval 500 Hz

• In HSUPA (UL)

• The power control of HSUPA channels in UL utilise both

• Fast closed loop power control

• Outer loop power control

• Both work according to similar principles as the dedicated channel power control


Handover Control (HC)

• HC is responsible for:

• Managing the mobility aspects of an RRC connection as UE moves around the

network coverage area

• Maintaining high capacity by ensuring UE is always served by strongest cell

• Soft handover

• MS handover between different base stations

• Softer handover

• MS handover within one base station but between different sectors

• Hard handover

• MS handover between different frequencies or between WCDMA and GSM


Soft/softer handover

• UE is simultaneously connected to 2 to 3 cells during soft handover

• Soft handover is performed based on UE cell pilot power measurements and

handover thresholds set by radio network planning parameters

• Radio link performance is improved during soft handover

• Soft handover consumes base station and transmission resources

BS1

BS2

BS3

Rec

eived

sig

na

l st

ren

gth

BS3

Distance from BS1

Threshold

Soft handover

BS2

BS1


Hard handover

• Hard handovers are typically performed between WCDMA frequencies and

between WCDMA and GSM cells

GSM/GPRS GSM/GPRS

f1

f2

f1

f2 f2 f2

Inter-System handovers (ISHO)

Inter-Frequency handovers (IFHO)


HSPA mobility

• HSDPA

• Soft handover on associated DCH channels (signalling, UL data)

• Serving cell change for HSDPA data channel

• Connected only to one cell at a time

• HSUPA

• Soft handover utilised for uplink channels as required due to near-far problem

• Only Serving Cell can allocate more UL capacity/power

HS-SCCH

HS-PDSCH

DPCH

DPCH Serving HS-DSCH cell

Notice that soft/softer handover is not supported for HS-SCCH/HS-PDSCH


Module 1 – WCDMA Fundamentals

Summary

• Radio interface technology of UMTS is WCDMA with FDD

and TDD versions

• WCDMA networks can be built on European, US-based and

Asian/Japanese frequency bands

• WCDMA air interface utilises combination of two spreading

codes

• Radio Resource Management is responsible of efficient

utilisation of radio resources while offering required quality of

service to users

wcdma fundamentals

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