WCDMA OverviewWCDMA Overview

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OutlineOutline

IntroductionWhat is different from GSMBasic Concept of 3G (UTRAN)WCDMA Coverage & CapacityCore network Architecture and EvolutionHSDPA Basics

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Introduction

Mobile networks established in mid 80’s

It is widely recognized that there are three different generations as far as Mobile communications is concerned.

• The first generation, 1G – Speech • The Second generation, 2G – Speech+ Data• The Third Generation, 3G – Speech+ High Data Speed

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Evolution from 2G to 3G

Basic GSM and VAS are basically meant to produce “mass services for mass people” but due to requirements raised from end-users, more individual type of services is required.

3G introduces the new radio access method, WCDMA. 3G introduces the new radio access method, WCDMA. WCDMA and its variants are global. WCDMA and its variants are global.

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Evolution from 2G to 3G

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GSM and WCDMA Comparison

Separate users through different codes

Continuous transmission and reception

Code planning – No Frequency Planning

Variable Cell Radius: Cell Breathing

Radio Link: 1 UE <-> Many Node-B’s

Power is Capacity

Scrambling Code Planning

Hard/Soft/Softer Handover

Orthogonal in time within a cell

Time Slot Synchronization in time

Frequency planning

“Fixed” Cell Radius

Radio Link: 1 MS <-> 1 RBS

# of Frequencies limit capacity

BSIC Planning

Hard Handover

GSM WCDMABTS NodeB

BSC RNCMS UE

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GSM Radio Access Network

Core Network

BSC

BSC

A/Gb

Abis

UmBTS BTS

BTS

MS

8

WCDMA Radio Access Network

Iu= Iu PS - GbIu CS - A

Core Network

RNC

RNC

Iu

Iur

Iub

UuNodeB NodeB

NodeB

UE

UTRANCore Network

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Development process for 3G

The third generation, 3G, is expected to complete the globalization process of the mobile communication. Again there are national and regional interests involved and difficulties can be foreseen.

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What is WCDMA.....

Wide Band Code Division Multiple Access is a third generation mobile communication system. It’s a wireless system where the telecommunication, datacom & media industry converge and is based on a Layered Architecture.

Convergence:Convergence:

1. User Service convergence

2. Device convergence

3. Network convergence

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YesterdaySingle-Service networks

Da

ta/I

P N

etw

ork

sD

ata

/IP

Ne

two

rks

PL

MN

PL

MN

PS

TN

/IS

DN

PS

TN

/IS

DN

Services

Access Transport & Switching Networks

Servers

Clients

IP Network

AccessAccess

TomorrowMulti-Service networks

From Single- to Multi-Service Networks

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Layered Architecture

The architecture of telecommunication networks, whether wireless or wire line has changed and they are now split into several horizontal layers that are more or less independent of each other.

Applications Layer

Control Layer

MSC-S HLR

GGSN

GMSC/TransitSG

Connectivity Layer

GSM/ EDGEAccess

WCDMAAccess

M-MGW M-MGW

InternetIntranet

PSTNISDN

SGSN

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Multiple Access

The cellular concept approaches the capacity limitation in terms of system coverage. Therefore, it does not alone help the per-cell capacity limitation as far as the simultaneous users are in question. From radio spectrum standpoint, it is extremely important how the radio resources are allocated to the simultaneous users.

Numbers of multiple accesses have been developed to combat the problem of simultaneous radio access allocation to the access requesters.

The main aspect of any multiple access scheme is the strategy how the available frequency band is allocated.

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Different Approaches

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WCDMA Band

From 3G point of view, it has been decided (in mid-1999 by OHG) that therewill be three CDMA variants in use. Those are:

DS-WCDMA-FDD: Direct Sequence- Wideband Code Division Multiple Access - Frequency Division Duplex

Uplink: 1920 -1980 MHzDownlink: 2110 -2170 MHzDuplex Distance: 190 MHz

DS-WCDMA-TDD: Direct Sequence- Wideband Code Division Multiple Access – Time Division Duplex

Lower Band: 1900 -1920 MHzUpper Band: 2010 -2025 MHz

MC-CDMA: Multi Carrier - Code Division Multiple Access

It was chosen for private indoor services

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WCDMA Bandwidth

In WCDMA, the data stream of the base station transmitter handles in downlink direction represents the traffic from the network to the terminal. This traffic uses several channels in the Uu interface. In the Uu interface the effective bandwidth for WCDMA is 3.84 MHz and with guard bands the required bandwidth is 5 MHz.

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WCDMA at a glance

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WCDMA Frequency allocations

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Basic Concept

The principles of WCDMA technique are based on Spread Spectrum.

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Spread Spectrum

The main advantages of the spread spectrum are:

– Its resistance to radio interference and jamming.

– It lowers the probability of intercept by an adversary.

– Its resistance to signal interference from multiple transmission signal branches.

– It providing multiple access facility with a reuse factor equal to one.

– It supporting means for measuring range, or the distance between two points.

– It yields the possibility of utilising diversity techniques, including multi-path diversity, as well as frequency and time diversity.

– It provides user access at any time without waiting for a free channel as far as the level of interference meets the system's tolerance.

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WCDMA Network

The WCDMA network is a multi-service “network of networks”, providing both traditional telecommunications services and new internet based services over the same network with support for high bit rates.

Network Architecture:3GPP (Third Generation Project Partnership) Reference Model:

Based on 3GPP reference network model, the WCDMA network can be considered to consists of four major components:

1. User Equipment (UE)

2. Access Network (AN)

3. Core Network (CN)

4. Network External to WCDMA

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3GPP Release 1999 Reference Architecture

Co-operatingNetworksUser Equipment Radio Access Network Core Network

Note: Not all interfaces areshown and named

BSCBTSBTS

Um

Abis

BSS

F

HLRHLR

D C

EIR

AU

C

EA

GMSCGMSC

Gf

Gn

SGSNSGSN

Gb Gr

Gn

SGSNSGSN

GGSNGGSN

Gs

Gc

Gi

Gd

IuCS

MSC/VLR

MSC/VLR

G

H

Gp

IuPS

RNCNode B

Uu

Iur

Iub

RNCNode BIub

RNS

RNS

UTRANIur

ME

Cu

or

SIM-ME i/f

USIM

SIMMS

ISDNPSTNPSPDNCSPDNPDN:- Intranet- Extranet- Internet- X.25

SMS

MSC/VLR

MSC/VLR SCFSCF

ME

SIM-ME i/f

SIM

MS

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WCDMA Channels

The WCDMA radio access allocates bandwidth for users and the allocated bandwidth and its controlling functions are handled with term ‘Channel’.

WCDMA uses 3 Layers:WCDMA uses 3 Layers:

1. Logical Channels: Describe the types of information to be transmitted

2. Transport Channels: Describe how the Logical Channels are to be transferred.

3. Physical Channels: These are the “transmission media” providing the radio platform through which the information is actually transferred.

In GSM the Physical Channels and their structure is recognised by the BSC but in WCDMA the Physical Channels really exist in the Uu interface and the RNC is not necessarily aware their structure at all. Instead of Physical Channels the RNC “sees” Transport Channels.

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Channel Architecture

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UTRAN

The main task of UTRAN is to create and maintain Radio Access Bearers (RAB) for communication between UEs and Core Network.

With RAB the Core Network elements are given an illusion about a fixed communication path to the UEs thus releasing them from the need to take care of radio communication aspects.

UTRAN is located between two open interfaces being Uu and Iu.

From the bearer architecture point of view the main task of UTRAN is to provide Bearer service over these interfaces.

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What is Radio Access Bearer (RAB) ?

RAB The Radio Access Bearer (RAB) is the entity responsible for transporting The Radio Access Bearer (RAB) is the entity responsible for transporting

radio frames of an application over the access network in UMTS.radio frames of an application over the access network in UMTS.

• Controlled by the core network (CN)

• CN determines traffic class and QoS

• Real-Time Applications– Streaming Class: Preserve time relation between entities

(packets) in a data stream

– Conversational Class: Preserve time relation between entities within a certain delay

• Non-Real Time Applications– Background Class: Destination is not expecting data.

Preserve Payload

– Interactive Class: Request / Response Pattern with preserved payload

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Conversational Speech 12.2 kbps Circuit switched

Conversational CS Data 64 kbps Circuit switched

Streaming 128/128 PS

Interactive Variable rate Packet switched

Multi-RABCombination of Conversational Speech and Interactive 64/64

RAB Examples

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RAB Attributes

• Transfer delay

RAB Service Attributes

• Traffic Class

• Maximum bit rate [kbps]

• Delivery order

• Maximum SDU size

• SDU format information

• SDU error ratio

• Residual bit error ratio

• Delivery of erroneous SDUs

• Guaranteed bit rate

• Traffic handling priority

• Allocation/retention priority

• Source statistics descriptor

• Relocation requirement

•RAB asymmetry indicator

RAB

UE RBS RNC CN

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UTRAN Architecture

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UTRAN & Interfaces

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NODE B

The BS is located between the Uu and Iub interfaces. Its main tasks are to establish the physical implementation of the Uu interface and, towards the network, the implementation of the Iub interface by utilising the protocol stacks specified for these interfaces.

Realization of the Uu interface means that the BS implements WCDMA radio access physical channels and transfers information from transport channels to the physical channels based on the arrangement determined by the RNC.

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Modulation Method

WCDMA uses Quadrature Phase Shift Keying (QPSK) as its modulation method in downlink direction and the Offset Quadrature Phase Shift Keying (OQPSK) in uplink direction.

The result is that the spectrum used for QPSK and OQPSK is the same but OQPSK has smoother signal. This allows the amplifiers to operate also on their non-linear operating area without problems.

The conventional QPSK could be used in both directions but then the UE would suffer power consumption problems and high prices.

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Receiver Technique

The WCDMA utilises multipath propagation.

On the other hand, to gain better capacity in the radio network, the transmit powers of the UEs (and BSs) should be relatively small. This decreases interference in the radio interface and gives more space for other transmissions and it is very useful that both the UE and the BS are able to “collect” many weak level signals.

This requires special type of receiver. One example of this kind of arrangement is called RAKE.

The purpose of the RAKE receiver is to improve the received signal level by exploiting the multi-path propagation characteristics of the radio wave.

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Diversity Technique

In general, diversity techniques are efficient means to overcome the radio signal deterioration due to shadowing and fading.

In addition to that utilizing diversity technique is a prerequisite for providing soft handover feature in the cellular systems.

In WCDMA technology, typically polarisation diversity is utilized both for uplink and down transmission.

The purpose of multipath diversity is to resolve individual multipath components and combine them to obtain a sum signal component with better quality.

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RNC (Radio Network Controller)

The RNC is switching and controlling element of the UTRAN. RNC is located

between the Iub and Iu interface. It also has the third interface called Iur for inter-RNS connections.

Referring to the Bearers, the RNC is a switching point between the Iu Bearer

and Radio Bearer(s).

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RNC Function

The whole functionality of RNC can be classified into two parts:

• UTRAN Radio Resource Management

• UTRAN Control Functions

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Radio Resource Management

The RRM is a collection of algorithms used to guarantee the stability of the radio path and the QoS of radio connection by efficient sharing and managing of the radio resources.

The RRM algorithms to be shortly presented here are:

Handover ControlPower ControlAdmission Control and Packet SchedulingCode Management

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Handovers

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WCDMA Handover Scenarios

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Soft Handover

In WCDMA system, the majority of handovers are intra-frequency soft handovers

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Concept of Soft/Softer Handover

Cell A

Cell B

Cell C

Single Link

The UE measured the CPICH Signal strenght (RSCP) and quality (Ec/No) to determine which cell to add in the active set

Add and remove from active set is based on relative measurments

Softer handover-two cells within the same RBS in Active Set

Soft handover-two cells from different RBS in Active Set

Soft/Softer handover-three cells in Active Set

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WCDMA Coverage GSM Coverage

Road

Using the WCDMA Frequency

Using the GSM Frequency

Inter RAT Handover

Inter Radio Access Technology (IRAT) handover

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Hand over from/to GSM

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POWER CONTROL

Power control is an essential feature of any CDMA based cellular system.

In WCDMA, power control is employed in both uplink and downlink.

Downlink power control is basically for minimising the interference to other cells and compensating for other cells' interference as well as achieving acceptable SIR.

To manage the power control properly in WCDMA, the system uses different two defined power control: Open Loop Power Control Closed Loop Power Control (CLPC), including Inner and Outer Loop Power Control mechanisms

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Types of Power Control

Open Loop Power Control (OLPC): Basically used for uplink power adjusting, the UE adjusts its transmission power based on estimate of the received signal level from the BS Common Pilot Channel (CPICH) when the UE is in idle mode and prior to Physical Random Access Channel (PRACH) transmission.

Closed-Loop Power Control (CLPC): Utilised for adjusting the transmission power when the radio connection has already been established. Its main target is to compensate the effect of rapid changes in the radio signal strength and hence it should be fast enough to respond to those changes.

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Admission Control and Packet Scheduling

WCDMA Radio Access has several limiting factors, but the most difficult to control is the interference occurring in the radio path. When the WCDMA cellular network is planned, one of the basic criteria for planning is to define the acceptable interference level with which the network is expected to function correctly. The main task of Admission Control is to estimate whether a The main task of Admission Control is to estimate whether a new call can have access to the system without sacrificing the new call can have access to the system without sacrificing the bearer requirements of existing calls. bearer requirements of existing calls.

Also responsible to handle packet connections with bursty Also responsible to handle packet connections with bursty traffic, having a very random arrival time, number of packet call traffic, having a very random arrival time, number of packet call per session, reading time, as well as number of packets per session, reading time, as well as number of packets within a call.within a call.

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Code ManagementRNC manages both Channelisation and Scrambling Codes used in the Uu interface connections.

In principle, the BS could manage them, but then the system may behave unstable when the RNC is otherwise controlling the radio resources.

The Uu interface requires two kinds of codes for proper functionality:

Every Cell uses 1 Scrambling Code, the UE is able to make separation between cells by recognising this code.

Under every Scrambling Code the RNC has a set of Channelisation Codes.

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Control Functions

In order for the UTRAN to control and manage the radio bearers, which is essential to provide the Radio Access Bearer (RAB) service, it should perform other functions in addition to the RRM algorithms.

These can be classified as:

System Information BroadcastingSystem Information BroadcastingRandom Access and Signalling Bearer SetupRandom Access and Signalling Bearer SetupRadio Bearer ManagementRadio Bearer ManagementUTRAN Security FunctionsUTRAN Security FunctionsUTRAN level mobility managementUTRAN level mobility managementDatabase HandlingDatabase HandlingUE positioningUE positioning

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WCDMA in nutshell

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What is Coverage in WCDMA

Signal does not mean “Coverage” in WCDMA

Pilot Signal - RSCPPilot Ec/NoService Coverage

Pilot RSCP

Pilot Ec/No

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Capacity Considerations Effect of different user distribution

High power usageLow capacity

Low power usageHigh code usage

Code limited scenario

Power limited scenario

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CELL CAPACITY

In GSM the TRX capacity calculation is very straightforward procedure but because In GSM the TRX capacity calculation is very straightforward procedure but because in WCDMA the radio interface is handled differently and the system capacity is limited in WCDMA the radio interface is handled differently and the system capacity is limited by variable factors, the capacity of the WCDMA TRX is not very easy to be by variable factors, the capacity of the WCDMA TRX is not very easy to be determined.determined.

The capacity of a cell depends on the downlink Scrambling Code amount assigned for the cell (minimum is 1). Every downlink Scrambling Code then has a set of Channelisation Codes under it and every call/transaction requires one Channelisation Code to operate.

In WCDMA technology, all the users share the common physical resource, being frequency band in 5 MHz slices. All users of the WCDMA TRX co-exist on the frequency band at the same moment of time and different transactions are for the people is the capacity of the WCDMA TRX.

Some assumptions: All the subscribers under the TRX coverage area are equally distributed so that they have equal distances to the TRX antenna. The Power level they use is the same and thus the interference they cause is on the same level. Subscribers under the TRX use the same baseband bit rate, i.e. also the same Symbol Rates.

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CALCULATIONS

Under these circumstances:Under these circumstances:

A value called Processing Gain (Gp) - Its a relative indicator informing what is the relationship between the whole bandwidth available (BRF) and the Baseband bit rate (B Information).

G G p = p = B B RFRF// B B InformationInformation

or

G G p = p = Chip rateChip rate// Data rateData rate

The system chip rate is constant; 3.84 Mcps (3840000 chips per second). Hence, as an example the Bearer having the bit rate 30 kb/s will have the Spreading Factor 128:

Assume that SNR = Eb/No is 3 dB, then

Users per TRX will be : 128/2 = 64Users per TRX will be : 128/2 = 64

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Designing for Load

RAB Coverage Unloaded

RAB Coverage High Load

Coverage shrinks with load due to cell breathing.

Coverage and capacity evaluation should be performed early in the design.

Capacity per sector is specified, then coverage is evaluated under corresponding load.

Coverage and capacity can be traded off.

• Large coverage footprint, low capacity.

• Smaller coverage footprint, high capacity.

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Transport Design

Design Criteria:Design Criteria:Up to 6 Node-Bs grouped into one cluster of a Sub-hubUp to 4 Sub-Hub clusters grouped into 1 hub.

STM-1 from Hub/Sub-Hub to RNC through media

Interfaces:Interfaces:End node-B: E1 interface.Sub-Hub: E1 interface southbound and STM-1 interface northbound.Hub: STM-1 interface.

RNC

Node

HubHub

Node Node

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3GPP (3rd Generation Partnership Project) release outline

3GPP Releases

• 3GPP Release 1999

• Release 4

• Release 5

• Future evolution with R6, R7..

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3GPP Releases - Time Schedule

1998 20011999 2000

3GPP Release 4

3GPP Release 1999

Q2Q1Q3 Q2 Q3Q4 Q4 Q1Q1 Q2 Q3 Q4Q4 Q3 Q1

1097 8542 3 11 121

3GPP TSGsPlenary Meetings

6

Q2

2002

1817 1916151413 222120 23

Q3 Q4 Q1 Q2 Q3 Q4 Q1

2003

3GPP Release 5

Versions of3GPP Release 1999

Versions of 3GPP Release 4

3GPP Release 6

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Core Network - Architecture and EvolutionCore Network - Architecture and Evolution

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How Does My Network Topology Look Today ?

SGSN

IP BackboneGGSN

SGSNGGSN

Internet

GPRS - Network Baseline

GSM - Network Baseline

BSC

BSC

GSM RAN

BSC

BSC

GSM RAN

TDM BackboneMSC MSC

HLR/AUC

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TDM/IP/ATM

How Would this look with WCDMA

SGSN

WCDMA Introduction

BSC

BSC

GSM RAN

BSC

BSC

GSM RAN

MSC MSC

GGSNSGSN

GGSN

Internet

MGw MGw

MSC-S MSC-S

RNC

RNC

WCDMA RAN

RNC

RNC

WCDMA RAN

HLR/AUC

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Soft switch Concept

Centralization & pooling of network control functions.

Payload uses shortest path & most efficient coding.

Free choice of Transport technologies.

Separate complex control & execution functions from service payload transport.

Layered Architecturenetwork

End-userapplications

Control

MSC-S HLR

GGSN

GMSC/Transit

SG

Connectivity

GSM/ EDGEAccess

WCDMAAccess

M-MGW M-MGW

InternetIntranet

PSTNISDN

SGSN

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What is Mobile Softswitch?

Classic MSC(control and switching)

MSC Server(Control)

Mobile Media Gateway (Switching)

Mobile Softswitch Solution Classic MSC Solution

MSC-S

MGW

MSC

TDM IP/ATM

Control Layer

Connectivity Layer

Classic circuit-switched network Layered Architecture network

MSC-S

MGW

MGW MGW

MGW

MGW

MSC MSC

MSC

MSCMSC

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Distributed switching, Local Switching

Main Site

Remote Site

MS12PSTN

BSC

PSTN

MS1

MS2

BSC

BSC

MS11

BSC

TDM

IP

M-MGw

MSC-S

M-MGw

MSS approach:Main Site

Remote Site

MS1

MS2

MS11

MS12PSTN

TDM

BSC

BSC

PSTN

Classical MSC approach:

BSC

BSC

MSC

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MSC Server

ApplicationServers

ApplicationService enablers

Services/applications

Control

Servers

Control

MSC HLR/AuC/FNR GMSC/Transit

ConnectivityMGWMGW

ServerServer

PSTN/ISDN

InternetIntranetsGGSNSGSN

SGW

User data

Main MSC Server functions

Service control

Mobility management

Charging control and CDR generation

Can control more than one MGWGSMEDGE

WCDMA

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Media Gateway

ApplicationServers

ApplicationService enablers

Services/applications

Control

Servers

Control

MSC HLR/AuC/FNR GMSC/Transit

ConnectivityMGWMGW

ServerServer

PSTN/ISDN

InternetIntranetsGGSNSGSN

SGW

User dataGSM

EDGEWCDMA

Main Media Gateway functions

Speech & media processing

Setup/release of user data bearers

Interfacing between different transport standards

Boundary between different networks

Can be controlled by several MSC Servers

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M-MGw Interfaces

MGW

HTTP, FTP,S-FTP, IIOP,

SSH,TELNET

ATM ATM IuUP, AAL2)

TDM Q.AAL2Q.AAL2

RANAP, 3GPP 24.008 BICC

O&M

ISUP

IP (NbUP, RTP)

BSSAP

TDM (A)

GCP

(GPS)Synch

M-MGw

-

(NbUP, I.trunk, AAL2)(

MSC/TSC Server

BSC

RNC

PSTNother networks

M-MGw

(Mc)

ATM, IP

IP

Positioning the M-MGw in the Network

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What is High Speed Downlink Packet Access (HSDPA)

STANDARDIZED Integral part of WCDMA (3GPP Release 5)

REDUCED DELAY Reduced round trip time

CAPACITY 2 – 3 times improved system throughput

SPEED Higher bit rates: up to 14 Mbps

Smooth Upgrade Short time to market with existing sites

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HSDPA Basic Principles

Shared Channel TransmissionDynamically shared in time & code

domain

Higher-order Modulation16QAM in complement to QPSK for

higher peak bit rates

2 ms

Short TTI (2 ms)Reduced round trip delay

Fast Hybrid ARQ with Soft Combining

Reduced round trip delay

Fast Radio Channel Dependent Scheduling

Scheduling of users on 2 ms time basis

Fast Link AdaptationData rate adapted to radio

conditions on 2 ms time basis

t

P

Dynamic Power AllocationEfficient power &

spectrum utilisation

Let´s be ready….Let´s be ready….