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IS 95 CDMA ArchitectureIS 95 CDMA Architecture
P K Divakaran
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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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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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Types of RegistrationTypes of Registration
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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Types of RegistrationTypes of Registration
(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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Types of RegistrationTypes of Registration
(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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Types of RegistrationTypes of Registration
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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Types of RegistrationTypes of Registration
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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Authentication ParametersAuthentication Parameters
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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Authentication ParametersAuthentication Parameters
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