Is 95 Cdma Architecture

IS 95 CDMA Architecture

P K Divakaran

Copyright 2003 P K Divakaran

MS

IS 95 System Architecture Base Station (BS) BTS

HLR

BSC/ MSC

PSTN Copyright 2003 P K Divakaran

VLR

AC

IS 95 System Architecture  HLR – Subscriber information  ESN  Mobile Directory Number ( similar to MSISDN in GSM)  IMSI  User profiles – Current Location Copyright 2003 P K Divakaran

BTS

IS 95 CDMA Architecture MSC

BSC/

P S T N

Transcoder (XC) BTS

•XC performs Transcoding of PCM coding to CDMA voice coding and vice versa •During Soft Handoff multiple BTSs forwards speech/ data frame to XC from MS. XC selects the best from Reverse channels. In Forward Direction it distributes traffic to all BTSs involved in Soft handoff

Copyright 2003 P K Divakaran

CDMA IS 95 Traffic cases

P K Divakaran

Copyright 2003 P K Divakaran

Mobile 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 of paging the entire network. Copyright 2003 P K Divakaran

Types of Registration Different types of Registrations are specified in IS 95. The Operator has flexibility to choose depending on system size & other considerations.  The

types of Registrations that are enabled are communicated to the mobiles in the Paging channels Copyright 2003 P K Divakaran

Types of Registration  Autonomous

Registration (inititated by

mobile) – 1. Power up Registration  When power is switched on – 2. Power down Registration 

When power is switched off

Copyright 2003 P K Divakaran

Types of Registration (Autonomous)  3.Timer

based Registration

– To avoid paging mobiles which did not perform

a successful Power down registration, Timer based 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 Copyright 2003 P K Divakaran

Types of Registration (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 Copyright 2003 P K Divakaran

Types 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 from mobile). In this case the System orders a Registration by mobile

 Implicit

Registration

– When a mobile successfully sends an origination

message or responds to paging message, it conveys sufficient info for the Base station to infer its location . This is Implicit registration Copyright 2003 P K Divakaran

Types of Registration  Parameter

change Registration

– Certain parameters in the mobile station affects

the delivery of call to it and therefore should be updated in the system whenever there is a change.

 Traffic

channel registration

– The method in which mobile receives

registration related information while on traffic channel.An instance is inter System Handoffs Copyright 2003 P K Divakaran

Authentication Authentication is the process of verifying that a mobile trying to access the Network is not a fraudulent one

Copyright 2003 P K Divakaran

Authentication 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

Copyright 2003 P K Divakaran

Authentication Parameters  Shared

Secret Data (SSD)

– A 128 bit secret “temporary key” calculated

and stored in mobile and the Network using: A key  ESN  Random Number (RAND) 

 SSD

comprises of SSD A and SSD B

– SSD A used for Authentication – SSD B used for encryption Copyright 2003 P K Divakaran

Authentication Parameters  RAND – Random Number generated by the Network

 The

essence of Authentication confidentiality is that “A “ key is never transmitted on air interface. Only the computed results are exchanged and compared at MS and Network for a decision Copyright 2003 P K Divakaran

Hand off  Types – Idle State Handoff  Initiated by mobile  Always Hard Hand off – Traffic State Handoff Soft Hand off  Hard Handoff 

Copyright 2003 P K Divakaran

Soft Hand off  Process

of establishing a link with a target cell before breaking the link with the serving cell  Prime requirement--- Both cells to be on same frequency  Mobile

and Network are involved in the process ( Mobile assisted) Copyright 2003 P K Divakaran

Soft 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

Copyright 2003 P K Divakaran

Soft Hand off Process MS

BSC/BTS Pilot Strength measurement Message (PSMM) Handoff Direction Message (HDM)

Includes Forward Traffic ch. Assignment in new cell MS demodulates New Traffic ch. Handoff Completion Message (HCM) Copyright 2003 P K Divakaran

Benefits of Soft Handover  Path

Diversity in Forward & Reverse Channels  Hence less power is required in each channel  Hence less “interference” and improved capacity  Less power means longer battery life of MS Copyright 2003 P K Divakaran

Hard 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 new Pilot(disjoint cell)

Copyright 2003 P K Divakaran

IS 95 Call Origination from MS BTS BSC MSC/ MS origination Access channel

origination

Traffic ch Assignment (Page ch) Acquires Traffic ch Reverse Traffic Ch. Preamble

Origination ack.

Speech path set up

Copyright 2003 P K Divakaran

HLR/AC

Subscribe validation

PSTN Call set u

IS 95 Call Termination to MS BTS

MS Page MS (Paging ch)

BSC Page request

Incoming call

Page response Page response (Access ch) Traffic ch. Assign Call treatment ment ( Paging ch) Acquires Tfc ch. Reverse Tfc ch Connection & Speech path set up Preamble Alert Copyright 2003 P K Divakaran

MSC PSTN

MS Base Station

ROAMING Visited MSC VLR

Call Forwarding SS7 IAM Normal call Processing. Call termination To MS

Home MSC

HLR From PSTN SS7 IAM

Query MS Location MS location info

Copyright 2003 P K Divakaran

SS7 IAM- Signalling System No.7, Initial Address Message

CDMA 2000  CDMA

2000 Radio Transmission Technology (RTT) is a spread spectrum Radio interface to satisfy the needs of 3G wireless systems  It is as per the IMT 2000 (International Mobile Telecommunications 2000) standards of ITU ( International Telecommunication Union) Copyright 2003 P K Divakaran

CDMA 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 )

Copyright 2003 P K Divakaran

Enhancements 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 Reverse directions  Pilot in the Reverse direction from Mobile Copyright 2003 P K Divakaran

Enhancements in Cdma 2000  Walsh

codes in Reverse link also  Variable Walsh code length upto 128 bits  Faster Power control in Forward direction

Copyright 2003 P K Divakaran

Advantages of Cdma 2000  Almost

twice the capacity of IS 95.  Higher Data Rates  Migration to 3G  Lower power mobiles and longer battery life

Copyright 2003 P K Divakaran