Wireless networks - Lecture 24: CDMA2000

Wireless networks - Lecture 24: CDMA2000. The main topics covered in this chapter include: cdma2000 introduction; new MAC and Physical layer features; physical layer of cdma2000; reverse Physical channels; new network elements in cdma2000; mobility management; handoff;...

Wireless Networks

Lecture 24 CDMA2000

Dr Ghalib A Shah

 Last lecture review

 Cdma2000 introduction

 New MAC and Physical layer features

 Physical layer of cdma2000

 Reverse Physical channels

 New Network elements in cdma2000

► Packet Control Function (PCF)

► Packet Data Serving Node (PDSN)

Last Lecture review

 Compressed mode measurements

 Handover measurements

► Intra-mode

► Inter-mode

► Inter-system

 WCDMA packet data access

 Transport channels for packet data

► Common, dedicated, shared

 Packet scheduling algorithms

► Time division scheduling

CDMA2000 Introduction

 Provides seamless and evolutionary upgrade path for

2G and 2.5G cdma technology.

 Centers on original 1.25 MHz radio channel

 CDMA operators may seamlessly and selectively

upgrade without changing entire BS equipment

 The first 3G cdma standard cdma2000 1xRTT using

single channel (1x => multi-carrier)

► Supports data rate up to 307 kbps in packet mode

► Can support up to twice as many users as 2G cdma

► Cdma 1xEV-DO dedicates the channel strictly to data user and

 Cdma2000 3xRTT

► The ultimate 3G solution relies upon multicarrier that

gang adjacent channels together into 3.75 MHz.

► Three non-adjacent channels may be operated

simultaneously and in parallel.

► Data rate in excess of 2 Mbps similar when

compared to W-CDMA

 Advocates of cdma2000 claim their standard

much more seamless and less expensive

upgrade path when compared to W-CDMA.

Power control frequency  1500 Hz  800 Hz 

Variable data rate implement.  Variable SF; multi code  Repet., puncturing, multi code  Frame duration  10 ms  20 ms (also 5, 30, 40) 

Coding  Turbo and convolutional  Turbo and convolutional 

Base stations synchronized?  Asynchronous  Synchronous 

Base station acquisition/detect  3 step; slot, frame,  code  Time shifted PN correlation  Forward link pilot  TDM dedicated pilot  CDM common pilot 

Antenna beam forming  TDM dedicated pilot  Auxiliary pilot 

 The new physical and MAC layer features and

techniques

► Link adaptation based on adaptive modulation,

coding and spreading

► Physical layer fast hybrid ARQ

► Enhanced channel coding and turbo codes

► Space and antenna diversity

► Fast forward link power control and coherent uplink

demodulation

Physical Layer

 The cdma2000 air interface is designed to provide

flexible framework for supporting voice and other

circuit-switched data as well as bursty packet data

bearer services with different QoS

 cdma2000 supports RF channel band width of SRx1.25

MHz currently SR 1 and 3 are supported and can be extended to 6, 9 and 12.

 A number of fixed and variable rate physical channels

are defined with new variable-length spreading codes and PN codes.

 The data rate, channel encoding and modulation

parameters are specified by radio configurations (RCs)

► For SR 1 and 3, there are 7 RCs for reverse link and 9 for

forward link

SR Forward 

Reverse Physical Channel

SR1

Max SR3

Reverse Enhanced Access

Channel 1 1 New channel used by MS to initiate communicate or respond to

BS when no dedicated channel is assigned to user

Reverse Common Control

Channel 1 1 Common channel used for short burst data and signaling

messages when traffic channels are not in use

Reverse Fundamental Channel 1 1 Basic traffic channel that carries voice, low-rate data and

associated signaling messages

Reverse Supplemental Code

Channel 7 NA Fixed rate data only channel to provide higher transmission rate

Legacy cdmaOne Network

 Designed to support voice and low-rate circuit-switched traffic

MSC

A Ref (A1, A2, A5)

A Ref (A1, A2, A5)

PSTN

STM over T1/T3 or AAL1 over SONET

BSC A-bis BTS

HLR

New Network elements in CDMA2000

MSC

PSTN

BSC A-bis BTS

A1 (S)

A5 (UT) A2 (UT)

A9 (US) A8 (UT)

MSC

Legacy IS-95 A/B

 MS: additional features to support data services and

enhanced signaling messages to both circuit-switched and packet-switched

 BS (BTS & BSC): enhanced radio interface (significant

hardware and software changes) to provide voice, data and multimedia traffic support

 Packet Control Function (PCF):

► an entity that manages the buffering and relay the packets

between BS and PDSN

► Maintain radio resource status (e.g active, dormant)

► Collects radio link related accounting info to be used by AAA

 Packet Data Serving Node (PDSN): new network entity

► Acting as a FA by providing routing services (maintaining

routing tables and route discovery) according to Mobile IP

► Managing the radio-packet (R-P) interface and PPP sessions

for MS

► Initiating authentication, authorization and accounting for

mobile user to the AAA server

► When part of VPN, it can establish a tunnel through the public

data network using layer 2 tunneling protocol (L2TP) to the VPN gateway

► PDSN may optionally use IPSec protocol to further protect the

tunnel

 Home Agent

► Network element within mobile’s home network

► Two major functions: mobile IP registration and

packet forwarding

► HA interacts with AAA to receive mobile IP

registration requests that have been authenticated and return registration response

► HA also forwards IP packets to and from current

point of attachment through FA

 AAA

► Authentication: verification of devices and subscribers for

network access as well as user-based QoS requests

► Authorization: whether a user or device is authorized for

particular service with a specific QoS based on service profile The requesting entity may cache the authorization info making further decision itself without going to AAA

► Accounting: involves collecting and storing billing-related data

concerning the offered services It includes session details (requested and offered QoS, duration of usage etc) and mobility records (dates and times of attach and detach etc)

Mobility management for packet data services

 When an MS originates a call

► Messages are exchanged to establish and close an

R-P connection between PCF/BSC and PDSN

► Once serial connection established between MS and

PDSN

• MS and PDSN negotiate authentication protocol according

to a challenge handshake authentication protocol (CHAP)

or a password authentication protocol (PAP)

• PDSN sends authentication response to AAA server, which decide to authenticate or not

• PDSN constructs a network access identifier (NAI) of the form MSID@realm (realm of the home network)

• The user is identified as a valid user and PDSN also knows

► When PPP session is established, PDSN assigns

the mobile an IP address from a pool of IP

addresses

► The routers in the packet network must be able to

route any packet with this IP to the PDSN that

provides service to the mobile

 Intra-PCF

► Supported by A8/A9 interfaces carrying user traffic and

signaling between BS and PCF

 Inter-PCF and Intra-PDSN

► On location change, must occur when causes to divert the

packet data session from one R-P interface to another

► New R-P connection between target PCF and serving PDSN is

established and PPP session will be moved to this

► Previous R-P session tear down

► PCF-PCF handoff may occur while MS is in active or dormant

state

► Dormant handoff is supported to maintain PPP session, where

 Inter-PDSN

► A network based on simple IP does not support

mobility beyond a PDSN coverage area because

• New IP will be acquired from new PDSN and traffic on existing IP will be undeliverable

• Needs to support fast handoff i.e Mobile IP

 Inter-PSDN Fast Handoff

► The target PDSN initiates establishment of a P-P

session with the serving PDSN.

► P-P interface is used to keep PPP session anchored

when PDSN to PDSN handoff is performed allowing existing PPP session to continue and reducing

service interruption time and data loss

 Cdma2000 introduction

 New MAC and Physical layer features

 Physical layer of cdma2000

 Reverse Physical channels

 New Network elements in cdma2000

► Packet Control Function (PCF)

► Packet Data Serving Node (PDSN)