introduction to third generation communications (3g...

Introduction to Third Generation Communications (3G) Technology

Wideband Code Division Multiple Access

www.3gpp.org

Timo Nihtilä , TLT-5606 Spread Spectrum Techniques www.tut.fi

Outline

• Background

• Key concepts

– Code multiplexing

– Spreading

• Introduction to Wideband Code Division Multiple Access (WCDMA)

• WCDMA Performance Enhancements

– High Speed Packet Access (HSDPA/HSUPA)

– Advanced features for HSDPA

Background

• Why new radio access system

• Frequency Allocations

• Standardization

• WCDMA background and evolution

• Evolution of Mobile standards

• Current WCDMA markets


Why new radio access system

• Need for universal standard (Universal Mobile Telecommunication System)

• Support for packet data services

– IP data in core network

– Wireless IP

• New services in mobile multimedia need faster data transmission and flexible utilization of the spectrum

• FDMA and TDMA are not efficient enough

– TDMA wastes time resources

– FDMA wastes frequency resources

• CDMA can exploit the whole bandwidth constantly

• Wideband CDMA was selected for a radio access system for UMTS (1997)

– (Actually the superiority of OFDM was not fully understood by then)


Frequency allocations for UMTS

• Frequency plans of Europe, Japan and Korea are harmonized

• US plan is incompatible, the spectrum reserved for 3G elsewhere is

currently used for the US 2G standards

• IMT-2000 band in Europe:

– FDD 2x60MHz

Expected air interfaces and spectrums, source: “WCDMA for UMTS”


Standardization

• WCDMA was studied in various research programs in the industry and

universities

• WCDMA was chosen besides ETSI also in other forums like ARIB

(Japan) as 3G technology in late 1997/early 1998.

• During 1998 parallel work proceeded in ETSI and ARIB (mainly), with

commonalities but also differences

– Work was also on-going in USA and Korea


Standardization

• At end of 1998 different standardization organizations got together and created 3GPP, 3rd Generation Partnership Project.

– 5 Founding members: ETSI, ARIB+TTC (Japan), TTA (Korea), T1P1 (USA)

– CWTS (China) joined later.

• Different companies are members through their respective standardization organization.

ETSI Members

ETSI

ARIB Members

ARIB

TTA Members

TTA

T1P1 Members

T1P1

TTC Members

TTC

CWTS Members

CWTS

3GPP


WCDMA Background and Evolution

• First major milestone was Release „99, 12/99– Full set of specifications by 3GPP

– Targeted mainly on access part of the network

• Release 4, 03/01 – Core network was extended

– markets jumped over Rel 4

• Release 5, 03/02– High Speed Downlink Packet Access (HSDPA)

• Release 6, end of 04/beginning of 05– High Speed Uplink Packet Access (HSUPA)

• Release 7, 06/07– Continuous Packet connectivity (improvement for e.g. VoIP), advanced features for HSDPA

(MIMO, higher order modulation)


WCDMA Background and Evolution

2000 2002 2004 2006 2007200520032001

3GPP Rel -99

12/99

3GPP Rel 4

03/01

3GPP Rel 5

(HSDPA)

03/02

3GPP Rel 6

(HSUPA)

2H/04

3GPP Rel 7

HSPA+

06/07Further Releases

JapanEurope

(pre-commercial)Europe

(commercial)

HSDPA

(commercial)HSUPA

(commercial)


Evolution of Mobile standards

EDGE

GPRSGSM

HSCSD

cdmaOne(IS-95)

WCDMA FDD

HSDPA/HSUPA

cdma2000

TD-SCDMA TDD LCR

cdma20001XEV - DO

cdma20001XEV - DV

TD-CDMATDD HCR

HSDPA/HSUPA

LTE


WCDMA markets• Graph of the technologies adopted by the wireless users worldwide:

• Over 3.5 billion wireless users worldwide

• GSM+WCDMA share currently over 88 % (www.umts-forum.org)

• CDMA share is decreasing every year

GSM (80.9%)

CDMA (12%)

WCDMA (4.6%)

iDEN (0.9%)

PDC (0.8%)

US TDMA (0.8%)

http://www.umts-forum.org/




WCDMA markets

• Over 200 million WCDMA subscribers globally (04/08) (www.umts-forum.org)

– 10 % HSDPA/HSUPA users

• Number of subscribers is constantly increasing

Millio

n s

ub

scri

bers




Key concepts

• CDMA

• Spread Spectrum

• Direct Sequence spreading

• Spreading and Processing gain


Multiple Access Schemes

• Frequency Division Multiple Access (FDMA), different frequencies for different users– example Nordic Mobile Terminal (NMT) systems

• Time Division Multiple Access (TDMA), same frequency but different timeslots for different users, – example Global System for Mobile Communication (GSM)

– GSM also uses FDMA

• Code Division Multiple Access (CDMA), same frequency and time but users are separated from each other with orthogonal codes

Code

Frequency

Time

12

N…

TDMAFDMA CDMA


Spread Spectrum

• Means that the transmission bandwidth is much larger than the information

bandwidth i.e. transmitted signal is spread to a wider bandwidth

– Bandwidth is not dependent on the information signal

• Benefits

– More secure communication

– Reduces the impact of interference (and jamming) due to processing gain

• Classification

– Direct Sequence (spreading with pseudo noise (PN) sequence)

– Frequency hopping (rapidly changing frequency)

– Time Hopping (large frequency, short transmission bursts)

• Direct Sequence is currently commercially most viable


Spread Spectrum

• Where does spread spectrum come from

– First publications, late 40s

– First applications: Military from the 50s

– Rake receiver patent 1956

– Cellular applications proposed late 70s

– Investigations for cellular use 80s

– IS-95 standard 1993 (2G)

– 1997/1998 3G technology choice

– 2001/2002 Commercial launch of WCDMA technology


Direct Sequence

• In direct sequence (DS) user bits are coded with unique binary

sequence i.e. with spreading/channelization code

– The bits of the spreading code are called chips

– Chip rate (W) is typically much higher than bit rate (R)

– Codes need to be in some respect orthogonal to each other (cocktail party

effect)

• Length of a spreading code code

– defines how many chips are used to spread a single information bit and thus

determines the end bit rate

– Shorter code equals to higher bit rate but better Signal to Interference and

Noise Ratio (SINR) is required

• Also the shorter the code, the fewer number of codes are available

– Different bit rates have different geographical areas covered based on the

interference levels


Direct Sequence

• Transmission (Tx) side with DS

– Information signal is multiplied with spreading code => spread signal

• Receiving (Rx) side with DS

– Spread signal is multiplied with spreading code

– Multiplied signal (spread signal x code) is then integrated (i.e. summed

together)

• If the integration results in adequately high (or low) values, the signal is meant for

the receiver


Direct Sequence


Spread Spectrum

Frequency

Despread narrowband signal

Spread wideband signal

W

R

Po

we

r d

en

sit

y (

Wa

tts

/Hz)

Po

we

r d

en

sit

y (

Wa

tts

/Hz)

Frequency

Transmitted signalbefore spreading

Received signalbefore despreading

Interference for the part we are interested in


Spread Spectrum

Frequency

Po

we

r d

en

sit

y (

Wa

tts

/Hz)

Po

we

r d

en

sit

y (

Wa

tts

/Hz)

Frequency

Received signalafter despreading butbefore filtering

Received signalafter despreading andafter filtering

Transmitted signal

Interference

Introduction to Wideband Code Division Multiple Access (WCDMA)

• Overview

• Codes in WCDMA

• QoS support

• Network Architecture

• Radio propagation and fading

• RAKE receiver

• Power Control in WCDMA

• Diversity

• Capacity and coverage


WCDMA System

• WCDMA is the most common radio interface for UMTS systems

• Wide bandwidth, 3.84 Mcps (Megachips per second)

– Maps to 5 MHz due to pulse shaping and small guard bands between the

carriers

• Users share the same 5 MHz frequency band and time

– UL and DL have separate 5 MHz frequency bands

• High bit rates

– With Release ‟99 theoretically 2 Mbps both UL and DL

– 384 kbps highest implemented

• Fast power control (PC)

=> Reduces the impact of channel fading and minimizes the interference


WCDMA System

• Soft handover

– Improves coverage, decreases interference

• Robust and low complexity RAKE receiver

– Introduces multipath diversity

• Variable spreading factor

– Support for flexible bit rates

• Multiplexing of different services on a single physical connection

– Simultaneous support of services with different QoS requirements:

• real-time

– E.g. voice, video telephony

• streaming

– streaming video and audio

• interactive

– web-browsing

• background

– e-mail download


Codes in WCDMA

• Channelization Codes (=short code)

– Codes from different branches of the code tree are orthogonal

– Length is dependent on the spreading factor

– Used for

• channel separation from the single source in downlink

• separation of data and control channels from each other in the uplink

– Same channelization codes in every cell / mobiles and therefore the additional

scrambling code is needed

• Scrambling codes (=long code)

– Very long (38400 chips = 10 ms =1 radio frame), many codes available

– Does not spread the signal

– Uplink: to separate different mobiles

– Downlink: to separate different cells

– The correlation between two codes (two mobiles/NodeBs) is low

• Not fully orthogonal


UMTS Terrestrial Radio Access Network (UTRAN) Architecture

• New Radio Access network

needed mainly due to new

radio access technology

• Core Network (CN) is based

on GSM/GPRS

• Radio Network Controller

(RNC) corresponds roughly

to the Base Station

Controller (BSC) in GSM

• Node B corresponds

roughly to the Base Station

in GSM

– Term “Node B” is a relic from

the first 3GPP releases

RNC

NodeB

NodeB

NodeB

UE

CN

RNC

UE

Uu interface Iub interface

Iur interface

UTRAN



• Radio network controller (RNC)

– Owns and controls the radio resources in its domain

– Radio resource management (RRM) tasks include e.g. the following

• Mapping of QoS Parameters into the air interface

• Air interface scheduling

• Handover control

• Outer loop power control

• Call Admission Control

• Setting of initial powers and SIR targets

• Radio resource reservation

• Code allocation

• Load Control



• Node B

– Main function to convert the data flow between Uu and Iub interfaces

– Some RRM tasks:

• Measurements

• Inner loop power control


Radio propagation and fading

• A transmitted radio signal goes

through several changes while

traveling via air interface to the

receiver

– reflections, diffractions, phase

shifts and attenuation

• Due to length difference of the

signal paths, multipath

components of the signal arrive

at different times to the receiver

and can be combined either

destructively or constructively

– Depends on the phases of the

multipath components


Radio propagation and fading

• Example of the fast fading

channel of a function of time

• Opposite phases of two

random multipath components

arriving at the same time

cancel each other out

– Results in a fade

• Coherent phases are

combined constructively


Diversity

• Transmitting on a single path only can lead to serious performance

degradation due to fading

• As fading is independent between different times and spaces it is reasonable

to use the available diversity of them to decrease the probability of a deep

fade

– The more there are paths to choose from, the less likely it is that all of them have a

poor energy level

• There exists different types of diversity which can be used to improve the

quality, e.g.:

– Multipath

• RAKE receiver exploits taps arriving at different times

– Macro

• Different Node Bs send the same information

– Site Selection Transmit Diversity (SSTD)

• Maintain a list of available base stations and choose the best one, from which the transmission

is received and tell the others not to transmit


Diversity

– Time

• Same information is transmitted in different times

– Receive antenna

• Transmission is received with multiple antennas

• Power gain and diversity gain

– Transmit antenna

• Transmission is sent with multiple antennas

WCDMA evolution

•High Speed Downlink Packet Access (HSDPA)

•High Speed Uplink Packet Access (HSUPA)

•Advanced receivers with HSDPA

•Advanced HSDPA scheduling

•Femto cells with HSDPA


High Speed Downlink Packet Access (HSDPA)

• The High Speed Downlink Packet Access (HSDPA) concept was

added to Release 5 to support higher downlink data rates

• It is mainly intended for non-real time traffic, but can also be used for

traffic with tighter delay requirements.

• Peak data rates up to 10 Mbit/s (theoretical data rate 14.4 Mbit/s)

• Reduced retransmission delays

• Improved QoS control (Node B based packet scheduler)

• Spectrally and code efficient solution


HSDPA features

• Agreed features in Release 5– Adaptive Modulation and Coding (AMC)

• QPSK or 16QAM

– Multicode operation

• Support of 1-15 code channels (SF=16)

– Short frame size

– Fast retransmissions using Hybrid Automatic Repeat Request (HARQ)

• Chase Combining

• Incremental Redundancy

– Fast packet scheduling at Node B

• E.g. Round robin, Proportional fair

• Features agreed in Release 7– Higher order modulation (64QAM)

– Multiple Input Multiple Output (MIMO)


HSDPA - general principle

• Fast scheduling is done directly in Node-B based on feedback information from UE and knowledge of current traffic state.

Channel quality(CQI, Ack/Nack)

Data

Users may be time and/or code multiplexed

New base station functions

• HARQ retransmissions

• Modulation/coding selection

• Packet data scheduling (short TTI)

UE

0 20 40 60 80 100 120 140 160-2

02468

10121416

Time [number of TTIs]

QPSK1/4

QPSK2/4

QPSK3/4

16QAM2/4

16QAM3/4

Inst

anta

neo

us

EsN

o [

dB

]


HSDPA functionality• UE informs the Node B regularly of its channel quality by CQI messages

(Channel Quality Indicator)


HSDPA functionality

• Node B can use channel state information for several purposes

– In transport format (TFRC) selection

• Modulation and coding scheme

– Scheduling decisions

• Non-blind scheduling algorithms can be utilized

– HS-SCCH power control


High Speed Uplink Packet Access (HSUPA)

• Peak data rates increased to significantly higher than 2 Mbps; Theoretically reaching 5.8 Mbps

• Packet data throughput increased, though not as high throughput as with HSDPA

• Reduced delay from retransmissions.

• Solutions

– Layer1 hybrid ARQ

– NodeB based scheduling for uplink

– Frame sizes 2ms & 10 ms

• Schedule in 3GPP

– Part of Release 6

– First specifications version completed 12/04

– In 3GPP specs with the name Enhanced uplink DCH (E-DCH)

Performance of advanced HSDPA features


Advanced receivers with HSDPA

• UE receiver experiences significant interference from different sources

– In a reflective environment the signal interferes itself

– Neigboring base station signals interfere each other

– One solution to decrease mainly own base station signal interference is to

use an equalizer before despreading

Own cell interference

Other cell interference

Own signal



• In a frequency-selective channel there is a significant amount of

interfering multipaths

• Linear Minimum Mean Squared Error (LMMSE) equalizer can be used

to make an estimate of the original transmitted chip sequence before

despreading

– The interfering multipath components are removed

– The channel becomes flat again



• LMMSE equalizer (Equ in the

figure) offers a very good

performance for the user

especially near the base station

• Using antenna diversity (1x2) the

throughput can be doubled

compared to a single antenna

• Both techniques increase the

cost of a mobile unit


Femtocells

• More and more consumers want to use their mobile devices at home,

even when there‟s a fixed line available

– Providing full or even adequate mobile residential coverage is a significant

challenge for operators

– Mobile operators need to seize residential minutes from fixed line providers,

and compete with fixed and emerging VoIP and WiFi services

=> There is trend in discussing very small indoor, home and campus NodeB

layouts

• Femtocells are cellular access points (for limited access group) that

connect to a mobile operator‟s network using residential DSL (digital

subscriber line) or cable broadband connections

• Femtocells enable capacity equivalent to a full 3G network sector at

very low transmit powers, dramatically increasing battery life of

existing phones

Zhong Zheng noppa.aalto.fi

Why femtocells?

• Low manufacturing cost, short radio coverage home base station

operates in licensed spectrum

• Radio traffic is backhauled by premises broadband connection (DSL)

to mobile network


Why femtocells?

• Macrocell base station covers up to a few hundred square meters

area and Signal quality decays along with transmit distance in the form

of

• Under non-line-of-sight condition, signal is blocked by large

shadowing or building wall at 2GHz band


Why femtocells?

• Technical motivation

• Reduced separation distance between transmitter and

receiver

• Interference is isolated by building structure

• Limited number of users

• Business motivation

• Half of voice calls and a majority of data traffic originate

indoor

• Operators expand network capacity and coverage

without much investments on infrastructure.

• Subscribers get better radio service at low price


3GPP standardization on femtocells

• New interface Iuh is created between femto base station and HNB-

GW (home node B gateway)

• HNB-GW utilizes standard Iu interface to mobile network

• Iuh traffic is tunneled through public Internet

• In 3GPP Release 8, femtocell access is granted to Close Subscriber

Group (CSG). Handover between femtocells is not allowed.


More about WCDMA

– WCDMA for UMTS – Harri Holma, Antti Toskala


END

Thanks for your attention!

arusu[@]comm.pub.ro

An Introduction to

3GPP Long Term Evolution (LTE)

www.3gpp.org

Tsung-Yin Lee http://ants.iis.sinica.edu.tw/ants_70/

Outline

History of 3GPP LTE

Basic Concepts of LTE

Introduction to LTE Protocol

Compare with LTE and LTE-Advanced


What is LTE ?

In Nov. 2004, 3GPP began a project to

define the long-term evolution (LTE) of

Universal Mobile Telecommunications

System (UMTS) cellular technology

Higher performance

Backwards compatible

Wide application


Evolution of Radio Access

Technologies

LTE (3.9G) :

3GPP release 8~9

LTE-Advanced :

3GPP release 10+

802.16d/e

802.16m


LTE Basic Concepts

LTE employs Orthogonal Frequency

Division Multiple Access (OFDMA) for

downlink data transmission and Single

Carrier FDMA (SC-FDMA) with Discrete

Fourier Transform for uplink transmission


LTE network architecture: Evolved Packet System

Geert Heijenk http://wwwhome.cs.utwente.nl

Multipath-Induced Time Delays Result

in Inter-Symbol Interference (ISI)

)()()()( tnmtStSty

y(t) : output signal

S(t) : input signal

S(t-m) : delayed m time input signal

n(t) : noise

y(t)

βS(t-m)

S(t)


FDM vs. OFDM


Frequency Selective Fading

the coherence bandwidth of the channel is

smaller than the bandwidth of the signal

It may be useless to increase the

transmission powerTsung-Yin Lee http://ants.iis.sinica.edu.tw/ants_70/

OFDM transmission scheme

Cyclic Prefix


Is a repetition of the last part of the symbol, placed at the beginning of the symbol

LTE-Downlink (OFDM)

Improved spectral

efficiency

Reduce ISI effect

by multipath

Against frequency

selective fading


LTE Uplink (SC-FDMA)

SC-FDMA is a new single carrier multiple access technique which has similar structure and performance to OFDMA

An advantage of

SC-FDMA over

OFDM is low to

Peak to Average

Power Ratio

(PAPR) :

Increasing

battery life


Multi-antenna techniques


LTE Release 8 Key Features (1/2)

High spectral efficiency

OFDM in Downlink

Single‐Carrier FDMA in Uplink

Very low latency

Short setup time & Short transfer delay

Short hand over latency and interruption time

Support of variable bandwidth

1.4, 3, 5, 10, 15 and 20 MHzTsung-Yin Lee

http://ants.iis.sinica.edu.tw/ants_70/

LTE Release 8 Key Features (2/2)

Compatibility and interworking with earlier

3GPP Releases

FDD and TDD within a single radio access

technology

Efficient Multicast/Broadcast

Tsung-Yin Lee http://ants.iis.sinica.edu.tw/ants_

70/

Evolution of LTE-Advanced

Asymmetric transmission bandwidth

Layered OFDMA

Advanced Multi-cell Transmission/Reception Techniques

Enhanced Multi-antenna Transmission Techniques

Support of Larger Bandwidth in LTE-Advanced

Tsung-Yin Lee http://ants.iis.sinica.edu.tw/ants_

70/

Enhanced Multi-antenna

Transmission Techniques

In LTE-A, the MIMO scheme is further improved in the area of spectrum efficiency, average cell throughput and cell edge performances

For LTE-A the antenna configurations of 8x8 in DL and 4x4 in UL are planned


LTE vs. LTE-Advanced


END

Thanks for your attention!

introduction to third generation communications (3g...

Documents