Telecom Fundamentals2

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Copyright 2003 P K Divakara

IS 95 CDMA ArchitectureIS 95 CDMA Architecture

P K Divakaran


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Copyright 2003 P K Divakaran

IS 95 System ArchitectureIS 95 System Architecture

BSC/MS

BTS

MSC

Base Station (BS)

HLR

VLR

AC

PSTN


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IS 95 System ArchitectureIS 95 System Architecture

HLR

Subscriber informationESN

Mobile Directory Number ( similar to MSISDN in

GSM)

IMSI

User profiles

Current Location


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IS 95 CDMA ArchitectureIS 95 CDMA Architecture

BSC/Transcoder

(XC)

MSC

TS BTS

XC performs Transcoding of PCM

coding to CDMA voice coding andvice versa

P

S

T

N

During Soft Handoff multiple BTSs

forwards speech/ data frame to XC

from MS. XC selects the best fromReverse channels. In Forward

Direction it distributes traffic to all

BTSs involved in Soft handoff


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Copyright 2003 P K Divakara

CDMA IS 95 Traffic casesCDMA IS 95 Traffic cases

P K Divakaran


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Mobile RegistrationMobile Registration

What is Mobile Registration?

It is the process by which mobile stations

make their locations and other particulars

known to the Cellular system

Location Registration enables the System to

page a mobile in a particular area instead ofpaging the entire network.


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Types of RegistrationTypes of Registration

Different types of Registrations are specifiedin IS 95. The Operator has flexibility to

choose depending on system size & otherconsiderations.

The types of Registrations that are enabledare communicated to the mobiles in thePaging channels


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Autonomous Registration (inititated by

mobile)

1. Power up RegistrationWhen power is switched on

2. Power down Registration

When power is switched off


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(Autonomous)(Autonomous)3.Timer based Registration

To avoid paging mobiles which did not perform

a successful Power down registration, Timerbased registration is enforced. If mobile fails to

register as per this, it is deregistered.

4.Zone based Registration Zones are groups of Base stations . Whenever

the mobile enters a new Zone, it registers


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(Autonomous)(Autonomous)Distance based Registration

Registration after the mobile has moved a

certain distance ( as determined by the Latitude& Longitudes of the Base stations ). Used in the

case of an environment where most mobiles are

fairly static and a small number mobile. Rather

than forcing Timer based registrations for all

mobiles to register, only those mobiles moving

beyond a certain distance only need to register


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Ordered Registration The cellular system may become aware of a mobile

within the network for which it doesnot have all the

info to connect a call (following a call origination frommobile). In this case the System orders a Registration

by mobile

Implicit Registration

When a mobile successfully sends an originationmessage or responds to paging message, it conveyssufficient info for the Base station to infer its location .This is Implicit registration


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Parameter change Registration Certain parameters in the mobile station affects

the delivery of call to it and therefore should beupdated in the system whenever there is achange.

Traffic channel registration

The method in which mobile receivesregistration related information while on trafficchannel.An instance is inter System Handoffs


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AuthenticationAuthentication

Authentication is the process of verifying that

a mobile trying to access the Network is not

a fraudulent one


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Authentication ParametersAuthentication Parameters

A Key

64 bit secret number used by mobile and the

Authentication Centre (AC) Stored in the mobiles permanent security and

identification memory and AC


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Shared Secret Data (SSD) A 128 bit secret temporary key calculated

and stored in mobile and the Network using:A keyESNRandom Number (RAND)

SSD comprises of SSD A and SSD B SSD A used for Authentication

SSD B used for encryption


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RAND Random Number generated by the Network

The essence of Authenticationconfidentiality is that A key is never

transmitted on air interface. Only thecomputed results are exchanged andcompared at MS and Network for a decision


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Hand offHand off

Types

Idle State Handoff Initiated by mobileAlways Hard Hand off

Traffic State Handoff

Soft Hand offHard Handoff


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Soft Hand offSoft Hand off

Process of establishing a link with a targetcell before breaking the link with the

serving cellPrime requirement--- Both cells to be on

same frequency

Mobile and Network are involved in theprocess ( Mobile assisted)


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Soft Hand offSoft Hand off

Mobiles search for Pilot frequencies on the

current frequency to identify candidate cells

for hand off.Each Pilot has the same PN code but with a

different time offset (n X 64 chips delay)

for Base station identification


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Soft Hand off ProcessSoft Hand off Process

MS BSC/BTS

Pilot Strength measurement Message (PSMM)

Handoff Direction Message (HDM)

Includes Forward Traffic ch. Assignment in new

cellMS demodulatesNew Traffic ch.

Handoff Completion Message (HCM)


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Benefits of Soft HandoverBenefits of Soft Handover

Path Diversity in Forward & Reverse

Channels

Hence less power is required in each

channel

Hence less interference and improved

capacityLess power means longer battery life of MS


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Hard HandoffHard Handoff

Connection with the old traffic channel is

broken before connection with new is

established. Possible reasons: Base stations have different frequency Carriers

Change from one Pilot to another Pilot without

first being in soft handoff with the newPilot(disjoint cell)


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IS 95 Call Origination fromIS 95 Call Origination from

MSMSMS BTS BSC MSC/HLR/AC

originationAccess channel

origination

Subscrib

validatioOrigination ack.Traffic ch

Assignment (Page ch)

Acquires Traffic

ch Reverse TrafficCh. Preamble

Speech path set up PSTNCall set


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IS 95 Call Termination to MSIS 95 Call Termination to MSMS BTS BSC MSC

PSTIncoming callPage requestPage MS

(Paging ch)

Page response

(Access ch)Page response

Call treatmentTraffic ch. Assign

ment ( Paging ch)

cquiresTfc ch. Reverse Tfc ch

PreambleConnection & Speech path set up

Alert


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ROAMINGROAMINGHLRHome MSCVLRVisited MSCBaseStation

MS

SS7 IAM

From PSTN

SS7 IAM- Signalling

System No.7, Initial

Address Message

QueryMS Location

MS location

infoCall Forwarding

SS7 IAMNormal call

Processing.

Call termination

To MS


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CDMA 2000CDMA 2000

CDMA 2000 Radio Transmission

Technology (RTT) is a spread spectrum

Radio interface to satisfy the needs of 3Gwireless systems

It is as per the IMT 2000 (International

Mobile Telecommunications 2000)standards of ITU ( International

Telecommunication Union)


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CDMA 2000CDMA 2000

Naming Conventions

3G1x RTT = 3rd Generation 1x 1.25 Mhz

carrier

3G 3x RTT = 3rd Generation 3x 1.25 Mhz

carrier ( total bandwidth 5 Mhz )


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Enhancements in Cdma 2000Enhancements in Cdma 2000

Backward compatibility with IS 95

144 kbps peak data rate in Phase 1 of Cdma

2000 (Cdma 2000 1x)2 Mbps data for fixed applications in Phase

2 (Cdma 2000 3x)

More channels in forward and Reversedirections

Pilot in the Reverse direction from Mobile


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Enhancements in Cdma 2000Enhancements in Cdma 2000

Walsh codes in Reverse link also

Variable Walsh code length upto 128 bits

Faster Power control in Forward direction


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Advantages of Cdma 2000Advantages of Cdma 2000

Almost twice the capacity of IS 95.

Higher Data Rates

Migration to 3G

Lower power mobiles and longer battery

life

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