1. Introduction to WCDMA

7/29/2019 1. Introduction to WCDMA

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2 © Nokia Siemens Networks WCDMA Network Overview/Jan2008

Customer Confidential

Introduction to WCDMADeepak Yadav

Jan’2008



3 © Nokia Siemens Networks WCDMA System Overview/Jan2008


Contents

Spectrum Availability

3GPP Structure

Network Architecture

Network Interfaces

Basic Concepts of WCDMASpreading and Despreading

WCDMA Radio Fundamentals

Radio Resource Management





Cellular Generations

People talk about mobile technology

in terms of generations

1st Generation or 1G

2nd Generation or 2G

2.5G

3rd Generation or 3G

But what do these mean?

time

Data

rate

Progress of data rates with

time and generation





Focus for today

GSM GSM WCDMA

HSCSD

GPRS

EDGE

The roads to 3G…

CDMA

IS-95ACDMA

IS-95B

1xRTT 1xEV-DO 1xEV-DV

CDMA2000

3xRTT

2G 2.5G 3G

Mult ip le phases





GSM evolution to 3G

GSM

9.6kbps (one timeslot)

GSM Data

Also called CSD

GSM

General Packet Radio Services

Data rates up to ~ 115 kbps

Max: 8 timeslots used as any one timePacket switched; resources not tied up all the time

Contention based. Efficient, but variable delays

GSM / GPRS core network re-used by WCDMA

(3G)

GPRS

HSCSD

High Speed Circuit Switched Data

Dedicate up to 4 timeslots for data connection ~ 50

kbps

Good for real-time applications c.w. GPRS

Inefficient -> ties up resources, even when nothing

sent

Not as popular as GPRS (many skipping HSCSD)

EDGE

Enhanced Data Rates for Global Evolution

Uses 8PSK modulation

3x improvement in data rate on short distances

Can fall back to GMSK for greater distances

Combine with GPRS (EGPRS) ~ 384 kbps

Can also be combined with HSCSD

WCDMA


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IS-95B

IS-95B

Uses multiple code channels

Data rates up to 64kbps

Many operators gone direct to

1xRTT

CDMA

IS-95A

IS-95A

14.4 kbps

Core

network re-

used in

CDMA2000

1xRTT

CDMA2000 1xRTT: single carrier RTT

First phase in CDMA2000 evolution

Easy co-existence with IS-95A air

interfaceRelease 0 - max 144 kbps

Release A – max 384 kbps

Same core network as IS-95

1xEV-DO

CDMA2000 1xEV-DO: Evolved Data Optimised

Third phase in CDMA2000 evolution

Standardised version of Qualcomm High Data Rate(HDR)

Adds TDMA components beneath code components

Good for highly asymmetric high speed data apps

Speeds to 2Mbps +, classed as a “3G” system

Use new or existing spectrum

1xEV-DVCDMA2000

3xRTT

CDMA2000 1x Evolved DV

Fourth phase in CDMA2000 evolution

Still under development

Speeds to 5Mbps+ (more than

3xRTT!)Possible end game.

CDMA2000 evolution to 3G




Clear direction for Internet communications

Internet communicationis going mobile

Voice has gone mobile




We Expected Data Tornado Years Ago but…

The mobile industry has expected data tornado since the birth of GPRS, but the

share of packet data traffic in 2G network was typically <<5% Why didn‟t data fly?

1. Low performance in terms of data rates and latency – no true broadband

2. Complex and expensive pricing – no flat rate

3. Complex connectivity – no plug-and-play

Data?




Diverse user requirements resulting multipletechnology needs

0.1 1 10

Vehicular

Pedestrian

Stationary M o b

i l i t y a n d c o v e

r a g e

Data Rate (Mbps)




Massive growth in fixed broadband connectivity creates demandand market potential for wireless broadband

Number of broadband connectionsis skyrocketing

Western European consumer adoption of

broadband and mobile telephony in first 10 years

(Source: Strategy Analytics)

70%

60%

50%

40%

30%

20%

10%

0%

Broadband penetration of total households

Mobile telephony user penetration of total population

Broadband penetration forecast

Time 1-10 years




Driversfor 3G

evolution

Drivers for 3G evolution and broadband mobile

Demand model• Analogies from fixed

broadband usage for both

business and consumers

• Average DSL user consumes

today 1-2 GB per month

(data, voice, video)

Advances in acc. Tech.development

• Flarion, WiMax, 3GPP2

camp, WLAN

• Technology politics

(e.g., Korea-US-Japan-China-

Europe)

Changing service &

underlying technology mix

• Refarming

• New spectrum

Spectrum and

regulatory drivers

• Volume & ARPU shift from

voice to data

• Circuit switched to packet

data (VoIP, IMS)

• Internet as a major sourcefor mobile services

Price/performanceof technology

• Efficient use of spectrum

• Improved broadband

experience





WCDMA Commercial Evaluation





WCDMA Forecast





WCDMA Handsets





3G Rollout in India has already been delayed due to various reasons.

Regulators and Government are occupied with various issues related tospectrum allocation.

Operators are taking time before committing themselves for such a Hughinvestments.

The way Indian Mobile Industry is growing, there is definitely need for a

more spectrum efficient technology – 3G is the right choice for thatTentative timeline for initial rollout looks like to be sometime this year then2009 will be the year when many more rollout may take place.

Future of 3G in India – The Question!!!!!





Future of 3G in India – Current Cellular Status





Future of 3G in India – Current GPRS Status

In spite of • Low speed

• Not user friendly

•Expensive tariffs

• Any Vision

•Creativity





Future of 3G in India – Data Traffic Growth





Benefits of 3G – Lower OPEX and CAPEX







• GSM configuration 4+4+4

• CDMA configuration IS2000

•WCDMA configuration 1+1+1

@25mErl

Benefits of 3G – Much higher capacity





Future of 3G in India – Projection





IMT-2000 frequency allocations – Rel 99

2200 MHz20001900 1950 2050 2100 21501850

JapanIMT-2000 P H S

IMT-2000

ITU M o b i l e

S a t e l l i t e

IMT-2000 IMT-2000

EuropeUMTS(FDD) D

E C T

U M T S ( T

D D )

GSM

1800

U M T S ( T D D )

UMTS(FDD)

USA P C S

u n l i c e n s e d

PCS PCS

U M T S ( T D D )

I M T

- 2 0 0 0 ( T D D )

M o b i l e

S a t e l l i t e

M o b i l e

S a t e l l i t e

M o b i l e

S a t e l l i t e

M o b i l e

S a t e l l i t e

M o b i l e

S a t e l l i t e

M o b i l e

S a t e l l i t e

M o b i l e

S a t e l l i t e





Spectrum Allocations – 3GPP rel4

3G(WCDMA 1900) for U.S

Uplink Uplink Downlink Downlink

SATELLITE FDD TDD FDD TDD SATELLITE

Duplex 190 MHz

Frequency MHz

2200 2025 2010 1980 1920 2170 2110

60MHz 60MHz

3G(WCDMA) 2GHz frequency band for Europe and APAC

Uplink Downlink

FDD FDD

Duplex 80 MHz

Frequency MHz

1910 1850 1990 1930

60MHz 60MHz





.

WCDMA/HSPA Spectrum – 3GPP Rel6

WCDMA/HSPA is standardized for all cellular band

800, 850

1800, 17001

1900

2100

2600

2x60 MHz

New 3G band190 MHz

Mainstream WCDMA band

1700/2100 2x60 MHz

= WCDMA/HSPA band in 3GPP today= WCDMA/HSPA band under work in 3GPP, target end of 2005

2x75 MHz

2x60 MHz

900 2x35 MHz

1800 in Europe, Asia and Brazil1700 in Japan and China

PCS band in USA and Americas

Americas, Japan, Asia 2x25 MHz

Europe, Asia and Brazil

Up to2

11800 completed, 1700 under work in 3GPP2Some regions may not have the full band available

Band I

Band II

Band III

Band IV

Band V,VI

Band VII





UMTS Release 99

UMTS Release 4

UMTS Release 5

UMTS Release 6

• UMTS CN

• UTRAN & WCDMA

• Bearer independent CS domain

• Low chip rate TDD mode

• UTRA repeater

• MMS

• etc.

• High Speed Downlink Packet Access (HSDPA)

• Wideband AMR

• Initial phase of the IP Multimedia Subsystem

• IP transport in the UTRAN

• Location Services enhancements

• etc.

• FDD Enhanced Uplink (HSUPA)

• IMS Phase 2

• Wireless LAN/UMTS Inter-working

• Multimedia Broadcast/Multicast Service (MBMS)

• Push Services and Presence.

• etc.

1999

2001

2002

2006

UMTS Releases





HSPA Peak Data Rate Evolution

14 Mbps

0.4 Mbps

14 Mbps

5.7 Mbps

21 Mbps

11 Mbps

42 Mbps

11 Mbps

Downlink peak rate

Uplink peak rate

3GPP R5 3GPP R6 3GPP R7 3GPP R8



29 © Nokia Siemens Networks WCDMA Network Overview/Jan2008


WCDMA Network Architecture and

Interfaces





UMTS NW Architecture

Iu

Uu

User Equipment(UE)

Iur Iub

UTRAN

RNC

WCDMABTS

WCDMABTS

WCDMABTS

WCDMA

BTS

RNC

Core Network(CN)





UMTS Network Architecture

Circuit SwitchedCore Network

GGSN

3GSGSN

GPRS

USIMcard

WCDMA

mobile

GSM/WCDMAmobile

RAN

WCDMABTS

WCDMABTS

RNC

RNC

MSC

HLR

MGW

IN SCP

SRR

PS Core Network

(PSTN/ISDN)

Internet

TCP/IP)

GSM/WCDMAmobile

CBC





Open interfaces of UMTS

CN

Circuitswitched

(cs)domain

packetswitched

(ps)domain

UTRAN

Radio Network Subsystem (RNS)

Radio Network Subsystem (RNS)

Iub

Iub

Iur

Iu-PS

Iu-CS

Uu

Uu

UE

UE

MSC/VLR

SGSN

RNC

RNC

G l UE A hit t





General UE Architecture

UU

UE

CU

USIM

ME

Mobile

Equipment

UMTS SIM

UTRAN Terminal

Equipment

G l UTRAN A hit t





General UTRAN Architecture

UU IU

UE

UTRAN

IUb

IUr

Node B

Node B

Node B

Node B

RNC

RNC

Radio Network

Controller

Radio Network

Controller

Iu-ps

Iu-cs

IUb

CN (MSC)

CN (SGSN)

El t f UTRAN





Elements of UTRAN

Radio Network Controller

Owns and controls radio resources in its domain (BSC in GSM)

Service Access Point for all services that UTRAN provides for the CN

Node B

Acts as the radio base station (BTS in GSM)

Converts the data flow between the Iub and Uu interfaces

Major Interfaces in UMTS





Major Interfaces in UMTS

There are four major new interfacesdefined in UMTS

• Iu – The interface between UTRAN and

the CN

• Iur

– The Interface between differentRNCs

• Iub

– The interface between the Node Band the RNC

• Uu – The air interface

RNC

Node-

B

RNC

UE

CN

Uu

Iu

Iub

Iur

Iu - the Core Network to UTRAN Interface





Iu the Core Network to UTRAN Interface

There are two parts to the Iu interface

• Iu-ps

connecting UTRAN to the PSDomain of the CN

• Iu-cs connecting UTRAN to the CSDomain of the CN

No radio resource signalling, travelsover this interface

• The Iu interface divides the UMTSnetwork into the radio specificUTRAN and the CN.

RNC

Node-

B

RNC

UE

CN

Uu

Iu

Iub

Iur

Iur - the Inter-RNC Interface





Iur the Inter RNC Interface

The Iur interface allows soft

handovers between Node-Bsattached to different RNCs

It is an open interface to allow theuse of RNCs from differentmanufacturers

Its functions may be summarised:Support of basic inter-RNC

mobility

Support of Dedicated andCommon Channel Traffic

RNC

Node-

B

RNC

UE

CN

Uu

Iu

Iub

Iur

Iub - the RNC to Node-B Interface



39 © Nokia Siemens Networks WCDMA System Overview/Jan2008Customer Confidential

Iub the RNC to Node B Interface

The Iub is an open interface to allow

the support of different manufacturerssupplying RNCs and Node-Bs

Its major functions are:

Carries dedicated and commonchannel traffic between the RNCand the Node-B

Supports the control of the Node-Bby the RNC

RNC

Node-

B

RNC

UE

CN

Uu

Iu

Iub

Iur

Uu - the Air Interface




Uu the Air Interface

Clearly the Uu must be

standardised to allow multiple UEvendors to be supported by anetwork

The major functions of the Uu are to:

Carry dedicated and commonchannel traffic across the air

interface

Provide signaling and control trafficto the mobile from the RNC andthe Node-B

RNC

Node-

B

RNC

UE

CN

Uu

Iu

Iub

Iur



41 © Nokia Siemens Networks WCDMA Network Overview/Jan2008Customer Confidential

Basic Concepts of WCDMA

UMTS Ai I t f T h i l A t




UMTS Air Interface Technical Aspects

UMTS Ai I t f T h i l A t




UMTS Air Interface Technical Aspects

WCDMA FDD technology




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

Access Technology Explanation




Access Technology Explanation

Multiple Access means “Many users share the same medium”

There are a number of different Multiple Access (MA) strategies : – Time Division Multiple Access (TDMA)

– Frequency Division Multiple Access (FDMA)

– Code Division Multiple Access (CDMA)

TDMA




f r e q u en c y

time

User 1 User 1

Timeslot Period Frame Period

Idealised TDMA(with no guard

periods)

Available

Frequency

Band

FDMA




f r e q u en c y

time

User 1

Frame Period (we may still need

frames/timeslots for signaling)

Channel

Bandwidth

Idealised FDMA(with no guard

bands)

CDMA - Direct Sequence Spread Spectrum




q p p

f r e q u en

c y

time

code

Frame Period (we may still need

frames/timeslots for signaling)

WCDMA Technology




WCDMA Technology

5 MHz

3.84 MHz

f

5+5 MHz in FDD mode5 MHz in TDD mode

F r e q u e n c y

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




UMTS & GSM Network Planning

GSM900/1800: 3G (WCDMA):

Spreading & Processing Gain




Frequency P o w

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

Unspread narrowband signal Spread wideband signal

Bandwidth W (3.84 Mchip/sec)

User bitrate

R

sec84.3

Mchipconst W

R

W dBG p Processing

gain:

Spreading & Processing Gain

Processing Gain Examples



52 © Nokia Siemens Networks WCDMA System Overview/Jan2008Customer Confidential Frequency (Hz)

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

Packet data user (R=384 kbit/s)

P o w e r d e n s i t y ( W / H z )

R

Frequency (Hz)

Gp=W/R=24.98dB

P o w e r d e n s i t y ( W / H z )

R

Gp=W/R=10dB

• Spreading sequenceshave a different length• Processing gaindepends on the user data rate

Processing Gain Examples

Transmission Power




Transmission Power

Frequency

5MHz

Power density

Time

High bit rate user

Low bit rate user

Chips and Spreading factor




Digitalencodeddata

A/D Modulator

Speech Symbols

Chip

..0101

Chips and Spreading factor

Speech when given to the A/D converter gets converted in to digital data. When digital data is given to modulator , the o/p is called as symbol . Symbol

when spread with code sequence is known as chips

Spreading factor (SF) = The number of chips per data

• Example : SF= 3840000/ 15000 = 256

Spread code

S di / D di




Spreading/ Despreading

Data xCode

Data

Code

Code(pseudonoise)

Data

+1

+1

+1

+1

+1

Symbol

-1

-1

-1

-1

-1

ChipChip

Despreading

Spectrum

Symbol

Spreading and Despreading




Spreading and Despreading

SpreadingEach user data bit is multiplied with a sequence of 'x' code bits called CHIPS. This'x' determines the SPREADING FACTOR!!!!

The resulting spread data is at a rate of 'x' times R

Despreading

The spread user data/chip sequence with the same 'x' code chips to recover theoriginal data.

Spreading




p g

WCDMA S di O ti




WCDMA Spreading Operation

In WCDMA two separate codes are used in the spreading operation

• Channelisation code• Scrambling code

Data

Bit rate

Chanelization

code (SF)

scrambling

code

chip rate chip rate

Chanelization(increases signal BW)- using orthogonal codes

Scrambling(doesn‟t affect signal BW)- using pseudo noise code

WCDMA C d




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, definesphysical 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

Channelisation and Scrambling Codes




Channelisation and Scrambling Codes

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 chipsOption (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

Operation in Multipath Environment/ Rake Reception




p p p

Radio propagation is characterized by multiple reflections, diffractions andattenuation of signal energy.

Operation in Multipath environment/Rake Reception




p p p

Effects of Multipath Propagation

Constructive

Destructive

The Multipath components can be combined coherently to obtain mutipath diversityby the WCDMA receiver if the time difference of the multipath components is at least0.26s.

At certain time delay positions ,many paths nearly equal in length may arrive atvirtually the same instant at the receiver. This results in FAST FADING.

Signal can drop down by 20-30dB

Operation in Multipath environment/Rake reception




p p p

Rake Reception

WCDMA requires some countermeasures against Fast fading!!!!The solution is RAKE RECEIVER!!!!!

So what is a RAKE RECEIVER????

Collection of Correlation Receivers called FINGERS!!

Fading????!!!

Fingers??!!

Spreading/Despreading???!!!

RAKE Receiver




RAKE Receiver

RAKE RECEPTION




C O

Operating Principle of CDMA Rake Receiver

Assign a RAKE finger to each time delay position where significant energy arrives.

Within each correlation receiver track the fast changing phase and amplitude

Combine the demodulated and phase adjusted symbols across all active fingers andpresent them to the decoder for further processing.

Transmitted symbol Received signal at each time delay Modified with channel estimate Combined Symbol

finger1

finger2

finger3

Scrambling Codes & CPICH




g

The Common Pilot Channel (CPICH) is broadcast from every cell

It carries no information and can be thought of as a “beacon” constantlytransmitting the Scrambling Code of the cell

It is this “beacon” that is used by the phone for its cell measurements for network acquisition and handover purposes (Ec, Ec/Io).

CPICH

Comments




Majority of the measurements are based on CPICH.

Thumb rule is that, if UE can‟t see the CPICH, it can‟t see the cell.

Initial optimisation is purely based on the CPICH measurements.

In the Downlink, WCDMA cells are identified by their SC.

Its like a BCCH in GSM but the difference is in using same frequency.

C t f RSCP d E /N




Concepts of RSCP and Ec/No

Two Important Terms

• RSCP

• Ec/No, Ec/Io

Total Received Power I o




o

In a WCDMA network the User Equipment (UE) receives signals from manycells

I o * = The sum total of all of these signals (dBm)

*Note: Sometimes Io is referred to as No, RSSI

I o

Received Power of a CPICH




Using the properties of SCs the UE is able to extract the respective CPICH levelsfrom the sites received

RSCP = The Received Power of a Particular CPICH (dBm)

Ec = Energy per Chip

E c1 E c2

The CPICH Quality (Ec/Io)




y ( )

From the previous two measures we can calculate a signal quality for eachCPICH (SC) received

Ec/Io = Ec - Io (dB)

*Note: Sometimes Ec/Io is referred to as Ec/No

E c1 E c2




RRM must be able to:

Predict the impact on interference (power) of the admitting a new user for UL & DL

Perform appropriate actions (e.g. new calladmissions, bit rate increase/decrease etc.) inaccordance with prevailing load conditions

Provide different quality of service for realtime (RT) and non-real time (NRT) users

Take appropriate corrective action when thedifferent cell load thresholds are exceeded inorder to maintain cell stability (i.e. load control)

Overload

Load Target

Overload Margin

P o w e r

Time

Estimated capacity for NRT traffic

Measured load caused

by non-controllable load(RT)


RT services must have higher quality assurance than NRT

RRM Functionalities




AC Admission Control

LC Load Control

PS Packet Scheduler

RM Resource Manager

PC Power Control

HC HO Control

PC

HCConnection based functions

LC

AC

Network based functions

PS

RM

Admission Control




Checks that admitting a new user will not sacrifice planned coverage or qualityof existing connections

Determines whether or not a new RT RAB can be admitted to the RAN

With PS decides whether to admit NRT RABs (PS handles all NRTconnections)

Also sets

– UL/DL BLER, Eb/No targets

– SIR target for outer loop power control

– Initial DL transmission power for the channel

– Radio Link Control parameters, e.g. transmission mode

– Transport Channel (TrCH) parameters, e.g. TFS

Provides RLC parameters to PS for NRT users;

– Bearer class

– Traffic handling priority

– Transport Formats

– MS capabilities

Admission Control




Radio Access Bearerson the air Interface

Allowed Range AC Procedure

...

Admission Control




Planned uplink interference

margin;defines the optimum operatingpoint up to which the AC canoperate.

Defines the limit (the first ULoverload threshold) for the ULinterference margin, after which the BS starts its loadcontrol actions to preventoverload.

0

5

10

15

20

25

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Load

I n t e r f e r e n c e M

a r g i n ( d B )

Offset

Load Control




Cell load is defined as a function of interference – main criterion in WCDMA

The load control function within RRM can be divided into:

Preventive load control (e.g. congestion)

Overload control (e.g. dropping of calls in worst case)

The load control functionality is done by measuring both UL (receivedinterference) and DL (transmit power) periodically on a cell basis

Load control is performed for UL and DL separately (asymmetric traffic)

Preventive actions are performed before the cell is overloaded (threshold y)

Overload actions are performed after cell is overloaded (threshold x)

RNP parameters define the thresholds for the RRM functionalities

The thresholds define a stable functionality within a cell and with surroundingcells

Load Control





Estimated capacity for NRT traffic.

Measured load caused by non-controllable load(RT)

Overloadthreshold x

Load Targetthreshold y

P o w e r

Time

Preventive Load Control

Overload Control

Load Control





LC performs the function of load control in association with AC & PS (LC worksas glue between these two functions)

Updates load status using measurements & estimations provided by AC andPS

Continuously feeds cell load information to PS and AC;

• Interference levels

• BTS power levels

• Non-controllable load

LC

AC

PSNRTload

Load changeinfo

Load status

Packet Scheduler





A non-real time call constitutes of a bursty sequence of packets.

In the downlink, the Packet Scheduler decides which channel to use, DC

The load target can be reached by scheduling the transmission of NRT pa

time

packet service session

packet call

reading time

packet size packet arrival interval

Packet Scheduler





Packet Scheduler

PS allocation times need to be fast to accommodate changing

conditions & accurate (up-to-date load info)

Capacity requests sent via traffic volume measurement reports

(governed by RNP parameters)

PS comprises two parts: MS specific & Cell specific

power

time

non-controllable load

controllable load

Total Load

Target threshold

Overload threshold

Responsible for scheduling radio

resources for both UL and DL NRTRABs

Scheduling period defined by RNP

parameters

PS relies on up-to-date

information from AC and PS

Capacity allocated on a needs

basis using „best effort‟ approach

Packet Scheduler





Packet Scheduler

Radio network planning

parameters

Periodical cellmeasurements

Periodical radio link

measurements

RBsetup/reconfiguration/releas

e information

Traffic volumemeasurements (triggers

for DCH allocation)

Updated power estimations

Control of trafficvolume

measurements

DCH allocations for NRTRB

Packetscheduler

Resource Manager





Resource Manager

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

Also looks after code tree management (to maintain orthogonality); – Initial code selection – codes concentrated to the same branch

– Code re-fragmentation – dynamic reallocation of codes as users enter/leave thesystem

Code Type Uplink Downlink

Scrambling codes

Spreading codes

User separation Cell separation

Data & control channels from same UEUsers within one cell

Power Control (PC)





Outer Loop Power Control

( )

Open Loop Power Control (Initial Access)

Closed Loop Power Control

RNC

BSMS

Power control in WCDMA





Power control in WCDMA

Fast, accurate power control is of utmost importance – particularly in UL; – UEs transmit continuously

– WCMDA often uses 1 frequency

– Poor PC leads to increase interference > reduced capacity

From BTS perspective every UE accessing network increase interference

WCMDA capacity is proportional to interference level > minimise interference

PC maintains link quality by adjusting UE (UL) and BTS (DL) powers every slot

Mitigates 'near far effect', by providing minimum required power for each

connection

UEs and BTSs should always be at the lowest possible transmission power

PC utilises Signal-to-Interference Ratio (SIR) – independently for each

connection

Provides protection against shadowing and fast fading

Open Loop Power Control





Controlled by UE

Determines how much power UE should use during random access procedure(UL)

Network informs UE of current network status;

– CPICH power (RNP parameter)

– UL required C/I ratio (RNP parameter)

– UL interference

UE uses these parameters to calculate initial power of RACH preamble

If access request is not detected power of preamble is increased in steps After detection of MS signal, the initial SIR is calculated in RNC

Preamble PreamblePreamble

Preamble

M S O u t p u

t P o w e r

AICH

Mesage Part

RACH

Fast Loop Power Control





Located in BTS and UE

Controls the power of the dedicated physical channels

Power control changes can occur every slot (i.e. 1500 times per second)

BTS and UE continuously compare recevied SIR with SIR target and inform eachother to either increase or decrease its power (using TPC commands)

With Optimum

Power Control

Without

Power Control

MS1

MS2

MS3

MS4

MS1 MS2 MS3 MS4

R e c e i v e d p o

w e r a t B S

R e c e i v e d p o

w e r a t B S

MS1MS2

MS3

MS4

Closed Loop Power Control





Adjust the SIR for every user based on BER/FER Observation. Initial, max. andmin. SIR values are set by AC

Needed to track changes in radio environment Aims to provide required quality

UL quality evaluation is made after MDC

RNP parameters control the threshold comparison process for SIR target and thereporting of these results

If SIR target reaches its maximum (I.e. radio conditions deteriorate even thoughSIR target is increased, system has to take action;

inter-frequency / inter-system handover

RRC connection release

Handover Types





Intra-Frequency Handovers

Softer Handover

– Handover between sectors of the same Node B (handled by BTS) – No extra transmissions across Iub interface – Maximum Ratio Combining (MRC) is occurring in both the UL and DL

Soft Handover

– MS simultaneously connected to multiple cells (from different Node Bs) – Extra transmission across Iub, more channel cards are needed (compared to non-SHO) – Mobile Evaluated Handover (MEHO) – DL/UE: MRC & UL/RNC: Frame selection combining

Hard Handover – Arises when inter-RNC SHO is not possible (Iur not supported or Iur congestion) – Decision procedure is the same as SHO (MEHO and RNC controlled) – Causes temporary disconnection of the (RT) user

Inter-Frequency Handover

• Can be intra-BS, intra-RNC, inter-RNC

• Network Evaluated Handover (NEHO)

• Decision algorithm located in RNC

Inter-RAT Handover

• Handovers between GSM and WCDMA (NEHO)

Handovers in WCDMA - Softer HO





Softer handover occurs between sectors of the same site

Handovers in WCDMA - Soft HO





Soft handover occurs between sectors of the different sites

For both softer and soft it is the Ec/Io levels used to determine whether a cellshould be added or removed from the active set

Handovers - Inter frequency HO





Inter frequency handover occurs between two WCDMA carriers

Will be used once operator deploys its second carrier, for microcell layer or capacity purposes

Handovers - Inter system HO





Inter system handover occurs between 3G and 2G sites

As with all handovers, accurate adjacencies will be required

3G 2G



Thank You

1. Introduction to WCDMA

Documents

Transcript of 1. Introduction to WCDMA