cdma and 3g
TRANSCRIPT
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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