UMTS Basic Principle_1

8/11/2019 UMTS Basic Principle_1

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Section 4

W-CDMA Principles



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What is UMTS?

Designed to be deployed under GSM/GPRS

network.(Key driver in standardization)

Frequency Division Duplex (FDD) and Time Division

Duplex(TDD) mode. Initial focus is on FDD mode, in

paired frequencybands.

Supports multiple services, multiple quality of service(QoS), and higher data rates (R99:up to 2 Mbps).



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UMTS overview

Multiple services

Higher data rates

Wireline voice quality

Improved capacity

Spectral efficiency



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UMTS Standards

Release 99

The fisrt version

Release 4

Bearer Independent CS Architecture

Release 5

High-speed Downlink Packet Access (HSDPA)

Release 6

HSUPA

R7,R8,R9,R10



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WCDMA Bandwith



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• The Spread Spectrum Principle

• The Channelization codes & Scrambling codes. Their main properties

• The importance of Eb/No

• The concept of Power Control

• The coverage limits

• The Rake Receiver

• The macro-diversity

• Handovers

Objectives

At the end of this session, you will be able to:

W-CDMA Principles



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Power

Power Power

FDMA TDMA

W-CDMA

Dedicated Channel : An indiv idual ly-assigned, dedicated pathway

through a transm ission medium

for one user’s information

Access Technologies



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Je parle français Ich spreche

deutsch

I speak

english

PARLO ITAL IANO !

Access Technologies

Analogy with the W-CDMA



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Duplex Spacing: 190 MHz

FDD

Time

Frequency

Power

5 MHz 5 MHz

Code Multiplex

UL DL

UMTS USER 1

UMTS USER 2

Time

Frequency

Power

TDD

5 MHz

Code Multiplex

&

Time Division

666.67 s

DL

UL

DL

DL

UL

UMTS USER 2

UMTS USER 1

Access Technologies

W-CDMA: FDD or TDD



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Binary data to transmit 0 1 0 0 1 0

The faster is the bit rate, the more the energy is spread on the spectrum

+ a

- a

a2T0

s(t)

T0

1/T0 2/T0 Frequency

Time

0 1 0 0 1 0

+ a

- a

a2T1

s(t)

T1

1/T1 2/T1 Frequency

NRZ

coding

Time

0 1 0 0 1 0

Power

spectrum

Spread Spectrum Principle

1 - Time - Frequency Duality



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Tbit

Tchip

Data sequence

spreading sequence

transmitted sequence

a2Tbit = Ebit

1/Tbit

Tchip = Echip

1/Tchip

Frequency

a2Tchip

1/Tchip

+a

-a

-1

+1

-a

+a

x

=

Data

sequence Transmitted

signal

Spreading sequence generator

Modulation

x(t)

Power spectrum


2 - Transmission



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4 - Code Multiplexing

Power spectrum

User 1

User 2

User 3

User 4

User 5

Spreading

Code 1

Code 2

Code 3

Code 4

Code 5

Composite signal

5 MHzCodes discriminate users



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Unwanted Power

from other sources

Using the “right” mathematical sequences

any Code Channel can be extracted

from the received composite signal


5 - Extraction



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Scrambling code

Channelization code 1



User 1 signal

User 2 signal

User 3 signal

BTS

Codes Multiplexing

1 - Downlink Transmission on a Cell Level



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BTS

Scrambling code 3

User 3 signal

Channelization code

Scrambling code 2

User 2 signal

Channelization code

Scrambling code 1

User 1 signal

Channelization code

Codes Multiplexing2 - Uplink Transmission on a Cell Level



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Cch,1,0 = 1

Cch,2,0 = 1 1

Cch,4,0 = 1 1 1 1

Cch,4,1 = 1 1 -1 -1

Cch,2,1 = 1 -1

Cch,4,2 = 1 -1 1 -1

Cch,4,3 = 1 -1 -1 1

SF = 1 SF = 2 SF = 4 SF = 8 SF = 16, 32, 64, 128, 256, 512

Cch,2,0 = 1 1

Cch,2,1 = 1 -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

Channelization Codes - OVSFOrthogonal Variable Spreading Factor: code tree generator

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+

-1 -1 -1

-1 -1 -1 -1

1 1 1 1

1 1 1 1

-1

*

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

Cj

Ck

T0 synchronization

= 0 +

-1 -1 -1

-1 -1 -1 -1

1 1 1 1

1 1 1 1

-1

*

1 1 1 11 -1 1 -1

Cj

Ck

no T0 synchronization

= 4

=> Orthogonal => Non orthogonal

No correlation Small correlation

Channelization Codes - OVSF

Orthogonality

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Orthogonal functions

Orthogonal functions have zero correlation

.Two binary sequences are orthogonal if theprocess of

―XORing‖ them results in an equalnumber of 1s and -1s:

Example:

-1 -1 1 1

-1 1 -1 1

1 -1 -1 1

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Physical Layer Structure

Frame #0 Frame #1 Frame #i Frame #4095

System frame = 4096 frames = 40.96 seconds

Slot #0 Slot #1 Slot #j Slot #14

Frame = 15 slots = 10 ms = 38400 chips

Slot = 0.667 ms = 2560 chips

Data or control or mixed: 10*2k bits, k from 0 to 6 (UL), from 0 to 7 (DL)

UMTS Frame Format

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A Tapped, Summing Shift Register

Sequence repeats every 2 N -1 chips,

where N is number of cells in register

Scrambling Codes

Scrambling codes Properties:

• 38 400 chip long sequences

• Repeated every 10 ms

• Issued form Pseudo Noise sequences

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Scrambling Codes Properties

Auto Correlation

Synchronized

=> Complete Correlation

Shifted

=> Almost Orthogonal

Almost orhtogonal

Cross Correlation

Random delay

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Uplink Scrambling Codes

Total of 224 long scrambling codesof 38,400 chips

225-1 chip longsequences

X25 + X3 + 1

X25 + X3 + X2 + X + 1

I

Q

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Downlink Scrambling Codes

8192scrambling

codes

512 sets of 1primary and 15

secondarycodes

512 primarycodes dividedinto 64 groups

• Possibility of 262,143 different downlink scrambling codes

• Only 8192 different scrambling codes have been defined

8192 ...

Cell #1

Cell #512

...

Primary scrambling code

Secondary scrambling code #1



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Exercise

UE1

How do UE1 and UE2 get them bits?

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Channelization Codes Multiplexing

-11 User 1

User 2

Code 1: Cch (SF= )

Code 2: Cch (SF= )

1-11 1-11

=

+

*

*

=

= 2

-2

0

1

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

1 -1-11

-1

-1

UsersComposite

Signal

1

1

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Scrambling code

Users CompositeSignal

Scrambling

Code

*

2

0

-2

2

0

-2

=

1

-1

TransmittedSignal

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Radio Interferences2

0

-2

Transmitted

Signal

0

0

Noise

ReceivedSignal =

1

-1

1

-1

+

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UE1: Reception & Decoding

0

Received

Signal

1

-1

1

-1

1

-1

Scrambling Code

Channelization Code

Data

Extraction

*

*

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UE2: Reception & Decoding

0

ReceivedSignal

1

-1

1

-1

1

-1

Scrambling Code

Channelization Code

Data

Extraction

*

*

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Basic W-CDMA Elements

C

I

N

C

C Eb /No

1 - Eb/NoW-CDMATDMA-GSM

Power spectrum

1

1

1 1

1

1

1

2

2

2

2

3

3

3

3

3

2

4

4

4

4

4

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Maximum noise level

Eb/No

required

Basic W-CDMA Elements

Power spectrum

a2Tbit = Ebit

gain

Unwanted power

from other sources

2 - Eb/No

Echip

Eb / No = C / I x processing gain

Available power to share

between users



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P C t l



Power Control

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P C t l



Power Control

1 - Open Loop

MS Access Pre Amble #1 with estimated power

MS Access Pre Amble #n with increased power

RNS Response with Power Control

MS Access Pre Amble #2 with increased power



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C Li it (1)



Interference level

Example: 2 UEs at thesame distance from theBTS using 2 data rates

Eb/No

require

d

S F

=

1 2 8

Service provided: Speech

Interference level

Eb/No

required

Service provided: Data 144

User 2 needs more power for theUL & DL for the same quality as

user 1

BTS

Received power Received power

Coverage Limits (1)

UE2 UE1

Speech 8 kbps Data 144 kbpsThe higher the SF, the less power required

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Coverage Limits (2)



SF = 128

Speech 8 kbps Data 64 kbps Data 384 kbps

BTS

SF = 32

SF = 4

Coverage Limits (2)

The coverage limits are determined by

the Uplink link Budget

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Uplink Limits (1)



UE2

UE3

UE2 UE3

BS Receiver

BTS

Maximum Noise Floor

Lowest Despread Signal Eb/No

ProcessingGain

Uplink Limits (1)

UE1

Receiver sensitivityUE1

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Uplink Limits (2)



Receiver sensitivity

BS Receiver

Maximum Noise Floor

Lowest Despread Signal

BTS

Cell Breathing

Eb/No

ProcessingGain

UE2 UE3

Eb/No

ProcessingGain

UE1 UE4

The more loaded the cell, the smaller the cell.

Uplink Limits (2)

UE4

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Capacity Limits (1)



BS Power Amplifier

50 W

0 W

BTS

BTS

UE1 UE

2 UE

3

UE4

Capacity Limits (1)

UE1

UE2

UE3

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Capacity Limits (2)



UE2 UE

3 UE

1

BS Power Amplifier

50 W

0 W

UE4

BTS

BTS

Capacity Limits (2)

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Rake Receiver



TX

D(t)

Delay 0

Delay 1

C(t- 0)

+C(t- 1)

Delay ( 1)

RX

C(t- n)

Delay ( 0)

Delay ( n) RX

RX

C(t)

0

1

n

Take advantage ofmultipath diversity

BTS

Rake Receiver

UE

Spreading &Scrambling

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Macro-Diversity



Macro-Diversity

Softer Hand Over

Node B(BTS)

RNC

Data UL

Data UL1Data UL2 Data UL

Data UL

Data DLData DL

Data DL1

Data DL1

Data DL2

Data DL

UE

Data DL2

Data UL

Core

Network

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Macro-Diversity



Macro Diversity

Soft Hand Over Intra RNC

RNC

Data UL1

Data UL1Data UL2

Data UL

Data UL

Data DL

Data DL1

Data DL1

Data DL1Data DL2 Data DL

UE

Core

Network

Data DL2

Data UL

Data DL2

Data UL2

Data UL2

Data UL1

Node B(BTS)

Node B(BTS)

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Macro-Diversity



y

Soft Hand Over Inter RNC: Serving RNC (SRNC) and Drift RNC (DRNC)

Node B(BTS)

SRNC

DRNCNode B(BTS)

Data UL

Data UL

Data ULData UL1

Data UL2

Data UL2

Data UL1Data UL2 Data UL

Data UL

Data DLData DL2

Data DL2

Data DL1

Data DL2

Data DL1

Data DL1Data DL2 Data DL

UE

CoreNetwork

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Different Types of Handover



Different Types of HandoverSoft Handover Softer Handover Hard Handover

SRNC DRNC

Node B

UE

Core Network

SRNC

Node B

UE

Core Network SRNC

UE

Core Network

GSM / GPRSBSS

SRNC

UE

Core Network

GSM / GPRSBSS

Inter RNC Intra Node B

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OVSF



OVSF A lower SF means a higher data rate, because this means lesschips per symbol. An SF of 4 means 4 chips per symbol, while

an SF of 128 is 128 chips per symbol— a difference of 32 timesthe data rates.

For example, a 12.2 kbps AMR may use an SF of 128,while adata application may require 384 kbps and need an SF of 4.

If a low spreading factor branch is used, you cannot use a

higher spreading factor branch that connects to it. This is dueto theorthogonalityproperty of OVSF. For example,

C2,0 is notorthogonal to either C4,0 or C4,1

over a 2-chip period.

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Logical Channels

–Carry signaling and user data between RLC and MAC.

Transport Channels

–Carry signaling and user data between MAC and PHY.

Physical Channels

–Carry signaling and user data over the radio link.

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Common

–Carries information to/from multiple UEs. Dedicated

–Carries information to/from a single UE.

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Logical

–Defined by what type of information is transferred,e.g.signalingor user data.

Transport

–Defined by how data is transferred over the air

interface, e.g., multiplexing of Logical Channels. Physical

–Defined by phy sical mappings and at t r ibutes

used to transfer data over the airinterface, e.g.,

spreading rate.

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PCCPCH



Primary Common Control Physical Channe

Carries system information such as systemID, cell ID,neighbor cell information,system frame number, etc.

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W-CDMA Questions



1. What is the link between bit rate, chip rate and SF?

2. What is the use of:• the downlink & uplink channelization codes?

• the downlink & uplink scrambling codes?

3. What is the relationship between Eb/No, Ec/No and the processing gain?

4. What are the different types of « Power Control »?

5. The higher the user data rate:

• the smaller is the cell?

• the wider is the cell?

6. The more loaded the cell:

• the smaller the cell?• the wider the cell?

7. Why is « macro-diversity » an important concept in UMTS?

UMTS Basic Principle_1

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