wcdma systems ok

8/11/2019 WCDMA Systems Ok

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1

WCDMA, HSPA and advanced

receiversTimo Nihtil, Ph.Lic. (Ph.D. def.)

Senior Research Scientist

Magister Solutions Ltd.


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Timo Nihtil2 TLT-5606 Spread Spectrum Techniques / 25.4. 2008

Readings related to the subject

General readings

WCDMA for UMTSHarri Holma, Antti Toskala HSDPA/HSUPA for UMTSHarri Holma, Antti Toskala

Network planning oriented

Radio Network Planning and Optimisation for UMTSJanna Laiho, Achim

Wacker, Toms Novosad

UMTS Radio Network Planning, Optimization and QoS Management ForPractical Engineering TasksJukka Lempiinen, Matti Manninen


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Outline

Background

Key concepts

Code multiplexing

Spreading

Introduction to WidebandCode Division Multiple Access (WCDMA)

WCDMA Performance Enhancements High Speed Packet Access (HSDPA/HSUPA)

Advanced features for HSDPA


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4

Background

Why new radio access system

Frequency Allocations

Standardization

WCDMA background and evolution

Evolution of Mobile standards

Current WCDMA markets


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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 andflexible 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)


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Frequency allocations for UMTS

Frequency plans of Europe, Japan and Korea are harmonized

US plan is incompatible, the spectrum reserved for 3G elsewhere iscurrently used for the US 2G standards

IMT-2000 band in Europe:

FDD 2x60MHz

Expected air interfaces and spectrums, source: WCDMA for UMTS


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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


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Standardization

At end of 1998 different standardization organizations got together andcreated 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 respectivestandardization organization.

ETSI Members

ETSI

ARIB Members

ARIB

TTA Members

TTA

T1P1 Members

T1P1

TTC Members

TTC

CWTS Members

CWTS

3GPP


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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)


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WCDMA Background and Evolution

2000 2002 2004 2006 2007200520032001

3GPP Rel -99

12/993GPP Rel 4

03/01

3GPP Rel 5(HSDPA)

03/02

3GPP Rel 6(HSUPA)

2H/04

3GPP Rel 7HSPA+

06/07Further Releases

JapanEurope

(pre-commercial)Europe

(commercial)

HSDPA

(commercial)HSUPA

(commercial)


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Evolution of Mobile standards

EDGE

GPRSGSM

HSCSD

cdmaOne(IS-95)

WCDMAFDD

HSDPA/HSUPA

cdma2000

TD-SCDMATDD LCR

cdma20001XEV - DO

cdma20001XEV - DV

TD-CDMATDD HCR

HSDPA/HSUPA

LTE


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


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Current WCDMA markets

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

10 % HSDPA/HSUPA users

Number of subscribers is constantly increasing

Millionsubscribe

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


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14

Key concepts

CDMA

Spread Spectrum

Direct Sequence spreading

Spreading and Processing gain


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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 fordifferent 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


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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


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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


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Direct Sequence

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

sequence i.e. with spreading/channelization code The bits of the channelization 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 channelization 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 theinterference levels


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Direct Sequence

Transmission (Tx) side with DS

Information signal is multiplied with channelization code => spread signal Receiving (Rx) side with DS

Spread signal is multiplied with channelization 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


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Direct Sequence


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Direct Sequence


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Processing gain and Spreading

Frequency

Despread narrowband signal

Spread wideband signal

W

R

Powerdensity(W

atts/Hz)

Pow

erdensity(Watts/Hz)

Frequency

Transmitted signalbefore spreading

Received signal

before despreading

Interference for the partwe are interested in


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Frequency

Powerdensity(W

atts/Hz)

Pow

erdensity(Watts/Hz)

Frequency

Received signalafter despreading b ut

before fi l ter ing

Received signal

after despreading and

after fi l ter ing

Transmitted signal

Interference


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Spread spectrum systems reduce the effect of interference due to processinggain

Processing gain is generally defined as follows:

G[dB]=10*log10(W/R), where W is the chip rate and R is the user bit rate

The number of users takes negative effect on the processing gain. The loss isdefined as:

Lp= 10*log10k, where k is the amount of users

Processing gain when the processing loss is taken into account is Gtot=10*log10(W/kR)

High bit rate means lower processing gain and higher power OR smallercoverage

The processing gain is different for different services over 3G mobile network(voice, web browsing, videophone) due to different bit rates

Thus, the coverage area and capacity might be different for different servicesdepending on the radio network planning issues


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Processing gain is what gives CDMA systems the robustness against

self-interference that is necessary in order to reuse the available 5

MHz carrier frequency over geographically close distances.

Examples: Speech service with a bit rate of 12.2 kbps

processing gain 10 log10(3.84e6/12.2e3) = 25 dB

For speech service the required SINR is typically in the order of 5.0 dB, so

the required wideband signal-to-interference ratio (also called carrier-to-

interference ratio, C/I ) is therefore 5.0 dB minus the processing = -20.0dB.

In other words, the signal power can be 20 dB underthe interference or

thermal noise power, and the WCDMA receiver can still detect the signal.

Notice: in GSM, a good quality speech connection requires C/I= 912 dB.


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26

Introduction to Wideband Code Division

Multiple Access (WCDMA)Overview

Codes in WCDMA

QoS support

Network ArchitectureRadio propagation and fading

RAKE receiver

Power Control in WCDMA

Diversity

Capacity and coverage


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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


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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


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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


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Codes in WCDMA

For instance, the relation between downlink physical layer bit rates and codes

SpreadingFactor (SF)

Channelsymbol

rate(ksps)

Channelbit rate(kbps)

DPDCHchannel bitrate range

(kbps)

Maximum userdata rate with -

rate coding(approx.)

512 7.5 15 36 13 kbps256 15 30 1224 612 kbps128 30 60 4251 2024 kbps64 60 120 90 45 kbps32 120 240 210 105 kbps16 240 480 432 215 kbps8 480 960 912 456 kbps

4 960 1920 1872 936 kbps4, with 3parallel

codes

2880 5760 5616 2.3 Mbps

Half rate speec

Full rate speec

144 kbps

384 kbps

2 Mbps

Symbol_rate =

Chip_rate/SFBit_rate =

Symbol_rate*2

Control channel

(DPCCH) overheadUser bit rate with coding =

Channel_bit_rate/2


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QoS Support

Key Factors:

Simultaneous support of services with different QoSrequirements:

up to 210 Transport Format Combinations, selectable individually

for every radio frame (10 ms)

going towards IP core networks greatly increases the usage of

simultaneous applications requiring different quality, e.g. real timevs. non-real time

Optimized usage of different transport channels for

supporting different QoS


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QoS support

Example:

DownlinkSharedChannel

DownlinkDedicatedChannels

USER 1

....

10 ms

USER 2 USER 3 USER 1 USER 1

USER 4

DataRate

2 Mbps

Code 5

Code 4

Code 3

Code 2

Code 1USER 1

USER 2

USER 3

USER 4

USER 2

Time

UMTS Terrestrial Radio Access Network (UTRAN)


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( )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 roughlyto 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



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( )Architecture

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



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( )Architecture

Node B

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

Some RRM tasks:

Measurements

Inner loop power control

f


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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, multipathcomponents 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

R di ti d f di


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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

RAKE i


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Every multipath component arriving at the receiver more than one chip

time (0.26 s) apart can be distinguished by the RAKE receiver

0.26 s corresponds to 78 m in path length difference

RAKE assigns a finger to each received component (tap) and alters

their phases based on a channel estimate so that the components can

be combined constructively

Finger #1

Finger #2

Finger #3

RAKE receiver

Transmitted

symbol

Received

symbol ateach time

slot

Phase

modified usingthe channel

estimate

Combined

symbol

P C t l i WCDMA


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The purpose of power control (PC) is to ensure that each user

receives and transmits just enough energy to have service but to

prevent:

Blocking of distant users (near-far-effect)

Exceeding reasonable interference levels

UE1UE2

UE3

UE1

UE2

UE3

UE1 UE2 UE3

Without PC received

power levels would

be unequal

With ideal PC

received power levels

are equal

P C t l i WCDMA


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1. Open loop power control

Only for the initial power setting of the MS

Based on distance attenuation estimation from the downlink pilot signal

2. Inner loop transmitter power control (CL TPC) at a rate of 1500 Hz

Mitigates fading processes (fast and slow fading)

Tx power is adjusted up/down to reach SIR target

Both in UL and DL

Uses quality targets in MS / BS

3. Outer loop PC at the rate of 100 Hz

Sets the quality target used by the inner loop PC

Compensates the changes in the propagation conditions

Adjusts the quality target Both in UL and DL



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Inner loop power control in the uplink

Outer loop PC (running in the radio network controller, RNC) defines SIR

target for the BS.

If the measured SIR at BS is lower than the SIR-target, the MS is

commanded to increases its transmit power. Otherwise MS is commanded

to decrease its power

Power control dynamics at the MS is 70 dB



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Inner loop power control in downlink:

Outer loop PC (running in the MS) defines SIR target for the MS

If the measured SIR at the MS is lower than the SIR-target, the BS is

commanded to increases its transmit power for that MS. Otherwise, BS is

commanded to decrease its power.

Power control rate 1500 Hz

Power control dynamics is dependent on the service

Theres no near-far problem in DL due to one-to-many scenario. However, itis desirable to provide a marginal amount of additional power to mobile

stations at the cell edge, as they suffer from increased other-cell

interference.



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Example of inner loop powercontrol behavior:

With higher velocities channel

fading is more rapid and 1500 Hz

power control may not be sufficient



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Inner loop power control tries to keep the received SIR as close to the target

SIR as possible.

However, the constant SIR alone does not actually guarantee the required

frame error rate (FER) which can be considered as the quality criteria of the

link/service.

Theres no uniqueSIR that automatically gives a certain FER

FER is a function of SIR, but also depends on mobility and propagation environment.

Therefore, the frame reliability information has to be delivered to outer loopcontrol, which can tune the SIR target if necessary.

Diversity


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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


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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 Handovers


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WCDMA Handovers

WCDMA handovers can be categorized into three different types

Intra-frequency handover WCDMA handover within the same frequency and system. Soft, softer and

hard handover supported

Inter-frequency handover

Handover between different frequencies (carriers) but within the same

system

E.g. from one WCDMA operator to another

Only hard handover supported

Inter-system handover

Handover between WCDMA and another system, e.g. from WCDMA to

GSM

Only hard handover supported

WCDMA Handovers


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WCDMA Handovers

Soft handover

Handover between different Node Bs

Several Node Bs transmit the samesignal to the UE which combines thetransmissions

Advantages: lower Tx power needed foreach Node B and UE

lower interference, battery saving forUE

Disadvantage: resources (code, power)need to be reserved for the UE in eachNode B

Excess soft handovers limit thecapacity

No interruption in data transmission

Needs RNC duplicating frame

transmissions to two Node Bs

WCDMA Handovers


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WCDMA Handovers

Softer handover

Handover between two sectors of the

same Node B Special case of a soft handover

No need for duplicate frames

Hard handover

The source is released first and then new

one is added

Short interruption in data flow

WCDMA Handovers


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WCDMA Handovers

Some terminology

Active set (AS), represents the Node Bs to which the UE is in soft handover

Neighbor set (NS), represents the links that UE monitors but which are not

already in active set

Received

signalstrength

BS1

BS2Threshold_1

Triggering time_1

Threshold_2

Triggering time_2

BS2 from the NS reaches

the threshold to be added

to the AS BS2 is still after thetriggering time above

threshold and thus added

to the AS

BS1 from the AS reaches

the threshold to be

dropped from the AS

BS1 dropped from the AS



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In WCDMA coverage and capacity are tight together:

When the load increases, the interference levels increases, too, and

therefore also increased transmit powers are needed in order to keepconstant quality.

Due to finite power resources, the more users Node B serves the less

power it has for each UE coverage will decrease

This leads to cell breathing: the coverage area changes as the load of

the cell changes. Therefore, the coverage and

the capacity have to be

planned simultaneously

Radio resource management

(RRM) is needed in WCDMA to

effectively control cellbreathing.



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Received power of one user as afunction of users per cell

Due to finite maximum Tx power ofthe UE coverage is usually limitedby the uplink

Node B does not have this problem

There is enough Tx power totransmit very far to a single user ifnecessary

However, downlink Tx power isdivided between all users and thus

capacity is limited by the downlink


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53

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)


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g p ( )

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


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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 (TTI = 2 ms)

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

16]


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g p p

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

Channel quality

(CQI, Ack/Nack, TPC)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 16

-20

2468

10121416

Time [number of TTIs]

QPSK1/4

QPSK2/4

QPSK3/4

16QAM2/4

16QAM3/4

Inst

antaneousEsNo[dB]

HSDPA functionality


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y

Scheduling responsibility has been moved from RNC to Node B

Due to this and the short TTI length (2 ms) the scheduling is dynamic

and fast

Support for several parallel transmissions

When packet A is sent it starts to wait for an acknowledgement from the

receiver, during which other packets can be sent via a parallel SAW (stop-

and-wait) channels

Pkt A

Pkt B

Pkt C

Pkt D

Pkt EPkt F

Ack B

HSDPA functionality


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

(Channel Quality Indicator)

HSDPA functionality


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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

HSDPA channels


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User data is sent on High Speed Downlink Shared Channel (HS-

DSCH)

Control information is sent on High Speed Common Control Channel

(HS-SCCH)

HS-SCCH is sent two slot before HS-DSCH to inform the scheduled

UE of the transport format of the incoming transmission on HS-DSCH

High Speed Uplink Packet Access (HSUPA)


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

Packet data throughput increased, though not as high throughput aswith 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)

HSPA Peak Data Rates


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5 codes QPSK

# of codes Modulation

5 codes 16-QAM

10 codes 16-QAM

15 codes 16-QAM

15 codes 16-QAM

1.8 Mbps

Maxdata rate

3.6 Mbps

7.2 Mbps

10.1 Mbps

14.4 Mbps

2 x SF42 ms

10 ms

# of codes TTI

2 x SF2 10 ms

2 x SF2 2 ms

2 x SF2 +2 x SF4

2 ms

1.46 Mbps

Maxdata rate

2.0 Mbps

2.9 Mbps

5.76 Mbps

Downlink HSDPA

Theoretical up to 14.4 Mbps

Initial capability 1.83.6 Mbps

Uplink HSUPA

Theoretical up to 5.76 Mbps

Initial capability 1.46 Mbps

f f S f


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63

Performance of advanced HSDPA features



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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



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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



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LMMSE equalizer (Equ in the

figure) offers a very good

performance for the userespecially 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



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Node B has a limited amount of scheduling opportunities

The amount of data transmitted by the network must be maximized

whilst offering the best possible quality of service to all users

The scheduling can be improved by an advanced algorithm



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An improved scheduling

algorithm (Proportional Fair,

PF) offers significant gain overa conventional algorithm

(Round Robin, RR)

PF has a very good price-

quality ratio User equipment needs no

changes

Node Bs need only minor

changes

Femtocells


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

even when theres a fixed line available

Providing full or even adequate mobile residential coverage is a significantchallenge 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 operators network using residential DSL 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, without needing to introduce WiFi enabled handsets

Femtocells


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The study considers the system performance of an HSDPA network consisting of macro cells andvery low transmit power (femto) cells

The impact of using 64QAM in addition to QPSK and 16QAM in order to benefit from the high SINR

is studied The network performance is investigated with different portions of users created in the buildings (0-

100%)

Femtocells


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Femtocells provide maximum of 15-

17 % gain to network throughput

already without dedicated indoor

users

The gain is visible with high load in

the network and comes directly from

the increased number of access

points in the network

Average load of a cell is decreased

and users can be scheduled more

often

SchemeOffered load

Medium High Congested

Rake 1x1 3 % 8 % 15 %

Rake 1x2 -1 % 19 % 13 %

Equ 1x1 -2 % 18 % 15 %

Equ 1x2 -1 % 3 % 17 %

Table: Network throughput gain of

femto cells to macro users

Femtocells


72/72


When the amount of dedicated indoor

users increase, the gain of femto cells

explodes

Gain is in the range of hundreds of

percents even with small portion of

indoor users

wcdma systems ok

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