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cdma2000 Radio Access Network






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cdma2000 Radio Access Network. Salih Ergut 7/7/2003. Outline. cdma2000 network architecture Call processing states and call flows CDMA evolution Essential elements in a CDMA system Power Control Mobility management Handoffs Registration Roaming Radio Admission Control.
cdma2000 Radio Access Network

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Cdma2000 radio access network l.jpgSlide 1

cdma2000 Radio Access Network

Salih Ergut

7/7/2003

Outline l.jpgSlide 2

Outline

  • cdma2000 network architecture

  • Call processing states and call flows

  • CDMA evolution

  • Essential elements in a CDMA system

  • Power Control

  • Mobility management

    • Handoffs

    • Registration

    • Roaming

  • Radio Admission Control

Network architecture l.jpgSlide 3

Network Architecture

BlackMountain

Packet Network

PSTN

PDSN

MSC

BSC

Ericsson

UCSD

Call processing pilot l.jpgSlide 4

Call Processing - Pilot

First MS monitors Pilot channel for

  • Initial acquisition

  • Channel estimation

  • Detection of multipaths for rake receiver

  • Handoffs

Pilot Ch

Call processing sync l.jpgSlide 5

Call Processing - Sync

Pilot channel is transmitted at all times by the base station. MS uses it to lock to Synch Channel to

  • Synchronize to CDMA system time

  • Obtain configuration parameters such as

    • Protocol Revision (P-REV)

    • Network Identifier (NID)

    • Pilot PN offsetLong-code state

    • Paging channel data rate

Sync Ch

Call processing paging l.jpgSlide 6

Call Processing - Paging

MS decodes the Paging Channel with the information received from the Sync Channel. Paging channel provides

  • Overhead messages: systems parameter, access parameter, neighborlist, channel list

  • Mobile directed messages: page request, SMS

Paging Ch

Call processing access l.jpgSlide 7

Call Processing – Access

MS uses Access channel to originate a call or to respond to a page request.

Access Channel is used in a random access fashion.

Access Ch

Call processing traffic l.jpgSlide 8

Call Processing - Traffic

  • Base station assigns a forward and reverse traffic channel to the mobile when it is in conversation

  • Traffic Channel conveys signaling and traffic information

  • When MS is on traffic channel it no longer listens to paging channel or uses the access channel

Mobile station states l.jpgSlide 9

Power Up

Call originationor page response

Synchronization

Initialization

State

IdleState

AccessState

Traffic

State

Paging Loss

Page response completed

End of call

Mobile Station States

Mobile originated voice call flow l.jpgSlide 10

Mobile Originated Voice Call Flow

MSC

BSC

MS

Overhead Info

Paging Ch.

Access Ch.

Origination Msg

BS Ack Order

Paging Ch.

CM Service Request

Null Frames

Fwd Traffic Ch.

SCCP Connection Cfm

Paging Ch.

Channel Assign Msg

Rev Traffic Ch.

Preamble

BS Ack Order

Fwd Traffic Ch.

Assignment Request

Rev Traffic Ch.

MS Ack Order

Service Connect

Fwd Traffic Ch.

Rev Traffic Ch.

Service Conn Cmplt

Assignment Complete

Cdma evolution 1 3 l.jpgSlide 11

CDMA Evolution (1/3)

  • IS-95A (2G)

    • First CDMA protocol, published in May’99

    • 14.4/9.6 kbps circuit/packet data

  • IS-95B (2.5G)

    • Most analog information is removed

    • Some technical corrections

    • New Capabilities, such as higher data rate

    • 64 kbps packet data

Cdma evolution 2 3 l.jpgSlide 12

CDMA Evolution (2/3)

  • CDMA2000 1X

    • High speed data (144 kbps packet data with Mobile IP)

    • Coding (Turbo) and Modulation (Hybrid QPSK)

    • New dedicated and common channels

    • Enhanced Power Control

    • Reverse link detection

    • Forward link modulation

Cdma evolution 3 3 l.jpgSlide 13

CDMA Evolution (3/3)

  • 1X EV-DO (1xRTT Evolution for high-speed integrated Data Only)

    • The objective is to provide the largest practical number of users to run high-speed packet data applications

    • 2.4 Mbps packet data

  • 1X EV-DV (1xRTT Evolution for high-speed integrated Data and Voice)

    • Voice and High Speed Data mixed on one carrier

    • Backward-compatible with CDMA2000 1X

    • 3.1 Mbps packet data

Multiple access methods l.jpgSlide 14

Dedicated band during entire call

Each user transmits at the same time,

at the same frequency with a unique

code

Certain frequency, time-slotted

Multiple Access Methods

Frequency re use patterns l.jpgSlide 15

B

E

A

A

G

C

B

A

A

A

A

G

A

A

F

D

A

A

A

A

E

F

A

A

Frequency Re-use Patterns

FDMA and TDMA vs. CDMA

Channelization l.jpgSlide 16

Channelization

  • Channelization is provided by orthogonal Walsh codes

  • cdma2000 uses variable length Walsh codes for supplemental channel data services

  • Walsh codes can be of length 8, 16, 32, 64, and 128

Walsh codes l.jpgSlide 17

Walsh Codes

  • Walsh codes are orthogonal to each other

  • The shorter the code the higher the data rate since the chip rate is kept constant

A code channel example l.jpgSlide 18

A Code Channel Example

Forward Traffic Channel Generation

Power Control bit

1.2288 Mcps

MUX

Encoder and Repetition

Block

Interleaver

19.2 ksps

Wt

1.2288 Mcps

800 Hz

Long Code

PN Generator

Decimator

Decimator

Cell separation l.jpgSlide 19

Cell Separation

  • Walsh code spreading is followed by quadrature spreading using PN chips with time offsets

  • Adjacent cells have different PN offsets.

  • This prevents interference since time shifted PN sequences are orthogonal to each other

I-PN

cos wot

Wt

BasebandFilter

Baseband

Filter

Q-PN

sin wot

Use of multipath in cdma systems l.jpgSlide 20

Use of Multipath in CDMA Systems

  • FDMA/TDMA (narrow-band)

    • multipath hurts

    • equalizers are used to cancel multipath

  • CDMA (wide-band)

    • can discriminate between the multipath arrivals

    • Rake receivers are used to combine multipath signals to reduce error rate at the receiver

Near far problem l.jpgSlide 21

Near – Far Problem

a user near the base station would jam the user far from the base station

Power control motivation l.jpgSlide 22

Power Control – Motivation

  • Overcomes near-far problem

  • CDMA wouldn’t work without it

  • Copes with path loss and fading

Power control algorithm l.jpgSlide 23

Power Control – Algorithm

  • Capacity is maximized

    • By having each user transmitting just sufficient SNR to maintain a target FER

  • Open Loop Estimate

    • Initial transmit power level for the mobile is determined by the received pilot strength

  • Closed Loop Power Control

    • Base station controls the power level on the mobile by the received quality information.

Mobility management l.jpgSlide 24

Mobility management

A CDMA system provides mobility:

  • Handoff – continuity of the service across adjacent cells

  • Registration – locating the mobile user

  • Roaming – continuity of the service across different service providers

Handoff l.jpgSlide 25

Handoff

  • Handoffs between cells are supported while the mobile is in traffic or idle

  • MS continuously keeps searching for new cells as it moves across the network

  • MS maintains active set, neighbor set, and remaining set as well as candidate set

  • There are 4 types of handoffs:

    • Idle Handoff

    • Access Handoff

    • Soft/Softer Handoff

    • Hard Handoff

Handoff parameters 1 2 l.jpgSlide 26

Handoff Parameters (1/2)

  • If a pilot strength (P) is greater than T_ADD it will be added into the candidate set

  • If pilot strength is less than T_DROP for T_TDROP, it will be moved from active set to neighbor set

  • If the new pilot strength is T_COMP units greater current pilots a Pilot Strength Measurement Message will be send

Handoff parameters 2 2 l.jpgSlide 27

Handoff Parameters (2/2)

Pilot Strength

Cell A

Cell B

T_ADD

T_DROP

T_TDROP

Time

Soft handoff l.jpgSlide 28

Soft Handoff

BlackMountain

Both cells have the same frequency

PDSN

MSC

BSC

Ericsson

UCSD

Soft handoff29 l.jpgSlide 29

Soft Handoff

  • Make-before-break

  • Both cells are at the same frequency

  • Reduces number of call drops

  • Increases the overall capacity

  • Mobile transmit power is reduced

  • Voice quality near the cell boundaries are improved

  • MS reports the SNR of the candidate sets

Soft handoff gain l.jpgSlide 30

Soft Handoff Gain

Power

(dBm)

Cell A

Cell B

Total at MS

Distance

Hard handoff l.jpgSlide 31

Hard Handoff

  • Break-before-make

  • Handoff between different frequencies, non-synchronized or disjoint cells which are controlled by different BSCs

Registration l.jpgSlide 32

Registration

  • It is sufficient to know the cell or the region that a MS is active for routing purposes

  • Mobile station identifier, desired paging slot cycle, and registration type is conveyed

  • Cell/LAC based paging is preferred to flood paging

Registration types l.jpgSlide 33

Registration Types

  • Autonomous Registration: power-up, power-down, timer-based, distance-based, zone-based registration.

  • Parameter-change registration

  • Ordered registration

  • Implicit registration

  • Traffic channel registration

Roaming l.jpgSlide 34

Roaming

  • Users that are outside their home area can receive service from another system by paying some additional charges

  • Mobile station can be:

    • Home state (not roaming)

    • Network roaming

    • System roaming

Network 2

Network 1

Network 3

System

Radio admission control l.jpgSlide 35

Radio Admission Control

  • cdma2000 allocates resources dynamically

  • Admission control is important to ensure quality of service for the existing users when new resources are requested

  • A new request can be call setup, supplemental channel set-up, handoff, data rate change

  • Available Walsh codes, residual power in the forward and reverse links are considered before granting a request

Summary 1 2 l.jpgSlide 36

Summary (1/2)

  • cdma2000 supports both voice and data services in the same carrier

  • provides enhanced voice capacity

    • Forward link

      • Fast power control in forward/reverse links

      • Lower code rates

      • New code channels

    • Reverse Link

      • Coherent detection

Summary 2 2 l.jpgSlide 37

Summary 2/2

  • Higher data rates: 1x up to 153.6 kbps and 1x EV-DV up to 3.09 Mbps

  • Battery life is improved

  • Introduction of Turbo codes provides better link quality for supplemental channels


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