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Wireless Networks3

CDMA, 3G and WiMAX

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Introduction to WiMAX

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Wireless Broadband

Wireless technologies

Proliferating in a major way into the first mile (computers) or the

last mile subscriber access(communication)

This technologies are generally called as Wireless LocalLoop(WLL) or Wireless in Local Loop(WiLL)

Wireless Local Loop

Known as fixed-wireless system

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Background Today world is moving towards a convergence of voice, data

and video

IEEE 802 committee set up the 802.16 working group to

develop wireless broadband or wireless MAN standards WirelessMAN

Offers an alternative to high bandwidth wired access network like

fiber optic, cable modems and DSL

Popularly known as WiMAX(Worldwide Interoperability forMicrowave Access)

Provides wireless transmission of data using a variety of transmission modes

from point-to-multipoint links to portable and fully mobile Internet access

Provides around 10Mbps bandwidth without the need for cables

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WiMAX Deployment Architecture

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Release of 802.16 standards in April 2002 has paved way for

the entry of broadband wireless access as a new bearer to

link home and business with core telecommunication

networks WirelessMAN

Facilitates network access to buildings through exterior

antennas communicating with radio base stations

Provides less expensive access with more ubiquitous broadbandaccess

Integrates data, voice and video services

Fast network deployment, using a small number of base stations

on buildings / poles

Can grow as the demand increases

At any point of time the number of active users are always a

fraction of the number of subscribers

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3 working groups of 802.16 standard

IEEE 802.16.1Air interface for 1066 GHz

IEEE 802.16.2Coexistence of broadband wireless access

systems

IEEE 802.16.3Air interface for licensed frequency 2 to11 GHz

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802.16 standard - layered architecture

Organized into 3 layered architecture

Physical layer

Specifies the frequency band

Modulation scheme Error correction techniques

Synchronization between transmitter and receiver

Data rate and the multiplexing structure

MAC layer Responsible for transmitting data in frames and controlling access to

the shared wireless medium through MAC layer

MAC protocol defines how and when a base station or subscriber

station may initiate transmission on the channel

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Convergence Layer

Provides functions specific to the service being provided

IEEE 802.16 bearer services include digital audio / video multicast,

digital telephony, ATM, Internet access, wireless trunks in

telephone networks and frame relay

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CS SAP

MAC SAP

PHY SAP

Frame Relay

IPTelephone ATM Multimedia

Outside WiMAX

Standards

Service-Specific Convergence Sublayer (CS)

MAC Common Part Sublayer (MAC CPS)

Physical Layer (PHY)

MAC

PHY

Within

WiMAX

Standards

WiMAX Protocol Stack

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Physical Layer

802.16 standards specifies 3 physical layers:

WirelessMAN-SC2This uses single carrier modulation format

Supports existing networks and protocols

WirlessMAN-OFDMThis uses orthogonal frequency-divisionmultiplexing with a 256-point transform

Access is by TDMA

Air interface is mandatory for license-exempt bands

WirelessMAN-OFDMAThis uses orthogonal frequency-division multiple access with a 2048-point transform

Multiple access is provided by addressing a sub-set of the multiple carriers

to individual receivers

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802.16 Medium Access Control

Designed for point-to-multipoint broadband wireless access

It addresses the need for very high bit rates (both uplink to base

station & downlinkfrom the base station)

Supports variety of services like multimedia and voice Accommodates both continuous and bursty traffic

Facilitates more demanding physical environment and different

service requirements of the frequencies between 2 and 11GHz

The 802.16 project is upgrading the MAC to provide automaticrepeat request (ARQ) and support for mesh

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Broadband Applications

Wireless broadband allows higher data rates in home,

offices and even mobile environment

Includes standard Ethernet LAN or WiFi indoor using

802.16d and outdoor mobile using 802.16e Introduced

IEEE 802.16 Broadband Wireless Metropolitan Area Network

Standards

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Broadband Mobile Cellular System

In mobile cellular system, the cellular network itself will be

mobile

Cellular system like 3G provides a high data rate

WirelessMAN has also geared up to support high data rate

High data rates are possible with low speed mobility

High speed mobility is still in its infancy, specially designed

for high-speed telematics application

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MOBILE BROADBANDCOMMUNICATION SYSTEM

WITH MOVING BTS

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The above diagram depicts mobile communication system

to support high-speed mobility, this is achieved by installing

Moving base stations

Fixed radio ports uniformly distributed along the median of theroadway

The moving base stations allow communication links to be

established between the mobile units traveling on the roadway

and a fixed communication network through the fixed radio ports The small-cell (picocell) architecture of the proposed system

enables the use of extremely lightweight low-power mobile units

that can be used almost anywhere

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The picocell here will move in the direction of the moving vehicle

so that the relative speed between them is low

This proposed infrastructure is suitable for high speed multilane

highways in cities, facilitating communication to devices traveling

at a speed up to 150kmph

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MOVING TO 3G

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Introduction

The world of telecommunications is changing as it is

influenced by

Trends in media convergence

Industry consolidation Perception of mobile phones has changed significantly over

the last few years and more changes predicted in future

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Changes predicted in future are:

Mobile device will be used as integral part of our lives

Data usage of 3G will become important and different from the

traditional voice business

The look of the phone will be as important as usage

A great deal of convergence will take place between information

and communication technology

Mobile communications will be similar to its social positioning,

people will have only a mobile device

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To address these challenges and opportunities, the mobile

telecommunication technology needs to adapt new

techniques, facilities and services

The 3G system will offer lot of telecommunication services

like voice, multimedia, video and high speed data

CDMA is the preferred approach for the 3G networks and

systems cdma2000 standards are being driven by

Telecommunication Industries Association (TIA)

CDMA uses air interface, which is based on IS-95 andcdmaOne

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Japan 3G standards users Wideband Code Division

Multiple Access (WCDMA) (DoCoMo) version

In Europe, Asia, Australia and many other parts f the world

of 3G has been accepted as Universal MobileTelecommunications System(UMTS) and WCDMA

UMTS / WCDMA is being driven by ETSI and is the

normal evolution of GSM / GPRS

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Goal of UMTS

Provide more attractive and richer services to the user

Universal Roamingany user will be able to move across the

world and access the network

Higher Bit Ratemore speed would open the path towardsmultimedia applications

Mobile Fixed Convergencethere is a need to offer user cross-

domain services

Flexible Service Architectureby standardizing no the servicesthemselves, but the building blocks that make up the services

l b l l

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International Mobile Telecommunications- 2000

(IMT- 2000)

IMT- 2000

Is the global standard for third generation (3G) wireless

communication

Defined by a set of interdependent ITU Recommendations Provides a framework for worldwide access of services by linking the

diverse systems of terrestrial and / or satellite based networks

through the synergy between digital mobile telecommunications

technologies and systems for fixed and mobile wireless access systems It was originally envisioned to be launched in the year 2000 with a

bandwidth of 2000K

Popularly known as 3G - includes EDGE, CDMA 2000, UMTS,

DECT and WiMAX standards

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Evolution beyond IMT-2000 and towards 4G

3GPP and 3GPP2 are researching on extensions of current

3G standards

Long Term Evolution (LTE)

Ultra Mobile Broadband Technologies would be fully based on an all-IP network

infrastructure

They are moving towards IMT-Advanced (4G) standards

These standards fall short of the speed requirements for 4G

Standards here are classified as 3.9G or Pre-4G

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CDMA - 2000

cdma2000 is the third generation version of cdmaOne / IS-95 Uses Radio Transmission Technology (RTT)

Is a spread spectrum, wideband radio interface

Uses CDMA technology as the underlying modulation technology and

IMT-2000

Addresses the specification for indoor, indoor-to-outdoor,

pedestrian and vehicular environment

Can operate in a wide range if environments like

Indoor / Outdoor picocell (35Km radius)

Wireless in Local Loop(WLL)

M l i i d Di S d i

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Multicarrier and Direct Spread in

cdma2000

Supports chip rates of N x 1.2288Mcps (where N=1,3,6,9,12) N=1 spreading is similar to IS-95

For N>1, if N=3 it is Multicarrier and Direct Spread (see figure)

Case Multicarrier

N>1

The modulation symbols are demultiplexed on to N separate 1.25MHz

carriers where N=3, 6, 9, 12

Each of these carriers is then spread with 1.2288 M chips Case Direct Spread

N>1

Modulation symbols are spread on a single carrier with a chip rate of

Nx1.2288 M chips where N=3,6,9,12

M l i i d Di S d

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Multicarrier and Direct Spread

Spectrum in cdma2000

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Services

Two types of data services under consideration in

cdma2000

Packet data

Used for asymetric, bursty traffic like Internet browsing / mails Circuit switched data

Used for delay sensitive real time traffic

Video applications are potential candidates

Needs dedicated channel for the duration of the call

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UMTS / WCDMA

Standard body for ETSI for 3G is called UMTS and 3GPP

Some of the CDMA encoding techniques are patented by

Qualcomm

To resolve copyright issuesget different flavors of CDMA ETSI in Europe

ARIB in Japan

Called as Wideband CDMA or WCDMA

WCDMA

Also known as UMTS Terrestrial Radio Access Network (UTRAN) FDD

(Frequency Division Duplex)

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Fixed Wireless

3G is commonly associated with mobile phones

3G specification includes the fixed wireless

Currently we use separate links for data and voice

A fixed wireless will make it only one common link

The IMT-2000 specification makes specific provision for 3G

Fixed Wireless Access (FWA)

FWA Is expected to become the mainstream technology in emerging

economies across the globe

In developed countries 3G residential wireless represents a new

horizon for competitive access providers

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1.5 Mbps2Mbps data to home

In India

Some operators are using CDMA 1X technology for WiLL

Offers both mobile and fixed phones Fixed phone line are example of fixed wireless access

Fixed wireless 3G is converged, multimedia-driven technology

3G utilizes point-to-multipoint network architecture

Transmit data and voice simultaneously at high speeds across core wirelessinfrastructure

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Application of 3G

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Background

3G can work in multiple ways

Can run in tunneling mode or in an application mode

Tunneling mode

Device works more as a pass through device or a modem

Mobile phone is connected to another device like a laptop and

functions as a wireless media interface

Here the intelligence of the phone is not used but only the

communication interface of the phone is used

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Application mode

Runs on phone

A 3G mobile phone supports SMS, WAP, Java etc.

A MExE classmark 3 mobile devicewill have an executionenvironment that will allow application development for the

client device

The application platform can be Java (JavaPhone, PersonalJava,

J2ME, JVM) , C / C++ (Symbian, Brew, or PalmOS) or VisualBasic(Windows CE)

Wireless Telephony Application Interface (WTAI) can also be

used in a WAP environment to access the telephone reosurce

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Types of client applications in 3G

Local Applications Games, cartoon and similar applications

May be downloaded over the air and used offline

Occasionally Connected Computing Environment The user will connect to the network occasionally

Downloading and uploading of emails are the best example here

Online Applications

Corporate applications like order booking, updating of inventory status

Real-time Applications

Could be real-time sock updates or applications for law-enforcement

agents for real-time tracking or navigational systems

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3G Specific Applications

Personal Applications

Content Applications

Communication Applications

Productivity Applications

Business Applications

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New and specific to 3G are

Virtual Home Environment (VHE)

Personal Communication Networks (PCN)

Universal Subscriber Identity Module (USIM)

Audio / Video

Voice over Internet Protocol (VoIP / Voice over Packet

Network)

Electronic Agents Downloading of Software and Content

ENUMprotocol emerging from work of Internet

Engineering TaskForces Telephone Number

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CDMA

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SPREAD SPECTRUM TECHNOLOGY

Conventional transmission system

Information modulated with a carrier signal

Transmitted through a medium

When transmitted, all the power of the signal is transmittedcentered around a particular frequency

This frequency represents a specific channel and generally has a

very narrow band

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Narrow Band and Spread Spectrum

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In spread-spectrum the transmission signal bandwidth is

much higher than the information bandwidth

There are numerous ways to cause a carrier to spread

All spread-spectrum systems can be viewed as two stepsmodulation processes

Firstdata to be transmitted is modulated

Secondcarrier is modulated by the spreading code, causing it to

spread out over a large bandwidth

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Different spread spectrum techniques

Direct Sequence (DS)

Spread spectrum used to transmit digital information

Mix digital information stream with a pseudo random code

Frequency Hoping (FH) Center frequency of a conventional carrier is altered many times

within a fixed time period in accordance with a pseudo-random

lists of channels

Chrip Called as chrip spread spectrum

Employs a carrier that is swept over a range of frequencies

Application in ranging and radar system

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Time Hopping Works in a timehopped signal

The carrier is on-off keyed by the pseudo-noise (PN) sequence

resulting in a very low duty cycle

The speed of keying determines the amount of signal spreading

Hybrid System

Combines the best points of two or more spread spectrum systems

The performance of this system is usually better than can be obtainedwith a single spread-spectrum technique for the same cost

The most common hybrids combine both frequency-hopping and

direct-sequence techniques

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Amateurs and business community

Are currently authorized to use only two spreading techniques

FH and DS techniques

Rest of the Spread-Spectrum technologies are classified andused by military and space sciences

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IS-95

Telecommunications Industry Associations (TIA)

developed the IS-95 standard

Standard formed the basis for the first CDMA systems

deployed in the cellular band in North America The IS-95 family of standards is known as cdmaOne

It is a second generation digital mobile communication

system

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Speech and Channel Coding Audio basics

The normal audio range of human being is between 20Hz to 20KHz

This range is normally used for high fidelity CD quality music

In case of telephonic communications where generally human voice is

used, the frequency range of 3003300Hz is sufficient

For digitization the speech it is sufficient to sample at 8000 samples

per second (assuming a bandwidth of up to 4000 Hz)

Thus for any telephonic quality speech, 12 bits are sufficient to encode

each sample

By logarithmic sampling 12 bits can be reduced to 8 bits per sample

This results in the PCM encoding of the speech and digitization of

the voice at 64Kbps

This digitized voice is then passed through a coding scheme using

Code-Excited Linear Prediction (CELP) algorithm

Case of mobile telecommunication

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Case of mobile telecommunication

environment

Signal strength varies with location and movement of themobile transmitter / receiver

Signal strength influence error ratewhich affects the quality

of communication

Due to varying signal strengths, the mobile

telecommunications system are susceptible to burst errors

What is burst error?

Grouping of errors in adjacent bits as compared to errors that aredispersed over the whole data block

IS-95 addresses the problem of burst errors by utilizing and

error correction scheme based on encoding and interleaving

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IS-95 Architecture

Similar to the network elements within a GSM network cdmaOne / IS-95 uses CDMA for its radio or last mile

communication

Varies only in the radio interface

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Main elements of the reference model are: Mobile Station (MS)

Base Station (BS)

Mobile Switching Center (MSC)

Home Location Register(HLR)

Data Message Handler (DMH)

Virtual Location Register (VLR)

Authentication Center (AC)

Equipment Identity Register (EIR) Operations Systems (OS)

Interworking Function(IWF)

External Networks

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The IS-95 Architecture Model

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Important Components

Data Message Handler (DMH) Responsible for collating the billing data

Equipment Identity Register (EIR)

Provides information about the mobile device for record purposes

The EIR may be located with the MSC or may be located independent

of it

Operating System (OS)

Responsible for overall management of the wireless network Internetworking Functions (IWF)

Enables the MSCE to communicate with other networks

External Networks (PSTN)

An ISDN, PLMN or PSPDN

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IS-95 Channel Structure

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About Channel Structure

IS-95 system operates on the same frequency band as the first generationAMPS

It uses FDD with 25MHz in each direction

Uses 824849MHz for forward link

In digital communication, one data path maps on to one communicationchannel

In FDMA system one channel occupies a distinct frequency band

In TDMA, it is a distinct timeslot within a frequency

In CDMA, a channel is defined in terms of a code sequence and

frequency

This results in offering a higher channel capacity, which translates into an

overall higher bandwidth

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IS-95 uses

Different modulation and spreading technique for forward and

reverse link

Forward link uses 64 Walsh codes to maps 64 logical

channels

The base station simultaneously transmits the user data for all

mobiles in the cell by using different Walsh codes for each mobile

This is spread using a PN (pseudonoise)of length 215 chips

The user data is spread to a channel chip rate of 1.2288Mchips

On the reverse link, channels are identified by long PN sequence

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For forward channels Base stations transmit information in 4 logical channel formats

Pilot channels

Sync channels

Paging channels (PCH) Traffic channels(Code)

On the reverse link, all mobiles respond in an asynchronous fashion

The user data is encoded, interleaved and then blocks of 6 bits are

mapped to one of the 64 orthogonal Walsh functions Finally the data is spread by a user specific code of 42 bits

The reverse channel is organized in access and traffic channels

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Pilot Channel

The pilot CDMA signal transmitted by a base station provides a

reference to all mobile stations

Assigned a Walsh code of p W0

The pilot signal level for all base stations is kept at 46dB, so that

the MS at the cell boundaries should be able to receive the pilot

signal from other cells to decide when to perform handoff

The pilot signals from all base stations use the same PN sequences,

but each base station is identified by a unique tone offset

These offsets are in increments of 64 chips to provide 512 unique

offsets

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Sync Channel

Is assigned the Walsh function W32

Is used with the pilot channel to acquire initial time

synchronization

W32 has a pattern of 32 consecutive 0s and 32s

Parameters of Sync channel are

System Identification (SID)

Network Identification (NID)

Pilot short PN sequence offset index

Long-code state

System time

Offset of local time

Daylight saving time indicator and Paging Channel data

Paging Channel

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Paging Channel

Up to 7 paging channels which transmits control information to the

terminals that do not have calls in progress

The paging channels are assigned the Walsh functions W1 to W7 Message carried by paging channel include:

System Parameter Messagelike base station identifier, the number of

paging channels and channel number

Neighbor List Messageinformation about neighbor base stationparameter, like the PN offset

Access Parameter Messageparameters required by the mobile to

transmit on an access channel

Page Messageprovides a page to the mobile station

Channel Assignment Messageto inform the mobile station to tune toa new carrier frequency

Data Burst Messagedata message sent by the base station to the mobile

Authentication Challengeallows the base station to validate the

mobile identity

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Role of Access Channel

Used by a terminal without a call in progress

Sends message to the base station for three principal purposes

To originate a call

To respond to a paging messages

To register its location

Each base station information operates with up to 32 access

channels

The messages carried by the access channel include:

Order message, registration message, data burst message,

originate message, authentication challenge response message

IS-95 Forward and Reverse Link

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S 95 o wa a eve se

Channel Structures

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IS-95 Call Processing

To set up a call or to transmit data, a data path needs to be

established through a traffic channel

To establish a traffic channel, a mobile station in IS-95 goes

through several states like: System initialization

System idle state

System access

Traffic channel state

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Phases in details

In system initialization state the mobile acquires a pilot channel bysearching all the PN offset and selects the strongest pilot (W0) signal

Once the pilot is acquires the sync channel is acquired using the W32

Walsh function and the detected pilot channel

Then the mobile obtains the system configuration and the timing

information

Then the mobile enter the system idle state where it monitors the

paging channel

If a call is being places or received the mobile enters the system access state

where the necessary parameters are exchanged The mobile transmits its response on the access channel and the base

station transmits its response on the paging channel

When the access attempts is successful the mobile enter the traffic state

In the traffic state voice or data is transcated

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CDMA Registration

The registration process is used by the mobile device to

notify its location, status, identification and other

characteristics

Location information is required to page the mobile for anincoming mobile terminated call

When the MS does power on or power off it goes through

the registration process as well, and the registration

information is stored in HLR

These functions are similar to GSM

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Handoff and Roaming

A handover in GSM is called a handoff in IS-95

When a subscriber moves away from a base station, the

signal power reducesdrop in connection

Ensuring call does not breaksome other base station closeto the mobile station needs to attach the mobile to it and let

the call continue without interruption

Handover in GSM is hard handover

The attachment with the current cell is broken first and then a

new connection is setup with another cell

Thus in GSM it is break before make

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Handoff in CDMA

Spectrum is spread and everybody gets the same signal

Logically a mobile station in CDMA is always connected to

different base stations at the same time

Handoff here is managed by changing the attachment Three types of handoffs

Soft handoff

Hard handoff

Softer handoff

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Soft and Softer Handoff

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Soft Handoff

Is an intercell handoff Control of a mobile station is assigned to an adjacent sector

or an adjacent cell without dropping the original radio link

The mobile keeps two radio links during the soft handoff process

Once the new communication link is well established the

original link is dropped

This process is called as make before break thisguarantees no loss of voice during handoff

In the above diagram as the user moves, a soft handoff takes

place from cell B to cell A

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Hard Handoff

This is case of interfrequency handoffs

CDMA to CDMA hard handoff is the process in which a

mobile is directed to handoff to a different frequency

assigned to an adjacent cell or a sector The mobile drops the original link before establishing the

new link

Similar to a GSM handover

The voice is muted momentarily during this process

This handoff is completely fast and cannot be noticed

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Softer Handoff

A mobile communicates with two sectors of the same cell

A rake receiver at the base station combines the best

version of the voice frame from the diversity antennas of

the two sectors into a single traffic frame This is a logical handoff where signal from multiple sectors

are combined instead of switching from one sector to

another

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IS -95 Channel Capacity

The channel capacity of CDMA system depends on thefollowing criteria:

Voice Activity Detection

Sectorization for Capacity Frequency Reuse Considerations

Note: The CDMA capacity is about four times that of TDMA and eight tomes

that of FDMA

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CDMA versus GSM

GSM

Relatively mature technology

Huge installation base

Experienced operators and equipment manufacturers Interoperability is well proven

Complete, open and has proven standards

Includes all the specifications from the handset other via the air,

switch, interconnect it with switching and every aspect of mobiletelecommunication

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IS-95

Mainly single vendor(Qualcomm cdmaOne) specification

Covers the air interface making it incomplete

CDMA is generally believed to have high potential to addresssome the difficult challenges of the past quite efficiently

(Check the table in next slide)

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GSM versus 3G

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CDMA DATA PROTOCOL STACK