presentation on wcdma

8/13/2019 Presentation on WCDMA

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1

WCDMA, HSPA and advanced

receiversMohammad Razaul Karim Rizvi

Manager, Teletalk Bangladesh Limited



© Timo Nihtilä2 TLT-5606 Spread Spectrum Techniques / 25.4. 2008

Readings related to the subject

• General readings

– WCDMA for UMTS – Harri Holma, Antti Toskala – HSDPA/HSUPA for UMTS – Harri Holma, Antti Toskala

• Network planning oriented

– Radio Network Planning and Optimisation for UMTS – Janna Laiho, Achim

Wacker, Tomás Novosad

– UMTS Radio Network Planning, Optimization and QoS Management ForPractical Engineering Tasks – Jukka Lempiäinen, Matti Manninen




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



4

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 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)




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”




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




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

12/993GPP 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)




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




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/







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

M i l l i o n s u b s c r i b e

r s







14

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 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

1 2

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 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




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




Direct Sequence




Processing gain and Spreading

Frequency

Despread narrowband signal

Spread wideband signal

W

R

P o w e r d e n s i t y ( W

a t t s / H z )

P o w

e r d e n s i t y ( W a t t s / H z )

Frequency

Transmitted signalbefore spreading

Received signal

before despreading

Interference for the partwe are interested in





Frequency

P o w e r d e n s i t y ( W

a t t s / H z )

P o w

e r d e n s i t y ( W a t t s / H z )

Frequency

Received signalafter despreading b ut

before fi l ter ing

Received signal

after despreading and

after fi l ter ing

Transmitted signal

Interference





• 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



26

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




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




Codes in WCDMA

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

Spreading Factor (SF)

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 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




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




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)




( ) 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





( ) 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





( ) Architecture

• Node B

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

– Some RRM tasks:

• Measurements

• Inner loop power control

f




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



RAKE i




• Every multipath component arriving at the receiver more than one chip

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

– 0.26 μs 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




Power Control in WCDMA

• 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





• 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





• Example of inner loop powercontrol behavior:

• With higher velocities channel

fading is more rapid and 1500 Hz

power control may not be sufficient






• 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.

– There‟s no unique SIR 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




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




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




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




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

Capacity and coverage





• 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.






• 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



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)




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




• 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]




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




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




• 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

HSDPA channels




• 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



HSPA Peak Data Rates




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 1.8 – 3.6 Mbps

Uplink HSUPA

• Theoretical up to 5.76 Mbps

• Initial capability 1.46 Mbps

f f S f



63

Performance of advanced HSDPA features



Advanced receivers with HSDPA




• 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



Advanced HSDPA scheduling




• 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 B‟s need only minor

changes

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 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 operator‟s 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




• 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




• 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

Scheme Offered 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




• 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

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